Class T r ^ ?>o Book 1^5 Ci2EmiGHT DEPOSm r MODERN TUNNELING DAVID W. BRUNTON ii AND JOHN A.^ DAVIS New Chapters on Railroad Tunneling BY J. VIPOND DAVIES SECOND EDITION Revised and Enlarged NEW YORK JOHN WILEY & SONS, Inc. London: CHAPMAN & HALL, Limited 1922 3^ Copyright, 1914, By David W. Brunton and John A. Davis Copyright, 1922 By David W. Brunton, John A. Davis and John Vipond Davies / -^ IP. if 1^ PRESS OF BRAUNWORTH & CO BOOK MANUFACTURERS BROOKLYN, N. Y. FEB 'iZ 1922 INTRODUCTION TO SECOND EDITION, REVISED AND ENLARGED The authors of the First Edition of Modern Tunnehng specifically limited the scope of their work by special reference to Mine a.nd Water Supply tunnels; that is to say, to those tunnels of small size in which the heading was excavated at a single operation. The increased use of large sized tunnels for railroad and highway purposes has advanced rapidly with the development of mechanical appliances which aid in the construction of these larger sized structures to furnish improved means for con- ducting the various classes of transportation. Consequently the authors of the original volume felt it to be desirable to widen the scope of the work by the addition of new matter deahng with the various classes of large sized tunnels, and the present writer was invited to undertake the work of the enlarge- ment of the subject matter. As a result of his great regard for Mr. D. W. Brunton, and the substance contained in the First Edition, the present author agreed to write this further work and presents it herewith as a brief study of enlarged tunnel construction. It is fully appreciated that book space of ten times the extent of the present volume would hardly cover the full scope, but it is hoped that the suggestions herein given will be helpful to the student of the subject. It will be realized that all matter in the original volume is equally suitable and applicable to the building of the larger sized tunnels up to the point of enlarge- ment of the headings to the full sized section. The author is indebted to so many Engineers, Corporations, Authors and PubHshers, for matter which has been woven into this revised edition, that it would be impracticable to select individuals to whom to express the sense of that debt; but begs herewith to offer to all those who are referred to or indicated in the text, his acknowledgments and appreciation. iii 1 CONTENTS PAGE Chapter I. Introduction 1—4 Purpose of book i Scope of book • 2 Acknowledgments 3 Chapter I!. The history of tunnehng 5~34 Tunnels driven by hand 'drilHng 12 Mining and water tunnels driven by machine drilling . . 19 Railway tunnels 24 Chapter III. Modern mining and water tunnels 35~52 Resume of data 35 Modern tunnels described in engineering magazines ... 49 Chapter IV. Choice of power for tunnel work 53~79 Sources of power 53 Production of power 54 Water powder 54 Steami 58 Internal-combustion 58 Electric motors 64 Transmission of power .64 Choice of power 65 Duration of plant 65 Accessibility 66 Cost of installation 66 Labor 74 Fuel consumption 74 Thermal efficiency 75 Purchase of current 76 Interest and depreciation 77 Conclusions 78 Chapter V. Air compressors •. . 80—110 Power required 81 Capacity 82 Types 85 Straight line 85 Duplex 88 Turbo-compressors 91 Comparisons 94 V VI CONTENTS Chapter V. Air compressors — {Continued) page Regulation 97 Steam driven 97 Water driven 98 Electrically driven 99 Heat loi Heat produced . loi Dangers of. high temperatures loi Removal of heat 102 Intercooling 104 Moisture 104 Accessories 106 Precoolers 106 Aftercooling 106 Air receivers 107 Drains 108 Conclusions 109 Chapter VI. Ventilation Ill— 124 Machinery ill Direction of current. . 113 Capacity 115 Pressure 118 Size of pipe 121 Comparison of fans and blowers 122 Conclusion 123 Chapter VH. Incidental surface equipment . . . - 125—129 Drill sharpening machines 125 Air meters 127 Chapter VIII. Rock-drilling machines 130—162 Types 130 Pneumatic drills 130 H^'draulic drills 138 Electric drills 141 Gasoline drills 147 Merits of each type 147 Pneumatic drills 147 Hydraulic drills 157 Electric drills 157 Choice of drills 160 Chapter IX. Haulage 163-180 Tunnel cars 163 Loading machines 1 70 Motive power 173 Dumping devices 178 CONTENTS vii Chapter X. page Incidental underground equipment 181—209 Tunneling machines 181 List of tunneling machine patents 188 Illumination 201 Telephones 205 Incidentals 207 Chapter XI. Drilling methods 208-235 Number of shifts 209 Mounting 212 Number of holes 218 Direction of holes 221 Depth of holes . 229 Chapter XII. Blasting 236-259 Ammunition 236 Loading 248 Firing 254 Storing 257 Thawing 258 Chapter XIII. Methods of mucking 260—269 Number of men . . 260 Positions of working 261 Handling cars 263 Use of steel plates -. 267 Chapter XIV. Timbering 270—288 Materials 270 Types 273 Chapter XV. Safety 289—327 Causes of accidents 290 Falls of roofs 290 Use of explosives 292 Premature explosions 296 Misfires 299 Suffocation by gases from explosives . 303 Suffocation by gases from other sources 305 Haulage 309 Electricity 311 Fire 313 Water 315 Intoxication 318 Prevention of accidents 318 Precautions for the manager or superintendent . . .319 Precautions for the foreman . . . 321 Precautions for the miner 324 i Vlll CONTENTS Chapter XVI. page Cost of tunnel work 328—359 Coronado tunnel 329 Gunnison tunnel 331 Laramie-Poudre tunnel 332 Los Angeles Aqueduct 333 Lucania tunnel 343 Marshall- Russell tunnel 344 Mission tunnel 345 Newhouse tunnel 346 Rawley tunnel 347 Roosevelt tunnel 348 Stihvell tunnel 352 Strawberry tunnel 353 Chapter XVI J. Bibliography 360-419 Tunnel descriptions 360 Water power 369 Steam power 371 Internal-combustion power 373 Electric power 378 Compressed-air power , . . . . 380 Power transmission 381 Choice of power 382 Power plant descriptions 382 Air compressors 385 Compression of air 388 Compressed-air accessories 1 .... 391 Ventilation 393 Air drills 394 Hydraulic drills 395 Electric drills 396 Drilling accessories 397 Haulage 398 Tunneling machines 401 Illumination 402 Methods of tunnel driving 402 Drilling methods 405 Blasting methods 406 Blasting supplies 408 Mucking 41 1 Timbering 411 Speed records 4^2 Safety and health 4^4 Costs 418 I CONTENTS IX Chapter XVIII. page Railroad Tunnels 420-460 Introduction 420-424 Economics 424-426 Design 426-458 Geology 426-429 Cross-section 429-431 Alinement . . . . . 432 Lining . 432-447 Backing of lining 447-448 Waterproofing lining 448-451 Drainage and pumping 451-456 Ventilation . . 456-457 Lighting 457-458 Contract Bids 458-460 Chapter XIX. Construction 461-481 Foreign systems. . 461-462 Survey 462-465 Plant Installation and Equipment applicable to all classes of enlarged tunnels 465-481 Plant 465-467 Air Compressors 467-468 DriHs 468 Loading equipment 468-470 Haulage equipment 470-475 Drainage and pumping 475-476 Ventilation 476-477 Lighting 477-47^ Surface equipment 478-479 Camp. 479-481 Chapter XX. Hard Rock Tunnels (Self-supporting) 482-509 Excavation methods 482-484 Size of heading 484-486 Comparative cost of tunnel excavation in trap rock, years 1906 and 1907 486-490 Drill mounting 490-497 Top or bottom heading 497-499 Center heading 499~505 Overbreakage and packing 505-508 Rotary cutters 508-509 Advanced test drilling 509 Chapter XXI. Loose Rock and Soft Ground Tunnels 510-543 Excavation methods 510-517 Needle beams 517-518 Steel sets 518-520 X CONTENTS Chapter XXI. — {Continued). Loose Rock and Soft Ground Tunnels — {Continued) page Pilot tube method 520 Lining methods 520-525 Collapsible forms 525-527 Pneumatic placement of concrete 527-531 Precast block lining 531 Brick lining 531-532 Cement Gun 532-533 Liberty Tunnels 533^542 Cost of soft ground tunnel 542-543 Chapter XXIL Subaqueous Tunnels 544-567 Tunneling shields 545-550 Shield equipment 550-553 Wood lining 553 Roof shields 553-554 Caisson method 554-557 Cofferdam methods 557-558 Construction Plant 558-563 Boilers 558 Compressed Air 559-561 Air Locks 562 Electricity 562-563 Hydraulic power 563 Miscellaneous plant 564 Cost of Subaqueous Tunnels 564-567 Shield driven, iron lined 564-566 Trench type 566-567 Bibliography to Chapters, XVIII-XXII ....... 568-576 Appendix (outline of tunnel data) 577-582 I CHAPTER I INTRODUCTION PURPOSE OF BOOK Up-to-date information concerning tunneling methods is difficult to obtain. There are but few books on the subject, and much of the material they contain, although it is very interesting and valuable historically, is now obsolete. The engineering periodicals, it is true, endeavor to keep abreast of the times and there are several of which scarcely an issue ap- pears without some article bearing upon tunnel work. But the very multiplicity of these magazines prevents one from reading all of them regularly, and the foreman or superintendent in charge of a tunnel, or the mining engineer designing one, and especially the business man financing the project, has no time for a labo- rious search after scattered articles in order to determine the present status of tunnel work. Then, too, knowledge of new methods travels slowly. Inventions and improvements of definite and practical value in mining as well as all the other industries, and important discoveries in science, frequently remain in the note-book of the investigator, or, as theses, are buried in university libraries or may be published only in the very locally distributed journals of small scientific societies. In biology, the work of Mendel on heredity (whose experiments in his cloister-garden are the foundation of a new conception of the nature of living things on the part of biologists, which bids fair to exert an influence not less than that associated with the name of Darwin), although pubKshed locally by him in 1865, remained unknown to the scientific world until its simultaneous discovery by three independent workers in 1900. In astronomy, the invention of the achromatic lens, without which the modern telescope would not be possible, by John Dolland in 1758, was antedated some twenty-five years by the investigations of Chester Moore Hall. So also in tunneling, up-to-date methods and equip- 1 2 - MODERN TUNNELING ment that ai'e proving safe, efi&cient, and economical may be totally unknown outside the district in which they originate. This book is intended to supply, if possible, such data concerning timnehng methods in the United States, and to make suggestions that, it is hoped, may result in a saving to the mining industry of life, energy, and capital that would otherwise be expended for inefficient or useless work. In most of the published accounts of tunnel work, the writers usually do not attempt to criticise the methods they are de- scribing. It is customary for such articles to contain accurate descriptions of equipment, various phases of working operations, and occasionally figures showing the cost of the work, but rarely do they include a discussion of the means for preserving the health and life of the employees, or data bearing upon the choice and efficiency of equipment or an analysis of methods and costs. As a result, the reader in drawing conclusions is dependent wholly upon his own resources. In this volume, on the con- trary, the making of such analyses will be a primary considera- tion. It is desirable, nevertheless, in an impartial, disinterested book of this character to use constructive rather than destruc- tive criticism. For that reason emphasis will be placed upon safe, efficient, and economical methods, and upon good points of equipment, while bad practice and obsolete machinery will be ignored except, perhaps, as examples of the inadvisable or as they have some bearing historically. Thus the authors hope to set forth a guide for future work rather than an unillumined record of past or present achievement. SCOPE OF BOOK This book will be confined chiefly to tunnels and adits* for mining purposes, such as drainage, transportation, or de- velopment, but it will also include those which are used to carry water for power, irrigation, or domestic use, in which the essential *It has been suggested by prominent authorities that the word " tunnel " be restricted to the • designation of such nearly horizontal passageways as extend completely through a mountain or hill from daylight to daylight, and INTRODUCTION 3 features are practically identical with mine tunnels. Tunnels of this sort are generally driven through at least fairly hard rocks in contrast to ordinary soil, quicksand, and other heavy material of a treacherous nature, and they are practically never driven through modern river-bed deposits. It will not be necessary, therefore, to consider the special methods and equipment for tunnel work in such materials. A distinction will be made be- tween tunnels or adits for which the excavation is wholly or in a large part in material containing no ore and those which follow the vein through any irregularity in direction. As far as possible, the discussion will be limited to the former, because in the latter instance the methods employed in driving along a vein are usually more akin to the distinctive operations for removing ore, and are, therefore, not so apt to be good examples of tunnel practice. ACKNOWLEDGMENTS In the preparation of this book valuable assistance has been received from numerous sources. The writers are deeply indebted to the officials of the New York Board of Water Supply, of the Los Angeles Aqueduct, of the United States Reclamation Service, and the Bureau of Mines, and to the officers, managers, superintendents, and foremen at the different tunnels, for favors granted, for information suppHed, often at no little inconvenience,' and, above all for that hearty co-operation which has been an unfaiHng source of inspiration. Many thanks, also, are due the the words "adit" and "drift" be used only for similar galleries which enter from the surface and serve to drain a mine or furnish an exit from the work- ings, but do not continue entirely through the hill. Such definition is eminent- ly desirable from a strict technical viewpoint and would undoubtedly result in a much to be desired precision of diction, but, although it was proposed over thirty years ago and the suggestion has been repeated several times since, it has been found difficult, if indeed possible, to establish it practically. The American usage of referring to any horizontal gallery as a tunnel, without considering its extent completely through a hill or not, is so firmly fixed in our mining literature (being used by authors and editors alike), and among practical mining men generally in this country, and is even embodied in the United States mining laws, that the proposed restriction has been thought scarcely justifiable in a practical work of this character. ^: 4 MODERN TUNNELING manufacturers of equipment and materials used in tunnel work for their promptness and courtesy in furnishing catalogues, data of tests, and similar material, and in supplying photo- graphs, blue-prints, and cuts, which have been of great assis- tance in the preparation of many of the illustrations in this volume. Obligation is also acknowledged for many valuable suggestions obtained from articles in engineering periodicals and from books on tunneling and related subjects. CHAPTER II THE HISTORY OF TUNNELING The art of excavating underground passageways has been known to mankind for many centuries. The ancient Egyptians and Hindus employed it in the creation of many wonderful subterranean temples and sepulchers in hard rock, and similar monuments are found in the works of the Hebrews, Greeks, Etruscans, Romans, Aztecs, and Peruvians — in fact, of all ancient civilized peoples. It is not surprising that the Egyptians, with their wonderful knowledge of quarrying as well as many other useful arts, should have been versed in methods of underground rock ex- cavation. Remains of their work, some of which dates back to 1500 B.C., may be found in the grottos of Samoun, the tombs near Thebes and Memphis, the catacombs of Alexandria, and the temples of Ipsamboul. A gigantic tomb has been found at Abydos, which was cut in the soKd rock during the Twelfth Dynasty by Senwosri HI.; also Rameses IL, who is perhaps the best-remembered personage of these ancient times, constructed, either because of vanity or the great length of his reign, many rock-cut temples, the grandest of which is probably that of Abu Simbel. The work was performed with hand tools, and the labor neces- sary to have fashioned monuments of such magnitude and grandeur niust have been stupendous. For cutting granite and other hard rock, the workmen used saws of copper which were either fed with emery powder or were set with teeth of that abrasive. A similar method was employed as early as the Fourth Dynasty for circular holes which were drilled by a tube having fixed teeth, or which was fed with emery powder. For removing rock in a quarry or in a tunnel, grooves varying in width from 4 to 20 inches were made on four sides of a block, which was then 5 b MODERN TUNNELING broken out by the swelling action produced by soaking with water a number of wooden wedges driven into these grooves. The excavations in India probably number at least a thousand, the majority of which are of Buddhist origin. They are usually of two types — chapels and monasteries. The former consist of a nave with a vaulted roof, separated from the side aisles by columns, and containing a small chapel at the inner circular end. The latter consist of a hall surrounded by a number of cells for the residence of monks and ascetics. Most of the Indian excavations are of much later date than those in Egypt. The earliest, the Sudama, or Nigope, cave, was constructed probably about 260 B.C.; the Lomas Rishi was built about 200 B.C., and those of Nassick about 129 B.C. These earlier caves imitated very closely contemporaneous timber- roofed temples, and for this reason the columns all slope inward, copying with great fidelity of detail the rafter supports of the wooden temples. In the Karli caves (about 78 B.C.) this feature is absent; the columns of the nave are quite plumb and the per- fection of architecture and ornamentation is unsurpassed by any of the later Hindu rock-temples. The galleries and rooms of the caves of Ellora contain a total of nearly five miles of sub- terranean work. Although the builders may possibly have known of gunpowder, it was not used in the construction of these tunnels, which, like all the preceding works, were accomplished laboriously with hand tools and probably by slave labor. The caves of Salsette belong to the sixth century a.d., while those at Elephanta were constructed about 800 and the Gwalior temples were excavated still l-ater during the fifteenth century. Modern archaeological investigation indicates that tunneling was possibly known to the Minyae, an ancient Grecian people dating back beyond 2000 B.C., whose cycle of myths includes, among others, that of the Argonautic Expedition. A series of shafts, sixteen in all, are to be seen near Lake Kopais in Boeotia, which are supposed to have been constructed by these peoples for the ventilation of an ancient drainage tunnel. The shafts are 200 to 1,000 feet apart, 6 to 9 feet wide, and have a maxi- mum depth of 100 feet. The tunnel was probably the enlarge- THE HISTORY OF TUNNELING 7 ment of a natural watercourse such as are commonly found in similar calcareous rocks. Krates of Chalcis, a mining engineer who Hved in the time of Alexander the Great, is credited his- torically with an attempt to drain this lake by utilizing and enlarging natural watercourses. Although the exact date of the introduction of mining into Attica, probably from the Orient, is unknown, it seems to have been subsequent to the time of Solon (about 600 B.C.). By 489, it is certain that the silver mines of Laurium were yielding a highly satisfactory return, and at the instigation of Themas- tocles, the net profits from them were applied by the Athenians to the construction of a fleet, so that these mines no doubt con- tributed largely to the prosperity and power of Athens. The workings, approximately two thousand in all, consisted of shafts and galleries in which the rocks were hewn out wdth hand tools and brought to the surface on the backs of slaves. Air was supplied to the large underground stopes or chambers by venti- lating shafts about 6 feet square and from 65 to 400 feet deep. Gold was mined in Macedonia and Thrace at least as early as the fifth century B.C., and Herodotus mentions a tunnel in the island of Samos built in the sixth century, which was 8 by 8 feet in cross-section, and nearly a mile long. The x^ztecs w^ere well acquainted with mining, and they secured copper from the mountains of ZactoUan, while the mines of Tasco furnished silver, lead, and tin; and the extensive gal- leries and other traces of their labor were of great assistance to the early Spanish miners. With no knowledge of iron, although iron ore was very abundant, their best tools were made of an excellent substitute in the form of an alloy of copper and tin. With tools of this bronze, they could not only carve the hardest metals, but with the aid of powdered silica they could cut the hardest minerals, such as quartz, amethyst, and even emerald. Although the mines of the ancient Peruvians were Httle more than caverns excavated in the steep sides of mountains, never- theless they knew of the art of tunneling, as is shown by tunnels of their aqueducts and by the extensive tunnel which they built to drain Lake Coxamarco. They, too, had no knowledge of 8 MODERN TUNNELING iron, and their tools were made of an alloy of copper and tin, which they probably discovered quite independently of the Aztecs, whom they rivaled also in the cutting of gems. The Romans, however, were undoubtedly the greatest tunnel- builders of early history. They drove tunnels for passage, drainage, water supply, and mining, not only in Italy, but wher- ever their conquests led them, as is evidenced both by records and by old workings left behind in the countries they dominated. One hardly needs to mention the numerous aqueduct tunnels and sewers of the ancient city of Rome, some of which are in use to-day, attesting the abihty of the Romans in this branch of engineering. Remains of their work, many of them remarkably well preserved, have been found in France, Switzerland, Portu- gal, Spain, Algiers, and even Constantinople. Their tunnels were of no mean size. A road tunnel near Naples constructed, according to Strabo, about 36 B.C., was approximately 4,000 feet long, 30 feet high, and 25 feet wide. About 359 B.C., Lake Albanus, which lies about fifteen miles southeast from Rome, was tapped for its supply of clear water by a tunnel over a mile long, 8 feet high, and 5 feet wide. Possibly the greatest Roman tunnel was driven by the Emperor Claudius to drain the overflow waters from Lake Fucinus, which is situated about seventy-five miles nearly due east of Rome and has no natural means of outlet. This tunnel, com- pleted in 52 A.D., after eleven years' labor, is over three miles long, and was designed to be 19 feet high and 9 feet wide; but it appeared to have been even larger than this when, in 1862, it was reopened to secure valuable land beneath the lake. These works seem all the more marvelous when one considers the primitive methods available at that time. Explosives were unknown, and machinery was not then used in mining. Rock openings were usually made by chipping, by channeling and wedging, as in Egypt, or by cutting large grooves around the block to be excavated, using hand tools made of iron, copper, and bronze, although it is quite possible that for certain classes of stone-cutting, diamonds or some similarly hard minerals were employed in conjunction with primitive tube-drills and saws. THE HISTORY OF TUNNELING 9 These methods were often supplemented by fire-setting, a method chiefly employed, however, in the large chambers or stopes, and not well adapted for driving small tunnels. It consists simply of heating the rock to a very high temperature and quenching suddenly with water (or sometimes with vinegar in calcareous rocks), producing shattering and disintegration be- cause of sudden con- traction. Many writ- ers have described the intense and fearful sufferings of men en- gaged in this work, usually slaves and prisoners of war who perished by the thou- sands — a fact, how- ever, of little concern to the ancient builders. The value of Spain as a storehouse of precious metals, oft'- setting somewhat the influence of Eastern wealth, was well ap- preciated by Roman leaders, and an armed force for the pro- tection of the mines was maintained there constantly, in many cases at the cost of serious political and financial embarrass- ment at home. In southern Spain, where the numerous silver and copper mines contained much water, Roman tunnels are very common. They are remarkable for their small size, being usually about 5 feet in height and, where timbered, from 16% to 36 inches in width, a fairly typical one being shown in Figure i. This adit, as far as explored, has a length of 1,850 Fig. I, Section of an old Roman adit in hard slate. 10 MODERN TUNNELING 1 _S1 -l-^H^ 3M X CM feet and a maximum depth of 183 feet. The timbered openings are even smaller than this, a fair type of them being shown in Figure 2, which gives the dimensions of the openings and the timbers supporting it. The particular tunnel from which this section was taken is 2,300 feet long and has a maximum depth of 215 feet. As nearly as can be ascertained to- day from discoveries in them of various objects of interest, including coins, it is certain that these adits must have been driven very early in the Christian era. Toward the latter end of the period in which these particular tunnels were used by the Romans, attempts were made to work the ore bodies below them by rais- ing water from the lower stopes by means of slave-operated water-wheels. Since artificial ventilation by means of blowers was at that time unknown, like most of the Roman tunnels, these were ventilated by shafts which were spaced in the tunnel illustrated above at about 25-meter intervals; in order, also, to minimize the depth to which the shafts were sunk, the tunnels corre- sponded very nearly in their course to that of the valleys or gulches above them, instead of being straight, as is the usual modern practice. Like the adits, the ventilating shafts were remarkably small. Where timbered, they were usually about 2 feet 10 inches square in the clear, and where the rock would stand without timbering they were circular and generally did not vary much from 2 feet 4 inches in diameter. With the fall of the Western Empire, tunnel work in Europe practically ceased for many centuries. Some excavations were made, it is true, for tombs and the crypts of monasteries; and underground passages leading to a secluded exit, to furnish the occupants a means of escape in time of defeat, were a necessary Fig. 2. Section of timbered Roman adit. THE HISTORY OF TUNNELING 11 part of the equipment of each castle. Crude attempts at mining, also, were practiced in Germany. The Teutonic tribes, whose main occupation was warfare and who were savage, barbarous, and essentially nomadic at the time of the conquests of Juhus Caesar, had probably learned from the Romans the value of gold; later, somewhat tempered and softened possibly by the civihza- tion they had destroyed, they began to search for precious metals and to pursue other peaceful occupations. During the Middle Ages tunneling was devoted almost exclu- sively to the needs of war and was seldom employed for con- structing aqueducts or other public works. There is, however, a record of a road tunnel begun in 1450 by Anne of Lusignan. It was intended to pierce the Alps at an elevation of nearly six thousand feet, and afford better means of communication between Nice and Genoa, but was never completed. Work was subsequently resumed in 1782 by Victor Amadeus III., but was finally abandoned twelve years later, after a total of nearly eight thousand feet of tunnel had been constructed. Although gunpowder in Europe, according to the consensus of opinion, was probably invented early in the fourteenth century and by the end of the sixteenth century was very com- monly used in military operations for gunnery and for blowing up fortifications, it was not applied directly to mining or tunnel operations during this period. Agricola's ''Bergwxrck Buch" "^ (pubHshed by Basel in 162 1), the third edition of ''De Re MetalHca," pictures the Roman methods and of hand work and fire-setting as the usual means of mining at that time. In the year 16 13, Martin Weigel is said to have introduced gunpowder into mining work. Gatschmann describes the use of wooden plugs for tampiQg at this time, which were later (about 1685) supplanted by clay. August Bayer (''Das Geseg- nete Markgrafenthum Meissen," 1732) and Henning Calvor (" Nachrichten liber das Berg- und Maschinenwesen am Harze," etc.) also confirm the date of 16 13 for the invention of drilling and blasting, but Honemann and Rossler make it fifteen or * A complete English translation is now published. Hoover, H. C, and Hoover, L. H., De Re Metallica, 637 pp., London, 1912. 12 MODERN TUNNELING twenty years later. Whatever may have been the date when blasting was first used in mining, it is certain that the practice had become fairly common by 1650, for powder is mentioned as having been purchased for the Harz mines as early as 1634, drill-holes are reported at Diillen, which bear the date of 1637, and blasting is known to have been introduced into the Freiberg district in 1643. The use of gunpowder in mining gave a new impetus to that industry which produced a large corps of men trained to over- come the difhculties of underground drifting, and it is not sur- prising therefore to note soon after an increased activity in tunnel work for other purposes. The chief of these allied interests was transportation, and in the eighteenth and early part of the nineteenth centuries a large number of tunnels were driven in connection with the canals, which, aside from wagon roads, were the onl}^ highways at that time. Later the develop- ment of steam railroads and the desirability of maintaining level gradients created a still greater demand for tunnel con- struction. A brief review will be given of the more important tunnels constructed for these purposes, both abroad and at home. TUNNELS DRIVEN BY HAND-DRILLING The first modern tunnel to be constructed for commercial transportation was the Malpas tunnel on the Languedoc Canal in France. It was 515 feet long, 22 feet wide, and 27 feet high, and was built between 1679 and 1681 * by Riquet, a French engineer. Although this tunnel showed that canals could be constructed through country before thought impassable, further advantage was not taken of this fact in France until nearly a hundred years later, when the Rive de Gier tunnel (1^656 feet long) was constructed on the Givors Canal in 1770, and the Torcy tunnel (3,970 feet long) on the Center Canal was built * The writers wish to acknowledge their especial indebtedness to Henry S. Drinker, from whose monumental work on tunneling this and other valuable information concerning the earlier history of tunnel driving has been ob- tained. THE HISTORY OF TUNNELING 13 in 1787. The Tronquoy and the Riqueval tunnels on the St. Quentin Canal were started in 1803 and the Noirou tunnel (approximately 39,400 feet in length), on the same canal, was begun in 1822. On the Bourgoyne Canal, the St. Aignan tunnel was started in 1824, so that by the middle of the nine- teenth century nearly twenty canal tunnels in France had been constructed, having an aggregate length of nearly 93,500 feet. The earliest transportation tunnel in England was the Hare- castle, situated on the Grand Trunk Canal, which was begun in 1766 and opened for trafhc in 1777. This tunnel was 8,640 feet in length, 9 feet wide, and 12 feet high. There were originally four other tunnels, but of shorter lengths, also on this canal. The Harecastle tunnel was found to be too small to accom- modate the trafhc through it, and was replaced in 1824 by a parallel tunnel, which was 16 feet high and 14 feet wide, 4 feet 9 inches of this width being used for a tow-path. The Sapperton tunnel on the Thames-Medway Canal was started in 1783. It was approximately 12,500 feet long, and six years were employed in its construction. The next large canal tunnel in England was the Blisworth (9,250 feet long), on the Grand Junction Canal, which was started in 1798, and required seven years for its completion. In 1856 there were over forty-five tunnels on the various English canals, aggregating some 220,000 feet in length. The first canal tunnel in the United States was the Auburn tunnel at the Orwisburg Landing on the Schuylkill Ns^vigation Canal. The tunnel (which was 450 feet long, 20 feet wide, and 18 feet high) was begun in 1818 and opened for traffic in 182 1. The hill it pierced was composed of red shale, and the highest point was only forty feet above the top of the tunnel. The tunnel was shortened in 1834-37 and again in 1845-6, and was finally taken out altogether in 1855-6 by an open cut. The ''Summit Level,'' or Lebanon Tunnel on the Union Canal, begun in 1824 and finished in 1826, was the second canal tunnel in this country. It was originally 720 feet long, 18 feet wide, and 15 feet high, being driven through argillaceous slate at a total cost of $30,464. It was followed by the "Conemaugh" and 14 MODERN TUNNELING "Grant's Hill" tunnels on the Western Division of the Pennsyl- vania Canal (1827-30), the Paw-paw tunnel on the Chesapeake and Ohio Canal (1836), and two tunnels on the Sandy and Beaver Canal, Ohio (1836-38). The first railroad tunnel of which we have any record was the Terre Noire tunnel, near St. Etienne, France, on the Roanne- Andrezieux horse railroad. This tunnel, which was begun in 1826, was 4,920 feet long, 9.8 feet wide, and 16.4 feet high. Some fourteen other tunnels were built on the road from St. Etienne to Lyons between 1826 and 1833. The first tunnels on a railroad using steam locomotives were those on the Liver- pool and Manchester Railway, constructed between 1826 and 1830. It was on this road that the famous trial between the "Rocket," "Novelty," and "Sans Pareil" locomotives took place in 1829. The following summary of early railroad tunnel- building in Europe is quoted from Drinker's "Tunneling," page 19. '' Tunnels, of course, multiplied rapidly in England with the extension of railways, and during the twelve or fifteen years following the construction of the Liverpool and Manchester line, there were a large number of tunnels built throughout the kingdom, among them being the famous Kilsby, Box, and Woodhead tunnels. The first tunnels on a steam railway in France were those built on the St. Germain line in 1837. Sub- quently, the ones on the Versailles, the Gard, and the Rouen lines raised the total length of tunnels in France in 1845 to 12,833 "^' (42,105 feet). The report of the Corps des Ponts et Chaussees on tunnels for 1856 shows at that date a total on French railroads of 126 tunnels, of a total length of 65,106 meters. Among the noted early French tunnels may be cited the Nerthe, Arschwiller, Rilly, La Motte, Lormont, and Alou- ette. In Belgium, the Cumptieh tunnel, built in 1835, on the Xhemin de I'Etat,' seems to have been the earliest. In Germany (Prussia and other States) the earHer lines were so located as not to require much tunnel-work; and Oberau tunnel (1839), on the Leipsic-Dresden line, in Saxony,- was the first. In Austria, Rziha gives the Gumpoldskirch tunnel as the THE HISTORY OF TUNNELING 15 first. A tunnel at Eriebitz (perhaps the same), on the ''North" line, is mentioned in the Fonts et Chaussees Report (above cited) as an early Austrian one. In 1856 there were some fifty tunnels in Austria of a total length of 13,522 meters. In Italy, the Naples-Castelamare line, opened in 1840, had several tun- nels. In 1856, the total Italian tunnels amounted to 10,181 metres; the Bologna-Pistoja line is especially remarkable for its semi-subterranean character. Among the early Swiss tunnels, especially to be noted is the Hauenstein, commenced in 1853 and finished in 1858." The first railway tunnel in the United States was constructed on the Allegheny Portage Railroad in Pennsylvania, between 1 83 1 and 1833. The tunnel (which was driven through slate) was 901 feet long, 25 feet wide by 21 feet high, and was lined throughout with masonry 18 inches thick. It was followed by the Black Rock tunnel (1835-183 7) on the Philadelphia and Reading Railroad, and the Elizabethtown tunnel (183 5- 183 8), on what is now the Pennsylvania Railroad; after this time, railroad- tunnel construction became so general that by 1850 as many as forty-eight tunnels had been completed on American railways. Among the early European mining tunnels driven with gun- powder and hand-drilling, mention should be made of the Tiefe Georg and the Rothschonberger Stollen in Saxony, the Joseph 11. Stollen at Schemnitz, Hungary, and the Ernst August Stollen, which was later driven under the Tiefe Georg. A number of tunnels, of which the Taillades tunnel was the most important, were also driven in connection with the Marseilles Aqueduct during this period. The Tiefe Georg Stollen* was driven between 1777 and 1799. The total length of the main tunnel is 34,529 feet; its various branches aggregate 25,319 feet more, and yet this immense undertaking, driven entirely by hand, was carried out to obtain a drainage depth of only 460 feet. It passed through graywacke for nearly the entire distance. * Drinker, p. 351. 16 MODERN TUNNELING Work was commenced on the Joseph II. Stollen, Schem- nitz, Hungary,* in 1782, but owing to various interruptions the tunnel was not completed until 1878. The portal is at Wornitz, on the left bank of the River Gran, about ten miles west of Schemnitz. The tunnel is 10.27 miles long, 9 feet 10 inches high, and 5 feet 3 inches in width, and its cost was $4,860,000. It is used entirely for mine drainage and the annual saving in pump- ing amounts to over $75,000. The Rothschonberger StoUen f was driven for the purpose of draining the mines of Freiberg, Saxony, and was commenced in 1844 and completed April 12, 1877. The tunnel starts in the Triebisch Valley at Rothschonberg, about 12 kilometers above Meissen on the Elbe. Its length on the line of the original loca- tion to Halsbriicke was 42,662 feet, but as completed to a con- nection with the Himmelfahrt, including its branches, had a total length of 95,149 and a depth below the Anna Stollen of 308 feet. Hand-drilling and black powder were used down to the end of 1875, when Burleigh drills were introduced. The work was carried on by the State, and perhaps no better example of the inefhciency of governmental control over industrial enter- prises could be cited than the record of this work. The tunnel was nine feet square and was driven from eighteen headings, yet thirty-three years were required for its completion, the average rate of progress in each of the headings being only about 15 feet per month. The Ernst August Stollen J was driven below the Tiefe Georg Stollen in 1851-1864. The main tunnel is about 34,218 feet long, but the entire length of the adit and its branches is 74,452 feet, all driven in rock similar to that in the Georg Stollen quoted above. The tunnel is 11 feet high and 5H feet wide, driven on a grade of 35.6 feet to the mile. Hand-drilling and black powder were used and, working seven-hour shifts, the rate of progress was fifty feet per month; four-hour shifts * Wochenschrift des Qisterreichischen Ingenieur- und Architekten-Ver- eines, 1886, p. 284. t Raymond, Trans. A. I. M. E., Vol. VI, pp. 542-558 (1877-1878). { Drinker, p. 351. I Fig. 3. Starting a tunnel by hand-drilling. 18 MODERN TUNNELING increased the rate of progress to 78.7 feet per month, and by crowding the miners to the limit during the last three weeks they made 75 feet, or at the rate of 107 feet per month. Some idea of the importance the early German miners attached to drainage may be gathered from the fact that this colossal enterprise only gave them an increased drainage depth of 315 feet. The Taillades tunnel * on the Marseilles aqueduct was begun in January, 1839, and compl'eted at the close of 1846. It was driven from fourteen shafts, and in their construction so much water was encountered that the work of sinking them was very difficult and at times seemed almost impossible. It was finally necessary to install at one of the shafts a steam engine of 100 horse-power in order to remove the water, which amounted to 3,300 gallons per hour. The cost of sinking the shafts was ap- proximately $40 per foot, while the tunnel itself cost approxi- mately $37 per foot, or, including the cost of the shafts, $48.50 per foot. The Assassin tunnel on the same project was some- what less difficult and cost but $25.50 per foot for 11,400 feet, while the Notre Dame tunnel, which was lined with masonry for its entire length of 11,500 feet, cost $32.50 per foot. The first large mining tunnel in the United States was com- menced as early as 1824. This was the ''Hacklebernie" tunnel near Mauch Chunk, Pennsylvania, and it was driven by hand- drilling and with black powder. When work on it was stopped in 1827, it had penetrated 790 feet through hard conglomerate, making an opening 16 feet wide by 8 feet high. Work in it was resumed once more in 1846 and the tunnel was extended to a length of 2,000 feet. The invention of machines to do the work of rock-drilling, which occurred almost simultaneously with the discovery of high explosives, gave another great impulse to tunnel-driving. The first extensive utilization of these aids was in the con- struction of the Mt. Cenis tunnel in Europe and the Hoosac * "M. de Mont. Richer et le Canal de Marseille." Felix Martin. Paris, 1878. Gallet et Brand. THE HISTORY OF TUNNELING 19 and Sutro tunnels in this country. The success attained with them soon led to further activity in tunneling, not only for rail- roads but in connection with mining, drainage, and water supply as well — an activity culminating in the immense amount of such work undertaken within the last ten or fifteen years. The following table gives in chronological order some of the more important events connected with these two wonderful improvements. A SHORT CHRONOLOGICAL HISTORY OF HIGH EXPLOSIVES AND ROCK-DRILLS* 1847. Sobrero discovered nitroglycerine. 1849. J. J. Couch, of Philadelphia, patented on March 29 the first percussion rock-drill. 1851. J. W. Fowle, of Philadelphia, patented on March 11 the first direct-action percussion-drill. 1854. Schumann invented his percussion-drill at Freiberg. 1857. Schumann drills used in Freiberg mines. 1857. Sommeiller invented a rock-drill for use at Mt. Cenis. 1 86 1. January i, Sommeiller improved drills commenced work in the Mt. Cenis tunnel. 1863. Nobel first applied nitroglycerine as a blasting agent. 1865. Gun-cotton tried at the Hoosac tunnel by Thomas Doane, chief engineer. 1866. Nitroglycerine tried with great success at the Hoosac tunnel by T. P. Shaffner. 1866- Burleigh drills tried and proved to be a success at the Hoosac tunnel. 1867. Nobel invented dynamite. 1868. Dynamite patented in America by Nobel. MINING AND WATER TUNNELS DRIVEN BY MACHINE-DRILLING The idea of draining the mines of Virginia City by a deep tunnel was first broached in the spring of i860, when Mr. Adolph Sutro began negotiations with the mines, the State, and * Drinker, pp. 54-55. 20 MODERN TUNNELING finally with the Federal Government for contracts, concessions, etc.. Actual work was first commenced at the portal of the tunnel in Carson Valley, three and one-half miles from Dayton, on October 19, 1869. The work was carried on by hand until September, 1872, when diamond-drilling was begun and experi- mented with, more or less unsuccessfully; in 1874, Burleigh drills were introduced, operated by compressed air generated in Fig. 4. Driving a modern tunnel with machine-drills. a compressor made by the Societe John Cockerill, of Seraing, Belgium. The tunnel was completed July 18, 1878, when the Savage vein was cut 20,000 feet from the portal and 1,922 feet below its outcrop. The tunnel, inside of the timbers, was 10 feet high by 14 feet wide, divided into two passageways by a central row of posts. The rate of progress varied greatly, rang- ing from 19 to 417 feet per month, the average monthly rate from start to finish being 192.3 feet.* * Report Commissioners Sutro Tunnel, and Drinker, pp. 337-350. THE HISTORY OF TUNNELING 21 The Tequiquac tunnel, which now forms the most important link in the drainage system of the valley of Mexico, was com- menced during the reign of the Emperor MaximiHan. The work was stopped, however, at the fall of the Empire and was not resumed until 1885; ^^^^ then the want of funds prevented any material progress until March, 1888. This tunnel is six and a quarter miles in length, driven through a mass of sand, mud, and soft calcareous sandstone. It is brick- lined throughout, the section ovoid, with an extreme width of 13 feet 9 inches and a height of 14 feet and has a gradient of I foot in 1,388. The calculated flow is 450 feet per second, or 200,000 gallons per minute. At first the headings were driven in the center, but they were soon forced to adopt the bottom heading system. The greatest completed tunnel advance in any one month was 182 feet and the greatest distance that any single heading was driven in a calen- dar month was 656 feet. (Trans. Am. Soc. C. E., Vol. XXXII, pp. 171-267.) The Kelty tunnel on the Glasgow Water Works System is 2.6 miles in length and 9 feet square. Work was commenced in June, 1887, and completed in December, 1889; driving was carried on from each portal and both ways from the bottom of two shafts. The average rate of progress in each heading was 4.5 feet per day. The rocks encountered varied from soft shale to hard conglomerate. The Shoshone tunnel, 1906-19 10, is owned by the Central Colorado Power Company, and its intake portal is located on the Rio Grande River, twelve miles above Glenwood Springs. It is 12,453 f^^t long, 12 feet high, and 16 feet 8 inches wide, and is driven for the entire distance through hard metamorphic granite. Where timber supports were necessary, vertical posts and a three-piece arch were employed, all of which were afterward completely covered by concrete hning. Driving was carried on from seven cross-cut adits, as well as from both intake and discharge ends. 22 MODERN TUNNELING Cost of tunnel, not including concrete lining, was $927,653, divided as follows: Construction costs per linear foot of tunnel: Test drifts $ .45 Drilling and blasting 20 . 66 Trenching and grading floor 1.15 Track work 1.76 Mucking and loading 17.28 Hauling 2 . 88 Dumping and maintenance 2.18 Blasting supplies 8.35 Drill steel 2.91 Sharpening and repairing 4 . 60 Timbering, temporary and permanent 3. 87 Light and wiring 1.57 Ventilating 59 Pipe, air hose, and connections 85 Power drills 2 . 94 Hoists and trestles 96 Pumping 21 Sundries 28 Total construction costs $74 . 49 Overhead costs, including surveying, management, office, etc 3091 Total cost per linear foot $105 . 40 The Corbett tunnel, of the Shoshone Irrigation Project, Wyoming, is approximately 17,000 feet in length, of the inverted horseshoe type, having a cross-section about 100 feet in area. The tunnel heads opposite the Corbett Station of the Chicago, Burlington & Quincy R. R., and its course is parallel to the general direction of the Shoshone River, which at three places was near enough to permit adits to be excavated from the faces of the bluffs to the tunnel, thus affording eight headings for construction purposes. The contract for its excavation was awarded on September 16, 1905, the price being $33 per linear foot. In August, 1906, however, the contractor defaulted after having driven 5,219 feet of tunnel, and the work was taken over H THE HISTORY OF TUNNELING 23 by the United States Reclamation Service. After doing con- siderable retimbering the work was carried on without any special difficulties until its completion in 1907. The material excavated throughout the tunnel consisted of dry clay, loose shales, and stratified sandstones of different degrees of hardness, and it decomposed very rapidly upon exposure to the air, thus requiring considerable timbering. The Big Bend tunnel, owned by the Great Western Power Co., is situated at Big Bend on the Feather River in Butte County, Cal. The main portion of the tunnel, about three miles in length, was driven by the Big Bend Mining Co., from 1883 to 1887, in order to divert the flow of the river across a narrow neck of land and leave the bend dry, allowing the company to work the gravels in its bed for gold. This tunnel was enlarged from 12 feet high by 13 feet wide to 18 feet high by 14 feet wide, and extended 3,400 feet by the present owners in 1 907-1 908. The entire tunnel is driven through shale with the exception of about 6,000 feet in the middle of the old tunnel, which is in diorite. It is lined with concrete about 29 inches thick, with an allowable minimum of 6 inches on the arch and 4 inches on the invert. The Coquitlam tunnel, which is part of the hydro-electric power system supplying Vancouver, B. C, and neighboring towns, is 12,650 feet long and is driven through solid granite. As originally designed it had a mean sectional area of 81 square feet. Work of enlarging the tunnel so that it would have a sectional area of 176 square feet was begun in November, 1908, but was seriously handicapped by the necessity of opening the tunnel frequently to maintain the supply of water in a storage reservoir, but it was finally completed in March, 191 1. The new tunnel is ovoid in cross-section with the point down and is unlined. The Big Creek tunnel, which is part of the system of the Pacific Light and Power Corporation, is 22,000 feet long and 12 feet in diameter. It was driven from nine adits and two portals, has a slope of 3.2 feet per 1,000, and will be used as a pressure tunnel throughout, the static pressure at the upper 24 MODERN TUNNELING end being approximately 30 feet and at the lower end approxi- mately 100 feet. The formation pierced was solid blue granite throughout, except for an occasional faulted zone. These were lined with concrete, the aggregate length of such linings being 2,000 feet. RAILWAY TUNNELS While this book is intended to deal chiefly with the con- struction of mining tunnels, there is much that can be learned from the study of tunnels driven for railroad purposes. Under ordinary conditions the rate of progress in a railroad tunnel is limited by the speed at which the advance heading can be driven, and as these headings do not differ materially from mining tunnels, the rates of progress which have been attained in them are of great interest to the miner. A railroad- tunnel heading must be driven to line and grade the same as a mining tunnel, and while it is desirable to maintain a uniform width and height, it is not absolutely necessary to do so, thus giving railway- tunnel headings a slight advantage over mining tunnels in this respect. On the other hand, the multifarious operations carried on between the heading and the portal of a railroad tunnel, even under the best possible organization, often obstruct tempo- rarily transportation to and from the face; the continuity of the work is sometimes interfered with by the shooting of the benches back of the face; and even where all the holes in the benches and headings are blasted together, it takes somewhat longer to clear out the smoke from so many groups of shots than it would in a mining tunnel from a single round in the heading. On the whole, in similar rock and with equally good equipment and organization, there should be little if any difference in the speed attained in driving a mining- tunnel or a railway tunnel- heading, because, although the conditions for rapid progress are not exactly identical, the opportunities are practically equal. The history of the more important railway tunnels of the world also shows forcibly the rapid increase in the rates of driving and the lessening of the cost of construction since the introduction of rock-drills and high explosives. THE HISTORY OF TUNNELING 25 PROGRESS AND COST OF SOME FAMOUS RAILWAY TUNNELS Construction Period Length, Miles Duration Boring, Months Avg. Daily Progress in Headings, Feet Cost per Linear Foot Mt. Cenis Hoosac St. Gothard Arlberg 1857-1870 1858-1874 1872-1882 I 880-1 883 I 898-1 905 1 906-19 1 1 7-97 4-75 9.26 6.2 12.4 9.3 157 ... 88 40 78 54 6.2 13-6 I3.69t 14.2 t $356.00 398.00 231.00 162.30 239.40 211.00 Simplon Loetschberg * Average east and west headings, 1 865-1 873. Allowing only for days on which drilling was carried on, advance was 7.45 feet per day. i Average for last 30 months, 17. feet. The Mt. Cenis tunnel was driven through the northern spur of the Cottic Alps to afford direct connection between the French and Italian railway systems. Work was begun on August 18, 1857, and the French and Itahan headings met on December 25, 1870. The length of the tunnel as completed was 42,157 feet and the cost $15,000,000, or $356 per linear foot. Its greatest depth below the surface was 5,275 feet, where the rock temperature was 85° F. The Sommeiller rock- drill, operated by compressed air, was first used in this tunnel January 12, 1861, or five years before the introduction of air- drills into the Hoosac tunnel in the United States. The rate of progress varied greatly with the rock encountered; the total time consumed in driving being thirteen years and one month, or an average daily progress in each heading of 4.4 feet.§ One of the most important early tunnels driven in the United States was the Hoosac, on the line of the Troy & Greenfield Railway. The project first came under consideration in 1825, but actual work was not commenced until 1858. Hand-drilling was employed until October 31, 1866, when Burleigh rock-drills were first introduced; two months later nitroglycerine was substituted for black powder, and the net result of these two most important improvements was greatly to increase the rate of driving. To be sure, many disheartening delays and interrup- § Drinker, pp. 354-357. Vernon-Harcourt, Pro. Inst. C. E., Vol. XCV, pp. 249-261. 26 MODERN TUNNELING tions occurred, due chiefly to failure of the earlier type of drilling machines and to change of engineers and contractors, but in March, 1869, a contract was let to the Shanly Brothers, of Toronto, who completed the work on December 22, 1874. The tunnel had a total length of 4^^ miles and was driven throughout the greater part of that distance in mica-schist. The maximum speed attained in a single heading was 184 feet in one month of twenty-six working days, and the average speed in the east and west headings for the last six months was 4.2 feet per day. The cost was $10,000,000, or $398 per linear foot.* The great undertaking of driving the St. Gothard tunnel was rendered possible through a joint treaty made by Germany, France, and Italy, and on May 7, 1872, a contract for the tunnel was let to M. Favre, of Genoa, who gave a bond for $1,600,000 for the successful completion of the work within a period of eight years. The tunnel is 48,887 feet, or 9.26 miles, in length, driven for the most part through various kinds of schist. After testing a number of drills, a final selection was made of Ferroux drills for the north side and McKean for the south side. The average rate of progress in the headings was 186 feet per month. In 1880 one of the headings passed through a zone of softened feldspar, which, under the weight of the superincumbent rock, squeezed into the tunnel with such force that granite walls and arches 6 feet 7 inches in thickness were required to hold it in place. The maximum rock temperature encountered was 88° F., at a point 5,575 feet below the surface. The headings met February 29, 1880, but the tunnel was not completed until 1882, nearly two years after the time called for in the original con- tract. The total cost was $11,300,000, or $231 per linear foot.f The success of the Mt. Cenis and St. Gothard tunnels, coupled with the desire of the Austrian Government to have a railway route to France which would not pass through Germany or Italy, led to the construction of the Arlberg railway, which runs from Innsbruck, in the Tyrol, to Bludenz, near the Swiss frontier, * Drinker, pp. 315-337- t Drinker, pp. 359-370. Vernon-Harcourt, Pro. Inst. C. E., Vol. XCV, pp. 261-268. I THE HISTORY OF TUNNELING 27 a distance of eighty-five miles, piercing the Arlberg range about twenty miles from Bludenz by a tunnel over six miles long. In the selection of the machinery and in planning the work, advantage was taken of the experience gained in the Mt. Cenis and St. Gothard tunnels. In consequence of this, the results obtained were as much in advance of the St. Gothard as the operations in that tunnel had been an improvement on those employed in the ^It. Cenis. The driving of this tunnel was commenced in July, 1880, and the headings met on November 13, 1883. The average rate of progress was thus nearly two miles per year. The greatest temperature of the rock was 64° F. at a point 2,295 ^^^^ below the surface. The Ferroux percussion drill, operated by compressed air, was employed in the eastern heading, and the Brandt rotary drill, worked by water pressure, in the western. The Ferroux drills drove 17,355 feet and the Brandt drills 14,880 feet, a difference of 2,475 ^^^^ in favor of the former. This variation was due more to the dissimilarity of the rock in the east and west headings than to any difference in the efficiency of the drills themselves, as is shown by the following figures, the average daily advance of the two drills being as follows: Ferroux Brandt Year 13-5 ft. 17.2 " 17.85 " 9.5 ft. I5.I " 17.82 " In 1881 In 1882 In the io>^ months of 1883 These figures show that as the nature of the rock became similar when the faces approached each other, the efficiency of the Brandt drill was practically the same as the Ferroux. The Brandt drill was much more cheaply operated than the other, and it necessitated the use of only seven miners in the heading as against twelve with the Ferroux. The total length of the tunnel was 32,235 feet and its cost was $5,877,684, or $182.30 per linear foot.* * Vernon-Harcourt, Pro. Inst. C. E., Vol. XCV, pp. 268-271. Charton, "Le Genie Civil," Vol. VI, 1885, pp. 3-18. 28 MODERN TUNNELING The Simplon tunnel consists of two parallel, single-track railway tunnels, 56 feet from center to center, driven from Brigue, Switzerland, to Iselle, Italy, a distance of 12.4 miles. Operations commenced at Brigue November 22, 1898, and at Iselle December 21, 1898. The headings met February 24, 1905, but the tunnel was not completed and ready for use until January 25, 1906. Brandt rotary hydraulic drills were employed in both headings and the average rate of heading advance was 13.69 feet per diem, although when conditions were favorable speeds of 16 feet per day in the Itahan end and 20 to 21 feet in the Swiss end were readily attained. The rock was principally gneiss, with occasional beds of slate, granite, and marble. When operating in hard rock, the cycle of operations was as follows : Bringing up and adjusting drills 20 minutes Drilling i3^-2>2 hours Charging and firing 15 minutes Mucking 2 .hours More serious difficulties were encountered in driving this tunnel than any which have yet been undertaken. Swelling ground was extremely common, and in places the pressure was so great that the roof and sides could only be held in place by steel I-beams, with the spaces between rammed with rapid-setting concrete. A portion of the tunnel where the pressure was the greatest is said to have cost $1,620 per linear foot. Many springs were encountered, and the volumes of cold water flowing into the tunnel amounted at times to 17,000 gallons per minute. Near the center of the tunnel large springs of hot water were encountered, amounting in all to 4,330 gallons per minute, one spring alone giving 1,400 gallons per minute at 116° F. At first it seemed that the high temperatures engendered would effectually prevent further advance, but by bringing both cold water and cold air into the headings in sufficient volumes, the temperature was reduced to a point where it was possible to resume work, although it took six months to drive the last 800 THE HISTORY OF TUNNELING 29 feet. The rapid average rate of progress maintained in the Simplon tunnel, in spite of the difficulties encountered, was due to superb equipment and an organization so efficient that 648 men and 29 horses at the Swiss end and 496 men and 16 horses at the Italian end were advantageously employed. Notwithstanding the care that was taken in ventilation and the precautions adopted for the health and safety of the work- men, sixty men were killed during the progress of the work. The total cost of tunnel was $15,700,000, or $239.40 per linear foot.* The Loetschberg tunnel was driven through the Bernese Alps in Switzerland and forms the last link in the railway sys- tem connecting the city of Berne with the village of Brigue at the north end of the Simplon tunnel. The desirability of con- necting the Bernese Oberland with the Rhone Valley was dis- cussed as early as 1866 and the present location of the tunnel was first proposed in 1889. The railway begins at Frutigen in the Bernese Oberland, about 32.5 miles from the north portal; 50.5 per cent of this length is on horizontal curves. There are about twelve short tunnels on the line, aggregating 16,000 feet in length, one of which is a spiral tunnel 5,460 feet long, with a 985-foot radius. The main tunnel is 47,678 feet long and was first planned to be run on a tangent, but a serious cave 1.6 miles from the north portal, which killed 25 men and filled up 5,900 feet of tunnel, compelled the abandonment of the original fine and the adoption of a curved tunnel to pass around the immense, peaty, mud-filled fissure which the heading had tapped. At the south end IngersoU-Rand air drills and compressors were used, while in the north end Myers drills and compressors were adopted. Transportation in the tunnel was handled by compressed-air locomotives running on 30-inch gauge tracks. From four to six drills were employed in each heading, mounted on a horizontal bar, which was carried on a carriage, thus neces- sitating mucking out after firing before drilling could be com- menced in the face. For the last thirty months of driving, the * Trans. A. I. M. E., Vol. XLII, pp. 441-446. Fox, Pro. Inst. C. E., Vol. CLXXIII, pp. 61-83. 30 MODERN TUNNELING average rate of progress in the south heading was 15.8 feet per day, and in the north end, where the driving was much easier, 18.6. feet per day. On the north side, when the heading was in limestone, it was advanced 5,623 feet in six months, or an average rate of 30.8 feet per day.* The Busk-Ivanhoe tunnel, on the Colorado Midland Railway between Leadville and Glenwood Springs, is 9,394 feet long, and has an altitude of 10,810 feet at Busk and at Ivanhoe 10,944 feet, making it the third highest railway tunnel in the world. It is driven almost the entire distance in metamorphic granite with some softened shear zones which gave considerable trouble in both driving and timbering. The tunnel cost $1,250,000, and thirty men were killed in the progress of the work.f The Severn tunnel (i 873-1887), which is on the line of the Great Western Railway in England, and passes under the estu- ary of the Severn River, has a length of 4.35 miles and traverses a great variety of strata consisting of conglomerate, limestone, carboniferous beds, sandstone, marl, and sand. The most serious difhculty encountered in driving was the great volume of water coming into the tunnel, not so much from the estuary above as from a huge spring on the land side. Several ineffectual attempts were made to bulkhead this spring, but before the work could be successfully carried on, it was necessary to erect an immense pumping plant with a capacity of 45,000 gallons per minute, but the maximum amount pumped for any considerable period did not exceed 20,000 gallons per minute. { The Totley tunnel, on the Dore & Chinley Railway, England, is 3.53 miles in length, and is on the line between Sheffield and Manchester. Work was commenced in 1888 and the completed tunnel was ready for traffic in September, 1893. It is driven almost entirely through carbonaceous black shale which con- tained some strata of sandstone and grit. The progress of the work was greatly impeded by heavy inrushes of water, some- * Saunders, Trans. A. I. M. E., Vol. XLII, pp. 446-469. Bonnin, La Nature, Paris, 1909, Vol. XXXVII, pp. 147-157. '\ Engineering News, August 25, 1872. IVernon-Harcourt, Pro. Inst. C. E., Vol. CXXI, pp. 305-308. THE HISTORY OF TUNNELING 31 times carrying vast quantities of sand and silt. For a time the discharge from the Padley heading amounted to 5,000 gallons per minute. At first the water was carried out of the tunnel in 12-inch pipes, but as these proved insufficient and liable to clog with sand, the headings were closed up with watertight bulkheads and center drains carried in from the portal. This work took six weeks, during which time the pressure behind one of the dams rose to 155 pounds per square inch.* The Aspen tunnel on the Union Pacific Railway between Cheyenne and Ogden, although only 5,900 feet in length, is interesting on account of the obstacles encountered in driving, the difficulty of holding back the swelKng ground, and the fact that mechanical loading of the broken rock was successfully employed in both headings. The tunnel was driven through carbonaceous shale containing an occasional stratum of yellow sandstone dipping 20° to 30° to the east, while the course of the tunnel was a little south of west. The opening is 22 feet 6 inches high and 17 feet wide in the clear, timbered with 12 by 12 -inch timbers with vertical posts capped with a seven-segment circular arch. These timber sets were spaced 2 feet apart, i foot apart, or close together, as the weight of the ground demanded. On a portion of the tunnel, walls of soHd 12 by 12-inch timbers would not stand the rock pressure, and the timbers were replaced by 12-inch steel I beams, which were sometimes buckled side- ways before the concrete filling could be rammed in place. Small steam shovels of ^-cubic yard bucket capacity, and operated by compressed air, were employed for loading cars in the headings, and effected a great saving in both time and expense.! Arthur's Pass tunnel. South Island, New Zealand, sometimes known as the Otiro, is on the Kne of the New Zealand Govern- ment Railway which connects Christchurch on the east with Greymouth on the west coast, and pierces the crest of the South- ern Alps for a distance of sH miles. Work began in May, 1898, and the contract called for the completion of the work in a *Rickard, Pro. Inst. C. E., Vol. CXVI, pp. 1 17-138. f Hardesty, Engineering News, March 6, 1902. 32 MODERN TUNNELING period of five years; price $5,000,000. Tunnel haulage was at first attempted with eight- ton benzine locomotives, but they were discarded on account of uncertain action and the annoying fumes, and electric locomotives were substituted.* PARTIAL LIST OF NOTED RAILROAD TUNNELS f Name of Tunnel Simplon St. Gothard Loetschberg Mont Cenis Arlberg Ricken Tauern Ronco Tenda Hauenstein Base Karawanken . . . . Somport Jungfrau Borgallo Hoosac Severn Marianopoli Turchino Grenchenberg . . . Wocheiner Mont d'Or Albula Totley Peloritana Gravehals Puymorens Standedge Woodhead Bosruck La Nerthe Biblo Kaiser Wilhelm. Echarneaux Blaisy Cascade Sodbury Country Switzerland- Italy . Switzerland- Italy . Switzerland France- Italy Austria Switzerland Austria Italy Italy Switzerland Austria France-Spain Switzerland Italy. United States .... England- Wales . . . Sicily Italy Switzerland ...... Austria France- Switzerl'nd Switzerland England Sicily Norway France-Spain England England Austria France Italy Germany France France United States. . . . England Length Feet 65,734 49,212 47,685 42,150 32,892 28,230 28,038 27,231 26,568 26,400 26,169 25,656 23,622 23,220 23,175 23,028 22,453 21,150 21,120 20,781 20,025 19,290 18,690 17,898 17,388 16,791 16,020 15,879 15,639 15,303 13,907 13,767 13,620 13,530 13,413 13,299 Summit level Feet 2,313 3,788 4,077 4,248 4,300 650 4,020 3,260 2,088 1,787 1,761 6,133 2,844 2,405 Opened for traffic 1906 1882 1913 1871 1885 191O 1909 1888 1899 X 1906 % I9I2 1887 1876 1886 1900 t 1909 X 1903 1893 1885 1909 X 1850 1845 1906 1879 1895 [903 * Gavin, Engineering News, May 9, 19 12. t Abstract from The Engineer, November 28, additions from other sources. I Under construction 1913— 14. [913, P- 561—2, with a few THE HISTORY OF TUNNELING 33 PARTIAL LIST OF NOTED RAILROAD TUNNELS— (Continued) Name of Tunnel Credo Vizzavona Khojak Suram Disley Col de St. Michel Bramhope Festinog ....... Cowburn Meudon Giovo Col des Loges . . . Cremolina Stampede Cairasca Busk-Ivanhoe. . . Caldera Hauenstein Beacon Hill Transandine . . . . Country France . . . . . Corsica . . . . . Baluchistan. Caucasus. . . England. . . . France . England Wales England France Italy Switzerland. . . . Italy United States. . Italy United States. . Peru Switzerland. . . . China Chile- Argentina Length Feet 12,960 12,894 12,867 12,810 11,598 11,430 11,262 11,178 11,106 10,962 10,695 10,560 10,514 9,850 9,840 9,394 9,240 8,910 7,212 6,933 Summit level Feet 2,791 890 200 944 775 10,500 Opened for traffic 1889 1892 1895 1902 I901 1849 1879 1893 1900 1906 1893 19IO 191I The following4s a list of some of the more important Japanese tunnels. Tsudo adit. Ashio Mine, driven September, 1 88 5-October, 1896, II feet high, 13 feet wide, and 10,000 feet long. Located on the bank of Watarase River. This tunnel is furnished with double- track electric railway, and has seven shafts, each installed with electric hoist. The mine contains an aggregate length of more than 600,000 feet of levels and winzes. Omodani Mine. Ono District. Has five levels, aggregating 58,380 feet in length; the longest having a length of 12,110 feet, while the drainage adit is 10,850 feet long. Yoshioka Mine. Kawakami District. Mine opened by eight levels and crosscuts, totaling 134,281 feet, the main adit being 39,193 feet in length. Okawamae adit. This adit is for draining the Kusakura Mine, Niigataken, and has a length of 10,000 feet. Sosuido tunnel* of Sado Mine, Island of Sado, 11,000 feet long. Sosuido adit.* This adit is to drain the Innai Silver Mines, and is 8 feet high, 10 feet wide, and 7,800 feet long. Nagara Yama tunnel. (No. if Lake Biwa Canal, near Kyoto.) * Sosuido means "Drainage level." t There are two Lake Biwa Canals, the first executed in 1886— 1890, and the second 1909— 191 1. 34 MODERN TUNNELING Executed in 1886-1890, 14 feet high, 16 feet wide, and 8,040 feet long. Rock of slate and sandstone chiefly. N agar a Yama tunnel. (No. 2* Lake Biwa Canal, near Kyoto.) Executed in 1909-1911, 13^^ feet high, 13 feet wide, and 8,826 feet long. Rock slate chiefly. Kamuriki Railway tunnel. Shinano District. Executed in 1896- 1900. i6>^ feet high, 15 feet wide, and the length is 8,712 feet. Hard rock. Kohotoke Railway tunnel. Kai District. (Imperial Government R.R.,in line from Tokyo to Kofu.) Executed in 1897-1900, i6>^ feet high, 15 feet wide, and 8,356 feet long. Clay rock chiefly. Sasago Railway tunnel. Kai District. (Imperial Government R.R. in line from Tokyo to Kofu.) Executed in 1896-1902, i6yi feet high and 15 feet wide. The length is 15,280 feet, being the largest railway tunnel (in one length) completed in Japan. Soft rock. Ikoma Yama tunnel.^ (Kyoto & Nara Electric Ry.) 17 feet io>^ inches high, 22 feet i}4 inches wide, and 11,088 feet long. Dokuritsu 2^^% tunnel. Mt. Ari R.R., Formosa. (Just completed.) From Kagi Entrance A to Ari Entrance B, three miles, and the length of the tunnels in that section i mile and 23 chains and 77 links. The dimensions of the tunnels are in accordance with the regular construction gauge of the Imperial Government Railways. Daishi Tsudo. (No. 4 tunnel.) Beshi Copper Mines, lyo District, 14 feet high, 16 feet wide, and 18,000 feet long. Rock, palaeozoic chlorite, and mica schist. * There are two Lake Biwa Canals, the first executed in 1 886-1 890, and the second 1909-1911. t Yama in this table means altitude or mountain. I 2^" means the same as Yama, only in Chinese pronunciation. CHAPTER III MODERN MINING AND WATER TUNNELS RESUME OF DATA The following paragraphs contain brief descriptions arranged alphabetically of tunnels and adits visited in the special field work upon which this book is based. In their examination, complete information was obtained, wherever possible, concerning surface and underground equipment, provisions for the safety of the men, the use of explosives, and the methods employed in driving, with regard to efficiency, cost, and other similar data bearing upon the problem. (See Appendix, page 421.) It is impossible, because of lack of space, to reproduce all of this some information here, but the following paragraphs convey briefly idea as to the main features of the different tunnels. Burleigh tunnel: Silver Plume, Colorado. Purpose, mine drainage and development. Length, 3,000 feet. Cross-section, rectangular, 6 feet wide by 7 feet high. Rock, granite and gneiss. Power, steam. Ventilation, exhaust fan, 10- and 12 -inch pipe. Drills, Burleigh drills used in 1869 (first use of machine drills in an American tunnel) ; Ingersoll-Rand and Leyner drills used in driving last 2,800 feet. Mounting, vertical columns. One shift per day. Two drillers, two helpers, and three muckers per shift. Horse haulage, one-ton cars. Six ty-per- cent gelatine dynamite. No timbering. Average monthly progress, 100 feet. Approximate cost per hnear foot, S20. Started in 1869 and driven 200 feet while testing Burleigh drills; extended later to 3,000 feet for mine drainage. Carter tunnel: Ohio City, Colorado. Purpose, mine drainage and transportation. Length, 6,600 feet. Cross-section, rect- angular with arched roof, 5.5 feet wide by 7.5 feet high. Rock, gneiss. Power, hydraulic and hydro-electric. Ventilation, ex- haust blower, lo-inch pipe. Two Leyner drills mounted on ver- 35 36 MODERN TUNNELING tical columns. One drilling and two mucking shifts daily. Two drillers, one helper, and two muckers per shift. Horse haulage, 2i-cubic-foot cars. Forty-per-cent and eighty -per-cent gelatine dynamite, 8 pounds per cubic yard. One hundred feet timbered. Approximate cost per linear foot, $io to $15. Started 1897; on November i, 191 1, had driven 6,550 feet; part of intervening time spent in drifting along laterals; three years shut down entirely, and five years only three men at work. Catskill Aqueduct: Ulster, Orange, Putnam, and Westchester Counties, and New York City, New York. Length, see list of various tunnels on this project given below. Cross-section, see Figure 5. This aqueduct includes the following tunnels: Fig. 5. Cross-sections of typical tunnels, Catskill Aqueduct. Peak: Length, 3,470 feet. Rock, hard. Started, November, 1908; completed, November, 1909. Rondout Siphon: Length, 23,608 feet. Cross-section, circular. Rock, Onondaga limestone, Binnewater sandstone, Hudson River shale, Esopus shale. High Falls shale, Shawangunk grit, Hamilton and Marcellus shale, Helderburg Kmestone. Power, steam. Ventilation, exhaust fan, 14- and 20-inch pipe. Four Ingersoll-Rand drills in each heading. Mounting, vertical col- umn. Two drilling and three mucking shifts per day. Four drillers, four helpers, and ten muckers per shift. Mule haulage, MODERN MINING AND WATER TUNNELS 37 40-cubic-foot cars. Sixty-per-cent gelatine dynamite, 4 to 5 pounds per cubic yard of heading. Lined with concrete. Aver- age monthly progress per heading, 220 feet. Started, March, 1909; completed. May, 191 1. Bonticou: Length, 6,823 feet. Cross-section, horseshoe. Rock, Hudson River shale. Started, November, 1908; com- pleted, February, 191 1. W allkill Siphon: Length, 23,391 feet. Cross-section, circular. Rock, Hudson River shale. Power, electricity, purchased. Ventilation, fan, 12- and 14-inch pipe. Four Ingersoll-Rand or SulKvan drills in each heading. Mounting, vertical column. Three shifts per day. Four drillers, four helpers, and eight muckers per shift. Electric haulage, 40-cubic-foot cars. Sixty- per-cent gelatine dynamite, 4.3 to 4.6 pounds per cubic yard of heading. Lined with concrete. Average monthly progress per heading, 300 feet. Started, October, 1909; completed, Decem- ber, 1910. Moodna Siphon: Length, 25,200 feet. Cross-section, circular. Rock, hard sandstone, granite, and Hudson River shale. Power, steam. Ventilation, jet of compressed air in 12-inch pipe. Four Ingersoll-Rand drills per heading. Mounting, vertical column. Three shifts per day. Four drillers, four helpers, and ten muckers per shift. Mule haulage, 40-cubic-foot cars. Seventy- five-per-cent gelatine dynamite. Lined with concrete. Average monthly progress per heading, 165 feet. Started, February, 1 9 10; completed, June, 191 1. Hudson Siphon: 1,100 feet below sea level. Length, 3,022 feet. Rock, granite. Started, December, 19 10; completed, January, 191 2. Breakneck: Length, 1,054 feet. Cross-section, horseshoe. Rock, granite and gneiss. Started, December, 19 10; com- pleted, April, 191 1. Bull Hill: Length, 5,365 feet. Rock, granite. Started, June, 1909; completed, January, 1911. Garrison: Length, 11,430 feet. Rock, hard gneiss. Started, June, 1907; suspended, November, 19 10, to April, 19 11; com- pleted, 191 2. 38 MODERN TUNNELING Hunters Brook: Length, 6,150 feet. Cross-section, horseshoe. Rock, schist of variable hardness. Started, September, 1909; completed, 191 2. Turkey Mountain: Length, 1,400 feet. Rock, Manhattan schist. Started^ October, 1909; completed, December, 1910. Croton Lake: Length, 2,639 ^^^t. Rock, Manhattan schist and Fordham gneiss. Started, July, 19 10; completed, January, 191 2. Croton: Length, 3,000 feet. Rock, Manhattan schist. Started, August, 1909; completed, December, 1911. Chadeayin: Length, 700 feet. Rock, Manhattan schist. Started, November, 1909; completed, September, 19 10. Millwood: Length, 4,750 feet. Rock, hard gneiss. Started, May, 1 9 10; completed, 191 2. Sarles: Length, 5,230 feet. Rock, hard gneiss and schist. Started, February, 1910; completed, 1912. Harlem Railroad: Length, 1,100 feet. Rock, hard gneiss and schist. Started, June, 19 10; completed, January, 191 1. Reynolds Hill: Length, 3,650 feet. Rock, schist. Started, October, 19 10; completed, 191 2. East View: Length, 5,388 feet. Rock, schist. Started, April, 1 910; completed, January, 191 2. Elmsford: Length, 2,375 f^^t. Rock, soft schist. Started, May, 1911; completed, 191 2. Yonkers Siphon: Length, 12,302 feet. Cross-section, circular. Rock, Yonkers gneiss and granite. Power, electrical. No ventilation supplied, except by opening compressed-air line. Four Ingersoll-Rand drills in each heading. Mounting, vertical columns. Two drilling shifts and three mucking shifts per day. Four drillers, four helpers, and eight to twelve muckers per shift. Mule haulage, 40-cubic-foot cars. Sixty-per-cent gelatine dynamite, 4 to 5 pounds per cubic yard of heading. Lined with concrete. Average monthly progress per heading, 155 feet. Started, July, 1910; completed, July, 191 1. Van Cortlandt Siphon: Length, 1,809 feet. Rock, Yonkers gneiss. Started, July, 19 10; completed, September, 191 1. City tunnel: Length, 18. 11 miles. Rock, Fordham gneiss and Manhattan schist. Started, December, 191 1; completed, 1914. MODERN MINING AND WATER TUNNELS 39 Central tunnel: Idaho Springs, Colorado. Purpose, mine drainage and transportation. Length, 9,000 feet. Cross-section, rectangular. Two thousand five hundred feet driven 12 feet wide by 8 feet high; the remainder 5 feet wide by 7 feet high. Rock, Idaho Springs gneiss. Power, steam. Ventila- tion, exhaust with blower through 19-inch pipe. Two Leyner drills in the heading. Mounting, horizontal bar. One shift per day. Two drillers, two helpers, and four muckers per shift. Horse haulage, 30-cubic-foot cars. Forty-per-cent gelatine dynamite, 5 to 7 pounds per cubic yard of heading. One hundred feet timbered. Average monthly progress in the heading, 200 feet. Coronado tunnel: Metcalf, Arizona. Purpose, mine develop- ment and transportation. Length, 6,300 feet. Cross-section, square, 9 by 9 feet. Rock, granite and porphyry. Power, steam with crude oil as fuel. Ventilation, blow and exhaust with pressure blower through a 12-inch pipe. Ingersoll-Rand and Sullivan drills were used in the first half of the tunnel, Leyner- Ingersoll drills were used in the last half. Three shifts per day. Two and three drillers, one helper, and four to six muckers per shift. Mule haulage, '* one-ton" cars. Sixty-per-cent and loo-per-cent gelatine dynamite. Average monthly progress, 415 feet. Average cost per linear foot, $22.64. (See page 329.) Started, June, 191 2; completed, August, 1913. Gold Links tunnel: Ohio City, Colorado. Purpose, mine drainage and transportation. Length, 3,900 feet. Cross-section, rectangular with arched roof, 6 feet wide by 8 feet high. Rock, gneiss, intruded granite, porphyry. Ventilation, exhaust with fan through 15-inch pipe. One Ingersoll-Rand drill. Mounting, vertical column. Two shifts per day. One driller, one helper, and two or three muckers per shift. Horse haulage, 25-cubic- foot cars. Forty-per-cent gelatine dynamite, 5 to 6 pounds per cubic yard of heading. Two hundred feet timbered. Average monthly progress, 200 feet. Approximate cost per linear foot, not including permanent equipment, $19. Started, May, 1906; driven intermittently; completed, December, 191 2. Gunnison tunnel: Montrose, Colorado. Purpose, irrigation. 40 MODERN TUNNELING Length, 30,645 feet. Cross-section, horseshoe, 10 feet wide, 12.5 feet high. Rock, chiefly metamorphosed granite, with som_e water-bearing clay and gravel, some hard black shale, and a zone of faulted and broken material. Power, steam. Ventila- tion, blow and exhaust with blower through 15-inch pipe. Four Sullivan drills per heading (Leyner drills also tried). Mounting, vertical column for SulHvan drills; horizontal bar for Leyner drills. Three shifts per day. Four drillers, four helpers, and five to eight muckers per shift. Electric haulage, 35- and 54- cubic-foot cars. Sixty- and 40-per-cent gelatine dynamite. 5.5 pounds per cubic yard of heading. Fourteen thousand five hundred feet timbered. Average monthly progress per heading, 250 feet. Cost per Hnear foot of tunnel, $70.66. Started, January, 1905; completed, July, 1909. Laramie-Poudre tunnel: Larimer County, Colorado. Purpose, irrigation. Length, 11,300 feet. Cross-section, rectangular, 9.5 feet wide by 7.5 feet high. Rock, close-grained granite. Power, hydraulic and hydro-electric. Ventilation, exhaust with blower through 14-inch and 15-inch pipe. Three Leyner drills in the heading. Mounting, horizontal bar. Three shifts per day. Three drillers, two helpers, and six muckers per shift. Mule haulage, i6-cubic-foot cars. Sixty- and loo-per-cent. gelatine dynamite, 3.9 to 4.9 pounds per cubic yard of heading. Six hundred and thirty feet timbered. Average monthly progress per heading, 509 feet. Cost per linear foot of tunnel, $39.54. Started, December, 1909; completed, July, 191 1. Lausanne tunnel: Mauch Chunk, Pennsylvania. Purpose, mine drainage. Length, 20,000 feet. Cross-section, arched roof, 12 feet wide by 8 feet high. Rock, shale, conglomerate, slate, and anthracite coal. Power, steam. Ventilation, blow with fan through two 16-inch pipes. Two Ingersoll-Rand drills in the heading. Mounting, vertical columns. Three shifts per day. Two drillers, two helpers, and four to five muckers per shift. Electric haulage, 78-cubic-foot cars. Sixty- per-cent gelatine dynamite. Average monthly progress per heading, 340 feet. Cost per linear foot of tunnel, $19. Started, July, 1906; completed, February, 191 2. MODERN MINING AND WATER TUNNELS 41 Los Angeles Aqueduct: Location, Inyo, Kern, and Los Angeles Counties, California. Purpose, water supply, power, and irriga- tion. Cross-section, see Figure 6. Fig, 6. Cross-sections of typical tunnels, Los Angeles Aqueduct. Little Lake and Grapevine Divisions: Power, electricity, pur- chased from separate plant owned by the Aqueduct. Ventila- 42 MODERN TUNNELING tion, blow and exhaust with pressure blower through 12-inch pipe. Two Leyner drills per heading. Mounting, horizontal bar. One and two shifts on Little Lake Division; two shifts per day on Grapevine Division. Two drillers, two helpers, and five muckers per shift. Mule and electric haulage on Little Lake Division; electric haulage on Grapevine Division, 32-cubic- foot cars both Divisions. Forty-per-cent gelatine dynamite, 4/^ pounds per cubic yard of heading. Grapevine Division; 14,745 feet timbered on Little Lake Division; 1,500 feet timbered on Grapevine Division. Started, 1909; completed, 1913- Tunnel iB: Length, 1,918 feet. Rock, medium granite. Started, June, 1909; completed, December, 1909. Tunnel 2: Length, 1,739 feet. Rock, medium granite, very wet. Started, May, 1909; completed, September, 1909. Tunnel 2 A: Length, 1,322 feet. Rock, medium granite. Started, May, 1909; completed, September, 1909. Tunnel j: Length, 4,044 feet. Rock, north heading, medium granite; south heading, variable granite, with pockets of CO2 gas. Started, March, 1909; completed, July, 191 1. Tunnel 4: Length, 2,033 ^^^t. Rock, medium to hard granite. Started, February, 1909; completed, November, 1909. Tunnel 5; Length, 1,178 feet. Rock, medium to hard granite. Started, February, 1909; completed, July, 1909. Tunnel 6: Length, 411 feet. Rock, medium granite. Started, February, 1909; completed. May, 1909. Tunnel y: Length, 3,596 feet. Rock, variable, soft, and swelling in parts. Started, March, 1909; completed, July, 1911. Tunnel 8: Length, 2,560 feet. Rock, medium to hard, swelling in parts. Started, November, 1909; completed, August, 191 1. Tunnel g: Length, 3,506 feet. Rock, medium to hard granite. Started, November, 1909; completed, February, 191 1. Tunnel 10: Length, 5,755 feet. Rock, medium granite. Started, December, 1909; completed, August, 191 1. Tunnel 10 A: Length, 5,961 feet. Rock, medium to hard granite. Started, March, 19 10; completed, December, 191 1. 4 modern mining and water tunnels 43 Grapevine Division: Tunnel 12: Length, 4,900 feet. Rock, hard granite. Started, July, 1909; completed, May, 191 1. Tunnel ij: Length, 1,958 feet. Rock, hard granite. Started, May, 1909; completed, April, 1910. Tunnel 14: Length, 859 feet. Rock, hard granite. Started, April, 1909; completed, February, 19 10. Tunnel 15: Length, 895 feet. Rock, hard granite. Started, May, 1909; completed, December, 1909. Tunnel 16: Length, 2,723 feet. Rock, hard granite. Started, April, 1909; completed, February, 19 10. Tw/zwe/ 17; Length, 3,022 feet. Rock, hard granite. Started, March, 1909; completed, November, 19 10. r^ww^/ 17/2.* Length, 1,364 feet. Rock, hard granite. Started, January, 19 10; completed, November, 19 10. Tunnel 17 A: Length, 5,330 feet. Rock, hard granite. Started, January, 19 10; completed, February, 191 2. Tunnel ly B: Length, 9,220 feet. Started, March, 1910; completed, 191 2. Elizabeth Lake Division: Elizabeth Lake tunnel: Length, 26,860 feet. Cross-section, rectangular with arched roof, 12.3 feet high by 12.75 feet wide. Rock, medium to hard granite. Power, electricity. Ventilation, blow and exhaust with blower through 18-inch pipe. Three Leyner drills in each heading. Mounting, horizontal bar. Three shifts per day. Three drillers, three helpers, and nine muckers per shift. Electric haulage, 32-cubic-foot cars. Forty-per-cent gelatine dynamite, 5 to 6 pounds per cubic yard of heading. Sixteen thousand four hundred feet timbered. Average monthly progress per heading, 350 feet. Cost per linear foot of tunnel, $40.50. Started, October, 1907; completed, February, 191 1. Lucania tunnel: Idaho Springs, Colorado. Purpose, mine development and transportation. Length, 6,385 feet. Cross- section, 8 feet square. Rock, hard granite. Power, purchased electricity. Ventilation, exhaust with blower through 18-inch and 19-inch pipe. Three Leyner drills in the heading. Mount- 44 MODERN TUNNELING ing, vertical column. One shift per day. Three drillers, two helpers, and three muckers per shift. Horse haulage, 22-cubic- foot cars. Fifty-per-cent gelatine dynamite, 8 to 9 pounds per cubic yard of heading. No timbering. Average monthly prog- ress, 125 feet. Cost per linear foot of tunnel, $23.06. Started, 1 901; driven intermittently; completed, 191 1. Marshall-Russell tunnel: Empire, Colorado. Purpose, mine drainage, development, mining, and transportation. Length, 6,400 feet. Cross-section, rectangular, 8 feet wide by 9 feet high. Rock, granite and gneiss. Power, purchased electricity with auxiliary hydraulic plant. Ventilation, exhaust with fan through 12-inch and 13-inch pipe. Two Leyner drills in the heading. Mounting, vertical column. One shift per day. Two drillers, two helpers, and four muckers per shift. Horse haulage, 28- and 25-cubic-foot cars. Forty- and 80-per-cent gelatine dynamite. One hundred and fifty feet timbered. Average monthly progress, 160 feet. Cost per linear foot of tunnel, $18.88. Started, 1901; driven intermittently; completed, 191 1. Mission tunnel: Santa Barbara, CaHfornia. Purpose, water supply. Length, 19,560 feet. Cross-section, trapezoid, 4.5 feet wide at the top, 6 feet wide at the base, and 7 feet high. Rock, shale, slate, and hard sandstone. Power, purchased electricity. Ventilation, blow and exhaust with blower through lo-inch pipe. One Leyner drill in the heading. Mounting, horizontal bar. Three shifts per day. One driller, one helper, and four muckers per shift. Electrical haulage, 22-cubic-foot cars. Forty- and 60-per-cent gelatine dynamite, 6 to 8 pounds per cubic yard of heading. Five hundred and sixty feet timbered. Average monthly progress, 210 feet. Cost per linear foot of tunnel, $19.91. Completed, 191 2. Newhouse tunnel: Idaho Springs, Colorado. Purpose, drain- age and transportation. Length, 22,000 feet. Cross-section, 8 feet square. Rock, Idaho Springs gneiss. Power, purchased electricity. A^entilation, exhaust with pressure blower through 18-inch pipe. Two and three Leyner drills in the heading. Mounting, horizontal bar and vertical column at different times. One and two drill shifts per day. Two and three drillers, two MODERN MINING AND WATER TUNNELS 45 helpers, and three muckers per shift. Electric haulage, 57- and 35-cubic-foot cars. Forty- and loo-per-cent gelatine dynamite. One thousand feet timbered. Started, 1893; driven intermit- tently; completed, November, 19 10. Nisqually tunnel: Alder, Washington. Purpose, hydro- electric power for City of Tacoma. Length, 10,000 feet. Cross- section, rectangular with arched roof, 9^ feet wide by 11 feet high. Rock, rhyolite. Power, hydraulic and hydro-electric. Ventilation, exhaust w^ith fan through 14-inch pipe. Two Ingersoll-Rand drills at the headworks end, two Leyner drills at the discharge end. Mounting, horizontal bar. Two drilKng shifts and three mucking shifts per day. Two drillers, two help- ers, and four muckers per shift. Electric haulage, 27-cubic-foot cars. Forty-per-cent gelatine dynamite. Practically no timber- ing. Average monthly progress per heading, 300 feet. Approxi- mate cost per linear foot of tunnel, not including permanent equipment, S15 to $20. Started, 1910; completed, 1912. Ontario tunnel: Park City, Utah. Purpose, mine drainage. Length, 24,000 fe^t. Cross-section, trapezoid, 5 feet wide at the base, 4 feet wide at the top, 7>^ feet high. Rock, porphyry, granite, quartzite, and limestone. Started, July 25, 1908; sus- pended for several periods of from one to fourteen months; still unfinished. Rawley tunnel: Bonanza, Colorado. Purpose, mine drainage and development. Length, 6,235 feet. Cross-section, trapezoid, 8 feet wide at the base, 7 feet wdde at the top, 7 feet high. Rock, andesite. Power, steam, wood fuel. Ventilation, exhaust with pressure blower through 12 -inch and 13 -inch pipe. Two Leyner drills in the heading. Mounting, horizontal bar. Two and three shifts per day. Two drillers, two helpers, and three muckers per shift. Horse haulage, 17-cubic-foot cars. Forty- and 6o-per-cent gelatine dynamite, 6 pounds per cubic yard of heading. One thousand six hundred and eighteen feet timbered. Average monthly progress, 350 feet. Cost per linear foot of tunnel, $19.88. Started, May, 1911; completed, October, 1912. Raymond tunnel: Ohio City, Colorado. Purpose, mine drain- age and development. Length, 3,200 feet. Cross-section, 9 feet \ 46 MODERN TUNNELING square. Rock, granite and gneiss. Power, steam. Ventilation, blow and exhaust with blower through 14-inch pipe: Three Leyner drills in the heading. Mounting, horizontal bar. One shift per day. Three drillers, two helpers, and two to three muckers per shift. Horse haulage, 32-cubic-foot cars. Forty- and 60-per-cent gelatine dynamite, 3 to 4 pounds per cubic yard of heading. One hundred feet timbered. Average monthly Fig. 7. Cross-section, Roosevelt Tunnel. progress, 200 feet. Approximate cost per linear foot of tunnel, $15. Started, 1903; driven intermittently; completed, 191 2. Roosevelt tunnel: Cripple Creek, Colorado. Purpose, mine drainage. Length, 15,700 feet. Cross-section, see Figure 7. Rock, Pike's Peak granite. Power, purchased electricity. Ven- tilation, exhaust with pressure blower through 16-inch and 17- inch pipe. Two and three Leyner drills in the heading. Mount- ing, horizontal bar. Three shifts per day. Three drillers, two helpers, and four muckers per shift. Mule haulage, i6-cubic- foot cars. Sixty- and loo-per-cent gelatine dynamite. No tim- bering. Average monthly progress per heading, 285 feet. Cost per linear foot of tunnel, $27.27. Started, February, 1908; com- pleted, November, 19 10. MODERN MINING AND WATER TUNNELS 47 Shepard^s Pass tunnel: Oakland, California. Purpose, elec- tric railway. Length, 3,000 feet. Rock, shale. Power, elec- tricity. Ventilation, fan. Three or four Ingersoll-Rand drills per heading. Horizontal bar mounting. One shift per day. Three to four drillers and helpers, four to six muckers (per head- ing) per shift. Electric haulage. Forty-per-cent gelatine dynamite. All timbered, ground very heavy. Average monthly progress, 160 to 175 feet. Started, 1911; completed, 1913- Siwatch tunnel: Leadville, Colorado. Purpose, development. Length, 5,000 feet. Cross-section, rectangular, 6 feet wide by 7.5 feet high. Rock, granite. Power, purchased electricity. Ven- tilation, exhaust with pressure blower through lo-inch pipe. Two Waugh stoping drills in the heading. Mounting, horizontal bar. Two shifts per day. Two drillers, no helpers, and two to three muckers per shift. Electric haulage, 33-cubic-foot cars. Forty-per-cent gelatine dynamite. Six hundred feet timbered. Driven intermittently; not yet completed. Snake Creek tunnel: Heber, Utah. Purpose, mine drainage and development. Length, 14,000 feet. Cross-section, rectan- gular, 9.5 feet wide by 6.5 feet high. Rock, diabase. Power, purchased electricity. Ventilation, exhaust with pressure blower through 16-inch pipe. Two SulHvan drills in the heading. Mounting, horizontal bar. Two shifts per day. Two drillers, two helpers, and three muckers per shift. Horse haulage, 20- cubic-foot cars. Forty- and 60-per-cent gelatine dynamite, 7 pounds per cubic yard of heading. Three hundred and fifty feet timbered. Average monthly progress, 250 feet. Started, May, 1 9 10; driven intermittently; not yet completed. Stilwell tunnel: Telluride, Colorado. Purpose, mine dramage and development. Length, 2,600 feet. Cross-section, 7 feet" square. Rock, conglomerate and andesite. Power, purchased electricity. Ventilation, exhaust with fan through lo-inch pipe. Two Ingersoll-Sergeant drills in the heading. Mounting, vertical column. One shift per day. Two drillers, two helpers, and three muckers per shift. Horse haulage, 22-cubic-foot cars. Forty-per- cent gelatine dynamite, 8 to 10 pounds per cubic yard of heading. 48 MODERN TUNNELING No timbering. Average monthly progress, 150 feet. Cost per linear foot of tunnel, $23.38. Started, 1901; driven intermit- tently; completed, 1906. Strawberry tunnel: Wasatch County, Utah. Purpose, irri- gation. Length, 19,100 feet. Cross-section, arched roof, 8 feet wide, gyi feet high. Rock, shale and sandstone. Power, elec- tric. Ventilation, exhaust with pressure blower through 14-inch pipe. Two Sullivan drills in the heading. Mounting, vertical column. Three shifts per day. Two drillers, two helpers, and six muckers per shift. Electric haulage, 47-cubic-foot cars. Forty-per-cent gelatine dynamite, 5 to 6 pounds per cubic yard heading. Two thousand five hundred feet timbered. Average monthly progress, 300 feet. Cost per linear foot of tunnel, $36.78. Started, 1906; completed, 191 2. Utah Metals tunnel: Tooele, Utah. Purpose, transportation. Length, 11,780 feet. Cross-section, rectangular, 10 feet wide by 8 feet high. Rock, quartzite. Power, hydrauHc. Ventilation, exhaust with fan through 12-inch pipe. Two Ingersoll-Rand drills in the heading. Mounting, horizontal bar. Two shifts per day. Two drillers, two helpers, and four muckers per shift. Electric haulage, 32-cubic-foot cars. Forty- and 60-per-cent gel- atine dynamite, 4 to 5 pounds per cubic yard of heading. Five hundred feet timbered. Average monthly progress, 250 feet. Approximate cost per linear foot of tunnel, $15. Started, 1906; driven intermittently; not yet completed. Yak tunnel: Leadville, Colorado. Purpose, transportation and development. Length, 23,800 feet. Cross-section, 7 feet square. Rock, sandstone, limestone, shale, porphyry, and granite. Power, electric. No ventilation supplied, except by opening compressed-air line. Two Ingersoll-Rand drills in the ' heading. Mounting, horizontal bar. Three shifts per day. Two drillers, two helpers, and two muckers per shift. Electric haul- age, 30-cubic-foot cars. Forty per cent, gelatine dynamite, 4 to 5 pounds per cubic yard of heading. Eight thousand feet tim- bered. Average monthly progress, 200 feet. Approximate cost per linear foot of tunnel, $20. Started, 1886; driven intermit- tently; completed, 19 10. MODERN MINING AND WATER TUNNELS 49 MODERN TUNNELS DESCRIBED IN ENGINEERING MAGAZINES The following tables are comparable with those above, and give practically similar information concerning certain tunnels which were not examined in the field, but which are quite fully- described in engineering periodicals. Although the information contained in these various accounts is, perhaps, somewhat less complete than similar data obtained at other tunnels actually visited, nevertheless it is generally sufficient in each case to convey a good idea of the main features of the work done. Bufalo Water Works tunnel: Buffalo, New York. Purpose, water supply. Length, 6,575 f^^t. Cross-section, nearly rect- angular, 15 feet wide by 15K feet high. Rock, limestone. Power, steam. Ventilation, tunnel driven under compressed air, no ven- tilation used. Four Ingersoll-Sergeant drills in the heading. Mounting, vertical column. Three shifts per day. Four drillers, four helpers, and ten muckers per shift. Electric haulage, 27- cubic-foot cars. Sixty-per-cent gelatine dynamite, 4.8 pounds per cubic yard of heading. Average monthly progress, 235 feet. Started, July, 1907; completed, April, 1910. Reference, Engin- eering Record, June 25, 19 10, page 802. Chipeta adit: Ouray, Colorado. Purpose, mine development. Length, 2,000 feet. Cross-section, 7.5 feet square. Power, steam. No ventilation supphed except by opening compressed-air line. Two Ingersoll-Rand drills in the heading. Mounting, horizontal bar. Two shifts per day. Two drillers, one helper, and four muckers per shift. Mule haulage, 20-cubic-foot cars. Five to 6 pounds of explosive per cubic yard of heading. One hundred and fifteen feet timbered. Average monthly progress per heading, 340 feet. Approximate cost per linear foot of tunnel, not includ- ing permanent equipment, $12. Started, August, 1907; com- pleted, March, 1908. Reference, Alining and Scientific Press ^ July II, 1908, page 60. Cornelius Gap tunnel: Near Portland, Oregon. Purpose, elec- tric railway. Cross-section, arched roof, 17.5 feet wide by 22.5 50 MODERN TUNNELING feet high. Length, 4,100 feet. Rock, basalt. Reference, Engi- neering News, June 29, 191 1, page 783. Fort Williams Water tunnel: Fort Williams, Ontario. Pur- pose, water supply. Length, 4,820 feet. Cross-section, rectan- gular with arched roof, 5 feet wide, 6.5 feet high. Rock, basalt. Power, electric. Ventilation, blow with fan through 15-inch pipe. One Ingersoll-Rand drill in heading. Mounting, vertical column. Two and three shifts per day. One driller, one helper, and three muckers per shift. Eighteen-cubic-foot cars. Forty- per cent, gelatine dynamite, 5 to 10 pounds per cubic yard of heading. Lined with concrete. Average monthly progress per heading, 85 feet. Cost per linear foot of tunnel, $27.89. Started, May, 1907; completed. May, 1909. Reference, Engineering and Contracting, May 25, 1910, page 472. Grand Central tunnel: New York City. Purpose, sewer. Length, 3,000 feet. Cross-section, circular, 8 feet in diameter. Rock, gneiss. No ventilation suppKed, except by opening com- pressed-air line. Two and three Ingersoll-Rand and Sullivan drills in the heading. Mounting, vertical column. One shift per day. Two and three drillers, two and three helpers, and two muckers per shift. Used a >^-cubic-foot bucket on a flat car. •Started, 1907; completed, 1908. Keierence, Engineering Record, April II, 1908, page 496. Joker tunnel: Red Mountain, Colorado. Purpose, mine drain- age and development. Length, 5,055 feet. Cross-section, rect- angular, 12 feet wide, 11 feet high. Power, steam. Ventilation, exhaust with fan through 15-inch pipe. Two and three Leyner drills in the heading. Mounting, vertical column. One drill shift and two mucking shifts per day. Two and three drillers, two helpers, and four muckers per shift. Mule haulage, 30-cubic- foot cars. Practically all timbered. Average monthly progress, 215 feet. Completed, 1907. Reference, Mines and Minerals , May, 1907, page 470. Kellogg tunnel: Wardner, Idaho. Purpose, mine development. Length, 9,000 feet. Cross-section, arched roof, 9 feet wide and 1 1 feet high. Rock, quartzite. Reference, Mines and Minerals , October, 1901, page 122. I MODERN MINING AND WATER TUNNELS 51 Mount Royal tunnel: Montreal, Canada. Purpose, railroad. Length, 3.25 miles. Cross-section, rectangular with arched roof, during construction 30.5 feet wide and 21.25 f^^t high, when completed will be twin tubes each 13.5 feet wide and 14 feet high, separated by an 18-inch wall of concrete. Rock, limestone and volcanic breccia. Power, purchased electricity. Ventilation, pressure blower. Three or four Sullivan water drills per heading. Mounting, horizontal bar and special drill carriage. Three shifts per day; four drillers, four helpers, and six muckers per shift. Electric haulage. Sixty-per-cent gelatine dynamite. Average progress in No. i heading, first eight months, 351 feet. Refer- ences, Engineering and Mining Journal, July 26, 1913, pages 147-49; Mine and Quarry, August 1913, pages 730-39. Northwest Water tunnel: Chicago, Illinois. Purpose, water supply. Length, 21,180 feet. Cross-section, horseshoe, area equivalent to 14-foot circle. Rock, limestone. No ventilation supplied, except by opening compressed-air line. Four Ingersoll- Rand drills in the heading. Mounting, vertical column. Two shifts per day. Four drillers, four helpers, and six muckers per shift. Mule haulage, 22-cubic-foot cars. Average monthly progress per heading, 400 feet. Reference, Engineering Record, August 7, 1909, page 144. Ophelia tunnel: Cripple Creek, Colorado. Purpose, mine drainage and development. Length, 8,500 feet. Cross-section, 9 feet square. Rock, granite and breccia. Power, steam. Ven- tilation, blow with pressure blower through 15-inch pipe. Two Sulhvan drills in the heading. Mounting, vertical column. Three shifts per day. Two drillers, two helpers, and three muckers per shift. Compressed air haulage. Average monthly progress, 350 feet. Started, 1905; completed, 1907. Reference, Mine and Quarry, May, 1907, page 118. Roger^s Pass tunnel: Between Ross Peak and Beaver Mouth, British Columbia. Purpose, railroad. Length, 25,900 feet. Cross-section, rectangular with arched roof. Will be driven from a center heading 14 feet wide and 8 feet high and from an auxil- iary heading 30-50 feet to one side of the main heading, 8 feet wide and 7 feet high. Rock, shale and quartzite. Power, steam. 52 MODERN TUNNELING Ventilation, pressure blower. Three Ingersoll-Leyner drills per heading. Horizontal bar mounting. Three shifts per day. Three drillers, two helpers, and four to six muckers per shift. Mule haulage. Work on portal excavation started August, 1913. Reference, private communication to the authors. Second Raton Hill tunnel: Raton Pass, Colorado. Purpose, railway. Length, 2,790 feet. Cross-section, horseshoe, 22 feet wide and 29 feet high. Rock, shale, sandstone, and a 3-foot bed of soft coal. Reference, Engineering Record, April 4, 1908, page 461. ^^SpiraV^ tunnels: Selkirk Mountain, British Columbia. Pur- pose, railway. Length, No. i, 3,200 feet; No. 2, 2,890 feet. Cross-section, arched roof, 22 feet wide, 27 feet high. Rock, limestone. Power, steam. Six and eight Ingersoll-Rand drills in the heading. Mounting, vertical column. Two shifts per day. Six and eight drillers, six and eight helpers per shift. A Marion shovel operated by compressed air used for mucking. Horse haulage, 108-cubic-foot cars. All timbered. Average monthly progress per heading, 105 feet. Started, January, 1908; com- pleted, June, 1909. References, Engineering News, November 10, 1 9 10, page 512; Compressed Air Magazine, February, 191 1, page 5.931- I CHAPTER IV CHOICE OF POWER FOR TUNNEL WORK SOURCES OF POWER While the power for tunnel operations may be obtained from various sources, in general practice at present it is produced primarily from either steam or flowing water. Although, as far as could be ascertained, the gas-producer used in connection with internal-combustion engines has been installed at but one tunnel, nevertheless it offers a third possibihty as a source of power which will have to be considered more and more seriously in the design of future plants. It is true that in the early stages of its development, when the principles governing its design, construc- tion, and operation were not well understood, the gas-producer was not rehable and acquired a bad reputation among tunnel men, a situation augmented perhaps by the extravagant claims of manufacturers or the overzealousness of salesmen. But within the last few years, as its principles have become better known through study and experiment, the gas-producer has developed rapidly — so rapidly, in fact, that few people realize that it is to-day as reliable and rugged a piece of apparatus as an ordinary boiler, or that its consumption of fuel is only one-third as great, or that the labor to operate it need not be one whit more skilled. It is true that gasoHne engines are occasionally used to furnish power in tunnel operations, but they have been confined either to temporary plants or to small and isolated units of machinery. In localities where petroleum is cheap, it is probable that an oil engine of the Diesel type, with its wonderful fuel economy, may be found the cheapest means of producing power. Elec- tricity, especially where it is used at tunnel plants to operate prime moving machinery, is sometimes considered a source of power; but since the current so employed has to be generated elsewhere, usually from steam or water, but possibly from pro- 53 54 MODERN TUNNELING ducer gas, petroleum, or gasoline, electricity is merely a conve- nient form for transmitting power instead of a source. PRODUCTION OF POWER Water-power. — In tunneling the machines most frequently employed for the utilization of water-power are of the impulse type, similar to the Pel ton wheel, illustrated in Figure 8. Such Fig. 8. Standard Pelton wheel. a wheel is driven by the force of a stream of water issuing from a nozle, acting against vanes or buckets on the circumference of the wheel, and is well adapted for use with a relatively small volume of water under high head. The efficiency of the machine is dependent upvon the way the vanes or buckets reverse the direc- tion of the water discharged upon them; hence they usually conform to a curve which is very carefully designed to avoid loss of power through eddies and friction as the water strikes the vane. There may be more than one nozle in order to obtain greater power, or, if high rotative speed is desired, a small wheel CHOICE OF POWER FOR TUNNEL WORK 55 with multiple nozles may be substituted for a large one. In order to obtain the best results, the peripheral speed of the cups or vanes should be between 42 and 48 per cent of the speed of the water issuing from the nozle. Impulse wheels are manufac- tured in many different designs, sizes, and speeds, adapted for working imder widely diverse conditions. Those observed at the different tunnels examined were, as far as could be learned, giving very satisfactory service. The turbine wheel, in which the force of the water is made to act through suitable guides upon all the vanes or blades simul- taneously, affords another means of utiHzing water-power and may be designed for either high or low heads. Its use is limited, however, especially with high heads, to localities where clear water is available (as, for example, at Niagara Falls) because of the destructive abrasive action of sand and grit upon the guides. With low heads this action is not so marked. Since the source of water-power in the vicinity of tunnels and adits is in most cases to be found in streams furnishing high heads and which at certain seasons of the year carry large amounts of sediment, the use of turbine wheels for such plants is prohibitive unless large setthng basins can be provided. The hydraulic compressor, converting the energy of water directly into compressed air, offers a third method for utiHzing water-power. The earliest type operates upon the principle of the hydraulic ram, in which a column of water is allowed to ac- quire velocity and is then suddenly checked, developing intermit- tently for a short space of time pressure much greater than that due to the head of the column of water. This pressure is em- ployed in compressing air. Sommeiller in about i860 designed a machine of this type for use at the Mt. Cenis tunnel. Such compressors require rather high heads and have low efficiency. Although conditions might be such as to make the use of com- pressors of this type desirable, the water-power they require can generally be utilized more advantageously in some other manner. The hydraulic compressor recently developed by C. H. Taylor, introducing air into a column of water and compressing it as they fall together to the bottom of a shaft where the air is separated 56 MODERN TUNNELING and collected, is very efficient and requires only a small amount of attention, although the cost of construction prohibits its use except for installations much larger than those ordinarily re- quired for tunnel work. The latest installation of this system, which was completed in June, 1910, is situated at Ragged Chutes, Fig. 9. Diagrammatic section through Taylor hydraulic compressor at Cobalt. on the Montreal River, and suppHes air to the mining district near Cobalt, Ontario. At this plant, a concrete dam diverts water from the river, above the rapids, to the tops of two circular shafts 8^^ feet in diameter, where, by means of suitable apparatus, a large quan- tity of air is introduced into the water in the form of bubbles. The mixed water and air descend the shafts (350 feet in depth) and start through a passage 1,000 feet long. The passage as shown in Figure 9 is so designed that the compressed air is permitted to rise to the surface of the water and is collected, CHOICE OF POWER FOR TUNNEL WORK 57 partly along the top of the passage and partly in a large collecting chamber which has been excavated near the end of the passage. The waste water then rises 298 feet through a shaft 22 feet in diameter and is discharged into the river below the rapids. The air is drawn from the top of the chamber at a pressure of 120 pounds to the square inch and is transmitted by a 20-inch main to the mines nine miles distant. The capacity of the plant is the compression of 40,000 cubic feet of free air per minute to 120 pounds per square inch. The famiHar overshot, breast, and undershot wheels are not used to drive machinery for tunnel work, because of their large size for the amount of power developed, as well as the trouble of their maintenance. The overshot wheel utilizes the weight of the water, chiefly, and is best suited for low heads. Its efficiency is greatest when enough water is supphed to fill the buckets completely. The breast wheel utihzes both the weight and the velocity of the water, and its efficiency is less, though it can be used with even lower heads of water than the overshot wheel. The undershot wheel uses only the velocity of the water, and has the least efficiency of the three types, but it requires practically no head. Its efficiency is at a maximum when the water is con- fined laterally. The following table, which is based upon actual results, shows the efficiency of different t>^es of water motors: PERCENTAGE OF THEORETICAL HORSE-POWER REALIZED BY X'ARIOrS WATER :\IOTORS Impulse wheels 7o~85% Turbine wheels 75~S5 Overshot wheels 60-65 Breast wheels 50-60 Undershot wheels 30~5o Results obtained at the testing flume of the Holyoke (Mass.) Water Company, whose tests are taken as standard by American engineers, show efficiencies for turbine wheels under favorable conditions of over 90 per cent,* but this is unusual, the figures * Trans. A. S. C. E., Vol. XLIV (1910), p. 2>22. 58 MODERN TUNNELING above being much nearer ordinary practice. The efficiency of hydraulic compressors of the ram type is about 30 to 40 per cent, while the Taylor compressor at Cobalt is said to utilize at least 75 per cent of the theoretical power of the water. Steam. — Steam engines are of two types, reciprocating and turbine. In the reciprocating engine, power is developed by the pressure and expansion of steam in a cylinder acting against a moving piston. Such engines may be either simple or compound, both forms being used in tunnel plants. In the former, the total expansion of the steam and consequent reduction of press- ure take place in one cylinder, while in the latter only a portion of the expansion takes place in the first cynnder, and the steam, under somewhat reduced pressure, is expanded further in a second cyHnder, necessarily larger because of the lower pressure of the steam. The steam turbine is similar in principle to the water-wheel, except that steam instead of water is the motive fluid. Owing to their economy, small size per unit of power, and freedom from vibration, their use is steadily increasing on both land and sea. Modern steam turbines in sizes of 250 to 500 horse-power, with a steam pressure of 150 pounds and a 28-inch vacuum, will develop a kilowatt-hour with a con- sumption of from 18 to 20 pounds of steam. A recently published series of shop tests on a 300-kilowatt Swiss condensing turbine showed that with ii2j^ pounds of steam and a 96.6 per cent, vacuum it was able to produce a kilowatt-hour with 16. i pounds of steam. The difficulty of reducing the high rotative speed of the turbine engine down to the restricted speed of reciprocating machinery has prevented, until recently, the use of turbine engines in tunnel installations; but, with the advent of the turbo-compressor, we may expect to see them dividing the field, or, perhaps, entirely displacing the cumbersome reciprocating plants now in vogue. Internal Combustion. — Internal-combustion engines devel- op power from the pressure produced by the explosion or rapid combustion (confined in a suitable cylinder) of a mixture con- taining the proper proportions of air and a gasified fuel. The CHOICE OF POWER FOR TUNNEL WORK 59 source of the fuel gas may be gasoline, kerosene distillate, or even crude petroleum, or it may be generated from coal by dis- tillation in a retort, or by a gas-producer, and the engines are usually designated by the kind of fuel for which they are adapted, as, for example, oil engines, gasoline engines, or producer-gas engines. As far as could be ascertained these latter two are the only types now used in tunneling. Although the gasoline engine has been developed with wonderful rapidity during the last twenty-five years in con- nection with the automobile industry, the use of engines of this t}pe for tunnel work has been confined to a very limited field, viz., the operation of isolated or not easily accessible machinery. As prime movers for tunnel plants of any magni- tude they cannot compete, under most circumstances, with machines using other forms of power, and, on this account, their appHcation has been confined either to enterprises small in scope or to the temporary and early development stage of larger projects, where they are sometimes installed to begin the work at locations by nature inaccessible for non-portable units of heavier machinery, pending the construction of a special road- way or a transmission fine. ^lost manufacturers of air com- pressors have recently begun to supply air compressors directly driven by internal combustion engines, although as yet only the smaller sizes of gasoline engines are being used. With suitable adaptations, the principle might be appKed equally well to the larger sizes using oil or gas as fuel. Within the last two years gasoHne engines have been successfully employed in locomotives for haulage in coal mines, and there are now over one hundred of them in operation. These machines are equally suitable for tunneling operations, and will, no doubt, be used extensively for this purpose in the near future. The only use of producer-gas engines in tunnel work to date, as far as could be learned, was at the power plant for the tunnel under the Thames River recently completed connecting North and South Woolwich. Since the tunnel was constructed under compressed-air pressure, absolute rehabihty in the power plant was required to avoid a stoppage of pressure which might 60 MODERN TUNNELING possibly result in serious damage to the tunnel. At this plant, as described in The Engineer,^ three engines, each of 150 b. h. p. when running at 180 revolutions per minute, were supplied with gas from suction producers using Scotch anthracite coal, and were connected to a central shaft which transmitted power to four air compressors and four dynamos. The plant was operated continuously from July, 1910, until the end of Decem- ber, 191 1, except during October and November, 1910, when after the vertical shaft had been completed the plant was pur- posely stopped while making preparations to start tunneling. Although it is not within the province of this report to discuss the gas-producer in any detail, the following brief descrip- tion is quoted from Bureau of Mines Bulletin 16: "The simplest form of gas-producer for power-gas generation is a vertical cylinder of iron or masonry, lined with fire-brick, having a grate near the bottom, an opening in the top for charging fuel, a smaller opening near the top for the outlet of the gas, and one near the bottom for the admission of air. Openings are also provided at various heights on the sides, through which the interior may be reached for poking the fuel bed, inspecting and cleaning the interior, making repairs, and removing ashes. To prevent the entrance of air except through the proper openings, which are covered by gas-tight doors, the charging opening is generally a small chamber, guarded by gas-tight doors at the bottom and top, which prevents the escape of the gas and the ingress of air while the producer is being recharged. Simple gas-producers such as described above furnish uncleansed gas, which contains so much dust and other foreign matter that it is unsatisfactory for use, especially in gas engines. Power-gas pro- ducers are therefore provided with apparatus for cleansing the gas, known as scrubbers, through which the gas passes after leaving the producer. The scrubber in its simplest form is a cylindrical chamber filled with some porous material like coke or shavings, which is kept constantly wet. The gas, in passing through this wet material, leaves behind most of the soUd and liquid impurities it contains. In addition to the scrubber, many gas-producers have attach- ments for preheating the air admitted for combustion, so that it enters the fire at a temperature sufficiently high to prevent cooling * The Engineer, London, January 12, 1912, p. 46: "Temporary Power Plant for Woolwich Footway Tunnel," two pages illustrated. CHOICE OF POWER FOR TUNNEL WORK 61 of the fuel. Such attachments make use of the heat of the off-going gases, and are called regenerators. The form of producer in most general use for generating gas for the development of power, especially in gas engines, is that supply- ing gas directly to the engine, which draws the air and steam through the fuel bed by means of the suction stroke of the piston. The suction-producer, as it is termed, has been largely restricted to the use of anthracite, coke, charcoal, and other fuels containing a low per- centage of tarry compounds. When bituminous fuels are used these tarry compounds are likely to be carried over with the fixed gases into the engine and, condensing there, clog the valves, pipes, and other working parts, despite scrubbing apparatus. Recent improvements in methods of scrubbing, however, have so modified the older practice as to make the use of fuels rich in volatiles comparatively free from such accidents, and their use in the suction type of producer is in- creasing. The pressure gas-producer is so designed that the air and steam necessary to develop the gas are forced into the fuel bed under enough pressure to drive the gases generated through the fuel bed and scrub- bing apparatus into a gas holder. The gas is thus generated indepen- dently of the piston stroke of the engine, and may be thoroughly cleansed of tars and ash before it is used. For this reason the pressure type of gas-producer is well titted for using bituminous coal, lignite, and peat. The down-draught or inverted -draught gas-producer, in which the heavier products of distillation are all decomposed and changed into simple permanent gases, constitutes a third t^'pe. In power-gas producers of this type the heated gases, rich in vaporized hydrocarbons, tars, and hea\y gases, are drawn by exhaust fans from the top of the producer, where they accumulate above the freshly added fuel, down through the fuel bed. In the fuel bed, by contact with the heated carbon, they are converted into carbon monoxide and hydrogen, which, after cleansing, can be either stored in receivers or used in engines." The essential principles in the process of making gas in a producer may be outlined very briefly as follows : In comparison with steam-boiler practice, the fuel bed is very deep and con- tains three zones — combustion, incandescence, and distillation. A portion of the coal is burned in the combustion zone, where a limited amount of air is suppKed for this purpose, and the resulting gases are passed through the remainder of the fuel bed. In the incandescent zone the hot gases combine chemically with some of the constituents of the glowing coal (unburnt 62 MODERN TUNNELING as yet, because of lack of air) and form new gases which have a fuel value. These, together with the gases driven off from the fresh coal by heat in the distillation zone, supply the fuel portion of the mixture exploded in the engine. Steam is also employed in most types of gas-producers because its introduction with the air for combustion assists in the formation of gases of the right composition. For a more detailed discussion of this subject the reader is referred to the bibliography accompanying this volume. Although, as far as could be learned, oil engines of the Diesel type have not yet been employed in tunnel power plants, their marked success in other fields more than -warrants the dis- cussion of the possibility of their use in tunnel work. The essential feature which differentiates the Diesel machine from other internal-combustion engines is the fact that instead of draw- ing into the cylinder an explosive mixture containing a com- bustible gas (such as producer-gas, gasoline vapor, kerosene, or even crude petroleum previously volatilized by heat), and then compressing this mixture and exploding it by means of an electric spark or some other suitable device, the Diesel engine compresses air alone, and when it is under its highest pressure (approximately 300 pounds per square inch, which is much greater than that usually attained in other types of internal combustion engines) injects into the cylinder a spray of finely atomized oil. During the compression of the air to the required pressure it will have reached a temperature of more than 1000° F., more than safhcient to ignite the oil instantly without the use of an electric spark, hot plate, or other similar device. The chief advantage of the Diesel engine is economy of fuel. It is a well-known fact that the rapidity and completeness of any combustion are greatly increased by pressure; it is not surprising, therefore, that under the higher pressures which prevail in this machine better results can be obtained from a smaller amount of oil. The extremely fine atomization of the fuel due to the jet of compressed air (under a pressure of 300 to 500 pounds per square inch higher than that in the cylinder) by which the oil is injected is undoubtedly another great con- CHOICE OF POWER FOR TUNNEL WORK 63 tributing factor. And again, since the scavenging of the exhaust gases from the previous explosion is effected by air only, instead of a mixture of air and fuel, as is the case in other types of internal- combustion engines, there is no possibility of loss of fuel through the exhaust valves during this process, a saving which is ex- tremely important where the engines are designed for a two- stroke cycle. In addition to the advantage of fuel economy, however, the Diesel engine does not require frequent cleaning, as is the case with oil engines depending upon a hot plate or a similar device for the ignition of the explosive mixture. It also dis- penses with the carbureter, so necessary for the gasoline engine, and which is always a source of more or less trouble and annoy- ance. And, in addition, since the mixture being compressed in the cylinder of a Diesel engine is not an explosive one, allowance does not have to be made in the design of the cylinder and other parts for undue stresses and strains which might result from a premature ignition of the charge, caused, perhaps, by a glowing piece of carbon on the cylinder wall or by a heated piston, an occurrence which is not infrequent in other engines, as any automobilist will testify. Although some provision can, of course, be made for these shocks, their force and violence cannot always be correctly foreseen or sufficient allowance made for them, and there have been many instances of disastrous results arising from premature ignitions in internal-combustion engines of the usual types. The principal disadvantage of the Diesel engine, on the other hand, is that of high first cost, and this would prohibit its use for tunnel work of short duration. The price of this machine has recently been greatly reduced abroad, however, and it is certain to be reduced in America, now that manufacturers in this country are equipped with suitable apparatus and prepared to execute the high class of workmanship required in its con- struction, so that in the near future this drawback may dis- appear. But even now, if the time required for the completion of the work is to be long enough, or the amount of power to be used is great enough to warrant a heavy initial outlay in order 64 MODERN TUNNELING to effect a saving in operating cost, the choice of a Diesel engine should be seriously considered. Electric Motors. — Electric motors may be designed either for direct or alternating current. Where used as prime movers at the tunnel plants visited they were of the second type only and operated at comparatively low voltages, 440 volts being the usual figure. Their power was generally transmitted to the remainder of the machinery by means of belts, but at one or two places on the New York Aqueduct, ''direct-connected" electric-driven air compressors were noticed. TRANSMISSION OF POWER Electricity, because of its economy and its freedom from limiting distances, is the favored means for transmitting to a tunnel the power generated at some remote station. It pos- sesses one well-known disadvantage, that of occasional inter- ruption, especially where distances are great and tension high, because of unavoidable hindrance to service due to electrical storms or other atmospheric agencies. On the other hand, producer-gas transmission has possibilities which deserve to be considered seriously in this connection. This form of conveying power has been recently taken up from the realm of mere con- jecture and demonstrated as a practical system, both in this country, at Pittsburgh where natural gas is piped over distances as great as 200 miles, and in England, where producer gas is supplied to points within a radius of 160 miles, with trans- mission losses even less than when electricity is used. In its apphcation to tunnel operations, producer gas can be generated in a plant conveniently situated on a railroad siding or some other readily accessible place, and the power piped to internal- combustion engines at the tunnel portal. Where distances are comparatively short (that is, less than five miles or so) electricity is rivaled by compressed air, and the competition grows more keen as the length of the trans- mission system decreases. This is possible because where pneumatic drills are employed, compressed air, in spite of its CHOICE OF POWER FOR TUNNEL WORK 65 low efficiency and high cost, is necessary for their operation; and even were electric transmission chosen, the power would need to be converted ultimately into compressed air at the tunnel. Hence it is the usual practice to produce the compressed air at once, thus avoiding the extra machinery and the additional operating losses of electric transmission. CHOICE OF POWER A number of factors enter into the choice of power for tun- nehng operations. To begin with, the plant is usually short lived. Then, too, the influence of such local conditions as accessibility, distance from a railroad, the availability of water- power, etc., is strongly felt. Each method of deriving power has also certain peculiarities which render it particularly adapt- able to different conditions. Among these may be mentioned the cost of installation, of labor, of fuel, of interest and deprecia- tion, and other operating expenses. Aside from all this, it is often necessary to decide between the production of power at the plant or elsewhere and the purchase of power from an established hydro-electric company. Some of these factors we shall discuss briefly. Duration of Plant. — At many tunnel power plants, in di- rect contrast with those used in manufacturing, the equipment is required only for the comparatively short time of actual tunnel construction. Thus it becomes a delicate problem to determine just how far one is justified in the purchase of machinery and apparatus for utilizing all the various economies that may be effected in the production of power. It is difficult to decide whether it would not be better in the end to install less costly machinery that would necessitate sKghtly higher expense in operating and maintaining than to tie up extra capital in equipment that would be of no further use when the tunnel is completed. Of course, the shorter the probable Kfe of the plant the more would one be justified in such a course ; although, if the equipment can be transferred upon the completion of the tunnel to other projects, this would so prolong its period of i66 MODERN TUNNELING usefulness that the original expenditure of capital could properly and with true economy be greater. A notable instance of this was observed on the Los Angeles Aqueduct, where as far as possible, upon the completion of one of the numerous tunnels, the equipment was transferred and used in power plants at other tunnels whose construction had not yet been begun. If a central station is being considered, where a large amount of power is to be generated, the purchase of apparatus from the main view- point of economy in operation is again the far-sighted policy. This was the case at the Rondout Siphon Tunnel, but at the average mining tunnel or adit the converse is more often likely to be true. Accessibility. — Tunnels are often located at places very difficult of access. They may be so situated as to make the installation of heavy machinery no easy matter, as, for example, where the road from the nearest railroad is poor and the grade very steep; or they may be at a great distance from the nearest siding, so that if a form of power be chosen that requires coal, the delivery of this fuel is not only very costly, but also most uncertain and difhcult in some seasons of the year. Such conditions are favorable for the adoption of power transmission in some form from a waterfall or rapid, if one be located near enough, or, lacking these natural advantages, from a fuel plant installed at some point more readily accessible. Cost of Installation. — The cost of installing water-wheels is entirely dependent upon local conditions, which are never twice alike. Where high heads are available and the quantity of water required is not large, it can be conveyed to the water- wheel by small flumes or pipes which are comparatively inex- pensive. For example, at the Carter tunnel (see Figure lo), with an available head of 145 feet, a flume 16 by 48 inches inside and 5,000 feet in length is sufficient to supply the 200 horse- power developed. At the Laramie-Poudre tunnel, with a static head of 268 feet, 400 horse-power was conveyed to the tunnel plant by a wooden-stave 22-inch pipe line, 8,500 feet in length. The Utah Metals tunnel secures water from two sources: the first has a 700-foot head, using 2,500 feet of 12-inch, CHOICE OF POWER FOR TUNNEL WORK 67 1,900 feet of lo-inch, and 100 feet of 8-inch spiral steel riveted pipe, furnishing 170 horse-power; the second, with 750 foot head, employs 2,000 feet of 12-inch, 1,000 feet of 8-inch, 3,000 feet of 6-inch pipe in producing 55 horse-power. Where heads are low, however, retaining dams are usually necessary. At Fig. 10. View showing end of flume, mill, dump, and other surface features at Carter tunnel. best these are a costly expedient and their expense increases enormously with their height. With low heads, larger flumes are also required to convey the greater quantity of water. At the Nisqually tunnel, illustrated in Figure 11, a low dam and a wooden flume 6 by 8 feet in cross-section and 1,200 feet long were used. The water was delivered to a turbine wheel under an effective head of 29 feet which generates 1,000 horse-power. One has only to consider some of the very expensive dams on the cr w IB B 3 CHOICE OF POWER FOR TUNNEL WORK 69 larger rivers, furnishing power for manufacturing purposes, in order to realize how great the cost of installation may be where low heads only are utilized. It is fortunately true, however, that where water-power is obtainable for tunnel work high heads are usually available also, and the less expensive flumes or pipe lines of moderate length can be utilized. The cost of the machinery actually within a tunnel power- house is greater for steam than for water-power or electricity; but if, as should be done to make the figures truly comparable, the cost of the dam and flume (or of the transmission line for electricity) be taken into consideration, the advantage. is usually reversed. It is somewhat cheaper to install a steam plant than one using producer gas and having engines of the same capacity, but the dift'erence is not great. R. H. Fernald,* after a study of many tables of costs, applying to other uses, however, than tunnel work, concludes that ''complete producer-gas installa- tions for the larger plants, say from 4,000 to 5,000 horse-power, cost about the same as those of first-class steam plants of the same rating. With smaller installations the balance is prob- ably in favor of the steam plant." Since it is not customary in tunnel work to install machinery designed to effect all the refinements of steam economy found in permanent plants, it is probable that the first cost of the average steam plant for tunnel work is less than those upon which Mr. Fernald's estimates are based, in which case the comparison would be even more favorable to steam. This is partly offset by the fact that the price of gas-producers and engines is constantly being lowered, and by the fact that the cost of actually placing the machinery would be less for the gas-producer — considerably in some cases, appreciably in all The initial expense of installing any of the various systems for transmitting power is dependent upon two factors: (i) the cost of the machinery required to produce the power, to convert it into the form suitable for transmission, and to reconvert it into the form adapted to the machines using it; and (2) the * Bull. 9, B. of M., p. 31. 70 MODERN TUNNELING cost of the transmission line. Except for a slight increase in capacity, to provide for losses in transmission, the factor of machinery cost under any given conditions is independent of the distance over which power is to be delivered, but the cost of the line, as will become apparent later, increases considerably faster than its length, other things being equal. If the power is required ultimately for the operation of air drills, practically the same size of compressor will be necessary whether electric, air, or gas transmission is employed, and the cost of boiler, engine, foundations, etc., in the case of electricity or air will approximately balance the cost of the producer, engine, founda- tions, etc., for gas. Air transmission would require practically no other machinery than that just mentioned; but gas, on the other hand, would need a blower of some sort to force it through the line, while electricity would require, in addition, a generator, motor, transformers, extra foundations, etc. A list of the three forms of power transmission made, according to increasing machinery-cost factor, would be air, gas, and electricity. The cost of an electric-transmission line may be divided into three parts: first, the metallic part of the circuit; second, in- sulating the conductor; and, third, erecting or installing the line. Although a detailed discussion of this subject is beyond the proper scope of this book, it can be shown that, for a stated power loss and a given distance, the weight of the metalHc conductor required to transmit a definite amount of power is inversely proportional to the square of the voltage employed. On the other hand, the cost of insulation increases rapidly with the potential, and the cost of erection, complicated by steel towers, etc., is greatly augmented at high voltages. Thus the economical transmission of a given amount of power for a stated distance is limited by the maximum voltage which may be used without the increased cost of installation and erection destroying the saving in the cost of copper. Any attempt to go into the complicated processes necessary to ascertain the most advantageous voltage for a long distance- transmission Kne would be out of place here; but, for the short CHOICE OF POWER FOR TUNNEL WORK 71 distances and small amounts of power commonly employed in tunneling operations, the following rule of thumb will suffice to give a close approximation to the most carefully made calcula- tions. Multiply the distance to be traversed in miles by i,ooo and select the voltage of the nearest commercial size of trans- former to this figure. The standard voltages of transformers now in use are 220, 440, 660, 1,100, 2,200, 6,600, 11,000, 22,000, 33,000, 66,000. For instance, if the distance from the power station to the tunnel plant is five miles, select a voltage of 6,600; if the distance is ten miles, a voltage of 1 1 ,000. Where the distance falls midway between transformer steps, use the voltage which will find most ready sale for the apparatus when the work is completed. Since there are certain difficulties in the construction of direct-current generators for voltages higher than 600, alternat- ing current is generally employed for transmission lines. This form also possesses a very important additional advantage in the ease with which it may be changed from low to high potential, and vice versa. When high tension is employed in transmission of electrical power, the voltage at the generating station is usually comparatively low, and is "stepped up" by transformers to the desired potential for the fine and is reduced again by transformers at the tunnel plant. The following figures, which show the installation cost of an electric-transmission line for different voltages and distances, assuming approximately 10 per cent drop in the line, are based upon data kindly furnished by the General Electric Co.^ * I. 200 H.P. — I mile — 440 v., direct current. Poles, cross-arms, insulators, and fittings (poles spaced 100 feet) $375 33,000 lbs. copper cable, 500,000 C. M. (four conductors required), at 18X cents lb 6,025 Cost of erection 300 Total $6,700 * Freight, right of way, surveying, and engineering are not included in these data. 72 MODERN TUNNELING 2. 200 H.P. — I mile — 440 v., 3-phase, 60-cycle, alternating current. Poles, cross-arms, insulators, and fittings (poles spaced 100 feet) $415 34,000 lbs. copper cable, 350,000 CM. (six conductors required) at 17^ cents 6,035 Cost of erection 375 Total $6,825 3. 200 H.P. — I mile — 1,100 v., 3-phase, 60-cycle, alternating current. Poles, cross-arms, insulators, and fittings (poles spaced 125 feet) $385 5,100 lbs. copper cable, B. & S. No. o (three conductors required) at 17^ cents 905 Cost of erection 265 Six transformers, 1,100: 440 volts, with switches, etc., erected 2,900 Total $4,455 4. 200 H.P. — 5 miles — 1,100 v., 3-phase, 60-cycle, alternating current. Poles, cross-arms, insulators, and fittings (poles spaced 125 feet) $1,870 122,000 lbs. copper wire, B. & S. No. 000 (nine conductors required) at 17^ cents 21,650 Cost of erection 1,580 Six transformers, 1,100: 440 v., with switches, etc., erected 2,900 Total $28,000 5. 200 H.P. — 5 miles — 6,600 v., 3-phase, 60-cycle, alternating current. Poles, cross-arms, insulators, and fittings (poles spaced 125 feet) $1,870 6,500 lbs. copper wire, B. & S. No. 6 (three conductors required) at 17^ cents 1,150 Cost of erection i ,080 Six transformers, 6,600: 440 v., with switches, etc., erected 3,700 Total $7,800 I CHOICE OF POWER FOR TUNNEL WORK 73 6. 200 H.P. — 25 miles — 6,600 v., 3-phase, 60 cycle, alter- nating current. Poles, cross arms, insulators, and fittings (poles spaced 125 feet) $9;35o 103,000 lbs. copper wire, B. & S. No. i (three conductors required) at 17^ cents 18,300 Cost of erection 5jI5o Six transformers, 6,600: 440 v. with switches, etc., erected 3,700 Total $36,500 7. 200 H.P. — 25 miles — 22,000 v., 3-phase, 60 cycle, alter- nating current. Poles, cross arms, insulators, and fittings (poles spaced 125 feet) $9,900 33,000 lbs. copper wire, B. & S., No. 6 (three conductors required) at 17^ cents 5, 860 Cost of erection 5,190 Six transformers, 22,000: 440 v., with switches, etc., erected 5,200 Total $26,150 The Pneumo-Electric Machine Co.* have estimated that if compressed air were used to transmit 200 horse-power one mile, allowing 10 per cent, loss at 80 pounds pressure, an 8-inch pipe would be required which, at $1.78 per foot, would cost $8,400. Calculations show that in order to transmit the same amount of power in the form of producer-gas containing 120 B. t. u. per cubic foot, the required pipe would need to be only 4 inches in diameter, costing, at 70 cents per foot, approximately $3,700. To both these values should be added the expense of la>ing the line, but this figure would be relatively small compared to the cost of the pipe. Where the power is ultimately required for use in air drills and is to be transmitted only for short distances, compressed air is' the cheapest of the three methods as regards installation cost, the higher machinery factor required by the other systems more than balancing the expensive air pipe-line. The field for producer-gas transmission (with its machinery factor slightly * Mining and Scientific Press, May 14, 1910, p. 700, 74 MODERN TUNNELING greater than air yet less than electricity, and its line factor just the reverse) lies in the medium distances — beyond the economical raiige for air, but still too short to warrant the cost of the extra electrical machinery. For long distances, on the other hand, electric transmission at high tension is, of course, preeminent. Labor. — Tunnel power plants are generally not large enough to occupy the entire time of even one operator, hence it is impos- sible to prevent their being over-m^anned. The amount of labor required does not as a rule, therefore, seriously affect the choice of power. At a tunnel plant using water-wheels, hydraulic air compressors, or electric motors as prime movers, one man per shift is sufficient. Even then, as was the case at the Laramie- Poudre tunnel, it is not unusual to make these 12 -hour shifts, thus requiring but two men per day; or, as at the Carter tunnel, for a portion of his time the engineer is employed at other work. If the results obtained from practice in other Hues be accepted, a producer-gas plant would require no more exacting attention, it being not unusual for one man per shift to operate plants which develop as high as 750 or 1,000 horse-power. A similar steam plant, on the other hand, would require at least two firemen in addition to the engineer. In larger steam installa- tions the amount of labor required is naturally not so great in proportion to the horse-power produced. For example, at the Rondout Siphon 8 men per 8-hour shift were able to operate a steam plant rated at 4,000 horse-power and containing 10 air compressors of 2,400 cubic feet capacity each. Fuel Consumption. — If the charge for delivering it be in- cluded in the price, at most tunnel plants the cost of fuel is high, hence the amount of it required is of great importance. Steam plants require much more coal than gas plants of the same size ; for although in large installations, with every means for eff'ecting thermal economies, steam plants may be operated with as Httle as two pounds of high-grade fuel per brake horse-power hour, in small plants such as are used in tunnel work a fuel consumption as low as three pounds would be exceptional, and four or five pounds is more likely to be required. With producer-gas, on the other hand, it has been repeatedly demonstrated that internal CHOICE OF POWER FOR TUNNEL WORK 75 combustion engines can be operated on less than one pound of coal per brake horse-power hour, and at the best plants this figure runs as low as three-fourths of a pound. The consumption at the Woolwich tunnel plant during a test was .727 pound of Polmaise Scotch anthracite per brake horse-power hour. The small inter- nal combustion engine has also the additional noteworthy char- acteristic of being decidedly efficient in small sizes. The gas engine of 50-60 brake horse-power has but a very Httle greater fuel consumption per horse-power than the large engines of 500 or 1,000 brake horse-power. The adoption of a producer-gas plant also makes possible the utilization of the fine sizes of an- thracite coal such as Nos. 1,2, and 3 buckwheat, which were for- merly considered waste, but which are now being screened and saved and may be procured at much less cost than the coal used in most steam boilers. Thermal Efficlency. — The comparatively high fuel con- sumption of the steam-engine is due to its low thermal efficiency. Although large and economically operated steam plants may real- ize perhaps as high as 12 to 15 per cent, of the theoretical energy contained in the coal, 5 per cent, is much nearer the value gener- ally obtained in ordinary tunnel work. The following table shows the distribution of the average heat losses for one year at a well- conducted steam plant where the thermal efficiency at the fly- wheel was 10 per cent. : LOSS OF THEORETICAL HEAT ENERGY AT A STEAM PLANT Losses due to imperfect combustion, heat absorbed in ashes, moisture, etc., heat in flue gases, radiation, etc. 25% Loss due to latent heat in exhaust steam 60 Loss in steam pipes and auxiliaries 3 Loss due to friction in steam-engines 2 90% The producer-gas engine, on the other hand, operates with a much higher thermal efficiency, 20 to 30 per cent, being not un- usual in actual practice. Recent exhaustive shop tests of a number of first-class foreign-built producer-gas engines, ranging 76 MODERN TUNNELING . in power from 70 to 120 horse-power, gave thermal efficiencies at full load of from 31.3 per cent, to 34.9 per cent., and a coal consumption of from .72 to .623 pounds per brake horse-power hour. The following table, introduced for comparison, shows the distribution of losses in a producer-gas plant operating with similar economy to the steam plant above: THERMAL LOSSES IN PRODUCER-GAS PLANT Loss in gas-producer 15% Loss in water jacket 21 Loss from radiation and friction 4 Loss in exhaust gases 35 75% Purchase of Current. — If the line of an estabhshed electric power company runs near enough to the tunnel plant, power is often purchased in preference to generating it at the tunnel. In such cases the price of current usually ranges from i^ to 2 cents per kilowatt hour. On the Los Angeles aqueduct the power used at all the tunnel plants is obtained from a private trans- mission line operated by a separate department of the aqueduct organization, and a fiat rate of 1.7 cents per kilowatt hour for power is charged against each tunnel, which it is estimated is sufficient to operate the system and eventually pay for its instal- lation. At one of the tunnels in Colorado, a fiat rate of $2.50 per horse-power month is charged, to which is added 1.3 cents per kilowatt hour used. On a 24-hour day basis this is equiv- alent to i^ cents per kilowatt hour. At another tunnel in Colo- rado, 2 cents per kilowatt hour is the price of current. At a third, the power for the compressor costs $5.50 per horse-power month, which is equivalent to i cent per kilowatt hour on a 24-hour day basis, but at the same tunnel 2 cents per kilowatt hour is charged for the current used in the motor generator set which operates the trolley system, making the average cost for the total power used approximately ij^ cents. At one tunnel plant using a very large amount of power, the current is said to have cost but yi cents per kilowatt hour, an exceptionally CHOICE OF POWER FOR TUNNEL WORK 77 low figure, but in this case other considerations were involved which really made the cost of the electricity greater than this. The following schedule is used by a number of western hydro- electric companies who claim that this method of making a charge is ''fair and rational." Fixed Charge per Month per Horse-Power of Maximum Demand Energy Charge For the first loo Horse-Power. . $3.25 For the next 400 Horse-Power. . 2.25 For the next 500 Horse-Power. . 1.75 For all additional Horse-Power . i .00 Add for all energy used as shown by meter thirteen mills per kilowatt hour for the first 40,000 kilowatt hours used each month, and five mills per kilowatt hour for all additional energy. The maximum demand shall be determined by the company's meters, disregarding starting peaks and those due to short circuits or accidents to user's apparatus. Interest and Depreciation. — The cost for interest per unit of power is dependent upon the amount of capital invested, but that for depreciation is somewhat more complicated. In the case of water-power, a dam or a ditch would have but very little salvage value after the completion of the tunnel; something further might be realized from a pipe-line or flume and still more from the machinery in the power-house, the total loss of capital invested being the sum of these separate items. Hence the charge for depreciation would depend upon the relation of the different factors to the total cost of installation. A similar analysis may be made for other means of producing power. Both interest and depreciation charges are dependent also upon the hourly use of the plant per day, it being evident that if the plant were used 24 hours instead of 12 the same total cost for interest and practically the same total loss by depreciation would be dis- tributed over double the number of horse-power hours, and hence be proportionally less. 78 . MODERN TUNNELING CONCLUSIONS In choosing the power to be used for tunnel plants, a water- fall or rapid, if either is available, should be given primary con- sideration. The chief arguments in favor of this source of power are as follows: no fuel is required; the cost for attendance and repairs is a minimum; it is comparatively reliable, hence obviating losses due to interruptions of service. The one factor which might prohibit its choice is the possibility of a high cost of installation, with resulting large charge for interest and depre- ciation per unit of power. This consideration, dependent entirely upon local conditions, usually determines the adoption or rejec- tion of a possible water-power plant. Again, where water-power is not obtainable directly at the tunnel plant, if it can be secured from a waterfall in the neighborhood, the essential factors re- main the same with the exception that a means of transmitting the power, such as air or electricity, must be chosen, and the cost of the transmission system be included in the cost of installation. Another possible means of obtaining the advantages of water- power is to be found in the purchase of current from an estab- lished hydro-electric company. Such a concern is in a position to utilize a waterfall, too distant to warrant its development for a single tunnel project, and by distributing a large amount of power among many permanent customers is enabled to sell it very cheaply. In such case, to the price of the power should be added the cost of attendance at the tunnel plant and the interest and depreciation charges on the necessary equipment. Allow- ance must be made for interruptions to service in long-distance electrical transmission which are neither unusual nor avoidable. The choice of machinery for utilizing water-power is also largely governed by local conditions. Since high heads, for which impulse- wheels are especially adapted, are generally to be found where water-power is available for tunnel work, this type of machine is properly chosen in most instances. Turbine wheels may be used where the water is clear or can be settled in a reservoir, but such conditions are not usually to be found at tunnel power plants. The hydrauHc compressor, although prac- CHOICE OF POWER FOR TUNNEL WORK 79 tically automatic and entailing but a small operating expense, is so costly to install that it is scarcely to be considered except for plants much larger than those usually designed for tunnels. According to usual practice, a steam plant would be installed if water-power were not available and electricity were not purchasable. This is difficult to understand unless it be attrib- uted to the supposed unreliability of the gas-producer. The usual steam plant for tunnel purposes is, as has been shown, very inefficient in its utilization of the energy of coal and has a fuel consumption rarely less than 4 or 5 pounds per horse- power hour. As regards cost of installation, the balance is slightly in favor of steam, but not sufficiently so to overcome the disadvantage of higher operating cost. The producer-gas plant, on the other hand, is several times more efficient in its utilization of heat energy, making possible the production of a brake horse-power per hour in some instances with as Kttle as one pound of coal. With this plant it is also pos- sible to utilize cheaper grades of fuel. The manufacturers of air compressors have recently adapted their machines for use with internal-combustion engines. It would seem, therefore, if a plant using fuel were necessary, that the installation of a producer-gas plant under most conditions were more desirable than a steam plant. As a means of transmitting power for any great distance the balance is preponderantly in favor of electric transmission at high tension. In tunnel work and over comparatively short distances, compressed air is able to compete with it because the air drills require this form of power for their operation. When it is necessary to obtain power from coal there seems to be a field for producer-gas transmission in the medium distances, where the cost of the line and the power losses in transmission prohibit the use of air, but where the cost of the extra electrical machinery is still not warranted by the saving in cost of line. CHAPTER V AIR COMPRESSORS Although an air compressor is the machine invariably chosen at tunnel plants to convert the power derived from steam, water, electricity, or fuel gas into a form suitable for use in pneumatic rock drills, many factors enter into the problem of its selection. After the question of motive power and capacity, the type of the compressor is, perhaps, the next thing to be consid- ered. The methods of regulation under varying load likewise deserve attention. And, finally, the devices and accessories for preventing or neutralizing the effects of heat produced during compression and for removing moisture from the air bear directly upon our problem. The most familiar types of air compressors consist essentially of a cylinder in which air is subjected to pressure by a moving piston. Automatic means are provided to insure the admittance of free air and its delivery after compression, and the momentum of a fly-wheel is required to equalize the irregular demands of the piston for power. When stfeam or internal combustion engines are the prime movers they are usually, though not neces- sarily, incorporated with the compressor, the power and air pistons being connected by a common piston rod or engine shaft. Where water or electricity is em^ployed, the power is usually developed in separate motors and transmitted to the air compressor by a belt, the fly-wheel of the compressor in this case serving also as a pulley; but there has arisen lately a grow- ing demand for the '' direct-connected" electrically driven machine in which the electric motor forms an integral part of the compressor, the armature serving as a fly-wheel. Such machines are now suppHed by all the leading manufacturers. ^'Direct-connected'' water-power driven air compressors are also obtainable in which the water-wheel carrying the buckets or vanes performs the additional function of fly-wheel for the com- 80 AIR COMPRESSORS 81 pressor. Air compressors of an entirely different type, operating on the principle of the reverse turbine, have recently been placed on the market. They are especially adapted to take advantage of the high rotative speed of electric motors and steam turbines. Although the Taylor hydrauHc system is, strictly speaking, an air compressor, it has been described somewhat in detail as a means of utihzing water-power; since its use is ordinarily con- fined to units too large for tunnel work, it will not be discussed further. POWER REQUIRED Although the kind of motive power is generally predetermined, in designing a given plant, by local conditions, the amount of power required for this purpose is worthy of brief discussion. E. A. Rix is authority for the statement* that, in compressing air from atmospheric pressure to 90 or 95 pounds, f 20 brake horse- power must be dehvered at the fly-wheel shaft of a reciprocating compressor for every 100 cubic feet per minute of piston dis- placement. This figure is deduced as the average result of a number of tests of air-compressor plants, comparing the capa- bilities of almost every kind of compressor with the actual power required to operate them. He also states that the figures given in trade catalogues for the amount of power required in compressing air are usually somewhat lower than this value, but it must be explained that such figures are theoretical and do not take into consideration the mechanical or volumetric efficiencies of the compressor. The following tables are computed from the catalogues of two leading manufacturers for a popular type of compressor in each case and show^ the rated brake horse-power per 100 cubic feet cylinder displacement, where the final gauge pressure is 100 pounds. * Address before the Mining Assoc, Univ. of Calif., February 19th, re- printed Compressed Air Magazine, June, 1906, p. 4894. t Throughout this book when air pressure is mentioned the figures given will be those above atmosphere, i.e., gauge pressure. In many books the pressures given are absolute, i.e., the pressure above vacuum, while in European works on the subject pressures are generally expressed in terms of atmospheres, which in this country would be liable to create considerable confusion. 82 MODERN TUNNELING RELATION BETWEEN REQUIRED BRAKE HORSE-POWER AND CAPACITY Compressor A Compressor B Brake Horse-Power Brake Horse-Power Required for Each Required for Each Capacity Cu. Ft. 100 Cu. Ft. Dis- Capacity Cu. Ft. 100 Cu. Ft. Dis- per Minute placement Com- per Minute placement Com- pressing to 100 lbs. pressing to 100 lbs. 144 18.7 248 193 247 18 6 338 19 2 372 18 4 537 18 I 534 18 3 680 18 I 704 18 I 873 18 1051 18 1056 18 1312 17 8 1188 18 1692 17 7 1414 17 9 2381 ^7 7 1845 17 9 It will be observed that these tables bear out the statement made by Mr. Rix, and that even in spite of the increased final pressure, the values are somewhat less than the one he proposes. They also show that in machines of large capacity proportion- ally less power is required. The following table, based upon published figures, shows the amount of power required or provided per 100 cubic feet of free air actually compressed at several turbo-compressor installations : POWER CONSUMPTION OF TURBO-COMPRESSORS ' Rated H.P.of Motor or Actual H.P. Required in Engine per loo Cu. Ft. of Compressing loo Cu. Ft. Pressure Capacity in Cu. Ft. Free Free Air When Com- Air per Minute pressing to Stated Pressure Stated Pressure 90 4,600 21.8 118 21,250 18.8 17. 135 20,000 18.5 170 22,000 18.2 CAPACITY The capacity of compressors is rated in free air,* and in reciprocating machines is equally based upon speed and piston displacement — that is to say, the number of cubic feet of cyl- inder space swept by the piston each minute at the given speed. *Free air is air at 14.7 lbs. pressure (atmospheric), and at a temperature of 60° F. AIR COMPRESSORS 83 I This is not, however, the actual capacity, because there are unavoidable losses in volume due to clearance, piston speed, leakage, and expansion, the sum of which may amount to as much as 30 per cent, of the rated capacity in a single-stage compressor at 100 pounds pressure. The capacity of turbo- compressors is based on the amount of free air drawn into the intake per minute. Although some of the more carefully designed reciprocating compressors may give a volumetric efficiency as high as 90 per cent., for compressors such as are customarily employed in power plants for tunnels 80 per cent, is more likely to be nearer the figure. While the tables shown in manufacturers' catalogues of air drills are in the main fairly accurate for new drills, the air consumption is often greatly augmented as the parts become worn. Provision must be made also for leakage in the pipe line and for the air required by drill sharpeners, black- smith forges, and an extra small drill which is sometimes used for blocking and trimming. It is therefore most desirable to have the air compressors, as based upon catalogue rating, considerably oversized, and in tunnel practice this usually ranges from 100 to 150 per cent. The following table shows a comparison between the rated compressor capacity and the catalogue air consump- tion for the drills employed in the heading at several tunnels : RELATION BETWEEN COMPRESSOR CAPACITY AND AIR CON- SUMPTION OF DRILLS Tunnel Carter Laramie-Poudre , Elizabeth Lake . Lucania Marshall-Russell Mission Rawley Snake Creek . . . Strawberry .... Compressor Cata- logue Values Capacity No. Speed Cu. Ft. in r.p.m. per Min. Heading 150 868 2 165 602 3 160 736 3 130 544 3 175 487 2 190 247 I 175 427 2 165 680 2 175 427 2 Drills Air Consumption from Catalogue Cu. Ft. per Minute 230 at 250 " 185 " 250 " 200 " 100 " 190 " 300 " 300 " 9,000 elev. 8,000 3,000 8,000 8,000 1,200 10,000 6,000 7,000 Oversize of Com- pressor* 280% 140 300 120 140 120 125 40 Not including drill sharpeners, forges, or leakage in pipe lines. 84 MODERN TUNNELING The decrease in effective capacity of the compressor caused by leakage in pipe lines is in many cases not fully realized, and steps are not taken either to determine the amount of this waste or to prevent it. Where the compressed-air lines are con- structed with great care and covered so as to protect them from accident or from extremes of temperature, the loss by leakage may be slight or almost negligible; but where they are not well built or where they remain uncovered, the lines on the surface are exposed to injury from numerous causes — not the least of which being diurnal and seasonal variation in temperature — and those underground are apt to be struck by falling rock, derailed cars, etc. In such cases the leakage is likely to be a very considerable item, and the greatest care should be taken to test the- lines at short intervals to ascertain the amount of loss in order that whatever is necessary may be done to stop it. Where reciprocating compressors are used, driven either by steam- or water-power, it is an easy matter to ascertain the amount of leakage by simply closing all of the outlet pipes from the line and noting the number of strokes per minute necessary to main- tain the desired pressure; but where turbo-compressors are used, unless a very careful table has been compiled showing the output at different speeds and pressures, the leakage can best be ascer- tained by stopping the compressor when the receiver and lines are filled, allowing the pressure to drop to 50 per cent., let us say, then starting up the machine and noting the length of time required to bring up the pressure to the original point. While this does not give exact results, still it will furnish a useful, if not exactly correct, index to the rate at which the compressed air is escaping. Such a method of ascertaining the amount of leakage is so simple that it would seem that it ought to be in general use; but unfortunately it appears to be the habit of workmen, especially of the ''chain gang," to assume that all air lines are much more free from leaks than they really are. A few years ago at one of the large mines in the West which operated a great number of drills, drill sharpeners, and pumps by com- pressed air, it was found impossible to maintain the required pressure, and bids for a new and expensive compressor were AIR COMPRESSORS 85 called for, when it occurred to the management to test the pipe lines by the method above indicated, and it was discovered that I, IOC horse-power were required to supply the loss by leak- age. In this case the ''chain gang," instead of the machine shop, ''got busy," and in a week the leakage was stopped and the waste of air reduced to such a point that, instead of buying another compressor, one of the largest machines w^as shut down. TYPES Reciprocating air compressors may be divided into two general types: " straight-Hne " (sometimes called "tandem") and duplex. Either of them may be single stage where the air reaches its final pressure in one cylinder, or multi-stage where only a portion of the compression takes place in the first cylinder and is finally completed in a second, third, or even fourth cylinder. Straight-line In the tandem compressor, if it be driven by steam or an internal combustion engine, the power and air cyHnders are placed tandem-fashion along a common piston rod, and the Fig. 12. Section through a single-stage straight-line compressor in which the power cyhnder is an internal combustion engine using gasoline fuel. power is thus applied in a straight line. (See Figures 12 to 14.) The fly-wheels, of which there are usually tw^o, may be at either n c/) 88 MODERN TUNNELING end or between the cylinders and are connected to the piston rod by a cross head and ordinary connecting rods. If it be driven Fig. 15. bin^lu-blage, power-driven compressor. by electricity or water, practically the only change is the omission of the power cylinder. (See Figures 15 and 16.) Duplex A duplex compressor consists of two tandem compressors placed side by side, having a fly-wheel between them on a com- FiG. 16. Belt-driven, straight-line, two-stage compressor. mon shaft. The two sides are connected to the fly-wheel shaft by cranks set at 90° so that when one side is encountering maximum resistance, the other is working under the Hghtest load. There are many different combinations possible with the duplex type. The steam cylinders * may or may not be compounded (see * Internal combustion engines have not as yet been applied to this type of compressor. Fig. 17. Duplex, simple-steam, two-stage air compressor. c 3 o a- S o u "a 3 Q AIR COMPRESSORS 91 Figures 17 and 18), and the air cylinders may be single, or multi-stage. (See Figures 17 and 18.) Again the steam cylinders may be omitted and the power transmitted to the Fig. 19. Duplex, belt-driven, two-stage air compressor. machine by a belt (see Figure 19) or by a directly connected motor. (See Figure 20.) Turbo-compressors The turbo-compressor operates upon the principle of a re- versed turbine in which air, instead of water or steam, is the fluid acted upon, and it consists essentially of a revolving im- peller (not unlike that of some forms of centrifugal fans) sur- rounded by a set of stationary discharge vanes supported in a suitable casing (see Figure 21). It is the function of the discharge vanes to recover the major portion of the energy which exists in the air as velocity upon leaving the impeller, and which is roughly almost one-half of the total energy suppHed from the driving machine, by converting this velocity into available press- AIR COMPRESSORS 93 ure. In the centrifugal fan, there being no such vanes, this energy is lost as heat produced by eddies and friction, hence it is not difficult to see the rea- sons for the higher efficiency of the new machine. Single-stage turbo - compressors are em- ployed chiefly in connection with blast furnaces, cupolas, etc., and could be used for mine ventilation; but where a high pressure is required, such as that needed for the opera- tion of rock drills and other pneumatic machinery, a num- ber of impeller units are mounted on a common shaft operating in series within a common casing, the air upon leaving the first set of dis- charge vanes being conducted to the intake of the second impeller, and so on. Com- pressors producing 170 pounds pressure and having as many as 29 stages have been con- structed, but where so many stages are employed the im- pellers are usually mounted in groups of from four to ten. The manufacture of turbo- compressors is just beginning in this country, but they have been in use for several years in Germany, where their design and manufacture have already 94 MODERN TUNNELING reached a high degree of perfection. The first large machine of this kind was built in 1909 for the Reden mines near Swar- brucken. It is driven by i ,000-horse-power, mixed pressure, steam turbine at 4,200 revolutions per minute, and compresses 4,600 cubic feet of free air per minute to a gauge pressure of 90 pounds to the square inch. Quite recently, six motor-driven compressors of this kind were built in Germany for the Rand mines in South Africa. Each of these six machines is operated by two 2,000-horse-power synchronous motors running at 3,000 revolutions per minute. The compressors have a rated capacity of 21,250 cubic feet of free air per minute at 68° F. to 118 pounds pressure per square inch. In a test, when compressing 23,750 cubic feet of free air per minute to 100 pounds pressure, the energy of consumption per hundred cubic feet of free air was 17 horse-power and the highest isothermal efficiency obtained was 67.04 per cent. The first large compressor built in this country went into service in May, 191 1, and has been in continuous oper- ation ever since. This machine (figure 22) is driven by a steam turbine at 4,700 revolutions per minute and has a capacity of 3,500 cubic feet of free air per minute delivered at a pressure of 105 pounds per square inch. It is of course not possible, nor is it within the proper scope of this volume, to describe all the numerous makes of air compres- sors; for such material the reader is referred to the trade cat- alogues issued by the various manufacturers, who will be glad to supply this information, and whose experts are prepared to render any assistance possible in the selection of a compressor. COMPARISONS The chief advantages of the straight-line compressor are that it is strong, simple, compact, and easily installed. It is usually self-contained, being mounted on a single bed plate, and requires relatively inexpensive foundations. The frictional losses in a good machine of this type are not large and, at or near ^ull load with moderate pressures, it may have a fairly good power economy. These features make it advantageous for less access- ible plants or those of a more or less temporary character. Fig. 22, Turbo-compressors. 96 MODERN TUNNELING A great advantage of the duplex type, on the other hand, is the faciHty with which either steam or air cyHnders may be "compounded" without increasing materially the number of parts. This makes it possible for the duplex type to take advantage of the great saving in power resulting from com- pound steam cylinders, as well as the economy resulting from two-stage air compression. Practical experience with the two types of machines fully confirms the theoretical investigations of their comparative efficiency, and carefully conducted tests extending over long periods of time have established the eco- nomical superiority of the duplex type. In this type, also, if properly designed, the mechanical losses through friction, etc., are but little greater, if any, than in the straight-Hne compressor, and it is much more easily regulated under varying loads. Most manufacturers are now making duplex compressors with a sub- stantial sub-base, giving the machines a strength and rigidity comparable with the other type, reducing the expense of foun- dations, thus meeting some of the conditions which have until recently been so much in favor of the straight-line type. The result is that, with perhaps a half-dozen exceptions, the air com- pressors at tunnel plants examined were of the duplex type. The entire absence of valves, reciprocating parts, and sliding friction in turbo-compressors, together with their freedom from vibration, their high capacity in proportion to weight and to floor space occupied, and their ability to take advantage of the high rotative speeds of electric motors and steam turbines, are certain to bring these new aspirants for engineering favor into general use. Using live steam, condensing or non-condensing turbine-engine turbo-compressor units are quite able to compete successfully with the very highest grades of reciprocating-engine compressor plants, and they can be operated successfully with exhaust steam from engines, pumps, or other apparatus, which forms one of the cheapest possible sources of power — because in utilizing steam which would otherwise go to waste, practically free fuel is obtained. Another advantage, and one that might easily be overlooked, is the fact that it practically eliminates the danger of explosions in air receivers and pipe lines. In piston AIR COMPRESSORS 97 compressors lubrication must be supplied to the inside of the cylinder in order to protect it from the friction of the sliding piston; there is, therefore, every opportunity for the oil (which becomes finely divided in this process) to commingle with the air as it is being compressed and to be carried with it into the receiver. But with the turbo-compressor the only surfaces re- quiring lubrication are those of the bearings to which the air being compressed has no access. When an electric motor or water- wheel is the source of power, the ease with which the turbo- compressor may be connected to either of them, thereby avoid- ing all loss due to speed reduction and friction, renders this a most desirable combination. The turbo-compressor is readily adapted to automatic control and may be regulated for the delivery of a constant volume or constant pressure as required. Its efficiency is maintained over a wide range of load within a few per cent, of the maximum, and the efficiency does not decrease with continued service. There is, therefore, every reason to expect that turbo-compressors will come into general use in the near future. REGULATION Steam Driven Although, when steam driven, a change in load with any type of machine results in a variation of speed, this works more to the disadvantage of the straight-Hne compressor, especially with high air and steam pressure, because this type will not run satisfactorily at low speeds, the momentum of the fly-wheel not being sufficient to carry it past dead centers. To avoid stop- page, either the steam cut-off must be lengthened (in which case there is a loss of steam as the machine speeds up under increasing load) or there must be a fixed limit below which the steam is not decreased, and when the demand for compressed air falls below that supplied regularly by the machine the excess must be per- mitted to escape through a safety valve. Both of these cases entail loss of power. For this reason the straight-line compressor cannot operate economically much below the Umit of 40 per cent, of full load. 98 MODERN TUNNELING In this matter of regulation the duplex, steam-driven machine has an unquestioned advantage over the straight-line machine. The quartered cranks, in addition to minimizing strains and reducing extremes, enable one cylinder to come to the help of the other just at the time when that help is most beneficial, and, a quarter of a revolution later, the favor is returned. There can be no dead center, and the machine will run so slowly as hardly to turn over if the compressed air in the receiver is not being drawn upon, and will speed up rapidly as there is an increased demand for air, doing it without any change in the cut-off. The duplex machine, therefore, has the same steam economy over the full range of load, without any loss of compressed air at the safety valve. With the turbo-compressor when steam-turbine driven, the regulation is merely a matter of controlling the amount of steam admitted to the turbine. Water Driven The regulation of compressors driven by impulse wheels may be accomplished by several methods, among which may be men- tioned the deflecting nozzle, the needle nozzle, and the cut-off. The deflecting nozzle is provided with a ball and socket joint and is controlled by air receiver pressure in such a manner that a portion of the stream of water may be shifted on or off the buckets of the wheel, thus increasing or decreasing the amount of power developed to correspond with varying loads. A steel plate may be made to accomplish the same effect by deflecting the stream of water, the nozzle in this case remaining stationary. The needle nozzle is merely a discharge valve in which a conical needle is inserted or withdrawn from an orifice, thus diminishing or increasing the amount of water passing through. The cut-off also regulates the water quantity by a change in the discharge area, produced by the shifting of a plate which fits tightly over the nozzle tip. The deflecting devices are capable of controlling rapid variations in power demand, but are, of course, wasteful of water, while just the reverse is true of the other types. At tunnel plants, however, water economy is rarely an essential consider- AIR COIVIPRESSORS 99 ation while variations in load are frequent and sudden ; the de- flecting devices are therefore most suitable. Electrically Driven The volume of air compressed in any reciprocating machine varies with the number of strokes per minute made by the piston; in the turbine compressor it is dependent upon the rota- tive speed. In electrically driven reciprocating compressors, whether directly connected or belted to a motor, the speed is necessarily reasonably constant and cannot be varied to meet fluctuating demands for air; and since economy obviously for- bids the discharge of excess compressed air through a safety valve, "unloaders" must be provided to overcome the difficulty. Ufiloaders. — The more common method is to limit the amount of air admitted to the machine. This type of unloader consists of a valve in the free-air intake pipe controlled by the pressure in the air receiver, which throttles the admission of air when the load is Kght, and allows more of it to enter when the demand for air increases. This device may be employed successfully with turbo-compressors, but with reciprocating machines it never- theless has its drawback, because when running with a partially throttled inlet, the smaller amount of air drawn into the cyhnder is rarefied and on the return stroke of the piston is consequently compressed through a greater range of pressure, giving rise to higher temperatures than ordinary and they may reach unsafe limits, especially where the terminal pressures are great. This is not so important with turbo-compressors because the temper- atures never become so high as they do in reciprocating machines. On some piston compressors an unloader of almost an ex- actly opposite type is employed and consists of a device for holding the intake valves open whenever the air pressure reaches a predetermined point. In one type of unloader for reciprocating machines the excess air is forced automatically into clearance tanks, the process being controlled by a predetermined receiver air pressure. Fig- ure 23 gives a diagrammatic representation of this de\dce. Under normal full load the controller is inoperative, but when working 100 MODERN TUNNELING at partial capacity a portion of the compressed air is forced into the tanks instead of going through the discharge valve, thus reducing the output of the compressor. On the return stroke this air expands, returning its stored energy to the piston. There are eight tanks in all, and four equal and successive unloading stages are possible by throwing in respectively two, four, six, or all of the tanks. The regulation is said to be unaccom- panied by shock due to sudden variations in load, and heating Fig. 23. Diagrammatic cut of clearance controller. caused by the compression of rarefied air is avoided — in fact, since there is a slight radiation from the clearance tanks, the air is probably returned to the cylinder slightly cooler than when it left. Another method of unloading is by holding open the discharge valves of the compressor, permitting compressed air instead of free air to fill the cylinder as the piston retreats, and thus bal- ancing the pressure on both sides of the piston. Although this unloads the compressor completely, it has a very serious draw- back. As the load is resumed the balance of pressure is dis- turbed, one side of the piston being subjected to something less AIR COMPRESSORS 101 than atmospheric pressure, while the opposite side is exposed to the full pressure of air in the receiver, the difference in pressure being thrown on the piston instantly and maintained throughout the entire stroke. As a result, serious strains are placed upon the structure of the compressor which prohibit the use of this unloader except in the smaller sizes. Still another type releases the partially compressed air during its passage from the low- to the high-pressure cylinders, but little can be said for this method except that it is not quite so wasteful as releasing high-pressure air. HEAT Heat Produced Heat is produced during the compression of air and the rise in temperature is largely dependent upon the difference between the initial and final pressure. For instance, if air at 60° F. be compressed in a single stroke from atmospheric pressure to 100 pounds gauge, the temperature attained would be 485° F., assuming no loss by radiation during the process. On the other hand, under the same conditions, if the final pressure were but 25 pounds gauge, the air would be heated only to 233° F., and if it were then cooled again to 60° and further compressed from 25 pounds to 100 pounds gauge the final temperature would approximately be 250° F. The effect of the increase in tempera- ture is to cause the air to expand to a larger volume, and hence more work is required to compress it. If the air could be used at once to operate a motor, before any of the heat escapes through radiation, etc., this work could be obtained again from the air; but since in mining work the heat is almost without exception entirely dissipated in the pipe line before the air reaches the drills, the production of heat during compression entails a serious loss of power. Dangers of High Temperatures Aside from the item of power waste, the temperature reached during compression has an important bearing on the question of 102 MODERN TUNNELING explosions in air lines. It can readily be imagined that if the dis- charge valves are not working properly and some of the highly heated compressed air is allowed to re-enter the cyHnder with the fresh intake air, compression may begin at a temperature much higher than normal, in which case, even with two-stage machines, the final temperature of the compressed air may be gradually built up from 250° to 500°, 600°, or even higher. It is often sufficiently high to volatilize lubricating oil, the vapors of which, mingling with the air, may be in proper amount to form an explosive mixture. If the temperature then becomes high enough to ignite this mixture, an explosion inevitably results. There have been numerous instances where this has actually occurred. Removal of Heat The ideal way to prevent the evil effects of heat would be to devise some means of removing it from the air as fast as produced during compression. Such a course is unfortunately impossible of attainment in practice, but various means have been invented which partly accomplish the result. A famiHar one is to surround the cylinder with a jacket of cooHng water, the piston also being sometimes cooled in this way. But when one considers that air is a very poor conductor of heat and that at the time when it. is hottest it occupies but the minimum volume in one end of the cyhnder, and even then but for a short space of time, it will readily be seen that this method cannot be very effective. In some modern compressors the inlet valves are placed in the piston and the discharge valves in the ends of the cylinders instead of in the heads, thus permitting the latter to be fully water-jacketed, a practice which is to be most highly commended. As water- jacketing is the only means used to cool the air during single-stage compression, it is not surprising that such machines are not economical of power. In two-stage compressors, however, a portion of the heat is actually removed during compression. The air is only partially compressed in the first cylinder, perhaps to 25 pounds gauge, and the heat produced is practically all removed during the AIR COMPRESSORS 103 passage of the air through an intercooler in its way to the second cylinder, where the final pressure, of perhaps loo pounds, is attained. By removing the heat in the inter-cooler, the temperature of the air is kept much lower than with single-stage compression, hence there is less expansion of the air to be over- come, resulting in a consequent saving of power. In a properly designed two-stage machine compressing to loo pounds gauge, this saving of power is approximately 13 per cent., and it increases with the higher terminal pressures. If the pressure is less than 80 pounds, the saving is hardly great enough to be a serious consideration and single-stage machines are customarily em- ployed in such cases, but for pressures higher than 100 pounds two-stage compression is imperative, because of the high temper- atures that are otherwise produced. As shown by the following table, the pressure ordinarily employed in tunnel plants ranges from 80-120 pounds, averaging about 100 pounds. Compressed Air Pressures at Different Tunnel Plants Carter 112 Marshall-Russell no Roosevelt no Central 120 Mission 100 Siwatch 80 Gold Links 100 Moodna 95-100 Snake Creek. ... no Gunnison 90 Newhouse no Stilwell 100 Laramie-Poudre 120 Nisqually 90-95 Strawberry 85 Mauch Chunk.. . 100 Rawley 100 Utah Metals. ... no Los Angeles Raymond 90 Walkill no Aqueduct 100 Rondout 100 Yak 90 Lucania 115 Because of the many stages required with turbo-compressors when delivering air for use in drilling, the difference between the pressures of the air on entering and leaving any one stage is extremely small compared with that of two-stage reciprocating machines. Hence the resulting increase of temperature in any one step is not great, and it is possible to remove the compara- tively small amount of heat generated effectively by the use of a suitably designed water-jacket. Some idea of the efficiency obtainable with such a cooKng system may be had from the fact that the air delivered into the receiver at 105 pounds 104 MODERN TUNNELING pressure from the turbo-compressor illustrated in Figure 22, page 95, has a temperature of only 120° F. Intercooling The efficiency of two-stage compression is largely dependent upon the intercooler. It is an essential part of this type of machine, and usually consists of a shell, generally cyKndrical in shape, containing a number of pipes, similar to those in a tubular boiler, through which cold water is made to circulate. See Figure 24. The heated air from the low-pressure cylinder enters Water outlet pipe, JJTatej drain Connection foe low-pressure air cylinder. Fig. 24. Typical Intercooler. near one end, passes through the nest of tubes, its passage being obstructed by baffle plates to insure the maximum contact between air and cooling surface, and is delivered at much lower temperature to the high-pressure cylinder at the other end. The success of the intercooler depends upon several considera- tions. In order that the least dependence need be placed upon the heat conductivity of the air itself, which is notably poor, the intercooler must subdivide the air completely, and insure that the maximum amount of it is thrown in contact with the cooling surfaces. This is accomplished by properly spaced water- tubes and baflie plates. At the same time the cross-section of the cooler must not be too small, in which case the velocity of the air past the cooling surface would be so great that sufficient time would not be allowed for the water to absorb all the heat. AIR COMPRESSORS 105 It is very desirable also to have the water and air flow in opposite directions in order that the final cooling of the air may be effected by the entering, and consequently the coldest, water. Theoreti- cally, the cooling surface should be sufficient to absorb all the heat in the air passed over it, reducing the temperature to the point at which the .air entered the low-pressure cylinder, but due possibly to mechanical difficulties, even in good practice, intercoolers usually fail to do this within five or ten degrees, while even 30 or 40 degrees are not unusual. Moisture The intercooler assists also in removing water from the air. Normal atmosphere always contains at least some water vapor, but for any combination of relative volume and absolute temper- ature, air is incapable of absorbing more than a certain amount of water vapor. This maximum at 60° F. and 14.7 pounds pressure is .0137 ounce, while under the same pressure and at 32° F., air can hold but .0046 ounce and at 0° F. but .0011 ounce. In the air compressor both of these factors of volume and temperature are suddenly and violently disturbed. The water vapor in the air would be released were it not for the fact that as the volume is reduced (a process which would ordinarily decrease the capacity of the air for moisture) the temperature is greatly raised at the same time, increasing the water-carrying capacity of the air; the increase in capacity for moisture, caused by the high temperature, being greater than the decrease due to reduced volume and no water is precipitated. But as the air passes through the intercooler the temperature is lowered greatly without a corresponding increase in volume, and the air is forced to give up its water. It is precipitated in such a finely divided state, however, that it requires some time to settle; for that reason only a portion of it can be collected in the intercooler and drawn off through drains provided for that purpose, the remainder being swept along with the air to the higher-pressure cylinder and revaporized by the tem^perature there attained. 106 MODERN TUNNELING ACCESSORIES Precoolers Cooling the air before its admission into the air compressor also assists in removing some water from it, and there are a number of devices for this purpose. One precooler described in the Engineering and Mining Journal * is a home-made affair consisting simply of a number of odd pipes set between two wooden boxes. The pipes are wrapped with cloth and water is arranged to drip on them constantly, so that the air is cooled by evaporation as it is drawn through them from one box to the other on its way to the compressor intake. At a plant in Johannesburg the air for the compressors is obtained through a subway leading to the center of a building with air-tight roof and floors, and with walls consisting of constantly wetted cocoa matting. At another plant a similar structure was used in which the sides and roof were covered with burlap both inside and out. A cooler of this type also filters dust and grit which might seri- ously injure the cylinder or piston of the compressor, and can- not be too strongly recommended in dusty situations. Pre- cooling the air also increases the capacity of the compressor, because the cooler air occupies less space than when it is heated, hence a larger actual arnount of air will be drawn into the cylinder and compressed at each stroke. After-cooling The after-cooler, t although it is not generally employed in tunnel plants, by cooling the air at once after it comes from the high-pressure cylinder, also precipitates some of the water vapor, but at the same time it reduces the volume of the air and practi- cally eliminates the danger of explosion in the air line. Although the air gives up its water vapor in the cooler because of the de- * November 27, 1909, p. 108 1. t In design and principle the after-cooler is practically the same as an intercooler, and it is usually placed between the compressor and the air receiver. AIR COMPRESSORS 107 crease in temperature, it is usually in so finely divided a state that all of it does not at once fall out, part being swept along with the air and deposited both in the air receiver and in the pipe line. There should, therefore, be provision for draining this water at some low point. The amount of the reduction in volume is somewhat speculative and probably not a serious consideration. Air Receivers The air receiver,* according to the popular notion, is supposed to perform the functions of storing, cooHng, and drying air, together with equaUzing irregularities in its production and use, but it is more than probable that in actual practice it accom- plishes these results, wdth the exception perhaps of the last one, very inefficiently. When one takes into consideration the fact that the receiver ordinarily installed in tunnel plants rarely has a capacity greater than one minute's run of the compressor, it will be seen that it cannot possibly furnish any great amount of storage space. Then, too, since the air in the receiver is being renewed each minute when the compressor is in operation the velocity of the air through the receiver must be enough to pre- vent any great amount of cooHng. There will, of course, be some radiation of heat from the air near the shell, but this is small compared to the heat in the mass of the air in the center of the receiver, so that the air leaves with a temperature but sKghtly lowered, if at all, below that at which it entered. And further- more, since there is practically no cooling of the air, there can be no great precipitation of water vapor. As a matter of fact this is the case in practice, for, although most air receivers are provided with a drain of some sort, only a ridiculously small amount of water is ever drawn off. On the other hand, instead of cooKng, the air receivers have actually in some instances become combustion chambers. Oil and grease in time collect on the inside of the shell and may become ignited if the tempera- ture of the air becomes high enough. Together with the pipe *The air receiver consists simply of a cylindrical shell of steel provided with inlet and outlet pipes and usually a safety valve. 108 MODERN TUNNELING line, which storage space may be considered as an auxiliary, the receiver does assist greatly, however, in equalizing the pulsations not only of the air dehvered from the compressor but also of that used by the drills, and in this way it reduces strain on the structure of the compressor. By regulating the flow, it does not permit the air to attain a high velocity in the pipes even irregu- larly, and hence power is saved since the friction losses increase greatly with the velocity. To secure the maximum benefit from this factor, a second receiver is often installed as near as possible to the place where the air is to be used. In this case the second receiver assists materially in maintaining a steadier air pressure at the drills. A tubular boiler, which it is often possible to buy cheaply at second-hand, makes an excellent receiver and a very efficient cooler. With a vertical tubular boiler it is only neces- sary to remove the fire and ash doors to provide for ventilation, while a horizontal tubular boiler should be placed on an incline sufficiently steep to insure a rapid draft of outside air through the flues. Drains Since practically the entire cooling of the air after leaving the compressor takes place in the pipe fine, it is here that most of the water is precipitated and causes serious inconvenience in several ways. During cold weather, through continued deposi- tion and freezing, the pipe fine may become closed altogether or so restricted as to cause serious drop in pressure or loss of power. Or the water getting into the exhaust from the driUs not uncommonly prevents their operation through freezing at the low temperature of the expanded air. The obvious remedy is to remove the water, which is done by draining the low places in the fine where the water collects. This can be accompfished automatically by the use of any good float design steam trap, but where the pipe is exposed to low temperatures the trap should be placed in a small pit or otherwise protected to prevent freezing. Where necessary, further provision for the efiminaticn of moisture from the compressed air and water from the pipes AIR COMPRESSORS 109 can be had by placing in the Hne any high-class standard steam separator, fitted with an automatic trap as described above. CONCLUSIONS In conclusion, let us sum up briefly the factors which enter into the problem of selecting an air compressor. The power required for both reciprocating and turbine machines is approx- imately i8 to 20 brake horse-power for every 100 cubic feet of free air compressed to 100 pounds gauge. The values given in trade catalogues for reciprocating compressors are generally a little below this figure, but it is a safe one to use in estimates. Such compressors ordinarily have a volumetric efficiency of approximately 80 per cent., and since they are rated on the basis of free air and since it is necessary to make allowance for loss due to clearance, etc., provision for increased air con- sumption above the catalogue rating for drills as they become worn, and for that used in sharpening machines and forges, must also be made with either reciprocating or turbine machines, and it is advisable to select an air compressor considerably over- size. In practice the amount of oversize, based upon drills only, ordinarily ranges from 100 to 150 per cent. Of the two types of reciprocating compressors the duplex is preferable to the straight line (in spite of the latter's simplicity and easier installation) because of the former's more economical and efficient use of power and the faciHty of its regulation, especially when steam driven and with high pressures. Since the air pressure at tunnel plants is rarely below 80 pounds, and in three out of every four it is 100 pounds or greater, two-stage compression is desirable because of its economy of power, if not indeed imperative because of the air temperatures that might other- wise be attained. Although the manufacture of turbo-compres- sors is just beginning in this country, they possess a number of advantages, especially for use with steam turbines and other rotary engines operating at high speeds, which will doubtless lead to their more general use in the future. Their development should therefore be closely watched. Steam-driven compressors 110 MODERN TUNNELING are regulated by varying their speed; but since in some power- driven machines the speed is necessarily constant, other means, of which the throttle inlet and the clearance controllers are the two most used, must be provided for that purpose. Heat is produced during compression and by expanding the air causes loss of power. Some of this loss is obviated in two-stage compres- sion by removing the heat during its passage through an inter- cooler between the cylinders. The numerous stages in the turbine machine enable this heat to be removed effectively by water- jacketing in this type of compressor. Another evil attrib- utable to this heat is the danger from the explosion of volatilized lubricating oils; but in the turbine machine this danger is elim- inated because there are no sliding surfaces to require lubrica- tion. Among the accessories which are designed to prevent or neutralize the effects of heat in piston machines are the pre- cooler, the intercooler, the after-cooler, and the air receiver. The last mentioned also equalizes the pulsations of the air and reduces friction losses. These devices assist, too, in freeing the air from water, which often causes serious inconvenience. The major portion of the water is deposited in the pipe line, however, where provision must be made for its removal. ^ CHAPTER VI VENTILATION MACHINERY Either blowers or fans are employed ordinarily for ventilat- ing tunnels and adits. In machines of the first type, a certain amount of air is trapped every revolution between the impellers and the enclosing casing, and has no means of escape (to omit from consideration a small amount of leakage) except through the exhaust pipe (see Figure 25). For this reason they are Fig. 25. Diagrammatic cross-sections illustrating the action of pressure blowers. often styled '' pressure" blowers and "positive blast" machines. Figure 26 shows one of these blowers in operation on the Los Angeles aqueduct. Where fans are employed in tunnel ventilation they are, almost without exception, centrifugal — the famiUar propeller form similar to the ordinary desk fan being rarely used. In ihe centrifugal fan the air enters near the center, traveling in a direction approximately parallel to the axis of the shaft, and is forced by the centrifugal action of the rapidly revolving blades toward their periphery, where it is collected and discharged. There are many modifications of this design, with the intention of preventing loss of efldciency through friction as the air strikes 111 112 MODERN TUNNELING the back plate and changes direction, or to prevent eddies, etc., due to the greater density of the air at that point caused by its momentum upon entering the fan. Turbo-compressors in which, by the adoption of one or two or even several stages, air can be deHvered at any required pressure, have been employed as blowers for blast-furnace and foundry work at a number of places. The capacities of those manufactured for this purpose thus far are too great for the requirements of tunnel work, but their greater efficiency as Fig. 26. Ventilating blower used on Los Angeles Aqueduct. compared with centrifugal fans and the possibility of designing them to secure any required pressure will doubtless soon lead to their being made in sizes suitable for tunnel work, where they should have a large field. At one tunnel a certain amount of vitiated air was removed from the heading by the use of a jet of highly compressed air which was directed into the ventilating pipe; but this method, in addition to being expensive, is inadequate as well, and is, therefore, not to be advised, except as a temporary expedient and for short distances. On short levels and cross-cuts, how- ever, or on larger work pending the installation of more expensive and efhcient machinery, jet blowers can often be used to good VENTILATION 113 advantage. They can be operated by either compressed air or water under pressure, and, while far from being as efficient as the mechanical types of ventilating machinery, will in many cases perform an extremely useful function. Jet blowers can frequently be used with good results to move large volumes of air for short distances against low frictional resistances, and their extreme economy in first cost makes them an excellent accessory in preHminary work. DIRECTION OF CURRENT The fan or blower ordinarily installed for tunnel work may be made, by a proper adjustment of the ventilating pipe, to exhaust the air from or deliver it to the heading. One of the chief advantages of the first method is that the dangerous gases and smoke produced in blasting are promptly removed from Fig. 2']. Arrangement of gates and pipe for changing direction of ventilating current. the tunnel, and it is therefore unnecessary for the workmen to pass through a thick bank of smoke which would otherwise travel very slowly to the portal. On the other hand, when fresh air is blown in, it passes very much faster through the pipe and is cooler and fresher than if it had worked its way slowly in through 114 MODERN TUNNELING the tunnel or adit and become heated from contact with the walls and contaminated by odors from the track; the men, therefore, feel more comfortable and are able to do better work when this method is employed. The advantages of both methods, however, may be readily obtained by an arrangement of pipes similar in principle to the one shown in Figure 27, which permits the air to be exhausted for a few minutes after blasting, by opening gates a and h and closing c and d (assuming the current through the fan or blower to be in the direction of the arrow), while at other times, by reversing this arrangement, air may be forced into the heading. The following table shows the direction of the air current at various tunnels visited, from which it may be seen that, almost without exception, it is customary to exhaust the smoke, after blasting at least, although at many places the ventilating current is reversed at other times. This arrange- ment is reported as giving excellent results, and its use is strongly recommended. DIRECTION OF AIR CURRENT AT VARIOUS TUNNELS Tunnel Carter Central ' . . Gold Links Gunnison, East Portal Gunnison, West Portal Laramie-Poudre Lausanne Los Angeles Aqueduct, Elizabeth Lake Little Lake Grapevine Lucania Marshall- Russel Mission Newhouse Nisqually Rawley Raymond Rondout Roosevelt Siwatch Snake Creek Stilwell Strawberry Utah Metals Walkill Yak Ordinarily After Shooting Exhaust Exhaust Exhaust Exhaust Blast Exhaust Blast Blast Blast Blast Exhaust Exhaust Blast Exhaust Exhaust Exhaust (Intermittently) Blast Blast Exhaust Exhaust Exhaust Exhaust Exhaust Exhaust Blast Exhaust Exhaust Exhaust Exhaust Exhaust Exhaust for two hours Exhaust Blast Exhaust 20-25 minutes Exhaust for one hour Exhaust >2 to I hour Exhaust. Exhaust Exhaust >4 to I hour Exhaust Exhaust Exhaust Exhaust for two hours Exhaust "for a while" Exhaust Exhaust Exhaust Exhaust Exhaust Exhaust Exhaust Exhaust VENTILATION 115 CAPACITY There is unfortunately no authoritative rule for determining the amount of air needed to renew that vitiated by the respira- tion of men and animals working in tunnels. For coal mines many States have provided a legal minimum which ranges from I GO to 300 cubic feet per minute for each man and from 300 to 600 cubic feet for each animal. These figures, however, have practically no bearing on tunnel work, because in coal mines a much larger volume of air than that actually needed by the men must be supplied in order to dilute and render harmless the inflammable and dangerous gases given off from the coal. In many States the laws provide that even these requirements must be increased at the discretion of the mine inspector. Condi- tions in metal mines, on the other hand, are more closely akin to those in tunnels, but, unfortunately, wherever any legislation exists at all it merely stipulates that the ventilation must be ''adequate." Robert H. Richards considers that the following air quantities are sufficient for proper ventilation in metal mining work : * Per light, i cubic foot per minute. Per man, 25 cubic feet per minute. Per animal, 75 cubic feet per minute. The Mining Regulations Committee of the Transvaal, on the other hand, provide (for metal mines) a minimum of 70 cubic feet per man per minute. t When a person is sitting in repose as in a theater or meeting-hall, 20 cubic feet of fresh air per minute is considered adequate provision by engineers making a specialty of ventilation, but much larger quantities are of course required when working. The following table giving the results of a test, conducted by Bernhardt Draeger,t shows the amount of air breathed in the first minute after performing various kinds of work. *" Mining Notes." Richards, Robt. H., Vol. II, p. 142. Thos. Todd, Boston, 1905. \ Eng. and Min. Jour., November 5, 1910, p. 899. X Gliickauf, 1904, No. 42. 116 MODERN TUNNELING QUANTITY OF AIR ACTUALLY BREATHED IN FIRST MINUTE AFTER EXERTION Kind of Work Subject Subject B Subject C Average Sitting 10 minutes Walking 270 yards Marching 550 yards Running 270 yards .... Rolling barrel weigh- ins: ^A cwt 8.5 liters 10.5 " 143 " 30. 38. 38- :: 52. 40 sees. 8.25 liters II. 3 " 17-5 " 30. ^^- ;: 42. 61. 42 sees. 9 . liters II. 7 " 13.0 " 30. 405 " 38. " 59- " 42 sees. 8 . 58 liters* 1 1. 2 14.9 " 30. 37-2 " 39- 51. 41 sees. Running 550 yards .... Race, 270 yards Time of race .... * I liter = 0.0353 cu. ft. These figures give the amount of pure air actually exhaled and inhaled, but of course, in order that the products of respiration may be diluted sufficiently for the air in the confined space of a tunnel to be kept pure, a much larger quantity than this must be supplied. Assuming that 20 cubic feet is sufficient for a man at rest, and applying the ratio deduced from Draeger's table, it would appear that the following volumes of air should be supplied for ventilation if the same exercise were undertaken in a small room or in a tunnel : Ventilation Required When Exercising in a Restricted Space Sitting, 20 cubic feet per minute. Walking, 26 cubic feet per minute. Marching, 35 cubic feet per minute. Running, 70-90 cubic feet per minute. Rolling barrel, 85 cubic feet per minute. Race, 130 cubic feet per minute. Although some members of the tunnel crew, such as the shovelers, ordinarily work as hard as men running or roUing a barrel, the work of the drillers as a rule more closely approximates the exertions required in walking; so, taking everything into consideration, it would seem that 75 cubic feet per minute should be adequate provision for tunnel ventilation, as far as the requirements of human respiration are concerned. Assum- ing that an animal requires two to three times the air needed for a person, on this basis 150 to 200 cubic feet per minute VENTILATION 117 should be furnished each of them. At mine tunnels where any attempt is made for even moderate progress, from 8 to 15 men, and possibly two animals, are employed in or near the heading. Under these conditions 600 to 1,500 cubic feet of fresh air per minute would be required for purposes of respiration. It is true that some air is furnished by the exhaust from the drills, but their action is intermittent and the supply never adequate, so that much dependence cannot be placed upon it; on the whole, it is much better simply to ignore this possible source when deciding upon the capacity of ventilating machinery. Although the above capacity is sufficient for ordinary require- ments, a much greater, and indeed the maximum, demand for ventilation occurs immediately after blasting, when it is obvi- ously important to remove the gas and smoke quickly so that the men may resume work with the least loss of time. The volume to be removed depends largely upon the amount of explosive employed; for customary charges under normal con- ditions it would probably not vary greatly from 60,000 cubic feet, the average result of practical experience at tunnels where information bearing on this question was obtainable. It is true that ordinarily the air is seldom contaminated by the blast for more than 150 feet from the face, which in a heading of 70 square feet cross-section would have a volume of but 10,500 cubic feet, and it might appear that the removal of this amount of bad air would clear the tunnel. Such might be the case provided the smoke could be removed instantly, but this is of course not attainable in practice. The readiness with which gases become diffused must be taken into consideration, es- pecially in this case, since it is customary, immediately after blasting, to turn a jet of highly compressed air into the heading. Such a practice is necessary because, to avoid injury from fl>dng rock, the ventilating pipe rarely extends nearer the breast than 100 feet, so to remove the gases they must be forced out of the extreme end of the tunnel into the influence of the suction of the ventilating pipe. The result is that as a portion of the bad air is removed its place is occupied by fresh air, w^hich quickly becomes contaminated, and it is necessary, therefore, to remove 118 MODERN TUNNELING nearly six times the amount of foul air to clear the tunnel. In order to be considered good practice, under ordinary conditions this should be done in fifteen minutes, requiring an exhauster capable of removing 4,000 cubic feet per minute. This capacity, however, is necessary for only a few minutes after blasting. It is desirable therefore to have the fan or blower so arranged that ijt can exhaust for a short time at full load and then be run at a lower speed and supply the heading with the smaller volume needed for respiration. Such was the case at the Laramie-Poudre tunnel, where the exhauster was directly connected to a water-wheel and commonly removed approxi- mately 1,300 cubic feet running at 100 r. p. m. But immediately after blasting the blower was speeded up to 300 r. p. m. when it exhausted nearly 3,900 cubic feet per minute, clearing the heading usually in 15 to 20 minutes. At the Rawley tunnel an attempt was made to secure the same result by operating the blower intermittently at or near full load. Although the operation of the blower or fan at full load for one-third of the time supplies the heading with an equal amount of air as when running at one-third capacity all the time, different results are obtained in practice. The purity of the air is not maintained so nearly constant with the intermittent system, and since the starting and stopping of the blower are usually dependent upon some man, they are apt to be forgotten or neglected. This method of ventilating, therefore, cannot be commended. PRESSURE It is, of course, essential that the required amount of air be actually delivered to, or removed from, the heading; to do this, pressure is necessary in order to overcome the frictional resist- ance to the flow of air in the pipe. This pressure must be generated by the fan or blower and may be either positive, when forcing air in, or negative, when exhausting it; in either case the amount required depends upon the quantity of air passed and the size and length of pipe. Although the relations between these several factors are somewhat complicated, they VENTILATION 119 arc shown in the following formula advocated by George S. Hicks, Jr.: q = 44.72 14.7^) Ig Where q d P = quantity of air in cubic feet per minute. = diameter of pipe in inches. = absolute initial pressure in pounds per square inch. = length of pipe in feet. g = specific gravity of gas referred to air as unity. From which we obtain by transposing: / P - ^ 216.10 + fl - 14.7 2000 d^ Where p = P — i^.jjOr the required pressure in pounds pei square inch, ^ = I- It must be borne in mind that the formula is theoretical and does not take into consideration leakage, the extra friction due to elbows in the pipe, etc., but it is said to be based on good general practice for air and gas transmission and to give fairly satisfactory results. The following table, calculated from the formula, shows the pressure, in pounds per square inch, required to pass air through various sizes and lengths of pipe, assuming its quantity to be 4,000 cubic feet per minute (the value derived above as a suitable maximum capacity for a ventilating blower or fan). Loss OF Pressure, in Pounds per Square Inch, When Forcing 4,000 Cubic Feet of Air per Minute Through Various Lengths and Sizes of Ventilating Pipe Diameter of pipe, Length of Pipe in Feet in inches 1,000 2,000 3,000 4,000 5.000 6,000 8,000 10,000 12.000 14.000 6 8 10 12 14 16 18 20 20.2 6.75 2.52 1.06 0.50 0.26 0.14 0.085 11:8* 4.69 2.05 0.98 0.51 0.29 0.17 6*65 2.90 1-45 0.76 0.43 0.25 8-45 3-87 1 .90 1.02 0.58 0.34 10. 1 4.71 2.32 125 0.70 0.42 552 2.77 1.48 0.84 0.50 7 3 I I 06 60 95 II 67 8 4 2 I 63 40 40 38 83 9 5 2 I 87 16 84 64 99 590 3-27 1.89 115 120 MODERN TUNNELING If the pressure cannot be increased to correspond with the length of pipe, the volume of air delivered is diminished (the size of the pipe remaining the same) . This is illustrated in the following table in which a maximum pressure (P — 14.7) of one pound per square inch is assumed. Maximum Air Capacities in Cubic Feet per Minute of Pipes of Different Sizes and Lengths When the Initial Pressure Is One Pound per Square Inch Diameter Length of Pipe in Feet of pipe, in inches 1,000 2,000 3,000 4,000 5.000 6,000 8,000 10,000 12,000 14,000 6 8 10 12 14 16 18 20 685 1410 2465 3890 5720 7985 10,720 13,950 485 1000 1745 2750 4045 5645 7580 9865 '815 1425 2245 3300 4610 6190 8055 705 1235 1945 2860 3990 5360 6975 630 1 105 1740 2560 3570 4795 6240 575 1005 1590 2335 3260 4375 5695 870 1375 2020 2825 3790 4930 780 1230 1810 2525 3390 4410 710 1125 1650 2305 3095 4025 660 1040 1530 2135 2865 3730 The following table shows the calculated pressure required to overcome frictional resistance in passing a volume of air Pressure Required to Force Amount of Air Equivalent to Catalogue Rating of Ventilating Machine to Proposed Length of Tunnel Through Pipe Chosen Tunnel Carter Central Laramie-Poudre Los Angeles Aqueduct: Elizabeth Lake .... Little Lake Grape- Vine Lucania Marshall-Russel Mission Nisqually . ; Rawley Roosevelt Siwatch Snake Creek Strawberry Utah Metals Rated Diameter Stated length Pressure capacity. vent. of vent, pipe required. cu. ft. per pipe. when tunnel in lbs. per minute inches is completed sq. in. 1560 15 7600 0.41 5540 19 9500 1-93 3900 14K 9200 3-34 6350 18 13000 4.14 2500 12 3000* 1.23 2500 12 1500* 0.63 3120 183^ 12000 0.87 4160 123^ II 000 8.30 2500 10 13000 10.25 2400 14 5000 0.87 2500 I2>^ 6200 2.02 4800 16K 15700 4.38 1560 ID 5000 I 94 4650 16 14000 4.27 4000 14 19000 7-50 4880 12 II 800 1324 * This division contains a number of tunnels. The distance given is the maximum. VENTILATION 121 equal to the rated capacity of the ventilation machine, through pipes of the sizes adopted, to the headings of some of the tunnels visited in the field work. It will be observed in these examples that the pressures needed ordinarily range from i to 5 pounds, 2 pounds being roughly the average. At two of the tunnels in this list, in order to secure the extra pressure required to furnish sufficient ventila- tion, it was necessary to use a ''booster," as it is called; that is, to install a second machine some distance within the tunnel and by operating both together virtually doubling the pressure otherwise attainable. At the ^lission tunnel, the booster was situated near the 5,500-foot station. At the Strawberry, both machines had been placed in the tunnel at the time of examination, the first one at 4,000 feet and the second at 11,000 feet. Two other tunnels had not penetrated far enough at the time visited to require such additional equipment, but doubtless extra provision for obtaining pressure will become necessary with continued progress. SIZE OF PIPE The necessity for high pressures (and hence the use of boost- ers) may be ob\dated in large measure by the choice of ventilating pipe ha\ing diameters of sufficient size. The difiference between a 1 2 -inch and an 18-inch pipe often exerts a great influence on the ventilation of the heading, but even aside from added cost, indiscriminate enlargement is undesirable, every inch of space in the average tunnel being jealously required for other purposes. By transposing formula (i) we obtain ^ qH 2000 (P2_ i4.y2) which gives the necessary diameter of the pipe in terms of the other variables. The following table shows a number of solu- tions of this formula (assuming again that ^ = 4,000 cubic feet per minute to be passed) and from it may be found the proper size of pipe for use with various pressures and distances. 122 MODERN TUNNELING Diameter of Pipe in Inches, Required in Order to Deliver 4,000 Cubic Feet of Air per Minute with Different Initial Pressures and for Various Distances n Length of Pipe in Feet 1,000 2,000 3,000 4,000 5,000 6,000 8,000 10,000 12,000 14,000 I oz. 2I>< 24K 2 " i8>^ 21K 23 24K .... .... 3 " 17 i9>^ 21H 22)4 23^ 24>^ 4 " I6>4 i8>^ 20 21K 22X 23 24K 5 " I5>^ 17H 19K 20X 21% 22 23^ 24^ .... 6 " 15 17 i8>^ I9K 20K 2I>< 22>^ 23 K 24K 8 " 14 16M 17^ i8>^ I9X 20 21^ 22 J< 23 23^ 10 " 13K 15X 1634 17^ i8>^ I9X 20;< 21^ 22 22K 12 " 12^ 14^ 16 17 17K 18K i9>^ 20>^ 2X4 21^ I lb.. I2>4 14 15X 16 1634 I7H i8>^ I9J< 20 20K iy2 " IlM 13 14 I4K I5K 16 17 173X 18K 19 2 " lOK 12K 13K 14 I4K 15 16 l63/< I7K 1734 3 9'A iiK 12 12^ I3K I33/< 14K I5X I5K I6J< 4 9 lOi^ iiM 12 I2>^ 13 I33/< I4>^ 15 I5>^ 5 83/< 10 iok: IlK 11^ ^2% 13 I3>^ 14 14^ 6 8^ qK loX II II>^ Il3/< I2>^ 13 I3K 14 8 7K 9 9^ lOX io>i IlK 11^ 12X 12^ 13K COMPARISON OF FANS AND BLOWERS Within certain limits, the speed at which fans are operated determines the volume of air delivered and the pressure gen- erated, but these machines are incapable of producing pressures much greater than i^ pounds per square inch, and many of them are limited to 8, or even 5, ounces. Therefore, as the frictional resistance against which air is to be forced or exhausted becomes greater through increasing lengths of pipe, the pressure generated in the fan must be increased (by greater speed) to the maximum limit at which the fan may be operated, and after that is passed, the volume of air dehvered necessarily becomes diminished. The blower, on the other hand, is capable of much higher pressures, 8 pounds per square inch being easily attainable, while with some makes 15 pounds is possible, and in tunnel work where distances are, as a rule, great, the ability to deliver air against high resistance is an important consideration in favor of the blower. It operates also at a much lower speed when delivering the same volume of air against an equal pressure (i : 10 is con- VENTILATION 123 sidered a fair ratio), and this lessens the wear and tear upon belts and machinery. Because of its higher pressure, the blower makes it possible to choose a smaller diameter of pipe, a factor worthy of consideration, since not only the initial cost, but also the space occupied, must be taken into consideration. The first cost of the fan, on the other hand, is less than that of the blower, and to economize room and obviate the wear on the belt it may be connected directly to electric motors, the greater cost of low-speed motors tending to prevent this possibility with a blower. CONCLUSION In most cases a machine of the blower type, capable of high pressure, is better adapted for tunnel ventilation where resist- ances are apt to be great. For best results the ventilating pipe should be so arranged that the direction of the air current may be alternated at will, exhausting for a short time after shooting, and blowing for the remainder of the time. The blower should be adjusted to operate at two capacities: a lower one supplying 600 to 1,500 cubic feet per minute as determined by the number of men and animals, and a higher one capable of exhausting approximately 4,000 cubic feet per minute, which would make it possible, under ordinary conditions, for the men to resume work in the heading about fifteen minutes after shooting. The press- ure generated in the blower must be properly adjusted to the size of the pipe and the length of the tunnel in order that the determined volume of air shall be actually dehvered to or removed from the heading. The pipe chosen should be of such size that only a moderate pressure at the blower is required, at the same time due consideration being accorded such items as cost of pipe, and the space such pipe must occupy. Turbo-compressors, however, which are especially suited for high rotative speeds of electric motors, making it easily possible to connect the two directly without loss due to speed reduction, which are capable of maintaining a high efficiency (nearly double that of the centrifugal fan and fully equal to, if not greater than, that of the blower) even after long service, and which may 124 MODERN TUNNELING be designed by using a proper number of stages to deliver air against any given resistance, will deserve serious consideration, as soon as they are made in suitable sizes, as a possible choice for ventilation machiner}' . CHAPTER VII INCIDENTAL SURFACE EQUIPMENT In connection with the blacksmith and repair shops, mention should be made of the drill-sharpening machine and the com- pressed-air meter. The use of the former is quite common, being employed at a majority of the tunnels visited; but the latter, so far as could be learned, has been used only in one or two places, although there appears to be a field for its employ- ment in tunnel plants. DRILL-SHARPENING MACHINES Several types of drill-sharpening machines are used in the United States, each consisting essentially of a frame on which two cyhnders are mounted (one vertically, the other horizon- tally), each containing a reciprocating piston. Compressed air is employed as the motive power, the consumption ranging from 30 to 100 cubic feet per minute at 85 to 100 pounds pressure, according to figures given by the manufacturers. Some device is necessary to hold the drill steel firmly in place. The sharp- ening is accomplished by means of suitable dies or dolhes, which are either attached to or struck by the proper piston and mold the hot steel into the desired shape. The piston and die acting vertically is used for drawing out the corners of a broken or a very dull bit, or swaging out the grooves between the points, or insuring that the bit is of the required gauge, while the horizontal one sharpens the cutting edges. With a suitable set of dies, the machine may be used also for the construction of new bits from ordinary drill steel. The use of a sharpening machine results in some saving of labor cost, for but one operator is required, who need not even 125 126 MODERN TUNNELING be high-priced. Such a man can ordinarily turn out several times the work of a skilled blacksmith and helper sharpening bits by hand. One manufacturer claims that his machine, when handled by an expert, is capable of sharpening 250 drills per hour, but he states also that half that number, under normal conditions, is good work. With another type, the capacity is given as 60 to 100 sharpened drills per hour. The lowest of these figures is more than ample for the usual requirements of tunnel work since, according to figures obtained at tunnels visited, the number of drills ordinarily sharpened ranges from 100 to 200 per day, although in hard ground as many as 400 were used. The labor saved in the blacksmith shop is only a minor consideration, however, for the real superiority of the machine over hand-sharpening lies in its ability to turn out perfect bits. Since the progress in tunnel-driving is often largely determined by the time required to drill a round of holes, this important part of the work deserves careful attention. It has been demon- strated repeatedly by practical experience that on comparing the cutting qualities of a machine bit with one sharpened by hand there is a marked difference in favor of the former. This is due to the fact that the bits come from the machine true to gauge, thus greatly reducing the danger of binding or sticking in the hole ; there is, therefore, less delay in drilling and a smaller loss of time from this cause for the driller and helper (or perhaps the entire crew), and there is less likelihood of ''lost" holes. Then, too, the bits being correctly shaped and properly sharp- ened, they not only ''stand up" better and stay sharp longer, but they also drill faster, and it is not necessary for the drill crew to change steel so often, thus reducing another source of delay. The use of drill-sharpening machines at the ordinary tunnel plant is, therefore, strongly recommended not only for its saving of time and labor both in the blacksmith shop and in the heading, but also for its abihty to make bits whose superior drilling quahties will easily pay, because of additional pro- gress, a handsome return upon the money invested in the machine. INCroENTAL SURFACE EQUIPMENT 127 AIR METERS Air meters are of various types, depending upon differences in principle and design. In one of them the volume of air is measured by causing it to impinge consecutively upon a number of turbine wheels mounted on a common shaft which is con- nected with a registering device by a properly designed master gear. The machine is calibrated to read in cubic feet per minute of free air and is claimed by the manufacturer to give accurate measurements of air under varying pressures. A second type operates upon the principle that, with a uniform difference of pressure on both sides of an orifice and a constant initial pressure and temperature, the quantity of air passed is proportional to the size of the orifice. In this machine the difference in pressure on the two sides of the diaphragm is kept uniform by the constant weight of a taper plug which closes the orifice until the difference in pressure is sufficient to raise the plug and support it. The taper is so designed that the amount of air passed through the orifice is directly propor- tional to the rise of the valve, and this movement is multipHed and transmitted to a needle which records it upon a moving sheet of paper, thus affording a means of measuring the volume of air passed. A third type consists in a device for determining the pressure due to the velocity of the flow of air in a pipe (which is proportional to the amount of air passed if the temperature and initial pressure are constant) and transmitting that pressure to one arm of a U-tube filled with mercury. The tube is bal- anced on knife-edges, and since the pressure causes a flow of mercury to the other arm, the balance is disturbed and the tube is deflected, the amount of deflection being commensu- rable with the flow of air. This is transmitted by levers to a recording needle. In a fourth type, although only a proportional volume ranging from % oi i per cent, to 8 per cent, is actually measured, the recording device registers in terms of the fuU loo per cent, volume. Any of these meters may be used to determine the amount of compressed air delivered to a purchaser. Their most im- 128 MODERN TUNNELING portant use, as far as tunnel work is concerned, is in determining the amount of air used by rock drills. It is well known that all pneumatic rock drills show an increased air consumption (which is less in some than in others, to be sure, but appreciable in all) caused by leakage, etc., as the various parts become worn through use. This fact is quickly discovered in practice and a large number of actual tests bear out the statement that after six months' or a year's steady use of the ordinary rock drill, the amount of this loss will range from 20 to 40 per cent. This additional air is not only expensive to compress, but, what is of more importance, the efhciency of the drilHng machine is lowered at the same time, and the man behind it is unable to do as much effective work, thus entailing further loss. If the drill repair man has to guess at the air consumption, it is very diffi- cult for him, even though he is an expert mechanic, to send a drill from the repair shop back to the heading that will do as good work as when it was new. But if the shop is provided with some means of determining the air required by the drill, he is much better able to remedy the defects and make the proper repairs. This results in a saving of expensive power and increases the efficiency of the drill and the amount of work done by the driller. It is very desirable also to keep a record every time the drill leaves the repair shop, not only of the cost of repairs, but also of its present air consumption, in order that upon its next return a comparison may be made with the last record, as well as with the nominal air requirements. By such a course necessary repairs may be made, if the air consumption is excessive, that would perhaps have been unsuspected otherwise, while at the same time the manager may keep an accurate statement of drill repairs and inefficient drills may be weeded out. The following sample gives a rough outline of such a system :* DRILL RECORD Tool Piston drill Maker Size 2/4 inches Purchased 2/1 /lo Serial No. 123,456 Shop No. 12 Normal air consumption, 90 cu. ft. per min. at 75-80 lbs. * By courtesy of the Kxeelsior I- rill and Mfg. Co. INCIDENTAL SURFACE EQUIPMENT 129 Date Air Consumption Pressure Repairs 2/24/10 94 76 2 side rods 3/10/10 99 78 2 pawl springs I leather cup I chuck bolt I chuck key 5/10/10 128* 75 I air chest and valve* back to 96 2 piston rings * Excessive air consumption corrected by repairs indicated. CHAPTER VIII ROCK-DRILLING MACHINES TYPES As a rule, rock-drilling machines are classified primarily according to the motive power by which they are operated. The great majority of those used in tunnels are of the pneumatic type, but hydraulic and electric drills have been employed. For surface work, steam is sometimes substituted for compressed air by making a few minor alterations in pneumatic drills, and machines using gasoline power are also to be found on the market; but the difhculty with the former in disposing of ex- haust steam and with the latter the products of combustion, prevent any extensive use of these types underground. The following paragraphs describe some of the principal features of the various rock drills employed in tunnel work. Pneumatic Drills The pneumatic rock drill consists essentially of a cylinder containing a piston or a hammer which is reciprocated by the proper admission, application, and release of compressed air. In the piston type of air drill, a drill steel provided with cutting edges is alternately made to strike and recede from the rock by the movement of the piston to which the steel is firmly attached. In the hammer drill, the steel does not reciprocate, but is held loosely against the rock to which it merely transmits blows received from a moving hammer. (See Figure 28.) Piston drills are, almost without exception, mounted in a shell or cradle which may be attached to some rigid support while the drill is in operation, but which is easily removed when necessary; a screw thread is provided also, permitting the drill to be fed forward in the shell as the hole grows deeper. In some types of hammer 130 ROCK-DRILLING MACHINES 131 drills, especially those used for sloping and trimming, the shell is omitted and the drill either is held in the hand or is provided with a telescoping feed, operated automatically by compressed air. In either type, some device is re- quired to rotate the drill steel in order that the cut- ting edges of the bit may not strike repeatedly in exactly the same place. In cradle-mounted drills this is generally accomplished by a mechanism (consisting of rifie-bar, ratchet, and pawls) which is arranged to turn the piston or ham- mer, this in turn rotating the chuck holding the drill. Where the telescoping feed is employed it is necessary to rotate the entire machine by hand. Figure 29 shows a section through a piston pneumatic rock drill and gives a Hst of the princi- pal parts. Pneumatic drills are often differentiated by the method employed in con- troUing the admission of air to the cyHnders. This may be accom_plished by tappet, air-thrown, or aux- Fig- 28. Section through a hammer dril 132 MODERN TUNNELING iliary valves, or the air supply may be regulated directly by the movement of the piston or hammer itself. The action of the tappet valve is illustrated in Figure 30, which shows a section through a drill equipped with the same. As the piston in operation moves from the position shown in Fig. 29. Section through a piston rock drill. I, Cylinder; 2, Air chest; 3, Inlet port; 4, Exhaust port; 5, Reverse ports; 6, Valve; 7, Valve bushing; 8, Buffer; 9, Check nut; 10, Top head; II, Oil chamber; 12, Ratchet ring; 13, Rifle bar; 14, Ratchet; 15, Plug; 16, Feed nut; 17, Lock washer; 18, Check nut; 19, Washer; 20, Feed handle; 21, Yoke; 22, Feed screw; 23, Shell; 24, Trunnion; 25, Lower head; 26, Clamp bolt; 27, Bushing; 28, Gland; 29, Packing; 30, Piston; 31, Clamp bolt; 32, Chuck bushing; 33, Chuck button; 34, Piston rings; 35, Cylinder ports. the cut tovv^ard the lower end of the cylinder, the crank end of the tappet rises, while the other end drops into the depression of the piston, thus producing a sHght rotation around the tappet pin, which is sufficient to move the sHde valve. This admits live air against the lower end of the piston, at the same time connecting the upper end of the cylinder with the exhaust pipe. The piston, therefore, starts in the other direction, and a similar, but reverse, process takes place. The operation of the air-thrown valve is somewhat more compKcated than the tappet, but by referring to Figure 29, which shows a section of a drill equipped with the usual form of air-thrown valve, the action is shown to be as follows: The piston is indicated as just starting on the down stroke, the valve being so placed that live air is entering the top cylinder port (35) from the air inlet port (3) by way of the connecting passages indicated by dotted lines, while at the same time the ROCK-DRILLING MACHINES 133 front of the cylinder is connected with the exhaust (4) by the lower cylinder-port and its air-ways. The upper end of the ''spool'' of the valve is connected with the lower end of the cylinder — and hence with the exhaust — by the reverse port (5) (shown unshaded in the illustration). As soon as the piston in its travel uncovers the other reverse port (5) (shown by dotted lines), pres- sure from the upper end of the cylinder will be transmitted to the lower end of the spool and throw it against the upper end of the valve chest, and this will alternate the connection of the ports for live air and exhaust, thus revers- ing the piston. A similar process is then repeated on the up- stroke. In a recent modi- fication of the usual air-thrown valve the spool is replaced by a cyHndrical shaft carrying two flat wings, which some- FiG. 30. Section of a tappet valve drill. 134 MODERN TUNNELING what resemble those of a butterfly. The operation of this valve is illustrated somewhat diagrammatically in Figures 31, 32, and 2)2)' In Figure 31 the piston P is represented as about Supply Fig. 31. S-Supply SS2 Fig. 32. S -Supply Fig. 33. Figs. 31, 32, and 33. Action of butterfly valve. to Start on the forward stroke. The valve is thrown so that live air is permitted to enter through the supply ports S, S2, and SS2, while the spent air in the front end of the cylinder is exhausting through the ports ^E^i, Ei, and the exhaust E. As soon as the piston in its forward movement uncovers the exhaust port EE2, live air will pass through EE2 to E2, and its pressure on the valve at this point will balance its pressure on the opposite wing ROCK-DRILLING MACHINES of the valve facing port 52. The valve will then be in equihb- rium, but will be held stationary with the ports 5*2 and Ei open because of the hnpact of the air opposite S2. Near the end of the stroke, however, the piston closes the ex- haust port EEi, and in passing from EEi to Fi it compresses the air which is trap- ped in the clearance space at the end of the cyhnder. This cushion pressure, communicated through the cylinder ports SSi to Si, is sufhcient to throw the balanced valve to the position shown in Figure 33. Live air is then admitted, through Si and 6*51, the exhaust ports ££2 are opened, and the piston starts on the return stroke. One form of aux- iliary valve used on a well-known piston drill is described as a mechanism in which Fig. 34. Section through a tappet auxiliary valve drill. 136 MODERN TUNNELING the strains, shocks, and jars to which the tappet or rocker is subjected are transferred from the main valve, with its vital and d6licate functions, to a smaller auxiliary valve weighing only a few ounces, especially designed to withstand the service. This drill is illustrated in Figure 34. When the drill is in operation, one end or other of the auxiliary valve projects slightly into the cyHnder, and is thrown by the piston in its travel. The movement is perfectly free and very short — only enough to uncover a small port and release pressure from one end of the main valve, which is at once thrown by the resulting unbalanced pressure, opening wide the main port and admitting compressed air to the other end of the piston for Fig. 35. Section through a steel-ball auxiliary valve. the return stroke. The auxiliary valve is simply "sl trigger which releases the main valve." In another form of auxiliary valve, the main air-thrown spool is controlled by two auxiliary valves consisting of steel balls which are positively actuated by the movements of the piston. See Figure 35. In this figure the piston A is repre- sented as having just started on the down stroke. Compressed air is entering the upper end of the cylinder through the port G and the spent air in the lower end is escaping through the port H and the exhaust chamber /. At the end of the stroke the ball C will drop on its seat and the ball D will be raised, thus allowing the air in the end of the valve chest at F to exhaust past D through the port between the upper and lower balls. The un- ROCK-DRILLING MACHINES 137 balanced pressure thus produced throws the valve to the other end of the chest, which reverses the connections between the cylinder chambers and the inlet and exhaust ports. The piston therefore starts on the return stroke and a similar but reverse process takes place. The valveiess air-regulating mechanism, in which the move- ment of the piston itself covers and uncovers various ports, is employed almost exclusively on drills used for stoping only. Although rarely chosen for tunnel work, a brief description of this method of regulating air supply is warranted by its extensive Fig. 37. Figs. 36 and 37. Cross-sections through valveiess drill. use in its own field. The principle of operation is illustrated in Figures 36 and 37, which are two cross-sections through the cylinder of one make of valveiess drill. In Figure 36, air under pressure enters from the feed cyhnder through the port a and passes to the front of the piston, where it exerts pressure at all times. The piston is forced back until the port e (Figure 37) is uncovered, when compressed air passes through the port / and exerts pressure on the top of the piston. Since the area of this face is greater than the striking end, the piston starts forward. Live air is shut off when the port e is closed, but the piston is pressed forward by the expansion of the air until the exhaust port h is opened just as the blow is struck on the drill steel. 138 MODERN TUNNELING Hydraulic Drills The best known hydraulic rock drill is, perhaps, one of the rotary type developed for use in the Simplon tunnel, which consisted essentially of a hollow steel tube armed with teeth which were held firmly against the rock by hydraulic pressure while at the same time the tube was slowly revolved by a water- driven motor. Although, as far as could be ascertained, it has SECTION' A-A 1-1- Scale Inches 12 1 9 3 1 2 Feet 1 0.5 1M« Fig. 38. Rotary hydraulic rock drill. never been used for tunnel work in the United States, the intro- duction of the following description (see Figure 2>^), as given by Prelini,* we consider warranted by its historically interesting foreign achievements: ''This rotary motion is given by a twin-cylinder single-acting hydraulic motor (e), the two pistons, of 2^ inches stroke, acting re- * "Tunneling," page 103. ROCK-DRILLING MACHINES 139 ciprocally as valves. The cranks are fixed at an angle of 90° to each 'Other on the shaft, which carries a worm-gearing with a worm- wheel iq), mounted upon the shell (r) of the hollow ram {i), and this shell in turn engages the ram by a long feather, lea\ing it free to slide axially to or from the face of the rock. The average speed of the motor is 150 revolutions to 200 revolutions per minute, the maximum speed being 300 revolutions per minute. . . . The press- ure on the drill is exerted by a cyhnder and hollow ram (z), which revolves about the differential piston (5), which is fixed to the envel- ope holding the shell (r). This envelope is rigidly connected to the bedplate of the motor, and, by means of the vertical hinge and pin (/), is held by the clamp (T^ embracing the rack-bar. When water is admitted to the space in front of the differential piston the ram carrying the drilling-tool is thrust forward, and when admitted to the annular space behind the piston, the ram recedes, withdrawing the tool from the blast-hole. The drill proper is a hollow tube of tough steel 2^ inches in external diameter, armed with three or four sharp and hardened teeth, and makes from five to ten revolutions per minute, according to the nature of the rock. When the ram has reached the end of its stroke of 2 feet lyi inches, the tool is quickly withdrawn from the hole and unscrew^ed from the ram; an extension rod is then screwed into the tool and into the ram, and the boring is continued, additional lengths being added as the tool grinds forward; each change of tool or rod takes about 15 seconds to 25 seconds to perform. The extension rods are forged steel tubes, fitted with four-threaded screws, and having the same external diameter as the drill. They are made in standard lengths of 2 feet 8 inches, i foot 10 inches, and 11^ inches. The total weight of the drilling-machine is 264 pounds, and that of the rack-bar when full of water is 308 pounds. The ex- haust water from the two motor cylinders escapes through a tube in the center of the ram and along the bore of the extension rods and drill, thereby scouring away the debris and keeping the drill cool; any superfluous water finds an exit through a hose below the motors, and thence aw^ay dow^n the heading. The distributor, already men- tioned, supplies each boring-machine and the rack-bar with hydraulic pressure from the mains, with w^hich connection is effected by means of flexible or articulated pipe connections, allowing freedom in all directions. The area of the piston for advancing the tool is i5>^ square inches, which under a pressure of 1,470 pounds per square inch gives a pressure of over 10 tons on the tool, w^hile for withdrawing the tool 2^ tons is available." A recently invented percussion hydraulic drill is described 140 MODERN TUNNELING fully in the Engineer,^ from which Figures 39 and 40 and the fol- lowing brief abstract are taken: The drill consists essentially of a cylinder, in which is a piston C, free to move, while at the other end of the cyhnder is a flap valve D, which is kept open by a spring. The interior of the cylinder is in Bolts for attacliing. to drill post Fig. 39. Hydraulic percussion rock drill. communication with a "striking tube" F G, at the end F of which is an air vessel. When the valve H is opened, water flows through the apparatus, out past the valve D, into the waste pipe E. The rush of water past the valves causes the pressure on the under side to be less than the pressure on the upper side, where the velocity is less. . . . . . . When the velocity attains a certain value the difference of pressure is sufficient to close the valve, and the column of water in Air^essel A Striking Tube rpom.Mains p Fig. 40. Section through striking tube, hydraulic percussion rock drill. the striking tube is suddenly stopped. The kinetic energy of the water in the tube is communicated to the piston C, which is impelled forward with high velocity, and the drill which is at the end of it strikes a heavy blow on the stone or rock being bored. The pressure in the interior of the cylinder is diminished by the moving out of the piston C, . . . enough for the valve to open. Water then streams through the open valve. The piston is meanwhile being brought back to its original position by springs, but before * " New Hydraulic Rock-boring Y)t\\\" t\iQ Engineer (London), January 7, 1910, page 24; 2}4 cols, illustration. ROCK-DRILLING MACHINES 141 it is right back . . . the valve D closes, and the direction of motion is reversed by the hydraulic shock. The drill then strikes another blow as before. The actual apparatus is shown in section and plan in Figure 39, which is roughly to scale, the overall length being about 4 feet. The actual magnitude of the blow depends primarily upon (i) the weight of the striking column; (2) the velocity of the water when the valve closes; and (3) the weight of the chisel and boring bar. The velocity of the column is fixed by the velocity at the valve required to produce the necessary difference of pressure to close the valve, i.e., it is fixed by the stiffness of the spring controlling the valve. The rapidity of the blows is Hmited by the fact that after each blow the striking column is brought to rest, and it must be accel- erated to the requisite velocity before the valve will close. The rapidity of w^orking depends, therefore, upon the pressure which is urging the column forward, i.e., it depends on the pressure in the supply mains. The actual magnitude of the blow is said to be un- affected by the varying pressure in the mains, and to depend only on the weight of the striking column and the strength of the spring controUing the valve. The inventor claims that machines of the type described strike from twenty to thirty blows per second, while the maximum speed of percussion machines of existing t}q3es is from three to five strokes per second. One of these machines has recently undergone a series of tests at the Millbank Pumping Station of the London Hydraulic Power Company. The pressure used was 450 pounds per square inch. . . . The tests were carried out on a block of hard Portland stone. The diameter of the drill used was 2 H inches, and on an average progress was made in the stone at the rate of 10^ inches per minute. This is equivalent to the removal of 46 cubic inches of stone per minute. The drills stood up to the work so well that after holes aggregating about 25 feet in depth had been drilled, it was not necessary to do anything to the edge. A stream of water plays on the chisel the whole time, and serves the threefold purpose of keeping the chisel cool, of rinsing the bore-hole, and of allaying the dust. Electric Drills An electric rock drill consists primarily of an electric motor and a means of applying the power developed in it to the work of drilling rock. In some machines the motor is mounted directly upon the drill frame, but in others it is removed a short distance and connected to the drill by a flexible shaft, or some similar 142 MODERN TUNNELING device for transmitting power. Provision must also be made for preventing the shocks and jars developed by the impact of the drill steel upon the rock from being transmitted back to the motor, which is a machine incapable of operating for any length of time under such conditions. In many of the earlier models, springs or cushions of some elastic material such as rubber were used for this purpose. These devices failed to give satisfaction either because of inability to do the work required or because of excessive wear, breakage, and annoyance. In two or three of the early models, an ingenious attempt was made to avoid these troubles by taking advantage of the fact that if an electric cur- rent is passed through a spiral coil of wire, a suitably placed bar of soft iron will be drawn into it. By providing two such coils or solenoids and causing the current to flow through them alternately, an iron piston carrying a drill steel was made to reciprocate between them. In order to have the blow sufficiently smashing to be effective, however, a prohibitive weight of copper wire was needed for the solenoids. To-day practically all elec- tric drills use compressed air in some manner to cushion the reac- tion of the blow, — a medium possessing the very desirable characteristic of extreme elasticity and at the same time not affected by wear and tear. In one machine, however, a hammer is made to strike the end of the drill steel by centrifugal force, the rebound giving the necessary flexibihty. One of the successful electrically driven rock drills that has been on the market for over five years is illustrated in Figure 41. In this machine the drill piston is reciprocated by alternating pulsations of compressed air, created by a double-cylinder air compressor driven by a standard electric motor. Two short lengths of hose connect the air compressor to the drill, each running from one of the compressor cylinders to opposite ends of the drill cylinder. The air in the system, which acts as an unwearing cushion between the pulsator and the drill, is never exhausted, but is simply used over and over. The drill is very simple — merely a cylinder containing a piston and rotating device — and valves, chest, side rods, buffers, and springs are omitted, while the compressor has neither valves nor water ROCK-DRILLING MACHINES 143 jackets. The motor may be designed for either direct or alter- nating current as desired, and it is mounted with the compressor on a wheeled truck for easy handling. A second air-cushioned electric drill of the piston type, but Fig. 41. Electrically driven rock drill, shown partly in section. one in which the motor is mounted directly on the drill frame, is illustrated in Figure 42. In this drill the motor M, which can be readily detached from the rest of the machine whenever it is Fig. 42. Section through an air-cushioned piston electric drill. necessary to move the drill to a new set-up, etc., is connected by reducing gears to a crank shaft 5, which drives a connecting rod R. This is attached and gives a reciprocating motion to a cylinder C, which slides in suitable guides and contains a piston 144 MODERN TUNNELING P, provided with a chuck for holding a drill steel. As the cylinder moves forward, air is compressed in the chamber B behind the piston and makes the piston move forward, which causes the drill bit to strike the rock. During the return stroke of the cylinder, the compression of air in the other chamber F brings the piston back again with it. Rotation is secured by means of a standard spiral nut and ratchet. Details of the feed screw, the carriage, and other features are shown in the illustration. In an electrically driven air-cushioned rock drill of the hammer type (Figure 43), power is transmitted by suitable gears and cranks from the motor to a piston and causes it to recipro- cate in an air cylinder. The same cylinder contains at its other end a hammer, which, however, is in no manner directly connected with the. piston. As the latter starts on the down stroke it compresses the air in the space between it and the hammer, which is projected forward until it strikes the end of the drill steel. Just as it does so it releases the compressed air by un- covering an exhaust port controlled by a poppet valve. When the piston starts on the return stroke the exhaust valve closes and a partial vacuum is created which pulls the hammer toward the piston. The latter in its travel uncovers an inlet port, also poppet controlled, admitting new air, which destroys the vacuum. The momentum of the hammer would cause it to strike the piston, which again starts on the down stroke were it not for the compres- sion of this air entrapped by the closing of the poppet valve as soon as the vacuum is destroyed. The drill steel is rotated by the motor through a shaft, gearing, and a ratchet. Hollow steel is used through which water is forced to the cutting edge by a small pump supplied with the drill; but if water under pressure is already available, however, the pump may be disconnected. Another feature of this drill is the automatic chuck which is adapted for using steel as it comes in the bar, thus obviating the necessity of forging shanks. A fourth electric drill, also having an air-cushioned hammer, is illustrated in Figure 44. In this drill as the yoke A moves forward, the piston B compresses the air in the chamber C, forcing the cylindrical hammer D against the anvil block E, u 146 MODERN TUNNELING which transmits the blow to the drill steel at F. On the return stroke of the piston, the compression of air in the chamber G brings the hammer back in readiness for another blow. Hollow Fig. 44. Sectional view of an electrically operated air-cushioned hammer drill. steel is employed through which water is forced by a small pump whose plunger reciprocates with the drill piston. So far as could be learned, the only electric drill in service to-day which does not use an air cushion is the one illustrated Fig. 45. Electric revolving hammer drill with motor and part of casing removed. in Figure 45. In the illustration will be seen the two hammers which, although free to sHde in their sockets in the revolving disk, are thrown out by centrifugal force and strike the anvil ROCK-DRILLING MACHINES 147 block, which transmits the blows to the drill steel. The steel, which is held in a chuck rotated by a worm gear as indicated, is of the auger type, the spirals acting in the capacity of conveyor for removing broken rock from the hole. Gasoline Drills Since the difficulty of disposing of the waste products of com- bustion, which are not only hot and disagreeable but also contain gases injurious to the health of the workmen, makes the gasoHne drill hardly suitable for service underground, and since as far as could be learned they have never been used in tunnel work, their design and construction will not be discussed here. A description of one of these machines having two explosion cylinders may be found, however, in the Engineering and Mining Journal for November 21, 1908, page 1,008; in the Engineering News for November 26, 1908, page 575, and in the Mining and Scientific Press for December 19, 1908, page 852. Another drill, one of English manufacture, in which a cam, driven by a gasoline engine, trips a spring-actuated piston, was described in the Engineer (London) for September 36, 19 10, and in the Engineer- ing News for November 17, 19 10, page 538. MERITS OF EACH TYPE Pneumatic Drills The chief advantage of the pneumatic rock drill is its ability to withstand rough usage and still perform efficient service. The work of a rock drill is done necessarily under conditions that would quickly destroy almost any other type of machinery. It is subjected to constant and severe vibration when in oper- ation, for although it is usually held firmly and securely, still it cannot be mounted rigidly. Lubrication, when supplied at all, is often administered in large doses most irregularly, and it is impossible to prevent sand and grit from getting into the machine, thus adding greatly to the wear and tear. In many cases, men who operate it have no conception of its construction, and ignorantly subject it to shocks and strains for which it was 148 MODERN TUNNELING never designed, their first impulse when things go wrong being to seize a sledge-hammer and hit the machine in the most con- venient place. All drill runners, of course, do not belong to this type, but the description fits a much too large percentage of them. Everything considered, the rock drill must be capable of being operated under the most adverse conditions. This necessitates the elimination of all unsuccessful details, the rejection of com- pHcated parts that are not absolutely essential, the determination of the proper size and strength of those remaining, and the selection of materials having the proper stability and wearing qualities. This can be accomplished in any machine only after patient development and experiment, and it is but natural that the pneumatic drill, which has been undergoing such a process for more than fifty years, should be able better to cope with these conditions and to operate more steadily with fewer inter- ruptions and a lower cost for repairing broken or worn parts than any of the newer types. Among other advantages of the pneumatic drill may be mentioned the facts that it furnishes a certain amount of venti- lation, that it does away with the introduction underground of electricity at comparatively high voltages (which is oftentimes a source of danger), and that it does not require pipes strong enough to withstand the pressures needed for the rotary hydrauHc drill. The air drill, however, should not be relied upon for ventilation, because, in the first place, the supply of air is intermittent, being arrested while the drill is stopped for the purpose of changing steel or moving it into position for a new hole, etc. ; in the second place, the drills are not in oper- ation immediately after the blast — the time when ventilation is most needed— although it is true that the use of pneumatic drills makes it possible to direct a jet of compressed air into the heading at this time to assist in removing the smoke; and, finally, there are on record cases in which the exhaust from the drills not only did not deHver fresh air but even filled the heading with carbon dioxide and other dangerous gases produced by combustion of oil and grease in the receiver, resulting, in one instance at least, fatally for several men. Again, at tunnels ROCK-DRILLING MACHINES 149 using electric haulage the adoption of electric drills would simply add a Httle to a danger already present rather than intro- duce a new one, and in such cases the advantage of the air drill in this respect is not so important. The most important disadvantage of the pneumatic drill, on the other hand, is its well-known lack of power economy. Since, as stated by E. A. Rix,* 'Hhe tables set forth in the trades catalogues for the consumption of standard piston rock drills are fairly accurate," let us determine from them the powTr required for rock drills by using his estimate of 20 b. h. p. per 100 cubic feet of free air per minute. The lowest figure given for any type of rock drill used at the tunnels examined for this report is 65 cubic feet per minute at 100 pounds press- ure, while drills using as much as 150 and even 175 cubic feet wxre very numerous. On this basis, then, without making allowance for loss of power through friction in the pipes or leak- age in the machines when they become worn, pneumatic drills require the application of from 13 to 35 brake horse-power at the compressor during the time the machine is operating. Al- though the rotary hydrauHc drill employed in the Simplon tunnel required as much as 13 horse-power f (exactly the min- imum figure just deduced for air drills) it is by comparing the power used in air drills wdth even the maximum of 6 horse-power for electric drills, many of which run on less than 2, however, that the large dift'erence in power consumption is revealed. Comparing the different t\^es of pneumatic drills used in tunneling, the piston machine has somewhat the advantage over the hammer type as regards reliabihty and as regards effi- ciency in drilling holes vertically or nearly vertically dow^nward. This rehabiHty may be attributed without doubt to its simpler construction. It does not contain any mechanism for intro- ducing a w^ater spray through a hollow drill steel, it is not troubled by crystallization of metal parts from the repeated * Address before the Alining Association, University of California, Feb- ruary 19, 1908. t Comstock, Chas. W. : "Great Tunnels of the World." Proc. Colo. Sci. Society., Vol. VIII., p. 363. 150 MODERN TUNNELING shocks of rapid blows, and it has a much greater range of feed. This last item is a feature of importance when the machine is handled by an inexperienced operator, giving as it does greater latitude before the piston begins to strike the front head. These considerations make the piston drill more nearly fool-proof, and hence better adapted to use by ordinary drill runners — especially those in the Eastern States, who, as a rule, are neither as intelHgent nor as careful as those in the West. Complexity of construction should not be confused, however, with the num- ber of parts; for if this were taken as the standard, and every screw, bolt, or nut counted separately, it could be shown that the hammer drill is the simpler machine. The greater efficiency in drilling holes which point downward was clearly brought out in the recent extensive drill competition in the Transvaal, according to the committee conducting the test, who reported that one of the main reasons for the better showing made by the piston drills underground was the fact that practically all of the holes drilled there were pointed down- ward. This is substantiated in several instances at tunnels in this country in which the excavation is accomplished by the heading and bench method; in such cases the piston drill is reported to have given better satisfaction in drilling the vertical holes required for the removal of the bench. The principal advantages of the hammer drill, of the type used in tunneling, are a somewhat lower air consumption and a greater speed in drilling holes that are horizontal or nearly so, and especially those pointing slightly upward, such as are necessary under the ordinary methods in driving tunnel headings. In hammer drills the air consumption, and hence the amount of power required, varies from 65 to 100 cubic feet per minute at 100 pounds pressure (catalogue rating at sea level) as compared with 125 to 175 cubic feet for piston drills. The rate of drilling is of course largely dependent upon the character of rock penetrated, but by observation of the table below (in which it will be seen that piston drills, even in shale and sandstone, rarely drilled over 10 feet per hour, while the hammer drills in granite and other hard rock rarely fell below that figure, 15 and even 20 feet ROCK-DRILLING MACHINES 151 E .S- a a < c . .2 > " **- o rt o o a; a 2" - rO 2 E 2 > w > "O rt g «3 ■M J3 >, a> o oj -o D OS u - JS O +j rt j= C^ o < ■'^ "Sy W S u ji <^ 00 O O C< O 'O lO -t O fO o o o ui " 1 1 1 00 « >- ri 1 fO ^ IR^ 00 00 c» lO o OO OC CjiOOOrO MM 1-1 O) MHH_HHhH0O 00 lO 00 O 00 lO vO «s ?^ a c -u o "rtld g rt g _ 8*S O 03 !5 2 2 2^ - S -M -M CJ -M O o o 2^ 2 2.2 c ^ 3 S ccEccES p oopoopp a cj a c £ c £ , O! ill 1.1 2i^ 3 ^ o o c ^es of valve mechanism for air drills, the tappet valve, which was one of the pioneers in the field, possesses advantages which still keep it in demand for use on piston drills intended for certain kinds of work. Since it is unaffected by condensed moisture, which greatly interferes with the action of some other types, it is especially adapted for use with steam or with air containing a large amount of water vapor. Its distinctive advantage, however, is that its movement is positive; if the piston makes a stroke the valve must be thrown, hence there is no uncertainty in the action of the drill, no ''fluttering." The tappet drill is at a disadvantage when working in ground that will not permit of the use of a full stroke, because it is necessary for the piston to travel far enough to throw the valve, and hence too short a stroke is not possible. Then, too, as it is impossible to prevent some air being trapped in front of the piston and compressed after the valve is thrown, it strikes a cushioned blow. This is not always a disadvantage; in elastic and "springy" rock an uncushioned blow will not give the best cutting eft'ect, while in sticky material compression assists the piston in starting on the return stroke. The tappet is subject to strains and wear which necessitate specially hardened material, not only in the tappet itself but in the bearing surfaces of the piston. Under conditions that require a snappy, vicious blow with high air pressure, the ordinary air-thrown valve gives the best results. This feature makes it particularly applicable to hammer drills in which, because of the small size and weight of the ham- 156 MODERN TUNNELING mer, it is essential that there shall be no cushioning of the blow, and it is customarily employed on such of these machines as are not of the valveless type. When used with piston drills, the air- thrown valve permits a variable stroke; it renders possible at will a change in length of piston travel and force of blow. The short stroke and light blow possible with this type of drill make it easy to start a hole or to drill through seamy rock. After the hole is under way, or if the rock is soKd, a full stroke is used to get the best efficiency from the machine. The air- thrown type of valve is not positive in its action, however, and is apt to be somewhat sluggish with air or steam containing much water. It is claimed for the butterfly type that it avoids this difficulty, as well as most of the troubles caused by freezing, and that it has a positive and at the same time a flexible action which permits of much higher speed than other valves. The auxiliary valve is designed to combine the advantages of the tappet and the air-thrown valves while avoiding their defects. The hghtness of the tappet auxihary is said to prevent the injury or retardation of the piston and also to obviate the rapid wear of rings, piston, and cylinders caused by crowding against the opposite cylinder wall due to an unbalanced tappet not readily moved. A drill equipped with this type of valve has a wide variation of stroke and delivers an uncushioned blow. The main advantage of the steel ball auxiliary valve is the great resistance to wear and the cheapness of replacing the wearing parts. It is claimed for this valve that it assures a positive action of the drill without sticking or fluttering, and yet possesses the necessary flexibility. The valveless method of regulating admission and exhaust has the advantage of simplicity and hghter weight due to the eHmination of the valve and valve chest. It also uses air ex- pansively, and this should result in economy of power. It strikes a cushioned blow, however, thus reducing the drilling power where the rock is hard and tough; but for medium rocks and especially with high air pressure the difference is said to be less pronounced because the lighter and more rapid blows chip rather than pulverize the rock and enable the drill to penetrate I ROCK-DRILLING MACHINES 157 readily. One real disadvantage is the fact that as the cylinder becomes worn there is a leakage of air past the piston, thus increasing the air consumption and interfering with the accurate working of the drill. Hydraulic Drills Among the advantages of the rotary hydraulic drill used at the Simplon tunnel should be mentioned the fact that the power was delivered to the cutting edge without the shocks, jars, and strains due to percussion, thus eliminating one source of wear and tear. The machine also utilized a very high percentage of the power stored in the motive fluid, its efficiency being given by one authority as 70 per cent. Again, by passing a portion of the waste water down the boring tube, chips and debris were promptly removed from the cutting edge, thus insuring the maximum boring power. On the other hand, the pressure required for operating this drill was enor.mous, ranging from 450 to 1,200 pounds per square inch according to one writer, and 1,470 pounds according to another. In any case the piping necessary to transmit the water under such high pressures must have been most expensive to install and main- tain. The drill also required extremely heavy and rigid mount- ings to withstand the back pressure; these made it cumbersome and hard to move so that it could not be easily placed for a new hole. The percussion type of hydraulic rock drill cannot as yet be said to have been demonstrated to be a practical success. It is an interesting possibility, however; because, like the hydraulic ram, it utilizes the shock that occurs in pipes at every stoppage of ,a moving column of water. Electric Drills Among the advantages claimed for the pulsator type of electric drill are saving of power, rapid drilhng speed, simpler construction, and less trouble with fitchered drills. The motors which are used to operate the pulsator require, according to the size of drill, from 3 to 5 horse-power — a very small amount when 158 MODERN TUNNELING compared with the necessities of the ordinary pneumatic drill. Although it is true that the cost of power used by a drill is not the only item which determines its efficiency, such a marked differ- ence in power consumption must necessarily exert a great influence. This fact holds especially in the case in hand, since it is claimed and apparently well substantiated by actual results that this machine is fully up to the drilling speed of any corre- sponding standard air rock drill and has practically the same cost for wages and fixed charges. The pulsator type also eliminates many parts, such as valves, springs, side rods, etc., which are sources of trouble and unreKability in other rock drills. It is able, moreover, to strike a very heavy blow because the pressure of air back of the piston is greatest just at the time of impact; and should the drill steel become caught in the hole from any cause the machine does not cease running, as is the case with air drills, but the pulsator continues to exert several hun- dred alternate pulls and pushes on the drill steel per minute; these in most instances are sufficient to loosen the drill at once, consequently saving considerable time and trouble. On the other hand, the combined drill and pulsator are cumbersome and occupy a large space, every inch of which is precious in the tunnel heading — a disadvantage that increases directly with the number of drills needed for the work. For tunnel work it is necessary either to place the truck and pulsator upon the muck pile — a feat consuming extra time and energy and a position where it is subject to damage and breakage if the muck is being removed simultaneously with the drilling — or one must wait until the tunnel is cleared of debris before starting to drill, a procedure which is prohibitive if speed in driving is required. But under circumstances where there is no particu- lar haste or in mining work where drilUng and mucking are alternated, this disadvantage is not so serious. The piston electric drill described on page 143 does away with the need of a pulsator, truck, and connecting hose, thus making a compact machine and one more comparable with an air drill. It is, however, quite heavy (weighing 490 pounds with the motor attached and 350 pounds without it, and is somewhat ROCK-DRILLING MACHINES 159 difficult to handle and move in a small heading. It has a marked advantage over air drills in power economy, operating as it does on 4 horse-power, and actual results show that its drilling speed is fully up to that of standard piston pneumatic drills. At the Elmsford tunnel of the Catskill Aqueduct these drills are reported to have attained a speed of loo feet in six to eight hours when driUing in a comparatively soft mica schist, but in the harder Fordham gneiss of the city tunnel the rate was but 60 feet per shift (eight hours) . This drill is still in the process of development, in which it is necessary to correct the small defects that always appear in any newly designed machine when put to actual use, but the results attained with it in one portion of the city tunnel, Catskill Aqueduct, were very encouraging. One of the machines is reported to have operated there for more than five weeks, drilKng over 4,000 feet of holes with none but minor repairs, such as pawl springs, etc. The weight of the air-cushioned hammer drill and motor described on page 144 is about 150 pounds less than that of an electric piston drill and motor. With the motor removed, although it weighs more than a pneumatic hammer drill, it is but Kttle heavier than a piston air drill of corresponding capacity. Its power consumption is rated at 2}^ horse-power and in the tests on the Catskill Aqueduct 6 to 8 feet per hour was the aver- age drilling speed attained in ordinary work, including delays. This speed will undoubtedly be increased as the delays from breakdowns become less frequent. The drill was still being tried out and in the process of being perfected at the time of examination, so no data could be obtained as to its reliability. The other air-cushioned hammer drill (see page 144) has been employed in several mines in Colorado, where, according to the testimonials, it is performing creditable service. The average power consumption of the rotary hammer drill (see page 146) is about i kilowatt per hour (iK horse- power). They were employed on the Elmsford contract of the Catskill Aqueduct and were reported as particularly efficient in comparatively soft rock, drilHng at times as high as 100 feet per machine in an eight-hour shift. 160 MODERN TUNNELING CHOICE OF DRILL The factors to be considered in the selection of a rock drill for tunnel work are, on the one hand, the cost of power, of at- tendance, of maintenance and fixed charges, and, on the other, the rate of drilHng, the best drill being the one which combines all these factors in such a way as to develop the greatest drilHng speed for the least cost. The power cost should include not only the actual power at the tunnel plant (with its charge for labor, fuel, interest, and depreciation), but all losses in genera- tion, in transmission, and utilization in the drill. The wages of the drill-runners and all helpers required are just as much an item of operating cost as the charge for power. The cost for main- tenance includes the cost of repair parts for the drill and the charge for the time of the machinist, together with the cost of sharpening drill steel. The fixed charges should include interest and depreciation on the cost of the drills and a proportion of the administrative expenses. The rate of drilling, on the other hand, should not be based upon the speed of penetration while the drill is actually hitting the rock, but should include all delays caused by the drill, such as loss of time in preparing the set-up, in shifting position to new holes, in changing drill steels, and any other interruptions properly chargeable against the machine. Applying these specifications to the various rock-drilling machines, the hammer pneumatic drill is apparently the one best adapted for use under ordinary conditions in driving mine adits and tunnels. To be sure, its power consumption is more than that for electric drills, but it is about equal to the hydraulic and is less than the piston air drill. In the matter of attendance it has somewhat the advantage. Most of the piston air and the electric types usually require at least two men to operate each drill — a drill-runner and a helper — and the hydraulic machine requires five men.* With the hammer drill a runner is necessary, of course, but one helper often is able to attend to two drills * Prelini, "Tunneling," p. 105. ROCK-DRILLING MACHINES 161 or two helpers to three machines. We have just seen that there is practically no difference between the piston and hammer air drills as to repair cost. The multipKcity of parts in the rotary hydraulic machine, however, is said to have been a source of much trouble in this respect. Theoretically the hammer drills do not dull the steel so rapidly, and hence should have an ad- vantage in this respect. Practically this is not an important difference because under ordinary conditions the blacksmith is rarely overtaxed, and hence the extra labor of sharpening a few bits more or less is not noticeable on the cost report. The fixed charges are such a small portion of the total cost of drilling that any discrepancy in them is rarely, if ever, large enough actually to decide the question. The rate of drilling is really the greatest factor in favor of the hammer type ordinarily used in tunnels. Not only does it penetrate faster when ac- tually drilling, but, since its reciprocating parts are lighter and its vibration less than that of a piston machine, it can be employed with a lighter set-up, with a saving of time. Then, too, its ability to start a hole at any desired point and to drill rapidly holes that point upward enables it to be used ad- vantageously on a horizontal bar with a saving of the one-half to one and one-half hours which are required to remove the debris before setting up the vertical column used almost without exception in tunnel headings for piston air drills. The hammer drill saves not only time in changing drill steels but energy as well, as any one who has wrestled with the ordinary piston chuck can testify. For large tunnels excavated by the heading and bench method and in which a large number of holes are drilled down- ward, or perhaps at other places where, because of acidity in the mine water or some other reason, the water feature of the hammer drill would be unsatisfactory, or for other work than tunneling, the piston pneumatic drill would doubtless give equally if not more satisfactory results. Or if speed is not especially required and the drilling and mucking shifts can be alternated, the pulsator electric drill with its large power economy might prove the most efficient. And again, if the self-contained 162 MODERN TUNNELING electric drills continue to be improved as they have been recently, their greater economy of power will without doubt soon out- weigh their lower driUing speed and present higher maintenance charges, especially at such places where electricity is readily available. On this account their development should be closely watched. CHAPTER IX HAULAGE TUNNEL CARS Most students of tunneling methods concede that an essen- tial, and possibly the chief, feature of the problem is the rapid removal of debris produced in blasting; but it is commonly not so well recognized that the speed with which this may be ac- comphshed is greatly influenced by the size of the tunnel-car. Large cars, even when empty, are heavy and cumbersome, but when full of rock they can be handled only with the greatest difficulty. To remove such a car from the heading and replace it with an empty one requires either several extra men to assist in the work or a horse or mule must be provided for the purpose. In the first instance men must be called upon who might other- wise be making arrangements for the rapid loading of the next car or doing any of the many things that make for speed and economy; while in the second, omitting altogether from consider- ation the cost and maintenance of the mule, delays and loss of time cannot be prevented. In addition to being unwieldy, large cars occupy a greater proportion of the actual space in the heading, constricted enough at best, thus preventing the shovel- ers from working to the best advantage ; the added height involves a waste of energy because each shovelful of rock must be lifted a greater distance, making it impossible for the men to handle sufficient material in a given time. With large cars it is neces- sary to maintain a switch or siding near the end of the tunnel in order to permit the empty cars to pass the loaded ones, and time and labor must be expended frequently in relocating the switch nearer the heading to keep pace with the tunnel advance. The smaller car, on the other hand, when empty can be tipped off to one side out of the way and replaced easily when needed, thus giving a clear track for a loaded car and obviating the 163 164 MODERN TUNNELING necessity for a switch. In case of derailment, an occurrence by no means rare in practice because of the poor condition of most tunnel tracks, the large car, even when empty, is harder to replace, and when full it is sometimes necessary to unload all the material in order to get the car back on the track. It is true that a larger number of the smaller cars, each of which occasions some delay in its arrival and departure, are necessary to remove n Fig. 46. Elevation of tunnel car used in the east end of the Gunnison tunnel. the same amount of debris, but the authors are of the opinion, based upon a study of actual conditions at a large number of tunnels, that with proper organization greater progress is at- tainable by using smaller cars, the size preferred being from 15 to 25 cubic feet capacity. The tendency at many American tunnels is toward the use of cars much larger than this, especially where electric haulage is employed; but the use of large cars, when analyzed, has been shown to be a handicap rather than an advantage even in those tunnels equipped with them where creditable progress has been made. In design, the cars at a majority of the tunnels visited follow the standard mining types with tilting bodies, but at a few of them other types were employed to meet special condi- tions. A car with a side-dumping, tilting-box body was used in HAULAGE 165 the west end of the Gunnison tunnel. End-dumping cars are similar to this except that the hinge is transverse instead of lon- gitudinal and the door is situated at the end instead of the side. The car used at the Laramie-Poudre tunnel, which is illustrated in Figures 48, 49, and 50, was of the turn-table type, which per- mitted dumping from both sides of the track as well as between the rails. As the system of car handling in the headings at this tunnel necessitated throwing all of the cars over on their sides once (and nine-tenths of them twice) on each trip, the connec- tions between the trucks and bodies of the cars were carefully planned and made unusually strong. The turn-tables were fitted with two concentric rings (Figures 49 and 50), and the locking mechanism for securing the bodies to the trucks was so designed ^' ^1 ..'■•<./" 1. • ! 1 •1 i. •1" . • .r : s f 1 < — 2'0" Fig. 47. End view of tunnel car. that when the releasing lever was fastened in place the cars were as rigid as if the bodies were riveted to the axles. A car of the rocker type (see Figure 51) was used with very satisfactory results in the tunnels of the Los Angeles Aqueduct. At the Nisqually tunnel a similar car, but one with a sHghtly different locking Fig. 48. Elevation of tunnel car used in Laramie-Poudre tunnel. t^ 18 Track gage >H Fig. 49. End \'iew of tunnel car. .Mr- :_4fh:J6"i'inTf'T ' I fe:^i^rrEi^ i i'i\V^. \\ ' III nrnj 1 1 1 ,mi m KO © Fig. 50. Plan of tunnel car. Compression-spring ^—^ drawhead cast steel '^ p i — IL. jr - 1 1 ] 1 1 ^ 1 E l< — ^1 ■^^— 1 - 1 =^ ||Kp^o|o 0^] -^ , u L cd o u 01 Si 03 ^ II 3 G TJ 3 T) O ^ i_ TJ o ?^ p u 3 bfl a a o Qc75 ^ o CJ c; c; 03 (1) flj Cl) 3 o 3 o 3 a; r c 03 U U U U U ^^ O O 03 Si ^wSu^^uj+ "^ ^ Ti-OO C4 rfri-Td-POnoOi-. -wrDiOi-iOO 3 S O 03 a E 3 13 C E S E-S 3 3 3 iS "VV? c ^^ C 3 c/^ Lo W H i- ^ +j 3 '^3 ii ^ a a E • 3 c V a, ^2 E E 3 3 aaag g E E E - •> — '. H ~ (11 o a a a E E E :2 a :2 yyy o c c c face-- fa--- 3 3 3-^ -Si a 3-^^^aaa -o-u-u-Q^ E -uxjxijo E E E ,' ,'..'. rt o3 -( ,'. 03 o3 o3 3 -3 -1 03 rt cti _ _ TO CO "3 O O O Y Ytd - . OOOl-.l-,aJXCJt- O O O 3 3^3 O O 3 3 3 i^ C"W O '-' W t: t oj-ujJ X E E 3 3 i i >- ^ T-^ Js X ^ Ji it: t: 3 03 fflU 3 =2 o en OS u — 03 =! O . 03 O—. a en' O 5 t« en -a 03 3 < o3ir-£ en hj -^ o V-^ ao3 ■liaC4-.'TDC§^rten^'-"-"^a32w^ CT^ F J5 rt -^ ^ C'-^u-T---='03^^i-3en oi3en^Sn^>iOtifrtjC >^ OJ 170 MODERN TUNNELING (see Figures 46 and 47, pages 164 and 165) a simple open box car with the body bolted directly to the truck was employed, and similar cars are now in use in the Strawberry and Newhouse tunnels. Although this car is ideal from the viewpoint of sim- plicity, it requires special equipment for dumping because the entire car must be turned completely over. The table on page 169 contains suggestive data concerning the cars used in tunnels and adits in the United States. LOADING MACHINES Many attempts have been made to utilize machinery for loading tunnel cars. In several of the larger tunnels intended for railway purposes, power shovels similar to those used in grad- ing or in open-cut mining have been very successfully used in Fig. 54. "Mucking machine" at the Hummingbird tunnel, Burke, Idaho. . removing the broken rock of the bench after blasting. In such cases the ordinary steam shovel is generally employed, making a few minor alterations so that it can be operated by compressed HAULAGE 171 air. Power shovels operated by compressed air are also employed in some of the mines in the JopHn, Missouri, district. The ''mucking machine" illustrated in Figure 54 was used successfully during the excavation of the Hummingbird tunnel, at Burke, Idaho. Its principal feature is an oscillating trough or shovel armed with teeth and driven by a compressed-air piston in such a manner that the forward stroke is appreciably faster, than the return. When in operation the teeth rest upon a steel plate under the muck pile, and as the shovel is fed forward the broken rock is forced by the jerky motion backward along the trough and discharged upon a belt conveyer which dehvers it to an ordinary mine car at the rear. The entire machine is mounted upon a wheeled truck or framework and is fed forward by a second compressed-air piston connected with a cross-bar which can be jacked against the sides of the tunnel. It is essential that the area of this piston be smaller than the one which drives the shovel; for then, if the latter encounters a boulder or other obstruction too solid for it to dislodge, the entire macliine can move forward and back with the stroke of the larger piston. By this means the machine is not only prevented from injury before the obstruction can be removed, but in many cases it will work the boulder aside without any assistance. One man is required to operate the machine, and two more are needed to tram the car to and from the end of the conveyer and to shovel the rock out of the corners of the tunnel into the trough, for the machine does not swing from side to side, but merely cuts a swath down the center of the tunnel, and hence leaves a certain amount of material piled on each side of it. The machine is reported to have reduced the time re- quired to clean the tunnel from 6 to 2^ hours and to have made it possible to increase the speed of driving quite materially. The shovehng machine illustrated in Figure 55 is very ingenious and closely simulates the actions of a man shoveling. At the front is a scoop or shovel, armed with teeth, which is pushed under the broken rock and raised by the action of a chain-driven crank, so that the material is dumped into a hopper just back of the shovel. The hopper in turn travels a short 172 MODERN TUNNELING distance, tilts up, and dumps the rock on a belt conveyer which deHvers it to cars at the rear. The machine was employed ad- vantageously during the excavation of a portion of the Catskill Aqueduct directly under New York City. In this work six men were employed with the machine; one to operate it, three Fig. 55. Shoveling machine. to pick down the muck pile in front, and two to handle cars in the rear, as compared with the usual crew of fourteen men when mucking by hand. The power consumption was 25 to 30 kilo- watts per shift. The machine would pick up a rock that ordinarily would take three men to put over the side of a car 30 inches high and a car holding 35 cubic feet could be loaded in A power loader of a somewhat different type was introduced in the excavation of the bench at the Yonkers Siphon. It consisted of a chain-and-bucket conveyer, similar to that used in mill elevators and on some gold dredges, which delivered the material to a hopper, whence it was carried to the tunnel car by a fiat endless belt. Owing to the hardness of the rock and the prevalence of huge boulders, weighing sometimes over a ton and necessitating frequent stops for repairs, this machine was unable to compete satisfactorily with hand loading underground. When operating on the surface, however, loading rock for use in concrete con- struction it is said to have given excellent satisfaction. The HAULAGE 173 material was taken from the dump pile produced in excavating the heading of the tunnel in which the rock was broken more uniformly into smaller fragments than the material produced in blasting the bench. It should be mentioned, however, that the size of this machine precludes its use without considerable modification in a small tunnel or heading. MOTIVE POWER In practically all tunnels of any length in the United States, either animals or electric motors have been or are employed to haul the tunnel cars. In Europe, notably at the Simplon and Loetschburg tunnels, compressed-air locomotives were used successfully. But although those machines are employed to some extent in this country in mining and industrial work, they have failed to give satisfaction at tunnels where they have been tried, chiefly because of the cost of high-pressure air, the maintenance of charging stations, the time lost in charging, etc. Many mines also are equipped with cable haulage; but because of the constantly increasing length of haul as the heading advances, the use of this system in tunnel work requires such frequent delays and loss of time in extending the cable system that it is hardly suited for tunnel practice. Gasoline locomotives, on the other hand, which have recently proved most successful for coal mining, are in most particulars especially well adapted for tunnel work and deserve equal consideration with animals and electric motors as a means of tunnel haulage. The principal advantage of animal haulage is the smaller cost of installation; what is more, it requires no special intelh- gence on the part of the driver, and the ability of the animals to step across the track at the tunnel headings obviates the necessity of a switch. On the other hand, the costs of main- tenance and operation for animal haulage not only are high, but these factors go steadily on whether the animal is working or not and are influenced but slightly if at all by the amount of tonnage handled. For these reasons animals are not economi- cal for use in long tunnels because the saving in installation expense is soon destroyed by the increased operating costs. 174 MODERN TUNNELING Then, too, the odors arising from the track are offensive and disagreeable when animals are employed and their respiration vitiates the underground atmosphere, necessitating more ample ventilation. As far as efficiency is concerned, there is little if any difference between horses and mules, although the latter are considered by some to be the sturdier animals. Mules, however, are better fitted for work in low tunnels because they are usually somewhat smaller than horses and, being less nervous, do not throw their heads violently up and back when anything touches their ears. Electric mine locomotives may be divided into two classes: those operated from a trolley system and those obtaining their electrical current from a storage battery. The former are so familiar as hardly to require description. They generally consist of two motors, ruggedly constructed to withstand rough usage and protected from dust and moisture, mounted upon a cast-iron or structural steel frame which also carries the trolley, controller, rheostat, and other accessories. The sides of the frame may be placed either inside or outside of the wheels. In the latter type more space is available for the motors and other equipment and the various parts of the machine are more readily accessible. The inside type, on the other hand, has a smaller over-all width and is therefore more suitable for narrow tunnels. The storage battery locomotive is similar in most respects to the trolley machine, except that provision must be m.ade for carrying the necessary batteries. In most cases the batteries are carried directly upon the motor itself, but the locomotive installed at the Central tunnel is somewhat unique in that the batteries arc- placed upon a separate battery car or tender. When the machine is handling cars in this tunnel it obtains its current from the battery; upon reaching the tunnel mouth, the tender is left on a side track, w^here it is accessible for recharging, and a trolley, with which the locomotive is also equipped, is employed for switching. Electric locomotives are compact and simple in construction and do not emit smoke, gas, or disagreeable odors. They are more rapid and are capable of hauHng a much greater load than HAULAGE 175 either a horse or a mule, while the cost of . the power used is not nearly so great as the cost of forage. But, on the other hand, they require the installation of extra machinery in the power plant, an expensive trolley- wire or a troublesome storage battery, and the road-bed and track must not only be heavier in con- struction, but usually the rails must be bonded to make them good electrical conductors. The disadvantage of the cost of the extra electrical machinery is of course partly offset by the fact that it can be utilized also to operate the ventilating machin- ery and to furnish illumination for the tunnel. The use of trolley wires in the restricted tunnel space, however, introduces the grave danger of serious and perhaps fatal injury to persons accidentally or ignorantly coming in contact with them. GasoHne locomotives consist essentially of a frame, as a rule of cast-iron, upon which are mounted the gasohne engine (usually Fig. 56. Gasoline mine locomoti 4-cylinder), the necessary transmission system containing gears and clutches, together with the carbureter, magneto, cooling system, and other accessories. In external appearance (see Figures 56 and 57) they are not unlike the electric locomotives 176 MODERN TUNNELING described above. Two forward and two reverse speeds are usually provided in the machines manufactured in this country, the lower one of 3, 4, or 5 miles per hour, and a higher speed double that of the lower. The draw-bar pull ranges from 1,000 to 4,000 pounds, according to the size of the locomotive. In Fig. 57. Gasoline mine engine. some of the machines the exhaust gases from the engine are passed through a tank containing a solution of calcium chloride, which cools the gases and is said to remove all offensive odors from them. In a German-made machine the exhaust gases are sprayed with water to produce the same effect. The gasoline locomotive combines most of the advantages of both electric and animal haulage. It is self-contained and independent of a central station or any other outside source of power, needing nothing but a track. It is fully as rapid as the electric motor ordinarily used in tunnels and is capable of handling an equal load. The fuel for a gasoHne locomotive can be obtained readily in almost any locality, and the machine does not consume fuel when it is not running, a matter of great importance in tunnel work, where interruptions occupy a neces- sarily large percentage of the time. Another advantage, although perhaps not so important for tunnel work, is the fact that the haulage system may be expanded by the addition of extra units without alteration in the power plant, hence the possibility of such future changes need not be considered in the design of the power plant. The following table, based upon replies from HAULAGE 177 o < < X u o < o o H on O U O g < Pi o ••03 3uiuip\[ 1B03 apBqs ON oT "0 NO NO 00 10 10 10 i '•ooSuiuipv IB03 30junj\j m <-< "^ n »o 4^ 10 s ^ 8 •^d 'uoiJnqiiM •03 |B03 AaiiBApiiv ^ 10 ON r^ vo Qo ^ 10 8§l, - 03 1 •^A-A\'ppyj3po-a '•03 35103 :81B03u3q3nBA vO rO i-< 00 NO 10 Ss 8 Ov •UU8X 'A;i3 Adbjx '•03 P03 pa;BpilOSU03 33SS3UU3X ■^ 10 »o t^ ON »0 to 4^ 10 10 NO r< iT 00 P-H q j •BJ •BJ3pBp\[ '•03 :^ adoMg 'a "H « n 10 10 4^ to '^ 00 00 q 10 q oc 3 ON vo 'xt- ro -, 00 10 8:?oo NO to 10 4^ 10 - CJ '•03 uoji auBo-a '•031B03 SSapiJOUlS SB^UOlJBDOd: '^ 10 lr> - fo ^10 10 ON NO - 100 lo^ Os to rh 00 c c Average number of trips each locomotive Average gross tonnage loaded trin - rt 2 B D G < -a > Cost of labor per day .... Cost of lubricating oil per day Operating cost, exclusive of repairs Cost per ton mile, not in- cluding repairs Average daily cost for repairs Cost per ton mile, in- 2 ■§ bi c z D 178 MODERN TUNNELING operators and users of gasoline locomotives received in answer to inquiries sent out by the Bureau of Mines, in 191 2, shows the cost of haulage with these machines. Practically the only disadvantage of the gasoline locomotive is the amount of carbon-dioxide given off in the exhaust from the engine, but this can be eliminated by proper and adequate ventilation. When the machine is properly regulated the amount of carbon dioxide should not exceed 2^ to 5 cubic feet, depending on the size of the engine. If this were confined in a small unventilated space the air would soon become unfit for breathing, but since the greater part of the time the motor is traveling back and forth in the tunnel and since a large volume of air is, or at a properly organized tunnel should be, supplied by the ventilating blower, the exhaust gases from the engine are quickly diluted to harmlessness. It is essential, however, that the blower be arranged to deliver the air to the heading through the ventilating pipe, rather than through the tunnel, in order that the air may reach the workmen as pure as possible, and it would doubtless be necessary to run the blower somewhat nearer its capacity. But even were it operated at full load, the added cost of doing so would be more than repaid by the saving effected by the gasoline haulage. DUMPING DEVICES The box cars used at the Strawberry tunnel were dumped b.y an electrically driven stiff-leg derrick. The hook in the derrick block carried a bail which engaged trunnions, one at each end of the car. The trunnions were placed in such a way that when an empty car was picked up by the bail the weight of the running gear would be sufficient to hold the car upright, but if the car was loaded its center of gravity would be above the trunnions. A spring-actuated pin, situated in one leg of the bail and engaging a hole in the car body above the trunnion, pre- vented the car from overturning until it was swung out over the place where the rock was to be deposited, when by pulling a rope the attendant could disengage the pin and permit the car to turn over and deposit its contents. It would then auto- I HAULAGE 179 matically right itself and could be swung back on the track. The derrick was mounted on wheels so that it could more easily be moved ahead, but this was necessary only at intervals of three to six months. Among the advantages claimed for this system of dumping is the fact that it could be operated by the train crew, the motor- man running the hoist and the brakeman adjusting the bail, thus saving the labor of a dumping gang. Then, too, it gave a much larger dumping area with a consequent saving of the time which with the ordinary mine car is lost in shifting tracks, etc. But this was offset in part by the setthng of the dump, and on this account the moving of the derrick was accompKshed with great difficulty. It is probable that some of this annoyance could be avoided at a future installation by using very wide wheels similar to the type used on roller trucks for moving houses. But the derrick is expensive, costing when erected at the tunnel approximately $3,600, of which hardly more than $1,500 could be reahzed from its sale after the completion of the work; for this reason its use must extend over a considerable length of time in order that the saving in wages may repay the original cost. At the Newhouse tunnel the loaded cars were run into a cylindrical steel framework having rails at the bottom and a set of angle-iron guides at the top with just enough clearance space between them to hold the car firmly. The entire apparatus was then revolved by an electric motor until overturned, emptying the contents of the car, and it was then righted by continued revolution and the car removed. Although used here only for ore cars, the material falling into a bin for shipment, it offers a satisfactory and reasonably inexpensive means of dumping the more durable soHd body and tmck cars, and could doubtless be applied to tunnel dumps by the use of a light trestle or similar structure. Almost an}^ of the various cradle dumps frequently used at coal mines can readily be adapted to tunnel work by mounting upon a stout frame of logs or large timbers, which could be pushed forward along the top of the rock pile as necessity arose. By this means it is possible to eliminate hinges and turn-tables 180 MODERN TUNNELING between the body and the truck of the car, thus simphfying and strengthening its construction. One of these cradle-dumps was used at the Lausanne tunnel. It was not expensive and saved a considerable amount of time in dumping cars and in keeping the rock pile in proper condition. It was pushed forward by the motor every two or three days, requiring but a few minutes for the operation. A similar dumping device is used at the Cameron mine, Walsenberg, Colorado. It has the added advantage of being mounted on a turn-table, thus giving nearly double the top width of dump attainable with ordinary cradle devices. As described in Mines and Minerals,"^ the dump consists essentially of three plates of one-eighth inch iron 3 by 4 feet in size. To the top plate are bolted a pair of mine rails with the ends bent up into horns. This upper plate re- volves on a mine car axle, the bearings for which are supported upon a mine rail and bolted to the middle plate. A piece of channel iron is bolted to the middle plate and upon it the dumper falls back after a load of rock has been discharged. The upper plates as a unit revolve upon the two annular pieces of iron, 22 inches in diameter. The king-pin is i inch in diameter, and the plates, where it passes through them, are reinforced by a piece of }4- by 3 -inch bar iron. The lower plate is supported by four short lengths of 12-pound mine rail. * October, 191 1, p. 158. CHAPTER X INCIDENTAL UNDERGROUND EQUIPMENT TUNNELING MACHINES Although tunnels have been constructed for mine drainage, irrigation, and supplying water to cities for thousands of years, they were so few in number during ancient times and constructed at such irregular intervals that there w^as no great incentive to improve upon the methods ordinarily employed in driving them. With the advent of the steam railroad, however, it w^as soon realized that the desirabihty of maintaining easy gradients would necessitate the driving of many tunnels, and the active minds of inventors were immediately directed toward the prob- lem of making a machine which would do this work more or less automatically. The first tunneling machine of w^hich any record could be found was constructed at Boston in 1851 for use in the Hoosac tunnel. It weighed 70 tons and was designed to cut a circular groove in the face of the tunnel, 13 inches w^ide and 24 inches in depth, by means of revolving cutters. The trial of this machine in the tunnel proved unsuccessful, and only a distance of 10 feet was cut with it before it was abandoned. In 1853 the Talbot tunnehng machine, which was designed to make an annular cut 17 feet in diameter and leave a cyHndrical core to be removed by blasting, was tested near Harlem, New York, but also proved unsuccessful. Later a smaller machine was con- structed, adapted to cut an 8-foot annular groove; this, while it was less unwieldy than its predecessor, also proved a com- plete failure after $25,000 had been expended upon it. Although numerous machines constructed upon almost every conceivable principle have been experimented with since 1853, the entire disappearance of most of them from sight, and almost from history, tells only too clearly that the problems of driving 181 182 MODERN TUNNELING through hard rock have been too difficult for the machines to overcome successfully. It is not safe to predict from this, however, that a tunnehng machine will not, or cannot, be constructed to perform this work in the future because, difficult as the problem of designing such a machine appears, the obstacles in the path are no greater than they have been in scores of other instances where slow and costly manual methods have been superseded by less expensive and more expeditious mechanical processes. The invention of some new rock-cutting device, or the material improvement of some of those now known, may simplify the problem to such an extent that the construction of a successful tunneling machine will be rendered comparatively easy. Further encouragement is also to be found in the fact that there have been two machines, designed for driving in the soft chalk formation underlying the Enghsh Channel, that have done practical effective work. The first of these is generally known as the Beaumont machine, because, although invented by Major English, it was developed and operated by Major Beaumont, of the EngHsh Army. This machine, which was not completed until 1883 (although patented as early as 1864), during a series of tests drove an aggregate of more than 6,000 feet of cylindrical tunnel 6^ feet in diameter. The maximum rate of progress attained was 81 feet per day, or 40 inches per hoiir. During the final test an average of 50^ feet per day was maintained for fifty-three consecutive days. The machine was afterward tested in the Mersey tunnel at Liv- erpool, where it made an average speed of 30 feet in twenty-four hours in soft red sandstone and a maximum of 40 feet per diem. As the Beaumont machine can be used only in soft rock, a description of its mechanism is hardly necessary here, but its record shows what can be accomplished in mechanical tunneling by a machine carefully designed for the work it is intended to perform. The first patent on the B run ton tunneling machine was issued July 21, 1868; since then a number of patents have been granted for different improvements. While this machine, like the Beaumont, was designed primarily for driving in the chalk INCIDENTAL UNDERGROUND EQUIPMENT 183 formation under the English Channel, it was the direct out- growth of the investigations and improvements on stone-cutting tools by the Brunton and Trier Engineering Company. The success of their stone-dressing machinery, now so largely used in this country and Europe, is due in a great measure to the perfection of the peculiar cutting tool which was employed in the tunneling machine, and which is described fully in an article on ''Modern Stone-Working Machinery," by M. Powis Bale, in Fielden^s Magazine for August, 1900, from which the following quotation is taken: "The cutters are of steel and circular in shape, somewhat after the form of a saucer, and have a rolling motion when in action, con- sequently the great friction resulting from dead pressure is done away with, the cutters having what might be termed a rolling wedge action. This system of rolling cutters was patented some years ago by Messrs. Brunton and Trier, and the pith of the invention may be said to consist in giving the circular cutters a determinate motion on their own axis, at the same time they are carried around in a circle, their cutting edges describing a circular path and the rates of cutter rotation and movement around the circle being so adjusted relatively one to the other that the cutting edge rolls in a slowly advancing cir- cular path." The pressure of the sharp wheel against the rock causes the latter to spring off the side of the cut in the form of spawls, very much on the same principle as a sharp-edged wheel-tire will throw a line of chips when passing over a sheet of ice. As there is no percussion, the machine works steadily and quietly, even on the hardest rock, and the durability of the cutting disks is some- thing phenomenal. Good descriptions of the Brunton tunneling machine may be found in the following: Drinker's ''Tunneling," pages 191-194. Zwick's "Neuere Tunnelbauten," page 68, with cuts. Johnson, Wm.: "Brunton's Heading Machine," Proc. Chester- field and Derbyshire Engineers, October 2, 1875. Engineering, Vol. VII, page 355, May 28, 1869. The machine was thoroughly tested out on both sides of the Channel, where it drilled an aggregate of approximately 8,000 184 MODERN TUNNELING feet, and it was found that a seven-foot machine would bore a tunnel and load the cuttings on dump cars at the rate of 30 inches per hour. Several thousand feet of tunnel were also driven with this machine in somewhat harder rock, but before it could be fully developed and placed upon the market further progress was stopped by the unfortunate death of the inventor. Any future tunneling machine, to be successful in hard rock, will have to be simple, durable, not hable to derangement, easily guided and controlled, and with all parts readily accessible for removal, adjustment, and repairs. It must be so designed as to permit the automatic removal and loading of the cuttings and at the same time afford free access to the face even when it is in operation. All actuating machinery and bearings must be completely housed and protected from mud and water and the framework so constructed that it will not be thrown out of alignment or its advance checked by openings or softened places in the rock. It must also permit of easy removal to and from the immediate face of the tunnel. Viewed in the light of present development, this seems a difficult problem, but the invention of some new cutting device or material improvement in some of those now known may so simplify the task that the construction of a successful tunneling machine for hard rock will be rendered comparatively easy. This has been the course of invention in numberless instances, and we have every reason to expect that here, as elsewhere, history will repeat itself. The simple device of putting an eye in the point of a needle made the sewing machine possible; the breech-loading gun was a com- plete failure until the brass cartridge was invented; and not even the genius of a Langley or a Wright could construct a flying machine until the internal-combustion engine had reached its proper development. At present, and during the last four or five years, inventors are and have been unusually active in this line of work, and there are several machines which are in the course of construction or are being experimented upon with the view of perfecting and correcting their mechanical details. The following are descrip- tions of some of the more prominent : INCIDENTAL UNDERGROUND EQUIPMENT 185 The tunneling machine which is being developed by Mr. O. O. App, of the Terry, Tench and Proctor Tunneling Machine Company, consists essentially of a rotating head with four arms, each of which carries four specially designed pneumatic hammer drills, so arranged that practically the entire face of the tunnel is covered at each revolution of the head. The drills carry a flat wedge-shaped bit and are arranged so that the action of the hammer is stopped automatically whenever the pressure of the bit against the rock is less than a predetermined amount, thus preventing damage to the drill whenever a tool breaks or a crack or seam in the rock is encountered. The drill bits are held against the rock at a definite angle, and in their operation they chip or flake away the rock instead of attempting to pulverize it. The head is provided with a flange and shield so arranged that the cuttings are hfted from the bottom of the bore and discharged upon a belt conveyer which in turn delivers them to the tunnel cars at the rear. Air is suppHed to the drills through the center of the rotating shaft which carries the head. The entire machine is mounted upon wheels to facihtate its movement in the tunnel. The Bennett tunneling machine consists of a battery of forty- six pneumatic hammer drills mounted in a rectangular head, arranged so that it can be given a vertical as well as a transverse motion, and thus be able to drill a tunnel of any desired size. The head is held rigid while the machines are running, and after the face of the tunnel has been drilled full of holes the head is backed away from the face and the cellular shell remaining between the holes is then broken down with hammers. Experi- ments are now being carried on with this type of machine in a rock heading near Golden, Colorado. The International Tunneling Machine Company's machine is manufactured under the Fowler patents, and consists of a narrow swinging rectangular cutting head, the full size of the tunnel, carrying a battery of forty-one rock drills. These drills are so placed as slightly to overlap each other's path as the cutting head swings from side to side, by which means the entire face is cut away. This permits the continuous operation 186 MODERN TUNNELING of the machine, so long as it is in working order, instead of inter- mittent attack as is necessary with the Bennett type of machine. A full-sized machine was built in 1909 at the Davis Iron Works in Denver, but, aside from some experimental cutting on a huge block of concrete, nothing was ever done with it, and it is now housed in the shop yard. The Karns machine is in principle a large reciprocating rock drill with a cutting head the full size of the tunnel. In the latest machine this head is six feet in diameter and contains forty-one cutter blades made of tool steel, each i inch thick, 5 inches wide, and of various lengths. Points like saw teeth are machined on one edge and the other edge is fastened in the face of the head. The reciprocating parts of the machine weigh seven and a half tons and make about 140 strokes per minute of seven inches each. The head is rotated sKghtly on each return stroke. The machine uses 2,000 cubic feet of air per minute. One runner, one helper, two muckers, one engineer, and a fireman are needed to run the machine, and a blacksmith and helper are required, one shift in three. The Retallack & Redfield tunnehng machine, now under con- struction at the Vulcan Iron Works in Denver, is intended to bore an eight-foot cyHndrical tunnel. A machine of this size carries twenty-eight percussion drills, symmetrically arranged on a revolving head, each drill having 3 >^ -inch pistons, carrying i%- inch steel bits with the regular cruciform cutting face 6 inches in diameter, so shaped that the twenty-eight drills in one revolu- tion cover and cut away the entire face. Behind the drills, immediately surrounding the cylinders which actuate them, is a steel tube about 6 feet in length and 7 feet 5 inches in diameter, or 7 inches less than the bore. The outside of this shell is sur- rounded by three-inch flanges arranged as a worm conveyer to force the cuttings back from the face. The rear end of this tube carries two small, pivoted, self-loading buckets or skips, which are filled at the lower part of their travel and emptied at the upper where they are inverted by a trip, discharging their contents on an endless rubber belt which carries the cuttings rearward and drops them into a car. INCIDENTAL UNDERGROUND EQUIPMENT 187 The Sigafoos tunneling machine is practically a horizontal stamp mill, the stamps being thrown forward by coiled springs and drawn back by a revolving cam. In practice ten heads are employed and the stamps, instead of being flat, carry an equip- ment of hardened steel faces designed to operate with as great a cutting effect as possible. To prevent the steel from heating and losing its temper, the entire face is sprayed with water, which not only lowers the temperature, but allays the dust and assists materially in removing the cuttings. Although a number of experimental machines have been built, all of the details of construction are not yet perfected. The American Rotary Tunneling Machine Co. is now ex- perimenting with an eight-foot machine near Georgetown, Colorado. One of the great obstacles encountered by legitimate in- vestigators in this field has been the difficulty of obtaining funds; for with the tunneling machine as well as with any other new and complicated machine built to operate under difficulties and strains which cannot be measured in advance, costly ex- perimental work is necessary in its development and process of perfection. It must be remembered that machines of the size and strength to cut the entire face of the tunnel in a single opera- tion are of necessity costly, and their maintenance during the trial stages is extremely expensive. For this reason, success can hardly be hoped for unless the inventor, or the company back of him, is in a position to command very considerable amounts of money. But the failure of one badly designed and inadequately financed machine after another, and the sus- picions which have been aroused in the minds of possible in- vestors by the untruthful and flamboyant ''literature" which has been issued by too many alleged tunnel-machine companies in their efforts to "work the public," have caused most people to look upon machines of this kind with extreme distrust, much of which is indeed just, for even a casual scrutiny of the claims of many of these concerns shows clearly that they are in reality fit subjects for investigation by the postal authorities. The following paragraphs contain a list of patents issued 188 MODERN TUNNELING in the United States for tunneling machines in hard rock, ar- ranged in the order of seniority. With each patent is given a condensed description of the "objects of the invention" or the "patent claim." At the time the examination was made the Patent Ofhce was rearranging this class of inventions, and therefore, although every effort was made to have the Ust com- plete, it is possible that one or two inventions may not have been included in it. List of Tunneling Machine Patents E. Talbot Stone-Boring Machine, U. S. Patent No. 9,774, patented June 7, 1853. Description not available, but Patent Office drawings show a machine adapted to boring a cylindrical tunnel with rotating disk cutters. Two pairs of disks are used, carried on a revolving head supported by a large hollow horizontal shaft. This head is intended to be slowly revolved by a worm-driven spur gear, and through the hollow shaft is carried a jointed connecting rod by means of which the cutting disks are traversed across the face of the revolving head so that all portions of the heading are subject to the cutting action of the disks. The machine is quite crude in its design, and it is plainly apparent that it had not passed the experimental stage. Charles Wilson, Springfield, Massachusetts, U. S. Patent No. 14,483, patented March 18, 1856. Claims: Invention "consists in so arranging, constructing, and fitting the parts of a revolving cutter wheel that the cutters are gradually forced forward with a very slow motion, while the wheel carrying the rolling disks, or cutters, receives a compound motion, the one motion a revolution on its shaft, which is at right angles to the axis of the tunnel being bored, and the other motion a gradual rotation of said cutter-wheel and parts carrying the same on the fine of axis or general direction of said tunnel. These two motions, in addition to the very slow forward feeding motion produced INCIDENTAL UNDERGROUND EQUIPMENT 189 by the rolling cutters, causes the gradual removal of the rock, or other substance, at the semi-spherical end of the tunnel.'' Charles Wilson, Springfield, Massachusetts, U. S. Patent No. 17,650, patented June 23, 1857. "The plan adopted in this method of tunneling is to bore a single ring and a central hole. By means of a charge of gunpowder, afterward placed in the central hole and ex- ploded, the rock intervening between the central hole and circular groove is detached." Claim: "Forming grooves in stone, or other mineral substances, by means of rolling disk cutters on axes set in alternate directions and arranging a series of rolUng disk cutters revolving in such a manner as to cut a deep annular groove into the rock." F. E. B. Beaumont, England (English Patent No. 1,904), patented July 30, 1864. "Gang of cutters; supplementary valve; tappet and annular projection; hand feed; rotation automatic by worm and feather." Thales Lindsley, Rock Island, Illinois, U. S. Patent No. 55,514, patented June 12, 1866. Machine devised, "first, to cut circular concentric channels in vertical planes of rock and thus form circular concentric rings in the heading; second, to disrupt these concentric rings of rock and thus prepare them for removal; third, to detach the fragments of the disrupted rings and deUver them for transportation," etc. Edward M. Troth, New York, New York, U. S. Patent No. 66,422, patented July 2, 1867. A reciprocating head carrying a number of drills arranged to vary the stroke. This head turns slowly, cutting a number of concentric grooves in the face. The rings of rock remaining behind are broken off by wedges. Richard C. M. Lovell, Covington, Kentucky, U. S. Patent No. 67,323, patented July 30, 1867. This is a chipping machine, the chisels being operated alternately by their respective engines, the leading chisel 190 MODERN TUNNELING cutting half the depth and the following one completing the cut, and being reversed and changed in cutting back; .the motor is operated by either steam or compressed air conducted to the engine by pipes from the exterior of the shaft or drift, etc. John D. Brunton, London, England, U. S. Patent No. 80,056, patented July 21, 1868. Patent claim: ''The use of an apparatus for excavating tunnels, galleries, or adits, wherein one or more cutting disks are caused to revolve on their axis, or axes, such axis, or axes, revolving around a center which also revolves around another fixed center." Edward Alfred Cooper, Westminster, England (English patent No. 1,612), patented June 20, 1871. Claim: ''The cutting of grooves, or chases, in stone or rock by the action of a series of chisels or jumpers, each worked by compressed air or steam acting in a separate cyHnder and moved along its groove or chase, and all«advance as the grooves or chases are deepened." Allexey W. Von Schmidt, San Francisco, California, U. S. Patent No. 127,125, patented May 21, 1872. Claim: "In combination with a cylindrical drumhead arranged to rotate on its axis, a series of rotary diamond- pointed drills mounted on the periphery of the drumhead." By this means an annular groove the size of the tunnel is cut in the rock to a depth of about two feet, when the machine is backed out and the central core removed by blasting. These diamond-pointed drills are cooled by a stream of water sprayed into the annular groove. Frederick Bernard Doering, Trefriw, North Wales, England, Enghsh Patent No. 4,160, September 27, 1881. "A tunneling machine on which is mounted by means of brackets, or otherwise, a series of rock-boring machines or drills, say four, more or less, around a central boring machine or drill, each carried at the end of an arm, prefer- ably consisting of a strong steel tube. This steel tube, which is accurately turned on its outer face, is supported INCIDENTAL UNDERGROUND EQUIPMENT 191 by one, two, or more accurately bored castings which are carried on a strong framework mounted on wheels. The boring machines or drills may be fitted with cross-heads carrying chisels, or they may have a single chisel attached with or without a cross-head. The drills strike and rotate a portion of the circle with each stroke in the usual manner.'* Thomas English, Hawley, Kent, England, U. S. Patent No. 307,278, patented October 28, 1884. *' Invention relates to a machine for boring a circular tunnel by means of a boring head which consists of a strong boss having two arms projecting radially from it, each arm having a number of cutters fixed in front of it, each cutter being a bevel-edge disk fixed to the holder so that it can be turned partly around when one part becomes blunted. Jets of water from small nozzles play on the cutters to prevent them from heating." Henry S. Craven, Irvington, New York, U. S. Patent No. 307,379, patented October 28, 1884. This patent ''relates to that class of machines which employ a drill or combination of drills constructed to cut or bore an annular groove the full size of the contemplated tunnel, leaving a cylindrical mass of rock at the end of the bore to be blasted out by a charge of explosives introduced in the central hole." Robert Dalzell, Waddington, New York, U. S. Patent No. 332,592, patented December 15, 1885. Claims: ''In a rock-drilling machine the combination of a suitable frame carrying a rotating or oscillating tubular shaft having near its forward end a series of laterally radiat- ing arms, having adjustably screwed to their outer ends one or more reciprocating or rotary drills with mechanism for operating the same both simultaneously or separately." F. 0. Brown, New York, New York, U. S. Patent No. 340,759, patented April 27, 1886. Patent claims: "A shell made in the shape and size of the required tunnel, provided with an air-tight cross parti- tion having manholes closed by plates in the tube, a 192 MODERN TUNNELING central worm-boring mechanism, and a steam pipe passing through the airtight partition in the tube." Reginald Stanley, Nuneaton, England, U. S. Patent No. 414,893, patented November 12, 1889. Claim: ''In a tunneling machine the combination of a frame carried on central tandem wheels working on the floor of the tunnel, a central threaded shaft carried by said frame and driving wheel working on said shaft, radial arms and horizontal arms on one end of said shaft and provided with cutters and scrapers depended for forming an annular groove around the face of the tunnel," etc. Reginald Stanley afterward devised numerous improve- ments on this machine which were patented June 14, 1892; May 9, 1893; August 29, 1893; August 11, 1894; and Febru- ary 16, 1897. Frederick Dunschede, Essenberg, Germany, U. S. Patent No. 507,891, patented October 31, 1893. ''Invention consists of an apparatus by means of which an annular groove and a central blasting hole are bored into the rock so that, on inserting into said central hole an explosive and exploding the same therein, the rock or other material forming the core between the central blasting hole and the circumferential cut will be smashed and blown away." Jonas L. Mitchell, Chicago, Illinois, U. S. Patent No. 537,899, patented April 23, 1895. Claim: "In a tunneling machine, the combination of a tunnel-forming cutter consisting of a tubular cutter head, a main frame having guides therein, and of a diameter ^ adequate to enter the tunnel formed by the cutter, a carriage sliding in said guides and lying in the transverse planes of the bed," etc. Harry Byrne, Chicago, Illinois, U. S. Patent No. 545,675, patented Spetember 3, 1895. Patent claims: "In a rock- tunneling apparatus, the combination of an upright supporting frame, having a marginal frame corresponding with that of the tunnel and a INCIDENTAL UNDERGROUND EQUIPMENT 193 series of traveling percussion channeling machines arranged to travel on the outer surface of said frame; a flexible connection attaching the entire series of machines together and causing same to travel in unison, and means for operating said flexible connection." Archie LE Bailey, Philipsburg, Pennsylvania, U. S. Patent No. 640,621, patented January 2, 1900. Patent claims: ''In a mining machine, the combination with a bed, the carriage, two reciprocating cutters, each forming a separate curve, and means for simultaneously reciprocating said cutters in opposite directions, whereby they balance the machine laterally, of a drill mounted on each side of the carriage and forming an aperture at the end of the kerf." John E. Ennis, Chicago, IlKnois, U. S. Patent No. 690,137, patented December 31, 1901. Claims: "A tunneling machine having a digger mechanism, including a plow movable in a circular sweep, means for imparting said sweep movement to the plow, and simul- taneously forcing forward in a spiral direction, and means for automatically shifting movements of the plow and causing it to travel from the perimeter of the machine inward, or from the axis of the machine outward, during its sweep movement." Pedro Unanue, City of Mexico, Mexico, U. S. Patent No. 732,326, patented June 30, 1903. Claims: "In a tunneling machine, the combination of a ram-head provided with a series of rammers having their rods inclined to the ram-head in and toward the direction of revolution of the ram-head, together with an incHnation from the axis of revolution of the ram-head, and means for rotating and feeding said ram-head," etc. John Prue Karns, Cripple Creek, Colorado, U. S. Patent No. 744,763, patented November 24, 1903. Claims: "The combination with a tunneling machine of a revoluble drill support comprising a pluraHty of ring and spoke members, each having grooved forward faces, 194 MODERN TUNNELING drills, or cutters, having their base portions adapted to said grooves, each of the drills or cutters having a rearwardly , projecting stem extending through an opening in the support, and means for locking said stems to said support." Other patents issued to Mr. Karns on this machine are as follows: No. 957,687, May 10, 1910, for improvements in machine structure, particularly for the front bearing of the cutter- head shaft. No. 977,955, December 6, 1910, for improvements in the cutter-head tool-carrying spider. No. 1,023,654, April 16, 1912, improvements on the structural form and mechanical arrangement of said machine. Chester T. Drake, Chicago, Illinois, U. S. Patent No. 747,869, patented December 22, 1903. Claims: ''In an excavating machine, the combination of a shaft provided on its end with a cutter, mechanism for revolving the shaft, mechanism for giving shaft and cutter an orbital revolution, and adjustable mechanism for varying orbit described." Alva D. Lee, of Brookline, and Francis J. E. Nelson, Jr., of East Boston, Massachusetts, U. S. Patent No. 874,603, patented December 24, 1907. Claim: "In a rock-drilling machine, the combination ' of an annular face plate provided with a pluraHty of de- pressions in its face, means for rotating said plate and a plurality of cutters secured in said depressions, with their axes radial to the axis of said plate and at different dis- tances from said center, thereby effecting in the revolution of said plate a cutting from the central opening to the outer periphery of said plate," etc. Silas A. Knowles and Walter E. Carr, Idaho Springs, Colorado, U. S. Patent No. 875,082, patented December 31, 1907. Claim: "In a tunneling machine, a narrow rectangular reciprocating cutter head of the full height of the tunnel to be. driven, provided with vertically and parallely ar- I INCIDENTAL UNDERGROUND EQUIPMENT 195 ranged rows of chisel-shaped drill bits having angular bases, means for securing said drill bits to said cutter head, said cutter head having slideway slots therethrough, a supporting guide arm having forward terminal arms which project into sHdeway slots on which said cutter head is reciprocally mounted," etc. William J. Hammond, Jr., Pittsburgh, Pennsylvania, U. S. Patent No. 885,044, patented April 21, 1908. Claim: ''In a tunneling machine, a rotary head having a series of diametrically arranged reciprocating hammers and separated from each other by distances slightly less than the hammers, whereby the entire breast of the tunnel may be disintegrated by the rotation of the head and the reciprocation of the hammers." George Allen Fowler, Georgetown, Colorado, U. S. Patent No. 891,473, patented June 23, 1908. "Invention is directed to the production of a pneumatic mining machine for a plurahty of thrust-actuated drills adapted particularly to tunnel or driving operations in which the drills are carried by a pivoted block, which, in its cutting operations, is automatically caused to travel back and forth, reducing the wall of the breast to an arc of a circle to give clearance to the sides of the machine." Olan S. Proctor, Denver, Colorado, U. S. Patent No. 900,950, patented October 13, 1908. Assigned to the Terry, Tench & Proctor Tunneling Machine Company. Claim: "In a rotary tunneling machine, the combination of a supporting frame, a tubular shaft revolubly mounted on said frame, a rotary cutter head secured to one end of said tubular shaft, a plurality of operative rock-drilling engines arranged to cut the breast area of a circular tunnel, said cutter head having ports leading from said tubular shaft to said rock-drilling engines, means, including a motor, for rotating said tubular shaft and cutter head, means for connecting the opposite end of said tubular shaft to a supply of suitable drilling engine actuating fluid, a muck-catching cylinder on said supporting frame sur- / 196 MODERN TUNNELING rounding said cutter head, and means for conveying the muck from said cutter head and cyhnder to the opposite end of said supporting frame from said cutter head." Russell B. Sigafoos, Denver, Colorado, U. S. Patent No. 901,392, patented October 20, 1908. ''The objects of this invention are: First, to provide a rotary tunnel machine adapted to automatically feed into the breast of a tunnel as fast as it cuts into rock, and to automatically feed forward and backward. Second, to equip it with a pluraHty of reciprocating cutter heads, each provided with a plurality of independent rock-cutting lips. Third, to provide a plurality of reciprocating rotary cutter heads adapted to strike spirally twisting blows. Fourth, to provide discharge jets of water throughout the circumference of the rock-cutting area. Fifth, to provide the machine with a plurality of independent rotating and spirally striking cutter heads arranged and adapted to permit any one or predetermined number of said cutter heads to be adjusted to strike blows at differential force. Sixth, to provide an automatic adjustable feeding mechanism that will feed the machine forward in any predetermined curved path as it cuts its way into the rock." Joseph Retallack, Denver, Colorado, U. S. Patent No. 906,741, patented December 15, 1908. This machine is especially designed for driving tunnels or drifts through rock, and it comprises, in general, "a revoluble tool head which may be idly rotated or fed forward or backward at pleasure. The head carries a large number of independently actuated rock drills which attack the face of the rock as the head is rotated. The head is carried by a threaded shaft that is hollow from end to end and serves as a duct for the passage of the air or other fluid to actuate the drills." Provision is also made for introducing water at the drilling point and for automatically gathering up and conveying away the fragments of rock as the tunneling operation proceeds. INCIDENTAL UNDERGROUND EQUIPMENT 197 Charles A. Case, New York, New York, U. S. Patent No. 910,500, patented June 28, 1909. ''This invention relates to means for disintegrating rock and other materials by suddenly changing their temper- ature, and then by concussion, hammering, or rasping, effecting their disintegration." Edward T. Terry, New York, New York, U. S. Patent No. 917,974, patented April 13, 1909. "The primary object of this machine is to cut a tunnel through rock without the necessity of blasting." . . . "The drill head consists of nine gangs of drills of such size and location that in their rotary motion they cover substan- tially the whole face of the tunnel, while the cutting action is produced by a rapid reciprocation of the separate heads." Louis Franklin Sleade, Denver, Colorado, U. S. Patent No. 945,623, patented January 4, 1910. Claim: "A tunneling machine comprising a revoluble cutter head, an electric motor for rotating said cutter head, an internal combustion engine for maintaining a reciprocating motion of the said cutter head in a forward direction, and means for connecting said electric motor with said internal combustion engine, imparting a returning movement to the cutter head." George R. Bennett, Denver, Colorado, U. S. Patent No. 958,952, patented May 24, 1910. Claim: "A tunneling machine comprising, in combination with a suitable support, a battery of rock drills, means for presenting said battery to a working face, means for pro- jecting said drills of said battery in said face, and means for automatically moving said battery laterally after each projection of said drills. "A tunneling machine comprising, in combination with a suitable support, a battery of rock drills, means for im- parting a series of rectilinear movements to said battery, and means for automatically performing said movements, in progressive cycles, each cycle comprising a longitudinal, lateral, and vertical movement." 198 MODERN TUNNELING William R. Collins, Georgetown, Colorado, U. S. Patent No. 973,107, patented October 18, 1910. "Invention provides a machine having a cutting head which will leave an uncut rock core, thereby saving a certain amount of expensive rock drilling, and further to provide an improved arrangement of chipping or cutting drills V whereby the recoil of the drills will be counteracted and the cutting head balanced." On August 8, 191 1, Mr. Collins obtained U. S. Patent No. 1,000,075 for certain mechanical improvements on this machine. Aron G. Seberg and Edwin G. Seberg, Racine, Wisconsin, U. S. Patent No. 976,703, patented November 22, 1910. Claim: ''In a drilling machine, the combination with a wheel, of shields yieldingly mounted in said wheel, drills slidably mounted in said shields, means to force said drills beyond the outer ends of said shields, and means to rotate said wheel. ''In a drilling machine, the combination with a rotating sleeve, of a wheel for said sleeve adapted to rotate there- with, a supporting axle around which said wheel revolves, means to rotate said wheel, a plurality of drills carried by said wheel, and rotating means adapted to force said drills outwardly and enter the same into an object." Franklin M. Iler, Denver, Colorado, U. S. Patent No. 986,293, patented March 7, 1911. Claim: "In a rock-drilHng machine, the combination with a suitable frame, of a hollow rotatable shaft, carried by said frame, divergent, rigid, hollow arm constituting a continuation of said hollow shaft and projecting therefrom at an angle, means for supporting fluid-operated drills by said arms in various adjusted positions at different points, and means for connecting the inlet ports of said drills with the interior of said arms." Mr. Iler has also patented, for use with his machine, a special drill bit which consists of a hollow tube about 7 inches in length, 3^ inches external diameter, and i^ inches INCIDENTAL UNDERGROUND EQUIPMENT 199 internal diameter. This tube is of cast iron or soft steel, and in it are embedded a number of rods about j^ inch in diam- eter of exceedingly hard alloy steel. The soft material wears away much more rapidly than the hard, thus forming a chipping tool which can be used without sharpening until it is worn out. George A. Fowler, Denver, Colorado, U. S. Patent No. 996,842, patented July 4, 191 1. Invention ''provides a suitable frame mounted on wheels, said frame being provided at its forward end with a drill head provided with a plurality of fluid-operated drills, said head being pivotally mounted on the frame and adapted to swing from side to side in the arc of a circle, upon a vertical axis, means being provided for admitting fluid under pressure to said drills, and for automatically swinging said head from side to side and for manually moving said machine forward against the breast of the tunnel." Robert Temple, Denver, Colorado, U. S. Patent No. 1,001,903, patented August 29, 191 1. ''Invention provides a machine for cutting tunnels through rock or ether materials, the cutter of which will be reciprocating and simultaneously moved transversely to its direction of reciprocation, thereby cutting a tunnel of greater cross-section than the machine." Claim: "In a rock-cutting apparatus, the combination with a transversely extending head, of a plurality of cutters mounted thereon, means for reciprocating said head, and means for simultaneously mo\ing the same in complete cycles over a substantially circular path adjacent to the surface worked upon and eccentric to the said head." John Nels Back, Seattle, Washington, U. S. Patent No. 1,011,712, patented December 12, 191 1. Claim: "A tunnel-excavating machine comprising an outer frame, traction wheels under said outer frame, an inner frame movable with relation to said outer frame, a head beam, a carrier slidably mounted upon said head beam, a shovel mounted in said carrier, means for sliding the 200 MODERN TUNNELING carrier, means for moving said inner frame, and toggle- joint braces to prevent movement of said outer frame." Edward O'Toole, Gary, West Virginia, U. S. Patent No. 1,011,955, patented December 19, 191 1. Claim: ''In an excavating machine, the combination of a frame, a pair of rotary pick-armed cutter heads mounted on parallel shafts therein, and geared to rotate in unison from a common source of power, said frame movable upon a bed-plate, and in movement causing the shafts of said cutter heads to move transversely in their common plane, said bed-plate provided with a passage for excavated material, and with an intake extending beneath the path of movement of said cutter heads." Henry F. Sutton, Salt Lake City, Utah, U. S. Patent No. 1,025,029, patented April 30, 191 2. ''Object of invention is to subject the rock alternately to the action of opposite extremes of temperature, it having been found that when rock is first heated and then sud- denly chilled it becomes softened or partially disintegrated so as to be easily removed by hand or by pneumatic tools or the like." Claim: "Apparatus for tunneling rock, including a hollow head having a mixing chamber therein, said head having a working face formed with a plurality of minute apertures, means for pivotally supporting the head close to the surface to be acted upon, means for directing fuel into the head, valves for controlling the passage of fuel through said means, and means for directing air under pressure into the head." Adolph F. Walther, Oakland, California, U. S. Patent No. 1,026,335, patented May 14, 1912. Claim: "A tunneling apparatus comprising a plurahty of main frames, detachable braced supports for holding said frames in a tunnel, a frame movable longitudinally in said plurality of frames, a rotary shaft and head mounted in said frame, radial bars provided with cutters mounted INCIDENTAL UNDERGROUND EQUIPMENT 201 on said rotary head, and mechanism for operating said rotary head and cutter bars." L. H. Rogers, New York, New York, U. S. Patent No. 1,039,809, patented October i, 191 2. Claim: ^'The combination of a central frame, a hollow shaft journaled in the frame, means to conduct a fluid to the interior of said shaft, a front head fastened to said shaft, grinding wheels journaled on said head, motors connected to the wheels carried on the head, means to conduct the fluid from said shaft to said motors, a rear frame sUdably connected to the shaft, a cylinder encircling said shaft and fastened to the rear frame, a piston in the cyHnder connected to said shaft, and means to lead a compressed fluid on either side of the piston." W. F. WiTTiCH, Erie, Pennsylvania, U. S. Patent No. 1,043,185, patented November 5, 191 2. Invention utilizes ''a rotating head in which is mounted a series of cutters actuated, preferably, independent of the head, so that the head may be advanced slowly or rapidly, depending on the material being operated upon, and the cutters given a speed which will assure the greatest efficiency. In the preferred form of the machine, also, the head is separated from the driving parts of the mechan- isms, so that the machine may be utilized and rapidly advanced where there is considerable leakage through the walls. The invention also contemplates a suitable mount- ing, or frame, for carrying the working parts, taking away the muck, and driving the several parts." ILLUMINATION With few exceptions, illumination for tunnels and adits in the United States at the present time is furnished by electricity, acetylene gas, or candles. The smoky open-flame miner's oil-lamp is occasionally used in tunnels situated in the coal-mining districts, and, of course, under conditions which prohibit the use of an open flame, safety lamps must be em- ployed. When acetylene gas is employed it is usually generated 202 MODERN TUNNELING in portable lamps, but during the work on the water conduit for Washington, D. C, in 1899, this gas was manufactured at a plant on the surface and carried by pipes underground where it was burned in jets at regular intervals. Coal gas was simi- larly employed at the Mt. Cenis tunnel, which was started in 1857 ^^^ opened for traffic in 1872. The following table, how- ever, shows the present practice with regard to means of illumi- nation. MEANS OF ILLUMINATION AT VARIOUS TUNNELS Tunnels Illumination Buffalo Water Electric lamps. Acetylene lamps and candles. Eleotric lamps at intervals and usually a cluster of lamps in the headings. Acetylene lamps. Electric lamps (16 c.p.) every 75 feet and one 32 c.p. in heading Candles, Carter Catskill Aqueduct Central ... Fort Williams . . Gold Links Gunnison Electric lamps. Cluster in heading and candles. Electric lamps. Acetylene lamps for drillers, candles for muckers. Miners' oil lamps and safety lamps. Electric lamps and candles. Acetylene lamps. Acetylene lamps. Electric lamps every 200 feet, cluster in head- ing, candles. Electric lamps at stations, acetylene lamps in heading. Electric lamps every 75 feet, cluster in heading. Candles. Joker Laramie-Poudre Lausanne Los Angeles Aqueduct .... Lucania. Marshall-Russell Mission Newhouse Nisqually Ophelia Raymond Rawley Electric lamps every 200 feet, cluster in heading. Acetylene lamps. Electric lamps. Electric lamps every 200 feet and candles. Acetylene lamps. Electric lamps in heading, candles. Electric lamps every 135 feet, cluster in heading. Electric lamp at switch, acetylene lamps in heading. Electric lamps. Roosevelt Siwatch Snake Creek. Stilwell Strawberry Utah Metals Yak Neither candles nor the open-flame oil lamp can be recom- mended as a means of hghting a tunnel or adit during con- struction. Practically everything that can be said in their favor is that they require a much smaller initial outlay than electricity INCIDENTAL UNDERGROUND EQUIPMENT 203 or acetylene, yet they are more expensive per unit of light than either acetylene or electricity, consume a greater amount of oxygen, and give off a correspondingly greater amount of noxious gases. Candles not only do not give enough light, but what they do supply is flickering and unsteady unless there are no drafts, and since they are quickly extinguished by the exhaust blasts from air drills they cannot be placed to light properly the work of the drillers; hence the efficiency of a high-priced drillman is greatly reduced. Candles are often wasted or dropped into the muck-pile, an item of loss which may amount to a consider- able sum in the long run. The open-flame oil lamp cannot be prevented from giving off soot and smoke which obscure and dim the light thrown on the work, while the soot collecting in the miner's throat and lungs irritates the mucous membranes and renders them easily susceptible to disease. Electric incandescent lamps possess a number of advantages for tunnel work. They give a brilliant and steady Hght — one that is not affected by drafts and neither pollutes the air with soot nor vitiates it by consuming the oxygen. By combining several of them in a cluster, plenty of light in the heading is obtained for the drillers and shovelers, tending toward efficiency. To offset this advantage, however, the fact remains that unless they are used in connection with electric locomotives, drills, or similar machinery, the cost of lamp installation is almost prohibitive; even with the electric appliances in use the extra wiring and the lamps themselves are expensive, while the latter are subject to considerable loss through breakage. Electric lights are also at a disadvantage because they are not easily portable and the removal and replacement of bulbs and wires in the heading before and after blasting compHcate an already involved situation. Moreover, this means of illmnination is uncertain, especially in wet tunnels, because the chance oc- currence of a short circuit through moisture, accident, or care- lessness throws the entire work in darkness, and if other means of Hghting are not at hand, stops all work until the trouble can be remedied. Again, whereas the use of electricity under ground is always attended with some danger, this is especially 204 MODERN TUNNELING true in the case of lighting appKances; the supposition is that the wires are protected, but the rough usage to which they are subjected soon destroys insulation, rendering persons who handle them (as they must do frequently) subject to severe shock. One is tempted to say that the ideal means of tunnel illu- mination is found in the portable acetylene lamp, combining as it does the advantages of other illuminants while avoiding most of their defects. It may be obtained on the market to-day in a number of different designs and sizes adapted for practically every kind of work; the one most generally observed at the tunnels visited was about the size of an ordinary can of fruit and capable of burning for from eight to ten hours on one charge of carbide and water. Although too large for use on a cap, it was provided with a hook so that it could be suspended from any convenient place. Lamps suitable for wearing on an ordinary miner's cap are obtainable and these lights will burn for two or three hours without recharging, an operation which can be done easily in two or three minutes. The initial ex- pense of an acetylene lamp is not high and it furnishes the brightest known artificial light used for underground work, with the possible exception of the electric arc, consuming the while only one-fifth as much oxygen as candles. The lamps are ordinarily provided with a reflector, which not only concentrates the light upon the work where it is needed, but shields the flame from drafts so that it will burn steadily unless placed directly in front of the exhaust from an air drill. Extensive use in some of the larger mining companies in this country has shown that the cost of the carbide is much less than either oil or candles and the use of acetylene lamps practically cuts the cost of light in half. At the Saginaw mine, Menominee Range, Michigan, the cost is reported as only two cents per shift of ten hours. Such lamps require practically no attention, are completely portable, and are not subject to breakage as are incandescent lamps. By giving the workman plenty of light his efliciency is not only increased, but he is better able to see and guard against the dangers of underground work, such as an insecure INCIDENTAL UNDERGROUND EQUIPMENT 205 roof, an unexploded stick of dynamite in the muck-pile, or any other of the many dangers to which he is at all times exposed. TELEPHONES Although it has been repeatedly stated in newspapers, engineering periodicals, and even by State legislatures, that every mine should be provided with a telephone system, the importance of telephones in tunnel work cannot be too often reiterated, not alone because of the greater safety they insure, but on the ground of efficiency and economy as well. The sources of accident in tunnel work are too numerous to mention — falls of roof, caves, premature or delayed explosions, water, and noxious gases being some of the more common. When an accident occurs in a tunnel that is equipped with a telephone system, not only can assistance be summoned quickly, but provision can be made beforehand for the care of injured men when they reach the surface; if professional help can be sum- moned and due preparation made while the men are still on the way from the /^ea^/m^, invaluable time is saved; for there have been, and doubtless will be in the future, many such instances where prompt medical attention has decided the question of life or death. Then, too, failure to obtain a proper round of holes in the given time, difficulty in blasting them to the full depth, or any of the many problems that commonly arise in tunnel- driving, call for a decision on the part of the foreman as to the method of procedure. Ordinarily the man entrusted with this position is capable of meeting such conditions as they arise, but it stands to reason that the work of the shift will be more efficient if the foreman can be in touch constantly with the mine superintendent and when in doubt receive suggestions and advice from the more experienced man's better judgment. Delay can be avoided in good part if the tunnel is equipped with a telephone, because the necessity that involves sending for fresh materials, tools, powder, etc., can either be foreseen and proxdded for promptly from the outside without the loss of a man from the heading crew, or when unexpected emergencies arise, only half the usual time is necessary to obtain the needed 206 MODERN TUNNELING supplies. It does not require many suspensions of work by the men in the heading, waiting while one of their number walks to the portal and back, to pay for the entire installation of such equipment. Causes of accident and delay cannot always be foreseen, it is true, but they can bo met promptly and further damage to men and property can be prevented by the use of the telephone; that these advantages are appreciated is shown by the fact that a majority of the tunnels and adits examined in the field were so equipped. The type of telephone-equipment should be carefully chosen, because every telephone is not suited for underground use. For use in tunnels it must be water-proof, dust-proof, and, since to be useful it must be placed as near the heading as possible, it must be designed to withstand the frequently recurring con- cussions of blasting. The most successful types of mine tele- phones meet these conditions by placing the mechanism in a heavy metal casing, in such a way that the essential parts shall be instantly accessible upon opening the outer door, but shall be tightly sealed when it is closed. The more delicate mechanism is guarded further by an inner door, also of iron, and the wires are protected so that water cannot enter the casing. The bells must necessarily be placed outside, but they are protected by a metal hood, which, however, does not prevent their being heard for a considerable distance. The telephone line for tunnel work is somewhat simpler than a similar line on the surface, because no poles are required and the wires can be strung from ordinary glass or china insulators fastened to plugs in the roof or to light cross-timbers. Common bare iron wire can be used, but much better results are obtain- able where rubber-covered wire is employed, and for the same reason a full metaUic circuit is desirable, although the telephone may be operated with only one wire by using a ground connec- tion for the return. But since the usefulness of a telephone system is measured entirely by its rehabiHty, the best is in the end by far the cheapest. It is not desirable to place the telephone nearer the heading than several hundred feet, not only because of the concussion, INCIDENTAL UNDERGROUND EQUIPMENT 207 but also because of the noise. While this arrangement is con- venient for any one in the tunnel desiring to call up the office, it makes it more difficult and sometimes even impossible to secure any response to a call originating on the surface. To obviate this difficulty, the use of an extension loud-ringing call-bell is recommended, which, if placed behind a jutting rock or in some similar protected position, apprises the foreman at the heading instantly of any call at the telephone. Such a bell should be connected with the telephone circuit by a flexible insulated cable mounted upon a reel in such a way that the bell may be advanced regularly to keep pace with the tunnel progress and need never be further than two hundred feet from the heading. When the cable is extended to full length, perhaps i,ooo feet, the telephone should be advanced to a point as near the heading as possible and the extra cable reeled up once more. INCIDENTALS Among the many devices used to save time and promote efficiency underground, those of the simplest are the hose sup- porter and the drill rack, both of which can be made readily by any tunnel blacksmith. The former consists merely of two telescoping pieces of iron pipe, the length of each being about three-fourths of the width of the tunnel. In operation the hose is placed over the pipes, which are then extended until their pointed ends fit into convenient niches on either side of the tunnel near the roof; the pipes are clamped into position firmly by a threaded key which is provided for this purpose. By using two or three of these spreaders the hose are kept clear of the shoveler, who is thus saved no Uttle trouble and annoy- ance and is able to work to better advantage. The latter device is simply a rack for separating different lengths of drill steel. A satisfactory form consists of an A frame made of 4-inch by 4-inch timbers, into which iron pegs are driven at convenient intervals. The segregation of the sharp drill steels on this rack enables the helper to pick out the proper length with assurance and dispatch. CHAPTER XI DRILLING METHODS The discussion of methods of tunnel construction in this and following chapters will be restricted chiefly to those employed where the entire cross-section is excavated in one operation. The majority of tunnels and adits driven for mining work, and many tunnels intended for irrigation and water supply, are small enough to be driven in this manner ; but in the construction of the larger undertakings, such as are required for railroad or similar purposes, it is customary to drive a pilot tunnel or heading, as it is some- times called — although the term is also employed to designate the advancing end of any tunnel — in front of the main body of the work which then consists in enlarging the smaller excavation to full size. The latter method, in addition to lowering the average cost of the entire work, since the process of enlarging is much easier and less expensive than that of driving the heading, also gives a valuable preliminary insight into the conditions which must be encountered later by the main tunnel, and enables the constructor to anticipate emergencies and make provision for them in his plans, thus aiding to prevent accidents and loss. Since, however, the scope of this bulletin is to be confined chiefly to mine adits and small tunnels, a discussion of the various phases of the ''heading and bench" system cannot be treated here as such, although the methods used in excavating in one operation the entire section of a small tunnel are in most cases appHcable to the driving of headings for larger tunnels. Local conditions at each project necessarily modify methods to such an extent that it is impossible to make a general analysis to fit all cases, but the discussion is intended to bring out some of the more important features of the methods employed in the various operations 208 DRILLING 209 of drilling, blasting, mucking, and timbering, as they are applied to the driving of mine adits and tunnels. NUMBER OF SHIFTS One of the chief advantages claimed for the single drill shift per day method is economy. By having, the debris cleared from the heading by the shoveling crew at a separate time, the drill men upon reaching the face are enabled to start immediately to work setting up the machines and preparing to drill the ground; there is therefore no waste of time or labor on the part of these men or the helpers in shoveling out debris preparatory to mount- ing the drills. This method is especially economical when vertical columns are employed. During the process of drilHng the operators and their helpers are not interfered with or hin- dered in any way by the shovehng crew, and there is therefore a saving of that loss of motion which can hardly be prevented when two crews are working simultaneously in the heading. Moreover, since there is no delay in getting started, it is ordinarily possible to complete the round of holes within the allotted time, and even if this cannot be done plenty of extra time is available without delaying the following shift. The drilUng and mucking shifts can be distributed so that there is no loss of time and wages while the men are waiting for smoke and gases produced in blasting to be removed from the tunnel — a matter of cardinal importance where the provisions for ventilation are inadequate. These considerations all go to support the contention that the actual excavation cost per foot of tunnel is lower with this method than with other systems. On the other hand, by employing a single drill shift the daily progress in driving the tunnel is necessarily limited to the advance gained from the one attack, and therefore the completion of the work must inevitably be delayed. Most tunnels are prac- tically worthless until completed. If their construction is not pushed as rapidly as possible, not only is the capital invested in the equipment, tools, etc., securely tied up much longer than necessary and the cost for interest and the depreciation charges proportionally increased, but there is also a delay in the realiza- 210 MODERN TUNNELING tion of the benefits to be derived from the tunnel, which in most cases is more than sufficient to offset any saving in excavation cost. For example, if an adit is being driven to drain a mine, the extraction of additional ore below water level is greatly delayed; or if the adit is intended to lower the cost of trans- porting the ore to the surface, the loss on the additional tonnage handled in the old way, owing to the delay in its completion, should be charged against this system of operation. Similarly with an irrigation tunnel, the entire season's crops may be lost from the longer time required to complete the tunnel if it is excavated by the one-shift method. Then again, the cost for administration and many other of the fixed charges are operative during the period of construction, independent of the number of shifts per day, and since the daily progress increases with the additional attacks per day, the proportionate charge against each foot of tunnel driven will be smallest when the greatest number of shifts are employed. Although, owing to a saving of the time and wages of workmen, there is an apparent economy in the cost of excavation by the one-shift method, when factors which reach deeper are considered, it will be found in most cases that the real and ultimate cost of the tunnel will be lowered by methods which make directly for speedier completion. Greater progress is undoubtedly attained with two shifts per day than with one, and if the work is properly organized there need be but little added excavation cost. It is the usual custom with this system to have the shovelers start work some- what in advance of the drillers, and to work first at removing the broken rock directly at the face to make it possible for the drillers to set up their m;achines promptly. At some adits aad tunnels where two drill shifts were used, the drilling and mucking took place simultaneously, the drillers themselves attending to the work of clearing out for the set-up. Of these two methods the former is preferable, not only because it economizes the time and exertion of higher-priced men, but also because the length of time when both crews are at work together in the heading — and consequently the inevitable amount of inter- ference and interruption — is thereby lessened. At a few places DRILLING 211 three crews of shovelers were required to remove the rock broken by two drilling attacks. This system is obviously ex- pensive because the cost of the extra shovelers must be charged against a footage but slightly, if indeed at all, increased by their efforts, and it entails, for two of the three shifts, the disadvantage of simultaneous work just mentioned; it is therefore not desir- able. When it must be resorted to it. may usually be taken as an indication that a change which would permit its discontinuance should be made either in the length of the holes drilled and blasted or in some of the other methods of work. The consensus of usage at tunnels and adits where the best results in driving have been achieved, both in this country and abroad, leads to the conclusion, however, that the three- shift system of attack is the most desirable. This method has a number of opponents who charge against it four chief disad- vantages: (i) that time is lost on the part of the drill men in getting the machines set up and in operation; (2) that the greater number of men crowded in the restricted space of the heading are in one another's way, and therefore unable to work to the best advantage; (3) that the men must be paid for time wasted in waiting for the smoke and gases produced in blasting to be cleared from the heading; (4) that the system makes no provision for delays due to adverse conditions. As will be pointed out shortly, the time consumed in setting the machines up can be made negligible by the use of suitable methods of mounting and by properly directing and blasting the round of holes. A certain amount of crowding is, of course, unavoidable, but it is more than offset by the gain in efi&ciency from the various incentives which can result only from the three-shift method. To begin with, the shovelers have constantly before them the necessity of removing the waste rock before the drillers have finished their work, and are therefore unconsciously speeded up by the competition. At the same time the drill men endeavor to have their holes finished by the time the tunnel is cleared in order that no delay may be attributed directly to them. And both crews are inspired to better work by the knowledge that a competing shift is to follow immediately 212 MODERN TUNNELING upon their heels, taking their places and performing similar work. Then, too, after the holes are drilled the extra men from the shoveling crew are of great assistance in taking down the machines and removing them, together with the mountings, hose, tools, and other articles that must be taken to a place of safety during blasting. As to the time wasted in clearing the tunnel of smoke, if it is properly and adequately equipped with ventilating apparatus this operation should require Httle more than fifteen minutes — just long enough for the men to eat their lunches, which time would have to be lost at any rate. Delays of course cannot always be prevented, but the men are encour- aged by rivalry to reduce these to the minimum, knowing that their work is to be compared with that of the shift to follow. These answers to the various objections are in no sense theories, but are deductions from actual observation and a study of con- ditions as they existed at tunnels and adits where some of the most efficient work in this country was being performed. The ideal results of the three-shift method, to be sure, are obtained only through perfected organization and good man- agement, but they utterly disprove the contention that efficient work is not possible under those conditions. That it is capable of the most rapid progress has never been gainsaid, and with proper handling the actual cost of excavation per tunnel-foot need be but little if at all greater than with other methods ; while, as has been shown, in most cases the system affording greater speed is within limits ultimately the more economical one. For these reasons, unless the conditions are indeed exceptional, the employment of three drilling shifts per day is recommended, and the discussion of other phases of tunnehng methods which follow will, unless otherwise noted, be predicated upon the assumption that three drilHng shifts are being employed. MOUNTING American tunnel practice is almost equally divided between the horizontal-bar and the vertical-column methods of drill mounting. The former consists essentially of an iron pipe, 4 to 6 inches in diameter, a Httle shorter than the average width I DRILLING 213 of the heading, and provided with a solid head at one end and a jackscrew with a capstan head at the other. The latter, which is rarely employed with more than two driUing attacks per day, is usually provided with a yoke and two jackscrews at one end, and its length is somewhat less than the height rather than the width of the heading. In several notable European tunnels a drill carriage was employed, however, so that a discussion of this method of drill mounting should not be omitted. The system employed with horizontal cross-bar method of mounting rock drills can perhaps be best illustrated by a descrip- tion of the procedure at the Laramie-Poudre tunnel. As soon after the blasting as ventilation permitted (ordinarily ten to fifteen minutes), the workmen returned to the face from a posi- tion of safety 1,500 to 2,000 feet away, bringing with them an ordinary tunnel car containing the cross-bar, drilling machines, tools, hose, etc. The three drillers, with the assistance of the foreman, first removed any loose rocks from the roof or walls which might fall later and possibly cause injury. This accomplished, they next cleared a space in the top of the rock pile, for two or three feet back from the face of the tunnel and perhaps four or five feet from the roof, in order that they might have room to work when drilling. Because of methods of blasting especially employed for this purpose, the rock pile usually occupied but a small part of this space, so that ordinarily but little work was required to clear it out. In the mean time, the helpers were expected to unload the bar and machines from the car, placing them on the rock pile conveniently at hand, and to connect the hose to the air and water mains. As soon as a proper space was cleared out, the bar was picked up by the drillers and helpers and held in position transversely across the tunnel at a measured distance from the face and roof, as directed by the foreman, where it was blocked, wedged, and finally screwed as tightly as possible in place. The drill men then placed the machines upon the bar and started drilHng as soon as the helpers completed connecting the hose to the drills. The necessary holes having been drilled from this position of the bar, and the waste rock having been removed in the mean 214 MODERN TUNNELING time by the shovelers (an operation which was carried on simul- taneously with drilling and which ordinarily was accomplished before the drillers had finished), the machines were taken off, the bar was lowered and set up again about eighteen to twenty- four inches from the floor, the drills were replaced, and one or two holes were drilled by each machine from this position of the bar. The machines and the bar were then placed in a tunnel car and removed from the heading during the blasting. This method, sometimes slightly modified, was used at several other tunnels and adits with almost equally good results. The procedure with the vertical-column method of mounting is similar to this in some respects, but there are also some im- portant distinctions aside from that of upright position. Owing to the vibration produced by the drills, neither method of mounting will give satisfaction unless the bar is firmly jacked against solid rock. The amount of vibration is intensified and the need of a substantial foundation is much greater in the case of the vertical column, because the drills are usually mounted on cross-arms projecting from the columns at right angles, thus affording a leverage for any movement of the drill. It is therefore necessary to remove all of the waste rock from the space immediately in front of the face of the tunnel prior to drilHng in order that the foot of the column may rest upon the soKd floor, which, at the two or three tunnels where this method was employed with the three-shift system, caused considerable delay even under normal conditions. But in the majority of places where this method of mounting was employed not more than two drilKng attacks were attempted per day, and the extra work of clearing away was performed by the crew of shovelers before the drillers started work. The best results with the carriage mounting for drills were obtained during the construction of the Loetschberg tunnel through the Bernese Alps. In the first type of carriage em- ployed there, the horizontal bar carrying the drills was mounted at the end of a steel beam which was pivoted to a truck and counterbalanced at the other end by a heavy weight. Before this carriage could be brought sufficiently near to the face, I DRILLING 215 even with the long beam, for the cross-bar to be jacked in posi- tion, it was necessary to clear quite a large passageway through the center of the rock pile down to the floor. In doing this, part of the material was carried away, and the remainder piled on either side of the tunnel to be carried away during driUing. When the passage was finished, however, the carriage, with the cross-bar and drills mounted upon it and extending longitudinally, was quickly rolled to the face, the bar swung around and jacked into position, and the drills were at once started to work. This carriage was superseded by one which abohshed the counterbalanced beam and carried the drill bar directly upon a short post mounted on the truck. With this device practically all of the broken rock had to be removed from the heading before the carriage was brought to the face, after which, however, the drills started promptly at work. One of the most important factors to be considered in choosing a method of mounting for tunnel work is the time required to get the drills in operation after blasting, including not only the actual time employed in setting up the necessary apparatus, but also the time consumed in the preparatory work of clearing away debris. The time spent in waiting for the smoke to clear is of course independent of the method of mounting, and can therefore be ignored in this connection. With the horizontal- bar system used at the Laramie-Poudre tunnel, the time normally employed in mucking back was rarely more than fifteen to twenty minutes. Jacking the bar in place occupied from five to ten minutes, and attaching the drills and making the water and air connections usually required from ten to fifteen minutes. The entire operation thus consumed under ordinary conditions from thirty to forty-five minutes, but it was not at all unusual, where circumstances were favorable, for the drills to be in operation within twenty or twenty-five minutes from the time the drill men reached the heading. At other tunnels and adits using this system the time required for similar work was reported as from thirty to sixty minutes. Owing to the much greater amount of material to be cleared out when the vertical-column 216 MODERN TUNNELING method is employed, the time consumed in getting the drills in position to start work at adits and tunniels where the three- shift system was used ordinarily ranged from two and a half to four hours, and even under the most favorable circumstances was rarely less than two hours. The time spent in the Loetsch- berg tunnel in removing the waste rock was approximately one and a half hours with the first type of carriage used and from one and a half to three hours with the later model; but in order to accompHsh this, nearly twice as many men were employed at the work as are usually found in American tunnel headings. After the Loetschberg tunnel was cleared of the necessary amount of debris, however, the machines could ordinarily be started in from five to ten minutes. Aside from the question of the time consumed in clearing, the amount of waste to be removed has another bearing on the problem of choosing a mounting. In order that there may be no delay in getting the drills at work, usually the attempt is not made to remove the waste rock entirely from the heading before the mountings are set up, much of it being merely shoveled to one side and removed later. This prehminary work is often performed by the drill men, especially with the three-shift system ; and where (as in the case of the vertical-column method) there is a great deal of it to be done, by the time the men have the machines set up and are ready to start drilling they are pretty well tired out and consequently cannot work so rapidly and efficiently in drilHng the required holes. Even if the work is performed by the regular shoveKng crew, these men certainly are not stimulated by the knowledge that they are performing dead work and that every shovelful handled in clearing back must be moved again later. This disadvantage obtains not only in the three-shift system, but in many cases in which two shifts are employed, and the shoveling crew start ahead of the drill men and commence work clearing away the face for a vertical column set-up. The horizontal-bar and, to a lesser degree, the drill-carriage methods have the advantage of requiring a much smaller proportion of duplicated work. The adaptabihty of the mounting for the work required of DRILLING 217 it after the drills are in operation is another factor to be reckoned with. The advocates of the vertical-column method claim that it enables the holes to be placed to better advantage, and this is quite truly the case where piston drills are employed. But hammer drills mounted on a horizontal bar can place the holes just as effectively, if not more so. But with either type of machine the drill carriage is badly handicapped. It was discovered with those used in the Loetschberg tunnel — and the same disadvantage was experienced at an adit in this country where a similar drill carriage was tried and soon abandoned — that it was impossible to point the inclined holes in such a way as to secure the maximum efficiency from the explosive used. Therefore, in order to make the holes break to the bottom it was necessary to use heavier charges of explosive, and the holes were not drilled as deeply as they might otherwise have been. The shallower holes made it necessary to spend a greater per- centage of the day's labor in the unproductive preparatory work of setting up and tearing down the drills, and increased the opportunities for delays in blasting. Then, too, it is impossible with one set-up of a horizontal bar, such as was used in the carriage method of mounting, to make the holes near the bottom of the tunnel sufficiently horizontal to secure an even floor, necessitating trimming and causing trouble in maintaining the proper tunnel grade. The fact must not be overlooked, however, that with the carriage method drills are subject to less wear and tear because they are kept on the bar continually and are not thrown around on the floor and muck-pile. When this is permitted the drills are apt to become filled with sand, grit, etc., and because of friction and abrasion, the cost of repairs is increased. Nor should the facihty in changing to a new hole possessed by the horizontal bar and the drill carriage be disregarded. When these methods of mounting are employed, all that is necessary in starting a new hole is to slide the drill along the bar and clamp it in place, but with the vertical column not only the machine, but the cross-bar as well, requires adjusting; since the adjustment is a vertical instead of a horizontal one, the entire 218 MODERN TUNNELING weight of both drill and cross-arm must be lifted or sustained at nearly every change. Taking, then, all of these factors into consideration, the horizontal bar proves to be the method of mounting drills best adapted for tunnel work. Its use enables the drills to be put in operation with the least loss of time and by the smallest number of men. It requires the rehandHng of the minimum amount of waste rock, §o that the drill men are not fatigued before they start drilling or the shovelers disheartened by dead work. It permits directing the holes in such a way that the maximum strength of the explosive is utilized, drilling deeply so that too great a portion of the time need not be spent in preparatory work, and placing the holes to insure the breaking of the roof and floor smoothly and at the desired grade. It is especially adapted for use with the more rapid-driUing hammer machines and lends itself readily to removal when necessary. In common with the vertical type it is subject to the danger of allowing grit to become lodged in the machines, but this can be partially prevented by care in handling. These considerations render the use of the horizontal bar highly desirable where an efficient method of mounting drills for tunnel work is desired. NUMBER OF HOLES Any determination of the proper number of holes to be used in driving a tunnel or adit of a given size is dependent upon several factors. A large number of holes in which a greater charge of explosive may be placed expedite the operations of driving, because the heavier blast tends to hurl the rock farther away from the face, and thus not only saves time in setting up the machines, but also gives the shovelers more room and enables them to work to better advantage on more widely scattered material. But, at the same time, holes that are not strictly a necessity entail an extra expense not only for the explosive used in them, but also for the time required in drilhng. This is especially true in those cases in which the drilling work requires more time than the operation of removing the rock, and hence any extra holes would delay both crews. If the proper DRILLING 219 O\00 lO •-I CO O lo o t^ T*-lO lO '+ rO - ^-3 03 03 o'^'-"-' ^^-^^i:^ 220 MODERN TUNNELING > a 03 cti o 2 c a'Z! i; -2 OS DRILLING 221 number of holes is being used, the major portion of the rock should be broken into fragments small enough to be shoveled readily, although an occasional boulder, because of the relaxa- tion it affords the workman from the steady grind of shovehng, is said to expedite rather than retard the speed with which the spoil can be loaded into the tunnel cars. The central factor and starting point, however, in a just determination of this question is undoubtedly the physical character of the rock being penetrated, which is never twice aUke in different locahties, and it is generally necessary to experi- ment at first in order to discover what number of holes will indeed produce the best results. Generally speaking, igneous rocks require more holes than sedimentary rocks, but there are wide divergences in both classes. The holes must be more closely spaced for a tough rock that is close-grained and massive than for one that is brittle and easily shattered, even though it may be harder and more difficult to drill. Bedding or joint planes or joint cracks are of great assistance, and a rock in which they occur will be more easily broken and hence require fewer holes. The preceding table shows the number of drill holes used in American tunnels penetrating different classes of rock. DIRECTION OF HOLES Chiefly because of the great influence of local conditions, the arrangement of drill holes is rarely identical at any two tunneling projects. For reasons to be explained later, however, it is cus- tomary to drill a part of the holes (called the ''cut" or "cut holes") in such a manner that when blasted they will first remove a core of rock from the solid face of the heading, thus decreasing the work to be done by the remaining holes. Practically all of the various means of arranging drill holes in the headings of American tunnels may be summarized as follows into three main types, according to the kind of cut employed. The wedge or ''V" cut is the one most commonly employed in tunneling operations in this country. It consists essentially of several pairs of holes directed toward each other from opposite sides of the heading in such a manner that when properly charged 222 MODERN TUNNELING and exploded they will break out a wedge-shaped core of rock usually extending from the roof to the floor of the tunnel. Figure 58 shows a typical wedge-cut round similar to the one employed in driving the Buffalo Water tunnel. Holes numbered i to 8 comprise the cut and were blasted simultaneously by electricity, while 9 to 14 are the side holes, and were next fired together, and 15 to 18 are the back or dry holes and were exploded last. Such a round must necessarily be changed somewhat where the heading is arched or semicircular. Figure 59 illustrates such a round, similar to those used in driving the heading of the large siphons on the Catskill Aqueduct. In this case holes i to 6, comprising the cut, were blasted together, followed by holes 7 to 12, which were called relievers, and finally by 13 to 22, which were called trimming holes. Either vertical columns, as was the case in the two examples just cited, or a horizontal bar may be used to mount the machines when drilling this type of round, but where the majority of the holes are to be drilled from one position of a horizontal bar the location of the holes must , necessarily be somewhat modified, although the general arrangement still remains a wedge-cut round. Figure 60 shows such an arrangement, similar to the one em-ployed at the Laramie-Poudre tunnel. Holes Nos. i and 2 were called short-cut holes, Nos. 3 to 6 long cuts, Nos. 7, 8, 9, 10, 19, and 20 relievers, 11 to 14 sides, 15 to 18 backs, and Nos. 21 to 23 lifters, the numbering indicating the order of blasting. The lifters, and two relievers (Nos. 19 and 20) which were used only in hard ground, were the only holes drilled from the lower position of the bar. Three machines were employed in drilling this round, and the following table (page 224) shows the holes drilled by each and the order of drilling (lettering the machines A, B, and C from left to right when facing the heading). A somewhat similar round was used with a horizontal bar at the Rawley tunnel, and there are, of course, many other variations of the V-cut arrangement of holes, but these figures illustrate the principles underlying the more common ones employed in tunnels and adits in this country. I Fig. 58. Wedge-cut round of holes. Fig. 59. Modified wedge-cut round for arched heading. Fig. 60. Wedge-cut round drilled from a horizontal bar. 224 MODERN TUNNELING ORDER OF DRILLING FOR EACH MACHINE AT LARAMIE-POUDRE TUNNEL Machine A Drill-hole numbered Machine B Drill-hole numbered Machine C Drill-hole numbered i ' O 2 1 3 a 5 a 7 17 II 5 13 7 I 19 I 2 3 4 5 l6 10 15 9 3 I 2 3 4 5 6 7 i8 12 6 14 8 2 20 Lower position 00 22 6 21 8 23 The second general, type of cut frequently employed will be designated as the pyramid cut, consisting usually of four cut holes drilled in such a manner that they meet, or nearly meet, at or near a common point — generally near the axis of the tunnel — and when properly blasted they remove a more or less pyra- midal core. Figure 6i shows a round of this type similar to the one employed at the Yak tunnel, in which the cut holes numbered I were blasted simultaneously, followed by the remaining holes in the order indicated. In most of the instances observed by the authors, the pyramid cut has been employed with vertical col' umns, but it can be drilled just as efficiently with the horizontal bar by drilHng two or possibly three holes with each machine from the lower set up. Figure 62 shows such a round. The third type is the bottom or draw cut which was employed at several places visited, the one at the Carter tunnel illustrated in Figure 63 being typical. The holes were blasted in the order indicated, Nos. i to 3 comprising the cut. Fig. 6] Pyramid-cut round of holes. Fig. 62. Pyramid-cut round for use with horizontal bar mounting. 226 MODERN TUNNELING It can easily be proved theoretically that where a bore hole is drilled in a homogeneous mass of rock the maximum efficiency can be obtained from a suitable charge of explosive placed in it when the line of least resistance (by which is meant the shortest distance from the charge to a free surface of the rock) is at right angles to the axis of the bore hole, and that the minimum efficiency will be obtained when the two are coincident. And practically, although a homogeneous rock is a rarity and hence the actual results will be influenced quantitatively somewhat by the various features of rock texture such as joints, cracks, fault fissures, bedding planes, etc., the results have been found to agree in the main with the theoretical deductions. It is obvious, therefore, that in the heading of a tunnel or adit where but one free face can be obtained, it is impossible to drill and blast a single hole in such a manner that the maximum efficiency can be obtained from it. But by drilling a number of holes arranged according to any of the preceding systems, and blasting the cut first so as to create more free surface, much better results can be obtained from the holes which remain. It is for this reason that the position and direction of the holes comprising the cut are generally considered the most important feature of the work, the spacing of the remaining holes being admittedly merely a question of having them sufficiently close together to break the rock into fragments of the required size for facile handling. When the wedge or V-cut is employed, the several pairs of holes should be placed close enough together for them to be of some mutual assistance. This is especially true when the entire cut is exploded simultaneously. What this distance shall be is controlled almost entirely (as in the determination of the proper number of holes) by the character of the rock, its tex- ture, toughness, the presence of cracks and bedding planes, etc. Its determination is often made by the foreman in charge, and if he is a man of wide experience, satisfactory results may follow; but the general efficiency of the work will often be increased greatly if experiments are made at the outset to determine just what combination will give the best results for the particular I DRILLING 227 rock being encountered. It follows, of course, that such experi- ments should be repeated whenever a marked change in the nature of the rock is observed. In order that the line of least resistance may approximate as closely as possible the perpendicular to the axis of the drill hole, the angle between opposite holes in the cut should be as large as can be obtained with any given depth of round. From this it follows that the drill holes should start as near as possible to the opposite sides of the heading; but obviously the full width of the heading cannot be utilized because provision must be made for the feed screw and crank of the drill, which usually extend three to four feet from the face. This works especially to the disadvantage of narrow headings, because in them a greater proportion of the actual width must be sacrificed for this purpose. But with broad headings the marked advantage of a wide angle is easily secured and possibly offers an explana- tion of the popularity of the wedge-cut system in such cases. Of even greater importance than the necessity of securing a wide angle between opposite holes is that of drilling them so that they meet, or at least bottom near enough to one another to be detonated simultaneously by the one first to explode. Owing to mechanical reasons, the width of the drill bit, and hence the size of the hole, must be decreased with each successive change of steel, and as a result the hole is necessarily smallest at its bottom end — the place where the explosive is most needed and where it is extremely desirable that the hole should be a*s large as possible. Omitting from consideration the expedient of chambering (that is, the enlargement of the bottom of the hole by the explosion of a small primary charge before loading it with the main portion of the explosive) which consumes en- tirely too much time to be considered for rapid tunnel driving, the defect can be overcome to a surprisingly large degree by the simple resort of connecting the drill holes, which concentrates the explosive at the point of the ''V." When fuse firing is employed, it is extremely essential that the holes be so directed that they are intercommunicating (or so nearly so that both holes will detonate together) or the desired effect will not be 228 MODERN TUNNELING gained, but when electric firing is employed direct connection, although very desirable, is not so absolutely essential. But in addition to the mere concentration of explosive thus secured, the combined efficiency of the two charges is much greater than when they are exploded separately. Assuming, again, that the holes are drilled in homogeneous rock and that they make equal angles with the shortest hne from their junction to the free face, if both are loaded with identical charges of explosive and detonated simultaneously, their maximum break- ing effect will be exerted along the resultant of their combined forces, which in this theoretical case coincides with the shortest distance to the free face (the line of least resistance). Practi- cally, of course, this will be somewhat modified; but it is a well-established fact that where the ground is tough and difficult to break, much better results are obtained when the cut holes are directed and drilled to intersect; although, unfortunately, this is not widely known, as evidenced by the too great number of cases observed in which no attempt was made to connect the cut holes. Practically the same conditions prevail with the pyramid cut. The number of holes comprising it may vary from three to six or even eight, according to the nature of the ground; and the proper number can best be determined by experiment. It is just as necessary to drill the holes with the widest possible angle between them, and it is even more essential that they meet in a common point, because one of the main advantages of this cut is the concentration of a greater amount of explosive at the narrow apex of the core of rock to be removed. All these advan- tages are thrown away if the charges of explosive in the different cut holes are not detonated simultaneously. The bottom cut, as it is usually drilled in practice, although it often enables the attainment of a wider angle between the axis of the drill hole and the line of least resistance, disregards entirely the important advantage to be obtained from connecting drill holes, and this circumstance, in the opinion of the authors, should be sufficient to prevent its use under any but exceptional condi- tions. For mine adits, however, whose excavation must of neces- I DRILLING 229 sity provide sufficient head room but whose lateral extent is limited, in which it would be impracticable, if indeed possible, because of the narrowness of the heading, to drill an effective wedge, or a pyramid-cut round, the bottom cut furnishes the only solution of the difficulty. In this event it is recommended that the cut holes be drilled from as near the top of the heading as possible, and directed in such a manner that they will connect with holes that are usually considered Kfters, and that both be detonated together. DEPTH OF HOLES During the past four or five years there has been some differ- ence of opinion among students of the problems of tunnel driving as to the proper depth for drill holes in tunnel headings. In view of some of the remarkable results attained in driving the Simplon and Loetschberg tunnels, where, as is admitted by every one, the holes were much shallower than those in American practice, the question has been raised whether the holes in tunnels of this country are not drilled too deep. Numerous tables have been prepared in support of this argument, in which it appears that at most of the European tunnels the progress is much greater (in some cases more than double) than that of tunnels in America. But at the same time, consideration is not always given the fact that in many instances these records are in their nature in no wise comparable; for in Europe, at the majority of tunnels thus cited, the work was conducted throughout the entire twenty-four hours of each day, while in America in many instances but two (and indeed in some only one) shifts were employed daily. Then again, the nature of the rock exerts an all-important influence upon progress, and in many cases this has been to the advantage of the European tunnels. A notable example of the influence of the rock encountered is found at the Loetschberg tunnel, where the same methods and practically the same equipment were employed at the different ends, the one at north end working in limestone, and the other in the south end in gneiss and schist. The progress attained at the south end was much less than that of the north, and in some months the 230 MODERN TUNNELING progress in the north end was nearly double that of the south. Other considerations also, especially the amount of labor and the cost of driving, enter into the problem in such a manner as to make it impossible to say (when everything is taken into account) that the greater speed in European tunnels is due solely to the use of extremely shallow holes. That in many instances the holes in American tunnel headings are too deep, however, is equally impossible of denial, and for these reasons a discussion of the factors which enter into the determination of the proper depth of holes is extremely desirable. One of the chief advantages arising from the use of shallow rounds is (when the holes are properly directed) the increased efficiency obtainable from a given charge of explosive; for, since the width of the heading is for all practical purposes constant, the angle between the line of least resistance and the axis of the bore-hole becomes a function of the depth of round, the width of the angle increasing with shallow holes. This advantage obtains especially with the wedge cut and with the pyramid cut, and it should be a fundamental consideration with the bottom- cut method of drilling the holes. Strangely enough, however, in the Loetschberg and the Simplon tunnels, which are so often cited as examples of the ''highly desirable" European practice of using shallow holes, this advantage was almost, if not entirely, thrown away, because the holes were drilled in vertical rows and were nearly parallel to the bore of the tunnel. In such a case the line of least resistance and the axis of the bore-hole are nearly coincident — a condition which results in the production of the least possible efficiency from the charge of explosive ; and it cannot be gainsaid even by the advocates of this method that a much greater quantity of explosive than is usual in American practice was required to break the same amount of rock. If to this is added the fact that such a system utterly ignores the advantage to be obtained from connected drill holes by the con- centration of explosive at the apex of the core of rock to be removed, there is strong ground for rational suspicion that the extreme shallowness of the holes used in these tunnels was adopted from necessity rather than from desirability; because with this DRILLING 231 system of drilling and directing the holes the difficulty of blasting out the rock with deeper rounds could not fail to be greatly increased. Among other advantages of the use of reasonably shallow holes may be mentioned the fact that such a method allows that the holes be of larger diameter at their further end, increasing their capacity for explosive and enabhng its concentration at the point where it is most needed. This is one of the chief factors which makes even possible the European practice of employing extremely shallow holes, but it can hardly be denied that in this case much more effective results in blasting might be accom- plished by a change in the direction of the cut-holes. Besides, since, in America at least, the holes are rarely charged with explosive to their full extent, the mass of rock between the ends of the charges of explosive in the dift'erent holes and the free face of the heading (which can be considered as a measure of the amount of resistance to be overcome) is not so great with the shallow holes. This fact, or the customary use of relatively heavier charges in shallow holes, may explain, perhaps, why in such cases the major portion of the rock is usually thrown farther down the tunnel instead of being piled high immediately in front of the new face, with the double advantage of making it easier to load the rock and saving time in getting the drills mounted. It is fairly well established, also, that the rock tends to break into smaller fragments where shallow holes are em- ployed. And again, where deep holes are not employed the same care in starting them exactly at a given point is not required, nor is it necessary to direct them with such great accuracy — although, of course, the need of connecting the cut holes must not be overlooked. The principal and very serious disadvantage in using the shallow-hole round, on the other hand, and one that it is impos- sible to avoid, is the fact that in order to secure the same daily advance a proportionately greater number of drilHng attacks must be made. This results in a waste of time in driUing; for it is possible under ordinary circumstances to drill one hole of a given depth more rapidly than two holes of the same aggregate footage because of the time lost in changing to a new position, 232 MODERN TUNNELING Starting, etc. But even granting that the difference in drilling time (perhaps because it is too small, or because in either case the drilling can be completed before the heading can be cleared of debris) is not an appreciable factor, each extra drilling attack required to secure the same progress causes a correspond- ing loss of time in loading and blasting the holes, in waiting for the smoke and gases to be removed, in clearing the debris from immediately in front of the face, and in setting up the drills, all of which is ordinarily dead work and cannot be avoided. This was seriously felt at the Loetschberg tunnel, because in the endeavor to compensate for it, it was necessary to employ four drills in the heading (6 feet x lo feet) ; and as a result the holes had to be drilled nearly straight, with disadvantages already described, because otherwise the drills in the center interfered seriously with the operation of those at the side. On the other hand, where the holes are too deep, as is some- times the case in America, the angle between the cut-holes may be so narrow and the mass of rock in front of the charge of explosive may be so great that it will be impossible for the cuts to break bottom on the first blast and thus the entire round is spoiled. The usual remedy in such cases is to blast the cuts separately and not to fire the remainder of the round until it has been ascertained by inspection that the proper depth has been reached by the cut-holes. A certain amount of delay can- not be avoided when this method is employed, even if the holes break to the end, for it is never possible to return to the breast for such inspection immediately after the cuts have been deton- ated. But when the cut-holes fail to break, the delay is greatly increased because the remaining portions must be cleaned out, reloaded, and fired, with an additional delay in waiting for the smoke to clear. This system was used at one of the Colorado tunnels, which at the time of first examination was being driven through some very tough rock, employing a round of holes slightly deeper than the average width of the heading. Holes of this depth had given satisfactory results in the somewhat more frangible ground previously penetrated, the round being drilled and blasted in an DRILLING 233 eight-hour shift without difficulty; but upon striking the harder rock it became necessary to blast the cuts separately, and more often than not to reload and shoot them for the second and occasionally for the third time, the cycle being lengthened to about ten hours, while several times at least fourteen hours were needed. If three drilling shifts had been employed at the time, such a condition would have been fatal; but since but two attacks were being made the diflerence was not so noticeable, though even in this case the cost of the extra explosives required and the overtime wages of the men added a considerable amount to the expense of the tunnel work. Shortly after the first examination of this tunnel by the authors, however, the depth of the rounds was reduced to about 75 per cent, of the width of the heading. This made it unnecessary to load and shoot the cuts separately, and instead of getting two seven-and-one-half- foot rounds in from twenty to twenty- two hours, by working three eight-hour shifts it was possible to drill and blast four, and sometimes five, live-foot rounds per day, thus increasing the daily tunnel progress from fifteen to nearly twenty-three feet with but a very small extra cost for labor. The consumption of explosive which was a very considerable item with the old system was also decreased fully 25 per cent., and the total cost of the tunnel per foot was greatly reduced. The disadvantage of too deep holes was strikingly brought out in the construction of the Laramie-Poudre tunnel. During the first part of the work a ten-foot round was drilled in a head- ing 9>^ feet wide, but the round was later changed to one of 7 feet in depth with much better results. To be more specific, during the seven months from April i, 1910, to October 31, 1910, at the east end of the tunnel, 3,171 feet were driven, an average of 453 feet per month, using a ten-foot round; but during the next 84/5 months, from November i, 1910, to July 24, 191 1, when the tunnel holed through, 4,798 feet were driven, or an average of 545 feet, with a seven-foot round. This is an increase of over 20 per cent., in spite of the fact that the higher speed was made when the work was at a greater distance from the portal; and, since there was no essential change in method, 234 MODERN TUNNELING equipment, or in the character of the rock penetrated, it is attrib- utable solely to the use of shallower holes. When the ten-foot holes were employed to secure an advancement of S}4 to 9 feet, it was unusual to be able to drill and blast more than two rounds in twenty-four hours, and oftentimes not so many, as the aver- age of 14^ feet daily testifies; but with the seven-foot round not only could three attacks be made, advancing on an average 6}4 feet per attack, but a comfortable margin of time was left to provide for delays and under favorable conditions this extra time meant extra footage. Thus in March, 191 1, the American hard-rock record of 653 feet, or over twenty-one feet per day, was established. This advantage of being able to complete an entire cycle of operations during a single shift should be given the weight in the problem it deserves. If crews of men could be found who would work as well without rivalry and without special incentive to push the work, it might be perfectly feasible to choose a depth of round that would require ten, or even twelve, hours to put it in; but under the present working conditions, where it is necessary to have some accurate measure of the work performed by each crew, a round is required for which the entire cycle can be completed during a single shift, with a sufhcient margin of safety to provide for any ordinary delay. It is, of course, impossible to set any definite standard or guide for the proper depth of hole which will be applicable to all cases. There are too many variables influencing the result. The proper depth can only be and must be determined by experi- ment in each individual case. But from an extended examination of American practice, investigating carefully the results obtained from the methods employed, from a careful analysis of European practice as far as could be found in published accounts, and from a study of all the available modern authorities, the authors are of the opinion that for the majority of cases the proper depth of drill-hole, the one which most equitably balances the advantages and disadvantages inseparable from the problem will be found after careful experiment to be a depth from 60 to 80 per cent, of the width of the tunnel heading. The following table gives an analysis of American practice in this respect: DRILLING 235 .oo 00 o 00 vc r^ lo iDvo o t^ t^oo OM^ r^ lo^o ovvo oo o o lovo o vo vo o -^ >-0 OJ3 1^00 00 O 00 \0 t^ lO lO^ Gn l>> t>.00 ON t~» t>" lO^ ONVO 00 OvO lOiOO^vOO •^ Sf^ vr 3 o ^ X X X X 5 OOO OMOoOOOOOt^OOOOOONOOOOOvOQOOl^ONOlt^ lOO 04 vO t^vO »o ^ lO lO rf Tj- Th -rt- lO lOO O O) ON O) 00 00 lO »O00 On rO On r^ ON O O OnnO t^OO O t>. 00 r^ 00 00 00 00 t^vo 00 ^ i-i \o 00 00 on t>. r^X) « o on r^ on no r^vo o r^vo oo t^ a; e bjO O :> o ppoJOJiDCajpcjpS'c 13 T3 TD bjObiObjObX)bjOO O bi0b.obflb)0tyo5 O 5 5 © biObiOtuObiObjOO biObJObobiOO _, 3 ?5 c 3 O 2 rt o 3 03 OS §^^S^?t2P^S3 OJ 05 2 J^, i- J= P-f. ^.2 >:^ o > - __ QJ r; ^ OS >-. -t-J Ij Jj "•-' ^ CHAPTER XII BLASTING AMMUNITION To be suitable for use in tunnel work, as distinguished from surface blasting operations, an explosive should not produce any great amount of poisonous gases and should not easily, if at all, be affected by moisture. In common with other usages, a sub- stance is required here that is stable in composition and not rapidly deteriorated by frequent changes of temperature or other causes; it must not, as, for example, is the case with liquid nitroglycerine, be so sensitive to shock that safe transportation and handling are wellnigh impossible. Although under some circumstances, especially in tunnels that are not wet, an explo- sive called ammonia dynamite can be and is employed on rare occasions, the one which best fulfills the necessary requirements and the one which is almost universally used in tunnel work is known as gelatine dynamite. Gelatine dynamite is a combination of a certain amount of blasting gelatine (varying according to the strength desired) and a suitable absorbent. The former is made by adding a small percentage of gun-cotton (nitrocellulose) to liquid nitroglycerin, thus producing a jelly-like mass that has greater explosive qual- ities than either of its constituents, but which is much less sen- sitive to shock than nitroglycerine. The absorbent is usually some combustible material (wood pulp is frequently employed) to which has been added a sufficient amount of sodium nitrate to supply the necessary oxygen for its combustion. By the use of such a combustible absorbent, instead of the inert one formerly employed with straight nitroglycerine dynamite, the gases gener- ated by the burning of the wood pulp add to the volume pro- duced by the detonation of the explosive constituent, and the extra heat generated in this combustion adds greatly to the 236 BLASTING 237 total intensity of the reaction. Ammonia dynamites, which are a somewhat more recent discovery, consist of a combina- tion of ammonium nitrate and nitroglycerine absorbed in a so- called ^'dope" similar to that just described. The following tables * show typical compositions of commercial samples of these two kinds of dynamite : GELATINE DYNAMITE Strength Ingredient 30% 35% 40% 50% 55% 60% 70% Nitroglycerine. . . 23.0 28.0 330 42.0 46.0 50.0 60.0 Nitro-cellulose . . 0.7 0.9 1.0 1-5 1-7 19 2.4 Sodium nitrate . . Combustible 62.3 58.1 52.0 45-5 42.3 38.1 29.6 materialsf .... Calcium 13 12.0 130 10. 9.0 9.0 7.0 carbonate. . . . I.O 1.0 1.0 1.0 1.0 1.0 1.0 t Wood pulp used with 60 and 70 per cent, strength; sulphur, flour, wood pulp, and sometimes resin used in other grades. AMMONIA DYNAMITE Ingredient Strength 30% 40% 50% 6o< 15 20 22 27 15 15 20 25 51 48 42 36 18 16 15 I I I ^ Nitroglycerine , Ammonium nitrate Sodium nitrate Combustible materialsj Calcium carbonate or zinc oxide . 35 30 24 10 I t Wood pulp, flour, and sulphur. For further discussion of the nature and composition of explosives, which is hardly within the province of this book, the reader is referred to various pubHcations of the Bureau of Mines; they may be had upon appHcation to the Director, Bureau of Mines, Washington, D. C. The harmful gases usually resulting from dynamite are carbon dioxide and carbon monoxide. Although the former will * From a paper by C. T. Hall before American Institute Chemical Engi- neers, Washington, D. C. Meeting December 20, 191 1. 238 MODERN TUNNELING not support respiration, and when present in sufficient amount may cause unconsciousness and even death from strangulation, it has no very injurious effects when sufficiently diluted. The latter, however, is not only exceedingly dangerous, but its effects are also cumulative; indeed if air containing even a very small amount of it is breathed for any length of time, serious and often fatal results will follow. The fact that gelatine dynamite (with the possible exception of ammonia dynamite, which approaches it very closely in this respect) produces under proper conditions the least amount of carbon monoxide is one of its chief advantages for use in tunnel work. Even with this explosive, however, if the cap is not strong enough to cause a complete detonation, and even more especially when the dynamite burns rather than explodes, much greater amounts of carbon monoxide are formed; in addition there are many other harmful gases produced, among which may be mentioned the dangerous peroxide of nitrogen and hydrogen sulphide, the former of which is especially virulent. The following table shows the results of tests conducted by the Bureau of Mines concerning the kind and amounts of gases produced by the detonation of samples of various kinds of commercial dynamites. In making the tests a charge of 200 grams (approximately 7 ounces) in the original wrapper was exploded in a Bichel pressure-bomb and the gaseous products retained and analyzed: GASEOUS PRODUCTS FROM EXPLOSIVES Elind of explosive §3 6^ s 0) C 1 m 40% straight nitro- glycerine dynamite. 60% straight nitro- glycerine dynamite. 40% strength gelatine dynamite 40% strength ^ am- monia dynamite. . . FFF black blasting powder (300 grs.). . 273 22.2 50.8 41.4 49-7 26.9 34-6 30 3-8 10.8 0.0 0.0 0.0 0.0 0.0 18.0 23.2 1.8 31 1.8 0.4 0.8 0.8 0.8 0.6 27.4 19.2 39-5 45-5 28.4 41 5-4 8.7 88.5 128.9 60.3 65.6 67.8 BLASTING 239 A further distinctive feature of gelatine dynamite, winning for it the advantage over ammonia dynamite for most tunnel work, consists in its practically waterproof quality, a condition largely due to the insolubility of the blasting gelatine which can be freely immersed in water with but Httle if any of it dis- solving. Ammonia dynamite, on the other hand, being hygro- scopic, has a great affinity for moisture and hence not only cannot be used in wet work (or even in damp work when it is necessary to spUt the original parafhned paper covering), but greater care must be used in selecting a dry place for storing it. Gelatine dynamite is somewhat less sensitive to direct shocks than other dynamites, and unUke them the sensitiveness does not increase with the strength; much stronger detonators must therefore be used even with the higher grades in order to insure complete detonation. This fact is often not sufficiently ap- preciated by practical mining men, many of whom are not aware of the greater ultimate economy obtainable if the more powerful, although somewhat higher-priced, detonators are used with gelatine dynamites. The strength of nitroglycerine dynamites as they are made to-day is generally rated according to the percentage of their nitroglycerine content, in spite of the fact that both the volume of gases and the temperature (and hence the disruptive force) are augmented somewhat by the combustion of the absorbent material. Although 40 per cent, is the strength most generally employed, they may be obtained in the following grades : 15, 17, 20, 25, 30, 33, 35, 40, 45, 50, 60, 70, 75, and 80 per cent. In the ammonia dynamites a portion of the nitroglycerine is re- placed by ammonia nitrate, but, as will be seen from the table on page 237, the rated strength of this dynamite is nearly the sum of the percentages of these two constituents. Ammonia dynamite is prepared in the same grades as nitroglycerine dynamite, between 25 and 60 per cent. Owing to the strength of the blasting gelatine being greater than either of its constitu- ents, the rated strength of gelatine dynamite is somewhat greater than the percentage of its explosive element. The usual grades of this dynamite correspond to those of nitroglycerine dynamite 240 MODERN TUNNELING between 2>5 and 80 per cent., but it may also be procured in '^loo per cent." strength. The proper grade for use at any particular tunnel must be determined solely by local conditions. Such widely divergent results are obtained at different locahties when using the same grade of explosive and in rock which, as far as can be deter- mined from its physical appearance and structure, is identical, that it is impossible to be dogmatic even with minute knowl- edge of local details. Generally speaking, however, a tough, close-grained, igneous rock will require a stronger explosive, while a sedimentary rock, or an igneous rock that has been altered and weathered, or perhaps shattered and broken, can be blasted just as effectively with a lower grade of dynamite. A notable example of the use of an extremely high-grade ex- plosive is that of the Roosevelt tunnel, where in the tough, close-grained. Pike's Peak granite "100 per cent." gelatine dynamite was required before satisfactory results were obtained. This is reported to have been the first "100 per cent." dynamite put to use in tunnel work. In all cases it is advisable to ex- periment at the beginning of the work with explosives of different strengths in order to determine which grade is best suited for the particular rock being penetrated, and it is, of course, obvious that similar experiments should be repeated whenever, owing perhaps to a change in the character of the rock, the dynamite used fails to give satisfactory results. The practice of loading the bottom portion of the hole with 80 and even 100 per cent, dynamite and using 40 or 60 per cent, in the remainder is not now uncommon, especially in tunnels and adits in the Western States. It has the advantage of pro- ducing a greater disruptive force at the bottom of the hole, where such force is most needed, and at the same time it reduces some- what the cost of explosives, especially when an excessive amount of lower-grade dynamite had hitherto been required. There is entailed, of course, the trouble of handhng two different kinds of dynamite, not only in the heading but in the thawing-house as well. Although in some cases where this procedure was tried the same results might possibly be achieved by the use of shorter BLASTING 241 rounds, an alteration in the type of cut, or some other change in method, still it is a very useful practice, especially for exceed- ingly hard, tough rock. The following table shows the grades of dynamite employed at various tunnels: DYNAMITE USED AT VARIOUS TUNNELS Kind Strength Remarks Carter Catskill Aqueduct: Rondout Wallkill Moodna Central Gold Links Gunnison Laramie- Poudre . . . Lausanne Los Angeles Aqueduct ; Little Lake Grapevine Elizabeth Lake , Lucania Marshall-Russell . Mission Newhouse Nisqually , Rawley . . Raymond . . . Roosevelt . . . Siwatch .... Snake Creek Stilwell Strawberry . , Utah Metals Yak Gelatine Gelatine Gelatine Gelatine Gelatine Gelatine Gelatine Gelatine Gelatine Gelatine Ammonia Gelatine Gelatine Gelatine Gelatine Gelatine Gelatine Gelatine Gelatine Gelatine Gelatine Gelatine Gelatine Gelatine Gelatine Gelatine 40 60 60 75 40 40 40 and 60 60 60 40 40 40 50 40 and 80 40 and 60 40 40 40 and 60 40 and 60 40, 60 and 100 40 40 40 40 40 and 60 40 Some 80% A small amount of 60% Mostly 60% Some 100% with the 60% in cut holes Some 25% and some 60% Some 60% and 75% gelatine Tried 60% & 70% also 80% also 100% with 40% in cut holes occasionally 60% in cut holes and lifters Some 35% and some 60% It is obviously impossible to make any set rule for the deter- mination of the proper amount of explosive to be employed in tunnel work, without special reference to given conditions. There are entirely too many variable factors, governed solely by local conditions, which control the fitness of quaHty and quantity, and 242 MODERN TUNNELING which cannot be foreseen. Various writers have derived from theoretical considerations formulas for the calculation of the proper charge of explosive for a blast hole, but the application of these rules is limited to other types of blasting, such as quarry- ing or general mining, and they are not suited to the practical and actual conditions of tunnel work. For this, the determi- nation of the proper amount of explosive is often left to the judgment of the foreman in charge, who, if he be widely ex- perienced, can often produce excellent results; but the proper amount can best be ascertained by a series of experiments in which the effects produced by different quantities of explosive are studied and compared. It is very essential, however, that the charge of explosive be large enough. If it is too small and the cut-holes fail to break bottom, or the rest of the holes do not blast out their full share of rock, it will be necessary to reload the remaining portion of them; this procedure not only requires fully as much explosive as if the holes had been properly charged in the first place, but also occasions a loss of time and footage, both of which are most expensive. For this reason, in a number of tunnels, it was customary to load the cut-holes nearly to the collar. Although this is perhaps extreme, as far as insuring that the cut-holes break bottom is concerned, the extra dynamite helps to shatter the rock in finer fragments, thus making it easier for the shovelers to handle. Also, since no tamping is usually employed in such cases, a certain amount of the explosive prob- ably acts in that capacity and increases the efficiency of the remainder of the charge. The very common practice of loading the lifters entirely full has a very different object in view — that of throwing the major portion of the debris some distance away from the new face of the heading, thus making it easier for the drill-men to get their machines at work promptly, and by scattering the rock over a greater area the shovelers can attack it to better advantage. Such a practice is highly to be commended. Data as to the exact amount of explosive actually employed in practice are difficult to obtain, chiefly because at many places BLASTING 243 an accurate record of powder consumption is not kept; but figures were secured wherever possible at the tunnels visited. At the Gunnison tunnel an average of nearly 30 pounds of 40 per cent, and 60 pounds of 60 per cent, gelatine dynamite were employed per round. This is equivalent to approximately 5.5 pounds per cubic yard excavated. In driving the south heading of the Elizabeth Lake tunnel, the average for 1909 was 32.09 pounds * of explosive per foot of tunnel, which is equivalent to 6 pounds per cubic yard. This figure, however, includes the dynamite used in trimming, hence it is somew^hat higher than the amount actually needed in driving. At the Rondout Siphon, 175 to 200 pounds per round were required to drive an average of 10 feet,t with a heading of approximately 120 square feet area — which is equivalent to 3.9 to 4.5 pounds per cubic yard of rock excavated. In advancing the heading of the Buffalo Water tunnel, 4.8 pounds of 60 per cent, dynamite were required per cubic yard. At the Laramie-Poudre tunnel, the powder consumption per cubic yard for March, 191 1, was 3.9 pounds; for April, 4.7 pounds, and for May, 4.9 pounds. The average on the Little Lake Division of the Los Angeles Aqueduct for May, 191 1, was 4.5 pounds per cubic yard. At the Wallkill Siphon the average powder con- sumption per cubic yard ranged from 4.3 to 4.6 pounds. At the Yonkers Siphon the powder consumption was approximately 4.5 pounds per cubic yard excavated. The figures for the explosive used in the Simplon and the Loetschberg tunnels are somewhat higher. At the Simplon tunnel the charge was 6.5 pounds per cubic yard,t while at the Loetschberg tunnel the charge per round to secure an average advance in the 6.5 by ten-foot heading of approximately 3.5 feet was 53 to 57 pounds. § This is equivalent to 6.5 to 7 pounds per cubic yard. * Mines and Minerals, September, 1910, p. 102: "The Elizabeth Lake Tunnel," C. W. Aston. 1; Engineering Record, January i, 1910, p. 26: "Progress on the Rondout Pressure Tunnel," J. P. Hogan. t Saunders, W. L., Trans. Am. Inst. Min. Eng., July, 191 1, p. 515. § Saunders, W. L., loc. cit. 244 MODERN TUNNELING The usual means of firing blasting charges, especially in tunnels and adits in the Western States, is by the use of a safety fuse. The term safety fuse originated from the fact that when properly used under working conditions this fuse burns at a uniform rate and does not flash or explode, as was often the case with the means employed for igniting blasting charges previous to its invention; but the term is somewhat misleading, because this fuse is not, nor has it ever seriously been claimed to be, safe for use in gaseous coal mines. The fuse used for tunnel work is universally of the waterproof type, composed of a core of gunpowder surrounded by various layers of waterproofing ma- terial. In one sample, examined by the Bureau of Mines, "the core consists of a powder train and one white cotton thread; the inner covering consists of ten hemp threads; the inner- middle covering consists of five fine cotton threads impregnated with an asphaltic composition; the middle covering and the middle-outer covering each consists of a f^-inch cotton tape impregnated with an asphaltic composition, and the outer cov- ering consists of a f^-inch cotton tape covered with whiting. Each covering of tape is wrapped in reverse order." * In other samples the hemp threads of the inner covering are replaced by cotton threads impregnated with sodium siK- cate; the inner middle covering is often omitted; the asphalt composition of the middle covering is replaced by gutta percha; the middle outer covering is also omitted, and intervowen cotton threads are substituted for tape in the outer covering. The weight of powder in different types of waterproof fuse varies from 50 to 220 grains per foot, the majority of which is finely granulated, and will pass through a 60-mesh sieve. Under ordinary conditions a safety-fuse burns at a uniform rate, with a variation rarely greater than 10 per cent., fast or slow. In European countries the normal rate is approximately thirty seconds per foot. According to tests conducted by the Bureau of Mines on fourteen samples of triple tape fuse pur- chased for the Isthmian Canal the average rate was determined * United States Bureau of Mines, Technical Paper 7, p. 7. BLASTING 245 ^^ ^^ ^^ >-i >-i rot^ lO OS 00 t>. 00 t^ 00 t^ II II II II . II II M rorc^ ^ c^r^^ cot^^ ^. a 6 Pi ^^d^-^.l £5t:"d*"^<=> [^idd^^.5 ^'^'^";;5,i >^^"{;5a >^'-5^5$ii fo"o "►-' "o 11 ^ o 00 vo >< 11 11 H^ o vo o_ 11 ^ ^^^^^00^ ^^^^^«>.^ ^^^r.^^^ ! Av. Max. = Min. = Range = Range fo Av. time Av. = Max. = Min. = Range = Range fo Time for Av. = Max. = Min. = Range = Range fo Av. time •a c ^. ...... :^. .... c :...... - o U 1 CCOO t-^ '^ O '^OO M r^vO \D\D ^-inch hose and a nozzle should be placed not less than 40 feet and not more than 100 feet from each building or group of buildings. Although most tunnels are themselves practically fireproof (except where timbered) , and hence underground fires in tunnel work are not common, it is, nevertheless, important even here to guard against the dangers of fire. Whenever underground fires do occur in tunnels, they usually start in some small way, either from candles or lamps being placed too near the posts or caps of a timber set, or from throwing a match or the coals from a pipe into a pile of rubbish, hay, or other combustible material which may in turn ignite the timbering. Although such fires can usually be extinguished at once and before any great damage or injury has resulted, if their presence is dis- covered soon enough and if means are at hand for that purpose, it is much better to prevent the ignition by obviating causes. Therefore, combustible rubbish should not be allowed to accumu- late in the tunnel and any supply of hay for the use of mules or horses underground should be carefully confined in a bin pro- SAFETY 315 vided for that purpose, while open lights or smoking should not be permitted in their neighborhood. Candles or torches should never be left burning near timbers, while the practice of wedging a lighted candle between two nails driven into a post should be cause for the instant dismissal of the guilty persons. Water Water under pressure is another source of danger in tunnel work, and men are hurt in jumping back to avoid the rocks and other debris often carried with it, or are perhaps buried under an accompanying rush of mud and sand. A good example of this may be found in the records of a foreign railway tunnel, where a cleft filled with water, sand, and gravel was encountered and the ensuing sudden and violent inburst of these materials filled up more than a mile of the tunnel in a very few minutes, burying twenty-five workmen and their tools beyond all hope of recovery. A somewhat similar occurrence in one of our American tunnels, although fortunately with less fatal results, was likewise due to water. The tunnel caved in at a point about 4,000 feet from the heading, but the men working there were warned in time to escape, although they had barely reached safety before the tunnel became entirely closed. When this happened, the mass of rock, composed chiefly of soft clay and running shale impervious to water, cut oft' the main flow in the tunnel, which was approximately 2,700 gallons per minute. As soon as the portion of the tunnel between the cave and the heading became filled with water, the full pressure of the head in the mountain over the tunnel was exerted against the dam, forcing it down the tunnel until the pressure was reheved. The additional length of the debris then offered greater resistance and remained stationary until the pressure had again accumu- lated enough to move it, and this process was repeated until 440 feet of tunnel had been filled. Several attempts were made at first to reheve the pressure by inserting a section of venti- lating pipe at the top of the dam; but after several men had narrowly escaped burial by the rush of mud as the dam moved forward, this scheme was abandoned and the tunnel was sealed 316 MODERN TUNNELING up by a concrete bulkhead, the men being protected by a tempor- ary bulkhead of wood during the construction of the permanent one. In driving through Hmestone and dolomite it is not unusual for a tunnel heading to tap immense caves filled with water, mud, and sand. In such cases the volume of the fluid mass flowing into the tunnel is determined by the size of the opening, while its velocity is proportionate to the head. Under a pressure of 300 or 400 feet the cutting action of the rock particles and sand carried by the water soon enlarges even a drill-hole to a size that permits the filling up of the heading in an incredibly short course of time. When a round of shots breaks into a cave of this kind, the heading and perhaps the completed tunnel for a distance of hundreds and sometimes even thousands of feet back from the face may be filled so fast that the escape of the workmen would be impossible if they were in the face. Fortunately, however, at the time of greatest danger, viz., shot firing, the men are always out of the heading. When an underground cave or reservoir filled with water, mud, sand, and loose rock is tapped in a tunnel heading one of two things* occurs : generally the cave or reservoir empties itself completely into the tunnel and, after the flow is over, the solid matter which the flood leaves behind can easily be shoveled up and hauled out; but it sometimes happens that the volume of solids is so great that the tunnel is completely choked up before the reservoir is emptied. In these cases, when the flow of water ceases, the men are usually set to work cleaning up the material with which the tunnel has been filled, but when this cleaning-up process advances sufficiently to weaken the dam which is holding back the flood, a new outburst occurs and, because the passage- ways have already been opened, the second outbreak is often more violent and dangerous than the first. If this operation were repeated often enough, the cave or reservoir would of course be drained and the heading be regained, but in many instances the operation of attempting to regain the heading has been found so dangerous that it has been abandoned and a curved tunnel put in to pass around the danger point. SAFETY 317 In the Cowenhoven tunnel, when the heading was in dolomite, caves of this kind, filled with water and dolomite sand, were fre- quently encountered, and it was no uncommon thing to have the tunnel completely filled for hundreds of feet back from the face after a round of shots. As soon as the water from the cave which had been tapped drained off, the mud and sand were easily loaded up and work in the face was resumed. On one occasion an immense cave of this kind was tapped by a drill-hole in a long cross-cut which was being driven from the tunnel to the Delia S. Mine, which, under the pressure and cutting action already described, enlarged so rapidly that the men fled from the face and, a few seconds after, the opening enlarged to a size which permitted the filling of the tunnel with such rapidity that the tunnel cars were hurled back and flattened against the posts. Several unsuccessful attempts were made to regain this face, which finally had to be bulkheaded and the tunnel run around it, as at the Loetschberg tunnel. In the 1,200-foot level of the Free Silver mine, which was likewise run through dolomite, numerous caves were also en- countered, but fortunately, while they must have extended to great heights, their horizontal cross-section was very much less than that of the caves 1,200 feet above. When these reservoirs were tapped with a drill-hole the water would spout out wdth such velocity that it was impossible to stay in the face, and in a short time the opening would be worn to a size which some- times increased the amount of water to be handled by the pumps to 3,000 and even 4,000 gallons per minute. At first the noise from the inrushing volume of water was exceedingly terrifying to the men, but "familiarity breeds contempt," and in a short time whenever a cave of this kind was tapped the men simply joined hands to assist each other in maintaining their footing and waded back with the torrent the same as they would do in crossing an extremely rapid stream. Many narrow escapes occurred, but, owing to the precautions taken by the manage- ment and workmen, no serious accidents occurred during any of these inrushes. 318 MODERN TUNNELING Intoxication Although few accidents in tunnel work are traced directly to intoxication, the extent to which it contributes to many mishaps that are ascribed to other causes is perhaps too little appreciated. The fact that a man who has put an enemy into his mouth to steal away his brains is much more Hkely to be careless or negligent of his own safety and the Hves of the men around him is so well established as to need no emphasis. Even a slight degree of intoxication, that might be allowable if the work had to be done on the surface, is dangerous under- ground, where it is very apt to be greatly aggravated either by the lack of fresh air or by the heat, either of which is common in tunnel headings. Therefore it is essential that a man in such a condition should not be permitted underground and, if dis- covered there, should be immediately sent out of the tunnel by the foreman, while repeated offenses should result automatic- ally in dismissal. PREVENTION OF ACCIDENTS In discussing the prevention of accidents in tunnel work little is to be gained by saying that the manager or the foreman or the miner is solely to blame for their occurrence. The greater responsibility lying, as ever, with those who have the broader vision, the manager or the superintendent is in duty bound to see that the place where the men are to work shall be made as safe as possible and to insist that they, themselves, exercise the greatest care and caution in conducting their work. Then, again, accidents are costly, not only of life and limb, but usually from a financial viewpoint; for in many cases they either seriously hinder the work or cause it to be shut down altogether for months at a time, as, for instance, after a fire, or flood, or cave-in — catastrophes which in many cases could have been prevented, if even but ordinary precautions had been taken beforehand. So, both from the humanitarian and from the economic point of view, safety should come first, and the business of making the SAFETY 319 tunnel safe for the men to work in should be considered more important than the driving of extra footage per month. Upon the foreman falls the responsibihty of carrying out the man- ager's orders, of seeing that the men are instructed in the proper precautions to be taken, and that these are constantly and consistently exercised, and, if necessary, of discharging either temporarily or permanently any man who wilfully or habit- ually disregards them. As for the miner, whose business is shown by statistics to be a hazardous one at best, it is only through the most extreme care on the part of each man, not only for his own welfare but for the safety of his co-workers, that he can hope to escape from the dangers that surround him. Each one has his share, therefore, of the responsibihty, and it is only by co-operation between all parties concerned that any progress can be made toward the prevention and reduction of the fataHties and the injuries now encountered in tunnel driving. Since it is impossible to reiterate too often the methods of obviating accidents, the following paragraphs are written directly for the parties most concerned, in the hope of bringing home to them once again some of the more important preventive measures. Precautions for the Manager or Superintendent Insist that necessary timbering be done at once and always keep an adequate supply of lumber at hand for this purpose, so that no delay may ensue from the lack of it. See that the min- imum amount of explosive is used (in order to prevent unneces- sary shattering of roof and walls) and inaugurate a systematic and regular examination of the roof to insure the removal of all loose pieces at once. Have all bent or breaking timber promptly replaced by new posts or caps. Pro\dde suitable magazines and thaw-houses for explosives.* Do not permit any disregard of the proper precautions in handhng, storing, or using explosives, such as are listed on * Specifications for such buildings recommended by the Bureau of Mines are to be found in Technical Paper i8, which may be had free on application to the Director, Bureau of Mines, Washington, D. C. 820 MODERN TUNNELING pages 293-96, and see that each man is provided with a copy of these or similar precautions.* Do not permit the transporta- tion of detonators or primers to the heading in the same bundle with the remaining supply of explosive for the blast. Have careful tests of the burning rate of the fuse made periodically, especially whenever a different brand of fuse is purchased, and warn the men of any discovered irregularity. Destroy any damaged fuse at once. Do not store fuse near any source of heat. Prohibit the reloading of a bore-hole before it has had time to cool from a previous blast. Give the men proper tools and have them instructed in the correct way to prepare a primer and see that these instructions are obeyed. Do not purchase caps weaker than 5 X for use with gelatine dynamite. See that the proper precautions are taken whenever a missed hole or evidences of one are discovered. Institute a regular and frequent inspection of the valves on the air compressor and insist that any defective valve be promptly and properly repaired, even at the cost of a possible shut-down, that there may be no explosion of gas or burning of grease in the receiver or pipe-line to produce harmful gases and jeopardize the safety of the men at the heading. Do not delay the installa- tion of adequate auxiliary ventilating equipment when natural deposits of harmful gases are encountered in the tunnel, and this is particularly important when such gases are of an explosive nature. In the latter instance, none but safety lamps or their equivalent should be permitted underground. Prohibit the men's riding on loaded trips and, whenever possible, provide for their use special cars either propelled by hand or drawn by a motor. Do not permit them to jump on or off moving cars, nor the drivers to "ride the chain." Tell all new men the proper side of the tunnel to take when meeting a trip, and caution them to shield any bright light when so doing. If there is a trolley wire or other electrical apparatus in the tunnel, caution the men against its danger, and do not allow * A Miners' Circular containing these precautions may be obtained free from the Director, Bureau of Mines, Washington, D. C, by forwarding the names and addresses of the men for whom it is desired. SAFETY 321 them to carry tools on their shoulders when passing in or out. See that the cables or wires leading to any temporary or movable cluster of lights in the heading are kept in good repair. Instruct the men, and especially the foremen, in the proper methods of resuscitation in case of electrical shock. Prohibit the accumulation of combustible rubbish anywhere in the vicinity of buildings or timbering and see that the supply of hay is properly confined to prevent danger from fire. Do not construct any wooden buildings nearer than 200 feet from the mouth of the tunnel, unless such are absolutely necessary, in which case provide a separate exit from the tunnel at least 200 feet away, with a fire door so arranged that it may be closed from a distance. In either event, provide an adequate water supply, with hydrants and hoses, at suitable distances from the several buildings. Exercise great precaution when driving tow^ard a place where a flow of water is Hkely to be encountered that might carry with it a rush of mud, sand, gravel, or other debris, and take immediate steps for the safety of the men as soon as such a flow is struck. Prohibit the drinking of intoxicating Hquors on property controlled by the tunnel company, institute a system of inspec- tion to prevent any intoxicated man from working in the tunnel, and discharge habitual transgressors of this rule. Precautions for the Foreman Insist that the least amount of dynamite required for the work shall be used in loading the top holes. Do not go yourself or permit the men to return to the face after blasting, without examining the new roof, and upon arriving at the heading detail immediately as many men as may be required to clean the roof before any other work is attempted under it. Never fail when passing in or out of the tunnel to inspect the roof, testing any doubtful piece for possible vibration. See that any loose piece of rock is either pulled down at once or properly supported, and never take any chances by postponing the work of timbering, no matter how pressing other matters may be, because a few 322 MODERN TUNNELING minutes' delay in timbering may cost several lives. Have any timbers showing the effects of too great pressure properly relieved as soon as they begin to fail. When timbering is neces- sary close to the face, see that the front sets are thoroughly braced and blocked before firing. When the roof ''breaks high" fill the space between the lagging and the roof with broken rock or blocking to prevent a large rock from crashing through the lagging upon the men beneath. See that the men read the precautions to be taken in handling explosives, or have a copy read to them. Do not permit any instance of careless or reckless handling of explosives to go unchallenged and do not fail to discharge men for the first grave offense of this character. Never permit a man to handle dyna- mite recklessly, either for the purpose of scaring some one or for any other reason. See that the detonators and primers are transported to the heading in separate boxes from the rest of the supply and that they are not placed side by side after arriv- ing. Insist that proper care be used in loading holes and that the tamping be done by pressure rather than by impact. Never allow anything but wooden bars to be used for this purpose. Do not permit a bore-hole to be loaded before it has had sufficient time to cool completely from the previous blast. Warn the men of any change in the rate of burning of fuse. See that they do not mutilate it by rough handling or that it is not cracked or broken by placing the primer in the hole fuse-end first, or by uncoihng the fuse roughly in cold weather. Do not use fuse that has been stored or kept near a boiler, steam - pipe, or other source of heat, or that has been exposed to moisture. See that the fuse is properly coiled close to the hole before blasting, in order that it may not be torn out by blasts from a neighboring hole. Instruct the men in the proper way to prepare a primer. See that the fuse is cut squarely; that an inch or so of it is discarded; that the grains of powder do not leak out of the end that is inserted into the detonator; that the crimping is done carefully with the proper tool; that the detona- tor is not buried too deeply in the dynamite, and that caps of sufficient strength are used. SAFETY 323 Always count the holes as they are blasted, and never fail to inspect the new face for evidences of missed holes. See that any such are detonated properly as soon as they are discovered, even at the possible cost of some delay. Insist that the shovel- ers use their picks properly when picking down the muck pile. Keep a close watch for any unexploded dynamite in the muck, and have the men do likewise; when such is found, remove it carefully to a place of safety and be particularly cautious when a piece of fuse accompanies it. Never start a new hole in the remains of one that has ever held dynamite. When the presence of any amount of dangerous gases, either from explosives or from natural sources, is suspected, see that the men are supplied with fresh air either by opening the com- pressed-air line or by breaking into the ventilating pipe, if the current is in the right direction. Do not willingly remain or permit the men to remain in any atmosphere that will not support a candle-flame, because there is no way to tell how bad it may be getting after the light becomes extinguished, although a man can exist for some time in such an atmosphere. See that the men do not use anything but safety lamps or their equivalent in tunnels where explosive gases are encountered, and do not permit any means of striking an open light to be carried into such a tunnel. Have the track and road-bed kept in as good condition as possible in order to lessen the risk of derailments. Do not permit men to ride upon loaded trains unless it is absolutely necessary, and in such cases warn them carefully as to the risk being taken. Even when the men are riding in empty cars, insist that they keep their feet and hands inside the car and that they watch carefully for low places in the roof. Never fail to discharge any driver caught ''riding the chain." See that the men give an approaching train of cars plenty of room, and, if animals are used to draw them, see that the men hide their lights when the animals approach. Warn the men of the danger from the trolley wire. Familiar- ize yourself with the proper means of resuscitation after an electrical shock. See that the men are not permitted to carry 324 MODERN TUNNELING on their shoulders tools or other instruments that are con- ductors of electricity. Inspect regularly any cables or wires for carrying electricity to lights in the heading, or any others that have to be moved frequently, and see that all worn parts are covered with insuL-^ting material or replaced if necessary. Do not permit the men to ride on electric locomotives. See that no piles of combustible rubbish are allowed to accumulate underground, and do not permit the use of candles or torches in the vicinity of hay or other inflammable sub- stances. Do not fail to discharge any men guilty of leaving candles or torches burning near timbers, and especially of wedging a candle between two nails driven into a post. Exercise special precautions when approaching a place where an inrush of water is to be expected. Be particularly cautious about drunkenness. Note the men when coming on shift and do not permit even slightly intoxicated men underground; if such a man is discovered in the tunnel, send him to the surface at once. Discharge those who are habitual offenders in this respect. Precautions eor the Miner Do not return to the face of the tunnel without testing the newly exposed roof for loose rocks, and if any such are discovered either clean them down yourself or report them to the foreman. Form the habit of carefully examining the roof as you pass in and out of the tunnel, testing doubtful places for vibration; call the foreman's attention at once to any ground that you think should be timbered or to any timbers that need reheving to prevent their breaking. If you are called upon to use dynamite, do so with great care, obc3rving the precautions outlined in previous paragraphs. Never attempt to scare any one by reckless handling of explo- sives, and never treat dynamite with roughness or rely in any other manner upon its not exploding. Never place or carry detonators or primers and the rest of the supply of dynamite for the round in the same box or bundle. If it is your duty to assist in the loading of the holes, do this with care, using pressure SAFETY 325 rather than a blow to tamp the powder in the hole, and always be careful not to use too much force in pushing it. Inquire as to the rate at which the fuse burns, especially when a new brand is being tried, and see that the fuse is cut long enough to give you and your companions time to reach a place of safety. Protect the fuse from mechanical injury, such as scraping, blows, or too great pressure either from falling rocks or from the bar when tamping the hole; never use a fuse that has been thus damaged. Never reload a bore-hole before it has had time to cool. Do not use fuse that you know has been stored near a boiler, steam pipes, or other source of heat, or one that has been exposed to moisture. If you prepare the primer, see that an inch or so is cut squarely from the end of the fuse before it is put into the detonator; that no powder runs out of the end of the fuse during this process; and that the detonator is properly crimped around the fuse. Under no circumstances use anything but the regular crimping tool for this purpose. Always inspect each new face for evidences of a misfire, and if one is discovered, call the foreman's attention to it immedi- ately, so that he may have it detonated. Never attempt to pick out the material from such a hole; either explode it with a primer, or, if this cannot be done, drill and fire another hole at least two feet away. Use great care in removing any unexploded dynamite from the muck pile and be especially cautious if a piece of fuse is discovered near it, for this may show that there still is a detonator in the cartridge. Never handle a pick like a sledge hammer; pull or scrape the material down rather than strike it with the pick. Do not start a new hole in the remnants of a former one that has ever held dynamite, for there is always a chance that it may not have been detonated. Whenever you feel that you are inhaling fumes from dyna- mite that has burned, or any other harmful gases, try to get to fresh air as soon as possible ; the quickest way to do this is often to open the compressed-air line, or to break down the ventilating pipe if you know that the current is in the right direction. Never use anything but a safety lamp or its equivalent in a tunnel 326 MODERN TUNNELING where explosive gases are known to exist, and do not carry any other means of striking a light into such a tunnel. Never attempt to ride upon a full car or a loaded trip; and when riding in an empty car see that your feet and hands are well inside and your head is low enough to clear the roof at all places. Learn which side of the tunnel has the most room and always take all of it you can when a trip of cars approaches. If it is drawn by an animal, hide any bright light you may be carrying. If it is your duty to drive a horse or mule or to run a locomotive, try to do everything possible to prevent derailments; report any places where the track or road-bed is in bad condition. Remember that the front end of the trip is the most dangerous place you can occupy, so that if this is necessary, you must take extra care; never under any circumstances ride with one foot on the chain by which the cars are being pulled. Take care that the animal does not step on you or kick you, and speak to him before approaching him from the rear. In placing a derailed loaded car back upon the rails, take care not to strain or other- wise injure yourself in so doing; keep your feet and hands in a safe position and see that the car does not topple over and crush you against the sides of the tunnel. Bear constantly in mind that the trolley wire is dangerous, and that you must pass within a few inches of it when going in and out of the tunnel, often when your attention must be given to your footing. This is especially true when you climb into cars. Never carry on your shoulders, when in a tunnel where there is a trolley wire, tools or drill steel or anything else that is of metal or wet. Do not handle any electrical equipment unnecessarily, nor ride on electric locomotives. Never cause any one to receive an electric shock; it is never possible to foretell its results. If it is your duty to repair electrical apparatus, see that you are prop- erly insulated, or that the current is cut off and cannot be turned on without your knowledge; keep your hands and body in such a position that a recoil from an accidental shock will throw you clear of any charged part of the apparatus. In removing and replacing the temporary cluster of electric Hghts in the heading, be careful not to touch any bare or injured place in the wires and SAFETY 327 call the foreman's attention to any damaged place you may discover. Familiarize yourself with the methods of reviving a person injured by electric shock, and put them into practice as soon as possible, whenever necessity occurs. Do not smoke or throw a lighted match near any pile of inflam- mable rubbish either in a building or near timbering, and do not carry a candle or a toroh near any piles of hay. Never wedge a candle between two nails on a post or other piece of timber; many disastrous mine fires have started in just this way. Never take a drink of liquor before or during working hours, and do not hesitate to report any man you see doing so or who is in an intoxicated condition; your safety and perhaps your life may be sacrificed to his carelessness when under the influence of liquor. CHAPTER XVI COST OF TUNNEL WORK From the viewpoint of publicity, the cost of tunnehng is per- haps the most neglected feature of the work. Although the last ten or fifteen years have witnessed a very considerable amount of tunnel driving, and there is presumably a large amount of cost data in existence, and although the articles describing methods, equipment, and other features of many of these tunnels have been numerous, only very few data regarding the cost of the work, which is a very practical means by which the efhcacy of methods and equipment can be measured, have found their way into the ordinary channels of publicity — the engineering periodicals. This is possibly due in part to the prejudice entertained by some contractors and tunnel men against a publication of their cost data; in other cases the men actually do not know what the work has cost them, aside per- haps from the difference between their bank account at the beginning and at the end of the job; while others possibly are unwilling to go to the trouble (for it does involve extra labor) of preparing such matter for the magazines or other publica- tions. In an attempt to remedy this condition somewhat, there are set forth on the following pages as complete and accurate data as could be obtained, showing the cost of various phases of tunnel work at a number of different tunnels. Although the writers have not had the advantage of auditing the books from v/hich these figures were taken, and hence cannot vouch per- sonally for the absolute accuracy of the figures, the data were in all cases secured from persons in charge or those who were in a position to know what the work actually cost. Accompanying the figures is a brief hst of the more important features of the tunnel, without which it is impossible to make even an ap- proximate comparison between any two pieces of tunnel work. 328 COST OF TUNNEL WORK 329 CORONADO TUNNEL Location: Metcalf, Arizona. Purpose: Mine development and transportation. Cross section: Square. Size: 9 by 9 feet. Length: 6,300 feet. Rock: Granite and porphyry. Type of power: Steam, with crude oil as fuel Ventilation: Pressure blower. Size of ventilating pipe: 12 inches. Drills: 3 pneumatic piston drills for the first half of the tunnel, 3 pneumatic hammer drills for the last half. Mounting of drills: Horizontal bar. Number of holes per round: 21 in granite, 17 in porphyry. Average depth of round: 6 feet. Number of drillers and helpers per shift : 3 drillers, i helper. Number of drill shifts per day: 3. Explosives: 60 per cent, and 100 per cent, gelatine dynamite. Number of muckers per shift: 4 to 6. Number of mucking shifts per day: 3. Type of haulage : Mules. Maximum progress in any calendar month: 606 feet, June, 19 13. Average monthly progress: Approximately 415 feet. COST OF DRIVING CORONADO TUNNEL Month Footage Labor Supplies Total June, 1912 . . . July August September . . . October November . . . December . . . January, 19 13 February .... March April May June July August Average . . . S29.04 15.88 13.22 21.60 22.47 28.24 25.60 35-82 28.24 21.79 23.12 2599 21.30 21.84 18.52 $22.64 330 MODERN TUNNELING DETAILED COSTS, CORONADO TUNNEL 5,799 Feet Labor ^°o?T^Snn^er Machine men $2,918 Mucking ^ 3.399 Tramming and dumping i . 001 Power-house o . 791 Track and temporary timbering o . 485 ■ Tool-dressing o . 461 Supervision o . 334 Repairs to equipment 0.625 Equipment installation i . 740 General o • 756 Total labor $13 • 512 $13 . 512 Supplies Explosives $2 . 820 Fuel oil 2 . 280 Drill parts 0.612 Stock feed o . 185 Water o. 195 Temporary timber o . 330 Candles and carbide ^ o . 150 Car repair parts o. 095 Electrical supplies o. 143 Blacksmith coal o . 100 Lubricants 0.158 Iron, sheet steel, etc 0.123 Belting, hose, etc 0.127 Building material o . 148 Drill steel o. 290 Miscellaneous 0.357 Total supplies $8. 124 $8. 124 Depreciation Machine drills (50%) $0. 274 Track material (25%) o . 240 Pipe and fittings (50%) o. 388 Drill-sharpener (25%) 0.039 Pumps (25%) o.oii COST OF TUNNEL WORK 331 Depreciation Motors and blowers (25%) $0,030 Compressor (5%) 0.013 Boilers (5%) 0.013 Total depreciation $1 . 008 $1 . 008 Total average cost of tunnel $22 . 64 GUNNISON TUNNEL Location: Montrose, Colorado. Purpose: Irrigation and reclamation. Cross-section: Horse-shoe. Size: 10 feet wide at the bottom; 10 feet 6 inches wide at the spring line; 10 feet high at the spring line; 12 feet 4 inches high at the center of the arch. Length: 30,645 feet. Rock: Chiefly metamorphosed granite with some water-bearing 'clay and gravel, some hard black shale, and a zone of faulted and broken material. Type of power: Steam. Ventilator: Pressure blower. Size of ventilating pipe: 17 inches. Drills: Pneumatic, hammer at first, four drills in the heading; pneu- matic, piston to finish, four drills in the heading. Mounting of drills: Horizontal bar for the hammer drills; vertical columns for the piston drills. Number of holes per round: 20 to 24 in the heading (approximately one-half of the tunnel). Average depth of round: 6 to 7 feet. Number of drillers and helpers per shift: 4 drillers and 2 helpers. Number of drill shifts per day: 3. Explosive: 60 per cent, gelatin dynamite, with some 40 per cent. Number of muckers per shift: 5 to 8. Number of mucking shifts per day: 3. Type of haulage: Electric. Wages: Drillers, $3.50 and $4.00; helpers, $3.00 and $3.50; muckers, $2.50 and $3.00; blacksmiths, $3.50 and $4.00; motormen, $3.00; brakemen, $2.50 and $3.00; power engineers, $4.00. Maximum progress in any calendar month: 449 feet. Average monthly progress: 250 feet, approximately. 332 MODERN TUNNELING COST OF DRIVING THE GUNNISON TUNNEL Cost per Foot of Tunnel 10,019 f^et driven by undercut heading and subsequent enlargement $87 . 23 20,626 feet driven by top heading and bench 62 . 18 Average cost of excavation of entire tunnel $70 . 66 These costs include all labor, all materials, all repairs, all power, depreciation figured as 100 per cent, on all equipment, with a pro- portionate charge for general (supervisory) and miscellaneous ex- penses of the entire reclamation project. LARAMIE-POUDRE TUNNEL Location: Home, Colorado. Purpose: Irrigation. Cross-section: Rectangular. Size: ()% feet wide by 7^ feet high. Length: 11,306 feet. Rock: Close-grained red and gray granite. Type of power: Hydraulic at the east end, electric at the west. Ventilator: Pressure blower. Size of ventilating pipe: 14 and 15 inches. Drills: 3, pneumatic hammer. Mounting of drills: Horizontal bar. Number of holes per round: 21 to 23. Average depth of round: 10 feet at first; 7 to 8 feet later. Number of drillers and helpers per shift: 3 drillers, 2 helpers. Number of drill shifts per day: 3. Explosive: 60 per cent, gelatine dynamite, with some 100 per cent, in the cut holes. Number of muckers per shift: 6. Number of mucking shifts per day: 3. Type of haulage : Mules. Wages: Drillers, $4.50; helpers, $4.00; muckers, $3.50; blacksmiths, $5.00; drivers, $4.50; dumpmen, $3.50. Maximum progress in any calendar month: 653 feet, March, 191 1. Average monthly progress: 509 feet (for the 16 months when complete plant operated). Special features: Inaccessibility; the tunnel was located about 60 miles from the nearest railroad siding and the roads were moun- tainous and very steep in places. COST OF TUNNEL WORK 333 COST OF DRIVING THE LARAMIE-POUDRE TUNNEL 11,306 Feet Per Foot of Tunnel Superintendents and foremen $1 Drilling 4 Mucking and loading 4 Tramming and dumping 4 Track and pipe Power house Blacksmithing '. Repairs Bonus to workmen i Maintenance of camps, buildings, and fuel Machinery repairs Air drills and parts i Picks, shovels, and steel Explosives 4 Lamps and candles Oil and waste ; . . Blacksmith supplies Liability insurance Office supplies, telephone, and bookkeeping $29 Permanent equipment (less approx. 10 per cent, salvage) .... 9 50 47 92 63 47 35 84 47 75 62 12 33 84 50 42 38 53 81 86 $39-54 The permanent equipment included power plant, camp buildings and furnishing, pipes, rails, etc. LOS ANGELES AQUEDUCT Little Lake Division, Tunnels i to ioa Location: Inyo County, CaUfornia. Purpose: Water supply, power, and irrigation. Cross-section: See Figure 6, p. 41. Size: See Figure 6, p. 41. Type of power: Electric power purchased at a nominal cost per kilo- watt-hour from a hydraulic plant constructed and owned by the acqueduct. Ventilators: Pressure blowers. 334 MODERN TUNNELING Size of ventilating pipe: 12 inches. Drills: Pneumatic hammer, usually 2 in each heading. Mounting of drills : Horizontal bar. Number of holes per round: Usually 14 to 16. Average depth of round: 6 to 10 feet. Number of drillers and helpers per shift: 2 drillers and 2 helpers. Number of drill shifts per day: Usually i, but sometimes 2. Explosive: 40 per cent, gelatine dynamite, with some 20 per cent, and some 60 per cent. Ammonia dynamite also tried. Number of muckers per shift: Usually 5. Number of mucking shifts per day: i usually, but 2 when 2 drill-shifts were employed. Type of haulage: Tunnels i to 5N, mules; tunnels 3S to loAN, electric; tunnel loAS, mules. Wages: Drillers and helpers, $3.00; muckers, I2.50; blacksmiths, $4.00; helpers, $2.50; motormen, $2.75; dumpmen, $2.50. COST OF DRIVING TUNNEL i-B-S, 1,341 FEET Driven through medium hard granite at an average speed of 225 feet per month* Cost per Foot of Tunnel Excavation ■ I9 • 1 5 Engineering .18 Adit proportion .28 Permanent equipment (estimated) 2. 35 Timbering (857 feet) i . 02 $12.98 In this tunnel, as in all of the tunnels of this division and of the Grapevine division, the cost of excavation includes the wages of the following: Shift foremen, drillers, helpers, muckers, motormen or mule drivers, dumpmen, blacksmiths and helpers, machinists, elec- tricians (part) , and power engineers. It also includes the cost of the following supplies: Powder, fuse, caps, candles, light globes, machine oil, blacksmith supplies and fuel, and machinists' supplies. It also includes the cost of power and of repairs for power, haulage, compressor, and ventilating machinery. ''Engineering" includes the cost of giving line and grade, etc. * The average speed given is computed on the basis of one heading per month. COST OF TUNNEL WORK 335 *'Adit proportion'* is a proportionate charge per foot of tunnel to defray the cost of an adit from the surface to the tunnel line. " Permanent equipment " costs were not segregated for each tunnel, but were compiled for the whole division, so that the charge repre- sents a proportionate charge per foot for the entire division cost, without salvage, of the following: Trolley and light lines, including freight and cost of installation; pressure air lines with freight and in- stallation; ventilating Hnes with freight and installation; water Unes with freight and installation; mine locomotives and cars, picks, shovels, drills and drill-sharpeners, with repairs for the last four items. COST OF DRIVING TUNNEL 2, 1,739 FEET Driven through medium granite, but very wet, at an average speed of 170 feet per month. Cost per Foot ' ^ of Tunnel Excavation $8.81 Engineering 19 Adit proportion 34 Permanent equipment 2.35 Timbering (1,590 feet) 3 . 28 $14-97 COST OF DRIVING TUNNEL 2-A, 1,322 FEET Driven through medium granite at an average speed of 150 feet per month. Cost per Foot ^ of Tunnel Excavation $8 . 05 Engineering 16 Adit proportion 34 Permanent equipment 2.35 Timbering (1,322 feet) 2.51 $13-41 COST OF DRIVING TUNNEL 3-N, 1,148 FEET Driven through medium hard granite at an average speed of 150 feet per month. Cost per Foot ■^ of Tunnel Excavation $10 . 00 Engineering 23 Adit proportion 51 Permanent equipment 2.35 Timbering (956 feet) 2 . 44 $15.53 336 MODERN TUNNELING COST OF DRIVING TUNNEL 3-S, 1,358 FEET Driven through granite of variable hardness, and containing pockets of carbon dioxide gas, at an average speed of 155 feet per month. Cost per Foot of Tunnel Excavation $12.38 Engineering 28 Adit proportion 16 Permanent equipment 2.35 Timbering (1,244 feet) 3 . 28 $18.45 COST OF DRIVING TUNNEL 3 COMPLETE (3 N AND 3 S) 4,044 FEET Driven through decomposed granite of medium hardness, dissected by sHps and talcose planes requiring timber where ground was wet, and also containing pockets of carbon dioxide gas, making work difhcult and requiring extra provisions for ventilation. Average speed, 140 feet per month. Cost per Foot of Tunnel Excavation $12.67 Engineering 24 Adit proportion 35 Permanent equipment 2.35 Timbering (3,570 feet) 2.71 $18.32 COST OF DRIVING TUNNEL 4, 2,033 FEET Driven through medium to hard granite at an average speed of 145 feet per month Cost per Foot of Tunnel Excavation $1 2 . 00 Engineering 24 Adit proportion 16 Permanent equipment 2.35 Timbering (1,705 feet) 2.16 $16.91 COST OF TUNNEL WORK 337 COST OF DRIVING TUNNEL 5, 1,178 FEET Driven through medium to very hard granite at an average speed of 120 feet per month Cost per Foot of Tunnel Excavation $11.10 Engineering 21 Adit proportion 08 Permanent equipment 2.35 Timbering (916 feet) i . 83 $15-57 COST OF DRIVING TUNNEL 7, 3,596 FEET Driven through basic biotite granite of variable hardness at an average speed of 140 feet per month Cost per Foot of Tunnel Excavation $13 . 55 Engineering 27 Adit proportion 13 Permanent equipment 2.35 Timbering (2,609 feet) 3 • 60 $19.90 COST OF DRIVING TUNNEL 8-S, 1,334 FEET Driven through medium to hard granite at an average speed of 135 feet per month Cost per Foot of Tunnel Excavation $12.82 Engineering 19 Adit proportion 18 Permanent equipment 2.35 Timbering (126 feet) 39 |i5-93 33? MODERN TUNNELING COST OF DRIVING TUNNEL 9, 3,506 FEET Driven through medium to hard granite at an average speed of 195 , feet per month cost per Foot of Tunnel Excavation $12.19 Engineering 18 Adit proportion 07 Permanent equipment 2.35 Timbering (305 feet) 29 • $15.08 COST OF DRIVING TUNNEL 10, 5,657 FEET Driven through medium to hard granite at an average speed of 200 feet per month cost per Foot of Tunnel Excavation $13 . 50 Engineering Permanent equipment 2 Timbering (194 feet) $16 19 35 II 15 COST OF DRIVING TUNNEL lo-A-N, 1,496 FEET Driven through medium to hard granite at an average speed of 165 feet per month cost per Foot of Tunnel Excavation $13 . 02 Engineering 13 Permanent equipment 2.35 Timbering (24 feet) 78 $16.28 COST OF DRIVING TUNNEL lo-A-S, 2,200 FEET Driven through medium to hard granite at an average speed of 200 feet per month cost per Foot of Tunnel Excavation $12.37 Engineering 20 Permanent equipment 2.35 Timbering (215 feet) i . 15 $16.07 COST OF TUNNEL WORK 339 Grapevine Division, Tunnels 12 to 17-B Location: Kern County, California. Purpose: Water supply, power, and irrigation. Cross-section: See Figure 6, p. 41. Size: See Figure 6, p. 41. Type of power: Electric power purchased from aqueduct plant. Ventilators: Pressure blowers. Size of ventilating pipe: 12 inches. Drills: Pneumatic hammer, usually 2 in each heading. Mounting of drills: Horizontal bar. Number of holes per round: Usually 18 to 20. Average depth of round: 6 to 8 feet. Number of drillers and helpers per shift: 2 drillers and 2 helpers. Number of drill shifts per day: Usually 2. Explosive: 40 per cent, ammonia dynamite, but 60 per cent, and 75 per cent, gelatine dynamite were employed in hard ground. Number of muckers per shift: 4 or 5. Number of mucking shifts per day: Usually 2. Type of haulage: Electric after the first 400 to 500 feet. Wages: Drillers and helpers, $3.00; muckers, $2.50; blacksmiths, $4.00; helpers, $2.50; motormen, $2.75; dump men, $2.50. COST OF DRIVING TUNNEL 12, 4,900 FEET Driven through hard granite at an average speed of 185 feet per month Cost per Foot of Tunnel Excavation* $22.10 Engineering* 32 Permanent equipment 2.25 Timbering (90 feet) 08 $24.75 COST OF DRIVING TUNNEL 13, 1,525 FEET Driven through hard granite at an average speed of 130 feet per month Cost per Foot of Tunnel Excavation ' $20 . 60 Engineering 10 Permanent equipment 2.25 Adit proportion 37 $23.32 * These items include the same costs as for the Little Lake division, see page 334. 340 MODERN TUNNELING COST OF DRIVING TUNNEL 14, 859 FEET Cost per Foot of Tunnel 70 Excavation $22 Engineering Permanent equipment 2 Adit proportion Timbering (22 feet) , 13 25 72 16 $25.96 COST OF DRIVING TUNNEL 15, 895 FEET Cost per Foot of T«nnel Excavation $23 . 28 Engineering 11 Permanent equipment 2.25 Adit proportion 2.42 $28.06' COST OF DRIVING TUNNEL 16, 2,723 FEET Driven through hard granite at an average speed of 145 feet per month Cost per Foot of Tunnel Excavation $20 . 07 Engineering ■. 17 Permanent equipment 2.25 Adit proportion 55 Timbering (18 feet) 04 $23.08 COST OF DRIVING TUNNEL 17, 3,024 FEET Cost per Foot of Tunnel Excavation $20 . 47 Engineering 21 Permanent equipment 2.25 Timbering (142 feet) 22 $23-15 COST OF TUNNEL WORK 341 COST OF DRIVING TUNNEL 173^^, i,345 FEET Driven through medium to hard granite at an average speed of 225 feet per month Cost per Foot of Tunnel Excavation $19 . 56 Engineering 31 Permanent equipment 2.25 $22.12 COST OF DRIVING TUNNEL 17-A, 3,275 FEET Cost per Foot of Tunnel Excavation $18 . 70 Engineering 17 Permanent equipment 2.25 Timbering (441 feet) i . 18 $22.30 COST OF DRIVING TUNNEL 17-B, 4,915 FEET Cost per Foot of Tunnel Excavation $2 1 . 09 Engineering 21 Permanent equipment 2.25 Timbering (163 feet) i . 90 $25.45 Elizabeth Lake Division, ELIZABETH TUNNEL Location: Los Angeles County, CaHfornia. Purpose: Water supply, power, and irrigation. Cross-section: See Figure 6, p. 41. Size: See Figure 6, p. 41. Length: 26,870 feet. Type of power : Electric power purchased from aqueduct plant. Ventilator: Pressure blower. Size of ventilating pipe: 18 inches. Drills: Pneumatic hammer, 3 in the south heading and 2 in the north. Mounting of drills: Horizontal bar. Number of holes per round: 25 in the south heading; 16 in the north heading. 342 MODERN TUNNELING Average depth of round: 8 to lo feet. Number of drillers and helpers per shift: 2 drillers and 2 helpers at the north end; 3 drillers and 3 helpers at the south end. Number of drill shifts per day: 3. Explosive: 40 per cent, and 60 per cent, gelatine dynamite. Number of muckers per shift: 6. Number of mucking shifts per day: 3. Type of haulage: Electric. Wages: Drillers and helpers, $3.00; muckers, $2.50; blacksmiths, $4.00; helpers, $2.50; motormen, $2.75; dumpmen, $2.50. Maximum progress in any calendar month: 604 feet, April, 1910. Average monthly progress per heading: 350 feet per month. COST OF DRIVING THE NORTH HEADING, ELIZABETH TUNNEL Driven through altered granite requiring much timbering' 1 3 » 3 70 fee t Cost per Foot ^'^' of Tunnel I Drilling and blasting $11 Mucking and tramming 11 Engineering and superintendence i Drainage Ventilation Light and power 5 Timbering (13,031 feet) 8 Cost of auxiliary shaft Permanent equipment (full charge, no salvage — estimated) 3 25 70 27 45 22 55 48 93 70 $43-55 COST OF DRIVING THE SOUTH HEADING, ELIZABETH TUNNEL Driven through medium to hard granite requiring but little timbering' I T, , c;00 feet Cost per Foot ^'"^ of Tunnel Drilling and blasting $14.65 Mucking and tramming 1 1 . 10 Engineering and superintendence 86 Drainage 17 Ventilation 41 Light and power 4 . 93 Permanent equipment (without salvage — es- timated) 3 • 70 Timbering (3,424 feet) 2.19 $38.01 COST OF TUNNEL WORK 343 LUCANIA TUNNEL Location: Idaho Springs, Colorado. Purpose: Mine development and transportation. Cross-section : Square. Size: 8 feet by 8 feet. Length: 6,385 feet. Rock: Hard granite. Type of power : Purchased electric current- Ventilator: Pressure blower. Size of ventilating pipe: 18 and 19 inches. Drills: Pneumatic hammer, 3 in the heading. Mounting of drills : Vertical columns. Number of holes per round: 25. Average depth of round: 8 to 9 feet. Number of drillers and helpers per shift: 3 drillers and 2 helpers. Number of drilling shifts per day: i. Explosive: 50 per cent, gelatine dynamite. Number of muckers per shift: 3. Number of mucking shifts per day: i. Type of haulage: Horses. Wages: Head driller, $5.00; drillers, $4.00; nipper, $3.50; boss mucker, $5.00; muckers, $4.00; drivers, $4.00; power engineers, $4.00; blacksmith, $5.00. Maximum progress in any calendar month: 263 feet, September, 191 1. Average monthly progress: 125 feet per month for the first 4,800 feet; 240 feet per month for the last 1,575 feet. AVERAGE COST OF DRIVING THE LUCANIA TUNNEL First 4,800 feet Cost per Foot of Tunnel Labor $8 . 86 Powder 7 . 86 Fuse and caps 17 Candles and oil 21 Horse feed and shoeing 18 Power 1 . 64 Repairs 14 Timnel equipment 2.75 Surface plant 1.25 $23.06 344 MODERN TUNNELING *' Tunnel equipment" includes the cost of materials and installa- tion of the pressure air line, the ventilating line, rails, ties and fittings, and the drainage ditch. "Surface plant" includes buildings, compressor, blower, trans- formers, motors, and drill-sharpener. AVERAGE COST OF DRIVING THE LAST i,575 FEET The contractor received $21.50 per foot to cover the cost of labor, powder, fuse, caps, candles, oil, horse feed and shoeing, power and repairs, and the installation of the timnel equipment. MARSHALL-RUSSELL TUNNEL Location: Empire, Colorado. Purpose: Mine drainage, development, and transportation. Cross-section: Square. Size: 8 feet by 8 feet. Length: 11,000 feet projected; 6,700 feet driven, January i, 1913. Rock: Granite and gneiss. Type of power: Purchased electric current; also a small auxiliary hydraulic plant. Ventilator: Fan. Size of ventilating pipe: 12 and 13 inches. Drills: 2, pneumatic hammer. Mounting of drills : Vertical columns. Number of holes per round: 18 to 20. Average depth of round: 9 to 10 feet. Number of drillers and helpers per shift: 2 drillers and 2 helpers. Number of drill shifts per day: i. Explosive : 40 per cent, gelatine dynamite with some 80 per cent. Number of muckers per shift: 4. Number of mucking shifts per day: i. Type of haulage: Horses. Wages: Drillers, $4.00; helpers, $3.00; blacksmiths, $4.00; helpers, $3.00; muckers, $3.25; trammers, $3.75; dumpmen, $3.25; power engineer, $3.50; shooters, $3.25. Maximum progress for any calendar month: 187 feet, June, 1909. Average monthly progress: 125 feet. , COST OF TUNNEL WORK 345 COST OF DRIVING THE MARSHALL-RUSSELL TUNNEL 6,700 Feet Cost per Foot of Tunnel Labor $9.37 Powder, fuse, caps, and blacksmith coal 3 . 35 Drills, steel, and repairs (less 30 per cent, salvage) i . 34 Power 1 . 41 Permahent equipment and general expense (less 30 per cent, salvage on permanent equipment) 3.41 $18.88 MISSION TUNNEL Location: Santa Barbara, California. Purpose: Water supply. Cross-section : Trapezoid. Size: 6 feet wide at the base; 4>^ feet wide at the top; 7 feet high. Length: 19,560 feet. Pock: Shale, slate, and hard sandstone. Ventilator: Pressure blower. Size of ventilating pipe : 10 inches. Drills: i, pneumatic hammer. Mounting of drills: Horizontal bar. Number of holes per round: 12 to 14. Average depth of round: 7 to 8 feet. Number of drillers and helpers per shift: i. Number of drilling shifts per day: 3. Explosive: 40 per cent, and 60 per cent, gelatine dynamite. Number of muckers per shift : 4. Number of mucking shifts per day: 3. Type of haulage : Electric. Wages: Drillers, $3.50; helpers, $3.00; muckers, $2.75; blacksmiths, $4.00; helper, $3.00; motormen, $2.75; dumpmen, $2.50; power engineers, $2.75. Maximum progress in any calendar month: 414 feet, February, 191 1. Average monthly progress: 210 feet. 346 MODERN TUNNELING COST OF DRIVING THE SOUTH PORTAL, MISSION TUNNEL May, 1909, to September, 191 1 5,515 Feet Cost per Foot of Tunnel Administration* $1.14 Labor 9 . 20 Power 2.12 Explosives 1.97 Timbering (563 feet) 30 Track and pipe 1.22 Miscellaneous suppliesf 2 . 46 Drill parts (including steel) 1.02 Bonus .48 $19.91 NEWHOUSE TUNNEL Location: Idaho Springs, Colorado. Purpose: Drainage and transportation. Cross-section : Square. Size : 8 feet by 8 feet. Length: 22,000 feet. Rock: Idaho Springs gneiss. Type of power: Purchased electric current. Ventilator: Pressure blower. Size of ventilating pipe : 18 inches. Drills: Pneumatic hammer. Mounting of drills: Vertical column. Number of holes per round: 14 to 22. Number of drill shifts per day: i and 2. Explosive: 40 per cent, gelatine dynamite, with some 100 per cent. in the cut holes. Number of muckers per shift: 3. Number of mucking shifts per day: i and 2. Type of haulage : Electric. Wages: Drillers, $4.00 to $4.50; helpers, $3.25 to $4.00; muckers, $3.50; motormen, $3.50; dumpmen, $3.00; blacksmiths, $3.50 to $4.50; helpers, $3.00. * Includes superintendence, office supplies, and general charges, t Includes candles, light globes, shovels, picks, blacksmiths' supplies and fuel, and machinists' supplies. COST OF TUNNEL WORK COST OF DRIVING THE NEWHOUSE TUNNEL 347 Jan. to Aug. 1909 2,233 feet Sept. to Dec. 1909 1.098 feet April to Aug. 1910 693 feet Labor $6.72 4-15 •39 1.49 1.99 1-57 1.50 1.74 •79 $6.98 3-52 •36 1.47 2.16 2.61 2.74 1.78 .80 $ii^73 4.57 •44 2.22 2.82 2.00 2.86 2.19 1.85 Explosives Fuse and caps Transportation of broken rock Power Blacksmithing Use of drills, repairs, and steel Equipment, ties, rails, pipe, etc. Sundries $20.34 $22.42 $30.68 RAWLEY TUNNEL Location: Bonanza, Colorado. Purpose: Mine drainage and development. Cross-section : TrapezoidaL Size: 8 feet wide at the base; 7 feet wide at the top; 7 feet high. Length: 6,235 feet. Rock: Tough hard andesite. Type of power: Steam with wood for fueL Ventilator: Pressure blower. Size of ventilating pipe: 12 and 13 inches. Drills: 2, pneumatic hammer. Mounting of drills: Horizontal bar. Number of holes per round: 23 to 25. Average depth of round: 8 to 9 feet at first; 5 to 6 feet later. Number of drillers and helpers per shift: 2 drillers and 2 helpers. Number of drill shifts per day: 2 at first; 3 later. Explosive: 40 per cent, and 60 per cent, gelatine dynamite (in the proportion of about 2 to i). Number of muckers per shift: 4. Number of mucking shifts per day: 2 and 3. Type of haulage: Horses and mules. Wages: Drillers, $4.50; helpers, $3.75; muckers, $3.50; blacksmiths, $4.50; drivers, $4.50; power engineers, $4.00. Maximum progress in any calendar month: 585 feet, July, 191 2. Average monthly progress: Approximately 350 feet. 348 MODERN TUNNELING COST OF DRIVING RAWLEY TUNNEL 6,235 Feet * Cost per Foot of Tunnel Drilling and firing $5.25 Mucking 2.16 Tramming i . 13 Track and pipe 44 Miscellaneous underground expenses i . 44 Power plant 2 . 50 Blacksmithing 73 Miscellaneous surface work 83 General expenses i . 98 Permanent plant 3 . 24 Timbering (1,618 feet) i . 18 Boarding-house, debit balance 04 $20.92 Credit by salvage on permanent plant i.ii $19.81 *' Drilling and firing" includes labor, powder, fuse, caps, supplies, and repairs. ''Mucking," "tramming," and "track and pipe" in- clude labor and supplies. "Miscellaneous underground expenses" includes wages of foremen, underground telephone, etc. "Power plant" includes labor, supplies, and fuel. "Blacksmithing" and "Miscellaneous surface work" include labor and supplies. "General expenses" include salaries, office supplies, telephone, etc. "Per- manent plant" includes machinery and buildings, with labor of installation, steel rails, permanent supplies, and repairs. "Timbering" includes labor and supplies. The salvage on the permanent plant is approximately 50 per cent, on salable articles, such as machinery, rails, cars, etc. ROOSEVELT TUNNEL Location: Cripple Creek, Colorado. Purpose: Mine drainage. Cross-section: Rectangular, with large ditch at the side. Size: 10 feet wide by 6 feet high. * A more detailed statement of the cost of this tunnel may be found in Trans. Am. Inst. Mining Engineers, February meeting, 1913. COST OF TUNNEL WORK 349 Length: 15,700 feet. Rock: Pike's Peak granite, chiefly. Type of power: Purchased electric current. Ventilator: Pressure blower. Size of ventilating pipe: 16 and 17 inches. Drills: 3, pneumatic hammer. Mounting of drills : Horizontal bar. Number of holes per round: 24, usually. Average depth of round: 6 to 7 feet. Number of drillers and helpers per shift: 3 drillers; 2 helpers. Number of drill shifts per day: 3. Explosive: 40 per cent., 60 per cent., and some 100 per cent, gelatine dynamite. Number of muckers per shift: 4, usually. Number of mucking shifts per day: 3. Type of haulage: Horses and mules. Wages: Drillers, $5.00; helpers, $4.00; muckers, $3.50; power en- gineer, $4.00; blacksmith, $5.00; helper, $3.50; dumpman, $3.50; drivers, inside, $5.00; outside, $4.00. Maximum progress in any calendar month: 435 feet, portal heading, January, 1909. Average monthly progress: Portal heading, 300 feet; shaft headings, 270 feet; all headings, 285 feet. COST OF DRIVING ROOSEVELT TUNNEL Total cost of portal work $111,980.06 Contractor's percentage 11,404.88 Cost of shaft headings 262,126.55 Total cost of tunnel $385,511.49 Number of feet driven I4ji67 Average cost per foot 27.21 COST OF DRIVING THE PORTAL HEADING Month Foo'age Cost per Foot Feb. and March, 1908 514 $22 . 690 April 262 30 . 970 May 268 26 . 760 June 187 35 . 010 July 203 29 . 600 August 300 2 1 . 760 September 351 19.600 October 287 23 . 000 350 MODERN TUNNELING COST OF DRIVING THE PORTAL HEADING— ConHnued Month Footage Cost per Foot November 360 21 . 1 20 December 334 18 . 350 January, 1909 435 16.410 February 290 22 . 206 March 340 21 . 745 April 316 21 . 266 May 402 18 . 762 June (8 days) 62 40. 600 COST OF DRIVING SHAFT HEADINGS Month Footage October, 1908 (2 headings) 49 November " 141 December " 177 January, 1909 " 261 February " 601 March " 639 April " 670 May " 552 June " 498 July (i heading) 319 August " 410 September " 355 October " 380 November " 298 December " 251 January, 1910 " 282 February " 259 March " 344 April " 376 May " 393 June " 373 July " 350 August " 372 September " 342 October " 372 November " 192 Cost per Foot I105 52 44 38 40 II 24 06 23 70 26 256 25 02 28 34 27 375 32 871 27 747 32 40 28 178 34 20 35 153 28.82 30 636 27 62 25-313 24 856 26.616 25 247 25 029 28 45 27. 361 27. 786 COST OF TUNNEL WORK 851 TYPICAL DISTRIBUTION OF EXPENSES Portal heading, July, 203 Feet 1908 Cost per Foot of Tunnel Machinery and repairs $0 Air drills and parts Picks, shovels, and steel i Ditch men i Explosives • 6 Candles Oil and waste Electric power 2 Blacksmith supplies General expense LiabiUty insurance Lumber ties and wedges Horses and feed Compressor men i Drillers and helpers 4 Blacksmiths and helpers 3 Muckers and drivers 4 Foremen i Bookkeeper 61 99 90 09 90 36 09 06 09 16 17 01 01 79 21 43 II 50 12 $29 . 60 TYPICAL DISTRIBUTION OF EXPENSES Shaft heading, February, 19 10 259 Feet Cost per Foot of Tunnel Maintenance of buildings, tents, etc $0. 096 Machinery and repairs 1158 Air drills and parts i . 930 Shovels, picks, and steel i . 930 Pipe and fittings 193 Ditch men i . 480 Explosives 5 • 032 Lamps and candles 217 Oil and waste 252 Electric power 2 . 440 Blacksmith suppHes 150 352 MODERN TUNNELING TYPICAL DISTRIBUTION OF EXPENSES— Continued Cost per Foot of Tunnel Liability insurance 213 General expense 342 Lumber, ties, and wedges 119 Horses and feed 324 Machine men and helpers 4 . 050 Muckers 3 . 065 Blacksmiths and helpers , i 362 Engineers i . 300 Pipe and track men 675 Drivers and dumpmen 2 . 355 Foremen i . 753 Mine telephone 008 Bookkeeper 193 $30,636 STILWELL TUNNEL Location: Telluride, Colorado. Purpose: Mine drainage and developmen Cross-section: Square with ditch at side. Size : 7 feet by 7 feet. Length: 2,950 feet. Rock: Conglomerate and andesite. Type of power: Purchased electric current. Ventilator: Fan. Size of ventilating pipe : 10 inch. Drills: Started with electric drills. Finished with pneumatic piston drills, using 2 in the heading. Mounting of drills : Vertical columns. Number of holes per round: 16. Average depth of round: 6 to 6}4 feet. Number of drillers and helpers per shift: 2 drillers and 2 helpers. Number of drill shifts per day: i. Explosive: 40 per cent, gelatine dynamite. Number of muckers per shift : 3. Number of mucking shifts per day: i. Type of haulage: Horses. Wages: Drillers, $4.50; helpers, $4.00; muckers and trammers, $3.50; blacksmith, $4.50. Maximum progress in any calendar month: 170 feet, August, 1904. Average monthly progress: 150 feet (last 10 months). COST OF TUNNEL WORK 353 COST OF DRIVING THE STILWELL TUNNEL Fiscal Year Footage Cost per Foot of Tunnel 1900-01 12 feet $23.88 1901-02 490 " 22.98 1902-03 377 '' 27.94 1903-04 702 - 21.69 1904-05 1,077 " 21.19 1905-06 292 - 2,950 feet 30.37 Average. $23. 38 These costs include all labor, supplies, repairs, powder, fuse, caps, candles, tools, lubricants, and general expenses, and the total value of the electric drill plant with which the tunnel was started and the total value of the air drill plant which succeeded it, together with tunnel buildings, pipe, rails, and the ventilator, with no credit for salvage on any of this permanent equipment. The fiscal year dated from September 30. The tunnel was driven in 1901-02-03 mth electric drills and the high cost for 1905-06 was due to station cutting where the tunnel was double size. STRAWBERRY TUNNEL Location: Utah and Wasatch counties, Utah. Purpose: Irrigation and reclamation. Cross-section: Straight bottom and w^alls, \nth arched roof. Size: 8 feet ^\ide by g^ feet high. Length: 19,100 feet. Rock: Limestone mth interbedded sandstone, and sandstone with interbedded shale. Type of power: Electric power generated in a hydraulic plant operated in connection with the tunnel. Distance of transmission from west portal to power-house, approximately 23 miles. Ventilator: Pressure blower. Size of ventilating pipe: 14 inches. Drills: Piston pneumatic, usually 2 in the heading. Mounting of drills: Vertical columns. Number of holes per round: 16 to 18. Number of drillers and helpers per shift: 2 drillers and 2 helpers. Number of drill shifts per day: 3. Explosive: 40 per cent, gelatine dynamite. Number of muckers per shift: 6. Number of mucking shifts per day: 3. 354 MODERN TUNNELING Type of haulage: Electric after first 2,000 feet. Wages: Drillers, $3.50; helpers, $3.25; muckers, $2.75; motormen, $3.25; brakemen, $2.75; blacksmiths, $4.00; helpers, $2.75. Maximum progress in any calendar month: 500 feet, November, 1910. Average monthly progress: 320 feet per heading. COST OF DRIVING THE STRAWBERRY TUNNEL West heading, previous to 1909 . 16 13 feet during 1909 3892 " during 1910 5021 " during 191 1 3491 " January to July, 1912.. . 2382 " East " ' Oct., 191 1, to July, 191 2. 2682 " Average for 19,081 feet ost per Fo of Tunnel $60 05 33 58 30 56 41 52 36 79 33 04 $36.78 DETAILED COST OF DRIVING THE STRAWBERRY TUNNEL, WEST HEADING, FOR THE YEAR 1909: 3,892 Feet Labor: Cost per Foot of Tunnel Engineering $0 Superintendence Shift bosses i Time-keepers Drillmen and helpers 3 Miners (for hand work, trimming, etc.) Muckers 2 Track and dumpmen Mule drivers , . Motormen and brakemen Electricians and blowermen Disabled employees Timber men Miscellaneous Materials : Powder, fuse, caps, etc Lumber Oils, candles, etc Ventilating pipe Track, including ties Pressure air pipe Drill repair parts (including hose) Miscellaneous $3 49 73 22 36 IS 23 96 74 39 44 07 19 22 40 08 29 22 64 68 40 18 19 $11.59 5-68 COST OF TUNNEL WORK 355 Repairs: Cost per Foot Machine shop expense (including labor and ^^ Tunnel suppUes) So . 93 Blacksmith shop expense (including labor and supplies) 1.22 $2.15 Power (all purposes) 7.65 Depreciation: Haulage equipment $0 . 09 General equipment i . 00 1.09 General expense . $3 . 96 Camp expense 1.21 Corral expense 25 5-42 Total $33.58 "General expense" includes a proportionate charge for the ex- penses of the Provo ofl&ce, such as salaries, stationery, telephone, and supplies; also a proportionate charge for the expenses of the Wash- ington, the Chicago, and the Supervising Engineer's offices. The Provo office covers approximately 68 per cent, of this charge, the Washington office 23 per cent., the Chicago office 2 per cent., and the Supervising Engineer's office 7 per cent. DETAILED COST OF DRIVING THE STRAWBERRY TUNNEL, WEST HEADING, FOR THE YEAR 19 10: 5,021 Feet LaDOr. of Tunnel Engineering $0.61 Superintendence 60 Shift bosses 1.25 Time-keepers 22 Drillmen and helpers 2.85 Miners 28 Muckers 2 . 93 Track and dumpmen 71 Motormen and brakemen . i . 49 Electricians and blowermen 13 Disabled employees 16 Timber men 28 Miscellaneous 07 $11.58 356 MODERN TUNNELING Materials: Powder, fuse, caps, etc Lumber Oils, candles, etc Ventilating pipe Track, including ties Pressure air pipe Drill repair parts (including hose) Miscellaneous Cost per Foot of Tunnel fe-52 22 20 65 74 28 24 07 Repairs : Machine shop expense (including labor and supplies) $0. 90 Blacksmith shop expense (including labor and supplies) 1 . 23 Power (all purposes) Depreciation : Haulage equipment $0. 20 General equipment i . 00 $5-92 2.13 5-70 1.20 General expense $332 Camp expense 63 Corral expense 08 Total 4-03 $30.56 DETAILED COST OF DRIVING THE STRAWBERRY TUNNEL WEST HEADING, FOR THE YEAR 191 1: 3,419 Feet Labor: Engineering $0 Superintendence Shift bosses i Time-keepers Drillmen and helpers 4 Miners Muckers 5 Cost per Foot of Tunnel 45 82 65 38 07 37 13 COST OF TUNNEL WORK 357 Cost per Foot of Tunnel Track and dumpmen $2 . oo Motormen and brakemen 1.87 Electricians and blowermen Disabled employees Timber men i Miscellaneous 08 48 72 05 $19-07 Materials: Powder, fuse, caps, etc $2.61 Lumber 80 Oils, candles, etc 43 Ventilating pipe 77 Track, including ties 1.52 Pressure air pipe 36 Drill repair parts (including hose) 34 Miscellaneous 25 7.08 Repairs: Machine shop expense (including labor and supplies) $2.16 Blacksmith shop expense (including labor and suppHes) 1 . 54 Power (all purposes) 3.70 5.20 Depreciation: Haulage equipment $1.85 General equipment 50 2.35 General expense $3 . 00 Camp expense i . 10 Corral expense 02 4.12 Total 1.52 358 MODERN TUNNELING DETAILED COST OF DRIVING THE STRAWBERRY TUNNEL, WEST HEADING, JANUARY TO JULY, 1912: 2,382 Feet T 1 ' Cost per Foot Labor: of Tunnel Engineering $0 Superintendence Shift bosses i Time-keepers Drillmen and helpers 3 Miners Muckers 4 Track and dumpmen i Motormen and brakemen , i Electricians and blowermen Disabled employees Timber men 2 36 56 08 26 08 43 95 55 33 18 48 59 Materials: Powder, fuse, caps, etc $2.72 Lumber 2.13 Oils, candles, etc 32 Ventilating pipe 70 Track, including ties i . 51 Pressure air pipe 30 Drill repair parts (including hose) . .32 Miscellaneous 39 $16.85 8.39 Repairs : Machine shop (including labor and supplies) $1.39 Blacksmith shop (including labor and supplies).. . 1.02 2.41 Power (all purposes) 3.75 Depreciation : Haulage equipment $2 . 20 General equipment 50 2.70 General expense $1 . 90 Camp expense 79 2 . 69 Total $36.79 COST OF TUNNEL WORK 359 DETAILED COST OF DRIVING THE STRAWBERRY TUNNEL, EAST HEADING, OCTOBER, 1911, to JULY 1912: 2,682 Feet Labor: Cost per Foot of Tunnel Engineering $0 Superintendence Shift bosses i Time-keepers Drillmen and helpers 3 Muckers 4 Track and dumpmen 2 Mule drivers Timber men i Electricians and blowermen Disabled employees Miscellaneous Power (all purposes) Pumping (labor and material) Total 49 77 36 31 62 03 00 89 80 30 09 21 Materials: Powder, fuse, caps, etc $2.67 Lumber 93 Oils, candies, etc 36 Ventilating pipe 45 Track, including ties 56 Pressure air pipe 12 Drill repair parts (including hose) ;^S Miscellaneous 21 Repairs : Machine shop expense (labor and supplies) $0.62 Blacksmith shop expense (labor and supplies) 65 Depreciation : Haulage equipment $0.47 General equipment 1.02 General expenses $1 . 86 Camp expenses 1.35 Corral expenses 95 $15-87 5.68 1.27 3.21 1.49 4.16 1.36 $33-04 CHAPTER XVII BIBLIOGRAPHY The following is a selected bibliography of tunneling and related subjects arranged by topics in chronological order. TUNNEL DESCRIPTIONS Raymond, R. W., ''The Rothschonberger Stollen," Trans. A. I. M. E., Vol. VI, p. 542, 1877. Full description of this famous old tunnel, giving its purpose, length, grade, cost, method of driving, rate of progress, etc. Anon., " Data of Tunnel Work, European," Min. Sci. Press, Vol. XL VIII, pp. 306-322-338. May 3, 1884, contains a descrip- tion of the Brandt drill and a table showing the monthly progress on the Arlberg tunnel. May loth gives more details of the drilling results. Bonus described. Also gives description of the use of the Brandt drill at the Son- stein and other places. May 17, 1884, work of the Brandt drill in the Pfaffensprung tunnel. Concludes with a statement of the advantages of the Brandt drill. Charton, a. Pierre, '' Arlberg Tunnel," Proc. Inst. Civ. Engrs., Vol. LXXX, p. 382, 1885, 4 pages. Concise description of this tunnel, the method of driving, ventilation, and costs. Trevellini, Luigi, " The Carrito Cocullo Tunnel," Proc. Inst. Civ. Engrs., Vol. LXXXII, p. 412, 1885. Description of the tunnel followed by the rates of driving Mt. Cenis, St. Gothard, Arlberg, Laveno, and Carrito tunnels. W. H. E., "The Longest Tunnel in the World," Proc. Inst. Civ. Engrs., Vol. LXXXVII, p. 496, 1886. A short description of the mining tunnel at Schemnitz, in Hungary, which was completed in 1878 and has a length of 10.27 miles. Cost of tunnel, $4,860,000. Anon., "A Long Tunnel Completed," Min. Sci. Press, Vol. LII, pp. 273-276, 4 cols., illus., Apr. 24, 1886. Describes the work at the Big Bend tunnel which was driven to divert the 360 i BIBLIOGRAPHY 361 waters of the Feather River and make it possible to secure the placer gold on the river bed at Big Bend. Searles, W. H., "The Westpoint Tunnel," Proc. Inst. Civ. Engrs., Vol. XCVI, p. 414, 1889. Description of the tunnel, method of construction, cave, and method of recovery. EspiNOSA, Luis, ''Tequiquiac Tunnel," Proc. Inst. Civ. Engrs., Vol. CXXVI, p. 426, 1896. Description of a tunnel 5.9 miles long to drain the valley in which the City of Mexico is situated. Hay, David H., and Maurice Fitzmaurice, ''The Blackwell Tunnel," Proc. Inst. Civ. Engrs., Vol. CXXX, p. 50, 1897, 48 pages. Full description of this tunnel, together with a discussion by the members of the institution. Clauss, H., ''The Simplon Tunnel," Proc. Inst. Civ. Engrs., Vol. CXXXVII, p. 474, 1899. Condensed description of the tunnel, giving grades, lengths, etc. House, F. E., "North Bessemer Tunnel," Proc. Eng. Soc, West Pa., Vol. XV, p. 238, June, 1899, 12 pages, 4 illus. Near Carnegie Steel Works at Bessemer, Pa. Tunnel is 2,900 feet long, 21.5 high in center of arch, and 26 wide. Av. speed, four feet per day. Air operated shovels for bench. Anon., "The Simplon Tunnel," Cassiers, Vol. XVH, p. 179, Jan., 1900, 12 pages, illustrated with photos. More or less popular account of this tunnel. Body, John B., "The Draining of the Valley of Mexico," Proc. Inst. Civ. Engrs., Vol. CXLIII, p. 286, 1901, 8 pages. De- scription of the valley and review of attempts to drain it. Gives full particulars of the work on the approaches to the tunnel, together with a short description of the tunnel itself. Rogers, A. E., "The Location and Construction of Railway Tunnels with particulars of some recent work," Proc. Inst. Civ. Engrs., Vol. CXLVI, p. 191, 1901, 10 pages. Treats principally of English practice and covers the field indicated by the title. Hough, Ulysses B., "The Kellogg Tunnel," Min. and Min., p. 122, Oct., 1901. Describes the methods used in driving this tunnel in Idaho. 362 MODERN TUNNELING Clapp, a. W., "The Aspen Tunnel," E. M. J,, Vol. LXXIII, p. 519, Apr. 12, 1902, 3>^ columns. Describes some of the difficulties in the U. P. R. R. tunnel, Wyoming. Use of steam shovel noted. Bain, H. F., *' Driving the Newhouse Tunnel," E. M. /., p. 552, Apr. 19, 1902, 6 columns, illustrated. Describes the methods, equipment, and costs of this work. Wilson, W. B., ''The Cripple Creek Drainage Tunnel," Min. Sci. Press, Vol. LXXXVI, p. 36, 3 cols., p. 336, i col., and Vol. LXXXVII, p. 130, % cols. . Describes the El Paso Drain Tunnel. HoBLER, George A., ''Tunnels on the Cairns Railway, Queens- land, Australia," Proc. Inst. Civ. Engrs., Vol. CLII, p. 221, 1903. Portion of a paper on the construction of the moun.- tain portion of this railway. Gives methods of driving, an illustrated description of timbering, etc. Anon., "The Simplon Tunnel," Min. and Min., Vol. XX, p. 390, J/2 col. Note concerning the use of parallel headings in this tunnel and the use of the Brandt hydraulic drill. Anon., "Katterat and Nordal Tunnels, on the Ofot Railway, Sweden," Proc. Inst. Civ. Engrs.; Vol. CLVI, p. 450, 1904. Description of the . hydro-electric power plant, air mains, drills, methods of driving, etc. Anon., "The Drainage Tunnel in Mining," Min. Sci. Press, Vol. LXXXIX, p. 203, Sept. 24, 1904, I col. editorial. Dis- cusses the drainage of 'mines by tunnels and mentions sev- eral examples. Trench, E. F. C, "Alfreton Second Tunnel," Proc. Inst. Civ, Engrs., Vol. CLXI, p. 116, 1905, 9 pages. Descriptions of methods of driving, drainage, ventilation, etc. Brunton, D. W., "Drainage of the Cripple Creek District," E. M. J., Vol. LXXX, p. 818, 12 cols. Report of the Con- sulting Engineer as to the feasibility of the project and the methods to be employed. Anon., "Simplon Tunnel," Min. Sci. Press, Vol. XCI, p. 399, Dec. 9, 1905, 2 cols. Ripley, G. C, and others, "The Newhouse Tunnel," Min. and BIBLIOGRAPHY 363 Min., Vol. XXVII, p. ^,6, Aug., 1906, 5 cols., p. 72, 5>^ cols. Describes the equipment and discusses the methods employed and the cost of driving. Herrick, R. L., ''The Joker Drainage Tunnel," Min. and Min.y Vol. XXVII, p. 470, 1906, 8>^ cols., 6 illus. Description of methods and equipment. Haupt, L. M., ''Great Tunnels," Cassiers, p. 175, Dec, 1906, 3 cols. Mentions several great tunnels both in this country and abroad. HiLDAGE, H. T., "Mining Operations in New York and Vicin- ity," Trans. A. L M. £., Vol. XXXVIII, p. 360, 1907, 37 pages. A very complete description of the tunnels in the neighborhood of New York City, with methods of driving them. Pressel, Dr. K., "Works of the Simplon Tunnel," Proc. Inst. Civ. Engrs., Vol. CLXVII, p. 411, 1907. A short review of a number of articles published in the Swiss scientific papers, bringing the history of the undertaking down to the open- ing of the tunnel for traffic. Fox, Francis, "The Simplon Tunnel," Proc. Inst. Civ. Engrs., Vol. CLXXV, p. 61, 1907, 50 pages, illus. A most complete and comprehensive description of the tunnel, methods of driving, plans adopted to overcome the difficulties encoun- tered, costs, etc. DiNSMORE, W. P. J., "Western Practice in Tunnel Driving," Mine and Quarry, p. 118, May, 1907, 5 pages, illus. Describes the equipment and methods used in driving the Ophelia tunnel. Cripple Creek, Col. Anon., "The Commercial Aspects of Present and Proposed Alpine R. R. Tunnels," Editorial, Eng. News, p. 613, Dec. 5, 1907, 3 pages, with excellent map, showing sixteen tunnels in the Alps. CoMSTOCK, Chas. W., "Great Tunnels of the World," Colo. Set. Soc., Vol. VIII, p. 363-386, Dec. 7, 1907. Discusses tem- perature and pressure in deep tunnels. Describes the Mt. Cenis, the Hoosac, the St. Gothard, and the Simplon tunnels. 364 MODERN TUNNELING Anon., ''Preliminary Work on the Los Angeles Aqueduct," Eng, Rec, p. 144, Feb. 8, 1908, 3^ pages, illus. Describes scheme of aqueduct and work done up to Jan. i, 1908. Describes power plants for supplying aqueduct. Describes equipment for Elizabeth tunnel. Anon., "The Second Raton Hill Tunnel of the A. T. and Santa Fe Railway," Eng. Rec, p. 461, Apr. 4, 1908, 7 cols, illus. Describes the methods and equipment used in this work. Anon., "A Private Sewer in Rock Excavation," Eng. Rec, p. 496, Apr. II, 1908, 8 cols., illus. Describes construction of a six-foot sewer draining submerged yards of the new Grand Central station. New York. Ridge WAY, Robt., "Sub-surface Investigations on the Catskill Aqueduct," Eng. Rec, p. 522, Apr. 18, 1908, 8 cols., illus., and Eng. Rec, p. 557, Apr. 25, 1908, 8 cols., illus. Describes preliminary explorative investigations. Abstract of a paper before municipal engineers. New York City. DiNSMORE, W. P. J., "The Second Raton Hill Tunnel of the Atchison, Topeka and Santa Fe Railway," Mine and Quarry, p. 225, June, 1908, 10 cols., 5 illus. Describes the methods and equipment used in this work. BuNCE, Walter H., "Tunnel Driving at Low Cost," Min. Set. Press, p. 60, July 11, 1908. Discusses the equipment, meth- ods, and costs of driving the Chipeta Adit at Ouray, Col. DiNSMORE, W. P. J., "Western Practice in Tunnel Driving," Min. and Met. Journal, Aug. 7, 1908, 3 pages, illus. Plan of work, arrangement of holes, handling of waste rock, and other important points in the driving of the OpheHa Tunnel in the Cripple Creek district. Col. Aims, Walter L, "Methods Employed in Driving Alpine Tun- nels, The Loetschberg," Eng. News, p. 746, Dec. 31, 1908, and also Comp. Air Mag., p. 5163, Feb., 1909. Description of methods and equipment. Anon., "Harvesting Tunnel, Norwegian State Railways," Proc Inst. Civ. Engrs., Vol. CLXXVI, p. 353, 1909. Short de- scription giving length, cost, time required to drive, etc. BoNNiN, R., "The Loetschberg Tunnel," Proc Inst. Civ. Engrs., BIBLIOGRAPHY 365 Vol. CLXXVII, p. 310, 1909. Short description giving methods of driving and difficulties encountered in the work. Describes the inrush of peaty material which swamped the working and drowned twenty-five men. Young, Henry A., "Methods of Tunnel Work and Cost Data on an Irrigation Project," Eng. News, p. 128, Feb. 4, 1909. Concerning three small tunnels in Montana. Anon., "The Roosevelt Tunnel," Min. and Min., p. 387, Apr., 1909, g}4 cols., 6 illus. Describes some of the difficulties encountered in this work and the methods employed to meet them. Chadwick, L. R., "Driving the Mauch Chunk Tunnel," Mine and Quarry, p. 304, June, 1909, 3 pages, illus. Describes some of the methods used in driving this tunnel. Anon., "Progress of the Northwest Water Tunnel in Chicago," Eng. Rec, p. 144, Aug. 7, 1909. Description of the tunnel and the methods used in driving it. McCoNNELL, I. W., "The Gunnison Tunnel of the Uncompaghre Valley Project, U. S. R. S.," Eng. Rec, p. 228, Aug. 28, 1909, 15 cols., illus. Describes the methods and equipment em- ployed in the construction of this tunnel. DiNSMORE, W. P. J., "The Gunnison Tunnel," Mine and Quarry, p. 315, Sept., 1909, 6 pages, illus. Describes the work of enlarging the heading to full size, and some of the difficulties encountered during the progress of the tunnel. Heinly, B. a., "The Longest Aqueduct in the World," Outlook, Vol. XCIII, pp. 215-220, Sept. 25, 1909. Good non- technical account of the Los Angeles aqueduct. Bagg, Rufus M., Jr., "Roosevelt Deep Drainage Tunnel, Col.," E. M. J., p. 106 1, Nov. 27, 1909, 2 pages, illus. Bain, H. F., "Tunnel Driving in Colorado," Min. Sci. Press, Dec. 4, 1909, pp. 733-47. Describes the methods used in driving the Newhouse, Roosevelt, and Gunnison tunnels. Anon., "Proposed Delivery System of the Catskill Water Sup- ply," Eng. Rec, Dec. 11, 1909, 1,500 words. Plan, profile, and description of the system. 366 MODERN TUNNELING McCoNNELL, I. W., '* Gunnison Tunnel, Uncompahgre Valley Irrigation System," Proc. Inst. Civ. Engrs., Vol. CLXXIX, -p. 381, 1910. A short description of the Gunnison tunnel, giving length, size, etc. Bagg, Rufus M., "Tunnel Driving in Colorado," Proc. Inst. Civ. Engrs., Vol. CLXXX, p. 362, 1910. Description of the method of driving the Roosevelt deep drainage tunnel at Cripple Creek. Jacobs, Chas. M., ''The Hudson River Tunnels on the Hudson and Manhattan Railway, Proc. Inst. Civ. Engrs., Vol. CLXXXI, p. 169, 1910. A very complete and compre- hensive description of these tunnels, followed by a discus- sion by the members, covering 88 pages. Anon., "The New Buffalo Water Works Tunnel," Proc. Inst. Civ. Engrs., Vol. CLXXXH, p. 340, 19 10. Short description of the concrete-lined tunnel, 10,845 f^^t long, under Lake Erie. WiGGiN, Thos. H., "The Design of Pressure Tunnels of the Catskill Aqueduct," Eng. Rec, Jan. 29, 1910. Describing deep concrete-lined tunnels which are to be subjected to hydrostatic pressure. Anon., "Walkill Pressure Tunnel," Eng. Rec, p. 45c, Apr. 2, 1910. Describes the preliminary investigations and the equipment installed for this work. Anon., "The Hunters Brook Tunnel Construction," Eng. Rec, p. 454, Apr. 2, 1 910. Describes the equipment and methods employed in this work. Anon., "Tunnels in Being and Tunnels to Come," Sci. Amer., Apr. 23, 1910, 1,200 words. Discusses length, elevation, cost, etc., of famous mountain tunnels. Hancock, H. S., Jr., "Method and Cost of Constructing a Water-Supply Tunnel Through Rock by Day Labor, and Costs of Supplementary Structures," Engng. Contng., May 25, 191 o, 6>3 pages, illus. Discusses the choice of power and describes the equipment and methods used in driving a water-supply tunnel for Fort WiUiams, Ont. Anon., "Report on the Proposed Board of Water-Supply Pressure Tunnel beneath New York City," Eng. News, p. 655, June 2, BIBLIOGRAPHY 367 1910, 4,000 words. Brief historical account of the project, with presentation of estimates and discussion of this and other distribution plans. Lavis, F., ''The New Buffalo Water Works Tunnel," Eng. Rec, p. 802, June 25, 1910. Description of methods of driving and lining a hard-rock tunnel under compressed air. Anon., " Laramie-Poudre Tunnel," Ettg. Rec, p. n, July 2, 19 10, 3 cols., illus. Description of work on Laramie tunnel. Herrick, R. L., "Tunneling on the Los Angeles Aqueduct," Min. and Min., p. no, Oct., 1910, approx. 8 pages. Re- printed in Leyner Bull., 1026. Describes the methods used and gives figures showing the cost of the work. Dodge, S. D., and Wm. B. Hake, "The Hudson River Siphon Crossing of the Catskill Aqueduct," Eng. Rec, p. 414, Oct. 8, 1910, and p. 435, Oct. 15, 1910. Abstract given before mining engineers. New York, describing preliminary investi- gations and sinking of shafts. HuLSART, C. Raymond, "Excavation of the Walkill Pressure Tunnel," Eng. News, p. 406, Oct. 20, 1910, 15 cols., 10 illus. Describes the methods and equipment used in driving this tunnel. Anon., "Driving Spiral Tunnels on the Can. Pac. Ry.," Eng. News, p. 512, Nov. 10, 1910, and also Comp. Air Mag., p. 5931, Feb., 191 1, 6X cols., 5 illus. Illustrated descrip- tion of this work. Palmer, Leroy A., "Utah Metals Company Tunnel," Mines and Minerals, p. 296, Dec, 1910, 3 cols., illus. Description of methods and equipment for driving tunnel which is intended for transportation of ores from Bingham to smelter at Tooele. G. H. S., "Tunnels of Switzerland," Proc Inst. Civ. Engrs., Vol. CLXXXIV, p. 369, 191 1. List of the 415 tunnels in Swit- zerland, giving their length and elevation. WiLGUs, Wm. John, "The Detroit River Tunnel," Proc. Inst. Civ. Engrs., Vol. CLXXXV, p. 2, 191 1. Comprehensive and complete description of the Detroit River tunnel, followed by a discussion of this paper by the members present. Coy, B. G., "The Laramie-Poudre Tunnel," Eng. Rec, Jan, 14, 368 MODERN TUNNELING 191 1. Reprinted in Leyner Bulletin 1029. Description of methods used in driving this tunnel. Lytel, J. L., "The Strawberry Tunnel, U. S. R. S./' Eng. Rec, p. 433, Apr. 22, 191 1, 8 cols., illus. Describes methods, equipment, and cost of driving this tunnel. Doll, M. G., ''Strawberry Valley Tunnel of the Strawberry Val- ley Irrigation Project of Utah," Mine and Quarry, p. 483, May, 191 1, II pages, illus. Describes the methods and equipment and gives some figures showing the cost of this work. Anon., ''Joining the Headings of the Loetschberg Tunnel," Eng. Rec, p. 491, May 6, 191 1. Contains a brief discussion of the methods used in driving this tunnel. Flynn, Alfred D., "Rondout Pressure Tunnel of the Catskill Aqueduct," Eng. News, p. 654, June i, 191 1, 7 pages, pro- fusely illustrated. Describes the tunnel chiefly from the point of view of design. Zalinski, Ed. R., "Driving the Strawberry Tunnel," E. M. /., p. 1 1 53, June 10, 191 1, 2 pages, illus. A description of the equipment and routine adopted by the U. S. R. S. in driving a four-mile concrete-lined tunnel for irrigation water for Utah Valley. Hardesty, W. p., "CorneKus Gap Tunnel, United Rys. Co., near Portland, Oregon," Eng. News, p. 783, June 29, 1911, 2 cols, illus. Brief description of the methods and equipment. Saunders, W. L., "Tunnel Driving in the Alps," Bull. Am. Inst. Min. Engrs., No. 55, p. 507, July, 191 1, 32 pages, illus. Describes and discusses the methods and equipment em- ployed in driving the Simplon and the Loetschberg Tunnels. Anon., "Newton Pressure Tunnel of the Metropohtan Water Works, Boston," Eng. Rec, Oct. 28, 191 1. Description of •a concrete-lined water-way in rock, with short section of 80-inch, mortar-lined and concrete-covered steel pipe at each end. Anon., "Work in the Snake Creek Tunnel," Min. Sci. Press, p. 108, Jan. 13, 191 2. A brief description of some of the methods used in this work. BIBLIOGRAPHY 369 Anon., *' Notes in Driving the Elizabeth Lake Tunnel," Eng. Rec, p. 72, Jan. 20, 191 2, 2 cols. An abstract from the annual report of the chief engineer of Los Angeles aqueduct for the year ending June 30, 191 1, describing several interesting features of the work. Anon., "A Tunnel Street," Municipal Journal, p. 199, Feb. 8, 191 2, 4 cols., illus. Proposed tunnel in upper part of New York City to provide access to subway. Concrete lining. Provision for removing seepage water. White cement finish. Electric Hghting. Unit contract prices. Coy, Burgis G., ''The Laramie-Poudre Tunnel," Proceedings of Amer. Soc. of Civ. Engrs., p. 217, March, 1912, 14 pages, 13 illus. Description of the equipment and methods of driving, Brunton, D. W., "Notes on the Laramie Tunnel," Bui. No. 64, Amer. Inst. Min. Engrs., p. 357, Apr., 191 2, and also abstract in Engng. and Min. Wld., p. 959, May 4, 191 2. Describes the equipment and methods used at this tunnel. Gavin, W. H., "Arthur's Pass Tunnel," Eng. News, p. 870, May 9, 191 2. A description of a five-mile railway tunnel in New Zealand. Russell, Will C, "Driving a Long Adit at Bonanza, Col.," Eng. and Min. Jour., p. 272, Feb. i, 1913. An adit, 7 x 8 ft. in the clear, was driven 6,235 feet, for drainage, exploration, and working, at a cost of $19.87 per foot. Two machines on cross-bars were used. The adit was completed in seven- teen months and two days. WATER-POWER Gray, J. W., "Useful Hydraulic Data," Min. Sci. Press, Vol. LXXVI, p. 179, 1897, 4K cols. Abstract of a paper in New Zealand Mines report by Alex. Aitken, Mgr. Govt. Water, Kumara, New Zealand. Power of water. Friction in pipes and channels, carrying capacity of pipes and channels, capacity of sluices. WooDBRiDGE, D. E., "The Hydraulic Compressed Air Power Plant at the Victoria Mine (Mich.),"£.ilf./.,p. 125, Jan. 19, 370 MODERN TUNNELING 1907. An illustrated article describing an installation of the Taylor system. The tested efficiency of this plant is given as 82 per cent. Edit., ''The Utilization of Small Water Powers," Editorial, Eng. Rec, p. 247, Sept. 7, 1907. Discusses the development of comparatively small streams. Anon., ''Efficiency of Hydraulic Air Compression," E. M. /., p. 228, Aug. I, 1908, 3 cols., illus. Abstract of article in Gluckauf for March 14, 1908, by O. Bernstein. Contains a description of a hydraulic compressor installed in one of the mines at Clausthal, together with tests of its efficiency. Stewart, Sylvester, "Water Power from Streams of Moderate Fall," Cassier^s Mag., p. 470, Sept., 1909, 9 cols., 8 illus. Dis- cusses the possibilities for power development with low dams. McFarlane, Geo. C, "Compressing Air by Water," Min. Sci. Press, p. 281, Feb. 19, 19 10, 2 cols., illus. Discusses ways of using water-power which is so often available in mining districts for the compression of air, and describes several devices for doing this. KoESTER, Frank, "A General Review of the Hydro-electric Engineering Practice," Engr. Mag., 5 articles: Introduc- tion, Dams, p. 24, April, 1910; Head Races, Pressure Pipes, Penstocks, p. 176, May, 1910; Turbines and Mechanical Equipment of Power Plant, p. 340, June, 19 10; Electrical Equipment, p. 494, July, 1910; High Tension Transmission, p. 659, Aug., 1910. Anon., "Taylor Hydraulic Air Compressor (Cobalt)," Comp. Air Mag., p. 5675, June, 1910, 6]A cols. Description taken from an article in Mines and Minerals, by C. H. Taylor. Gray, Alex., "Power Plants of the Cobalt District, Ontario," The Min. World, p. 131, July 23, 1910, 11^ cols., 10 illus. CoY, B. G., "The Laramie-Poudre Tunnel," Eng. Rec, Jan. 14, 1911,4 cols., illus. Contains a description of the water-power plant used in driving this tunnel. VON ScHON, H., "The Most Resourceful UtiHzation of Water Power," Eng. Mag., p. 69, April, 191 1, 21 cols., 5 illus. ^ BIBLIOGRAPHY 371 Bateman, G. C, ''Cobalt Hydraulic Company," E. M. /., p. 998, Nov. 18, 191 1, 1,000 words. Description of a Taylor . compressor in which the air is drawn into a faUing column of water. Compressed air is sold at 25 cents per 1,000 cu. ft. at 120 lbs. pressure. Coy, B. G., ''The Laramie-Poudre Tunnel," Proc. Am. Soc. Civ. Engrs., p. 217, March, 191 2. Contains a description of the water-power plant at this tunnel. Smith, Cecil B., "Power Plants for Mines in the Cobalt Dis- trict," Min. and Eng. World, p. 503, March 2, 191 2, 3^ cols., 2 illus. Description of water-power plants furnishing power to the Cobalt camp. Brunton, D. W., "Notes on the Laramie-Poudre Tunnel," Trans. Am. Inst. Min. Engrs., p. 357, April, 191 2, also abstract in Min. and Engng. World, p. 959, May 5, 191 2. Contains a description of the water-power plant at this tunnel. STEAM POWER Webber, Wm. O., "Comparative Costs of Gasoline, Gas, Steam, and Electricity for Small Powers," Eng. News, p. 159, Aug. 15, 1907, 2}4 cols., tables. Gives itemized cost tables for 2, 6, 10, and 20 horse-power plants. Anon., "The Second Raton Hill Tunnel of the Atchison, Topeka and Santa Fe Ry.," Eng. Rec, p. 461, April 4, 1908. Con- tains a description of the steam-power plant for this tunnel. Anon., "Steam vs. Compressed Air in Mining (Coal)," Comp. Air Mag., p. 5174, Feb., 1909, i col. Compressed air is much better than steam for pumping, coal cutting, etc., in mines. Anon., "The Compressed Air Plant for the Rondout Siphon," Eng. Rec, p. 490, April 10, 1909, 4^ cols., illus., also Comp. Air Mag. (reprint), p. 5291, June, 1909, 7 cols., illus. Anon., " Compressed Air in Construction Work," Eng. Rec, p. 179, Aug. 14, 1909, 4 cols. Discusses the advantages of com- pressed air over steam for the operation of drills, pumps, etc., in construction work. McCoNNELL, I. W., "The Gunnison Tunnel of the Uncompaghre 372 MODERN TUNNELING Valley Project, U. S. R. S.," Eng. Rec, p. 228, Aug. 28, 1909, 15 cols., illus. Contains a description of the steam-power plants used in this work. Chance, T. M., ''Costs of a Gas Engine and of a Combined Steam Plant," Eng. Rec, p. 273, Sept. 4, 1909, 7 cols., 4 illus. Power economy of gas engine is greater than steam, but its first cost and difficulty of operation are also greater. A- corresponding plant using low-pressure turbines and high- economy Corliss engines solves the problem in many places. Anon., "Cost of Power for Various Industries," Eng. Rec, p. 711, Dec. 25, 1909. Review of paper before the Boston Society of Civil Engineers, by Chas. T. Main. Concerns steam power for textile mills, under varying conditions, assuming that it is ultimately converted into electricity. Webb, Rich. L., "Cost of Producing Compressed Air at a Cana- dian Mining Camp," Can. Min. Jour., p. 102, Feb. 15, 1910, 20 cols., 10 tables. Results of tests on two steam-driven air compressors. Haight, H. v., "Steam Driven Air Compressors in Cobalt," Can. Min. Jour., p. 209, April i, 19 10, 3^/^ cols. Discussion of the paper by Rich. L. Webb, Can. Min. Jour., Feb. 15, 1910, p. 102. Anon., "The Hunters Brook Tunnel Construction," Eng. Rec, p. 454, April 2, 1 9 10. Contains a description of the steam- power plant for this tunnel. Anon., " Cost of Power Production in Small Steam Plants," Eng. Rec, p. 570, April 30, 19 10. Discusses the cost of steam- electric power in small stations. Anon., "The Moodna Pressure Tunnel of the Catskill Aqueduct (Power Plant)," Eng. Rec, p. 731, June 4, 1910. Descrip- tion of the two power plants used to furnish the compressed air used in driving this tunnel. Anon., "Driving Spiral Tunnels on the Can. Pac. Ry.," Eng. News, p. 512, Nov. 10, 1910, 6 cols., 5 illus. Contains a de- scription of the steam-power plant for this work. Anon., "Exhaust Steam Turbines at Mines," Min. and Min., p. 371, Jan., 1912, 5 pages, illus. Abstract of a paper before BIBLIOGRAPHY 373 Australasian Inst. Min. Engrs., June, 191 1. Describes use of turbine engines to utilize exhaust steam from various engines of a mine plant. Clark, S. M., ''The Fuel Cost of Making Steam," The Isolated Plant, p. 129, April, 191 2, 12 cols., 3 illus. Discusses the means of judging and comparing coal. INTERNAL-COMBUSTION POWER Webber, Wm. 0., ''Comparative Costs of Gasoline, Gas, Steam, and Electricity for Small Powers," Eng. News, p. 159, Aug. 15, 1907, 2}4 cols., tables. Gives itemized cost tables for 2, 6, 10, and 20 horse-power plants. Thwaite, B. H., "The Blast Furnace as a Center of Power Pro- duction," Cassier's Mag., p. 23, Nov., 1903, 36 cols., 15 illus. Adams, E. T., "The Development of the Large Gas Engine in America," Gassier' s Mag., p. 41, Nov., 1907, 22 cols., 15 illus. Development of gas engine supplied with gas from blast furnace. Humphrey, H. A., "By-product Recovery Gas-producer Plants," Gassier' s Mag., p. 55, Nov., 1907, 17 cols., 11 illus. Mr. Humphrey treats of the recovery of such a valuable com- mercial article as sulphate of ammonia from the waste of the gas-producer, showing the success which has been attained by Dr. Ludwig Mond and his associates. Bibbins, J. R., "Recent Applications of Gas Power," Gassier' s Mag., p. 147, Nov., 1907, 13 cols., 9 illus. Discusses the recent installations of producer-gas plants in this country, showing the amount of power so used and the sizes of the plants. Rowan, F. J., "The Suction Gas Producers," Cassier's Mag., p. 174, Nov., 1907, 48K cols., 24 illus. Harvey, Elbert A., "Power Gas from Bituminous Coal," Gas- sier's Mag., p. 199, Nov., 1907, 14 cols., 8 illus. States that the bituminous gas-producer is no longer an experiment, and describes several such producers which will give satis- factory service. RoBSON- Philip W., "Power Gas-producers, their Design and 374 MODERN TUNNELING Application," published by Edward Arnold, London, Eng., 1908, 247 pages, 105 illus. FernalD; R. H., ''Producer-gas Power Plant in the United States," Cassier's Mag., p. 582, Feb., 1908, 13 cols. Anon., "Test of a Small Gas-producer Plant," Eng. Rec, p. 375, March 28, 1908, 2^ cols. Describes the 15 horse-power plant of the Weber Wagon Works, Chicago, and gives the results of tests. Barbezat, Alfred, "Recent Developments in the Gas Turbine," Gassier^ s Mag., p. 617, April, 1908, 6 cols., 3 illus. Anon., "The Loomis-Pettibone Gas-generating System," Cas- sier^s Mag., p. 685, April, 1908, 2 cols. A discussion of the principles underlying this system for use with bituminous coal. Anon., "A Producer-gas Power Plant," Eng. Rec, p. 478, April 4, 1908. A brief reference to a test of a 600 horse-power pro- ducer-gas plant at the works of David Rowan & Co., at Glasgow. Lewis, W. Y., "The Carbon Monoxide Gas-producer," Gassier^ s Mag., p. 223, July, 1908, id>}4 cols. Discusses the advan- tages of a straight carbon monoxide gas-producer as devel- oped at the Phoenix Tube Mill plant in Long Island City. Anon., "The Suction Gas-producer Plant at the Shops of Fair- banks, Morse & Co.," Eng. Rec, Sept. 5, 1908. Description of this plant, giving also results of tests. White, T. L., "The Reliabihty of the Gas-producer Plant," Gassier^ s Mag., Oct., 1908, $% pages. Describes a test made upon a small gas-producer plant, and discusses gas plants from a point of view of reliabihty as compared with other plants. Burt, T. W., "The Suction Gas-producer," Gassier^ s Mag., p. 124, June, 1909, II pages. Description of the theory and design of the suction gas-producer with drawings of four important types. Anon., "Test of a Double Zone Bituminous Gas-producer," Eng. News, p. 13, July i, 1909, 7 cols., 4 illus. Results of experi- mental work at the plant of the Westinghouse Machine Co., at East Pittsburgh. BIBLIOGRAPHY 375 Atkinson, A. S., ^'Gas Engines for Mining Purposes," Min. Set. Press, p. 300, Aug. 28, 1909, 3^^+ cols. Discusses the advantages of gas engines for mining power plants, showing some of their advantages over steam and electricity. Chance, T. M., ''Costs of a Steam Engine and of a Combined Steam Plant," Eng. Rec, p. 273, Sept. 4, 1909, 7 cols., 4 illus. Power economy of gas engine is greater than steam, but its first cost and difficulty of operation are also greater. A cor- responding plant using low-pressure turbines and high- economy Corliss engines solves the problem in many places. Gradenwitz, Dr. Alfred, ''A New Gas-producer for Low, Grade Fuel," Power and the Engineer^ p. 653, Oct. 19, 1909, 3^^ cols., 3 illus. Discusses a gas-producer designed to oper- ate upon anthracite, coke, and smoke-chamber dust and other rubbish, giving figures showing the consumption of these materials per horse-power hour. SuPLEE, Henry H., ''The Explosion Gas Turbine," Gassier^ s Mag., p. 79, Nov., 1909, 6 cols., 2 illus. Describes an experi- mental explosion gas turbine of 2 horse-power as developed by M. Karavodine in Paris. Anon., "Tests of a Suction Gas-producer," Univ. of 111. Bull. 50, 90 pages, illus. and tables. Reviews theory of gas-producer, explaining object of tests, methods of experimenting, giving results and conclusions. Fernald, R. H., "Features of Producer-gas Power-plant Devel- opment in Europe," (U. S.) Bureau of Mines Bulletin 4, 1910, 27 pages, 4 plates, 7 figs. Briefly summarizes some features of gas-producer practice with particular reference to the use of low-grade fuels. Miller, J. C, "Power Gas and Gas-producer," published by Popular Mechanics Co., Chicago, 111., 1910, 184 pages. Clement, J. K., L. H. Adams, and C. N. Haskins, "Essential Factors in the Formation of Producer-gas," (U. S.) Bureau of Mines, Bulletin 7, 191 1, 58 pages, i plate, 16 figs. De- scribes laboratory experiments bearing on the rate of forma- tion of carbon monoxide at high temperatures and the effect of temperature on the rate of formation and the 376 MODERN TUNNELING composition of water gas. Indicates how the results of the tests apply to the operation of boiler furnaces and gas- producers. Fernald, R. H., and CD. Smith, ''Resume of Producer-gas Investigations," Oct. i, 1904, to June 30, 19 10, (U. S.) Bureau of Mines, Bulletin ij, 191 1, 393 pages, 12 plates, 250 figs. Summarizes the results of producer-gas investigations at the Government fuel- testing plants. Incidentally dis- cusses gas-producer development in this country and in Europe. Is intended especially for mechanical engineers and power-plant officials interested in gas-producer design and in the operation of gas-producers on the coals available at different points in the United States. Davis, C. A., "The Uses of Peat for Fuel and Other Purposes," (U. S.) Bureau of Mines, Bulletin 16, 191 1, 214 pages, i plate, I fig. Summarizes recent developments in the utilization of peat. Treats pf the origin and formation of peat, its fuel value, and the manufacture of peat fuel. Also summarizes progress in utilizing peat for other purposes. Smith, C. D., J. K. Clement, and H. A. Grine, ''Incidental Problems in Gas-producer Tests," (U. S.) Bureau of Mines, Bulletin Ji, 29 pages, 8 figs. Considers the factors affecting the proper length of gas-producer tests and the differences in temperatures at different points in the fuel bed. Reprint of the (U. S.) Geol. Survey Bulletin jpj. Strong, R. M., "Commercial Deductions from Comparisons of Gasoline and Alcohol Tests of Internal-combustion Engines," (U. S.) Bureau of Mines, Bulletin J2, ^S pages. Summarizes deductions based on 2,000 tests of gasoline and alcohol. Reprint of (U. S.) Geol. Survey Bulletin jg2. WiTZ, A., "The Use of Gas Engines in Central Stations (L'Em- ploi des moteurs a gaz dans les stations centrales d'electri- cite)," Genie Civil, No. 28,861 D.,Nov. 11, 191 1, 5,600 words. Discussion of the feasibility of the use of gas, and results of some of the tests made. Meriam, J. B., "The Relative Economy of Gas Engines and Other Sources of Power," Jour. Cleveland Engng, Soc., p. 121, BIBLIOGRAPHY 377 Dec, 191 1, 2,200 words, illus. Discusses the advantages and disadvantages of oil and gas engines in plants of moderate size and gives examples of recent installations. Anon., ''New Bituminous Gas-producer," Iron Age, Dec. 14, 191 1, 1,200 words, illus. Illustrates and describes the Nor- densson furnace gas-producer. Weil, J. A., ''Producer- gas," Mech. Engr.,p. 755, Dec. 15, 1911, 3,000 words. Discusses the proper design of plant. Strong, R. M., and Lauson Stone, "Comparative Fuel Values of Gasoline and Denatured Alcohol in Internal- Combustion Engines," (U. S.) Bureau of Mines, Bulletin 4j, 191 2, 243 pages, 3 plates, 32 figs. A detailed statement of the results of 2,000 tests made to determine the comparative value of the two fuels for use in internal-combustion engines. Is a technical report, written for mechanical engineers and per- sons interested in the utilization of liquid fuels. Fernald, R. H., "The Status of the Gas-producer and the Internal-combustion Engine in the Utilization of Fuels," (U. S.) Bureau of Mines, Technical Paper g, 191 2, 42 pages, 6 figs. Relates the progress in the application of the gas- producer to commercial uses, and in the development of gas power. Anon., "An English Wood Refuse Suction Gas-producer," Sci. Amer., p. 3, Supplement No. 1879, Jan. 6, 191 2, i col. Describes the machine and discusses its advantages. Anon., "Temporary Power Plant for the Woolwich Footway Tunnel," Engineer (London), p. 46, Jan. 12, 191 2, 2 pages, illus. Description of a plant using suction gas-producers as a source of motive power to operate the air-compressors for a tunnel under the Thames driven under compressed air. Anon., "The Gas Power Field for 191 1, a Review of the Past Year," Sci. Amer., p. 58, Supplement No. 1,882, Jan. 27, 191 2, 6 cols. Paper read before the Gas Power Section of the American Association of Mechanical Engineers. Anon., "The Bituminous Gas Engine in South Africa," The En- gineer, p. 258, March 8, 191 2, 4 cols., 3 photos. Describes 378 MODERN TUNNELING the producer and gives results of its use at the Groenfontein tin mines in the Transvaal. Percy, Paul C, '' Combination Power and Ice Plant," Power, p. 418, March 26, 191 2, 8 illus. Describes a plant using wood-refuse gas-producers as prime movers and gives results of tests. Anon., '' What is the Diesel Engine? " Eng. News, pp. 654-6, April 4, 191 2, 6)4 cols. An excellent recitation in non- technical language of the principles upon which this machine operates. Chorlton, Alan E. L., " Gas Engines for Collieries,'' Coal Age, pp. 876-9, April 13, 191 2, 5 illus. Gas engines are being largely used at British colHeries for the generation of power. The gas is generated either in producers or in coke ovens. Producers can be sometimes made to yield such products from by-products, where the fuel is of low grade, that even without using the gas produced, the in- stallation will justify its erection. (Paper read before Mid- land Institute of Mining, Civil, and Mechanical Engineers.) Diesel, Rudolph, " The Present Status of the Diesel Engine in Europe," Jour. Am. Soc. Mech. Engrs., June, 191 2, 40 pages, 50 illus. Garland, C. M., '' Bituminous Coal Producers for Vower/Uour. Am. Soc. Mech. Engrs., p. 833, June, 191 2, 20 pages, 2 illus. Describes the apparatus and general arrangement of bituminous-coal producers as designed for power. Dis- cusses also the efficiency of the plant, composition of the gas, and operating costs. ELECTRIC POWER ScHAEFER, E. F., '' Compressed Air vs. Electricity," Min. and Min., p. 425, April, 1906, 2}^ cols. Discusses the advantages of compressed air over electricity for mining purposes. Webber, Wm. 0., '' Comparative Costs of Gasoline, Gas, Steam, and Electricity for Small Powers," Eng. News, p. 159, Aug. 15, 1907, 2>^ cols., tables. Gives itemized cost tables for 2, 6, 10, and 20 horse-power plants. BIBLIOGRAPHY 379 Kerr, E. W., ''Power and Power Transmission," 1908, 366 pages. Published by John Wiley & Sons, New York City. , " Electric Power Costs in Small Station," Eng. Rec, p. 30, Jan. 9, 1909, i^ cols. Discusses the power costs at several small towns near Boston, Mass. Spellmire, W. p., " The Use of Electricity as Applied to Coal Mining," E. M. J., p. 507, March 6, 1909. Discusses the advantages of electricity as a source of power for coal- mining plants. Anon., " Cost of Power for Various Industries," Eng. Rec, p. 711, Dec. 25, 1909. Review of paper before the Boston Society of Civil Engineers, by Chas. T. Main. Concerns steam power for textile mills under varying conditions, assuming that it was ultimately converted into electricity. KoESTER, Frank, ''A General Review of the Hydro-electric Engineering Practice," Engr. Mag., 5 articles: Introduction, Dams, p. 24, April, 1910; Head Races, Pressure Pipes, Penstocks, p. 176, May, 19 10; Turbines and Mechanical Equipment of Power Plant, p. 340, June, 19 10; Electrical Equipment, p. 494, July, 19 10; and High Tension Trans- mission, p. 659, Aug., 1910. Anon., '' Cost of Power Production in Small Steam Plants," £;z^. Rec, p. 570, April 30, 1910. Discusses the cost of steam- electric power in small stations. Anon., '' Cost of Power Transmission, Electricity vs. Compressed Air," Min. Set. Press, p. 700, May 14, 1910, }^ col. Esti- mates prepared by the Pneumelectric Machine Co., for the cost of dehvering 200 horse-power one mile by com- pressed air and electricity (direct current, 250 volts). Anon., " Methods and Costs of Constructing a Water Supply Tunnel," Engng. Contng., p. 472, May 25, 1910, 6 cols., 6 illus. Describes the electrically driven power plant for this work near Ft. Williams, Ont. Anon., " Electricity in the Construction of the Los Angeles Aqueduct," Eng. Rec, July 16, 1910, 6 cols., illus. De- scribes central generating station and cost of trans- mission line. 380 MODERN TUNNELING HuLSART, C. R., '' Excavation of the Wallkill Pressure Tunnel, Catskill Aqueduct," Eng. News, p. 406, Oct. 20, 1910, 15 cols., 10 illus. Contains a description of the electrically driven power plant for this work. Yerbury, H. E., '' Electricity as Applied to Modern Tunnel Work," Proc. Inst. Civ. Engrs., Vol. CLXXXIII, p. 296, 191 1, 8 pages. Discusses the application of electricity to tunneling work; giving description of power station, tunnel equipment, tunnel driving, etc. Edit., " High Tension Line Problems," Editorial Eng. Rec, p. 289, March 18, 191 1. Discusses some of the difficulties connected with high-tension electric lines. Knowlton, H. S., " Developing Electrical Energy from the Los Angeles Aqueduct," Elec. World, p. 301, Feb. 10, 191 2, 12 cols., illus. Plans for estabHshing a large hydro-electric system in connection with the creation of a new water supply. Electrical energy will be sold as a by-product of a $23,000,000 water system. Maximum delivery 90,000 kilowatts into city of Los Angeles. Extensive use of electricity in aqueduct construction. COMPRESSED AIR POWER ScHAEFER, E. F., ''Compressed Air vs. Electricity," Min. and Min., p. 425, April, 1906, 2}^ cols. Discusses the advantages of compressed air over electricity for mining purposes. Gray, Alex., "Compressed Air for Mining in Cobalt District," Min. Wld., p. 877, Dec. 12, 1908, 6}^ cols., 2 illus. Factors influencing the supply of air for mines. Marked increase in steam and gas-producer plants in last four years. Cost of compressing air. Taylor hydraulic air-compressor system. Anon., ''Steam vs. Compressed Air in Mining" (Coal), Comp. Air Mag., p. 5174, Feb., 1909, i col. Compressed air is much better than steam for pumping, coal cutting, etc., in mines. Anon., ''Compressed Air in Construction Work," Eng. Rec, p. 179, Aug. 14, 1909, 4 cols. Discusses the advantages of compressed air over steam for the operation of drills, pumps, etc., in construction work. BIBLIOGRAPHY 381 Anon., "Cost of Power Transmission: Electricity vs. Compressed Air," Mi7t. Sci. Press, p. 700, May 14, 1910. Estimates prepared by the Pneumelectric Machine Co. for the cost of delivering 200 horse-power one mile by compressed air and electricity (direct current, 250 V.). \'iLLETARD, H., ''AppUcation of Compressed Air in Tunnels (Applications de I'air comprime a la perforation des grands sou terrains)," Tech. Mod., Nov., 191 1, 2,500 words, illus. With particular reference to large European railway tunnels. POWER TRANSMISSION LucKE, Charles E., "Power Transmission by Producer-gas," Gassier' s Mag., p. 210, Nov., 1907, 6 cols. Discusses the advantages of producer-gas as a means of power transmission. Richards, Frank, "Compressed Air Leakage," Comp. Air Mag., p. 4717, Jan., 1908, 2^ cols. Examples where pipe did not leak. Smith, C. A., "Power Transmission," Cassier^s Mag., p. 275, July, 1908, io>^ cols. A comparative study of the merits of gas and electricity. Emerson, Harrison Dexter, "Long-Distance Gas Transmis- sion," Cassier's Mag., p. 275, May, 1910, 2 cols., 4 illus. Facts connected with the long-distance pumping of natural gas through pipe Hnes from the fields of Pennsylvania and West Virginia. Anon., "Cost of Power Transmission: Electricity vs. Compressed Air," Mm. Sci. Press, p. 700, May 14, 1910, H col. Estimates prepared by the Pneumelectric Machine Co., for the cost of deHvering 200 horse-power one mile by compressed air and electricity (direct current, 250 volts). Edit., "High Tension Line Problems," Eng. Rec, p. 289, March 18, 191 1. Editorial discusses some of the difficulties connected with high-tension electric lines. Richards, Frank, "Draining Compressed Air," Comp. Air Mag., p. 5997, April, 191 1, 4 cols. Abstract of article in Eng. Rec, Feb. 18, 1911, p. 203. 382 MODERN TUNNELING Edit., "Freezing up of Compressed Air Lines," Comp. Air Mag., p. 6017, April, 191 1, 2 cols. Editorial. MacIntire, H., "Power from Compressed Air," Power, Nov. 7, 1911, 1,550 words; also Comp. Air Mag., p. 6259, Dec, 1911. Discusses air transmission in pipe lines and developing power from an air system. Anon., "Proportion of Air Mains and Branches," E.M.J., p. 1027, Nov. 25, 191 1. A table showing diameters of branches that can be supplied by mains of certain sizes. Anon., "Power from Compressed Air," Amer. Mech., Nov. 30, 191 1, 1,200 words. Considers the transmission of power by an air system; the ec'onomy and applications. CHOICE OF POWER Webber, Wm. 0., "Comparative Costs of Gasoline, Gas, Steam, and Electricity for Small Power," Eng. News, p. 159, Aug. 15, 1907, 2>^ cols., tables. Gives itemized cost tables for 2, 6, 10, and 20 horse-power plants. Moses, Percival R., "Power Plant Waste," Cassier^s Mag., p. 497, Oct., 1909, 16 cols.; p. 12, Nov., 1909, 13 cols.; p. 320, Feb., 1910, 13 cols. A series of articles dealing with waste in power plants and the means of preventing it. Anon., "Methods and Costs of Constructing a Water Supply Tunnel through Rock," Engng. Contng., p. 472, May 25, 1910, 6 cols., illus. Discusses the choice of motive power for this work near Fort Williams, Ont., electricity being chosen. POWER PLANT DESCRIPTIONS Anon., "Preliminary Work on the Los Angeles Aqueduct," Eng. Rec, p. 144, Feb. 8, 1908. Contains a description of the electric power plant for supplying power to the aqueduct work. Anon., "Test of a Small Gas-producer Plant," Eng. Rec, p. 375, March 28, 1908, 2}^ cols. Describes test of 15 horse-power plant of the Weber Wagon Works, Chicago, 111. BIBLIOGRAPHY 383 Anon., "The Second Raton Hill Tunnel of the Atchison, Topeka and Santa Fe Railway," Eng. Rec, p. 461, April 4, 1908. Contains a description of the power plant for this tunnel. Anon., ''The Suction Gas-producer Plant at the Shops of Fair- banks, Morse & Co.," Eng. Rec, Sept. 5, 1908. Description of this plant, giving also results of tests. Anon., "The Compressed Air Plant for the Rondout Siphon," Eng. Rec, p. 490, April 10, 1909, /^yi cols., illus., and also in Comp. Air Mag., p. 5391, June, 1909, 7 cols., illus. Descrip- tion of a compressed-air plant of 24,000 cubic feet capacity for the Rondout Siphon tunnel of the Catskill Aqueduct. McCoNNELL, I. W., "The Gunnison Tunnel of the Uncom- paghre Valley Project, U. S. R. S.," Eng. Rec, p. 228, Aug. 28, 1909, 15 cols., illus. Contains a description of the steam- power plants used in this work. Atkinson, A. S., "Gas Engines for Mining Purposes," Min. Set. Press, p. 300, Aug. 28, 1909. Contains a brief description of the gas-engine power plant for the Powell Duffryn ColHeries in South Wales. Moses, Percival R., "Power Plant Waste," Gassier' s Mag., p. 497, Oct., 1909, 13 cols. The last of a series of three articles deahng with this subject. In this number several specific examples are given, showing the defects and preventable waste and the remedial methods therefor. Anon., "Wallkill Pressure Tunnel," Eng. Rec, p. 450, April 2, 1 9 10. Contains a description of the power plant installed for this work. Anon., "The Hunters Brook Tunnel Construction," Eng. Rec, p. 454, April 2, 1910. Contains a description of the power plant for this tunnel. Anon., "Cost of Power Production in Small Steam Plants," p. 570, Eng. Rec, April 30, 19 10. Discusses the cost of steam- electric power in small stations and describes four examples. Anon., "Methods and Costs of Constructing a Water Supply Tunnel," £w^w^. Contng.,p. 472, May 25, 1910, 6 cols., 6 illus. Describes the electrically driven power plant for this work near Fort Williams, Ont. 384 MODERN TUNNELING Anon., "The Moodna Pressure Tunnel of the Catskill Aqueduct (Power Plants)," Eng. Rec, p. 731, June 4, 19 10. Descrip- tion of the two power plants used to furnish the compressed air used in driving this tunnel. HuLSART, C. R., ''Excavation of the Wallkill Pressure Tunnel, Catskill Aqueduct," Eng. News, p. 406, Oct. 20, 1910, 15 cols., 10 illus. Contains a description of the electrically driven power plant for this work. Anon., ''Driving Spiral Tunnels on the Canadian Pacific Rail- way," Eng. News, p. 512, Nov. 10, 1910, 6 cols., 5 illus. Contains a description of the steam-power plant for this work. Palmer, Leroy A., "Utah Metals Company Tunnel," Min. and Min., p. 296, Dec, 1910. Contains a description of the water-power plant at this tunnel. Coy, B. G., "The Laramie-Poudre Tunnel," Eng. Rec, Jan. 14, 191 1, 4 cols., illus. Contains a description of the water- power plant used in driving this tunnel. Lytel, J. L., "The Strawberry Tunnel, U. S. R. S.," Eng. Rec, p. 433, April 22, 191 1. Contains a description of the power plant for this project. Anon., "Temporary Power Plant for Woolwich Footway Tun- nel," Engineer (London), p. 46, Jan. 12, 191 2, 2 pages, illus. Description of a plant using suction gas-producers as a source of motive power to operate the air-compressors for a tunnel under the Thames, driven under compressed air. Coy, B. G., "The Laramie-Poudre Tunnel," Proc. Am. Soc. Civ. Engrs., p. 217, March, 191 2. Contains a description of the water-power plant at this tunnel. Smith, Cecil B., "Power Plants for the Mines in the Cobalt District," Min. and Engr. World, p. 503, March 2, 191 2, 3^ cols., 2 illus. Description of water-power plants furnish- ing power to the Cobalt camp. Anon., "The Bituminous Gas Engine in South Africa," The Engi- neer, p. 258, March 8, 191 2, 4 cols., 3 photos. Contains a description of a bituminous producer plant at the tin mines on the Groenfontein farm in the Transvaal. BIBLIOGRAPHY 385 Brunton, D. W., "Notes on the Laramie-Poudre Tunnel/' Trans. Am. Inst. Min. Engrs., p. 357, April, 191 2; also abstract in Engng. and Min. World, p. 959, May 4, 191 2. Contains a description of the water-power plant at this tunnel. AIR COMPRESSORS WiGHTMANjL. I./' Electrically Driven Air Compressors for Metal Mining Purposes," Comp. Air Mag., p. 3054, Aug., 1904, 10^ pages, illus. ■-, ''The Air Power Plant of the Modern Mine," Min. Mag., p. 357, Nov., 1905, 20 cols. Discusses the advantages and disadvantages of different types of air compressors. , ''Compressed Air, its Production, Transmission, and Application," Proc. Eng. Soc. West Penna., Vol. XXII, p. 197, June, 1906, 42^2 pages. A detailed discussion of the problems encountered in air compression, including stage compression, cooling devices, types of compressors, and receivers. Cone, J. D., "Selection of Proper Air Compressor," Min. and Min., Vol. XXVII, p. loi, Oct., 1906, 6K cols., 6 illus. Economic and mechanical considerations influencing the purchase. WooDBRiDGE, D. E., "The Hydraulic Compressed Air Power Plant at the Victoria Mine (Mich.)," E. M. /., p. 125, Jan. 19, 1907, 5 pages, illus. Description of the Taylor system. Tested efficiency, 82 per cent. Hart, J. H., "Compressed Air in Mining," E. M. J., Vol. LXXXIII, p. 855, 1907, 214 cols., illus. Describes principle of the Taylor air compressor and suggests a simple applica- tion of it for use in mine shaft. Halsey, F. a., "A New Development in Air Compressors," E. M. J., Vol. LXXXIV, p. 397, Aug. 31, 1907, 11 cols., illus. A constant speed electrically operated, variable delivery air compressor that automatically varies the delivery to meet fluctuating demand. Anon., "Efficiency of Hydraulic Air Compression," E. M. J., p. 228, Aug. I, 1908. Abstract of article in GlUckauf, March 386 MODERN TUNNELING 14, 1908, by P. Bernstein. Contains a description of a hydraulic compressor installed at one of the mines at Clausthal, together with tests of its efficiency. Brown, C. Vessey, "Air Compressors," Cassier's Mag., p. 511, Oct., 1908, 27 pages. Discusses the important features in the design of air compressors, and describes a number of types and makes. Anon., "Rock Excavation with a Portable Air Compressor Out- fit," Eng. Rec, p. 25, Jan. 2, 1909, 3 cols., illus. Describes and discusses portable gasoline compressor. Anon., "High Pressure Gas Transmission," Comp. Air Mag., P- 5306, June, 1909, 3 cols. Describes a compressor used in pumping the gas for high-pressure transmission. Webb, Rich. L., "Cost of Producing Compressed Air at a Canadian Mining Camp," Can. Min. Jour., p. 102, Feb. 15, 1910, 20 cols., 10 tables. Results of tests on two steam- driven air compressors. McFarlane, Geo. C, " Compressing Air by Water," p. 281, Min. Sci. Press, Feb. 19, 1910, 2 cols., illus. Contains descriptions of several devices for converting the water-power, which is so often available in mining districts, into compressed air. Anon., "Taylor Hydraulic Air Compressor (Cobalt)," Comp. Air Mag., p. 5675, June, 1910, 6>^ cols. Description taken from an article in Mines and Minerals, by C. H. Taylor. Rice, Rich. H., "Commercial Application of the Turbo-compres- sor," Proc. Am. Soc. Mech. Engrs., p. 303, 191 1, 12 pages, 6 illus. Describes a turbo-compressor for blast-furnace work and its automatic governing mechanism. Gives data upon the sizes, capacity, and performance of the compressor. Bateman, G. C, "Cobalt Hydraulic Company," E. M. /., p. 998, Nov. 18, 191 1, 1,000 words. Description of a Taylor compressor in which the air is drawn into a falling column of water. Compressed air is sold at 25 cents per 1,000 cubic feet at 120 pounds pressure. LowENSTEiN, L. C, "Centrifugal Compressors," series of arti- cles in the Gen. Elec. Review, p. 136, March, 191 2, 8 pages, 7 illus. : theoretical discussion of the principles of the cent- BIBLIOGRAPHY 387 rifugal compressor and the factors that influence efficient operation; p. 185, April, 191 2, 11 pages, 14 illus. Describes the application of centrifugal compressors to various kinds of work; p. 317, May, 1912, 8 pages, 7 illus. Discusses the rating of centrifugal compressors and the amount of power required for their operation. Anon., "Free-Piston Internal- Combustion Air-Compressor," Engineering J p. 285, March 1,1912, 2}^ cols. , 3 illus. Descrip- tion of a machine recently developed by Signor Matricardi, Palanza, Italy, in which a heavy piston is propelled from one end of a cylinder to the other, and during its motion compresses air in front of it. Sibley, Robert, "Power Computation of Rotary Air Compres- sors," Jour. Elec. Power and Gas, p. 270, March 23, 191 2, 4>^ cols., 3 illus. An elementary discussion of the theoretical computation of power required in rotary air compression. LowENSTEiN, L. C, "The Centrifugal Compressor in the Man- ufacture of Gas," Am. Gas Light Jour., p. 204, March 25, 191 2, 10 cols., 6 illus. Describes and discusses the principles of operation of turbo-compressors. Describes an automatic governing device in detail and cites a number of examples of the use of turbo-compressors. Anon., "Turbo-compressors in Practical Service," Iron Age, April 4, 191 2, 4 cols., 2 illus. Discusses the commercial promise of turbo-compressors and blowers and the efficiency of the different means of driving them. Also cites several installations. WiGHTMAN, L. I., "The Compressed Air Plant for Use at Mines," Min. and Eng. World, p. 757, April 6, 191 2, 4 cols. Dis- cusses the advantages and disadvantages of different types of air compressors, together with the difficulties encoun- tered with pipe lines. Davy, Norman, "The Gas Turbine," The Engineer (London), p. 421, April 26, 1912, 7 cols., 4 illus. The fifth of a series of articles on the gas turbine and contains a description of turbo-compressors as one of the accessory machines required with the gas turbine. 388 MODERN TUNNELING Stone, S. R., "Increasing the Efficiency of Air Compressors/' Min. and Eng. World, p. 1039, May 18, 191 2. Discusses the means of preventing losses in air compression due to heat, clearance, and rarefaction. HoLDSWORTH, F. D., "Volumctric Efficiency of Air Compres- sors," E. M. J., p. 1028, May 25, 1912, 4 cols., i illus. Dis- cusses the unavoidable losses in air compression. Describes an apparatus for measuring the quantity of air delivered by the machine, which is the only way to secure an accurate determination of its efficiency. Anon., "Turbo Blowers and Compressors," The Engineer (Lon- don), p. 578, May 31, 191 2, 2}4 cols., 4 illus. Describes a 20-stage machine installed at Manchester and discusses the advantages of turbo-compressors. Anon., "Turbo Blowers and Turbo-compressors," Iron and Coal Trades Rev., p. 874, May 31, 191 2, $}4 cols., 10 illus. Gives results of tests of a single-stage rotary blower and illustrates several turbo-blowers and compressors. COMPRESSION OF AIR Hiscox, Gardner D., " Compressed Air and Its Application," 800 pages, 535 illus. Published by Norman W. Henley & Co., New York, 1901. Saunders, W. L., '^Compressed Air Information, 1903," 1165 pages, 490 illus. PubHshed by Compressed Air Mag., New York, 1903. Saunders, W. L., '' Notes on Accidents Due to Combustion within Air Compressors," E. M. J., p. 554, April 11, 1903. Discusses the occurrence of accidents and the means for their prevention. Anon., ''Air Compression at High Altitudes," Min. and Min,, Vol. XX, p. 324, 1903, 1% cols. GoFFE, E., " Causes of Explosions in Air Compressors," E. M. /., p. 686, April 28, 1904, 4^ cols. An elaborate discussion of the causes of air explosions. Concludes that the chief one is probably the accumulation of dust which absorbs BIBLIOGRAPHY 389 oil and when heated by the compressed air gives off explosive gases. Go w, Alexander M.," Ignitions and Explosions in the Discharge Pipes and Receivers of Air Compressors," Eng. News, p. 220, March, 1905, 2}^ cols. Detailed results of an elaborate study of the causes of air-receiver explosions, with recom- mendations as to means of preventing them in the future. WiGHTMAN, L. I., '' Compressed Air: Its Production, Trans- mission, and Application," Proc. Eng. Soc. West Pa., Vol. XXII, p. 197, June, 1906, 42>^ pages. A detailed dis- cussion of the problems encountered in air compression, including stage compression, cooling devices, types of compressors and receivers. Cone, J. D., " Selection of Proper Air Compressor," Min. and Mm., p. loi, Oct., 1906, 6K cols., 6 illus. Discusses the econ- omic and mechanical considerations influencing the purchase. Peele, Robert, " Compressed- Air Plant for Mines," published by John Wiley & Sons, New York, 1908, 320 pages, 112 illus. Brinsmade, Robt. B., " High z;5. Low Pressure for Compressed Air in Mines," E. M. J., p. 161, Jan. 18, 1908, t,}^ cols., illus. Contains a discussion of the effects of heat during compression, together with the devices for its removal. Redfield, S. B., '' Imperfect Intercooling and Efficiency of Compression," Comp. Air Mag., p. 4887, June, 1908, 11 cols., illus. Discusses relation of cooHng to efficiency. Rix, E. A., " Compressed Air Calculations," Comp. Air Mag., p. 4894, June, 1908, 10 cols. Paper read before the Mining Association of the University of California. Discusses calculations" for design of compressed-air plants, to be used for a definite purpose, giving methods of procedure in cal- culating sizes, etc., of equipment. Anon., " Efficiency of Hydraulic Air Compression," E. M. J., p. 228, Aug. I, 1908, 3 cols., illus. Abstract of article in Gluckauf, March 14, 1908, by P. Bernstein. Contains a description of a hydrauKc compressor installed in one of the mines at Clausthal, together with tests of its efficiency. 390 MODERN TUNNELING Burgess, J. A., '' Explosion in Compressed-Air Main," Min. Sci. Press, p. 731, Nov. 28, 1908, 3>^ cols., letter to the editor, and also Comp. Air Mag., p. 5186, Feb., 1909. Describes an explosion at the Tonopah Mining Co., discusses the probable causes, and gives the precautions being taken to guard against a similar occurrence. Richards, Frank, " Probable Cause of Compressor Explosions," Comp. Air Mag., p. 5250, April, 1909, 2 cols. Redfield, Snowden B., '' Compressed Air Calculation Short Cuts," E. M. /., p. 1 163, Dec. 11, 1909. A chart by which M.E.P. and H.P. may be determined without formulae having fractional exponents, together with explanations of its use. Webb, Richard L., '' Cost of Producing Compressed Air at a Canadian Mining Camp," Can. Min. Jour., p. 102, Feb. 15, 1910, 20 cols., 10 tables. McFarlane, Geo. C, " Compressing Air by Water," Min. Sci. Press, p. 281, Feb. 19, 19 10, 2 cols., illus. Discusses ways of utilizing water power which is so often available in mining districts for the compression of air and describes several devices for doing this. Anon., " Air Compressor Accidents in the Transvaal," Eng. News, p. 301, March 17, 1910, 2 cols. Discusses the probable cause of several explosions and gives the precautions taken to prevent their recurrence. Haight, H. v., " Steam-Driven Air Compressors in Cobalt," Can. Min. Jour., p. 209, April i, 1910, 3^ cols. Discussion of the paper by Richard Webb, Can. Min. Jour., Feb. 15, 1910, p. 102. Redfield, S. B., ^' Efficiency of Compressed Air," Comp. Air Mag., p. 5656, May, 1910, 3 cols. Abstract of article from American Machinist, discussing the work done in compressing air. Anon., '' The Energy of Compressed Air," Comp. Air Mag., p. 5775, Sept., 1910, 3K cols. Theoretical discussion of the energy employed in compressing air and the ways it is dissipated as heat. Taken from the American Machinist. BIBLIOGRAPHY 391 Anon., '' Compressed Air Efficiencies," Comp. Air Mag., p. 5877, Dec, 1910, 3K cols. Discusses the efficiency of com- pressed air, especially when used in a rock drill. Saunders, W. L., '' Compressed Air Explosions," E. M. /., p. 713, April 8, 191 1, also in Comp. Air Mag., p. 6028, May, 191 1, 4 cols. Discussion of possible causes and means of prevention. Matthews, F. E., '' Air Cooling and Moisture Precipitation," Comp. Air Mag., p. 6201, Oct., 191 1, 3 cols., i table. Dis- cusses the effect of moisture in the air upon the difficulty of cooling it. Gives a table showing the amount of moisture in the air at different temperatures and degrees of saturation. Rix, E. A., '' Operation of Air Compressors," Min. Sci. Press, p. 13, Jan. 6, 191 2. Describes some of the main causes of loss in air compressors and suggests remedies for such as are not inherent in the design. Stone, S. R., '' Increasing the Efficiency of Air Compressors," Min. and Engng. World, p. 1039, May 18, 191 2. Discusses the means of preventing losses of air compression due to heat, clearance, and rarefaction. HoLDSWORTH, F. D., '' Voluinetric Efficiency of Air Com- pressors," E. M. J., p. 1028, May 25, 1912, 4 cols., I illus. Discusses the unavoidable losses in air compression. Describes an apparatus for measuring the quantity of air delivered by the machine, which is the only way to secure an accurate determination of its efficiency. Affelder, Wm. L., '' Air Compressor Explosions," Min. and Min., p. 651, June, 191 2, 2% cols., i illus. Some unique data upon the initial temperature of an air-compressor explosion furnished by a recording thermometer. COMPRESSED AIR ACCESSORIES WiGHTMAN,L.I.," Compressed Air: Its Production, Transmission, and Application," Proc. Eng. Soc. West Penna., Vol. XXII, p. 197, June, 1906, 42K pages. A detailed discussion of the problems encountered in air compression, including 392 MODERN TUNNELING stage compression, cooling devices, types of compressors and receivers. Brinsmade, Robert B., " High vs. Low Pressure for Compressed Air in Mines," E. M. J., p. i6i, Jan. i8, 1908, 3^^ cols., illus. Contains discussions of the functions of intercoolers, re- heaters, and air receivers. Edit., " For the After Cooler," Comp. Air Mag., p. 5185, Feb., 1909, lyi cols. Editorial discusses the value of the after- cooler in the prevention of compressed-air explosions. Anon., " Air Receivers," Comp, Air Mag., p. 5302, June, 1909, 4 cols. Discusses the important functions of an air receiver. Richards, Frank, " Air-Receiver Practice," Comp. Air Mag., p. 5419, Oct., 1909, 7 cols., illus. Discusses the functions and efficiency of air receivers. Anon., " Tunnel Used for Compressed- Air Storage," Comp. Air Mag., p. 5443, 'Oct., 1909, 2 cols. Describes the use of an old cross-cut as an air receiver, giving a storage capacity equal to the output of the compressor for twenty-three minutes. Anon., '/ Compressor Pre-Cooler," E. M. J., p. 1081, Nov. 27, 1909. Describes a simple, home-made pre-cooler consisting of a number of odd pipes kept constantly wet. Anon., ^'Compressor Pre-Cooler," iS.ikf./., p. 550, Sept. 17, 1910. Describes a pre-cooler consisting of a subway leading to a building having walls and floor of cocoa matting. Richards, Frank, " Things Worth While in Compressed Air," Comp. Air Mag., p. 6059, June, 191 1, 14 cols., illus. Describes economical devices in use at the Rondout and Yonkers' compressors plants, including after-coolers, drains, re-heaters, intake filters. Jones, J. W., '' The Inter-Cooler in Stage Compression," Comp. Air Mag., p. 6100, July, 191 1, 7 cols., illus. Abstract of an article in Machinery describing and giving the functions of inter-coolers. Richards, Frank, '^ Development in Compressed Air Power Storage," p. 6199, Comp. Air Mag., Oct., 191 1, 4 cols. De- scribes a means of maintaining constant pressure in a BIBLIOGRAPHY 393 receiver, although volume of air is changing, by use of water- stand pipe. Richards, " The Disappointing Air Receiver," Comp. Air Mag., p. 6211, Oct., 1911, 4 cols. Some of the things an air receiver is popularly supposed to do but which it fails to do. Anon., ''A Novel Device for Re-heating Compressed Air for Use in Rock Drills," Engng. and Contng., p. 542, Nov. 22, 191 1, 3 cols., 2 illus. Describes an automatic re-heating device using vaporized liquid fuel. Bateman, C. G., '' Electric Heater for Air-Line Drains," E. M. /., p. 831, April 27, 1912, 2 cols., I illus. Description and drawing of an electric heater used to prevent the freezing of the drains in the pipe Hne of the British Canadian Power Co. (Cobalt District). Anon., " Unloading Device for Air Compressors," The Engineer (London), p. 542, May 24, 191 2, 2 cols., 2 illus. Describes a device which, when the compressor is not working at full load, permits a portion of the air being compressed in the cylinder to flow back to the atmosphere or the inter- cooler, as the case may be. VENTILATION Thrikell, E. W., '' Adequate Ventilation," Min. and Mm., p. 245, Jan., 1898, 4>2 cols. Abstract of a paper before the Midland Inst. Min., Civ. and Mech. Engrs. Discusses the ventilation required in mines and the influence of gases on men and lamps. Churchill, C. S., " Ventilation of Tunnels," The Engineer (London), Vol. LXXVIII, p. 799, 15 cols. Anon., " Improved Methods in Mine Ventilation," E. M. /., p. 1059, Nov. 28, 1908. Discusses the use of cepitrifugal fans in mine ventilation. Fitch, Thos. W., Jr., " Mine Resistance," West Va. Coal Min. Inst., June 7, 1910. Discusses the calculation of mine resistance and gives a number of tables showing the friction in air- ways. 394 MODERN TUNNELING AIR DRILLS Anon., ^' Burleigh s Pneumatic Rock Drill," E. M. /., Vol. VIII, p. 129, I col. Anon., ''Air Consumption of Rock Drills," E.M.J.,p. 648, Oct. 6, 1906, ^ col. Gives figures for the air consumption of drills at 80 pounds pressure. Davies, W. a. T., " Mining Hard Ground," E. M. /., p. 779, Oct. 27, 1905, 8 cols., illus. Abstract of "The Science of Economically Mining Hard Ground Rock with Percussion Rock Drills and Compressed Air." Trans. Australasian Inst. Min. Engrs., Vol. II, No. 4, April, 1906. Sinclair, H.L.," Development of an Air Hammer Drill," E.ikf./., p. 714, April 13, 1907, 8 cols. Discusses some of the diffi- culties experienced with the early types of hammer drills and the modifications made to meet them. Patterson, Samuel K., "Air Drills and Their Efficiency," Min. Sci. Press, p. 467, Oct. 3, 1908, 2^ cols. Describes briefly several types of drills and outlines the methods to be used in determining their efficiency. Weston, Eustace M., '' Ways of Improving Piston and Hammer Drills," E. M.J., p. 549, March 13, 1909. Recommendations for improving the efficiency of drills based upon the recent South African Drill Competition. LiPPiNCOTT, J. B., '' Comparative Tests of Large and Small Hammer Rock Drills," Eng. News, p. 449, April 22, 1909, 2 cols., tables. Give the results of tests made on the Los Angeles Aqueduct. Weston, Eustace M., " Surface Trials in Rand Stope Drill Competition," E. M. J., p. 998, May 15, 1909. Descrip- tion of the tests, giving a fist of the competing drills and some conclusions based on the surface trials. Anon., '' Ray Consolidated Mines (Arizona)," Min. and Min., July, 1909. Contains a discussion of the drilling equipment and methods used in these mines. Anon., " Hammer Drills for Small Sewer Work," Comp.Air Mag., p. 5464, Nov., 1909, 5 cols. Abstract from Eng. News of description of sewer construction at Bloomington, 111. BIBLIOGRAPHY 395 Anon. /'Air Hammer Drills," Comp.Air Mag., p. 5539, Jan., 1910, I col. Discusses the merits of air hammer drills. Edit., " Respect the Rock Drill," Com p. Air Mag., p. 5633, April, 1 9 10, Editorial. Some requirements for a good rock drill. Saunders, W. L., '' The History of the Rock Drill," E. M. J., p. 12, July 2, 1910, and also Comp. Air Mag., p. 5679, June, 1 9 10. Brief history of pneumatic rock drill. HiRSCHBERG, Chas. A., '' History of the Water Leyner Drill," Min. Sci. Press, p. 596, Oct. 29, 19 10, i col. Dana, Richard T., and W. L. Saunders, " Rock Drilling," John Wiley & Sons, New York, 191 1, 300 pages, 125 illus. Harding, J. E., '' Piston or Hammer Drills," Comp. Air Mag., p. 5886, Dec, 1910, 3K cols. Discusses the advantages and disadvantages of the two types of drill. Marriott, Hugh F., " Mining in the Transvaal in 1910," E. M. J., p. 80, Jan. 7, 191 1, 10 cols. Contains a brief discussion of the stope drill competition. Anon., " Transvaal Stope Drill Competition," E. M. J., p. 163, Jan. 21, 191 1, 6 cols. Abstract of official report. Gordon, W. D., '' The Transvaal Stope Drill Competition," E. M. /., p. 356, Feb. 18, 191 1, 4^ cols. Comments on the report of the committee in charge, with a reply by the editor of E. M. J. Anon.,'' A Comparative Test for Air Drills " Coal Age, p. 842-3, April 6, 191 2, 3 cols., i illus. Describes a convenient method of testing the air consumption of drills. HYDRAULIC DRILLS Anon., '' Data of Tunnel Work in Europe," Min. Sci. Press, Vol. XL VIII, pp. 306, 322, 338, 1884. Contains a discussion of the advantages of the Brandt hydraulic drill with a de- scription of its use at several European tunnels. Talbot, F. A., "The Walski HydrauUc Rock Drill," E. M. J., p. 1278, June 18, 1910, and also Comp. Air Mag., p. 5582, March, 19 10, 6 cols. Describes a rock drill which utilizes water hammer effect produced when a moving column of water is suddenly stopped. 396 MODERN TUNNELING ELECTRIC DRILLS Anon., " Meissner Electric Rock Drill," E. M. J., p. 759, Dec. 24, 1898. This drill had a separate electric motor connected with the drill by a flexible shaft. Anon., " Low Cost Tunneling with Electric Drills," E. M. /. p. 759, April 20, 1905, yi col. Cost of driving 10 x 10 tunnel in diorite where electric drills were used during Sept., Oct., and Nov., 1904. Palmer, Granville E., '^ Comparative Merits of Air and Electric Drills," E. M. /., Aug. 18, 1906. Gives disadvantages of electric drills. Barnes, H. B., " Air Drills vs. Electric Drills," E. M. /., p. 503, Sept. 15, 1906, 2}4 cols. Describes briefly and discusses the merits of several types of electric drills as compared with air drills. Chase, Chas. A., " Electric vs. Air Drills," E. M. /., p. 552, Sept. 22, 1906, 1 3/^ cols. Gives the results from the use of electric drills in the Stilwell tunnel and in the Liberty Bell Mine. Richards, Frank, '' The Piston Action of the Electric Air DriU," E. M. /., p. 699, Oct. 13, 1906, 5 cols., 2 illus. Illustrates and describes the action of the ''Electric Air" drill. Anon., ^^Two Electric Drill Records with Costs," Comp. Air Mag., p. 5300, 2 cols. Drilling in slate, sandstone, and limestone with " Electric Air " drill. Gradenwitz, a., '' A Novel Rock Drill," E. M. /., p. 1181, June 12, 1909. Describes a German electric drill having the motor connected directly with the drill. Anon., '' Fort Wayne Rock Drill," Min. Sci. Press, p. 548, April 5, 191 1, 1/4. cols., illus. Illustrated description of a rotary hammer electrically driven rock drill. Hutchinson, R. W., Jr., " Modification of Mining Methods by Electric Machinery," Eng. Mag., p. 592, July, 191 1, nj^ cols., 4 illus. Discusses the development of the electric drill and describes several types which are giving satis- faction at the present time. BIBLIOGRAPHY 397 GASOLINE DRILLS Anon., ''A Gasoline-Driven Rock Drill," E. M. /., Vol. LXXIX, p. 827, 1905, 2 cols., illus. Anon., '' The Scott Gasoline Rock Drill," E. M.J., p. 1008, Nov. 21, 1908. Also Min. Set. Press, p. 852, Dec. 19, 1908, and Eng. News, p. 575, Nov. 26, 1908. Brief description of a two-cycle gasoline rock drill. Anon., " An English Gasoline Rock Drill," Eng. News, p. 538, Nov. 17, 1910, and also Compressed Air Mag., p. 5873, Dec, 1910, I col., illus. Illustrated description. DRILLING ACCESSORIES O'RouRKE, D. J., '' The Proper Shape for Rock Drill Bits," Mine and Quarry, p. 220, June, 1908, 8 cols., 10 illus. FiCHTEL, C. L. C.,'' Calumet and Hecla Drill Sharpening Device," E, M. J., May 29, 1909, 1,200 words, illus. Illustrated description of plant that handles 4,000 drills daily. DE Gennes, M., '' Selection and Use of Bits for Power Drills," E. M. J., p. 1183, June 12, 1909, 1,500 words. Discusses the different types and effect of size, shape, and cutting edge on the results. JuDD, Edw. K., " Design of Bits for Power Drills," E. M. /., p. 1220, Dec. 18, 1909. Discussion and comment on M. de Gennes' article in E. M. J., June 12, 1909. Weston, E. M., " Ejecting Sludge from Drill-Holes," E. M. /., p. 799, April 22, 191 1, I col., illus. Describes a method of cleaning holes by utilizing the plunger action of piston drills to force the sludge back through a hollow drill steel and out through a vent in the side of the steel near the chuck. McDonald, P. B., '' Drilling with Double Screw Columns," E. M. J., p. 1049, May 27, 191 1, i col. Discusses the advantages of the vertical column over the horizontal bar mounting for drills. Anon., " Long Column Arms in Tunnels," Mine and Quarry, p. 540, Aug., 191 1, I col., illus. Describes the use of long arms on columns in tunnels of circular or oval cross-section. Blackburn, Ward," Notes on the Design of Drill Bits," E. M. /., 398 MODERN TUNNELING p. 927, May, 191 2, 5 cols., illus. An article on the proper shape of drill bits. Advocates the use of sharpening machines. HAULAGE Clarke, W. B.,'' Electric Mine Locomotives," Min. andMin., p. 389, April, 1901, 5^ cols., illus. Discusses things to be observed in choosing, operating, and caring for mine loco- motives. Clarke, W. B.,'' Electric Mine Haulage," Min. and Min., p. 252, Jan., 1902, 4^ cols., illus. Discusses design of electric motor equipment. Anon., '' Electric Haulage in Metal Mines," E. M. J., Vol. LXXVn, p. 324, 1904, 3 cols. Clarke, W. B., " Electric Mine Haulage," Min. Mag., p. 269, Oct., 1904, 14 cols., illus. First practical electric locomo- tive built in 1887 still in use in 1904. Describes some of the advantages of electric haulage and some of the more familiar types. Anon., " Mine Car Running Gear," £. Af./.,p.938, May 18, 1905, 6^ cols., illus. Discusses the design of running gears for mine cars. SoLiER, A., '' Electric Traction in the Simplon Tunnel," Proc. Inst. Civ. Engrs., Vol. CLXVI, p. 465, 1906. Descrip- tion of the electric traction system adopted in the Simplon tunnel. Norman, Fred, '^ Advantages of Electric Haulage," Min. and Min., p. 383, March, 1908, 3 cols. Abstract of a paper read before the Y. M. C. A. Mining Inst, at Dubois, Pa., July, 1907. Compares electricity with rope haulage, compressed air, and steam. DeWolf, E. C, " Haulage System at the Yak Tunnel," Min. and Met. Jour., June 26, 1908, 2^3 pages. A description of the method of handling ore and waste at the Yak tunnel. Foote, Arthur B., '' Dumping Waste with Locomotive Train," E. M. J., p. 711, Oct. 10, 1908. Describes a plow which could be attached at the end of a train of dump cars and push the rock over the edge of the dump when pulled by BIBLIOGRAPHY 399 the locomotive, thus obviating the need of shifting the track so frequently. SiNNiBALDi, Paolo/' Electric Traction and the Simplon Tunnel," Proc. Inst. Civ. Engrs., Vol. CLXXVIII, p. 439, 1909. Description of the electric traction plant used in and about the tunnel. Anon., '' Cost of Compressed Air Haulage," Min. and Min., p. 518, June, 1909, K col. Gives results obtained with com- pressed-air haulage at an industrial plant where the longest run is 2,400 feet. Johnson, J. E., Jr., ''An Improved Type of Mine Car Wheel," E. M. /., p. 1 180, June 12, 1909. Advocates tight-and- loose wheel construction. Perkins, F. C, " Electric Storage Battery Mining Locomotives," Min. Wld., p. 597, Sept. 18, 1909, i page, illus. Describes a German storage-battery mine locomotive. Saunders, W. L., " Compressed Air in Mines — Underground Haulage," E. M. /., p. 500, March 5, 1910, and also Comp. Air Mag., p. 5579, March, 1910. Discussion of a portion of D. W. B run ton's paper on Mining and Metallurgy in the United States, in Bull. A. I. M. E., j/, 1910. Anon., ''Internal Combustion Locomotives in Mines and for Surface Haulage," Petrol Rev., May 21, 19 10, 2^ cols., illus., and also Gas Power, p. 16, June, 1912, 3 cols., i^ pages, illus. Describes and gives some of the advantages of an English gasoline locomotive. Anon., ''Gasoline Mine Locomotives," Min. and Min., p. 30, Aug., 1910, iK pages, 3 cols., 3 illus. Discusses the advan- tages and disadvantages of gasoline locomotives, and de- scribes a German type. Anon., "Gasoline Locomotives for Mine Use," Min. and Min., p. 542, April I, 191 1. Results of the use of a gasoline loco- motive at the Mid valley Coal Co. mines, giving a table of costs. Sylvester, Geo. E., "Gasoline Motor Haulage," Min. and Min., p. 629, May, 191 1. Describes and gives results of the use of a gasoline locomotive in the mines of the Roane Iron Co., • at Rockwood, Tenn. 400 MODERN TUNNELING Anon., ''Gasoline Motors for Mines," E. M. /., p. 292, May 20, 191 1, 2 cols. Discusses some of the advantages of gasoline mine locomotives. Kenner, Alvin R., ''Mine Tracks," E. M. /., p. 1047, May 27, 191 1. Discusses the laying of mine tracks and describes a method of extending rails near breast. Spahr, Jacob, "Rock Dump at Cokedale," p. 48, Min. andMin., Aug., 191 1. Illustrates and describes a rock dump con- sisting of a platform 22 feet long, carrying rails, pivoted at one end and having under the other end a wheel which travels on a curved rail with a radius of 22 feet. Simmons, Jesse, "Gasoline Mine Locomotive," E, M. /., p. 652, Sept. 30, 191 1, 2 cols., I illus. Description of mine locomo- tive for use in Trojan Mine, Portland (Black Hills) . Anon., " Rock Dump at Cameron Mine, Walsenburg, Colo.," Min. and Min., p. 158, Oct., 191 1. Describes a swinging rock dump. Anon., "Tireless Locomotives," Sci. Am.Supp., p. 388, Dec. 16, 191 1. Discusses locomotives using superheated water in place of a coal fire and their possibilities for mining work. Barnes, H. B., "Storage Battery Mine Locomotive," E. M. /., p. 1278, Dec. 30, 191 1, and also in Elec. Review and Western Electrician, p. 52, Jan. 6, 191 2. Description of storage battery mine locomotives recently installed at Big Tive tunnel, Idaho Springs. Anon., "Testing Gasoline Mine Locomotives," Min. and Min., p. 341, Jan., 191 2, i^ cols., illus. Description of testing plant for gasoline mine locomotives. Anon., "Motor Trucks for Hauling Blasted Rock from City Aqueduct Tunnel, New York," Engr. Rec, p. 351, March 20, 191 2, >^ col., 3 illus. A two-mile haul from shaft to dump on Contract 65 required facihties for rapid transportation of large loads through city streets. Gives the costs of this work. Van Brussel, J. B., "The Otto Internal Combustion Locomo- tive," E. M. J., p. 657, March 30, 191 2, i}4 cols., i illus. Description of a German gasoHne locomotive. BIBLIOGRAPHY 401 King, A. F., ''Use of Gasoline Motors in Coal Mines," Coal and 'Coke Operator, p. 355, June 6, 191 2, 2 cols. Describes and discusses the advantages and disadvantages of gasoline loco- motives for use in coal mines. Perkins, Fr.\nk C, ''Gasoline Locomotives for Underground Haulage," Engng. and Min. Wld., p. 1251, June 15, 191 2, 3 cols., I illus. Discusses some of the advantages of gasoline locomotives for underground haulage. TUNNELING MACHINES Anon., "New Boring Machines for Tunneling," E. M. /., p. 969, Nov. 23, 1907, 7 cols. Discusses three types of tunneling machines, giving their defects. Bancroft, Geo. J., "A History of the Tunnel Boring Machine," Mining Science, Vol. LVHI, July-Dec, 1908, p. 65, 3^ pages, illus.; p. 85, 3 pages, illus.; p. 106, 2}^ pages, illus.; p. 125, 2}4 pages, illus.; p. 145, 2 pages, illus.; p. 165, 1)4 pages, illus. Everest, H. A., "Tunnel Machines," Min. and Met. Jour., p. 4, Sept. 5, 1908, 5 pages, illus. Thesis, Col. School of Mines; an elaborate study of tunnel machines. Gives dates of pat- ents and results of experiments with the various machines. Hoskins, a. J., "Brunton Tunnel Machine," Min. and Met. Jour., p. II, Sept. 5, 1908. Part of an article on recent progress in tunneling machines, and gives a short description of the Brunton Tunneling Machine and the work accom- plished with it. Herrick, R. L., "Karns Tunneling Machine," Min. and Min., p. no, Oct., 1908, 2}4 cols., illus. Contains a general descrip- tion of the machine and gives tr^e results of a test run made with it near Denver. Anon., "Machine for Boring Rock Tunnels," Eng. News, p. 556, Nov. 19, 1908, 3 cols., illus. Description of one type of tun- neling machine. Tyssowski, John, "Trial of a Tunnel Boring Machine," Proc. Inst. Civ. Engrs., England, Vol. CLXXVIII, p. 411, 1909. 402 MODERN TUNNELING Description of a test of the Terry, Tench & Proctor tunnel- ing machine at New York, June, 1910. Saunders, W. L., ''Driving Headings in Rock Tunnels," Bull. A. I. M. E., p. 337, Feb., 1909, 25 pages. Discusses methods of tunnel driving, with special reference to Euro- pean practice. Contains also brief descriptions of several tunneling machines. Tyssowski, John, ''Practical Test of a Tunnel Machine," E. M. /., p. 1296, June 26, 1909, illus. Describes the attempt to use a tunneling machine in connection with the excavation for the New York Central Railway Station. Describes the machine. Walton, Philip R., "Great Augers to Bore Holes in Moun- tains," Tech. Wld., p. 709, Feb., 191 2, 4 cols., illus. Popular description of one type of tunneling machine. ILLUMINATION Morrison, A. Cressy, "Acetylene Lamps," Comp. Air Mag., p. 5180, Feb., 1909, 2 cols. Grimshaw, Robert, " Importance of Acetylene in Mine Opera- tions," Min. Wld., p. 779, Oct. 16, 1909, 2/i pages, illus. Describes German practice as abstracted from an article by R. Penkert, " Kohle und Erz." METHODS OF TUNNEL DRIVING See also Tunnel Descriptions. Bowie, August J., " Tunnels Used in Hydraulic Mining," Trans. A. I. M. E., Vol. VI, 1877. Portion of an article on hydraulic mining in California; discusses the selection of tunnel sites, grades, costs, methods of driving, timbering, etc., in gravel. Drinker, Henry S., "Tunneling, Explosive Compounds, and Rock Drills," published by John Wiley & Sons, New York, 1878, 1025 pages, 1085 illus., several plates. Foster, C. Le Neve, "A Text Book of Ore and Stone Mining," pubHshed by Charles Griffin & Co., London, 1901, 730 pages, 715 illus. BIBLIOGRAPHY 403 Brunton, D. W., '' The Opening of Mines by Tunnels," E. M. /., Vol. LXXI, p. 147, Feb. 2, 1901, 2}i cols. Discusses the drainage of mines by tunnels, with some suggestions as to the methods of driving. Prelini, Charles, "Tunneling," published by Van Nostrand, New York, 1902, 307 pages, 150 illus Foster, C. Le Neve, ''The Elements of Mining and Quarrying," published by Charles Griffin & Company, London, 1903, 300 pages, 280 illus. Gillette, H. P., ''Rock Excavation, Methods and Cost," published by M. C. Clark, New York, 1904, 370 pages, 56 illus. Stauffer, David McNeely, "Modern Tunneling Practice," published by Eng. News, New York, 1906, 300 pages, i38illus. Adkinson, Henry M., " Advancing the Hot Time Lateral of the Newhouse Tunnel," E. M. J., p. 758, Oct. 17, 1908, Description of the methods used in this work. Edit., '' Speed in Small Drifts," E. M.J., p. 773, Oct. 17, 1908. Editorial discusses methods to be used in driving tunnels and drifts where speed is sought. Saunders, W. L., " Driving Headings in Rock Tunnels," Bull. A. I. M. E., p. 337, Feb., 1909, 25 pages, illus. Dis- cusses methods of tunnel driving, with special reference to European practice. Contains also brief description of several tunneling machines. HoGAN, John P., '' Progress on the Rondout Pressure Tunnel," Eng. Rec, p. 26, Jan. i, 19 10. Describes the methods employed on the Rondout Siphon in making the record run of 488 feet during Nov., 1909. H. R. S., "Freezing Ground in Tunnel Operations," Proc. Inst. Civ. Engrs., Vol. CLXXX, p. 361, 1910. A short description of driving through an unusually difficult piece of ground in the city of Paris by the freezing method. Hennings, F., "Long Railway Tunnels in the Alps," Proc. Inst. Civ. Engrs., Vol. CLXXXI, p. 506, 1910. A short but comprehensive review of the author's opinions on construction and operation of Alpine tunnels. 404 MODERN TUNNELING Saunders, W. L., " Our Best Rock Tunnel Record/' Eng. Rec, p. 87, Jan. 15, 1910. Discussion of the methods used in making a record drive on the Rondout Siphon and a com- parison of them with European practice. Rollings WORTH, C. H., " Rock Tunnel Records," Eng. Rec, p. 797, June 18, 1910. Comment on the methods used at the Loetschberg tunnel and a comparsion of them with those at the Buffalo Water tunnel. Saunders, W. L., " Rock Tunnel Records," Eng. Rec, p. 224, Aug. 27, 1 9 10. Comparison of the methods employed in driving the Buffalo Water tunnel and the Loetschberg tunnel. Aston, C. W., ''The Elizabeth Tunnel (Methods)," Min. and Min., p. 102, Sept., 19 10, 6 pages, 4 illus., 4 tables. De- tailed description of the methods employed in this work. Anon., '' Tunneling Record on the Catskill Aqueduct," Eng. Rec, p. 441, Oct. 15, 1 9 10. Discusses the methods employed in making a record run (Sept., 19 10, 523 feet) on the Wallkill Siphon. Lauschli, E., '' Short vs. Long Headings in Tunnel Driving," Eng. News, p. 661, Dec. 15, 1910, i^ cols. Discusses the advantages of driving long headings. Anon., " The Top Heading and the Bottom Heading Method of Attack in Tunnel Construction," Comp. Air Mag., p. 5942, Feb., 191 1, 3 cols. Discusses the merits of the two S3^stems. Becker, Arnold, '' Bottom Heading Driving on the Hunter Brook Tunnel," Eng. Rec, Sept. 23, 191 1, 3,600 words. Also Comp. Air Mag., p. 6224, Nov., 191 1. Describes and discusses the advantages of the methods used in driving this tunnel. Anon., '' Comparison of Speed of Drilling the Laramie-Poudre Tunnel with Recent European Tunnel Records," Engng. Contng., p. 630, June 5, 191 2, 6% cols. Abstract from Proc. Am. Soc. Civ. Engrs., Vol. XXXVHI, p. 707, 1912, of a discussion by W. L. Saunders of B. G. Coy's paper on the Laramie Tunnel. Compares methods employed. BIBLIOGRAPHY 405 DRILLING METHODS Bain, H. F., '^ Driving the Newhouse Tunnel," E. M. /., p. 552, April 19, 1902. Contains a description of the methods of drilling employed in this work. DiNSMORE, W. P. J., "Western Practice in Tunnel Driving," Mine and Quarry, p. 118, May, 1907. Contains a discussion of the methods of drilling used in the Ophelia tunnel. McFarlane, Geo. C, "Notes on Machine Rock Drilling," Min. Science, p. 291, Oct. 8, 1908, 3 cols. Gives a number of experiences in the use of rock drills and includes some data taken from actual practice concerning means of expediting this work. Aims, Walter L, "Methods Employed in Driving Alpine Tun- nels, the Loetschberg," Eng. News, p. 746, Dec. 31, 1908. Contains a description of the methods of drilling with a drill carriage. Anon., "The Roosevelt Tunnel," Min. and Min., p. 837, April, 1909. Contains a description of the drilling methods used in driving this tunnel. Anon., "Ray Consolidated Mines (Arizona)," Min. and Min., July, 1909. Contains a discussion of the drilling equipment and methods used in these mines. LA\n[S, F., "The New Buffalo Water Works Tunnel," Eng. Rec, p. 802, June 25, 1910. Contains a description of the methods employed in drilling. Hulsart, C. R., "Excavation of the Walkill Pressure Tunnel," Eng. News, p. 406, Oct. 20, 1910. Contains a discussion of the methods of drilling employed in this work. Saunders, W. L., "Shallow vs. Deep Holes in Headings," Comp. Air Mag., p. 5995. A discussion of the factors that enter into the determination of the depth of holes. Compares American and European practice. Doll, ]M. G., "Strawberry Valley Tunnel of the Strawberry Valley Irrigation Project of Utah," Mine and Quarry, p. 483, May, 191 1. Contains a description of the methods of drilling in driving this tunnel. McDonald, P. B., "Drilling with Double Screw Columns," 406 MODERN TUNNELING E. M. J,, p. 1049, May 27, 191 1, i col. Discusses the ad- vantages of the vertical column over the horizontal bar mounting for drills. Saunders, W. L., "Tunnel Driving in the Alps/' Bull. Am. Inst. Min. Engrs., No. jj, p. 507, July, 191 1. Contains a discus- sion of drilling methods with a drill carriage at the Loetsch- berg tunnel. Anon., ''Long Column Arms in Tunnels," Mine and Quarry, p. 540, Aug., 191 1, I col., illus. Describes the use of long arms on columns in tunnels of circular or oval cross-section. Coy, B. G., ''The Laramie-Poudre Tunnel," Proc. Am. Soc. Civ. Engrs., p. 217, March, 191 2. Contains a description of the methods of drilling used at this tunnel. Anon., "A Remarkable Bore-hole," Coal Age, p. 778, March 23, 191 2, 1% cols., I illus. Describes and illustrates a method of drilling a bore-hole to tap an old working containing water under 287 pounds pressure. Brunton, D. W., "Notes on the Laramie Tunnel," Bull. Am. Inst. Min. Engrs., No. 64, p. 357, April, 191 2. Contains a discussion of the methods of drilling used in driving this tunnel. BLASTING METHODS Daw, Albert W., and C. W., "The Blasting of Rock in Mines, Quarries, Tunnels, etc.," published by E. and F. N. Spon, London, 1898, 264 pages, 90 illus., 19 tables. Walke, Willoughby, "Lectures on Explosives," Wiley & Sons, New York, 1902, 425 pages. Anon., "Loading a Hole with Dynamite," E. M. J., p. 491, March 7, 1907, i col. Discusses mistakes commonly made in loading a hole and the methods of avoiding them. Stovall, D. H., "Position and Direction of Holes for Blasting," Ores and Metals, p. i, April 5, 1907. Discusses the greater importance of the location than the number of holes, and shows how the arrangement is determined by the character of the ground. Turner, H. L., "Loading Blast Holes," E. M. J., p. 433, Aug. BIBLIOGRAPHY 407 29, 1908. Discusses the preparation of the primer and its position in the hole. Bell, Robt. N., ''A Selective Electric Fuse Spitting Device," E. M. J., p. 528, Sept. 12, 1908, illus. Description of electric firing board. Anon., ''Loading Blast Holes," E. M. /., p. 918, Nov. 7,. 1908. Gives reasons for placing the primer at the bottom of the hole. Hay, J. K., ''Loading Blast Holes," E. M. /., p. 971, Nov. 14, 1908. Gives reasons for placing the primer at the top of the charge. CoLBURN, E. A., Jr., "Loading Blast Holes," E. M. /., p. 11 11, Dec. 5, 1908. Gives reasons for placing the primer at the bottom of the hole. McFarlane, Geo. C., "Loading Blast Holes and Driving Small Drifts," E. M. /., p. 225, Jan. 23, 1909. Discusses the position of the primer, the use of tamping, and describes a device to remove the tamping from a missed hole. Anon., "Details of Blasting Operations," Comp. Air Mag., p. 5464, Nov., 1909, I'jA cols. Description for the layman of blasting methods. Thomas, H. Musson, "The Theory of Blasting with High Explo- sives," E. M. /., p. 352, Aug. 21, 1909. Discussion of blasting in s topes on the Rand. Walker, Sidney F., "Firing Shots in Mines by Electricity," E. M. /., p. 228, Jan. 22, 1910. A discussion of the causes leading to misfires and suggestions with respect to the selection of electric fuses. Hosier, M. T., "Preparations for Blasting," E. M. /., p. 1006, May 14, 1910. Discusses cutting the fuse, crimping primers, loading the hole, and spitting the fuse. Semple, Clarence C., "Where the Primer Should Go," E. M. /., p. 441, March 2, 191 2, 4 cols. Gives reasons for placing the primer at the top of the charge. Brown, H. S., "Where Should the Primer Go?" E. M. /., p. 533, March 16, 191 2, i col. Gives reasons for placing the primer in the bottom of the hole. 408 MODERN TUNNELING Semple, Clarence C, ''Where Should the Primer Go?" March 23, 191 2, I col. Reply to the contention of H. S. Brown {E. M. J., March 16, 191 2, p. 533) that the primer should be placed at the bottom of the hole. Barbour, Percy E., "Where Should the Primer Go?" E. M. /., p. 825, April 27, 191 2, 3 cols. Sums up the recent discussion on this subject, quotes from various contributors, and concludes that the primer should always be placed last in drill holes, and that wherever there is a valid argument against putting it there, there are still stronger arguments for doing so. Anon., "Don'ts Governing Handling of Explosives in Mines," Min. and Eng. Wld., p. 915, April 27, 191 2, i col. Rules of the Oliver Mining Co. for employees. Twenty-five " don'ts." BLASTING SUPPLIES Oliver, Roland L., "Detonating Caps for Blasting," E. M. J., p. 682, Oct. 13, 1906, 13^ cols., 15 illus. Discusses the choice of proper strength of caps and the various ways of preparing the primer. Anon., "Blasting Gelatine," Min. and Min., p. 282, Jan., 1909. Discusses the use of "100 per cent, strength" gelatine dynamite at the Roosevelt tunnel. CuLLEN, Wm., "Gases from High Explosives," p. 297, Min. Set. Press, Aug. 28, 1909, 4 cols. Discusses the results obtained from a study of the gases given off from the gelatine dyna- mite used in Rand mines. Edit.", "Gases from Explosives and Mine Economy," Min. Sci. Press, p. 272, Aug. 28, 1909, i^ cols. Editorial comment on Mr. Cullen's article on page 297 of the same issue. Hodges, A. L., "Principles and Composition of Explosives," Min. Wld., p. 501, Sept. 4, 1909, 2 pages. Describes and gives the composition of different kinds of explosives. Anon., "The Necessity for Strong Detonators," E. M. J., p. 498, Sept. 10, 1910. Discusses the advantages from the use of strong detonators. Anon., "Explosives for Tunneling," Min. and Min., p. 159, Oct. I BIBLIOGRAPHY 409 1910, 2}i cols., 2 illus. Discusses the factors to be consid- ered in the selection of an explosive for tunneling. Anon., ''Circuit Tester for Blasting," E. M. J., p. 1195, Dec. 17, 1910, and also Min. Set. Press, p. 543, Oct. 22, 1910. De- scribes a galvanometer for testing a blasting circuit before firing. Hall, Clarence, W. 0. Snelling, and S. P. Howell, (U. S.) Bureau of Mines Bulletin ij, "Investigations of Explosives Used in Coal Mining," with a chapter on the ''Natural Gas Used at Pittsburgh," by G. A. Burrell, and an introduc- tion by C. E. MuNROE, 191 1, 197 pages, 7 plates, and 5 figs. Is intended especially for explosive chemists, but contains information of interest to all persons who have occasion to supervise the purchase or use of large quantities of explo- sives. Discusses the thermo-chemistry of explosives and the equipment and methods used by the Bureau of IMines in testing explosives. MuNROE, C. E., and Clarence Hall, "A Primer on Explosives for Coal Miners," (U. S.) Bureau of Mines Bulletin ly, 61 pages, 10 plates, 12 figs. Discusses combustion and ex- plosion, the composition of explosives, the handling and use of explosives and of squibs, fuse, and detonators, and con- cludes with notes on the safe shipment and storage of explo- sives, and the requirements of permissible explosives. Reprint of (U. S.) Geol. Survey Bulletin 42^. Brinsmade, R. B., "Explosives Used in Mining," Com p. Air Mag., p. 6076, June, 191 1, 6 cols. Discusses the nature of explosives used in mining, and some of the factors influenc- ing their choice. RuTLEDGE, J. J., and Clarence Hall, "The Use of Permissible Explosives," (U. S.) Bureau of Mines Bulletin 10, 191 2, 34 pages, 5 plates, 4 figs. Discusses the manner in which per- missible explosives can be used to best advantage in blasting coal. Is intended especially for coal miners and mine officials. Hall, Clarence, and S. P. Howell, "The Selection of Explo- sives Used in Engineering and Mining Operations," (U. S.) 410 MODERN TUNNELING Bureau of Mines Bulletin 48, 191 2, 50 pages, 3 plates, 7 figs. States the characteristics of different classes of explosives and sets forth the results of tests showing the suitability of explosives for different kinds of blasting. The pamphlet is written for the information of all persons interested in the use of explosives for blasting rock. Snelling, W. O., and W. C. Cope, "The Rate of Burning of Fuse as Influenced by Temperature and Pressure," (U. S.) Bureau of Mines Technical Paper 6, 191 2, 28 pages. Dis- cusses the composition of fuse used by miners and the effects of differences of pressure, temperature, etc., on the normal rate of burning. Hall, Clarence, and S. P. Howell, "Investigations of Fuse and Miners' Squibs," (U. S.) Bureau of Mines Technical Paper 7, 191 2, 19 pages. Discusses the essential features of squibs and miners' fuse, and gives the results of various tests. The salient features of specifications adopted for the purchase of fuse for use on the Canal Zone, and suggestions regarding the transportation and use of fuse are given. Snelling, W. O., and Clarence Hall, "The Effect of Stem- ming on the Efficiency of Explosives," (U. S.) Bureau of Mines Technical Paper ly, 191 2, 20 pages, 11 figs. The gain in efficiency by the use of stemming was demonstrated by firing small charges of explosives in bore-holes in lead blocks. The pamphlet is of interest to all persons who use explosives for blasting coal or rock. Hall, Clarence, and S. P. Howell, "Magazines and Thaw- houses for Explosives," (U. S.) Bureau of Mines Technical Paper 18, 191 2, 34 pages, i plate, 5 figs. Describes a mag- azine and a thaw-house, each constructed of cement mortar, and gives the quantity of material required for construction. Points out the features essential for safe storage of explosives. Is of interest to persons who supervise the storage and use of large quantities of explosives. Anon., "Hydraulic Cartridge for Mining," Sci. Amer., p. 364, April 20, 191 2, i>2 cols. Describes a cartridge which expands by hydraulic pressure and is very useful for break- BIBLIOGRAPHY 411 ing rock where it is essential that no shocks be imparted to the surroundings. MUCKING PoLHEMUS, J. H., ''Automatic Steam Shovel for Underground Work," Min. and Min., p. 575, July, 1909, 2 cols., illus.; and also E. M. J., p. 1056, Nov. 28, 1908, 2 cols., illus. Describes a steam shovel operating with compressed air in the mines of the Am. Zinc & Smelting Co., Carterville, Mo. Herrick, R. L., ''Mucking Problems in Tunnels," Min. and Min., Vol. XXX, p. i, Sept., 1909, i page, illus. HuLSART, C. R., "Excavation of the Wallkill Pressure Tunnel," Eng. News, p. 406, Oct. 20, 19 10. Contains a description of the methods of mucking employed in this work. Doll, M. G., "Strawberry Valley Tunnel of the Strawberry Val- ley Irrigation Project of Utah," Mine and Quarry, p. 483, May, 191 1. Contains a description of a stiff -leg derrick used for dumping muck cars on this project. Rice, Claude T., "The Use of Long- and Short-handled Shovels," E. M. J., p. 155, Jan. 20, 191 2, 3 cols. Discusses the merits of each type of shovel for mucking work. TIMBERING Sanders, W. E., Bernard McDonald, N. W. Parlee, and others, "Mine Timbering," published by Hill, New York, 1907, 175 pages, 140 illus. Meen, J. G., "The Bracing of Tunnels and Trenches, with Prac- tical Formulae for Earth Pressures," Proc. Am. Soc. Civ. Engrs., Vol. XXXIII, p. 559, 1908, 60 pages. Crane, W. R., "Notes on the Use of Concrete in Mines," Con- crete and Constructional Engineering Mag., p. 39, March, 1908, 6 pages, 7 illus. von Emperger, Fritz, "Notes on the Use of Concrete in Mines," Concrete and Constructional Engineering, p. 134, May, 1908, 7 pages, 12 illus. Crane, W. R., "The Use of Concrete for Mine Supports," Con- crete and Constructional Engineering, p. 172, July, 1909, II pages, 12 illus. 412 MODERN TUNNELING Fleming, W. S., "Selection and Framing of Timber," Eng. Min. Jour., Aug. 28, 1909, }4 page showing cuts. Anon., "Method of Making Water-tight by Grouting the Yon- kers Pressure Siphon of the Catskill Aqueduct," Engng. Con., Feb. 9, 1910, 1,500 words. Description of grouting machine, giving dimensional drawings and method of using in grouting the Yonkers Siphon. Humes, James, "False Set for Spiling Ground," E. M. /., p. 698, April 2, 1910, 3 col?., illus. Describes swinging false set pivoted at the center of the post. Herrick, R. L., "Tunneling on the Los Angeles Aqueduct," Min. and Min., Oct., 19 10. Contains an excellent descrip- tion of the methods of timbering used in the north end of the Elizabeth Lake tunnel. Rice, Geo. S., "Some Special Uses of Concrete in Mining," Cement, p. 432, Jan., 191 1, 12 cols. Young. Geo. J., "Driving in Loose Ground," E. M. J., p. 161, Jan. 21, 1911, 1% cols. Describes methods used on the Comstock Lode. Parrish, K. C, "Comparative Strength of Several Styles of Framed Timber Sets," E. M. /., p. 208, Jan. 28, 191 1, 2 cols., illus. Anon., "Methods of Handling Running and Swelling Ground," Min. Eng. Wld., Dec. 9, 191 1. Describes customary prac- tice of timbering tunnels. ZiPSER, M. E., "Tunnel Lining, Catskill Aqueduct," Eng. News, p. 820, May 2, 191 2, 28 cols., 11 illus. A detailed descrip- tion of the methods of lining with concrete the tunnels on the Catskill Aqueduct of both the grade and the pressure or siphon types. McKay, Guy R., "Lining a Tunnel in Swelling Rock," Eng. Rec, p. 565, May 25, 191 2. Describes a concrete lining, reinforced by steel rails, placed in the Snake Creek tunnel. SPEED RECORDS Anon., "Mount Cenis Tunnel," E. M. J., Vol. IX, p. 344, K col. Contains a tabulation of the monthly progress on the Mount Cenis tunnel for the year 1869. BIBLIOGRAPHY 413 Anon., '^ Rapid Tunnel Work," Min. Set. Press, Vol. XLVI, p. 241, April 7, 1883, K col. Anon., ''Tunnel Work," Min. Sci. Press, Vol. LI, p. 292, Oct. 31, 1885, yi col. Notice of record drive in Big Bend Tunnel, 405 feet, in Sept., 1885, due to good drills and good ventilation. Anon., ''Big Bend Tunnel," Min. Sci. Press, Vol. LII, p. 237, April 10, 1886, }i col. Anon., "Records in Rock Tunneling," Eng. News,^.^^^, April 2, 1908, 2]/4 cols. Contains a compilation of the maximum rates of progress at a number of American and European tunnels. Anon., "Rates of Progress of C. M. and St. P. Tunnel through Bitter Root Mountains, Montana," Eng. News, p. 9, July 2, 1908, I col. Gives the progress on this work for March, April, and May, 1908. LiPPiNCOTT, J. B., "A New Record Established in Driving Hard Rock Tunnels," Eng. News, p. 570, Nov. 19, 1908, 2 cols. At the Elizabeth Lake tunnel, Oct., 1908, 466 feet. Contains also a short list of other tunnel records. Anon., "Records of Driving Rock Tunnels and Some Comments on the High Cost of the Elizabeth Tunnel," Engr. -Contract- ing, p. 393, Dec. 9, 1908, 3^ cols. Contains a compilation of tunnel records both American and European. Herrick, R. L., "Tunnel Driving Records," Min. and Min., p. 422, April, 1909, 8^2 cols. Discusses the factors that make for rapid tunnel work and contains a compilation of tunnel records. Saunders, W. L., "European Tunnel Driving Records up to Feb., 1909," Trans. A. I. M. E., Vol. XL, p. 439, 1910. Contained in an article on driving headings in rock tunnels. , "American Tunnel Driving Records up to Feb., 1909," Trans. A. I. M. E., Vol. XL, p. 437, 1910. In an article on driving headings in rock tunnels. Anon., " Uncomparable Records," Comp. Air Mag., p. 5537, Jan., 1910, 1% cols. Discusses the futility of attempting to compare different records of tunnel progress without con- sidering all the factors that influence them. 414 MODERN TUNNELING SAFETY AND HEALTH Carter, T. L., '' Miners' Phthisis," E. M. /., Vol. LXXV, p. 474, March 27, 1903, 4 cols. Describes prevalence of miners' phthisis, which materially shortens Hfe of miners. Gives dust and oil (vaporized) as causes; powder gas, a possibility; and suggests free use of water as a preventive. SAUitoERS, W. L., ''Notes on Accidents Due to Combustion Within Air Compressors," E. M. J., p. 554, Apr. 11, 1903. Discusses the occurrence of accidents and the means for their prevention. CuLLEN, Wm., ''Miners' Phthisis, and Dust in Mines," E. M. J., p. 633, Apr. 25, 1903. Discusses dust in mines as one of the chief causes of this disease, and describes the methods used to prevent it. Anon., "Danger in the Cut-Off Hole," Min. and Sci. Press, Vol. LXXXVI, p. 405, June 27, 1903, i col. Describes danger of the cut-off hole, especially in shaft-sinking. Hoffman, Fred. L., "Fatal Accidents in Metal Mining," E. M. J., Vol. LXXVn, 1904, p. 79, 4 cols., p. 119, 3^^ cols. Statistics and discussion of causes of death. GoFFE, E., " Causes of Explosions in Air Compressors," E. M. /., p. 686, April 28, 1904, 4^ cols. An elaborate discussion of the causes of air explosions. Concludes that the chief one is probably *the accumulation of dust which absorbs oil and when heated by the compressed air gives off ex- plosive gases. Edit., '' Prevention, Miners' Phthisis," Editorial, E. M. /., Vol. LXXVni, p. 91, July 21, 1904, i^ cols. Mentions competition conducted by Transvaal Chamber of Mines for best methods of preventing miners' phthisis. Atomizer and water-drill reported favorably. Atomizer produces supersaturated atmosphere. Water lays dust at point of production. Edit., '' Miners' Phthisis," Min. and Min., p. 21, August, 1904, i^ cols. Editorial upon the investigation by the British Government into the causes of this disease. BIBLIOGRAPHY 415 Gow, Alex. M., " Ignitions and Explosions in the Discharge Pipes and Receivers of Air Compress," £wg. News, p. 220, March, 1905, 2% cols. Detailed results of an elaborate study of the causes of air-receiver explosions, with recom- mendations as to means of preventing them in the future. Anon., " The Miner's Responsibility for Accidents," Min. Mag., Vol. XIII, p. 223, i>^ cols. Haldane, J. S., and R. A. Thomas, '' The Causes and Prevention of Miners' Phthisis," Trans. Inst. Min. and Met., Vol. XIII, P- 379, 1903-4- Burgess, J. A., " Explosion in a Compressed-Air Main," Min. Sci. Press, p. 731, November 28, 1908, and Comp. Air Mag., p. 5186, Feb., 1909. Describes an explosion at the Tono- pah Mining Co., and discusses the probable causes and gives the precautions being taken to guard against a similar future occurrence. Anon., " Prevention of Mine Accidents," E. M. /., p. 1088, Dec. 5, 1908, 7 pages. Report of Committee of Am. Mining Con- gress to investigate laws relating to metal-mining. Edit., " For the After Cooler," Comp. Air Mag., p. 5185, Feb., 1909, i}4 cols. Editorial discusses the value of the after- cooler in the prevention of compressed-air explosions. Anon., " A Pipe Explosion and a Runaway Compressor," Comp. Air Mag., p. 5188, Feb., 1909, i col. Describes a pipe explosion, which caused the compressor to run away and burst the fly-wheel. Richards, Frank, " Probable Cause of Compressor Explosions," Comp. Air Mag., p. 5250, April, 1909, 2 cols. , '' Flames in Compressed-Air Pipes,'^ Comp. Air Mag., p. 5378, Aug., 1909, I col. Discussion of the causes of flames in compressed-air pipes. Bell, Robt. N., " Some 'Don'ts' for Explosives and Blasting," E. M. J., Vol. LXXXVI, p. 1281, Dec. 25, 1909, i col. Munroe, C. E., and Clarence Hall, " A Primer on Explosives for Coal Miners," (U. S.) Bureau of Mines Bulletin ly, pp. 61, 10 pis., 12 figs. Discusses combustion and explosion, the composition of explosives, the handling and use of 416 MODERN TUNNELING explosives and squibs, fuse and detonators, and concludes with notes on the safe shipment and storage of explosives and the requirements of permissible explosives. Reprint of United States Geological Survey Bulletin 42 j. Anon., ''Accidents at Metal Mines," Mines and Methods, Jan., 1910, pp. 10., illus. HoFEMAN, Fred'k L., " Fatal Accidents in American Metal Mines," E. M. J., p. 511, March 5, 1910. Gives statistics and discusses the need for legislation. Anon., " Air Compressor Accidents in the Transvaal," Eng. News, p. 301, March 17, 1910, 2 cols. Discusses the probable causes of several explosions and gives the precautions taken to prevent their recurrence. Wilson, H. M., and A. H. Fay, " First National Mine-Safety Demonstration, Pittsburgh, Pa.," (U. S.) Bureau of Mines Bulletin 44, with a chapter on " The Explosion at the Ex- perimental Mine," by G. S. Rice, pp. 75, 191 2, 8 pis., 4 figs. Describes the various exhibits at this demonstration; gives the addresses made and the names of the prominent visitors. Presents a summary of the investigations conducted at the Pittsburgh experiment station of the Bureau of Mines. Clark, H. H., " The Electrical Section of the Bureau of Mines, Its Purpose and Equipment," (U. S.) Bureau of Mines, Technical Paper 4, 12 pp., 191 1. Briefly describes equip- ment for testing electrical mining machinery, and some of the tests that have been made. Clark, H. H., W. D. Roberts, L. C. Ilsley, and H. F. Randolph, " Electrical Accidents in Mines, Their Causes and Prevention," (U. S.) Bureau of Mines, Miners' Circu- lar 5, 10 pp., 191 1, 3 pis. Presents suggestions as to measures that mine foremen, mine electricians, and miners should take to prevent electrical accidents. Also gives directions for the treatment of shock. Saunders, W. L.," Compressed Air Explosions, "E. M. J., p. 713, April 8, 191 1, and also in Comp. Air Mag., p. 6028, May, 191 1. Discusses their possible causes and means of prevention. BIBLIOGRAPHY 417 GooDALE, Stephen L., "Underground Safety Appliances," Min. and Min., Oct., 191 1. Illustrates and describes devices employed and scheme of working with reference to the mine of H. C. Frick Coke Co. Harrison, Geo. B., "Accidents in Mines Caused by Fall of Ground," Iron and Coal Trades Rev., Nov. 17, 191 1. Dis- cusses methods for reducing such accidents. Snelling, W. O., and W. C. Cope, "The Rate of Burning of Fuse as Influenced by Temperature and Pressure," (U. S.) Bureau of Mines. Technical Paper 6, 28 pages, 191 2. Dis- cusses the composition of fuse used by miners and the effects of differences of pressure, temperature, etc., on the normal rate of burning. Hall, Clarence, and S. P. Howell, "Investigation of Fuse and Miners' Squibs," (U. S.) Bureau of Mines, Technical Paper 7, 191 2, 19 pages. Discusses the essential features of squibs and miners' fuse and gives the results of various tests. The salient features of specifications adopted for the pur- chase of fuse for use on the Canal Zone and suggestions regarding the transportation and use of fuse are given. Hall, Clarence, and S. P. Howell, "Magazines and Thaw- houses for Explosives," (U. S.) Bureau of Mines, Technical Paper 18, 34 pages, 191 2, i pL, 5 figs. Describes a maga- zine and a thaw-house, each constructed of cement mortar, and gives the quantity of material required for construction. Points out the features essential for safe storage of explosives. Is of interest to persons who supervise the storage and use of large quantities of explosives. Clark, H. H., "The Factor of Safety in Mine Electrical Instal- lations," (U. S.) Bureau of Mines, Technical Paper ig, 191 2, 14 pages. The author points out the factors that tend to make electrical installations less safe in mines than above ground, and gives some general directions regarding the adoption and maintenance of a high factor of safety. Rice, G. S., "Mine Fires, a Preliminary Study," (U. S.) Bureau of Mines, Technical Paper 24, 191 2, 50 pages, i fig. A com- prehensive summary of the causes of fires in mines and the 418 MODERN TUNNELING equipment and methods to be used for preventing and extinguishing such fires. The pamphlet is addressed chiefly to mine owners and mine officials. Rice, G. S., ''Accidents from Falls of Roof and Coal/' (U. S.) Bureau of Mines, Miners^ Circular g, 191 2, 16 pages. Calls attention to the high death rate from roof falls in the coal mines of the United States and the need of constant watch- fulness by miners and mine foremen. Paul, J. W., "Mine Fires and How to Fight Them," (U. S.) Bureau of Mines, Miners' Circular 10, 191 2, 14 pages. Tells what the coal miner can do to prevent fires, and how incip- ient fires can be extinguished. Jones, L. M., ''Accidents from Mine Cars and Locomotives," (U. S.) Bureau of Mines, Miners' Circular 11, 191 2, 16 pages. Gives precautions that should be followed in traveling haul- age roads, and in handling mine cars. Anon., "Miners' Phthisis," So. Afric. Min. Jour., p. 153, March 30, 191 2, i}^ cols. The first of a series of several abstracts from the official report of the Medical Commission's findings in their investigation of this disease. Affelder, Wm. L., "Air Compressor Explosions," Min. and Min., p. 651, June, 1912, 2j^ cols., i illus. Some unique data upon the initial temperature of an air-compressor explosion fur- nished by a recording thermometer. COSTS Ralston, W. 0.,"Cost of Tunneling at the Melones Mine, Cala- veras County, Cal.," Trans. A. I. M. E., Vol. XXVIII, p. 547, 1898. Gives description of the equipment, method of operating, and the cost of driving at the Melones Mine. Bain, H. F., "Driving the Newhouse Tunnel," E. M. J., p. 552, April 19, 1902. Contains a statement of the costs of this work for the year ending Aug. 31, 1900. BuNCE, Walter H., "Tunnel Driving at Low Cost," Min. Sci. Press, p. 60, July 11, 1908. Discusses the cost of driving the Chipeta Adit at Ouray, Col. BIBLIOGRAPHY 419 Richards, C. H., ''Some Detail Tunnel Costs in No. 7 of the Los Angeles Aqueduct," E7ig. News, p. 542, Nov. 18, 1909, 2 cols., tables. Hancock, H. S., Jr., ''Method and Cost of Constructing a Water Supply Tunnel through Rock by Day Labor," Engng.- Contng., May 25, 1910. Contains figures showing the cost of this work. Anon., "Some Published Costs of Tunnel Work in the Los Angeles Aqueduct," Engng.-Contng., June i, 1910, 2^ pages, illus. Herrick, R. L., "Tunneling on the Los Angeles Aqueduct," Min. and Min., Oct., 1910. Contains much information concern- ing the cost of tunneling on this project. Oke, a. Livingstone, "Standards of Work," E. M. J., p. 302, Aug. 13, 1910. Discusses the necessity of knowing all the factors that enter into each case before comparing two projects as to the amount of work performed, the kind of labor, and what is considered the standard of work for that particular class in that locality. Anon., "Bonus System on the Los Angeles Aqueduct," Min. and Min., p. 679, June, 191 2, 5 cols., illus. Discusses the rules of operation, the method of computing bonus, footage, and the earnings of the men. Lavis, F., "The New Buffalo Water Works Tunnel," Eng. Rec, p. 802, June 25, 1 9 10. Contains a schedule of the wages paid during the construction of this tunnel. Lauschli, E., "Hard Rock Tunneling," Eng. Rec, p. 719, Dec. 17, 19 10. Gives a list of the wages paid on the Loetschberg tunnel work. Collins, Glenville A., "Ef!iciency of Engineering Applied to Mining," Min. and Engr. Wld., pages 869-70, April 20, 191 2, 4 cols. Discusses the ways and means of applying "scientific management" to mining work. I CHAPTER XVIII RAILROAD TUNNELS INTRODUCTION In the last section of Chapter II a brief schedule of ^'Railway Tunnels" is given, all of which were built, for the most part, in solid rock. The chapters III to XVI, following, deal with the con- struction methods and equipment as applied to the tunnels, usually of comparatively small cross-section, which are involved in mining work and for the conveyance of water and the informa- tion given is confined, to a large degree, to cases where such tunnels are driven through solid and self-supporting rock. The information and conclusions given as to these types of small sized tunnels apply equally to the heading construction of the enlarged tunnels hereafter to be considered. This, and the suc- ceeding chapters, on Railroad Tunnels, on the other hand, deal with tunnels of comparatively large cross-section for the purpose of railway trafhc, for highway purposes, for canals, or for any other imaginable purpose in which the necessary cross- section is so large that the excavation cannot be performed as one operation but involves {a) The driving of a ^'heading" or advance drift, and (h) the subsequent enlargement of such heading (or headings) to the full cross-section of the finished work. For convenience in reference, all these large size tunnels are considered under the general title ''Railroad Tunnels" notwith- standing that their purpose or use may not be for railroad traffic. The name is merely meant to imply that the cross-section is of such size that the excavation has to be in stages instead of in one operation. It is perhaps worth noting that the first tunnel built in the United States was on the Schuylkill Navigation Canal. This 420 RAILROAD TUNNELS 421 tunnel was opened for use in 182 1, was 20 feet wide, 18 feet high and 450 feet long. The widest tunnel in the world is also for canal purposes; this is the Rove tunnel near Marseilles in France which has a clear excavated span of 79 feet, a height of 51 feet and is 4I miles long. The following chapters on Railroad Tunnels take up the various methods which have been developed, starting with simple cases of tunnels driven through hard, self-supporting rock, and proceeding through the successively more complex conditions presented by loose rock, firm earth, loose running grounds and quicksands and lastly to the subaqueous tunnel, driven under a body of water through ground saturated and permeated with water under the head of the overlying river, estuary or arm of the sea under which the tunnel is driven. In this part of the work the word ''heavy" as applied to ground may be found to occur. To the miner this term is used to mean that the ground so designated is lacking in self-sustain- ing power, so as to require support to hold it in place when any excavation is made within it. To the extent to which the ground requires such support it is "heavy"; to the extent to which it is self-supporting it is ''light." Some grounds are both light and heavy; for example, certain clays, which, when first excavated will stand without support but which, after exposure to the air swell and disintegrate so that ultimately they are of the heaviest description and will bring almost unbelievable pres- sures upon the supporting timbering. In self-sustaining, non- weathering rock, the enlargement of the advance heading to the full cross-section is a simple matter of drilhng, blasting and mucking, but as the ground, whether rock of a loose, shattered or partly disintegrated character, or whether some variety of "soft" ground, by which is meant the various sands, gravels, clays or other materials not usually requiring the use of explosives in excavating, becomes less able to sustain or arch itself across any excavation or bore opened within it, then the process of excavation is complicated by tlie necessity for increasingly elaborate temporary support or "timbering" to retain the aperture excavated, until the 422 MODERN TUNNELING permanent "lining" can be placed to receive and withstand the pressure of the earth. In loose rock the timbering is solely to hold the weight of crumbling rock or to prevent falls of loose rock from the roof, up to the point where the material will arch and thereby sustain its own weight, but in real soft ground the timbering must be a continuous, unbroken surface or "sheathing" covering the periphery of the excavation, both roof, sides and face and even in some instances the floor also. It is not uncommon to have to build tunnels through ground which will flow like a liquid under the influence of its pressure, such grounds are "quicksands" to the miner. In such a case no opening whatever can be made by the miner, until he has ready the means for extending the covering and support of such further area of soil exposed. These soils are, in effect, fluids having angles of repose not greatly removed from zero and must be treated as fluids. These grounds are known in tunnel parlance as "treacherous" and they will take their toll of human life on the slightest provocation. The writer remem- bers a case in which a tunnel was being driven in clean, sharp sand, which was so dry as to have little cohesion. An advance heading, close timbered, had been driven. In this a defective joint, or gap, between two face boards permitted a leak of sand. Two miners, experienced men, sent in to secure these boards must have disturbed or loosened one, without being prepared to replace it. The sand flowed in so fast that the men were buried before they could make their danger known to others, distant only a couple of hundred feet. Each kind of ground, however, has a certain, though possibly variable, from point to point, degree of cohesion. This gives such ground the power to sustain by arching action a certain load across a certain opening. Each such soil has also a definite angle of repose and a definite unit weight or specific gravity. Upon these basic characteristics will depend, whether consciously or unconsciously on the part of the practical miner, the methods of excavation and timbering which will be suitable to a given case. The main principle of tunnel building in such soft ground is RAILROAD TUNNELS 423 that no opening or excavation must be made greater in dimen- sions than that over which the ground will carry its own load unless such opening is at once supported by timbering. Each portion of such timbering must mrther be so con- nected with, and supported by, all other portions of the timber- ing system, that a structure well braced in every direction from external pressure results. For example, although perhaps pres- FiG. 8i. Tunnel timbering. American system. sures normal to the tunnel periphery are the chief ones to be provided for, it does not follow by any means that longitudinal bracing may be omitted. If that were done, and some longi- tudinal pressure, such as for example that from a run of ground at the face or from the blow of a flying fragment of rock being blasted, were to act on a portion of the timbering, such unsup- ported timbering would fall like a stack of cards and the collapse of the tunnel would follow. The methods of enlargement in soft ground are essentially the same as those used in driving the heading. The important thing is to prevent the ground from starting to move. 424 MODERN TUNNELING As will be seen from the illustration, Figure 8i, the timbering of a tunnel resembles the hull of a ship. Outside against the ground, come the sheathing or "poling," corresponding to the skin of the ship's hull and serving the same purpose, namely, to exclude the soil, as the ship's skin excludes the water, and to transmit the pressure of the ground to the main timbers, which correspond to the frames and girders of the ship's hull. The softer the ground, the smaller its angle of repose the nearer it approaches a fluid the more nearly will the timbering be like a ship. The subject of Railroad Tunnels divides itself into two main headings: 1. Economics of the proposition and design of structures. 2. Construction. (a) Hard Rock Tunnels (self-sustaining) ; (b) Loose Rock and Soft Ground Tunnels (heavy) ; (c) Subaqueous Tunnels. The magnitude of the subject necessitates the elimination from detailed consideration of special problems in extremely long, deeply overlaid tunnels, as well as the various types of subways in cities which have been developed in connection with city transportation. Economics The primary object in the construction of a railroad tunnel as differing from small tunnels for mining, drainage or power purposes, is the conservation or production of revenue and so the relation between the cost and earning capacity of such an undertaking must be carefully considered. The total production cost of any tunnel, even under the most favor- able conditions, is so great that the only justification for the undertaking Hes in either, (a) PubHc necessity irrespective of monetary returns, or (b) Operating economy which will produce net revenue after deduction of operating expenses, mainte- nance and depreciation, ample to return interest on the investment. I KAILROAD TUNNELS 425 It is obvious then that the first requisite is a broad consider- ation of each individual problem as presented, a preliminary estimate of probable cost, which must include not only the cost paid to the contractor for work executed, but also the amounts due to preliminary investigation,, engineering supervision and inspection, property and easements, cleaning up, cost of pre- liminary testing of structures in actual operation, and also cost of money, interest charges, financing, legal and general overhead expense. The other necessary factor in the deter- mination of justification, that of operating economy, is usually much harder to arrive at, but commonly there are certain outstanding reasons showing that the omission to incur these heavy costs would produce, as an alternative, a prohibitory operating condition. The most usual reasons for construction of tunnels are : (i) To shorten distance or reduce curvature. These cases are most common and such tunnels are usually short in length. A railroad following a valley finds it to be impossible to make bends without curvature greater than the allowable limit. The alternative then is to cut into the projecting land. In this case it is usual to extend the open cut approaches to such depth in rock or soil requiring flat slopes, until the estimated cost is equal to that of construction of a tunnel, at which points the portals will be estabhshed, except as modified by economies which might be obtained in future maintenance due to snow, slides, drainage, etc. (2) To reduce gradients. (3) To reduce extreme altitudes, the bad climatic conditions incident thereto and thereby to improve operating conditions. Reasons (2) and (3) are closely inter-related. They include the numerous class of "Summit Tunnels" introduced in crossing ''divides." In cross-country railroad location it is the almost invariable practice to predetermine a controlling allowable gra- dient dependent on the general valley topography and conditions of operating traffic. The location leads up a valley, on the established gradients, to a point where the line must go under ground to cross to the similar valley point on the other side of 426 MODERN TUNNELING the divide which has been reached at the controlling rate of grade which has been established for operating traffic in the contrary direction. Between those points a tunnel is essential, as the only alternative would be a break and increase in the adopted limiting gradient. (4) The elimination of grade crossings in city streets. In these cases there is commonly a direct return to productive use of surface areas previously occupied by trackage. (5) Crossing of rivers and waterways in cases where bridges would obstruct navigation or are not suited to local conditions or in other cases where the requisite spans are so great as to necessitate a bridge structure so costly as not to be warranted by the traffic accruing. Assuming then, that the analysis of the economic situation warrants the further prosecution of the project, the next step is the development of the design. DESIGN This may be considered under the following heads: (A) Geology; (B) Cross-section; (C) Alinement; (D) Lining; (E) Waterproofing of Lining; (F) Drainage and Pumping; (G) Ventilation; (H) Lighting. (A) Geology The preliminary exhaustive study of the geology of any tunnel problem is essential in the first place to the proper con- sideration of the economics as bearing on the probable cost of construction and feasibility of the undertaking; in the second place to the consideration of the type and design of the struc- ture and in the third place, to the contractor to determine the character and capacity of the plant necessary and the probable progress of construction as affecting his unit prices bid on con- tract, and his methods of laying out his work. A large part of the information necessary will be obtained by the geologist from extended surficial examination of soils and outcrops, but it is usually necessary to supplement this informa- tion by digging pits through overlying soils to rock, and by core I RAILROAD TUNNELS 427 or Other drill borings, to determine at intervals the particular characteristics of the rock. Even with the most careful advance investigation, actual conditions in construction are commonly found materially different from the assumptions. It is there- fore strongly recommended to the engineer preparing contract plans and specifications for any tunnel, that as much positive information as can be obtained should be stated for the informa- tion and guidance of the contractor ; but that nothing whatever should be stated which is not actual fact and that no assumptions, opinions or conclusions of either the geologist or engineer should in any way be given except under definite agreement that the contracting parties accept no responsibihty for such opinions. The Courts of the United States and nearly every State have decisions in large numbers making liable the party responsible for any information given, which in the final result may have proved misleading or in error and thereby have occasioned greater cost and expense upon the contractor. An interesting illustration of the influence of the study of geology on the consideration of a great problem is given by the Channel Tunnel between England and France. Historical Geology shows that in prehistoric times the British Isles were continuous with the continent of Europe and that the present location of the gap between Dover and Calais was the divide of a highland. Subsidence has produced the channel way. The cretaceous formation is continuous and in all probability without fault, the dip of the strata rising on easy gradient from England to France, so that if a tunnel is started from England within the broad stratum of the Grey Chalk, which is practically free from flints, it can be carried through to France without penetrating the beds between the grey chalk and the underlying or over- lying strata which would undoubtedly yield great volumes of water and give uncertainty in the construction. This grey chalk is ideal material to excavate to full-size section with rotary cutting machines which break down the face and deliver onto conveyor belts for disposition into haulage at a convenient distance back of the working face. The advance study of the geology is necessary to the pre- 428 MODERN TUNNELING determination of the probable cost of an enterprise. " To the designer it affords an understanding of the earth pressures as affecting the strength and character of the permanent hning; it will assist in the location of the portals and shafts and in the design of the approaches, and in the provisions he must make for proper drainage. To the constructor it affords assistance in the determination of his contract bid, as it gives information affecting the type and size of the drills, the compressed air and power plant, the probable earth temperature and the necessary ventilation to be provided, the probable volume and tem- perature of the water to be encountered, the extent and type of the timbering that will be required and the probable average progress of driving, all of which factors will affect the cost of the work. In many cases the geology is not the only or a controlling factor, as the tunnel has to be built directly between two given points, regardless of the geological conditions which lie between. Even in such cases, however, a knowledge of the rock structure is of great importance and value as affording a rational basis for a more accurate forecast of the probable cost in time and money of the proposed work. In other cases alternative routes may be possible, in some of which the geological conditions may be such that a great saving may be indicated, even though the route followed be not the shortest. A striking example of this is to be found in the Catskill water supply tunnels for the City of New York. A most careful and thorough analysis of the geology of the region traversed was made,* and the aqueduct tunnels were located so as to avoid crossing the East River at a point where the geology indicated that a fault zone would be inter- sected, while the tunnel to carry the gas mains of the Astoria Light, Heat and Power Company, at New York,t from one side of the same river to the other, had of necessity, on account of property ownership and the location of objective points of origin * "Geology of the Catskill Aqueduct," by C. P. Berkey. Published by The University of the State of New York. t See Paper No. 1359 of the American Society of Civil Engineers, by J. V. Davies. Transactions Am. Soc. C. E., Vol. LXXX, 1916, page 594. RAILROAD TUNNELS 429 and termination, to be driven on a line which intersected this zone, resulting in grave difficulties due to excessive influx of water at great pressure. (B) Cross-section The cross-section of a tunnel depends on three factors, namely: the function of the tunnel, the nature of the material penetrated and the method of construction. As to the function of the tunnel : the minimum internal cross- section must be large enough for the passage of the rolling stock Soction for yielding material that exerts 6ide pressure- ^^ 1 Radius varies wlA | ^\^^ /^ 1 distance between 1 /\ / ^ 1 Tracks ' /' \ -V Spacing of Tracks to ' Conform to Railway ' Standard ] 4 > 1 " o .t:iri V 8'0--* ■r- -1 T *^ r , j-^*^ — — »H ^ r^ ^^ ?, ^,\^- 7T"JI( Subgrade '''. (5 "Drain Pipe of Cast Tron ~^ 6 "Openings Fig. 82. Clearance diagram for single and double railroad track tunnels. or vehicles, as the case may be. Practically all railroads in this country are of standard gage and therefore every railroad tunnel must have clearance for standard rolling stock. This clearance has been standardized by the American Railway Engineering Association, see Figure 82, which shows the present (1920) standard. Track centers are usually fixed at from 13 to 14 feet for double-track construction. If the tunnel is to handle the traffic of a double-track line the alternative of one tunnel for two tracks or two tunnels each carrying one track will be presented. This is often a aifficult matter to decide. In self-sustaining rock the choice is unfet- tered by considerations of construction difficulties and the rela- tive advantages of each may be summed up thus : One double- 430 MODERN TUNNELING track tunnel (a) allows more room for track repairs and renewals; (b) provides more space for clearing a wreck and (c) is generally cheaper than two single tunnels. Two single-track tunnels (a) give greater safety, as a wreck or derailment in one tunnel does not affect the other; (b) the ventilation is simplified, as a con- stant relation between the direction of the air current and that of the trains can be maintained, which cannot be done in a double- track tunnel, through which trains move in opposite directions. In respect to highway tunnels, the limiting size of automo- biles has not yet been fixed by statute, although this seems an inevitable development of the future. An exhaustive investigation into this matter, made by C. M. Holland, Chief Engineer for the New York and New Jersey Bridge and Tunnel Commission,* indicates that, with proper control and limitation of speed, automobiles require a clear headroom of 13 feet 6 inches above the roadway surface, including the maximum height of vehicle 1 2 feet under any con- dition of load, and clearance of i foot 6 inches to permit for possible necessity for jacking up. That the limiting outside width of an automobile body is to be taken as 8 feet, which is that agreed upon by manufacturers and State Highway authori- ties as the maximum desirable or necessary for highway opera- tion. An allowance beyond this width has to be made for irregular driving, clearance at curbs and clearance between lines of traffic. It has therefore been considered that for a single line of vehicle traffic there should be provided 13 feet between curbs; for a tunnel to serve two lines of vehicles in the same, or contrary, direction, the width between curbs should be 20 feet, while to provide for three lines of vehicles a width between curbs of 28 feet is to be considered the minimum, as those widths would provide adequately for mixed freight and pleasure vehicles. The design must consider the nature of the material to be pene- trated, which may range from the hardest and most durable rock to the softest and most liquid mud. In the former case no * Reports of the New York State Bridge & Tunnel Commission to the Governor and Legislature, N. Y., 1920 and 192 1. RAILROAD TUNNELS 431 lining for the sole purpose of supporting the rock will be neces- sary, and the cross-section may be excavated to a shape dictated wholly by the clearance imposed by traffic requirements. In the latter case, while the clearance must be such as will admit the traffic, the cross-section of the tunnel Uning will be deter- mined primarily by the pressures imposed by the surrounding material. This is also true to some extent of all materials excepting those which are permanently self-sustaining. Before concluding the question of the type of cross-section selected in relation to the function of the tunnel, it may not be amiss to warn the engineer unfamiliar with the practical work of tunneling against a tendency, sometimes seen, of breaking the outside line of the tunnel cross-section with ditches, recesses, or duct chambers to carry minor utilities such as cables, drainage fines, etc. Anything which breaks the continuity of the outside periphery adds materially to the cost of the work, both in time and money, and should be avoided. As regards the influence of the method of construction on the cross-section this will usually be negligible, except in so far that the arch design must advantageously carry exterior pres- sures. The case is different, however, in the subaqueous tunnel driven with a ''complete" shield, in which case the cross-section will almost certainly be circular. The word ''complete^' is used in the previous sentence to distinguish the case from that in which a roof shield only is used, when the shape of the tunnel may be a regular horse-shoe cross-section or one with straight side-walls and an arched roof, as the engineer may elect. In ground which is not self-sustaining the problems of construction play a larger part in affecting the decision, but even so, the con- struction difficulties will probably be subordinate to the traffic requirements, especially since in most railway tunnels the extent of the soft ground offering exceptional difficulty will be a relatively small part of the total length, as those difficulties are usually confined to the vicinity of the portals. 432 MODERN TUNNELING (C) Alinement In common with any other raihoad extension or improve- ment, the maximum rate of grade or degree of curvature allow- able for a tunnel is fixed by the requirements of operation rather than by constructional considerations. Wherever possible, tun- nels should be straight, as this simpHfies greatly the ventilation, reduces track maintenance and increases the safety of employees. Sometimes, it is true, in mountain country, spiral tunnels are introduced into a line for the purpose of gaining elevation, and in cities it is commonly necessary to follow lines of streets or properties which break up the continuity of the tangents. Due partly to condensation and partly to seepage of water, it is fre- quently the case that the rails in tunnels are damp and the trac- tive power of the locomotive and the braking effect is thereby reduced, and this fact should be given consideration in flattening the tunnel gradient below the general controlHng gradient of the railroad. A straight highway tunnel is desirable from the point of view of safety in use. The gradients should be kept, if possible, within a maximum of 3.5 per cent. Under no circumstances, for any kind of tunnel, should there be any level stretch, otherwise water will pool in the tunnel. While water will flow readily at a gradient of 0.25 per cent., it is better to provide a minimum gradient of 0.5 per cent., which will give free and rapid drainage flow. (D) Lining The two main questions which confront the engineer with regard to lining are: (i) Is any lining at all required and (2) if so, of what material shall it be built? When the tunnel is in loose rock or earth, as well as in solid rock tunnels in the lengths adjacent to the portals, or in clay or silt, as in the case of subaqueous tunnels, a lining is obviously essential. As a general rule it may be said that railroad tunnels that have not required a permanent lining, for some part of their length at least, are rare. Aside from providing for stability, in some cases RAILROAD TUNNELS 433 considerations such as cleanliness or appearance may neces- sitate a lining, even where the permanent stability of the rock is certain. Many tunnels, among them some of the most noted in this country, were opened to traffic unUned, but subsequent weathering of the rock, vibration of trains, seepage of water or the exhaust of the locomotives resulted in falls of rock, which were a menace to safety and necessitated lining these tunnels under traffic at greatly increased cost, although sometimes this increased cost may have been warranted by the economy resulting from interest saved on deferred expenditures. As to the materials of which the lining should be built, the following have been used: (i) timber; (2) masonry; (3) brick; (4) plain concrete; (5) reinforced concrete; (6) concrete pre- cast blocks; (7) cast iron or cast steel; (8) structural steel. The choice of one or more of these m.aterials for lining a railroad or, to a less extent, a highway tunnel, will depend upon the com- parative availability and cost of the materials in place and on the earth pressure to be supported. In the early development of the railroads of the United States it has been common practice to line the rock tunnels with timber, when this would serve, in order to reduce the first cost of construc- tion, postponing the substitution of a more permanent lining until it could be paid for from earnings or from bonds floated on better terms after the traffic development of the property. With the increasing scarcity and rising cost of timber, its relatively short life, the menace of fire and, in particular, the excessive cost of relining a tunnel without interruption to traffic, it has become the practice to Hne such tunnels at the outset with material of a permanent nature. Where a temporary timber lining is built, for any reason, the excavation must be increased in order that there will be room enough within the timber lining to place the permanent lining, as it is generally impracticable to remove any of the original timber lining. If the second lining is designed so that no timber is to be incorporated within it, the original excavation will be particularly excessive, as will the cost of plac- ing concrete or brick masonry lining and packing behind it. If, on the other hand, the timber lining is to be surrounded to some 434 MODERN TUNNELING extent by a concrete Kning, the quantity of concrete will be unnecessarily great for the resistance it offers to ground pressures. In lining a tunnel permanently, during initial construction, these disadvantages may be obviated, and in many cases the cost of temporary timbering can be greatly reduced by intelligently planning the sequence of excavation and permanent lining so that the latter may be kept close to the finished excavation. The general system of timbering in use in this country — the so-called American system — is shown in Figure 83. Its chief advantages are simpHcity of erection and the reduction of the amount of timber used to a minimum. Its disadvantages are Cross Section. Longitudinal Section. Fig. 83. American system of tunnel timbering. tliat in heavy ground the last mentioned advantage tends to disappear, it is especially ill-adapted for unsymmetrical pres- sures and, finally, most rock excavation cannot be made with anything like the uniformity of outline of the timber sets, thus involving the necessity for much filling or packing back of the timber. In this system square timber is used almost exclusively, although round timber was formerly common and still is used for the posts. Certain climatic conditions may warrant the use of a preservative. If a subsequent concrete lining in which the timber may be embedded is contemplated, the timber used should be well seasoned. If round timbers are used for posts, the bark should be stripped to retard decay. Timber Hnings are generally restricted to cases where the ground is to all intents and purposes self-sustaining, and where RAILROAD TUNNELS 435 the chief function of such lining is to prevent accidental falls of rock; consequently its design is chiefly empirical. With the more permanent types of Hning there is usually earth pressure to be resisted and the design of the hning there- fore takes on a more rational form, and may warrant, where possible, an analysis of the stresses. In a chapter such as this it is impossible to lay down any rules or to give any formulae which will enable the engineer to evolve a design suitable for the case he may have in hand. In the past, most tunnel lining designs have been based on precedent, experience and judgment, owing to our limited knowledge of the true character of earth pressures and the laws which govern them. Even with the most complete geological investigation it is impossible, at least with tunnels of any length or depth, to know precisely the nature of the rock, its stratification and other characteristics with enough accuracy to warrant any particularly refined analysis as to the probable earth pressures. The most a man can do is to get the best information he can as to the rock, make a design based on whatever theoretical considerations appear appHcable, check the tentative design by reference to other previously built tunnels of similar size and characteristics, then start the work, reahzing that the driving of the tunnel itself will disclose far more information than can be got in any other way and that he must be continually on the alert throughout the period of con- struction, so that he may modify the design of the Hning when- ever and wherever the conditions call for such action. As a suggestion it may be well to watch for faults in the rock, wet clay seams, or contact zones between contiguous strata which may result in unsymmetrical forces acting on the lining; the danger from rock, normally sound, becoming shattered from excessively heavy blasting and the presence of locally heavy water pressure. Further, there are many rocks (notably of volcanic origin) and soils which on exposure to the air between the excavation and permanent hning, weather and swell so as to exert extraordinary pressures on the Hning. In these cases extreme rapidity of Hning operations is essential to success. In the subjoined bibHography reference is made to several 436 MODERN TUNNELING papers dealing with the mathematical side of tunnel lining design. Having determined or estimated, from theoretical consider- ations, aided by precedent, upon the extraneous pressures that the Hning will be required to withstand, the next step is to decide upon the material of which the hning may be formed. In the earliest times permanent lining was made of stone masonry, either ashlar, squared or rubble. With the increasing availabiHty of brick having a fairly high compressive strength, brick masonry began to displace stone masonry as a lining material, especially for the arch, owing to the greater ease of laying brick in cramped quarters, so that many early examples of tunnels will be found with stone masonry side walls and invert and brick arches. The present tendency, however, is away from stone and brickwork and toward concrete in some form, owing partly to the higher strength of the latter, partly to the fact that, being plastic, it conforms readily to the irregularities of the outside hues of the excavation, thus reducing leakage, and partly to the fact that a suitable hning of concrete can be procured at a lower cost, since a smaller proportion of skilled labor is required for this material. It is conceivable, however, that local conditions may enable a suitable masonry or brick lining to be laid at a lower cost than one of concrete and this should be looked into by the engineer before making a final decision. In fact, a comparison should be made of the relative costs of all the types of lining suitable for a particular tunnel before deciding which material to use. If a lining of concrete which has to withstand appreciable earth pressures is selected, it may be either plain or reinforced. In any design, due attention should be given to the inherent difficulty of placing concrete Hning in a tunnel. Very thin Hn- ings should not be attempted. For this reason it is worth while to sound a note of caution as to the matter of reinforced con- crete. The designer may be tempted at some time to achieve a figured saving by the use of reinforcement which, in reahty, will lead to added expense on account of the difficulty of placing and maintaining the reinforcement behind the forms and of placing the concrete properly around the reinforcement. The designer I RAILROAD TUNNELS 437 must bear in mind that tunnel lining is usually placed under the disadvantages of cramped quarters, poor lighting, often large quantities of water and interference from timbers. The design therefore, should be one of rugged simplicity with a reasonable prospect of being built as planned, rather than one of such com- plexity as to require a constant vigilance in the inspection which cannot be assured. It seems well to point out that while a designer should not slavishly follow precedent, he must consider that should his reinforced alternative for a rugged simple Hn- ing prove to be a failure, it would have to be repaired or renewed under operation at greatly increased cost. Highly reinforced concrete is out of its element as a tunnel lining. It need hardly be said, although this section deals with design and not with construction methods, that nevertheless the method by which the Hning is to be placed, necessarily has a profound influence on the design; it should not be forgotten that the net cost of a concrete lining is dependent, not only on the quantity of concrete, but also on the extent of overbreakage, the cost of the forms, the labor of placing the concrete, the cost of waterproofing, if any, the backfilling or packing and other operations. Hence in some cases a thick lining, perhaps of leaner concrete, may be cheaper and better than a thin lining with its attendant backfilling and packing. In this connection, it may not be amiss to remind the reader of the possibilities of the pneumatic placement of concrete and even of the " cement gun," the latter being particularly useful where very thin linings are unavoidable, as well as for the repair of old linings. There is another form in which concrete may be used, namely in pre-cast blocks. This form is especially applicable for arches subject to symmetrical pressure and has several important advantages. They may be summarized as follows: (a) The quality and uniformity of the concrete may be made better than when placed in situ in the tunnel, (b) The contraction takes place before the material is placed in the tunnel, (c) A large part of the labor is employed on the surface w^here it is cheaper and more efficient than below, (d) The form work is reduced to a minimum, (e) Temporary timbering for support can often 438 MODERN TUNNELING be largely dispensed with, (f) The full strength of the arch is early attained, (g) A definite thickness of arch and a suitable surface for waterproofing is obtained, (h) The labor involved in rock packing behind the arch may be reduced. ^!kc^^ For inverts and side walls, the advantages of pre-cast blocks are not nearly so pronounced, as block construction is best adapted for taking compressive stresses only. The size and form of these pre-cast blocks may vary with circumstances. For a single-track tunnel it may be possible to erect a full arch span in as few as three sections. The number would of course RAILROAD TUNNELS 439 increase with the span in order to keep the blocks from becoming unwieldy, although this may be compensated for by the use of a mechanical erector. The blocks may be plain or arranged to interlock and it is worth noting that some details of the latter type are protected by patents. Figure 84 ; this does not, however, exclude modifications which do not infringe on the patented features. As an illustration of what has been done along this line, the following table shows the size of the blocks which have been used on various important tunnels. Name ot Tunnel Span of Arch Size of Blocks Granges, Europe 17 feet ins. 14 feet 6 ins. 37 feet ins. 13 feet II ins. 23ins. X4-6 insX 9-5 ins. 12 ins. X 9.0 ins. X 18.0 ins. 28 & 31 ins. X92.0X60.0 ins. 24 ins. X60 ins. X32 ins. Arthur Pass, New Zealand Barrientos, Mexico Mount Royal, Canada The blocks in the Mount Royal were of the O'Rourke patented inter-locking type. As regards cast iron or cast steel as a lining material, the real field for these is in shield-driven tunnels, to which indeed, they are almost wholly confined. The form which this type of lining takes is that of "seg- ments," usually of a circle and consisting of the lining proper or "skin," from the four edges of which flanges project inwardly and normal to the skin, except that the short "key" has reversed angle joints longitudinally of the tunnel. The function of the flanges is to give construction depth to the lining and .thus enable it to carry the stresses and incidentally to afford a means of connecting the segments together by bolts in order to build up the lining, which is formed of successive "rings" of segments. These points are more clearly shown in Figure 85. This type of lining was originally used in England as "tub- bing" for lining mine shafts, and the first tunnel so lined was the seven-foot diameter Tower Subway for foot passengers across the Thames at London. This tunnel was also the first one driven with a circular shield which was the prototype of the modern tunneHng shield. 440 MODERN TUNNELING ■pao«3.' RAILROAD TUNNELS 441 This type of lining has several important advantages, which may be summarized thus: (a) For a given condition of loading, the thickness is less than that required with masonry or con- crete, thus reducing the quantity of excavation to be dene. (b) The full strength is developed as soon as it is erected. This makes it of especial value in shield driven work, (c) The labor of erection is less than with the foregoing types of lining, as it is a machine-operated process, {d) By caulking the joints and grummeting the bolts it may be made practically waterproof, even against a considerable head, (e) Since the Hning consists of successive rings of short length it is permanently erected and secured within the tail of the shield and thus the expense and hazard of timbering can be largely avoided, as the ground can be supported by the permanent lining without' delay. (/) This, together with (b), makes it possible to grout outside this lining promptly after it is erected, thus filUng every void and reducing settlement to a minimum, (g) The lining is durable and not subject to decay or appreciable corrosion. To increase its resist- ance to corrosion it is usual to hot dip the segments in a preserva- tive coating having a large proportion of pitch or asphalt before they leave the foundry. The disadvantages of iron as a Hning are its relatively high first cost as compared with other Hnings and its lack of flexibil- ity. By this latter is meant that, in its ordinary use in shield- driven work, the cross-section of the tunnel is almost always con- fined to a circle (although one or two examples of oval cross- section are to be found) and that as the lining consists of rings of uniform length, direction can be altered only by the use of special tapered rings, which are machine faced to definite angles of deflection. Ordinarily cast iron is the material used, but where special strength was required cast steel has been substituted. Notwithstanding that this type of lining has been used almost exclusively in shield-driven work, its possibiUties for other tun- nels should not be overlooked, especially for the arches of wet tunnels. This type is especially valuable and has been frequently 442 MODERN TUNNELING Utilized for strengthening or waterproofing existing tunnel Knings of other material, which may show signs of being overstressed or which require waterproofing, and within which there is not enough room for any other type of reinforcement. As an internal reinforcement, where clearances have been extremely close, cast iron has been used in corrugated section form giving great strength for very shallow depth of construction. The detail of the design, namely: the number of segments, the length of the ring, the thickness of the skin and of the flanges, the depth of the flanges, the details of closing the ring by ''key," the question of machining the abutting faces of the flanges or of using wood packing strips (which is seldom if ever used in the present day), the size and spacing of the bolts and the method of rendering waterproof the joints and the bolts are matters which have to be studied to suit the circumstances of each case. Reference to previous successful examples of similar work will form the surest guide. Up to the present, judgment, experience and precedent have largely guided the designers of this type of tunnel, but of late years several attempts have been made to discuss the subject on more or less rational grounds and the reader is referred to such articles quoted in the BibHography. The table on page 443, however, giving the particulars of the cast-iron lining of several tunnels may be of value. It is to be noted that cast-iron lining is often supplemented by an interior lining of concrete extending wholly or partially around the perimeter. This is done to give a smooth interior surface, to increase the strength, and to afford protection against corrosion for the metal lining, especially the bolt heads and nuts. Since most iron-lined tunnels are circular in cross-section, while the clearance lines of the vehicles using them are approximately rectangular, there is usually a considerable amount of space at the sides not needed for traffic. This space is often utilized as benches, in which are embedded ducts for carrying electric power cables and telephone and telegraph wires. The top of the bench forms, incidentally, a good foot-walk clear of the traffic for maintenance employees and in cases of emergency. As will be understood, the possibility of water leaking into an RAILROAD TUNNELS 443 DETAILS OF CAST-IRON LINING FOR SOME SUBAQUEOUS TUNNELS Name of Tunnel Exter- nal Di- ameter of Ring Length of One Ring Thick- ness of Web Depth of Flange No. of Seg- ments in One Ring Exclud- ing Key Weight of Cast Iron in One Ft. of Tun- nel 1 Diam- eter of Bolts con- necting Seg- ments Hudson & Manhattan R.R., Hudson River, New York, 1906 Ft. Ins. 16 7 Ins. 24 Ins. Ins. 8 No. 9 Lb. 5,670 Ins. Battery Tunnel, East R., New York, 1901 16 81 22 li ih 8 4.540 I Pennsylvania R.R., Hud- son R., New York, 1 906 23 30 2 II II 11.594 T •'' Blackwall Vehicular Tun- nel, River Thames, London, Eng., 1892. . . 27 30 2 12 14 14,784 a Rotherhithe Vehicular Tunnel, River Thames, London, Eng., 1908. . . 30 30 2 14 16 16,845 i^ Proposed Vehicular Tun- nel, Hudson R., New York, 192 1 29 6 30 l| 14 14 17,000 If iron-lined tunnel is confined to the joints between the segments and to the bolt holes, which have an allowance for a clearance over the diameter of the bolt. The joints of cast-iron segmental lining are nowadays invariably machine faced to limit gages over nearly the entire area of all flanges. To provide for water- proofing, a narrow caulking groove is provided in each casting on the interior edge of each flange so that when two plates are erected together the two recesses oppose each other so as to make a caulking cavity of a slightly dovetailed form about I inch to I J inches deep and | to J inch wide. As every jointed structure will change its form upon imposition of earth pressures 444 MODERN TUNNELING and these deformations extend over a considerable period of time before a final and stationary condition is reached, it is desirable that the waterproofing of the joints should be made in the first instance with a flexible fibrous or soft metalHc sub- stance which will permit repeated recaulking during this period of adjustment of form, after which the grooves may be finally filled and caulked solid with lead or the preliminary lead caulk- ing may be backed up by a final introduction and caulking with either a mixture of iron filings and sal-ammoniac (rust jointing), or cement mortar or any combination of these. The bolt holes are waterproofed by rings of hemp dipped in red lead, or of stamped or cast washers of lead placed under the iron washers — at both ends — around the shank of the bolts. These rings are called grummets. This process of caulking joints can by care and repeated recaulking be made to produce an almost abso- lutely water tight structure even in wet soil. The operation of waterproofing such a tunnel is best performed as a separate one, after the strains and stresses due to driving have ceased, as even slight movements destroy the efficacy of the waterproofing. In some cases the caulking has been done exclusively with rust jointing, but there is great danger of an inelastic joint material failing of its purpose when subjected to settlements and changes of form. As an example of the efficacy of the waterproofing in such a tunnel, it may be remarked that the Hudson River twin tunnels of the Pennsylvania Railroad, which are 23 feet in diameter and 5000 feet in length, under a maximum head of 98 feet of water and in a silt which is saturated with water, give a leakage of only 200 gallons per 24 hours for each tunnel. A further development of metal fining, especially for sub- aqueous tunnels, is to be looked for in the use of structural steel. Several examples of this material used as lining are to be found. For instance, one across the Elbe at Hamburg; another across the Spree at Berhn and a short length of discharge tunnel under the Hudson River at Jersey City, N. J. The development of this material into a fixed type has not progressed to the point already reached by cast-iron lining, and the various examples RAILROAD TUNNELS 445 cited differ widely in their details. For the most part, the structural steel examples now existing are ineffective designs, in that the details of the cast-iron type have been copied in steel and thus the valuable properties of the structural steel have been partly lost. When steel lining is designed along rational lines, however, certain valuable advantages are gained and these may be summarized as follows: (a) The tunnel is made completely and permanently w^aterproof by the enveloping skin of steel. {b) The elements of the lining are readily fabricated in any bridge shop, (c) A lining can be designed to be self-sustaining under any load w^hich may come upon it and to be capable of resisting any stresses, tensile or compressive, without deforma- tion except that due to the elasticity of the material, (d) For any given case the weight of the steel required is about one-third that of cast iron of equal strength; consequently the steel lining can be brought into the tunnel and erected in larger and fewer units, leading to an increased rate of progress and greater ease of waterproofing, (e) By means of electric welding, which has now become a perfectly practical process, the joints can be made absolutely waterproof, (f) The cost of such a lining, compared with cast iron or other material, depends obviously on local con- ditions and the prices of materials. For the city of New York, in the year 1920, structural steel lining in place has been esti- mated to cost about one-half that of cast-iron lining in place, for the same tunnel, {g) Steel as a material is inherently more reliable, more homogeneous and therefore safer to use than cast iron, which, on account of its defects, has been abandoned long since by bridge builders. It would be desirable, usually, to provide a secondary lining of concrete for a structural steel lining, to save the frequent painting which otherwise would be required and to afford a smooth interior finish to the tunnel. In any metal Hning its strength is a function of the depth of the flange. As the diameter of the tunnel increases the required depth of flange rapidly becomes greater and with a subaqueous tunnel the practical limiting depth of flange is reached when the tunnel reaches a diameter approximating 30 feet. In structural 446 MODERN TUNNELING RAILROAD TUNNELS 447 steel, on the other hand, as the depth of flange is provided for by plates no limitation of the depth of flange is set, and conse- quently no limitation on the diameter of the tunnel, except such as may be imposed by the difficulty of adjusting the air pressure in the tunnel to balance the great difference in water pressures. Figure 86 shows the details of a steel lining. (D) Backing of Lining The actual kind of lining and its dimensions having been determined, it must be remembered that the tunnel as excavated will be of a cross-section in excess of the limits of the lining. This is done so that sufficient space is available for the lining and to avoid trimming, which is expensive. Even in a shield-driven tunnel there is a small, annular space outside the lining caused by the necessary clearance for the shield. Economically, over- breakage cannot be avoided and is frequently more pronounced in stratified than in igneous rocks. There is the further necessity for allowing space for timbering in certain kinds of material. Good practice does not permit the encroachment, within the predetermined limits of the lining, of any projecting portions of timbering or the rock itself. The space thus unavoidably left outside the limits of the permanent lining should be packed solid as the fining advances, in order to take up the soil pressures and so prevent any movement of the ground and to distribute properly the earth pressures over the permanent fining. The material generally used is rock from the tunnel excavation, carefufiy placed by hand. This is readily available when the lining is built in the first instance. In tunnels which have been lined after being put into operation it has been a frequent prac- tice to use cordwood or scrap timber for packing, the perma- nence of which seems disproportionate to that of the lining to which it is an adjunct. If it is desired to drain whatever water is present, this packing is left ''dry." In cases where it is desired to have a lining which is completely waterproof, it may be necessary to grout the packing with mortar forced by air pressure through pipes in the permanent lining. Speaking generally, for railway or highway tunnels piercing 448 MODERN TUNNELING hills or mountains, the rock packing will be left dry and the water, if any, allowed to enter the tunnel through drains pro- vided for it. Usually the profile of the tunnel will be such that water thus entering will flow by gravity to one or both portals,, there to enter the general drainage system of the territory. In certain special cases, however, as where tunnels are built under waterways, the profile will be such that water entering the tun- nel cannot flow out by gravity. In these instances the engineer may have to choose between rendering the lining of his tunnel so waterproof that little or no water can enter or allowing it to enter as in the other case, conducting such water to a sump at the lowest point of the profile and pumping it thence to the surface. (E) Waterproofing Lining Apart altogether from the special case of the shield-driven subaqueous tunnel and considering only the rock or soft ground tunnel driven in the usual way, the methods of waterproofing such a structure are as follows: (a) The periphery of the tunnel is enclosed by a waterproof envelope or membrane, made up of several thicknesses or plies of a fabric such as cotton or felt. Each ply is put in place and covered with a layer of pitch or asphalt swabbed on in a heated and semi-liquid state. Another ply of fabric is laid on the first one and breaking joint with it and swabbed with pitch as before. This process is repeated until the desired number of plies is in place. The number depends on the head of water and may vary from three to eight. The various plies of fabric may be applied in long continuous roll form or when the working space is very constricted may be laid in sheets in every respect like laying shingles. Figure 87. A modification of the multiple ply system consists in using one ply only of a very heavy duck fabric treated with pitch and with broad overlap wherever the sheets of duck are joined. In this case when the waterproof sheet is laid all joints are seared with hot irons to effect a tight joint. In order to place the mem- brane it is usually necessary to build a thin concrete surface (called "sand walls") outside the net line of the permanent RAILROAD TUNNELS 449 invert and walls, on which to lay the fabric. After laying this type of waterproof in places where it is accessible it should be ^ "S ° 1 .2 '5 C c c o c o o protected by laying concrete for mechanical protection before back filling or packing. 450 MODERN TUNNELING If the arch is built of concrete in situ it may be necessary to use a back form so that a fairly smooth outer surface is given on which to lay the membrane. Clearance has to be allowed between the timbering and the extrados of the arch in which the waterproofing can be laid and the back filling or packing over the arch has to be done with great care so that the membrane is not pierced by sharp corners of stones. With the small clearances usually allowed in tunnels the difficulty of laying such waterproofing, especially over the arch, is great. On the sidewalls and invert the difficulty is less. One grave fault in the membranous type of waterproofing is that a defective joint in laying up the fabric in wet ground may permit flow of water, which finding its way between the concrete lining and the fabric may percolate through the concrete lining at points quite remote from the original leak, giving considerable trouble to trace and stop. This trouble is one of those due to inefficiency of labor and lack of proper inspection oversight of construction. (&) Another form of waterproofing is to use brickwork set in a waterproof mastic consisting of hot melted asphaltic pitch mixed with clean sharp building sand and, or, limestone dust applied hot instead of in ordinary cement mortar. Here also sand walls will be generally needed on the invert and sidewalls, and back forms on the arches. For waterproofing arches, brick- work in mastic is more convenient than cotton or felt sheets, as the unrolling and handling of the sheets is awkward in the narrow clearance over the arch. (c) Many structures which have been intended to be water- proofed when built have proved to be not so after completion. A great deal of good has often been achieved by ejecting mortar under air pressure through pipes set through the Hning for this purpose. Notable examples of this are the aqueduct tunnels of the Catskill supply for the City of New York and the Astoria Tunnel. In the latter'case a pressure of 500 pounds per square inch was used and this was the first example where such a high pressure was attempted. The possibiHty of this method of waterproofing should be considered carefully in every case where RAILROAD TUNNELS 451 it is desired to reduce pumping to a minimum. If the tunnel is to be waterproofed and the pumping eliminated it must be remembered that the lining may be subjected to the full head imposed by the water and the hning must be proportioned so that it is strong enough to withstand this pressure. If the water is to be allowed, under control (which in most cases is the proper policy), to enter the tunnel it is generally necessary that the arch and sidewalls, at least, shall be kept dry and the water should be made to enter the tunnel close to the bottom of the sidewalls. (d) Extensive use has been made of the so-called "Integral" method of waterproofing with very questionable success. This method depends on adding oils, soaps, lime or other materials to the mass of concrete as mixed, thereby reducing percolation. (e) Plaster coats. A certain measure of success has been attained in waterproofing tunnel structures by the surface appHcation of so-called Hydrolithic or other preparations in form of plastered coats. These usually consist of quick-setting silicates, or portland cement mixed with sal soda (Hot stuff), or other substances which will set quickly and will temporarily check the percolation of water through the voids in the concrete so long as to permit the sediment in the soil overhead washing into the watercourses and voids so as to choke themselves. (F) Drainage and Pumping The amount of attention that this phase of tunnel design necessitates from the engineer varies within wide limits but in general the problem is rather simple. It is particularly so in the case of a tunnel which has been driven and in operation for some time, and which, for one or more of the reasons previously given, it is deemed expedient to line. There should be no uncertainty about the amount of water to be taken care of, as the permanent provisions for pumping are not usually made until near the completion of the work when the amount can be actually gauged. In some geological formations there may be a seasonal variation. It is true that the engineer must decide, when he has the latitude so to do, whether or not the 452 MODERN TUNNELING water is to be excluded from the lining or conducted through it by drains. If the quantities are Hkely to be excessive, attempt is usually made to exclude by waterproofing, otherwise free entry, reHeving pressures, is more usual. If the tunnel has been driven through a solid igneous rock or through a stratum of relatively impervious metamorphic or sedimentary rock, in a stratum which is thick compared to the cross-section of the tunnel, and so situated as to approximate a horizontal or convex bedding over wide areas, it is probably best to arrange to conduct through the tunnel lining such water as is flowing. It is only reasonable to assume that if the water is excluded by the Hning, it may accumulate consider- able hydrostatic head before rehef is obtained by its finding an outlet through some superimposed and more pervious stratum, or through seams, fault zones or other defined channels.- If the tunnel has been driven through water-bearing and at least fairly pervious sedimentary rocks, such as sandstones or shales, and particularly if the stratification is inclined to the horizontal and is known to outcrop at a level lower than that of the tunnel, at a not very remote distance, it would be in order to waterproof the tunnel lining, if conditions warranted the increased cost, over putting in drains and allowing the water to come into and run through the tunnel. It will be understood readily that the basis of this reasoning is that a comparatively low static head only will be sufficient to force the water through the surrounding rock rather than through the more impervious tunnel lining. A word of caution is given about omitting drains from the sidewalls in sections which, at the time of lining, may be dry. The course of underground waters is quite variable and good practice dictates the placing of drains at frequent and regular intervals, even although there may be, at the time, no apparent purpose to be performed. For a prospective tunnel which has to be both driven and lined the engineer must rely, for the basis of his estimate of the probable water flow, on such geological and topographical exami- nations as he can make or feels warranted in having made. RAILROAD TUNNELS 453 Examination should be made of the outcrops on either side of the proposed tunnel, particularly in respect of the surface source of supply of underground waters which the tunnel is likely to tap. Inquiries also should be made of the flow in other tunnels in similar material and sometimes wells sunk to tunnel grade and pumped to gauge flow, may be of advantage as advance information. It is plain that the question of drainage will not influence the selection of a gradient for any railway tunnel — excluding subaqueous examples — of the length hmited in this chapter, namely not exceeding two or three miles. Even where a tunnel could be driven level it would not be so driven any more than would an open cut, but some inclination given to make it drain itself. In general then (again excepting subaqueous tunnels) the drainage problem resolves itself, with respect to water which is to be anticipated within the tunnel, to disposing of this water by gravity down a gradient which may lie anywhere between 0.25 per cent, and the ruling gradient of the line. Occasionally two plus gradients converging in a vertical curve at a summit or two minus gradients converging in a dip may be found, but since the former miHtates against good ventilation during opera- tion, and the latter involves pumping drainage water, both will be avoided unless overbalanced by other advantages. In considering how best to conduct the water through the tunnel certain facts should be borne in mind. The cardinal principle in laying out drains is to place them so that they ofifer the minimum exposure to becoming clogged and the maximum accessibihty to inspection and cleaning. Another, it would seem, is that the drains be placed so that the passage of water over the invert is reduced to a minimum. In a single-track railway tunnel, either lined completely or w-lthout invert or wholly unlined, drains should be provided adjacent to the sides of the tunnel and the invert or bottom, as the case may be, slightly crowned in the center. In a highway tunnel, also, the drains might be similarly placed, as the passage of water across the driving surface to a middle drain would not be desirable. 454 MODERN TUNNELING In a double- track railway tunnel which is unlined, in addition to the two side drains, there may be a center drain as well, especially if there is an appreciable drip from the middle portion of the roof. If the tunnel is fully or partially lined, however, there might be only two side drains, with the bottom crowned between them. The dimensions of the drains should be determined from the known or estimated quantity of water to be handled. It may not occur to everyone that, in most instances, the water which comes into a tunnel carries with it extremely fine mud or sand in suspension and often also alkaHne or metalKc salts in solution. These various substances are liable to be deposited in and at the outlets of the drains, so that these should be generously pro- portioned with this in view and regularly inspected. Subaqueous tunnels, in general, require that much attention be given to the subject of drainage. Since they are constructed to afford a means of crossing a body of water, there must be at least two descending gradients from the shores outward. It will be found usually that the physical conditions impose the selection of a gradient which is, or closely approaches, the limiting gradient of the line. This means that the water which enters the tunnel will readily flow to the low point, at which a sump is built. In the usual single-track subaqueous tunnel we have the following conditions which influence the drainage problem, namely : A practically waterproof lining , a smooth-lined invert , steep gradients, circular cross-section and relatively small clear- ance. These conditions have resulted in the general practice of draining such tunnels by a central drain. In subaqueous tunnels driven by shield and lined with metal rings it is possible to render the Uning Hterally waterproof and no pains should be spared in reaching this result. The reason for this is, not only to escape the constant expense of pumping, but tunnels driven through soft, water-bearing mud, as such tunnels often are, will be subject to a constant settlement if water is allowed to percolate through the lining. With such tunnels it is important to provide a safeguard against flooding from surface water and in large cities this danger RAILROAD TUNNELS 455 is greater from bursting water mains and overflowing sewers than from the natural rainfall in the catchment area. It is good prac- tice to provide intercepting sumps of large capacity just within the portals of such tunnels to intercept the flood waters before they can flow to the lowest point of the tunnel. There will be a sump at the lowest point also and all sumps will be provided with pumps of large capacity to remove accidental flood waters, as well as with pumps of small capacity to remove the normal infiltration or seepage. In such tunnels the pumps, whether for emergency flood water or for ordinary infiltration, are usually driven by compressed air or electrically operated, but in either case they will be controlled by automatic starting and stopping devices, thrown into or out of action by the level of the water in the sumps. These devices can be adjusted to reduce the pumping to a short daily period of continuous work rather than to be pumping intermittently throughout the twenty-four hours. As an additional safeguard the pumping equipment is sometimes duphcated. In view of the increasing use of electric motive power on railroads, particularly in those divisions where there is most hkehood of employing tunnels, the question of the presence of water in the tunnels is of materially greater importance in respect of maintenance than simply the questions of draining and pumping. It is almost always the case that the walls of a tunnel are in the summer months cooler than the external air, and particu- larly in warm damp climates the condensation and drip in the tunnel keeps the rails and ties wet. Again if the drainage is not provided for and maintained adequately the ballast may also be wet. Under electrical operation, particularly with direct-current, there will usually be an escape of current through the running rails to the earth which will rapidly cause serious electrolytic corrosion of the base of rail, the fastenings and ultimately deterioration of the concrete lining, all of which should be studied with a view to possible elimination , 456 MODERN TUNNELING (G) Ventilation In the earlier tunnels no artificial ventilation was provided, except that when intermediate shafts were used in the construc- tion, these were often lined with masonry, carried up above the surface of the ground and used as a means of escape for the locomotive smoke and gases. At the present time, where the traffic is frequent and heavy, it is becoming the practice to install mechanical ventilation on all but tunnels of short length. The old standards of comfort have changed and people are no longer content to suffer dis- comforts which at one time caused no comment, because con- sidered unavoidable. The presence of quantities of smoke and gases in a tunnel is, moreover, a positive menace to safety, as the operating crew of a locomotive or train may be overcome by poisonous gases under ordinary conditions, and even the passengers also, in the event of a stoppage or wreck. The same condition of danger applies with even greater force to the maintenance of way gangs. Unless the engineer can satisfy him- self that the tunnel, by reason of its short length, advantageous gradient or other contributing causes, will be able to clear itself readily of smoke and gases, he should give serious consideration to the question of mechanical ventilation. One fixed principle that can be stated is that a tunnel, the gradients of which rise from each portal to a summit within the tunnel, is certain to give poor ventilating conditions and for that reason such a profile should be avoided so far as possible where steam operation is contemplated, unless it is possible to install a ventilation shaft at the summit ; and even then the natural draft through this shaft may have to be supplemented by mechanical ventilation. A single-track tunnel will probably ventilate itself better than a double-track tunnel, as the train fills the bore more com- pletely and the piston action of the train helps greatly in clear- ing the tunnel, especially if all trains using it move in the same direction. The modern practice (based on the ''Saccardo" system) is to install fans or blowers and to force a strong current of air through RAILROAD TUNNELS 457 an annular space surrounding the trainway on three sides. This induces the flow of an additional volume through the train space, thus either blowing the smoke and gases ahead of the train or clearing the tunnel quickly behind it.* In the case of highway tunnels in which a dense traffic of gasohne driven automobiles is to be provided for, a special prob- em is presented by the fact that such motors give off large amounts of highly poisonous carbon monoxide gas. This matter is a comparatvely new subject and is now under exhaustive study for the New York and New Jersey Interstate Bridge and Tunnel Commissions.! The results of this investigation, which will have high scientific and practical value, will be pubHshed at an early date; but it is now safe to say that, even with the dense traffic certain to use the long tunnels now projected to cross the Hudson River between New York and Jersey City, no insuperable difficulties in keeping the air wholly safe and even comfortable for human consumption are to be apprehended. The question is one of adequate dilution of the poisonous gas by mechanical ventilation within the tunnels, so as to reduce the carbon monoxide in the tunnel atmosphere to a limit of 4 parts per 10,000, which is found to be harmless for protracted exposure. (H) Lighting In the past, when railway tunnels were exclusively steam operated, when the tunnels were often built in locations remote from electric energy and when the volume of traffic and the conse- quent frequency of inspection and renewals were relatively slight, no attempt was made to provide for illumination after construc- tion. The locomotive headlight served the purpose during the passage of trains and the trackmen and inspectors relied upon lanterns. At the present time, due to the comparative density * "The Ventilation of Tunnels," by Chas. S. Churchill; International Engineering Congress in 1904 (see Trans. Am. Soc. C. E., Vol. LIV. part C, page 525). t Reports of the N. Y. and N. J. Interstate Bridge and Tunnel Commis- sions to the Governors and Legislatures of N. Y. and N. J. 1920 and 1921. Report of Chief Engineer C. M. Holland. 458 MODERN TUNNELING of population in the East and Middle West and, in the moun- tain states, to the abundance of hydro-electric energy, which is distributed to great distances, it is almost always feasible to arrange for lighting a tunnel. Furthermore there is an increas- ing tendency to use electricity for motive power, which tends to make electric lighting readily available. Adequate lighting con- duces to safety in operation, lowers the cost and increases the efficiency of inspection and facilitates maintenance. It will be understood that unless the traffic is relatively heavy the lights should not be constantly burning, but arranged to be switched on as necessary. The wiring system should be as simple as possible and so placed and protected as to be immune from wet, sparks or gases, and well outside the standard clearance line of the rolling stock. Since the lights are of particular advantage in the event of clearing a wreck, they should be placed, so far as may be, so as to avoid being damaged in case such an accident should occur. All electric lighting circuit cables in tunnels must be laid in iron pipe with protected conduit boxes for making connection. In considering Hghting for highway tunnels there may be instances where, because of its short length, the tunnel will be illuminated adequately by natural light during the day. In general, short highway tunnels in isolated districts will not be lighted, in this respect being in the same state as the adjacent road. This indicates the need of having a footwalk at the side to safeguard pedestrians, and for policing purposes. In cities where traffic is dense and constant, every facihty is afforded for lighting such tunnels and this should be done, care being taken to give the maximum illumination with the minimum glare. CONTRACT BIDS In the consideration of the estimated cost of any railroad tunnel structure it should be noted that the ideas of cost and consequent bids of experienced contractors on tunnel work vary widely. In fact it is seldom that a group of bids on what would appear to be straightforward work do not vary as much as from 50 to 100 per cent. As illustrations: a group of tunnels varying between 4000 feet and 400 feet in the construction of a rail- RAILROAD TUNNELS 469 road in 1898, through the carboniferous strata of West Virginia, the quotations varied from $2.40 per cubic yard to $3.90 per cubic yard, or 62 per cent. In New York City subway tunnels awarded prior to the war, the bids on rock tunnel for one section ranged from $6.60 to $9.00 per cubic yard, a variation of 36 per cent.; another contract ranged from $9.00 to $15.00 per cubic yard, a variation of 72 per cent, above the low figure; the average bid by all contractors on this work being $12.60 per cubic yard. For another section, also before the war, bids ranged from $21 to $37 per cubic yard, a variation of 76 per cent;; and still another section bids ranged from $16.25 to v$3o per cubic yard, a variation of 83 per cent. Assuming in the case recited on page 541, that each con- tractor allowed (in preparing his figures) for a net anticipated profit of 20 per cent, above actual cost, then it would appear that based on previous experience, with accurate knowledge of prices of labor and materials, plant available and all overhead conditions defined, the average judgment of the group of 12 bidders considered the actual cost of production was 25 per cent, higher than the low bidder believed to be practicable. It is usually the case, when a number of bids are received, that one or two contractors will tender exorbitantly high bids which may be due to various causes with which is interwoven the idea that they are not anxious to spend time and money to figure closely or to obtain the work but desire to be retained in the lists of bidders for future opportunities. EHminating such bids from consideration, it is commonly the case that the remaining bids will vary within 20 or 25 per cent, only, but at the same time there may be wide variation between those bidders upon the individual unit prices under classification schedules. The prin- cipal reason for this condition arises in the fact that a contractor after preparing his bids on all direct costs of labor and materials apportioned to each individual item, has a very large general overhead account, as well as his general power and fuel account, which is appUcable to the entire work, parts of which may be proceeding at irregular periods. It is seldom that the wise con- tractor will make this apportionment evenly distributed over 460 MODERN TUNNELING each item but will on the other hand weight most heavily the items on which payments will be earliest received. The dis- tribution has to be carried out carefully and intelligently so as not to unbalance the bids improperly, since a large proportion of specifications and forms of contract provide that improper unbalancing between units of classification constitutes good and sufficient cause for rejection of any quotation so unbalanced. CHAPTER XIX CONSTRUCTION FOREIGN SYSTEMS Since this book is written particularly for the American foreman, superintendent, engineer and financier, it appears unnecessary to devote much space to any description of the various foreign systems of excavating, timbering and Hning soft ground tunnels. These systems have been evolved in the countries after which they have been named and are known, respectively, as the English, Belgian, French, German, Italian and Austrian systems. These various methods were slowly developed in the countries of their origin, over long periods of time, to meet the local and geological conditions. Excepting in special cases these methods are not used in this country and it seems outside the scope of this book to describe them. They are peculiarly adapted to very heavy rock pressures, such as have been encountered in the long deep Alpine tunnels and where, in consequence, there has been developed a class of tunnel work- men particularly skilled in this art.* These foreign systems for soft ground were developed dur- ing a period when mechanical appliances for driving and lining tunnels had not reached the stage of development at which they now stand. Consequently in those days, some elaborate mining system might have been necessary where the same work would be done nowadays in a much simpler manner, for example, by means of compressed air, with or without a shield. In this country it is probable that there will be few instances of condi- tions which will compel recourse to any of these foreign systems. * Cf. "Tunneling, Explosive Compounds and Rock Drills," by Drinker; "Modern Tunnel Practise," by D. M. Stauffer; "American Civil Engineers' Pocket Book," article by Alfred Noble and S. H. Woodard. 461 462 MODERN TUNNELING The far simpler American system has been thoroughly proved in rock and in soft ground tunnels for many years under nearly every kind of condition with complete success, and any engineer who is thoroughly conversant with the basic principles and with the possible modifications of this system has enough theoretical knowledge, at least, for this phase of any tunnel problem — other than shield driven — that may be presented. One of the main factors in the adoption of the American or some other foreign system of timbering lies in the fact that the skilled miners, upon whose efficiency the success of any method depends, obtainable in this country, are familiar with and expert in the use and capabilities of this system so that there is the greater certainty of successful results accruing from the employ- ment of the system which is well known. Following the outline stated at the beginning of Chapter XVII, the remaining pages will cover American practice as re- gards the construction methods and examples of (i) rock tunnels, (2) soft ground tunnels and (3) subaqueous tunnels. Before passing on to these separate classes of tunnel construc- tion, it may be well to devote a few words to the matters of tunnel survey work. Survey The location of a tunnel is a matter governed largely by the physical condition of each specific case and no hard and fast rule can be laid down. In order to determine the general fine and grade a reconnais- ance survey is requisite. This may be made quite perfunctory in territory already well mapped, as for example, by the United States Geological Survey. The route having been selected, it is usually necessary to know the exact distance and bearing as well as the elevations between the two portals. For some tunnels it may be easier to obtain such information by traversing than by triangulation. The latter method, however, is indis- pensable when the projected route crosses a waterway or other territory which is not readily traversed. This system reduces the actual work of taping to a minimum and substitutes therefor CONSTRUCTION 463 the reading of angles which, with modern instruments and aver- aging repeated observations, can be carried to an extraordinary degree of precision. The accuracy of the work can be found from a "check base." This base hne is determined by averaging repeated measurements with standardized steel tapes, corrected for temperature and at constant tension and level and the base points established by solid monuments. Usually it is possible and desirable to locate the governing points of the triangulation so that they are removed from the active construction areas at the portals and thus are immune from being disturbed or covered, yet close enough to be readily used. In straight tunnels, where the shafts or openings are mutually visible, it will be good practice to locate instrument towers above points on this line as closely as can be calculated behind the respective shafts or portals, as the case may be, and then to adopt as the line of driving that between these two towers. This avoids subsequent possible errors of calculations, angle turning and the effect of local dis- turbances and movements of main reference points. In surveys to establish lines for the extension underground of a tunnel location so that the opposing headings when meeting may have a divergence of less than an inch in a distance of a mile or more, extreme care and accuracy in every operation are neces- sary and among others the following points must be carefully observed. All permanent points which are to be used either as base measurements or for transferring lines should be substantial monuments of bed rock or of cut stone or concrete embedded in the ground, in which a hole about one inch diameter has been drilled and a bronze plug cemented in, upon which the actual point is X-cut and drilled. Extending lines into the tunnels, it is usual to estabUsh all points both temporary and permanent in the roof and there- from to plumb down to working points in the floor. This is of course particularly the case when using top headings. The per- manent reference points must be established with great care as the work proceeds so as to avoid thereafter any necessity for repeating the running in of external lines after these tunnel points 464 MODERN TUNNELING are once established. . Such points also should be drilled into the rock and bronze plugs inserted or in case of a fully timbered tunnel established on main timbers and thoroughly referenced. For temporary points, drill holes in rock plugged with wood or upon the main timber sets, using as the points a good sized nail drilled for plumb bob holes. A rough micrometer screw with sliding block, attached to roof timbers, is very useful in establish- ing points and a Hght screen consisting of a powder box over the front of which is a sheet of ground glass or a screen of tracing Hnen and inside the box an electric lamp, or candles, makes an excellent background for illuminating the hanging plumb bob lines. For the daily carrying forward of lines the plummet lamp is a very useful auxiliary but should not be considered sufficiently accurate for the permanent extension of the center line. The engineer must bear in mind that the atmosphere in tunnel work is almost always thick from fog and smoke, so that the length of sights is short and both temporary and permanent points must be established much more frequently than in out- side work. In some locations a single foresight can be established on the axis of the tunnel on the summit of the mountain under which such tunnel passes. This simplifies the laying out. In other cases lines have to be transferred from the surface down vertical shafts in which case plumb lines of small-sized hard brass wire are used making a wire line base as long as the shaft will permit on the axis of the tunnel below. In this case the plumb bobs used consist of lead weights cast with sheet metal wings pro- jecting so that when hung on the wires and oscillating in a tub (barrel cut in half is the best) of water they will quickly come to rest and remain stationary. At the top rigid and secure attachments must be made above the top of shaft for hanging the wires so that hanging freely each wire may be visible from the instrument set up on center line. The top suspension had better be made with sliding micrometer attachments and in use the two wires must be brought into transverse position so that the far wire is entirely hidden by the near wire from the instru- ment on center line. Transferring to the bottom the instrument CONSTRUCTION 465 must be set up on a transversely sliding plate with micrometer screw and brought into perfectly true alinement with the wire lines and permanent points then established. In any case the engineer must carry forward his lines so close to the face that the foreman is furnished with two points, within clear sight at all times of the face, that he may hang his plumb bobs in Hne to chalk the center mark on the breast wall from which to set up drills or to lay out his timber sets for the next round in advance. Further details may be found in papers referred to in the bibhography. Since tunnels have to be driven without any ocular proof of their direction, complete reliance has to be placed on the instru- mental work to insure correct grade and ahnement. Conse- quently, all survey work has to be most accurately done and requires extreme care, patience and skill on the part of the aline- ment corps. The basic principles of laying out curves and tan- gents and of levelling apply as on the surface, but the engineer will have to exercise some resourcefulness to do his work in a thorough manner and at the same time keep from interfering with the progress of the actual construction. PLANT INSTALLATION AND EQUIPMENT APPLICABLE TO ALL CLASSES OF ENLARGED TUNNELS (A) Plant Generally the plant necessary is the same as that installed for the heading or small tunnels previously considered, except that the larger and more extended operations necessitate a large increase in the power employed and the use of mechanical means for economical execution of the work. Supplementing the resume in Chapter IV of the various kinds of energy and their applicabihty to tunnel operations, the following points are to be noted : There are, not infrequently, cases of short railroad tunnels in rock when it is advantageous and usual to drill and muck entirely by hand labor and omit the hauling in, location and operation of a power plant. These cases occur when the rocks 466 MODERN TUNNELING are shales, soft sandstones or such other grades as may be easily drilled and will part readily under blasting. The results depend very largely on the experience and efficiency of the labor employed. The capital charges are reduced to a minimum, haulage can be done by hand labor in the heading and by mules in the enlarged tunnel, and under competent direction the unit costs will, in such cases, compare most favorably with a power operated layout and while the progress may not be quite as rapid, it is seldom in a railroad construction that the short tunnels constitute any controlling factor in the time of com- pletion of the undertaking. In the early days of machine drilHng, steam was often used directly to drive the drills and, in some cases, for short tunnels economy may still be obtained by this practice. It has serious disadvantages: thus, it involves long Hues of piping hot enough to burn and yet subject to great loss of heat from radiation; the exhaust steam from the drills makes the working place most uncomfortable and even dangerous. In cities or other places where electric energy is readily avail- able and the supply dependable, electricity has many advantages. It certainly reduces the prime cost of the plant and only as much power as is consumed during the progress of the work has to be paid for. The reduction in the amount of plant required may result in the work being started earher than would otherwise be possible. This would be true especially if electricity was the only kind of energy used. The disadvantages are the habiHty of interruption of the power supply from numerous and obvious causes. When not only the surface plant but the equipment in the tunnel itself is electrically driven, we have the added danger from conductors which may be poorly insulated and insecurely strung, the great aptitude for getting out of order which elec- trical apparatus at present has and the susceptibiHty of electric motors to the usually wet tunnel atmosphere. Electrical appa- ratus does not admit of receiving the crude treatment usually accorded to ailing machines by tunnel workers. Where fuel is costly and electric energy can be advantage- ously obtained; particularly by the purchase under contract of CONSTRUCTION 467 power from local power-producing sources, considerable econ- omy may be effected by using electric drive for compressing air and other uses of the plant. As regards internal combustion engines, using any form of petroleum product or producer gas engines, it must be admitted that these all have possibilities for ultimate economies in the pro- duction of power, particularly in regions where the grades of fuel are obtainable. However, they have, to date, been very infrequently used on tunnel work and the engineer with a pro- ject of any magnitude in hand should make a thorough investi- gation of the possibilities and relative economies of this source of power as appHed to the particular work. At the same time the internal combustion engine is not adapted to work in the tunnel itself due to the poisonous fumes ejected and the compara- tively poor character of the ventilation within the tunnel itself. (B) Am COIMPRESSORS In all modern tunnel construction compressed air is entirely used for drilHng and pumping as well as, to a considerable extent, for ventilation and other mechanical operations in the tunnel. The reason for this is the simplicity and rugged character of the tools which are run by compressed air and the fact that the exhaust air is perfectly safe and in fact helps the ventilation. The choice of the proper air compressor for any particular work is therefore of great importance. The matter of air compressors is covered in Chapter V of this work. Due attention should be given to the difficulty of transportation of the machinery, of obtaining spare parts or of having repairs made, of obtaining labor skilled in the maintenance and operation of the type chosen, to securing excess capacity to take care of emergencies and of decreased efficiency at high altitudes. In many cases it may be desirable to use many small rather than fewer large units, not- withstanding the higher cost and loss of operating efficiency, and in such cases the machines should be of the identical kind, as this standardization simplifies maintenance and repairs. The average reader of this book will do well to suspend any decision to adopt any tyi^e of equipment that has not been 468 MODERN TUNNELING thoroughly tested, with success under constant operation for long periods, even when such proposed equipment seems to promise initial economy. In tunnel work nothing is more essential than to keep the work going without interruption, and micro- scopic plant economies are of relatively small value compared with this feature. Remember that unsatisfactory workers can be discharged and others soon hired in their places, but to scrap or revise a plant which does not fulfill the needs, means a delay of weeks, as well as great expense. (C) Drills Supplementing what has been said in Chapter VIII, the following remarks may be added for the particular case of these larger tunnels. The factors which would influence the choice of a certain kind of drill are: the kind of motive energy, the quality of the rock, the size of the cross-section and the kind of labor available. Ordinarily at the present time some form of pneumatic drill would be used so that the choice narrows down, as a rule, to the hammer drill as compared with the piston drill. For driving a heading, all other things being equal, a hammer drill, especially when using hollow steel and flushing attach- ment and mounted on a horizontal bar across the heading, has proved itself very effective. On the other hand, the heavier piston drill is perhaps the better for drilling "down" holes, but if mounted on a tripod has disadvantages due to weight, trouble to set up and remove, etc. Further reference is made to this subject later. Progress in rock-tunnel construction is dependent on the successive operations of drilKng, blasting and mucking, and as the blasting and consequent smoke interrupts the other opera- tions it should be so planned as to reduce this interruption to a minimum. (D) Loading Equipment Speed in tunnel driving depends to a very large extent upon the rapidity with which the excavated material is removed from the working faces. Up to the present decade, tunnels have been CONSTRUCTION 469 almost universally mucked by hand labor. In a few instances, however, mechanical equipment has been tried, such as steam shovels (usually converted to air operation) loading machines and shovelling machines. Types of these latter are described in Chapter IX and it is perhaps only necessary here to say that these machines suffer from the disadvantage of occupying a great deal of room, w^hich often cannot be spared and of neces- sity being very heavy, they thus entail an elaborate track sys- tem. See Figures 88 and 89. There are material advantages to be obtained from the use of shovels fitted with flat wheels to operate on the floor of tun- nel instead of on a fixed rail- road track while the adaptation of the caterpillar drive to shov- elling machinery for tunnel use gives promise of still further improvement. The mechanically operated shovel is particularly adapted to use in bench enlargementof large size tunnels w^here there is ample space for track layout which will faciUtate the rail operation and the loading of the cars. Consid- erable success has been obtained with the adaptation of conveyor belts as adapted to loading. , — - - '^ 3" SECTION AT A.-A 470 MODERN TUNNELING In cases of top heading tunnels, the heading muck is almost invariably loaded by transferring it in small cars from the head- ing face to the bench enlargement where a traveUing tower, having a height equal to the height of the heading floor above the enlargement floor, operates on a rail on each side of the main tunnel so that it can be brought up to the face and a bridge Fig. 89. Power shovel in rock tunnel. thrown over to the heading track for loading the heading muck into the big main track haulage cars below, except at times when bench blasting is to be done, when the tower is hauled back out of the way. In narrow tunnels this is simphfied by using port- able ladders each side and forming the bridges with heavy planks. (E) Haulage Equipment Under this heading are included the cars for the spoil exca- vation, as well as the machinery necessary for hauling them within the tunnel, transporting to the surface and disposition CONSTRUCTION 471 thereafter. As affecting the decision on the most advantageous means for removing the muck from the tunnel, there is to be considered definitely, in the first place, the general plan of pro- cedure under which the tunnel is to be built, under contract plans and specifications, particularly in the matter of the rela- tions of heading driving to bench enlargement; the question of whether a top or bottom heading is adopted and whether the enlargements are carried out in one or more benches. In the event that a bottom heading of large size is employed, then it becomes obvious that one or more substantial tracks can be laid on the permanent invert, and that a large size car can be advantageously employed, since the track will remain at its permanent grade right up to the face of the heading. In this case muck will be shot down and loaded by a power shovel or hand labor, at the enlargement of the main tunnel bench; while at the various break up points, if any, from the bottom heading, the muck excavated will be thrown down, through chutes, into cars standing on the permanent track directly below those points. In the case, however, of a top heading, then the following notes may be of assistance in guiding the constructor : (a) If the heading face is maintained at a constant and very short distance ahead of the bench enlargement, so that the blasting of the heading will throw the muck down, over the face of the bench, in order to be loaded on the floor level, then there is no necessity for the consideration of any haulage in the heading as separated from the enlarged tunnel; excepting in respect, possibly, of hand shovelling and wheel-barrows, and the only question remaining, in that case, is the character of haulage in the full size tunnel. (6) If the heading driving advances at a faster rate than the bench, so that the face of the heading is a considerable but variable distance ahead of the bench enlargement, then the haul- age in the heading would be by wheel-barrows if the distance is short, or by a narrow gage (21'' to 24'') light portable track, utiUzing a low type of dump car suitable to the track gauge, which can be pushed by man-power to the dumping bridge and 472 MODERN TUNNELING chutes at the face of the bench; where the heading spoil is then loaded into the main haulage cars in the full size tunnel. If cars are used in this case they should be as Kght as possible so that derailments may be replaced as easily as possible. A port- able track in sections is advantageous as permitting, more readily, the carrying forward of the track to the shovelling plates at the face of the heading. (c) If the bench enlargement is mucked-out by hand labor then it is desirable to use, for the main haulage in the enlarged tunnel, a medium size car of a capacity of say 40 to 50 cubic feet, and in this case a solid non-dumping car will easily give the best service. If such a car as this is used, then the installation of a tipple at the top of the shaft, or outside the portal, is desirable to dump the spoil out of the tunnel car into the main line steam railroad dump car for hauHng to the spoil banks. Using a car of this type, then the main tunnel haulage can be either by wire rope, or pneumatic or electric locomotives, or even by mules. {d) In case the bench is mucked with a power shovel, then it is desirable to eliminate from consideration the small 2 -yard cars for the main haulage, and to utilize a larger size car, say 6 to 10 yards capacity, depending upon the space available in the tunnel for swinging the power shovel, built as low as possible, of a dumping type, so that the shovel may load directly into a car which is suitable for hauling out over the main line for final disposition. In this case either a standard gage track, if the tunnel is large enough, or a track of ^6" gage, or thereabouts, will be suitable, and in that case the haulage within the main tunnels should be with either pneumatic or electric locomotives. In this case it is essential before deciding on any plan of haulage to lay out carefully the space available within the finished tunnel for the operation of the shovel and for the track- layout which can be utilized in connection with the operation of the power shovel. A power shovel is a very useless tool, excepting with efficient car service, upon which the shovel is absolutely dependent. If the tunnel to be constructed is small in dimension, it may be necessary to use a small-size car, so as to give room to the shovel to swing. If possible, it is desir- CONSTRUCTION 473 able to maintain two car service tracks, one on each side of the shovel. In any case a system of turnouts and sidetracks immedi- ately in the rear of the shovel, and as close to it as possible, will be essential to maintain the proper feeding of the cars to the shovel, and the removal of loaded cars as quickly as possible. Usually, in tunnel work, head-room, as well as side-room, is very restricted, so that the cars to be used with the power shovel should be built as low-sided as possible to permit proper loading. These cars, if there is sufficient space, can be self-dumpers, or otherwise a large substantial sohd car which can be operated over a tipple at the shaft or portal to discharge into the main line steam railroad equipment, but, failing that, it is advan- tageous to use a wide fiat deck car with side pockets, allowing of erection of drop sides, and to discharge these cars with a rail- road plow at the dump. For serving the power shovel with car equipment, it is very convenient to have the shovel fitted with capstan heads or winches, to be used in pulling up empties to the shovel and to pull out the loads, which can be advan- tageously done by using fair-leads and ropes. In the arrangement for mucking the heading excavation over the bench to the main haulage in the enlarged tunnel, the arrangements for bridge, chutes or other dumping facilities should be made as flexible as possible, so as not to interfere with procedure with drilling and mucking on the bench heads. The track construction for the main haulage of the full size tunnel should be of a character, gage and weight of rail corre- sponding with the adopted equipment which the conditions of a particular job indicate to be most advantageous. In any case the main haulage track should be built substantially, well-sur- faced and ahgned, as a Httle money expended on the proper maintenance of the main haulage track will be more than repaid in the elimination of derailments, wrecks and other troubles, which are always liable to occur on construction tracks of any character. For the main haulage, rails should be of good weight and even for smaller size equipment a rail of not less than 30-lbs. is desired. In this track all joints should invariably be spliced efiiciently, and not secured by simply spiking to the ties. The 474 MODERN TUNNELING track itself with turnouts and sidings should be efficiently installed with proper switch levers, so that they may be kept S- & W c. •§ Fig. 90. Car dumping tipple used in Astoria tunnel con- struction. 2-10}^- always in good operating condition. The cost of such small items as these is vastly less than the cost of delays to the power shovel and equipment, in turn reacting upon the entire work CONSTRUCTION 475 at the face, which is sure to occur if these matters are not properly attended to. If man power loading at the bench is employed then it should be considered that the car body should be as low as possible to reduce the labor of man-handhng or shovelling. While there have been some instances where cars of from 40 to 80 cubic feet capacity were used with apparent success, it is the writer's opinion that for disposing of spoil from a tunnel driven with the ordinary heading and bench, a capacity of 40 cubic feet is about the largest economical size. It is better also to depend upon dumping the car by some separate device on the surface rather than by introducing any side or end dumping or tilting features into the car itself. These devices usually increase the height of the car and also its weight and complexity. It is beheved that equal strength is obtained with less weight with a wooden body, reinforced with steel bands and corners, rather than with an all-steel box. The former is likely to become worn or broken, but is easily repaired; the latter are liable to be deformed and are much more difficult to restore. It will be noted that the use of a bottom heading somewhat simplifies the question of car equipment or haulage. After the description of haulage methods in Chapter IX very Uttle remains to be said. It may be well in passing to point out that the delay and loss of time in extending the cable system is of less importance when the work is so organized that this extension may be made between shifts or during week ends. Further, attention is called to the fact that electric locomotives of the trolley type are not suitable for bottom heading methods of excavation. In the matter of dumping at the surface it may be noted that this is usually done by means of derricks or by tipples. One of the latter which gave entire satisfaction is shown in Figure 90. (F) Drainage and Pumping As tunnels are seldom planned with level grades and as they are usually driven from opposite ends, water, if present, will col- lect near one working face, whence it must be pumped to the 476 MODERN TUNNELING open. For this purpose a rugged simple pump, capable of hand- ling dirty water, should be considered when there is the requisite steam or air supply available. These pumps have to be moved along, from time to time, as the work of the heading and bench advances, the discharge mains being extended at the same time. On the suction end the foot valve is usually connected with the pump by a long length of flexible hose which can be withdrawn to avoid injury by blasting. If centrifugal pumps, driven as above or by electricity, are used, care should be taken to see that a sand pump and not a water pump is selected. One great disadvantage in the use of electrically driven pumping plant for down grade tunnels is that there is danger of the tunnel becoming flooded by interruption of the power supply or motor trouble, and if this should occur, the motor would be ruined. It is neces- sary in such cases to make arrangements for pulling such pumps out of the tunnel on short notice. This also shows the further desirabihty of having dupHcate pumping equipment on hand. On the other hand a compressed air pump will usually start even when completely submerged. An inexperienced engineer who may be laying out his pumping system largely by copying some previous example, is warned that proper consideration should be given to the avoidance of sharp bends; the provision of ample diameter of pipe, and to full allowance for the friction head developed on discharge lines of long length. For tunnels where the flow of water is naturally away from the face, nothing but ditches are required. Where the flow is very large, it may be necessary to raise the track system high enough above the bottom of the tunnel, so that the entire width of the tunnel acts as the ditch during the construction period. (G) Ventilation The ventilation of tunnels under construction is one of the most important things that can be considered by the engineer. Not only is a badly ventilated tunnel an act of inhumanity but from the point of view of dollars and cents alone it is most short-sighted not to keep the air in the working space in a healthful condition for the workers. When the face of a rock tunnel is fired the CONSTRUCTION 477 workings become- filled with dense smoke, gas and dust, and until this clears so that men can see and breathe freely, the work is at a standstill. The only way to cut down this loss of time is to exhaust the foul air or to blow in fresh, or both. Probably the most usual arrangement is to blow the air into the tunnel through ducts laid for that purpose and which terminate near the working face. The practical details of proportioning a ventilating sys- tem are described in Chapter VI and it is only necessary to say here that in very long tunnels under construction, it may be necessary to introduce additional blowers (Boosters) on the main Hne, where the size of the ventilating pipe has been kept so small that the fan at the portal cannot force the air to the face. Intermediate blowers may also be required for subsidiary work- ing points, for example, at places where lining work is in progress. It has lately been emphasized in industry that good ventilation and Hghting are prime factors in increasing output and this is also true in tunnel work. The use of an auxiliary tunnel for access and ventilation at Rogers Pass or "Connaught" Tunnel, in Canada hereinafter referred to, is a solution of many difficulties in very long tunnels, but such a system must be studied on its own merits in relation to the particular job under consideration. (H) Lighting The same thing applies to lighting as to ventilation, namely, that good light is essential to good progress. The days of candles are fortunately past, as far as railroad tunnels are con- cerned, and the only methods of lighting that need be discussed here are electricity and acetylene gas. As to the former, the ordinary incandescent lamp will be used for the general hghting through the tunnel, but a good word should be said for the arc Hght at points where actual work is in progress. This type of Hght hterally turns night into day and is of great help in securing speed and good quality of work. Probably, moreover, actual economy in current consumption for the same degree of Hght is obtained by their use. For the general illumination by incandescent lam.ps it is 478 MODERN TUNNELING necessary to use lamps with anchored filaments which will stand the rough handling incident to tunnel construction. In tunnels which are subject to flooding to the extent of possible danger of forcing men to flee for their lives, it is good policy to keep lighted oil lanterns hung at intervals through the workings to provide against the possible failure of the electric lighting system, in such an emergency. The acetylene lamp is the only rival to electric lighting, and has the advantage that no plant or conduc- tors are needed. It is self contained and can be moved wherever needed. It is now provided in large units for general illumination and has an advantage that a man can carry an individual lamp for local use wherever he may be although the care of these lamps is apt to be troublesome, an excuse for loafing and the loss and breakage is large. For any work of sufficient magnitude to war- rant the use of compressed air for various purposes, there seems on reason for not installing sufficient electrical apparatus to give adequate lighting in the tunnel. It can only be because of the habit formed by custom that any tunnels driven in recent years have not been well Kghted. A Hberal provision of illumination is a most important factor in the reduction of personal injury and in the promotion of the safety of employees and the work, so that, if for no other reason, the expense is amply warranted by resultant economy. (I) Surface Equipment This will vary to some extent, depending upon whether the work is conducted from shafts or portals. In the former case part of the surface equipment will consist of winding gear to raise and lower materials. It is usually found economical to install regular elevators or ''cages" for this purpose — after lining the shaft, if this is desired, rather than to rely on the cruder forms, such as a derrick, which is necessary during the shaft sinking operation, and which for the tunnel operations would be not only slower but unsafe. Even with a portal, hoisting arrange- ments of some kind may be needed as when the spoil has to be removed by wagons or loaded into a crusher. Unless the local conditions permit immediate disposal into a spoil bank, the use of surface plants ^ York [Face page 479] Fig. 91. Ari-angement of surface plants for the the North River tunnels of the Pennsylvania Railroad at New York CONSTRUCTION 479 of a locomotive crane is a very valuable means of assisting in disposal at the surface. One of the essentials in tunnel excavation is to empty the muck cars as quickly and cheaply as possible and to keep the cars in active operating use. In general the topography adjacent to the portal or shaft, the requirements of fills for the line, if any, whether or not any rock is to be set aside for crushing for concrete or for rock pack- ing and similar considerations, govern largely the selection of the most desirable surface layout. Other items of plant which will be located and operated entirely on the surface are the blacksmith shop, which for a tunnel of any magnitude, must certainly be equipped with a mechanical drill sharpener in addition to the ordinary forges; the machine shop for lathes, shapers, drill press, bolt and pipe- threading machines, saws and other equipment to whatever extent the local conditions may require; the carpenter shop, which should be equipped with the more generally used kinds of mechanical tools, such as rip saw, swing saw and band saws, planing machines, pneumatic augers, etc., so that expensive hand carpenter work may be minimized. Provision must be made for the concrete mixing plant if the tunnel is to be hned with that material, cement sheds, storage piles for sand and stone, storerooms, etc. Figure 91. (J) Camp Too much emphasis cannot be placed on the importance to the conduct of an important tunnel enterprise, of a practical and thorough study of the camp layout and equipment at each working point. In remote localities where the men employed have to be provided with Uving accommodations at the site of the work, camps will have to be built and maintained. It may be set down as a general principle that the better the faciUties furnished the better will be the work done, the less the turn- over of labor, and the greater the ultimate resulting economy. In some places the minimum requirements from the stand- 480 MODERN TUNNELING point of general well being, are prescribed by law; but it must be kept in mind that such requirements are minimum and not in all cases a desirable standard. In general, the least a competent and self-respecting workman is entitled to expect is that he will not be compelled to share a sleeping compartment with more than one other. An ideal worth striving for is indi- vidual sleeping quarters. Since the World War the living standards of all classes of workmen have advanced and as there bids fair to be no great surplus of labor, at least of the kind here discussed, for some time, the reader is warned against arranging for the very crude living conditions which have been associated generally with construction work in the past. As to living quarters, the method of construction, the arrangement of houses, the size of the camp, whether or not provision is to be made for wives and children, with schools for the latter, recreation build- ings, etc., depends upon the location of the work, its size, the duration of the construction period and to the kind of labor employed. Speaking generally, running a camp is apt to be a vexatious problem. For this reason, while it is felt that the engineer or superintendent should have full jurisdiction over all camp matters, it is best that he does not attempt to take direct charge of it, as there are many petty problems that cannot get adequate attention from an otherwise busy man. The better plan is to chose a camp foreman, selected for his tact and firm- ness, put him in sole charge and hold him responsible for results. If there is a medical officer the camp foreman should be made to cooperate with him. An essential feature for the support of the conscientious, capable camp foreman is the hearty backing of his superior. The question of farming out the commissary is one about which a good deal of hesitation may well be used. The feeding of a large number of men in an isolated district is naturally a troublesome matter but if done well, warrants the trouble. It is probably a truism to say that a well-fed man does the best work and is most contented, and the converse is also true — that a badly fed man will not give his best services. It will pay an organization to look in any other direction than the commissary to make supposed economies. With the exception CONSTRUCTION 481 of married men, no workers should be allowed to prepare their own food, as the result is inevitably poor. Nothing more can be said here about field offices other than to point out that too often the tendency is to construct poorly built, inadequately furnished and feebly heated shacks in which the engineering and construction forces have to work, under such conditions that their efficiency is impaired. Every project of any size warrants the construction of decently built and equipped offices. In addition no camp should be without steam-heated drying rooms and locker equipment should be provided so that men coming wet out of the tunnels may change their clothing, besides which there should be covered ways between top of shaft and drying rooms, if the work is carried on at high alti- tude or in cold climates. In these days the study of social and industrial welfare work has become a definite branch of science. As appHed to certain camp equipment for tunnel work, it can be considered of vital importance to efficient service and consequently to the progress and economic results of the work. Tunnel work, to the workers, is at all times hazardous, most of the work is carried on in the dark or under artificial fight and often in wet conditions and some times at high temperatures, all of which tend to sap the vitahty of the worker. If added to this, the work is in a remote locality, away from any town or community, it can be readily understood why, in former years, the saloon established, just beyond the limits of camp, often by local politicians, was such a thriving source of revenue to the promoters and such a source of demoralization to the working forces of the contractor. The addition to any such camp of a hall and provision for definite programme of amusements will be of immense service in main- taining the morale of the organization and will in reality, increase efiiciency and promote economy. CHAPTER XX HARD ROCK TUNNELS (Self-supporting) EXCAVATION METHODS One essential difference between the tunnels described in Chapter XI and those to be now considered, is that in the exca- vation of the former, the rock was taken out to the full cross- section of the tunnel at one operation, whereas in railroad and other tunnels of large cross-section it is almost universal to carry- on the excavation in two or more stages, the arrangement of which will depend upon the size and shape of the cross-section of the tunnel, the nature of the rock and other local conditions. If a railroad tunnel were excavated with the full cross-section in one plane, it would mean that all the rock would have to be blasted with only one free face, which would require the expen- diture of much drilling and explosives. In addition the work of drilHng would be awkward and expensive, as scaffolding would be required to reach all points of the face, with many conse- quent disadvantages. Hence methods have been developed whereby only a small portion of the full cross-section is first driven. This is called the ''heading." After the heading has advanced a sufficient distance to permit separate operations of drilHng, blasting and mucking, to prosecute work behind with- out interfering with work at the face, a gang is started at the task of enlarging the heading to the full cross-section. It will be seen that the driving of the heading has resulted in giving the rock to be removed in this enlargement, one other free face and has provided the further advantage of permitting a larger number of men to work at the drilling without interfering with each other and to reach and attack their work without any scaffolding. The advance heading may be placed in any part of the full 482 HARD ROCK TUNNELS 483 cross-section. It has been and still is the usual practice in this country to place the heading at the top. The width of this top heading may or may not be the full width of the tunnel. Sup- posing for the moment that the heading is at the top and for the full width of the tunnel, which is the simplest cast, the next stage is to excavate the remainder of the cross-section, which is known as the ''bench." In some cases even, as will be seen, this latter may in turn be removed in two stages. In the less gen- eral case, where the heading has been driven for the full width and is located at the bottom of the cross-section, the remainder or upper portion of the cross-section will be removed by drilling upward from the roof of the heading. Again, there have been instances where, what has approximated a full width heading, has been driven in or near the middle of the cross-section, with subsequent enlargement of the top and bottom, which are, how- ever, not conveniently done simultaneously. Finally, there has been a conspicuously successful example of a small central heading from which radial holes were drilled to enlarge to the full cross-section. This is summarized later on. While the practical tunnel man in this country will naturally lean to a top heading, the engineer nevertheless is cautioned not to follow bhndly any precedent, however general, until he has satisfied himself, by a comprehensive study in his particular case, that the proposed method of driving best fulfills the follow- ing requirements: rapid progress, low unit cost and safety during construction. The chief factors which will give these results are: reduction of drilling and explosives to a minimum, especially in the head- ing, ease of removal of water, facihty for ventilation, working the maximum number of men at any one time that can be effi- ciently employed without mutual interference, the reduction of the slow and expensive heading work to as small a proportion of the cross-section as is possible, consistent with obtaining the other advantages which a heading gives, planning the work, both drilling and mucking, that wherever possible the work goes with the force of gravity rather than against it, and the simpli- fication of the transportation of the spoil. 484 MODERN TUNNELING In the consideration of the relative merits of top or bottom headings in connection with a railroad tunnel in rock, it should always be borne in mind, if there is the probability of finding as the work advances that the roof is bad and heavy, that then a top heading will be of great advantage in enabhng proper sup- port of the roof and consequently faciHtate the prosecution of the work; in which case the selection of a top heading would be amply warranted as against other objections. On the other hand in soft ground mining with timbering methods, the selec- tion of bottom headings to give permanent foundation to main posts and side wall lining is much to be preferred, as the later removal of the arch is greatly simpHfied and enlargement is safer if the foundations are first secured. Railroad tunnels of the length discussed in this book are generally driven from the two portals, without the use of any intermediate shaft or adits. Nevertheless, as the speed of driv- ing depends upon the number of points of attack, the possibilities of multiplying the number of headings by means of a shaft or adit should be carefully examined. SIZE OF HEADING The size of the heading should be governed primarily by the fact that what is sought is speed of driving it. This means that considerations as to the method of drilling the heading, as for example, vertical columns versus horizontal bar mountings, shallow versus deep holes, the quality of the rock, character of temporary and permanent lining, etc., all will influence the width of heading adopted. Whatever the width, however, the height should be sufficient for men to stand erect comfortably. In order to enlarge the remainder of the cross-section with the most economy, the size of heading should be planned to permit of the subsequent enlargement drilling to be done as cheaply as possible. There are endless varieties and combinations of the three main methods, viz., top, bottom and center headings — which have been used. The cross-section of the tunnel may be so large (as for instance in a double-track tunnel) , that two advance HARD ROCK TUNNELS 485 headings at the sides may be necessary to excavate rapidly and economically. It will be seen that this arrangement enables the number of men engaged to be doubled, both as regards the driving and subsequent enlargement. In each case, careful consideration and experimentation should be given to determine the best location and size of the advance heading or headings. It should be stated here, however, that in homogenous rock, the size alone of the heading having been decided on, whether or not it is to be placed in one or another part of the full cross-sec- tion will depend upon the advantages or disadvantages which it offers to the removal of the remainder of the cross-section. The pages w^hich follow contain points on drilling, blasting and muck- ing which bear on the choice of top, or bottom heading. Further- more considerations of drainage may have a large part in deter- mining the location of the heading, bottom headings being useful in draining large flows of water. In the case of very wide tunnels in variable rock, two side headings have the advantage of dis- closing in advance the nature of the material that will be encountered over the full cross-section. The heading affords a void space into which to break the rock in the enlargement, whereas the excavation of the heading itself involves the penetration of the virgin rock As may be sup- posed, the cost per unit of volume of excavation is higher in the heading than the cost of the same volume in the enlargement. In order, therefore, to keep the general average cost of the total excavation to a minimum, it may be necessary to keep the cross-section of the heading as small as possible. There are certain limitations imposed by the fact that the heading must be large enough to work in. Therefore, it should be high enough for men to stand upright, allowing sufficiently for the possible necessity for temporary timber to support the roof. This would indicate therefore a clear height of not less than 7 feet. It must be wide enough so that the drills can be mounted to give the proper inclination to the holes to take out the cut, which will usually be the ^'V" or ''wedge" type described in Chapter XI, and it must be large enough so that the muck cars can be run into the heading and loaded without cramping the 486 MODERN TUNNELING men. The most usual widths used vary from a minimum of 6 feet to the full width of heading at the heading floor grade. COMPARATIVE COST OF TUNNEL EXCAVATION IN TRAP ROCK. YEARS 1906 AND 1907 liem Headings Enlargement Whole Work Superintendence Plant running Drilling and blasting Explosives Timbering Mucking Disposal Lighting Ventilation Freight Insurance Interest Dismantling plant . . . Miscellaneous So. 30 1-55 5-23 1. 00 1.20 2.48 0.30 O.OI 0.02 0.42 O. 12 0.44 So. 12 0.78 2.24 0.29 0.03 0.76 0.63 0.15 0.02 O.OI 0.22 0.03 0.47 ?0.24 1.07 2.83 0.43 1.05 1.09 0.18 O.OI O.OI 0.23 0.03 0.47 Total cost per cubic yard |i3-07 $5-75 $7-64 In this case the current rates of wages were : Drill runner S3 • 50 per day Drill helper 2 . 00 per day Heading foreman 5 . 00 per day Walking boss 7 . 50 per day Many factors enter into each specific case presented and no two cases are alike. So much depends on the degree of hard- ness of the rock, the way it breaks, the lie of the strata, the amount of water present, whether the tunnel is down grade so that the water flows to the face or up grade so that it flows away, the degree of skill and experience of the superintendence and of the labor, the type of drills used, the grade of powder and so on, that the only proper guide is experience and experiment. In certain cases, within the author's experience, it has been found that, instead of a small heading being the most economical a large heading reaching across the entire width of the finished HARD ROCK TUNNELS 487 tunnel section may give better results. One thing should be remembered and that is that the controlling economy in most tunnels is speed of advance. The more feet of tunnel that can be driven in a unit period the cheaper the work will be. As the speed of advance of the heading controls the speed of advance of the enlargement, usually that section of heading which will admit of the greatest speed of advance will be the most economi- cal section. To show, in a general way, and as illustrations only, the difference in cost between driving a heading and enlarging to full cross-section, the preceding figures are given. The first figures are obtained from the construction of the Bergen Hill tunnels of the Pennsylvania Railroad through the trap rock of the Palisade ridge at Weehawken, N. J. and repre- sent the cost to the contractor only. The average advance made in the heading per 24 hours was 5 feet. The depth of the holes was 10 feet, the diameter of the holes 2f inches, the depth of hole drilled per drill per hour was 2.7 feet, the depth of hole drilled per cubic yard was 50 feet. The dynamite used per cubic yard was from 3.4 to 5.7 pounds. The following figures have been taken from the records of the Astoria Gas Tunnel driven in the years 1911-1912 through gneiss and dolomitic limestone under the East River at New York. Average per Actual Cubic Yard Item Gneiss Dolomitic Limestone Heading Bench Total Heading Bench Tocal Drilling, in feet Pounds of dynamite 60 % No. of exploders 564 4.20 0.79 304 1-35 0.38 4.22 2.65 0.57 5 09 4-35 0.71 2.03 1.08 0.26 3 42 2.57 0.46 This is another striking confirmation of the high cost of heading work as compared with that of the enlargement. The amount of drilling required in the heading is roughly double 488 N TUNNELING that in the bench. The amount of explosive is about 3! times as great. The general actual cost of tunnel driving on this work, including all operations, in the gneiss and dolomite together was as follows: item Cosu per Actual Cubic Yard Per cent of Total Cost General supervision Field engineering Field administration Plant and equipment General labor and supplies Contingencies Drilling Blasting Timbering Mucking Disposal Power and plant running. Drill sharpening, labor . . . Lighting Extending lines Pumping Total I0.078 0135 0.563 0.846 0.293 0.690 0.861 1.003 0.003 1.462 1-379 0.807 0.258 0.154 o. 141 0.133 $8 . 806 0.90 1-53 6.40 9.61 330 7 . 83 Tot. indirect 29.57 9.80 11.38 0.03 16.60 15 63 9.18 2.93 1.76 1.60 1 . 52 Total direct 70.43 [OO.OO 100.00 The current rates of labor paid on this work were Superintendent $250.00 per month Assistant superintendent . . Heading foreman Bench foreman. Drillers Drillers helpers Muck boss Muckers Pipe fitters Pipe-fitters' helper 200 . 00 5 . 00 per 8-hour shift 4-50 3-50 2.50 3-50 2.00 3.00 2.50 The cost of the 60 per cent ^'Forcite" dynamite used was 12.30 cents per pound. The cost of drill steel averaged $0,067 per pound. HARD ROCK TUNNFXS All these costs of labor and materials would be increased two or three times at the present day. In the city of New York at the present day the lowest rate of labor in tunnels under normal air pressure is $6 per 8-hour shift. This tunnel had a theoreti- cal cross-sectional area of 331.76 square feet or 12.29 cubic yards per Hnear foot. There was actually an overbreakage of 17.9 per cent over the net cross-section so that instead of 12.29 cubic yards excavated per foot there was taken out some 14.52 cubic yards. The overbreakage in the heading was 22.6 per cent and in the bench 14.3 per cent. The entire work was con- ducted from the two terminal shafts, one on each side of the waterway and 4662 feet apart. The shaft on one side was 277 feet deep and on the other 242 feet deep. The strike of the rock cut the course of the tunnel at an angle of some 2 2§ degrees and the dip of the strata was close to being vertical. It is perhaps worth emphasizing that these detailed figures are given as merely illustrative of the results obtained under certain conditions and are in no sense to be taken as a guide or index for any other case which may be presented. The only way to make a proper estimate of the cost of a proposed piece of work, and the way which an experienced contractor would follow in making a bid, is to consider the local conditions under which the work will be performed to conform to the contract specifications, the governing wage rates, the material prices and the size and character of the tunnel. To estimate the complete staff and force required to carry out the work, the plant required, the haulage expense, the camp expense (if any), the transportation, the charges for insurance and guarantee bonds and the financing, and thus to arrive at a total monthly expense. Then to estimate the probable monthly progress, which will give the duration of the job, and thus arrive at a probable total actual net cost. To this has to be added an allowance for contingencies and profit. To use previous prices at which other work has been per- formed in the past, under unknown or different conditions of locality, rock, climate or date, may be, not only misleading but positively dangerous. 490 MODEHN TUNNELING It is worth noting that the costs of excavation given in the foregoing illustrations do not by any means represent the same costs at each heading on the same work but are average costs of the various points of attack. It is almost invariably the case, that there is a material difference in actual cost, whether of heading or enlargement excavation, between the opposing ends or even between two parallel tunnels executed at the same time and under the same conditions and general direction. These differences are due in part to the personal factors but also to variations in working conditions. In the been DRILL MOUNTING eastern states, at least, the method of drill mounting almost always by column (Figure 92) and not by horizontal bar (Figure 93). In many cases, no doubt, this is a result of con- servatism rather than of analysis and may be attributed in part to a lack of knowl- edge of the advantages of the horizontal bar mounting. In other cases, where a wide tunnel has been driven with a full width heading, a bar was not feasible. Where the upper part of a tunnel is a half circle and is taken out as a top heading in one operation the shape of the section is ill adapted to the support of a bar. Very considerable success was obtained in the Loetschberg tunnel with a travel- ling drill carriage in the advance bottom heading.* This consisted of a carriage on wheels running on rails laid each side of the heading and mounting a long mas- s-ively built arm carrying at the extreme end an adjustable arrangement of drill Fig. 92. Drill Column. * Engineering News, December 31, 1908. HARD ROCK TUNNELS 491 bars with drills attached in position for commencing next round of driUing. The function was to save time in drill set up at the face after shooting a round. The modus operandi is to withdraw out of danger the drill carriage before blasting a round. The blast piles up debris for some distance back from the face. Consequently the carriage is advanced so that the arm carrying drills reaches over the pile of muck and as soon as the air is clear enough for drill runners to work, the drills Fig. 93. Horizontal bar for drill mounting. are in position without waiting for mucking to clear space for the new set up. The carriage is designed so as not to inter- fere with mucking operations. Figure 94. In most railway or other large tunnels, the ''V" cut is the one commonly used in the heading. The depths of holes and their location is determined largely by the fact that in such tunnels the work is arranged, if possible, on the basis of three 8-hour shifts per day. As it is desirable for the work of each shift to include a complete cycle of setting up, drilling and firing, the depth of holes is influenced by this factor. In common 492 MODERN TUNNELING o HARD ROCK TUNNELS 493 with the smaller sized tunnels discussed in the earHer portion of the book it is believed that three shifts is the most economical method of work on railroad tunnel driving With this arrange- • • • • • • 11 i Fig. 95. Arrangement of drill holes suited to a single track railroad tunnel in sound hard rock. ment in mind, the character of the rock will be next in importance in determining the size, depth, location and number of holes in the heading. It seems necessary to repeat here, that in a tunnel of some length, no fixed program of drilling should be settled without carefully conducted and thoroughly analyzed tests being made, to find a basis for the best method. To guide the reader. Figures 95, 96 and 97 show typical drilling methods in various railroad tunnels. For railroad tunnels, the use of electric firing is advocated for blasting, especially for the cut. Since only three rounds are fired, there will be only three periods of delay to the work caused by the necessity for waiting for the smoke and gases to disappear ; and except in unusual cir- cumstances, the drilling progress is such that ample time is provided for these delays, especially where the drillers are permitted to knock off when they have done their task. In the relievers and trimming holes, it is of less importance to use electric firing, but usually it will prove to be better and more convenient to do so. 494 MODERN TUNNELING If a top or bottom heading, for any reason, has not been excavated to the full width of the tunnel, steps should be taken to do this as soon as the face of the heading is far enough advanced to permit of this being done without interference with the driving of the advanced heading. Since the rock to be / * ■ / • • • '• • • • • •^ • • • • 1 1 Hammer Cut Top Heading Fig. 96. Arrangement of drill holes suited to a single track railroad tunnel in moderately hard, seamy rock. removed has two free faces, the point of attack usually will be along the side of the heading, rather than along the bottom ; and the amount to be removed at one lift is best found from trial. It is to be noted that the blasting of such enlargements will take place simultaneously with the main heading. Since the speed of tunnel driving is dependent primarily on the speed of heading progress, none of these sub- sidiary operations must be allowed to interfere with that work. After a top heading has been removed to the full width, the remaining portion of the cross-section, or the bench, will next be attacked. This is usually done one lift at a time, by a row of holes drilled along the floor of the heading, parallel to the verti- cal or free face of the bench. It is often advantageous to assist the previously mentioned holes, by drilhng what are known as '' lifters " horizontally in from the foot of the bench. In some cases only the former kind, and in very infrequent instances only the latter kind, of holes are found necessary. HARD ROCK TUNNELS 495 Up to recently, bench holes, whether vertical or horizontal, have usually been drilled from tripod mounts. Figure 98. The Top Heading by Side Drifting for Wall Plates U ^:^ Fig. 97. Arrangement of drill holes suited to a single track railroad tunnel in soft rock or hard clay requiring timbering for temporary support. recent development of the air hammer drill, held in the hand, the efhcacy of which was so clearly demonstrated in shaft sinking, is tend- ing to supplant the tripod mounting. Tri- pods are cumbersome to carry from and to the point of work before and after blasting, awkward to set up, not particularly well adapted for lifters or side holes because of the necessity for clearance; and any other type of drill which obviates these disadvan- tages, as does the jack hammer, is obviously an improvement. Again, the tripod mount- ing shows to best advantage on holes of large diameter and depth, and usually bench drilling can be so planned as to substitute for these shallower and if necessary smaller diameter holes. Hand drills require less skill to operate, use less air and probably unconsciously result in reducing the amount of explosives used, as they use, in general, steel of a smaller diameter than the mounted drills. They are, however, better adapted to the softer rocks than to the extremely hard rocks, such as trap or granite which need more piston diameter and power to effect efficient drilling. • • L _J • • • • • • • • • • • • • • 496 MODERN TUNNELING Of almost equal importance with the drilling and blasting is the question of the disposal of the blasted material. This has a great effect on the speed of tunnel driving, as no advance can be made if the workings are encumbered by heaps of muck. Since the speed of driving a tunnel is dependent upon the speed of driving the heading a primary requisite in the cycle of operations Fig. 98, Tripod for drill mounting. is to get the blasted rock out of the heading so that the drills may be set to work on the next round. In some cases, particularly where the rock is likeily to weather and falls or disintegration of the roof are to be expected, so that the roof may have to be timbered as the heading proceeds; the plan is adopted of maintaining rigid and exact relation of the heading face, at a few feet only in advance of the bench. The obvious advantage of this, with a full width top heading, is that the muck from shooting the heading is blasted clear down over the bench and can be removed by the power shovel. (Cf. Liberty Tunnel, page 536.) The disadvantage is that the prog- ress must be set by the slower advance whether of heading or bench, and the operations at heading and bench must be considered as interlocked rather than as two operations proceed- ing independently. HARD ROCK TUNNELS 497 The different appliances for mucking have been described in this Chapter and in Chapter IX. It is only necessary here to consider mucking methods as affected by the cognate sub- jects of sequence of excavation, drilling and blasting. Top or Bottom Heading In the top heading method, which is the more general, the drillers will usually shovel the rock only far enough back from the face to permit them to set up their columns and the muckers will attack the pile from the back end, load it into wheel barrows or small-size hand cars and work back to the bench face over a plank runway, supported on a travelling tower or from ladders set up each side of tunnel, extending back behind the face of the bench, from which the barrows can be dumped, direct or through chutes, into cars standing on the construction track on the floor of the completely excavated tunnel. It will be seen from this that the distance between the heading and the face of the bench should be at least enough to permit the sepa- rate drilling gangs to work without interference but not any greater, as this would mean unnecessary wheeHng of the heading muck. It is, of course, desirable to place and charge the holes drilled, so that the amount of drilHng and explosives will be a minimum and the length of advance a maximum. These advan- tages should not be gained at the expense of breaking the rock in a manner which leaves it heaped against the face or in chunks so large that they are not easily handled. Blasting of heading should be heavy enough to shoot the rock well away from the face. It appears that the tendency in this country is to use too httle powder. The shooting and mucking of the bench proceeds simultaneously with the same operations in the heading and the mucking of the bench is carried on below and to the sides of the overhead bridge platform previously mentioned. It is obvi- ously an advantage to keep the head end of the construction track as close to the bench as is possible. See Figure 99. cf. p. 536. Although the top heading has been used almost to the exclu- sion of the bottom heading in this country, it must not be taken for granted that the latter has not several important advantages, 498 MODERN TUNNELING the chief being that it takes advantage of the force of gravity in a way not possible with the top heading. After driving a bottom heading the remainder of the section can be broken down by s toping, and the broken rock allowed to fall into the cars through openings in movable timber platforms, provided for that purpose. This means that the work of mucking of at J' Fig. 99. Removable scaffold for mucking heading. New York. Astoria gas tunnel, least 50 per cent, of the section is greatly reduced. In the top heading method any decrease in the progress of the bench is liable to slow down the heading driving. With the bottom heading on the contrary, if the enlargement work falls behind, new upraises can be started at any convenient places, and fresh points of attack thereby opened up. In the meantime the prog- ress of the heading is quite unaffected, as the heading muck, by this method, is not wheeled but shovelled directly into cars HARD ROCK TUNNELS 499 at the face. In timber tunnels, the bottom heading has still further advantages, as will be shown further on. as the timber is built from the bottom up and has secure foundation and, once in place, is in less danger of being shot down. Center Heading The most striking example of the center heading method of tunneling is the Rogers Pass Tunnel, on the Canadian Pacific Railway through the Selkirk range in British Columbia. As the American records for hard rock tunnel dri\dng were achieved here by employing unusual methods and so far as can be learned without sacrificing economy, this work will be con- sidered in some detail. In addition the reader is urged to read the paper on this work, reference to which is made in the bibli- ography. It is slightly more than 5 miles long, and with the exception of 1200 feet and 400 feet respectively of soft ground at the east and west portals, it is driven through what the Canadian Gov- ernment geologists have called quartzite. The tunnel is double track and the line of excavation is 26 feet 6 inches wide, the upper part a semicircle of 13 feet 3 inches radius and the height at center line 21 feet 9 inches. (Figure 100.) Another feature connected with this tunnel is the use of a separate small and distinct timnel located some distance from and parallel to the main turmel and which is driven in advance of the latter. The purpose of this auxiHary or pioneer tunnel as it is called, will be understood from a survey of the general prob- lem of driving this tunnel. (See Figure loi.) It must be understood at the outset that the rapid comple- tion of the main tunnel was deemed essential by the railway com- pany. The logical procedure was to drive from as many points as could be secured in addition to the two portals. Shafts and adits were found impracticable. Recourse was then had to the system which had been used in Europe, namely, the driving of a small heading parallel to the main line and distant from it, in this case 50 feet; then to branch off from this small tunnel with cross drifts driven to intersect the main tunnel. This would 500 MODERN TUNNELING H— .- ROGERS PASS TUNNEL HALF SECTION OF MAIN TUNNEL AND CENTER HEADING, SHOWING COLUMN AND DRILL SETTING, FOR RING DRILLING Note: Columns and Arms 101)6 set as Bhown, by measurements from Engineer's Lines. Each hole to ■•. Ije pointed by using Clinometer s Board, and length of Steel shown \ to be fully run out. Fig. ioo. Rogers Pass tunnel. Cross-section and arrangement of center heading and drill holes. HARD ROCK TUNNELS 501 ^ 502 MODERN TUNNELING permit a pair of headings of the main tunnel to be started at each cross drift. Such a pioneer tunnel not only speeded up the time of driv- ing the main tunnel by providing more headings, but the officers of the railway company claim the following advantages which appear to have been proved.* ■ I. The ventilation of the tunnel was simpHfied, brought under a positive control and made entirely adequate and com- fortable. The air was forced through pipes in the pioneer tunnel and thence through the forward cross-cut to the main heading and back to the portal through the main heading. Stops across intermediate cross-cuts prevented short circuits. The venti- lation was so good that the heading blasting did not foul the workings where men were enlarging the heading. 2. Work could be resumed immediately after blasting the enlargement holes. 3. It permitted the drilHng of the center heading for subse- quent enlargement far ahead of and without interference from or with other blasting. 4. The main heading muck could be removed through the nearest cross-cut and thence out through the pioneer tunnel, thus avoiding interference with the men and equipment engaged in enlarging the tunnel at other points. 5. It served to conduct air, water and ventilation pipes to the heading without their being disturbed by the enlargement operations. 6. Finally, it provided free access for men and materials to all points of the heading or enlargement workings at all times. The pioneer tunnel gave the further advantage of disclosing in advance the nature of the ground. Another point that developed was that the east and west portals of the main heading, which had to be driven through 1200 feet and 400 feet, respect- ively, of soft ground, required 12 months and 8 months, respect- ively, to do this work. If the driving of the rock main headings * Cf. Trans. Am. Soc. C. E., Paper 1390, Vol. LXXXI. Construction methods, Rodgers Pass Tunnel, by A. C. Dennis, Engineering Ne^i's, Vol. 75, No. 8, Feb. 24, 1916, pp. 382, 383, by J. G. Sullivan. HARD ROCK TUNNELS 503 had been contingent upon these soft ground lengths the work would have been very much delayed. As it happened, the rock of the main tunnel Hne was reached by the first cross-cuts from the pioneer headings at the east and west ends in 4 and 2 months respectively after starting driving the pioneer tunnels. By going 60 feet and 150 feet above the main tunnel grade at the east and west tunnel portals and driving the pioneer tunnels on an incline, the soft ground work for them was more than cut in half. After the first cross-cuts above mentioned, others were introduced at intervals of from 1500 to 2000 feet. It is to be noted that the pioneer tunnels did not extend the full length of the main tunnel. A stretch of a mile near the middle of the tunnel was omitted, and that portion of the main heading driven from the last cross-drifts. The pioneer tunnel was 7 feet high by 4 feet wide. It is of interest to note that air hammer drills mounted on horizontal bars and using hollow steel with water attachment were used; that three drills usually, and four in tough rock, were employed. The average number of holes per round was 21 to 28. The rounds were usually 6 feet. Three 8-hour shifts were employed. The first set up of the drill bar was about 18 inches from the top. There was rarely any muck to be handled before this set up could be made as the bottom holes were heavily loaded and shot last to throw the muck away from the face. After the mucking was done the bar was dropped to near the floor and the balance of the round drilled. Shooting was done with fuse. Forty per cent and 60 per cent, gelatine was used. An average of 15 pounds per cubic yard was used in the pioneer tunnel. The cost of the pioneer is stated to have been $28 per linear foot. In the west pioneer tunnel the American hard rock record of 932 feet per month was made. In the east, the best month was 776 feet. The daily averages were 24 feet and 20 feet respect- ively. The pioneer tunnels were mucked by hand. Steel sheets were used and muckers loaded wheeled cars and rested in turn. Half -yard cars, hauled by mules conveyed the spoil back as far as the nearest cross-drift beyond which the enlarge- ment had proceeded, at which point they were taken through I 504 MODERN TUNNELING the cross-drift and dumped into standard gage 12 -yard cars hauled by compressed-air locomotives to the dump. The one- half yard cars were not switched when empty at the heading, but overturned and rerailed when needed. The center heading of the main tunnel was 11 feet wide and 9 feet high and its bottom was 6 feet above the subgrade of the main tunnel, with their center lines coincident. (See Figure 100.) This position of the heading enabled it to be made smaller without militating against the drilling of the enlargement holes as other- wise would have been the case. On account of water being pres- ent, a pair of headings was not drilled from each cross-cut, but instead usually only one, that in a westward direction. The system of driving was similar to that in the pioneer tunnels. The rounds averaged 7 feet and 3 2 holes were drilled in the hard- est rock. The average daily progress was 16 feet and 20 feet for the east and west ends respectively, and the maximum cor- responding monthly progress 631 feet and 762 feet, respectively. It must be remembered that driving of the main heading was in progress from several faces simultaneously. The men employed in the driving were given a bonus for exceeding a pre- scribed progress and earned it. When it was further agreed that the bonus, however large, would not be reduced, they earned still more. The main heading enlargement is a good example of the benefit to be derived from the engineering supervision of drilling methods. The enlargement drilling was done from two vertical columns on either side of the center line, each of which drilled a series of radial holes, as shown in Figure 100. The noteworthy point is that the engineering force located exactly the position of the columns and calculated the position and direction of the holes so that when drilled to the prescribed depths they termi- nated at a uniform distance — about i foot — beyond the theo- retical excavation line. Errors in the ahnement of the heading were thus obviated. The holes were pointed by clinometers. The series of holes were drilled about 6 feet apart as a rule but it was found cheaper to make them 5 feet apart when explo- sives increased in price. One of the results which the manage- HARD ROCK TUNNELS 505 ment sought was to provide large quantities of muck for the power shovel which loaded the enlargement mucking. Hence, from four to twenty rings (from 20 feet to 100 feet of tunnel) were blasted at a stretch. It is to be noted that this blasting was done by batteries. The shovel loaded the muck into large cars of the size previously described, which were hauled to the portal by compressed air and beyond to the dump, by steam locomotives. The best monthly run for the shovel was 947 feet of tunnel at the east and 1030 feet at the west end of the tunnel, respectively. Summarizing the advantages of this method of tunnelling it is claimed that: "It enabled the heading progress, enlargement drilling, enlargement blasting and mucking to go on continu- ously without any interference whatever with one another." OVERBREAKAGE AND PACKING In further reference to the backing of lining considered on pages 447 and 448; any tunnel blasted in solid or loose rock involves irregularities in cross-section from the neat line estab- lished by the plans for the exterior Hne of permanent lining con- struction, by an indeterminate and very variable amount known as underbreakage or overbreakage of the rock section. The contractor is usually made responsible under the construction specification for this contingency of his work, excepting that in some contracts the necessary condition is recognized, by providing for payment for excavation, to a line (6) six inches, more or less, outside the neat line of permanent Hning con- struction; which might represent a percentage of overbreakage of something Hke 5 per cent, to 7 J per cent, over the neat section, depending on the general dimensions of the tunnel. This allow- ance would usually not be adequate to represent the actual overbreakage; and it is not important to the competent con- tractor whether any allowance is made, or not, providing it is definitely specified, in what way measurements for payments will actually be made; as the contractor will judge of the prob- able extent of overbreakage and packing likely to be incurred, and will make the necessary allowances in estimating on unit 506 MODERN TUNNELING bid prices for contract. At the same time it is a matter of great importance that the contractor in estimating should allow an adequate margin to cover his construction costs, as it is not humanly possible (except with a Rotary Cutter in extremely soft rock) to avoid this loss, to a greater or less extent. The aim of every competent tunnel superintendent is to reduce the overbreakage to a minimum, but at the same time it is most desirable to avoid taking out the section too small, necessitating trimming to permit of lining to the neat section. Trimming, particularly in hard rocks, is slow work and involves very large cost per cubic yard removed, excepting in the case of occasional projecting points. In order, however, to obtain the neat section, a considerable overbreakage is necessary. If the rock is igneous and very hard, requiring heavy blasting to part it, the result is usually to break out large masses, even when the drill holes have been extended only a few inches beyond the neat lines. In stratified rocks, the breakage may be reduced by careful experimentation, as to the placing of the exterior line of trimming holes and light blasting. In such rocks as the shales of the carboniferous series, it is not uncommon for break- age to extend in pot holes or cones 8 or lo feet above neat lines. Illustrations are stated, elsewhere, of overbreakage involving from lo per cent, to 25 per cent, over the neat section of the finished tunnel. The relation of length of perimeter of lining to cross- section has a considerable bearing on the percentage allowable, as in a double- track large tunnel an allowance of as low as 7.5 per cent, might be adequate while for a single track tunnel the figure might commonly be set at 15 per cent. This element of overbreakage involves, not simply the additional cost of drilling, blasting and mucking the excess quantity of unremunerative excavation, but it involves, further, the necessity for segregating that quantity of suitable loose rock, handling, hoisting and hand placing back of the finished lining to fill the voids. The pre- war cost of this backfilling and packing might range from 75 cents to $1.50 per cubic yard in place, all which costs must be absorbed by the contractor, from what otherwise would repre- sent profit. HARD ROCK TUNNELS 507 CQ '^j^'/^^'^wii^m-irnvxii^'^'-'i^m^^^^^^^ 508 MODERN TUNNELING The engineer should never overlook or neglect the absolute requirement that all voids should be tightly packed. If lining is required at all, it should not be subjected to the possibility of unsymmetrical earth pressures being imposed, by absence of packing, which may tend to destroy the arch. Where such earth pressures are great it is not uncommon to require that concrete lining be placed solid up to the actual surface of rock; in which case the overbreakage loss entails the further cost of concrete in place, instead of simply loose filling. "ROTARY CUTTERS" One other type of solid rock tunnel should be very briefly considered and that is the type represented by the proposed English Channel Tunnel of which short sections have many years ago been constructed. This is in chalk formation, a soHd rock able to support the pressures for a considerable period at any rate before Hning but which may be excavated without drilling or blasting. This has been done by excavating machines. * Two different types of machine were installed and used respect- ively on the French and English ends. These machines excavate by rotary action to a circular form for full cross-section. The J. D. B run ton machine, patented in 1866, installed and operated on the French end, utilized the principle of a revolving wheel pressed with great force against the face thereby spalling ofi slivers of rock which are delivered onto belt conveyor for de- posit into cars. An improved modern adaptation of the origi- nal Brunton tunneling machine has been recently brought out by Messrs. Brunton and Trier of Denver, Colo. (Figure 102.) The Beaumont-English machine, patented in 1875, operated as a rotary head cutting the face of rock. A number of new types of revolving machines have been patented and suggested for such a purpose, and certain types of the rotary cutter machines have been used with considerable success in small-sized tunnels in clay formations. Some of these consist of scoops revolving against the face and reproducing the action of a spade, feeding * Cf. The Engineer (London), Decern. 8, 1916, ff. 502-504. HARD ROCK TUNNELS 509 the debris at the same time onto a conveyor belt. Very great speed of excavation is anticipated from such machines in the chalk. ADVANCED TEST DRILLING In soHd or loose-rock tunnels where there are known to be faults, or contacts with varying rock strata are anticipated, it is usually the measure of prudence to maintain ahead of the ''V" cut of heading excavation, advanced drill holes to a penetration several feet beyond the cut so as to disclose any possible great volume of water or bad ground which by sudden blasting might cause serious trouble. CHAPTER XXI LOOSE ROCK AND SOFT GROUND TUNNELS EXCAVATION METHODS A TUNNEL built through loose rock or soft ground needs temporary support to prevent caving in, before the permanent lining is placed. As has been previously mentioned only the American system of timbering will be considered in detail. It therefore becomes necessary at this point to describe what this system is. The essential feature of the American system is that the roof of the tunnel is supported by an arch formed of timber blocks or voussoirs. (Figure 103.) The spacing of these arches is governed by the need for support of the rock or soil. The foreign systems, on the other hand, have a general resemblance to one another in that the ground is supported primarily by longitudinal members or "bars," in turn supported by radiating props or vertical posts and with the back end of the bars some- times supported by the permanent lining. Figures 104 and 105. The American system is a development from the simple cap and legs of an ordinary small heading, developed to conform as closely as practicable to the shape of the roof of the tunnel. The early tunnels driven in this country, contemplated no other lining than the timber, and the general type shows a cap, two raking legs one on each side of the cap, and vertical posts supporting the rakers and in turn supported sometimes by a cross-sill extending across the whole width of the tunnel at subgrade. In certain cases a wall plate is interposed between the rakers and the verti- cal posts and in others the vertical posts are supported at their bottom ends by a separate wall plate or sill These designs, which date from the years 1820 to 1830, were almost invariably for single-track tunnels having a clear span never more than 19 feet 510 LOOSE ROCK AND SOFT GROUND TUNNELS 511 and usually of about 15 feet 6 inches. Although the three-piece system has been used for spans up to 26 feet, as in the Mus- conetcong Tunnel, Drinker says, that ''the variation from the three-piece form to multiple-block timber arching was first made by the late James Archbald, Chief Engineer of the Delaware, Lackawanna & Western R. R. in the construction of the Oxford or Van Nest Gap Tunnel in New Jersey in 1854; it proved most successful, and subsequently has been used in the construction e^fff^t^srt Hf^frt^ <*/-..'V.2J4 7 --.-._• Fig. 103. American system of tunnel Fig. 104. General type of European timbering. system of timbering. of SO many tunnels, throughout all parts of the country, that it has become, in fact, the national system of tunnel timbering." It will be understood that longitudinal strength is given to the American system of timbering by stretchers or braces between the sets or bents of arch timbers. This is a most important point; without such strutting the American system would be most unstable. The system which has just been briefly summarized is capable of many modifications, and some of these will be described, start- ing with the simplest cases and working to the more difficult. The simplest instance is a rock tunnel normally self-sustain- ing but which requires some support for the roof to prevent occasional falls of rock from weathering, vibration, etc., as dis- 512 MODERN TUNNELING tinguished from cases requiring resistance to live rock pressures. The heading for such a tunnel would probably be taken out to its full cross-section at one operation. The timbering will con- sist of segmental arches, usually of sawed timber spaced two, three, four or more feet apart. The only lagging which will be used outside the sets of timber will be here and there where the rock may be particularly loose. Packing and wedging will in Fig. 105. Typical sequence of operations in tunnel construction under English method most places be needed to give a bearing between the rock and the timber bents. The lower end of the bottom segments or blocks will rest on a hitch cut in the rock. Such a method of supporting the timbering can only be considered as temporary in character, as the weathering of the rock will inevitably destroy the support. Hence it will be usually economical, in the first instance, to have the lower ends of the bottom segments rest on a continuous longitudinal wall plate, which will be under-pinned by vertical posts in the same plane as the arch sets, after the LOOSE ROCK AND SOFT GROUND TUNNELS 513 bench has been taken out. The posts themselves will be sup- ported on foot blocks, transverse or longitudinal sills. Figure io6. The next case in order of difficulty is that of driving through rock which is not self-supporting, even during the short interval which might elapse between the time of excavating and placing the permanent lining. The general method of attacking such Fig, io6. American system of timbering Astoria gas tunnel, New York. work is first to drive a pair of small headings in which to place the two wall plates for the support of the full arch timbering. (Figure 103.) These headings themselves are usually timbered by simple square sets without lagging. After a length of wall plate has been set and the lowest leg of the full set placed, the next step is generally to drive a center top heading to enable the central member or members of the timbering to be set. These are supported temporarily by props to the floor of the top heading. Widening out from either side of the top heading, usually only to sufficient depth to enable the work to be carried 514 MODERN TUNNELING out, will permit the balance of the main set to be placed. , The roof being now held, the remainder of the full heading can be done in safety. The next step for this kind of material will be to remove the bench and underpin the wall plate with posts. The next more difficult case is where the material penetrated is classed as soft ground, that is to say, ground which will run when opened up and in which therefore earth pressures are brought to bear against the timbers. The chief difference between this case and the last considered is that the completed timbering must be provided with lagging both at roof and sides. With the exception of boulders that may be encountered and which must be cautiously shot, no blasting will be necessary for the excavation of the material, which will be done by hand mining methods. As with the other cases considered, as far as American prac- tice is concerned, the location of the heading for soft ground may be either at the top or bottom. The latter has certain advantages where water has to be drained. It must be remem- bered that the chief aim of the American system is to build up the timbering system so far as possible by excavation around the periphery, so that the main portion of the exca- vation, or core, can be removed quickly and cheaply within the protection of the inserted timber. In soft ground such as is being considered, it is impossible to open large workings in any one operation without bringing the ground to a run, so that the entire excavation (excluding that of the core) is in the nature of closely poled or lagged timber heading work. See Figure 107. Whatever the location of the heading, it will be necessary, in the ordinary kinds of soft ground, to lag or pole the top and sides. In worse ground, the face also may have to be supported by close poling and in very wet or swelling ground the floor also may have to be timbered. Within the limits of a chapter it is quite impossible to give a detailed discourse on such a difficult and intricate art as that of heavy soft ground tunnel mining. Chapter XIV of this book touches on a few main principles apphcable to the ordinary cases and the bibhography at the end of this chapter gives a list of articles deahng with specific LOOSE ROCK AND SOFT GROUND TUNNELS 515 instances which should be studied by anyone with a problem of this nature in hand. In this type of work more than is custom- arily so in most engineering operations, the engineer will have to rely in a great measure upon obtaining the services of foremen and men skilled in this kind of work, as no amount of theoretical knowledge, unless aided by men skilled in these methods, will be sufficient to prevent disaster. Fig. 107, American system of excavating and timbering, hattan Railroad, Jersey City, N, J. Hudson & Man- If it is elected to do the work from the bottom, the usual course will be to drive the two advanced headings, one on the hne of each side wall footing, followed by a pair on the level of the wall plates. The dimensions of the headings will be selected with the idea in mind that when a pair on the same side have been excavated there will be sufficient room to put in the plumb posts, foot blocks and wall plates. Next there is the alternative of continuing to work upward, around the arch, putting in seg- mental timbers the while, or of beginning a central crown drift and widening down and out to meet the wall plates. It may be that it will be decided to start with a pair of wall 516 MODERN TUNNELING plate headings. Sub- sequently the sequence of excavation will be to complete the arch tim- bering, after which the underpinning of the wall plates can be done by one or more headings below them. Figure io8. Whatever system is used, the strictest care should be taken to min- imize the settlement. To the efficient exe- cution of any type or design of timbering for support of either rock or soft ground; the value of the timber Hning in fulfilling the intended function, is absolutely dependent on accurate fitting and solid block- ing and securing of every member. The accuracy of dimension and fit is necessary to produce a true structure to cor- respond with the design. The blocking and wedg- ing of every joint solidly to the exterior rock or soil is essential to main- tain the security and integrity of the complete set; otherwise there is a danger of kicking out LOOSE ROCK AND SOFT GROUND TUNNELS 517 and collapse. Joints should be lapped with spiked plank to hold in position. Posts must always be thoroughly wedged to bear their full load and dapped into the wall plates or otherwise secured to maintain correct position. Head-sills must be scarfed and bolted to take longitudinal thrusts. In soft ground all poling boards must be slipped in back of posts and caps so as to obtain proper reaction and strapped to prevent kick out in case of under- mining. There is nothing in tunnel construction which so clearly indicates the efficiency of the miner as the regularity, uniformity and security of the timbering and nothing is so vital to the suc- cess of the work. For swelUng or running ground, which induces lateral pres- sures, the American system will have to be supplemented by the addition of transverse struts and bracing between the plumb posts. For aggravated instances of heavy pressure, running sand, swelling earth, etc., the tunnel shield may be the most economical as well as the most certain method of driving. This method is dealt with in the last section of this chapter. Needle Beams As an aid to construction of timbering in soft ground mining, the needle beam is invaluable. This consists of a stiff rigid beam held in stirrups attached to the crown timbers of the leading two or three completed timber sets and free to slide forward in the stirrups, having a length equal to about four frame spaces. This beam acts as a "cat head" or cantilever girder. When pushed forward a full frame space ahead of the leading set, it is wedged at the tail end against the cap timber and is then able to support, by blocking and wedging therefrom, the soil and timbers being set up for the next frame ahead or equally it can be used with blocks and falls or hoisting rig for hoisting timbers into place. The needle is commonly of timber, although if loads are heavy it is more usual and convenient to use a deep broad flanged I-beam from lo inches to i6 inches deep, according to the load to be carried. These needle beams can be used singly or in multiple, according to construction needs, the usual equipment being one in each heading, or in 518 MODERN TUNNELING working out a full width heading for a Railroad Tunnel, com- monly two are used in pair. See Figure 109. Steel Sets It may be remarked that of late years it is becoming custom- ary to use steel I-beams instead of timbers for the sections of the arch timbering in bad ground. By its use several important advantages are gained. See Figure no. 1. The outside flanges form a convenient support for the poling boards and a non-compressible support for such wedges as may be required. 2. The inner flange serves as a shelf to support boards out- side of which concrete can be placed to fill the space out to the top lagging. This has the very important advantage of sealing off the ground from the action of the air, thus preventingjswelling or running. 3. For equal strength the depth of member is less than that of wood, thus reducing the requisite amount of excavation. 4. The quality of the steel is more uniform than that of wood and the members can be fabricated in a machine shop with a high degree of accuracy. 5. The segments are united to one another by splice plates on either side of the webs of the segments and bolted through them through accurately drilled bolt holes. 6. The abutting ends of the section are machined to give bearing value. 7. The steel is more permanent than timber and not subject to rot or fire; this may be important if for any reason the work has to be shut down. It should not be assumed off hand that the first cost of steel sets is greater than that of timber, and the increasing use of steel and scarcity of timber tends to eliminate any difference against steel that there may be at present. The essence of soft-ground excavation and timbering is to prevent the movement of the ground or to reduce it to harmless proportions. Once ground starts to cave, the force it exerts is almost irresistible. Experience has shown that a useful means of preventing movement starting, is to open up and attack the LOOSE ROCK AND SOFT GROUND TUNNELS 519 Fig. 109. Use of needle beam in heading. Fig. 1 10. Steel I-beam sets for roof timbering. American system. Hudson & Manhattan Railroad, Jersey City, N. J. (The piles projecting through the roof were afterwards sawn off and the butts embedded in concrete lining.) 520 MODERN TUNNELING ground by removing the lagging board by board, packing the lagging with hay, straw, manure, etc., grouting the ground i behind the lagging with cement, reducing effects of water pres- sure by draining, and in general to conduct every operation with extreme circumspection and skill. The extent and character of'timbering used may be greatly ' modified by outside conditions, as, for example, if such tunnel is being built in open country where external surface settlenaent is unimportant and no abutting property damage is incurred, there may be considerable economy effected in the timbering which would not be warranted when such work was being exe- cuted under the streets of a densely built-up city. Pilot Tube Method In soft-ground mining, considerable success has been attained in treacherous soil by the method developed by Anderson, in the, ■ first Hudson Tunnel in 1881* and later in the 16-foot diameter, main-relief sewer in Greene Avenue, Brooklyn, using a steel pilot tube instead of the usual heading and thereafter propping radially from the pilot tube as enlargement is carried forward. The "pilot" consists of a large steel tube about 6 feet diameter, aggregating about 40 feet long, consisting of smalk steel sheets ' connected internally by sraall angle irons bolted 'together. These sheets are taken down in the rear as they are put in place at the face to form the heading which thereby is continually advanced, the enlargement and permanent lining proceeding simultaneously. The pilot is driven as nearly as possible on^the central axis of the tunnel. Lining Methods for Rock and Soft-ground , Tunnels The type of lining to be used in any specific case, in accord- ance with the principles enunciated in Chapter XVII, necessi- tates the consideration in some detail of the actual work of placing the lining. In this connection the term lining is used * "Tunneling under the Hudson River," S. D. V. Burr. John Wiley & Sons. 1885. LOOSE ROCK AND SOFT GROUND TUNNELS 521 to designate some type of permanent lining as distinguished from one of timber. In a tunnel of the cross-section of a railway or highway tunnel, it is usually inconvenient to build the entire perimeter of the lining at one operation, so that as a matter uf practical policy the placing of the lining will be divided into that of doing (a) The sidewalls with skewbacks to take the thrust of invert later constructed; (b) The arch; (c) The invert. It may be said that wherever possible the Hning should be built in the order stated, as by following this sequence, under- pinning, with the consequent tendency to subsidence, is avoided. Moreover, a better joint between an arch and sidewall and between a sidewall and an invert is obtained if the higher of the respective sections is placed after the lower. This question of good joint between the stages may be of great importance where there is water present in the ground and where a dry tunnel is desired. Where such water is under pressure and possibly adds to the earth pressure it is essential to approximate as closely as possible the design that has been prepared to meet such pres- sures. Where an arch is placed first and underpinned, with the sidewalls following, it becomes almost impossible to get even a fair approximation to the designer's ideal condition. Circum- stances may be seen to impose the necessity for constructing the arch first, but this should not be done until the point is made absolutely certain. In rock tunnels which are self-sustaining it may be possible to concrete the full section in one operation, although it is not often feasible. In short tunnels it may be advisable to post- pone lining until the excavation has been finished. As regards the use of forms for placing Hning, attention will first be given to those for concrete, either plain or reinforced, as this will be found to be by far the most common type of Hning to be used. For such a Hning in a tunnel, forms will be required for invert, sidewalls and arch, although if the invert is flat, forms 522 MODERN TUNNELING will not be necessary. On the other hand no attempt should be made to build an invert with any appreciable curvature with- out a form. Due to the plastic nature of the material the result is generally unsatisfactory. Invert forms are designed to permit the concrete being poured from the sides and worked by spading and tamping to the center. This point must be borne in mind when suspending the forms, as also must the tendency of the plastic concrete to raise the form. It must not be forgotten that the invert form should make provision for whatever drains are embodied in the design and adequate V-shaped key-ways or dowels provided to ensure a bond with the sidewalk The length that may be attempted to be concreted in one time may vary within wide limits. As a sug- gestion, where possible it is desirable to make the length such that one shift of men can complete it. Sidewall and arch forms may be of wood or steel. If of the former the sidewall forms almost certainly will be set separately from the arch forms. The sidewall forms are filled by pouring the concrete from the top, the men standing on a temporary platform, the floor of which is approximately level with the top of the form. Wherever possible one or two men should be put in the form to work the concrete as it is deposited in order to keep the layers level, to produce as dense a product as possible and, by spading the plastic concrete back from the face of the forms, to give a smooth finished surface to the concrete. The way the concrete is brought to the working platform varies in different cases. In small work the concrete ingredients may be brought into the tunnel and mixed by hand or machine on the platform. Usually, however, this will interfere with the continuity of pour- ing, and it is preferable to bring the ready mixed concrete to the concrete gang, so that the latter only has to place the material. In such cases the mixed concrete is placed in watertight cars which are brought to the working platform, either being hauled up an incline or raised by a small elevator. Once the car is on the level of the patform it is dumped either onto the plat- form, whence it is shoveled by hand behind the forms, or, when the thickness of the side walls is sufficient, the contents LOOSE ROCK AND SOFT GROUND TUNNELS 523 of the car may be dumped bodily behind the forms. In order to get best results, it is important to build up the concrete in horizontal layers of not more than a foot or so at a time and to build the concrete up on each side at the same rate. Work should not be stopped until the form is completely ill led. Figure iii shows a t>T)ical set of such wooden forms. As in the case of the invert, key- ways, plum-stones or dowels should Fig, III. Wooden forms for invert and sidewalls, Astoria gas tunnel, New York. be inserted at the top of the sidewall to make a good bond with the arch. The arch forms are usually supported on cross-timbers set across the turmel between the sidewalls, to which they are tightly wedged or otherwise supported, further support being afforded by posts to the invert. The arch form is of the usual construc- tion namely, of ribs formed of segments of planking, spiked together and sawn to the required radius. These ribs support "lagging" w^hich are strips of planking laid horizontally over the ribs and built up from the bottom towards the top as the concrete is poured. Owing to the curvature of the arch, the 524 MODERN TUNNELING width of the lagging should not be more than 4 inches, otherwise the finished surface of the arch will be irregular and probably not retain the cement when poured. There will be no necessity for beveling the sides of lagging of such width. It is not neces- sary to tongue and groove the edges of lagging, in fact it is pref- erable not to do so. The pressures induced by wet concrete are so great that the arch form, in general, will have the shape of a truss, with a horizontal lower chord and such intermediate members as may be necessary for the span and the thickness of, concrete being deposited. t In this connection the engineer is warned, to design the c^n^. ters for his work himself and not to allow the foreman carpenter; to evolve his own design. It must be remembered that the men- who are pouring the arch concrete have to stand .and , do their work between the ribs, so that the working space should ;be as free and unhampered as possible. This calls for rational design and for the ribs to be made as self-supporting as possible. Use- ful economy of space has been achieved by the .use of steel for; the ribs, particularly by the use of old rails bent to the neces- sary curvature. It is surprising what a difference a few insig- nificant inches of headroom may make in the possible speed .of the work. The concrete is brought to the pouring gang on the plat- form, which will be about the level of the spring line, in cars which are either hauled up an incline or raised by a small ele- vator, and shoveled from the platform into the space behind the ribs. The concrete should be brought up on both sides of the arch simultaneously, so as to avoid unsymmetrical pressures on the ribs and the surface of the concrete should be kept radial to the arch. After the concrete has been brought up on each side to within 18 inches or 2 feet of the center line on either side, this method of pouring the arch is discontinued and a special lagging rabbeted in order to support the key- or cross-laggings, (which are set transversely to the longitudinal axis of the tunnel), is set on either side of the center line. The arch is then keyed in, working from the back end of the length toward the leading end, filling the space between the already poured concrete on either side. It is usually necessary to mix the concrete for the LOOSE ROCK AND SOFT GROUND TUNNELS 525 upper part of the arch and for the key somewhat stifTer and somewhat richer in cement than in the rest of the work, so that the fresh concrete may stand at a steeper slope and not flow out of the form. Owing to the inevitable shrinkage and settlement of the concrete it is inherently impossible to fill every void above the key and crown, and where such voids cannot be permitted, it is now usual to build in pipes leading to the outside of the concrete. Through these pipes cement grout is subsequently forced under air pressure, so that such voids may be completely filled after the concrete has thoroughly set. In placing grout pipes, it must not be forgotten that vent pipes for the escape of air are essential, otherwise the voids cannot be filled. In some cases it is not desired to build the concrete out to contact with the rock, but to fill the space beyond the specified thick- ness of the concrete arch, with some form of packing, usually of rock broken to a ''one-man" size. In such cases the rock packing is placed simultaneously with the concrete and the con- crete mixed stiffly enough not to incorporate any more than pos- sible with the rock which adjoins it. There are certain details of placing the concrete; the making of forms, etc., peculiar to concrete arches which are to be water- proofed on their exterior surface. These will be readily under- stood from what is said in the section on waterproofing in con- nection with what has been said just above. The arch forms should be rigid enough to prevent any appreciable settlement after the concrete has taken its initial set. They should also be designed so as to be easily dismantled, salvaged and re-erected. Collapsible Forms Tunnel work offers a good field for the use of the modern collapsible steel form, as the work is a continual repetition of the same cross-section, where this type of form shines to special advantage. (Figure 112.) The economy is gained by the saving of carpenters' time in erecting and moving the forms and in the saving of the large amount of lumber which is consumed for the forms in a tunnel of any length. The steel form is virtually 526 MODERN TUNNELING indestructible and as the surface, against which the concrete is deposited, is non-porous, the surface of the concrete is usually much smoother and denser than when wooden lagging is used. These forms are usually made in lengths of 30 to 50 feet, the length being governed by local conditions, and the sidewalls Fig. 112. Collapsible steel forms for tunnel arch lining. and arch are usually combined in one structure. The whole apparatus travels on a wide-gage track set on the tunnel invert, and the form is made collapsible so that it may be withdrawn from the surface of the concrete and moved forward through the already completed lining till it reaches the place where it is to be used again, at which point it is expanded once more to normal section, brought to line and grade and is once more ready for use. These forms are built by firms who make a specialty of LOOSE ROCK AND SOFT GROUND TUNNELS 527 this apparatus and the engineer will do well to place the detail design for these forms in their hands, since their experience in this Une must be vastly wider than that of any individual. Quite marked economy and improved quality of work result from the use of these forms when the extent of the work for which they are to be used is considerable and involves a material number of repeats, and the possibihty of their adoption should be carefully considered in each case. In modern work of any magnitude, such forms are used almost as a matter of course. In these combined arch and sidewall steel forms, the side wall concrete will be poured first, from a level just above the spring Hne, the panels of steel plate, which take the place of wood lagging in such forms, being left out until the sidewall concrete is to grade, after which the panels are added as needed to retain the advancing concrete of the arch. These forms are equipped with mechanical hoists for raising the concrete to the upper platform ; in fact it may be said that these forms are self- contained units. PNEUMATIC PLACEMENT OF CONCRETE Of late years use has been made of compressed air to deposit concrete behind forms. This process is adapted to heavy work with aggregate measuring up to 4 inches or 4! inches diameter, if necessary. The plant required consists of a mixer, a pipe conveying system and a compressed air plant. The mixer consists of a steel shell, having a vertical cylindri- cal body and terminating at the bottom in an inverted cone. At the top is the door through which the materials are fed, unmixed, a batch at a time. The door is operated by a small air piston. It is opened by releasing the air in this cyHnder so that the door drops open by its own weight. At the bottom of the inverted cone chamber is a 90° elbow and this forms the connection to the discharge pipe. The door and the door piston are the only moving parts of the mixer and the inside is entirely smooth and free of obstruction. The main air jet is at the heel 528 MODERN TUNNELING of the bottom elbow and this jet is the primary method by which the concrete is mixed and conveyed. The mixing and discharge are supplemented, however, by air jets which enter the mixer at the top. The conveying pipe consists of any standard smooth steel pipe with bolted flanges or any other convenient type of joint. An example of a conveying pipe is shown in Figure 8i, in the roof of the tunnel. The most rapid wear occurs at the small irregularities at the joints. For making deflections or turns cast elbows are used. Cast iron will usually last less than a day. Manganese steel is the most durable. A radius of 3 feet is the least that can be used for bends as a smaller radius will cause plugs in the Hne. To deflect or guide the discharge of concrete into the forms a series of sHghtly tapered pipes, fitting together like stove pipe, is used. Two or three of these sections, each about 3 or 4 feet long is all that is needed in a tunnel form for diverting the dis- charge from one side to the other. The compressor should compress to at least Sopounds per square inch; from this to 125 pounds per square inch is a suitable range. An air receiver must be provided to store at least 100 cubic feet with an additional capacity of 30 cubic feet for each 100 foot of pipe Kne and a greater capacity still if the mixer is more than 300 feet from the compressor. The amount of air required varies with the specific gravity of the materials, the smoothness of the pipe, the number of bends and their radius, the distance conveyed (both horizontal and vertical) and the pressure and velocity of the air. For the usual size of mixer the amount of air required has been found to be 2 cubic feet of actual free air at 100 pounds per square inch for each linear foot of pipe per batch, e.g., to convey one batch 500 feet it will require 1000 cubic feet of actual free air at 100 pounds per square inch. Concrete has been conveyed up to 4900 feet in an 8-inch pipe with a 16 cubic foot mixer. This was at the Twin Peaks Tunnel at San Francisco. LOOSE ROCK AND SOFT GROUND TUNNELS 529 The plants may be stationary or portable. Tests show that concrete deposited by this method will develop a crushing strength up to 3000 pounds per square inch with two parts of stone to one part of Portland cement. With eight parts to one, a crushing strength of 1400 pounds per square inch was developed. These tests were on 12 -inch cubes, tested at 30 days. Blocks of a tunnel Hning were cut out. These blocks were from 9 inches to 1 2 inches square and from 1 2 inches to 20 inches high. The crushing strength ran between 1200 pounds to 3000 pounds per square inch and the average was 2000 pounds. Incidentally, it has been found that these mixers will effect- ively place dry rock packing in the form of broken stone crushed to sizes of dry concrete aggregate and in places where it would be difficult or impossible for men to work. The same advantage holds good for placing concrete and the system seems to have special application for such cases as the relining of tunnels under traffic, where the question of allowing clearance for the trains through the concreting operations is a controlling factor. The work is one of those special varieties where the engineer should call in the expert and thus gain the advantage of the specialist's wide knowledge of the possibilities of the method, rather than to waste time and money on experiments which might be avoided. The information given here has been taken from a paper by H. B. Kirkland, printed in the ''Journal of the Western Society of Civil Engineers," May 13, 1918. Supplementing the foregoing information and, as the result of further experience, the following points may be added. Concrete may be pre-mixed before blowing, using an ordi- nary rotary mixing machine for preparing the batch, or may con- sist of unmixed materials which are satisfactorily mixed in transit through the blower and pipe system by adjustment of the air jets in the blower. Better success is commonly obtained by keeping the convey- ing pipe line in an upwardly inclined position. There is a tend- 530 MODERN TUNNELING ency for the air, if not applied correctly, to travel through the thinner material, or over the top of the mix, leaving the stone to drag along in the bottom of the pipe. This tendency is reduced by creating a resistance to the air by inclining the line upwards, so that there may be a head to work against. In blowing concrete, it is vitally necessary to prevent plugging in either the blower or pipe line. The assumption that the batch should be premixed very wet is erroneous as it is usually easier to maintain perfect discharge and prevent plugging when blowing ''jelly" concrete instead of ''soupy" concrete; as in the latter case, the water segregates from the solid matter. In freeing the line or blower from plugs, by hammering or pounding it should be seen that air pressure is shut off at the same time, as tending to tighten up the plug instead of freeing it. Nozzles of rubber or of hard steel may be used. The wear is very rapid and the latter are usually more economical and give better results. The blower operates best when controlled by one man, the air valves being so arranged as to permit one-man operation. The bottom air is the primary force and is always applied first, about 5 to lo seconds before the top air is applied. This bottom air starts the materials travelling through the pipe from the blower while the top air, or secondary force, feeds the mix to the bottom air. The top air should never be applied first as this plugs the mix in the bottom of the blower. The door should be kept free and clean of the mix. When blowing unmixed materials, this is -no trouble as the materials are dumped into the blower dry, while the water enters the blower through a separate pipe. When blowing premixed concrete, the mix is dumped generally over the door sill, though chutes are sometimes used. The mix should be cleaned from the door and frame, otherwise the door will leak air, resulting sometimes in a plug and in tearing the rubber gasket. When properly blown the mix should leave the nozzle in a steady flow, like meat from a sausage machine; not in spurts of water, and concrete, at intervals. The prevention and immediate removal of plugs, and the LOOSE ROCK AND SOFT GROUND TUNNELS 531 cleaning out of the blower and conveying line at the end of the shift, are important. The materials should be watched to pre- vent large pieces entering the blower. The cleaning should be done by blowing one or more batches of water after the work is finished and it is well to also blow a batch or two of dry stone or gravel through, as this scours the pipe. A system of operating signals, from the form to the blower, is also essential. Steel forms should, if possible, be used with blower concrete. If wood is used they must be sheathed, where nozzle discharges, with sheet iron for protection. Blower concrete is used more satisfactorily where reinforcement is npt used, as the velocity of discharge is very Hable to displace the reinforcement. The discharge nozzle should be moved frequently to prevent seg- regation of aggregate and the concrete deposited must be well spaded and the unfilled skin of the form kept clean of splash. Precast Block Lining As pointed out previously, another form in which concrete can be used is that of pre-cast blocks. By this use of concrete the necessity for forms for the invert and sidewalls is avoided, all that is needed being mould boards to guide the masons. In the arch, centers will be required to support the blocks until they are keyed up, but close lagging will not be necessary. While this use of concrete may be better adapted for tunnels in more or less self-sustaining ground, it has considerable possi- bilities for other kinds of ground, as the operations in the tunnel, where labor is more expensive, are reduced. It has one other advantage in that the extrados of the arch formed of such blocks, affords a smooth surface on which waterproofing may be laid. The concrete having reached its final set before being placed in the tunnel, the flow of water cannot harm it. In general, the use of blocks eliminates a good deal of skilled labor. Brick Lining As has been previously mentioned the use of brick for tunnel lining is on the decline and the tunnel brick-layer is virtually 532 MODERN TUNNELING extinct. In essence the work resembles that of the concrete block, with very much smaller units and consequently much more labor in laying. It is particularly important that no settle- ment occur in the arch forms. The brick should have a uni- formly high crushing strength, and be laid in Portland cement mortar. Care should be taken to see that there are ample headers and that the joints are properly broken. The bricks should be soaked in water before being laid, in order not to absorb the moisture from the mortar. A wire-cut brick is usually better than a pressed brick as its rougher surface gives it a better adhesion to the mortar. For first class work, it is used to specify the thickness of the mortar bed, which should be kept as low as possible, say from one-quarter to three-eighths of an inch. After a length of arch has been keyed up, it is proper to slack down the centers a httle, so that the mortar may attain its set under the pressure of the brick work. Cement Gun Another method of placing a lining which is thin or of repair- ing an existing lining is by the use of the cement gun. This machine blows, under air pressure, a mortar of sand, cement and water against any surface it is desired to cover. It is necessary to place the gunite, as it is called, on a metal lath v/hich may be triangular or square wire mesh, or even, in light cases, of ordi- nary chicken netting. The gunite is built up in thin layers on and around this lath and forms a very dense a.nd strong mass of reinforced mortar. Usually the thickness of such a structure will not be more than 3 or 4 inches and the process has great advantages in cases of repair to existing concrete structures, the covering of exposed steel work and as a means of covering a sur- face of rock which is self-sustaining but which is Hable to spall under weathering. The great density and strength of gunite lies in the fact that the impact of the mixture as it rushes from the nozzle against the surface to which it is being appHed, causes a rebound of the inert portions of the cement, together with some of the sand, thus eliminating useless constituents. In using a cement gun it must be absolutely certain that the sand LOOSE ROCK AND SOFT GROUND TUNNELS 533 and cement are dry passing through the machine until hydrated by the water supply at the nozzle as otherwise the hose will become clogged and inoperative. Liberty Tunnels As a recent illustration of loose rock tunnels, now in process of construction, the following information obtained through the courtesy of A. D. Neeld, Engineer in Charge for the County of Allegheny, Pa., and J. C. Scott, Resident Engineer; is given as elucidating the subject under consideration. The twin Liberty Tunnels are to pass through Mt. Washington on south side of Monongahela River at Pittsburg, Pa., to serve for Highway pur- poses. The contractors are Booth & Flinn, Ltd. The design provides two tunnels, 59 feet apart between centers, and extending from the south side of Mt. Washington at Warrington and West Liberty Avenues, to the north side at Carson Street, at about 1000 feet east of the existing Mt. Wash- ington tunnel. The tunnels, with approaches, are each 6280 feet long, and the tunnels proper, from portal to portal, are each 5690 feet long. Both tunnels are carried at the same elevations and the gradient is ^ per cent downward from the south portal to the north. Trafific is to be operated in one direction only, in each tunnel, south to the city in the East Tunnel and north from the city in the West Tunnel. Both tunnels are identical in cross-sectional design, except- ing that the positions of the sidewalk, sewer, roadway, and rail- way tracks, are reversed in each. The tunnels are concrete lined and have a maximum finished height of 20 feet 7 J inches above the roadway, and a maximum finished width of 26 feet 6 J inches. The finished tunnel provides one street railway track, a vehicular roadway for one line of traffic, and a footwalk. The railway track is on the opposite side of the tunnel from the footwalk and is constructed of 4|-inch by 84-inch steel ties laid on a 6-inch stone ballast roadbed and concreted in. Power will be supplied the electric cars from an overhead trolley. 534 MODERN TUNNELING The roadway is 13 feet 3! inches wide from the track rail to the opposite curb. It is constructed of 4-inch vitrified brick paving laid on a J-inch sand-cement cushion overlying a 6-inch concrete base. The brick paving extends between the track rails and to the opposite curb so that the roadway, for emergency use over the tracks, is 21 feet wide. The footwalk is 4 feet wide and 10 inches above the roadway and is on the opposite side of the tunnel from the tracks. Pro- tection is afforded the pedestrians by a pipe railing 42 inches high. A 14-inch by 30-inch space is provided under the footwalk for telephone ducts. A 1 5-inch diameter terra cotta sewer, with concrete manholes 500 feet apart, extends through the tunnels on the sidewalk side, as well as a 6-inch water main. The plan provides a 24-inch concrete arch to a radius of 13 feet 3 J inches, reinforced with i-inch twisted steel rods on 18 inches centers. A 3 -inch enameled wrought-iron electric light conduit is carried along the centerline in the crown of the arch, with junction boxes for 100 Watt lamps every 50 feet. The trolley feeder line is supported by two f-inch by 18-inch expansion eye bolts set in opposite sides of the arch, every 50 feet. The arch is supported on concrete sidewalks, 24 inches thick at the spring line, and battered down to 27! inches thick at the curb line (78 inches below spring line). The side walls are supported on concrete footings, differing in dimensions. On the sidewalk side the footing is 36! inches wide and extends to the bottom of the sewer trench, 68 inches below curb line. On the opposite side the footing is 39! inches wide and extends 54 inches below curb line. The tunnels are being driven through soft laminated rock, consisting of shales and fireclays, with some harder sandstones. The rock is not self-supporting and as a tunneling material is undesirable, as it requires continuous timbering and cannot be opened up for any length of time without strong and sound timbering being immediately placed. An 8-foot heading advance requires timbering before the expiration of 24 hours, and this LOOSE ROCK AND SOFT GROUND TUNNELS 535 advance has been found to be the maximum that may safely be opened at a time. The sandstone is a grayish blue, generally stratified, and easily worked when not folded with the softer shales and fire- clays. It does not weather upon exposure and does not usually develop water. It offers a firm footing for the heading timber- ing and is more easily drilled than the softer rocks, especially the clays and decomposed shales, which plug up the air exhaust holes in the drill steels. It is the common building stone for cellar foundations in this section. The shales are extensively laminated, soft, and difficult to blast without shattering, but not as much so as some of the fireclays. These shales run in thin layers, often with the cleavage planes of a greasy soaphke film, that results in sHdes if not immediately timbered, and is especially treacherous if water develops, as this soapy film deteriorates rapidly when wet. The shale proper weathers quickly upon exposure to the air, and it has been found to lose any dependable strength after about three weeks' exposure. The fireclays are not hard, but may be distinguished as hard and soft. They are found in both stratified layers and unstratified masses. Usually the cleavage planes are of the greasy, soapy, film noted above. This film contains quite a little lime but the rock proper does not. The soapy film, when tested with hydrochloric acid, develops an agitated reaction, while the rock so tested shows no reaction at all. The softer of the fireclays is a reddish brown in color, and does not appear to be affected by exposure to the air, but if immersed in water, it flakes off immediately and in ten to fifteen minutes, it is reduced to a finely pulverized substance. Fortu- nately, no water has been encountered during the driving of the tunnels through the fireclays and, in fact, the rock has been absolutely dry excepting for the first two or three hundred feet in from the portals, where only a little water was met, not more than a trickle at any one place. The harder of the fireclays is green in color and Hke the brown, has the soapy cleavage planes. It is very brittle and 536 MODERN TUNNELING shatters badly from the blasting, requiring immediate propping even during the erection of the heading timbering. It is not affected by water as is the brown, and while the rock proper does not appear to weather, it splits up along the soapy planes after exposure. The air appears to dry these soapy planes into a white limelike powder that allows the rock to split up. Intru- sions of iron pyrites have been found in this green fireclay. The contract price includes the completed construction of the tunnels from portal to portal, as shown on the contract plan, while the approach work is to be done by the tunnel con- tractors at various unit prices, in addition to the tunnels proper. The tunnels when completed will cost about $5,000,000, which represents approximately $400 per lineal foot. The tunnels are being driven from one end only, the south, mainly because of the fact that this end offered cheaper dis- posal of the spoil than did the other end. The foundations for the plant buildings were started about January ist, 1920, while the tunnels were not headed until May ist, 1920. To date the tunnels have been driven 750 and 780 lineal feet each and work is now going on at the rate of an 8-foot advance in each tunnel daily. These tunnels are unusually large, with a consequent large volume of rock, spoil and concrete, to be handled daily, so that one of the chief difficulties is the question of tunnel transporta- tion. A system has been developed that gives an admirable solution to this problem, and it appears to be the most economical that can be devised with the existing plant and local conditions. This system consists of the following daily routine : 7 p. M. to II P. M. Drilling heading and jDcnch. Blasting heading and bench. Mucking out heading for timber wall plates. Concreting. Erecting and packing heading timbering. Disposal of muck from tunnel. Moving, setting and fitting up concrete forms. This arrangement permits of the use of the tracks at night for hauling the concrete and for the hauling of the spoil in the day- time. Night Shift II P. M. to I A. M. I A. M. to 4A M 7 P- 7 A. M. M. to to 7 A. 2 P. M. M. Day Shift 7 A. 7 A. M. M. to to 4 P. 5 P. M. M. LOOSE ROCK AND SOFT GROUND TUNNELS 537 The tunnels are being driven by the top heading and bench method, with the bench face kept within lo feet of the heading face. This has proved the best method in every respect, both from the point of speed and economy, as well as safety. With the bench face close to the heading face, the heading muck is thrown over the bench by the blasting, to the invert below, where it, together with the bench muck, is loaded into cars by a Marion shovel. This reduces the amount of hand mucking, and the consequent repeated handling of the muck, to a mini- mum, as very little time is required to clear the shift length of bench for wall plates. The use of a mucking machine, with a necessarily longer bench, would have required additional hand- ling and costs. The full width tunnel heading is carried, being about 15 feet high and 35 feet wide. As the rock is not self-supporting, the whole length of the headings has been timbered and it is believed that this will be necessary for the entire length of the tunnels. The heading timbering consists of 8-inch 32 J pound segmental steel H beams, covered with 3 -inch yellow pine lagging. Each set of steel segments, or ''ring," is made up of 7 segments bolted together in the tunnel as erected. The five upper segments are each 6 feet 4 inches long and cut with radial joints. The leg segments on each side are each 6 feet long, cut with a square joint, and have a 15-inch steel foot plate riveted on the base. The rings are erected on 1 2-inch by 1 2-inch yellow pine wall plates cut and set in 8-foot lengths, and recessed out to fit the footplates. The steel rings have been erected on 42, 48, 54 and 60-inch centers, depending on the progress attainable and the nature of the rock. In general, the 48-inch span is about the maximum safe limit. The positioning of the rings is made by two f-inch tie-rods and two 3-inch by 6-inch timber joggle blocks, to each segment, and the latter are wired to the tie-rods to prevent displacement by the blasting. The space between the lagging and the rock is dry packed with sound rock and, after the construction of the concrete 538 MODERN TUNNELING lining, this packing will be grouted with a cement-sand mix of I to I. The space behind each joint is rigidly blocked to the rock with short 1 2-inch posts and the packing is well placed to protect this blocking from displacement by the blasting. Two-inch grout pipes are set in through the 3 -inch lagging as the heading is timbered, and carried back into the high, or wide, points in the packing. Three such pipes are set every 25 feet, one in the crown segment and one in each haunch, and these pipes are extended through the arch form, before concrete is placed. Additional pipes are also set in the arch form, under the foot-plates and the grout will be injected through these additional pipes, using the haunch and crown pipes as tell-tales, or for injections if necessary. The bench is shot down to the bottom of the concrete side- wall footings, as it is believed to be more economical to remove this extra muck with the shovel than to later cut out trenches in the rock invert. Rock fill will be placed in the low invert to the bottom of the concrete roadway base. All drilling is performed with small one man dry machines, some Ingersoll-Rand Butterfly drills and some Denver Rock Drill "Nineties," with compressed air power. From 24 to 30 holes are drilled in the heading face, consist- ing of 2 rows of cut-holes of 4 holes each, and started about 4 feet on each side of the center-line, while the balance of the holes are spread over the face on each side of the cuts, about 4 feet apart. The cut-holes are 10 feet deep and give a pull of 8 feet while the other holes are 9 feet deep. The bench is drilled with two rounds about 4 feet apart for an 8-foot advance. Generally, 16 holes are drilled, 6 in each round, vertical, and 4 lifters or toe-holes, the cuts 12 ft. deep and the lifters as necessary. The blasting is done with 40 per cent, dynamite, in i-inch sticks of 0.6 pound each. The heading holes are loaded with 4 or 5 sticks each, or 2.4 to 3 pounds each. The bench holes are loaded with 10 sticks, or 6 pounds each. The blasting averages about I pound of dynamite to the cubic yard of rock. A Marion shovel of ij cubic yard capacity, is used in loading LOOSE ROCK AND SOFT GROUND TUNNELS 539 the muck from the foot of the bench into 3-yard side dump cars. The shovels are operated with compressed air, and the air exhaust from the shovels is an aid in ventilating the head- ings. Two 30-inch gage tracks of 8o-pound rails are laid on the tunnel invert and the muck is hauled in 6-car trains. The haulage in the tunnels is made. with electric locomotives, while outside to the dump it is performed with steam locomotives. The dump is in a public park about J mile from the south portal and is reached up a 6 to 7 per cent grade. Two 6 car trains are operated back and forth to the dump, one pushed by a large Climax geared locomotive, and the other pushed by 3 small dinkey locomotives. The round trip requires about 12 minutes and from 65 to 75 cars of muck are taken out of each tunnel daily, depending on the nature of the rock as the softer rock breaks smaller and can be more solidly loaded. The heading and bench work is done by "piecework," the men being paid for 11 hours each shift and allowed to go off as as soon as the daily advance has been attained, as 7, 8, or 9 feet, depending on the ring span decided upon. The drilling, blasting, and mucking out for wallplates, which are all performed on the night shift, are generally finished by 3 or 4 A. M., while on the day shift the timbering is usually com- pleted by I or 2 p. M., and the muck disposal by 3 or 4 p. m. Only two shifts, of 10 hours each, are worked daily, and on six days a week. The concrete lining is being placed at night and at present about 650 feet of each tunnel is lined complete, with the exception of the concreted roadway base, which is not considered as lining, and the final grouting of the concreted lining. This latter has not yet been started. Two Blaw Knox steel forms are used in each tunnel, one 35-foot side- walls form, and one 25-foot arch form. Additional wooden forms, both sidewalls and arch, were used in emergency to expedite the concreting in order to cover some sections of sliding rock. The concreting plant is about 500 feet from the south portal and located on a spur of the Wabash Railroad and materials 540 MODERN TUNNELING are delivered by freight. A trestle has been constructed on the side of a hill and 7 sand and gravel bins built underneath, each about 16 feet by 25 feet by 12 feet deep, and sand and gravel are delivered in hopper cars and dumped directly into the bins. These bins are piped and steam heated to prevent freezing of the materials during the winter. Two cement sheds are built on top of the trestle, one on each side of the track. The mixing plant is under the bins and the mixed concrete is hauled in side- dump " V " cars of 4 cars to a train. All concrete is of gravel aggregate of i : 2 : 4 mix, the materi- als being Alpha Portland cement and Allegheny sand and gravel. The cement is tested at the mills while every car of sand and gravel is tested at the tunnels for organic matter and percentage of loam. The concrete lining is poured in 3 different operations and sections as : sidewall footings, sidewalls, and arch. The footings are poured with wooden forms in about 50-foot sections the mix being dumped onto platforms on the tunnel invert and shoveled into place, 6-inch by 6-inch wooden key strips are laid into the top of the footings and sidewalls, for bonding the structures. The steel sidewall form has a plank decking across the top just above spring line and is attached to a travelling steel inclined track, about 80 feet long. The cars are pulled up this incline with a cable attached to an electric locomotive running on the tunnel invert tracks. The concrete is dumped onto the decking, and shovelled behind the form. The concrete is spaded in the forms, but is not tamped other than the tramping of the spaders. The concrete is mixed as dry as workable and requires consider- able spading for this reason. The spades are perforated with 10 or 12, ^-inch dia. holes in order to secure a good finish. The arch concrete is blown into the form through a i-yard Caniff blower. This blower is secured under the steel sidewall form decking, and the cars are hauled up the incline and dumped into the blower dumping box. The concrete is blown with about 80 pounds air pressure, 100 to 200 feet through a 6-inch discharge line. A branch tee is used on the end of the discharge LOOSE ROCK AND SOFT GROUND TUNNELS 541 line, distributing the mix to each side simultaneously. The wooden joggle-blocks are removed just before concreting a sec- tion while the tie-rods are left in place, and to these the steel arch reinforcement is securely wired. The grout pipes through the steel ring lagging are extended through the form section to the form skin, while additional grout pipes are placed, one between each steel ring, from under the lagging to the skin. These latter pipes are for flood grouting of the concrete arch, to fill any voids that may exist in the lining proper, up under the lagging. With these methods of concreting the chief item is the prep- aration of the forms, the actual placing proceeding faster than the forms can be moved, set, and fitted, as the forms are not stripped until i8 hours set. Placing sidewall concrete is of course the cheapest and quickest operation; but the blowing of the arches has been developed exceptionally well. When blowing the arch concrete, an average of 6 trains, or 24 cars totaling 16 cubic yards, is placed each hour, or 200 cubic yards for a 12-hour shift. In an emergency period over 1700 cubic yards of arch concrete were blown in a week, concreting 325 lineal feet of arch. The footings have averaged i.i actual cubic yards of con- crete per lineal foot of tunnel, the sidewalls 1.5 cubic yards, and the arch 5.2 cubic yards, or a total of 7.8 actual cubic yards of concrete lining per lineal foot of tunnel. The rock packing averages about 1.75 cubic yards (of space) per foot of heading, or an overbreakage to the timbered design of about II per cent. The actual excavation exceeds that required by the Construction Plan about 30 per cent in the head- ing, 37 per cent in the bench, or a total of about ^1, per cent. Electric power for plant operation is purchased of the Duquesne Light Company. The principal plant equipment con- sists of 3 Ingersoll Rand 1200 cubic foot air compressors; two I J yard Marion shovels; one Ransome and one Foote, i- yard rotary concrete mixers ; 4 Canift' concrete blowers ; 2 Caniff grout machines; Butterfly Jack hammer and Denver Ninety rock drills; Lakewood steel V concrete cars; 3-yard side dump 542 MODERN TUNNELING muck cars ; 4 Westinghouse mine locomotives (electric) , 3 dinkey steam locomotives; i Climax geared steam locomotive. The comparative labor costs of the heading and bench work are given below, on the basis of the daily 24-hour payroll taken as 100 per cent. These percentages only cover the direct labor at the point of work. The discrepancy between their totals and the igo per cent, basis, represents supervision, plant oper- ation and maintenance, and miscellaneous charges. This com- parison covers a period when no concreting is being performed, and therefore represents the labor costs per lineal foot of exca- vation. Daily 24-hour payroll 100 . 0% Heading: Drilling, blasting, and mucking for wallplates 12.2% Timbering 26.1 Muck disposal 11. 9 Heading Total 50.2 Bench : Drilling and blasting 1 1 • 5% Muck disposal 11. o Bench Total 22.5 As the disposal of the muck from the heading and the bench is a single operation, the above percentages for this item were distributed on a yardage basis. Below is given an itemized distribution of this disposal cost. Disposal of IVi'ick: Loading 9-2% Tunnel transportation 4.7 Dump transportation 4.1 Dumping 4.9 Disposal Total 22.9% COST OF SOFT GROUND TUNNEL A good illustration of the uncertainty of results obtained in estimating the cost of soft ground tunnels is that of the Flat- bush Avenue double-track railroad for New York City rapid transit service alongside Prospect Park, Brooklyn. These tun- nels are throughout in soil consisting mostly of sands and gravels LOOSE ROCK AND SOFT GROUND TUNNELS 543 of varying quality with earths and some small boulders, the general character of which was ideal, the roof being at an aver- age depth of approximately 55 feet below the surface. The contract involved simply three shafts for access and to allow of prosecution of the work, in addition, to the twin tunnels designed with a central concrete wall. The entire excavation was taken out by mining methods, timbering and concrete permanent Hning having semicircular arches and segmental arch inverts. Practically no water was encountered as the loca- tion was entirely above the level of ground water. The length of the structures from end to end was 4310 feet. Total exca- vation in tunnels 134,000 cubic yards. The contract bids were opened February, 1916, twelve bids being received from exper- ienced contractors and which ranged for the complete work, from $1,370,098 (low) to $2,610,892 (high), the average aggregate being $1,716,000. The two largest items of construction ranged, for excavation in tunnel including timbering, from $4.30 to $12 per cubic yard and for concrete in tunnel lining from $7.50 to $15 per cubic yard. CHAPTER XXII SUBAQUEOUS TUNNELS The use of tunnels for the crossing of rivers or bodies of water for railways is one of the resources of the engineer that has developed within the last half century. Although Brunei's Thames tunnel was completed in 1843, ^-nd was constructed as a highway tunnel it was never used as such, but has been used for railway purposes since 1866. The use of subaqueous tun- nels as part of the city passenger transportation system of such cities as London, Paris, New York, Boston, Glasgow and Liver- pool, has become quite usual, but such tunnels have not been so generally used by trunk Hne railways. The following are the chief trunk line railway subaqueous tunnels: The Sarnia tunnel of the Grand Trunk Railway crossing the St. Clair River, the Detroit Tunnel of the Michigan Central Railway, the Pennsyl- vania Railroad tunnels under the Hudson River, and the Long Island Railroad tunnels under the East River, both to afford access to the Pennsylvania Terminal in New York City, the Severn tunnel of the Great Western Railway in Great Britain, and the Mersey River tunnel on the line of the Mersey Railway at Liverpool, England. In contradistinction to bridges, the cross-section of a tunnel is independent of the width of the span of the waterway to be traversed, hence there is no necessity to provide at any one place any more tracks than the traffic requires at that point. If the amount of trafhc justifies additional tracks crossing the stream they can generally be built at some other point con- venient to the traffic. Most subaqueous tunnels have been built in soft ground by means of a shield with the aid of compressed air, although they have also been built in rock without air pressure or a shield, the 544 SUBAQUEOUS TUNNELS 545 Mersey tunnel, the Severn tunnel and the Astoria Gas tunnel being built in this way. It may be noted here that, although the shield has been used in the past very greatly for subaqueous work it is not necessarily confined to such situations, but may be used in per- fectly dry ground which, by any other system of excavation, would require timbering. Many miles of shield driven tunnel have been bored in the perfectly dry clay under London at a speed far greater than possible by any other method and on the Hudson & Manhattan Railroad, a large portion of the tube tunnels under streets and lands in New York and Jersey City were constructed with shields. TUNNELING SHIELDS The tunneling shield is the invention of Sir Marc Isambard Brunei, and was patented in Great Britain in 1818.* See Figure 113. This was circular in cross-section and embodied many of the features of the modern shield, although the shield used in the construction of the Thames tunnel was rectangular in section made up of a number of sections, each capable of being advanced independently. See Figure 114. Following this in 1864, Barlow in England and Beach in the United States, ob- tained patents on shields. In 1869 the Tower footway tunnel was constructed in London with the use of a shield and cast-iron lining and it was this use of a metalHc Hning with a shield which has led to the great development in soft ground tunneling. In the year 1879 compressed air was first used in tunnel construc- tion at two places, the Hudson River tunnel in New York and a small tunnel in Antwerp. The construction of tube tunnels on a large scale for city passenger transportation, starting in London in 1886, led to the rapid development of the tunneling shield. This was followed by the introduction of the shield into the Hudson River tunnel in 1889 since which time shields in large numbers have been used in New York, Boston and other places in the United States. * British Patent No. 4204 of 1818. 546 MODERN TUNNELING SUBAQUEOUS TUNNELS 547 The shield consists of a cylinder made up of several thick- nesses of steel plates, within the protection of which the exca- SCALE OF FEET 4 5 6 7 Fig. 114. Vertical section of Thames tunnel shield; Brunei's design. vation is made and the tunnel lining is erected. See Figure lis- 548 MODERN TUNNELING Longitudinally the shield is generally divided into two parts by a diaphragm fitted with doors. ISlJg HALF SECTION A-B HALF SECTION C-D HORIZONTAL SECTION D Fig. 115. Tunneling shield used for Hudson River tunnels of Pennsylvania Railroad at New York. In the kinds of ground which are more or less self-supporting, either with or without the action of air pressure, it is necessary for the excavation to be removed in front of the diaphragm. The erection of the lining is invariably done behind the dia- SUBAQUEOUS TUNNELS 549 phragm. The extent to which the excavation may be carried out freely in front of the diaphragm depends on many things — not the least of which is the diameter of the tunnel especially when being built under air pressure. If compressed air is being employed in the tunnel, it can be adjusted only to balance a certain head of water and in any open ground it is impossible to balance the water pressure at the invert without carrying so much excess pressure at the roof that the air will blow through the ground, thus leading to loss of air pressure and consequent flooding of the tunnel. It is therefore necessary to compromise, using a pressure equal to that at, say, half-way down the face so that there will usually be flowing water and ground on the lower half. This may entail very cautious work on the face with only very small areas exposed at a time and complete breasting of the entire face and sides so that the shield is shoved each time into a completely timbered and sheeted chamber, the space to be occupied by the advancing cutting edge having been excavated and refilled with mud, clay or other material into which the shield will penetrate. In other cases where the ground is close and dense and does not permit the escape of air or the influx of water the miners may go in front and excavate freely for the next shove with Uttle or no timbering or other safe- guards. In ground of the softest kind, the most notable example of which is the silt of the Hudson River, no excavation is done by hand in front of the diaphragm, but the shield is shoved bodily through the silt, either with all doors closed taking in no ground or with one or more doors partly opened so that a portion of the ground flows through the openings into the tunnel, where it is loaded into cars and taken out. Quite often a shield for a sub- aqueous tunnel which will pass through mud or gravel for most of its journey will have to be started in a full face of rock. This rock has to be taken out by drilHng and blasting so that a com- pletely clear passage is left for the shield. It is usual in such cases to drive at least a bottom heading in front of the shield in which a concrete bed or cradle shaped to the invert of the shield is laid, so that no damage may come to the cutting edge. 550 MODERN TUNNELING The shield is ill adapted for rock work, and tunneling through rock with a shield is slow and expensive. The earliest work in which roqk was blasted in the invert ahead of the operation of the shield and under air pressure was in the Ravens wood Gas Tunnel under the East River at New York. At a somewhat later date, this was extensively done in the Hudson River Tunnels of H. & M. R. R., as well, as in the Pennsylvania tunnels and in the subway tunnels of the City of New York. Such blasting has to be exclusively ''pin blasting, ' ' using small holes and extremely light charges, as the soft ground overlying the rock must first be mined out and timbered, while the process of drilling and blasting proceeds in the removal of the rock bit by bit. The excavators work in advance of the diaphragm, passing the material through the doors and the erectors of the lining work in rear of same. The front end of the skin of the shield is protected by a cast-steel cutting edge, and the space in front of the diaphragm is generally divided into compartments partly to protect the men and partly to strengthen the shield. The shield is advanced by hydraulic rams, the cyhnders of which are placed in pockets or recesses in the diaphragm, the rams thrusting against the lining previously erected. The small annular space left between the outside of the Kning and the outside of the shield, as the latter advances, is filled with cement grout, gravel or both, or with unslaked lime which after injection swells up and fills the voids without setting hard for a considerable period. The general features of a typical shield are indicated in Figures ii6 and 117. Shield Equipment The equipment of the shield varies with the characteristics of the material through which the tunnel is being driven. In a stiff and reHable soil the diaphragm is reduced to its simplest terms and made as open as possible. The design of the doors in the diaphragm, must be made to suit the special needs of each case. The doors sometimes are hinged at the side, and some- SUBAQUEOUS TUNNELS 551 times at the top, and sliding doors have also been used. What has been proved to be a useful t^^e of door is one where the opening is closed by slats each one of which can be removed independently of the others. ' m ' ■ .^^^^ s^^^WWHIHF^ : ^ ■ . .L... . . c^'i^^p^. ,' . -.ai ..*,fe— ■1 ■ < '■ ) 'oc^,^T i ^^^^^■^^^'''^^'^wm^ *W '4^^^^^^^^'. ^ f -i^^Bp Fig. 116. Shield of Pennsylvania Railroad tunnels under Hudson River, New York. The earlier shields were advanced by screw jacks reacting against the completed lining, but this was soon abandoned for hydraulic rams, the power being supplied by a hydrauHc pump, either attached to the shield or in the main power house from which it is piped to the shield. In order to control the direction of movement of the shield the valves admitting the pressure are generally concentrated in several groups on the shield so that 552 MODERN TUNNELING the force can be increased, or diminished, on one side or the other the top or the bottom. The hydrauHc pressure used varies from 2000 to 5000 pounds per square inch and is usually supphed from hydrauHc pumps at the surface plant transmitted by hydrauHc pipe of steel to near the face. The flexible connections between the main and the moving shield are made up with heavy, small-size copper tubing. Fig. 117. Shield of Hudson & Manhattan Railroad under Hudson River, New York. The rams react against the previously erected tunnel lining. With a cast-iron lining in order to avoid damage to the flanges, the head of the ram is offset '' "| " shaped so as to bear against the axis of the skin of the iron instead of on the flange, thus reducing the danger of breakage of flanges but introducing occasional bending of the rams. In a concrete-Hned tunnel it is usual to embed steel or iron members in the concrete to take this thrust. Practically aU shields for railway tunnels are equipped with a revolving crane or erector to pick up and place in position the lining segments. Frequently the erector is not attached to the SUBAQUEOUS TUNNELS 553 shield but is supported by temporary brackets attached to the Uning at the sides at about the level of the axis of the tunnel. In suitable material various types of excavating and loading machinery have been attached to the shield. In some places rock is encountered at varying heights with soft material above. In such cases the shields are pro\^ded with fixed or movable sliding platforms to furnish protection by an overhead cover from the soft material to the miners while drilling the rock. Some material is so unstable as to require breast-boarding of the face which must be supported continually, excepting for the width of a board at a time, and some shields are equipped with devices to support the face while this is being done and the shield is being advanced. Wliere this is not done the face is supported by bracing from the shield as the excavation progresses. To permit the advance of the shield, this bracing is transferred to struts passing through the shield doors, or through openings in the shield diaphragm provided for the purpose, bearing on a cross-beam reacting against the lining as indicated in Figure 1 18. Wood Lining In the approach tubes to the Detroit River Tunnels as well as in the Dorchester Tunnel at Boston, and elsewhere, a lining has been sucessfully employed in conjunction with a shield, using, instead of iron plates, segmental blocks of w^ood breaking joints and dowelled to each other, making up an exterior lining of soHd wood from 8 to lo inches thick, inside which is afterwards placed a permanent backing of concrete. Roof Shields In suitable material roof shields have been used at various places. The procedure on the Boston subway, which was com- structed in a stifif clay, w^as to excavate two narrow headings on the line of each sidewall, then to construct the sidewalls of concrete, laying a channel bar as a track for the shield on top of each sidewall and then advance the roof shield which ran on rollers on the channel bar track. As the arch was also con- structed of concrete, metal struts were embedded in same to 554 MODERN TUNNELING avoid damage from the thrust of the rams. After the construc- tion of the arch the centra] core in the lower half of the section Fig. ii8. Vertical section through tunnel and shield showing face breasted and strutted through the shield while shoving. was excavated and the invert constructed, thus completing the section. Figure 119. CAISSON METHOD Another method of building a subaqueous river crossing is to make the passage inside a succession of caissons sunk into the bed of the stream. This method was used in one of the river crossings of the Seine by the Metropolitan Railway in Paris. The two arms of the river were crossed by five caissons 66 feet SUBAQUEOUS TUNNELS 555 to 142 feet long sunk separately and joined together after being in position. These caissons were made of structural steel and concrete, an internal lining of cast-iron plates being added after the caissons were in position. In this case the method proved 556 MODERN TUNNELING -s 3 -O SUBAQUEOUS TUNNELS 557 to be very expensive and slow the only advantage being that the rail level was placed at a higher plane than would have been possible by driven tunnehng * (Figure 120). Reinforced concrete caissons were also used by the Hudson & Manhattan Railroad in Jersey City as short sections of the tunnel structure, in constructing enlargements for switches at junctions in Jersey City. These were of a simpler and more economical construction.! Another method which also enables the rails to be placed on a higher plane was that followed by the crossing of the Detroit River at Detroit by the Michigan Central Railroad. The method was to dredge a trench in the bed of the river, into which a steel box-shaped form, in the center of which was a steel tube riveted and caulked watertight, w^as sunk in sections and around which concrete was deposited through tremies. These sections were joined together, unwatered and an interior concrete lining placed, the approaches being constructed with a shield. { COFFERDAM METHODS Several tunnels have been constructed across the Chicago River by enclosing a portion of the stream at a time, between cofferdams within which, after unwatering, the excavation was made and the structure built. A variation of this method was used in the construction of the first New York subway under the Harlem River. This involved the closing of half of the river to navigation at a time, the dredging of a trench to a little below the springing line of the arch and the driving of sheet piling on the sides. This piling was cut off at the springing line. The upper half of the tunnel was constructed on floating supports above the surface of the water and then lowered to a bearing on the sheet piles and intermediate temporary piles, after which * "Les Travaux Chemin de Fer Metropolitain Municipal de Paris a la traversee de La Seine," by L. Biette, Paris. 1910 Dunod et Pinat. t " The Hudson River Tunnel of the Hudson & Manhattan R. R. Co.," by Chas. M. Jacobs, Minutes of Proc. Inst. C. E., Vol. CLXXXI. t Trans. Am. Soc. C. E., Vol. LXXIV, p. 288, by Wilson S. Kinnear and Minutes of Proc. Inst. C. E., Vol. CLXXXV, p. 2, by William J. Wilgus. 558 MODERN TUNNELING air pressure was installed, the tunnel unwatered, the excavation completed and the lower portion of the tunnel constructed in place.* In the construction of the four-track crossings of the Harlem River by the Lexington Avenue subway, similar methods to those used in Detroit were followed. CONSTRUCTION PLANT For subaqueous tunneling the first essential is compressed air for the working headings, generally not exceeding 50 pounds per square inch pressure, and at a higher pressure up to say 150 pounds for the operation of drills and machinery of all sorts. This apparently high pressure has to be carried as the exhaust is into the working chamber which thereby acts as back pressure on the drills or machines. Electricity is also used for lighting and is often also used for haulage, hoisting and the operation of machinery of all kinds. BOILERS The capacity of the boilers is naturally dependent on whether or not the power for constructing the tunnel is obtained from steam or by electricity for producing compressed air. Sufficient power must be provided for supplying the compressed air in the tunnel itself and for rock drills, haulage, hoisting, lighting, pumping and operating tools of all kinds. For a railway tunnel under average conditions from 500 to 1000 boiler horse power per heading should be sufficient. This should be provided in convenient units with some reserve capacity so that one boiler can cut out at a time for cleaning or repairs. With the boilers, the auxiliaries such as feed pumps, condenser plant, circulating water pumps must be considered, and provision for storage and handling coal and ashes must be made. Trans. Am. Soc. C. E., Vol. LXXVIII, p. 252. Engineering News, Vol. 72, p. 1250. SUBAQUEOUS TUNNELS 559 COMPRESSED AIR The amount of low-pressure air required depends on the porous character of the soil. For a railway tunnel from 2000 to 4000 cubic feet per minute of free air per heading is provided. The amount of high-pressure air required depends upon the number of drills or other machinery to be operated in that way. The most authoritative figures on requirements for com- pressed air for carrying on pneumatic tunnel construction are contained in the specifications under which the Pennsylvania Railroad, Hudson and East River Tunnels and the tunnels of the Public Service Commission (New York City) have been constructed. Practically an air pressure of 50 pounds per square inch above normal atmosphere constitutes the limit at which labor can carry on the construction of works of this character. The Pennsylvania specifications provide for tunnels driven with shields under compressed air, that the contractor must provide at each shaft an adequate plant of boilers, air compres- sors, hydraulic machinery, electric generators, and all necessary plant, with a reasonable duplication to meet unusual and unexpected emergencies. Compressors to be of sufficient capacity to dehver regularly into each heading at least 300,000 cubic feet of free air per hour at a pressure of 50 pounds per square inch above normal atmos- phere, and for a larger amount if found necessary during the progress of the work. Air for the compressors must be drawn from the exterior of the power house and the intake so located as to give pure cool air. The air shall be further cooled and oil and other impurities removed as completely as practicable before delivering into the headings. In order to provide a reasonable margin for repairs and con- tingencies a spare compressor and boiler plant shall be provided at the shaft, and kept in good condition and repair ready for immediate use. The capacity of the spare plant shall be 25 per cent, of that required in the preceding paragraph for regular operation. 560 MODERN TUNNELING The air shall be dehvered into each heading through two supply pipes of such capacity that the velocity of air through them, in regular working shall not exceed 40 feet per second. A foul air vent pipe 8 inches in diameter shall be carried back from the shield through each lock bulkhead to the outer atmosphere to ventilate the heading, and shall be provided with a lo-inch regulating valve near the shield to maintain the pres- sure required. Bulkheads to be built in each tunnel at intervals not to exceed 1000 feet and there shall, at no time, be an interval of more than 1000 feet between a shield and the bulkhead nearest to it. Each bulkhead shall be provided with two air locks near the bottom at least 6 feet in diameter and 20 feet long for the passage of men and materials, one near the roof as an emergency lock for the passage of men only, and one pipe lock 12 inches in diameter and 31 feet long with a gate valve for passing pipes, rails, etc. The specifications of the Public Service Commission simi- larly provide for complete and adequate plant, indicating a preference, however, to the operation of the air compressing machines by electricity which could be advantageously pur- chased from public central station supply at reasonable rates. The specific requirements are as follows: "The air-compressing plant shall be capable of furnishing simu- taneously to each heading an air supply sufficient in volume and pres- sure to enable work to be done as nearly as possible in the dry and to afford the degree of ventilation hereinafter specified, including to each heading where a shield is used an air supply at a pressure of forty-five (45) pounds per square inch above atmospheric pressure equal to at least 10,000 cubic feet of free air per minute as measured by piston displacement at a piston speed for any machine not exceed- ing the speed corresponding to the safe working capacity of such machine." The specifications require continuous record of the operation of all compressors and the equipment of cooling apparatus for cooling the air supplied to the tunnels. These specifications require that if the air furnished in the headings exceed 22 pounds per square inch above atmospheric SUBAQUEOUS TUNNELS 561 conditions, two stages of air pressure shall be used, and further that the distance from the heading to the next bulkhead shall not exceed 800 feet, and that there shall be provided two main operating locks and also an emergency lock. The air to be supphed to the headings to be by two pipes, each at least 10 inches in diameter. It is further provided as follows : ''The supply of fresh air to the tunnel shall be sufficient to per- mit work without danger or discomfort; and where work is in com- pressed air, such supply shall be sufficient at all times and places to prevent the accumulation of carbon dioxide to a greater amount than one (i) part in a thousand (1000) by volume." In the State of New York, due to the great amount of air pressure tunnel work which has been executed, the Legislature enacted legal requirements in respect of the operation of employ- ment of labor under varying degrees of air pressure and by Act (Chapter 36 of Laws of 1909 as amended to July, i, 191 7) provided for other matters relating to the operation under air pressure. Briefly the requirements in respect of the duration of employment is as follows: Between normal and 21 pounds pressure per square inch, 8 hours in 24 with interval of at least 30 minutes. Between 22 pounds and 30 pounds, 6 hours in 24 with division in two periods of 3 hours each with at least i hour interval between each such period. Between 30 pounds and 35 pounds, 4 hours in 24 with division in two periods of 2 hours each with at least 2 hours interval between each such period. Between 35 and 40 pounds, 3 hours in 24 divided into periods of not more than i^ hour each, with intervals of 3 hours between each such period. Between 40 pounds and 45 pounds, 2 hours in 24 divided into periods of not more than i hour each, with interval of at least 4 hours between each such period. Between 45 pounds and 50 pounds, Not more than 90 minutes in 24 hours, divided into periods of 45 minutes each, with an interval of 5 hours between each such period. 562 MODERN TUNNELING AIR LOCKS In order to install air pressure on the working face of a tun- nel, it is necessary to build a bulkhead wall across the tunnel to restrain the compressed air, and in order to obtain access to the working face, air locks for both materials and men are provided in these bulkheads. These air locks are merely cylinders of steel plate with doors in each end, opening against the pressure side, and having valves inside and outside for equalizing the pressure. A construction track is laid through the center and a bench along each side. A plate glass ''bulls eye" is placed in each door. The main materials locks are set up so that the tracks through the locks are on the same level as the main operating construc- tion tracks in the tunnels. This means that the main locks are low down in the tunnel section and are side by side. The usual size of these locks is from 6 feet to 7 feet diameter and about 20 feet long. A small sized man-lock called also an emergency lock is usually installed as near as possible to roof grade. Timber- lock at the side above track grade is usually a pipe 18 inches diameter, by 31 feet long, with gate valves at both ends. The concrete setting for these locks varies in thickness according to pressure carried and diameter of tunnel, but commonly 5 feet to 12 feet thick. The purpose of locating the man-lock at roof grade is to provide safety for workmen in the event the workings are partially flooded and the lower locks are inaccessible, escape is then provided at a higher level. When a considerable length of tunnel has been built it is the practice to install a second or third set of locks and the full pressure is only used in the forward lock and the men pass through the intermediate stages at a reduced pressure. This has been found to diminish the occurrence of compressed air illness. ELECTRICITY The underground workings are lighted by electricity, and as work is generally carried on throughout the 24 hours, they are also needed on the surface at night, If any electrically operated SUBAQUEOUS TUNNELS 563 machinery is to be used this must be included in the estimate of the amount of electricity to be generated. If there is a rehable source of electricity available it is commonly purchased and if not it must be generated in the power plant. HYDRAULIC POWER The operation of the shields by hydraulic power and the use of hydrauUc power, also, in many designs of erectors for the erection of the plate lining, necessitates the installation of a hydrauhc power plant carrying a working pressure of from 5000 to 6000 pounds per square inch. It is usual to generate the hydrauhc power for these purposes at the tunnel power plant on the surface as thereby the care and maintenance of the machinery can be looked after much better. Water under pres- sure is conveyed through the tunnels to the shield in extra heavy hydrauhc pipe carried continuously through the lock bulkheads and maintained as near as possible to the face. In some cases the hydrauhc pumps are installed in the tunnels and moved along as the shield advances, this being done in order to save the cost of the hydrauhc pipe for the entire lengths of the tunnels, but is generally not as advantageous, as particularly with the high pressure carried, the friction loss in the hydrauUc pipe is very small. The usual type of pump used for this purpose is a steam operated geared pump with a heavy fly- wheel, which equalizes advantageously the load factor of the machine. At the same time the pumps are frequently driven by electric or other power depending upon the source of power used in the plant installation. The pumps are only operated when power is needed at the face, upon notice given to the engine-room by telephone from the superintendent in charge of the operations at the shield. An accumulator should always be used in the hydrauhc circuit, both to provide storage capacity and to give smooth action in the operation ot the hydraulic machinery. 564 MODERN TUNNELING MISCELLANEOUS PLANT Plant is also needed for the conveying and removal of the excavated material and for the handling and erection of the tunnel lining and materials built into the tunnel, but as this problem does not differ materially in subaqueous tunnels from others, no special description is necessary. Endless wire rope haulage has been the most successful in general use for this purpose. COST OF SUBAQUEOUS TUNNELS Shield Driven Iron Lined Any attempt to state the cost of the various types of sub- aqueous tunnels would be of practically no value as a guide to the probable cost of any other work. There are comparatively few works of this character which have been executed in the United States, or elsewhere, and there is such tremendous vari- ation in the conditions in all of these cases, that little can be learned from the cost of one undertaking to enable us to know what is likely to be the cost of others under different conditions and surroundings. Taken generally, the production of subaqueous tunnels represents one of the most costly works the civil engineer is likely to undertake. Labor conditions are constantly changing and the tendency of Legislatures to enact laws governing the conditions of labor on this class of work, makes it particularly difficult to anticipate what the conditions will be under which any work may be carried out. Under pre-war conditions, the cost of iron plates for tunnel construction varied from $26 to $30 per 2000 pounds ton, delivered New York. These prices being based on No. 2 Foundry pig iron, averaging approximately $16 a ton. Under present conditions of transportation, labor and price of pig iron, it is difficult to foresee what the cost will be. The following table shows the approximate cost per cubic foot of volume excavated for several subaqueous shield-driven tunnels. These figures are obtained by dividing the total con- SUBAQUEOUS TUNNELS 565 tract price for each tumiel by the total number of cubic feet of tunnel displacement. There is thus obtained an average price per cubic foot of volume and this average price includes all the work incidental to the production of the complete tunnel structure, excluding the track or roadway, and including the shafts or other works of access, the plant, permanent materials, temporary materials, labor, suppHes, all miscellaneous expenses and profit to the contractor. Date Name of Tunnel Diameier Outside Approx. Cost per Cubic Ft. 1892 I 904- I 909 I 904- I 909 I 904- I 909 I 903- I 909 1914-1918 1914-I918 1916-1918 1916-1919 I921-1924 Blackwall, River Thames, England Rotherhithe, River Thames, England Pennsylvania R.R,, Hudson River, N. Y. . . . Pennsylvania R.R., East River, N. Y Hudson & Manhattan R.R., Hudson River, New York N. Y. Rapid Transit, East River (Sand) N. Y. Rapid Transit, East River (Sand) N. Y. Rapid Transit, East River (Sand) N. Y. Rapid Transit, East River (For larger part in solid rock) N. Y. Vehicular Tunnel, Hudson River, N. Y . 27.0 30.0 23.0 23.0 16' 7" 18' o" 18' o" 18' o" 18' o" 29' o" $1.10 1.08 1.62 1-73 1-65 2.15 1-93 1.94 1-55 3.60* Estimated. While the figures stated above, as cost of shield -driven, iron- lined tunnels, are approximate only, they nevertheless reflect the influence of rapidity of progress in construction. The tun- nels under the Hudson (or North) River were excavated in silt or in part rock and part silt. In silt the progress is extremely rapid; the Hudson & Manhattan R. R. ha\dng excavated and lined as much as 72 feet of full-sized tunnel in a single day and from one working point. The work in a mixed face of rock and silt is on the other hand extremely slow, the progress often not yielding more than 2 feet per day. The average rate of progress between end points is the governing factor in cost. It will readily be seen that while the cost of hning in place is practically a fixed rate per lineal foot of tunnel, the cost of oper- 566 MODERN TUNNELING ating the plant and the labor employed both in the tunnel and on the surface is more or less constant per diem irrespective of advance. The rate of progress in the sands, gravels and glacial formations under the East River indicate the greater cost on account of the generally slower average rate of advance. When a tunnel shield is progressing in silt the labor cost per foot of tunnel becomes very small (less than $20 per foot). Under these conditions cost of lining bears a very large propor- tion of total cost of tunnel and other costs line up approximately as proportions of the total per foot cost. Cast-iron lining 54 per cent. Labor 22 per cent. Fuel, supplies and overhead 24 per cent. On the other hand when progress is retarded by rock or bad materials or other interferences these figures change tomore nearly: Cast-iron lining 40 per cent, per foot cost Labor 40 per cent. Fuel, supplies, etc 20 per cent. These figures are irrespective of the cost of internal lining of concrete which may be executed subsequently. TRENCH TYPE COST As to the cost of various types of caisson and trench tunnels there is little information of value. The Harlem River subway, for which a contract was awarded in 191 2, included a four-track structure for rapid transit rolling stock equipment. It was awarded to the contractor at a price of $375 per linear foot of track. The depth of water in the chan- nel way was 26 feet and the distance between bulkhead lines was 600 feet. The river bed consisted of sand and gravel over- laid with about 6 feet of mud. The velocity of current in the water-way was about i mile per hour. Similar sized iron-lined tunnels were later awarded for con- struction under the East River at much greater depths, and in more difficult operating conditions at prices varying between $390 and $420 per foot. The Detroit River Tunnel, described elsewhere, was designed SUBAQUEOUS TUNNELS 567 for double-track main-line steam railroad equipment, on which the subaqueous section, which was that portion sunk in trench and completed with tremie concrete, cost $1,772,444. This would represent a net cost of approximately 48 cents per cubic foot of external displacement of structure or $331.50 per foot of track. These two works represent practically the only tunnels of this type which have been constructed in the United States. A tunnel of a somewhat similar character, previously referred to, was built under the Seine in Paris at a very great expense, the work extending over an unprecedented period. The real advantage presented by this mode of construction lies in the possibility of keeping the elevation of the tunnel at a higher plane than would be the case with a driven tunnel, since the question of adequate earth cover during the construc- tion period does not enter in the case of a trench tunnel. By this means the approach gradients may be shortened or made less severe and the operating conditions thereby improved. It will be realized that, within the limits of these four chapters, it has been impossible to do more than touch on the most salient features of such a wide subject as railroad tunneling. A fairly full bibhography, confined to the English language, is appended. This includes papers read before Engineering Societies and articles which have appeared in the technical journals, mostly between the years 1910 and 1920, but including also a few papers and articles prior to that period dealing with certain outstanding pieces of work. It also includes several books on the subject. The title of each paper, article or books gives, as a rule, an indication of the specific part of the general subject which it covers and readers who desire to go more fully into the details of the matter are referred to the bibliography. It may be stated, particularly for the benefit of those who may not be able to reach any public library, that the Engineer- ing Societies Library will furnish, at a small charge, photostat copies of any paper or article desired. Requests for this service should be addressed to the Director, Engineering Societies Library, 29 West 39th Street, New York. BIBLIOGRAPHY TO CHAPTERS XVIII-XXII Papers in Engineering Societies and articles in the technical journals. Note. — For the most part, the papers and articles listed are those which have appeared during the last ten years, 1910 to 1919 inclusive. A few impor- tant papers prior in date to this have been included and one or two of the year 1920. Only articles and books in the English language have been listed. The list does not profess to be exhaustive but it is believed that the field is well covered. 1895. — "The City and South London Railway (London) with Some Remarks on Subaqueous Tunneling by Shield and Compressed Air." J. H. Greathhead. Min. Proc. Inst. C. E,, Vol. CXXIII, p. 39. 1896.— "Iron Tunnels." W. O. Leitch. Min. Proc. Inst. C. E., Vol. CXXV, p. 377. 1897. — "The Blackwall Highway Tunnel. The River Thames, London." D. Hay and M. Fitzmaurice. Min. Proc. Inst. C. E., Vol CXXX, p. 50. 1902. — "The Greenwich Footway Tunnel" (London). W. C. Copper thwaite. Min. Proc. Inst. C. E., Vol. CL, p. i. "Subaqueous Tunneling through Thames Gravel. The Baker Street and Waterloo Railway." A. H. Haigh. Min. Proc. Inst. C. E., Vol. CL, p. 25. 1904.— "The Ventilation of Tunnels." Chas. S. Churchill. Trans. Am. Soc. C. E., Vol. LIV, Part C, p. 525. "The Ventilation of Tunnels." F. Fox. Trans. Am. Soc. C. £., Vol. LIV, Part C, p. 553. 1906. — "The Scranton Tunnel of the Lackawanna & Wyoming Valley R. R." G. B. Francis and W. F. Dennis. Trans. Am. Soc. C. £., Vol. LVI, p. 219. .508 BIBLIOGRAPHY 569 1907. — ''The Simplon Tunnel " (Switzerland and Italy). F. Fox. Min. Proc. Inst. C. £., Vol. CLXVIII, p. 6i. 1908. — ''The Rotherhithe Highway Tunnel" (River Thames, London). E. H. Tabor. Min. Proc. Inst. C. E. (London), Vol. CLXXV, p. 190. "The New York Rapid Transit Subway." Wm. Barclay Parsons. Proc. Inst. C. E., Vol. CLXXIII, 1907-1908, part 3. 1909. — "Caisson Disease and its Prevention." H. Japp. Trans. Am. Soc. C. E., Vol. LXV, p. i. "Cwm Cerwyn Tunnel, Port Talbot, Wales. Relining a Portion of This Railway Tunnel." By W. Cleaver. Min. Proc. Inst. C. E., Vol. CLXXXVIII, p. 380. "Construction of the Tunnel System of the Hudson & Manhattan Railroad Company." J. V. Davies. Ry. Age Gaz., 1909, Sept. 17, 24; Oct. i, 8, 15, and 22. 1910.— ''New York Tunnel Extension of the Pennsylvania R. R." Trans. Am. Soc. C. E., Vol. LXVHI, Sept., 19 10. "The North River Division." Charles M. Jacobs. "The East River Division." Alfred Noble. "The Bergen Hill Tunnels." F. Lavis. "The North River Tunnels." B. H. M. Hewett and W. L. Brown. "The Crosstown Tunnels." J. H. Brace and F. Mason. "The East River Tunnels." J. H. Brace, F. Mason and S. H. Woodard. "The Contractors' Plant for East River Tunnel." H. Japp. Trans. Am. Soc. C. £., Vol. LXIX, Oct., 1910. "Some Features of the Alignment Work on the Pennsyl- vania Tunnels." F. Mason. Harvard Eng. Jour., Apr., 1910. "Subaqueous Section of the Detroit River Turmel." Eng. Rec, Dec. 18, 1909, serial, ist part. 570 MODERN TUNNELING ''The Bergen Hill Four-track Tunnel." Eng. Rec, Dec. i8, 1909. ''Engineering Features of Detroit River Tunnel." Ry. Age Gaz., Apr. 29, 1910. "The Tunnel Construction of the Hudson & Manhattan R. R. Co. J. V. Davies. Proc. Am. Philosoph. Soc, Vol. XLIX, No. 195, 1910. "Construction of Rapid Transit Railroad in Relation to the Handling of Passengers as Illustrated by the Hudson & Manhattan R. R." J. V. Davies. Proc. Eng. Club of Philadelphia, Vol. XXVII, No. 4, Oct., 1910. 191 1.—" Tunnel-Driving in the Alps." W. L. Saunders. Bull. Inst, of Min. Eng., July, 191 1. "Driving Spiral Tunnels on the Canadian Pacific Ry." Eng. News, Nov. 10, 1910. "Hudson River Tunnels of the Hudson & Manhattan R. R." Charles M. Jacobs. Minutes of Proc. Inst, of C. E., Vol. CLXXXI, 1909-1910, Part 3. "Rebuilding La Salle Street Tunnel, Chicago." Eng. News, Jan. 12, 191 1. "The Transandine Summit Tunnel." John Pollack. Engng. (London), Dec. 30, 1910. "The Loetschberg Tunnel." E. L. Corthell. Eng. News, Jan. 5, 1911. "The Detroit River Tunnel." W. S. Kinnear. Trans. Am. Soc. C. E., Vol. LXXIV, Dec, 1911. 1912. — "Notes on a Tunnel Survey." F. C. Noble. Proc. Am. Soc. C. E., Dec, 1911. "Discussion on Above." Pro. Am. Soc. C. E., March, 191 2, and Apr., 1912. "The Detroit River Tunnel." W. J. Wilgus. Min. Proc. Inst, of C.E., Vol. CLXXXV, 1910-1911, Part 3. "Subaqueous Tunneling." H. Japp. Proc. Eng. Club of Philadelphia, July, 191 2. BIBLIOGRAPHY 571 "Air Resistance to Trains in Tube Tunnels." J. V. Davies. Proc. Am. Soc. C. E., Apr., 191 2. ''Methods of Construction-Sand Patch Tunnel B. & O. R. R." Engng. Contng., June 26, 191 2. "The Concorde Tunnel of Paris MetropoHtan Ry." P. Seurot. Proc. Inst. C. £., Vol. CLXXXVIII, 1912, Part 2. "Seepage in Subaqueous Railroad Tunnels." Eng. Rec, Aug. 31, 1912. "Ventilating Equipment of the Pennsylvania Tunnels at New York." B. W. Bennett. Eiig. Rec, June 8, 191 2. "West Shore Weehawken Tunnel Ventilation." Ry. Age Gaz., Aug. 9, 191 2. "The Sanitation of Construction Camps." H. F. Gray. Trans. Am. Soc. C. E., Vol. LXXVI, p. 493. "Paris Metropolitan Railway Concorde Tunnel across the Seine River." P. Seurot. Min. Proc. Inst. C. E. Vol. CLXXXVIII, p. 380. 1913. — "Elimination of Timbering in Rock Tunneling." J. F. O'Rourke. Eng. News, Feb. 13, 1913. "Relining the Mauvages Tunnel on the Marne Ship Canal." F. B. Mann. Eng. Rec, Feb. 22, 1913. "Tunnel Relining on 18 Tunnels of the Virginian Pvy. under Traffic." Ry. Age Ga7-., June 20, 19 13. "Building a Four-tube Steel Tunnel in Sections." Iron Trade Rev., Sept. 25, 1913. "The Astoria Tunnel, East River, New York." H. Car- penter. Eng. News, Oct. 16, 1913. "Difficult Tunnel Work on the Metropolitan Railway in Paris." Eng. News, Sept. 11, 19 13. 1914. — "Concrete Blocks for Tunnel Lining." Munic Jour., March 19, 1914. 572 MODERN TUNNELING ''Concrete-lined Highway Tunnel Carrying Heavy Loads from Railways above It. The Corliss Steel Tunnel, . Pittsburgh." Eng. Rec, Aug. 15, 1914. ''Lining Long and Deeply Overlaid Tunnels." E. Lauchli. Eng. News, Aug. 6, 1914. "Lining Tunnels on the Grand Trunk Pacific in British Columbia." Eng. Rec, Aug. 8, 1914. "Problems in Driving Long and Deeply Overlaid Tunnels." E. Lauchli. Eng. Rec., Nov. 8, 1913. "Subway Tunnel, Harlem River, New York." Eng. Rec, Nov. 15, 1913. "Proposed Tunnel under EngHsh Channel." C. O. Burge. Eng. Rec, Nov. i, 19 13. "The World's Greatest Tunnels (Except Town Tunnels)." Engnr., London, Nov. 28, 19 13. "Construction Methods of Mont d'or Tunnel." Engng. Contng., Nov. 26, 1913. "The Four-mile Mont d'or Tunnel. French Jura. Heavy Water Flow in Firm Rock." Eng. News, Jan. 15, 1914. "Driving and Lining Point Defiance Tunnel with Poling Boards and Semicircular Shield." Eng. Rec, Feb. 7, 1914. "The Second Simplon Tunnel." Engnr., London, Feb. 13, 1914. "Subaqueous Tunneling." P. Seurot. Trans. Soc Can. C. E., April 23, 1914. "Tunnel Ventilation during Construction." E. Lauchli. Canadian Eng., July 2, 19 14. "Whitehall Street Tunnel, New York. Cast-iron Tunnels Under the East River." Eng. Rec, July 25, 19 14. "Old Slip Tunnel, East River, New York." Eng. Rec, Aug. 22, 1914. "The Havens tein Tunnel, Switzerland." Engnr., London, July 24, 1914. BIBLIOGRAPHY 573 1915. — "The Relation of Geology to Railway Tunnel Location." E. C. Eckel. Contract Rec. (Toronto), Oct. 28, 1914. "Tunneling and Geology." E. Lauchli. Canadian Eng., Sept. 16, 1915. "Lining Long Tunnels and Tunnels Subjected to Heavy or Eccentric Ground Pressure." E. Lauchli. Canadian Eng., Jan. 7, 1915. "Determination of Stresses in and Design of Cast-iron Lining for Subaqueous Tunnels." P. Seurot. Engng. Contng., Jan. 3, 1915- "The Ventilation of Allegheny Summit Tunnel, Virginian Ry." Gen. Elec. Rev., Dec, 1914. "The Astoria Tunnel, under the East River, New York." J. V. Davies. Trans. Am. Soc. C. E., Vol. LXXX, 1916. "Flooding and Recovery of the Astoria Tunnel." H. Carpenter. Eng. News, October 7, 191 5. "Extensions of the Hudson River Tunnel of the Hudson & Manhattan Railroad." J. V. Davies. Proc. Inst. C. £., Vol. CXCVn, Session 19 13 and 19 14, Part 3. "The Largest Tunnel in the World, 4 Miles Long, 72 ft. Wide, at Marseilles, France." Eng. News, Aug. 26, 191 5. "Piercing the Selkirk Mountain for a 5-mile Double- track Tunnel, Rogers Pass, B. C." Eng. Rec., Dec. 5, 1914. "The Snoqualmie Summit Tunnel, 11,886 Feet Long, Cascade Mountains." Eng. News, Feb. 18, 191 5. "The Stockton Tunnel, San Francisco. 50 Feet Wide." Engng. Contng., Feb. 3, 191 5. "Subaqueous Highway Tunnels." Geo. D. Snyder. Trans. Am. Soc. C. E., Vol. LXXVHI, p. 252. 1916. — "Tunnel Drill Carriages." S. P. Brown. Eng. Rec, Jan. 8, 1916. "Tunnel Lining by Compressed Air Mixing and Placing." Engng. Contng., Jan. 12, 1916. 574 MODERN TUNNELING ''Nicholson Tunnel on D. L. & W. R. R. Brick-lined." Ry. Engng. and Main, of Way, Jan., 1916. "Construction Methods. Rogers Pass Tunnel." J. G. Sullivan. Can. Soc. C. £., Jan. 13, 1916. ''Rapid Tunneling in Brazil." J. C. Balcomb. Eng. News, May 18, 1916. "The Laxaxalpam Aqueduct Tunnels, Mexico." J. Forgie. Proc. Inst. C. E., Vol. CC, 1914-1915, Part 2. "The City Tunnel of the Catskill Aqueduct, New York." W. E. Spear. Am. Water Works Assn. Jour., June, 1916. "The Construction of the Dorchester Tunnels under Fort Point Channel, Boston." A. A. Cohill. Boston Soc. of C. E. Jour., May, 191 6. "Needle Beam Heading Method in Dry Ground, Newark, N. J." Eng. Rec, Mar. 4, 1916. "Wall Plate Drift Method. Twin Peaks Tunnel, San Fran- cisco." Eng. Rec, Feb. 26, 1916. "Repairing a Tunnel Lining under Difficult Conditions. Concrete Atomizer Used by Chicago Great Western R. R. at Winston, 111." ^^3;. Age Gaz., Dec. 17, 191 5. "An Economic Comparison of European and American Methods of Tunnel Driving." E.Lauchh. Engng. Contng., Nov. 24, 1916. "Modern Methods of Railway Tunnel Construction." Chas. S. Churchill. Ry. Rev., October 30, 191 5. "East River Tunnel Shields, New York. Details of 18 Ft. Shields." Eng. News, Nov. 11, 191 5. "Construction Plant and Methods Employed in Concrete Lining and Double- track Railway Tunnel under Traffic." R. Meacham. Engng. Contng., Nov. 17, 191 5. "Completing the Mount Royal Tunnel into Montreal." Ry. Age Gaz., Nov. 5, 1915. "Methods Used in Building the Rogers Pass Tunnel." Eng. News, Nov. 11, 191 5. BIBLIOGRAPHY 575 ''Construction Progress on the Twin Peaks Tunnel, San Francisco." Eng. News, Nov. 4, 191 5. 1917. — ''Tunnel for Marseilles Canal, Largest in the World." Eng. News, Nov. 30, 1916. "Construction Methods for Rogers Pass Tunnel." A. C. Dennis. Proc. Am. Soc. C. E., Jan., 1917. "New Methods in Tunneling in Soft Ground. L. G. Warren. Eng. News, Feb. 8, 191 7. "The Harlem River Subway Tunnel, New York." F. W. Skinner. Engng., July 13, 191 7. "Subaqueous Tunneling at its Worst." C. M. Holland. Comp. Air Mag., Apr., 1917. "Tunnel under Hudson River, New York, Designed for Vehicular Traffic." Eng. News-Rec, Apr., 19, 191 7. 1918. — "The Use of the Air Hammer-drill in Tunneling." B. Owen, Commonwealth Engineer, Melbourne, AustraUa. July, 1918. "Repairing Tunnel Linings with Gunite." Com. Air, Mag. June, 1918. 1919. — "The Mount Royal Tunnel." J. L. Busfield. Jour. Eng. Inst, of Canada, Vol. 2, No. 4, Apr., 1919. "Concrete Block Tunnel Lining at River Rouge, Mich." Bull. Gen. Contr. Assn., Vol. X, No. 8, Aug., 1919. "Hudson River Tunnel Problems, Structural and Construc- tion." W. C. Parmley. Eng. World, Vol. XV, No. 3, Aug. I, 1919. "Proposed Vehicular Tunnel under the Hudson River at New York." Ry. Rev., Vol. LXIV, No. 25, June 21, 1919. "Vehicular Tunnels under the Hudson River at New York." M. Schreiber. Jour. Frank. Inst., Vol. CLXXXVII, No. 3, Mar., 1919. 1920. — "The Proposed New York and New Jersey Vehicular Tunnel, New York, Hudson River." Trans. Am. Soc, C. E., Vol. LXXXm, 1920. 576 MODERN TUNNELING ''Notes on Tunnel Lining for Soft Ground." B. H. M. Hewett and S. Johannesson. Trans. Am. Soc. C. E., Vol. LXXXIII, 1920, 192 1. —"Tunnel Widening on the Virginian Railway. Enlarge- ment of Tunnel Bores Necessitated by Double Tracking Involving Special Engineering Features." Ry. Rev., Chicago, Vol. LXVIII, No. 11, Mar. 12, 1921. BOOKS " Tunneling, Explosives Compounds and Rock Drills." Henry S. Drinker. Published by John Wiley & Sons, New York, 3d Edition, 1888, 1143 pp., 20 plates, 1000 cuts. " Practical Tunneling." Frederick Walter Simms. With addi- tional chapters illustrating recent practice, by D. D. Kinnear Clark. Crosby Lockwood & Son, London, 1896; 548 pp. " Tunneling. A Practical Treatise." Charles Prelini. With additions by Charles F. Hill. David Van Nostrand Co., New York, 1901; 307 pp. " Tunnel Shields and the Use of Compressed Air in Subaqueous Works." W. C. Copperthwaite. D. Van Nostrand Co., New York, 1906; 389 pp. '' Subways and Tunnels of New York." G. H. Gilbert, L. I. Wightman and W. L. Saunders. John Wiley & Sons, New York, 1912, ist Edition; 372 pp. " Tunneling. Short and Long Tunnels of Small and Larger Section Driven through Hard and Soft Materials." Eugene Lauchli. McGraw-Hill Book Co., New York; I st Edition, 191 5; 230 pp. APPENDIX OUTLINE OF TUNNEL DATA The following outline is intended to cover the more im- portant features to be considered in making a tunnel examina- tion: General: Name of company operating. Head office. Officials. Consulting engineer. Field superintendent. Names and officials of former companies. Superintendent of each. Dates of starting, etc. Tunnel: Size. Form. Length. Elevation of portal. Character of rock. Grade. Size and shape of water drain. Style of timbering where necessary. Amount of timbering. Power Plant: Description and arrangement. Sizes of machinery. Cost of plant. Efficiency. Cost of power. Compressors : Make. Size. Speed. 577 578 MODERN TUNNELING Rated capacity. Actual capacity. Efficiency. , Repairs. Length and size of delivery pipe. Arrangements for removing water in air. Ventilation: Make of fan or blower. Size. Speed. Amount of pressure or vacuum. Rated capacity. Actual capacity. Efficiency. Repairs. Size of ventilating pipe. Thickness of metal. Method of jointing. Length of sections. Where carried in tunnel. Distance of end of pipe from face of tunnel. Direction of air current. Length of time required to clear after each round of shots. Drilling: Make. Size. Number of drills in face. Cost of repairs. Method of mounting. Air pressure at drills. Air consumption. Number, depth, and direction of holes in each round. Rate of drilling. Brand, size, and form of steel used. Durability of same. Method of sharpening. Number sharpened per day. Number of drill shifts per day. Number of drillers and helpers. Time required in setting up drills, in drilling the round, and in taking down drills. APPENDIX 579 Blasting: Make of explosives. Brand. Size of sticks. Strength. Method of loading. Tamping. Method of firing. Size of wire, make of battery, precautions against short circuits if electric firing is used. Speed of fuse. Method of igniting same. Order of firing. Method of making primers, and size of detonators. Their position in the holes. Time required to clean out holes, load, and shoot. Temperature of rock at the face. Temperature of dynamite when placed in the hole. Amount of rock broken per pound of explosive. Arrangements for storing explosives. Arrangements for thawing explosives. Mucking: Number of mucking shifts per day. Number of muckers. Position in which they work. Size and form of shovels used. Is shoveling done from tunnel floor, planks, or steel plate ? Method of handling cars in heading. Time of loading each car. Time of mucking for each round. Tramming: Horses, mules, electricity, or compressed air. Gauge of tracks. Weight of rail. Arrangement of switches in tunnel and at face. Dimensions of cars. Capacity of cars. Type of cars. Arrangements for facilitating dumping. Design, size, and material in wheels. Method of oiling. 580 MODERN TUNNELING Method of coupling. Brakes. Repairs. Durability. Wages : Division of labor for entire work. For each individual shift. Class of men employed. Wages paid each. Details of bonus if offered. Speed: Per shift. Twenty-four hours. Month. Observations on contributing causes. Cost: Labor: Engineering. Superintendence. Shift foremen. Bookkeepers. Time-keepers. Drillers. Helpers. Muckers. Motormen. Mule drivers. Dump men. Blacksmiths. Helpers. Machinists. Electricians. Power engineers. Track men. Carpenters. Tram men. Any others, stating nature of duties. Materials: Powder. Fuse. APPENDIX 581 Materials (Continued) : Caps. Candles. Carbide. Light globes. Timber Lumber. Ties. Track. Ventilating pipe. Pressure air pipe. Water pipe. Hose. Machine oil. Shovels. Picks. Steel for drills. Blacksmiths' supplies. Blacksmiths' fuel. Machinists' supplies. Horse feed. Miscellaneous. Repairs: Power machinery. Haulage equipment. Compressors. Ventilating machinery. Other machinery. Drills. Pipe. Track. Electric line. Telephone. Buildings. Picks and shovels. Miscellaneous. Power, not including labor, repairs, or depreciation' For drilling. Tramming. Ventilating. Miscellaneous. 582 MODERN TUNNELING Depreciation: Power machinery. Haulage equipment. Compressors. Ventilating machinery. Other machinery. Drills. Pipe lines. Track. Electric line. Telephone. Buildings. Miscellaneous. General expenses. Miscellaneous expenses, stating nature. Illumination: Permanent. Hand. Signaling: Electric bell. Mine telephone. Other methods. Special Difficulties: Water. Bad air. Loose ground. Poisonous gases. Inaccessibility. Excessive freight rates. Any others, stating nature. Conclusions: Observations, commendations, and criticisms of methods em- ployed. INDEX PAGE Accessibility of tunnel, influence of, on choice of power 66 Accidents, electrical, causes of 311 prevention of 313, 321, 324, 326 from explosives, causes of 293-304 prevention of 293-304, 319, 322, 325 from roof falls, causes of 290-292 prevention of 290-292, 319, 321, 324 in tunneling, frequency of 289 haulage, causes of 309 prevention of 309, 320, 323, 326 Acetylene, advantages of 204 cost of 204 use of, in tunneling 201, 204 Adit, definition of 2 Aftercooler, for air compressors, purpose of 106 Agricola, on mining 11 Air, compressed, consumed by drills 83 cooling of 102 danger from high temperatures in loi, 107 for transmitting power 64 losses of 83 See also Compressed air Air compression, dangers of high temperatures produced during lOl heat produced during loi moisture produced during 105 Air compressors, aftercooler for, purpose of 106 air receivers for, purpose of 107 belt driven, straight-line, two-stage type, figure showing 88 capacity of, loss of, causes of 83, 84 rating of 82 and power required by 82 cause of explosions in 102 direct-connected, electrically driven, duplex, two-stage type, fig- ure showing 92 duplex, features of 88 duplex, compound-steam, two-stage type, figure showing 90 duplex, simple-steam, two-stage type, figure showing 89 efficiency of 109 features of 80 heat losses in 102 intercooler for 104 583 584 INDEX PAGE Air compressors, power required by 82 power requirements of 109 precoolers for, need of 106 production of harmful gases in 305 proper size of, determination of 82, 83 regulation of, methods used for 97-100 relative merits of types of 94-97 selection of, factors determining 80, 94, 109 single-stage, power-driven type, figure showing 88 single-stage, tandem type, figure showing 86 straight line, features of 85-88 straight-line type, figure showing 87 turbine type, power required by 82 types of 80, 85, 94, 96 unloaders for 99 volumetric efficiency of 83 Air consumed by man at work 116 Air drills, advantages of 147, 148 air thrown valve type, merits of 155 auxiliary valve type, merits of 156 bar mounting for 212 column mounting for ; ; 212 cost of repairs for 153, 154 features of 130 hammer type, merits of 160 piston type, figure showing 132, 133, 134, 137 merits of 149 selection of, factors influencing 160, 161 tappet valve type, merits of 155 types of 130 valveless, features of 136 figure showing 137 merits of 1 56 valves for 131-136 ventilation supplied by 148 Air, for ventilation, quantity needed 115-1 18 pressure of 1 19-12 1 Air locks 562 Air meters, types of 127, 128 Air pipe lines, drains for, need of 108 leakage in, methods of determining 84 precautions in construction of 84 Air receiver, functions of 107, 108 Air required, by man for breathing, table showing 116 for ventilation of tunnels 1 15, 1 16 Air-thrown valve rock drill, features of 132 merits of 155 INDEX 585 PAGE Air transmission, size of pipe required for 121, 122 Alinement ; 432 Ammonia dynamite, See Dynamite Animals, accidents from, causes of 311 amount of air required by 115 for tunnel haulage, merits of 173 Anne of Lusignan, early tunnel started by 1 1 Arch sets, arrangement of timber in 277, 278 Arlberg tunnel (Austria), cost of 25 features of 26 progress of 26 Arthur's Pass tunnel (New Zealand), mention of 31 Aspen tunnel (Wyoming), mention of 31 Assassin tunnel (France), cost of 18 Auburn tunnel (Penn.), mention of 13 Austria, early railway tunnels in 14 Automobiles, clearance for 430 exhaust gases 457 Auxiliary valve rock drill, features of 135, 136 merits of 1 56 Aztecs, tunneling by 7 B Bar mounting for drills 212 Beams, needle 517 Beaumont-English rotary tunneling machine 508 Bench drilling 494-495 Bench and heading, kept close together 496 Bennett tunneling machine, features of ' 185 Bethell process for preserving timber 272 Bibliography 361-419 air drills 394 air compressors 395 blasting methods 406 blasting supplies 408 Chapters XVIII-XXII • 568-576 choice of power 382 compressed-air accessories 391 compressed-air power 380 compression of air 388 costs 418 drilling accessories 397 drilling methods 405 electric drills 396 electric power 378 gasoline drills 397 haulage 398 586 INDEX PAGE Bibliography, hydraulic drills 395 illumination 402 internal-combustion power 373 methods of tunnel driving 402 mucking 411 power-plant descriptions 382 power transmission 381 safety and health . . * 414 speed records 412 steam power 371 timbering 411 tunnel descriptions 360 tunneling machines , 401 ventilation 393 water-power 369 Bids, contract : 458-460 Big Bend tunnel (Calif.), features of 23 Big Creek tunnel (Calif.), mention of 23 Black Rock tunnel (Pa.), mention of 15 Blast-holes, arrangement of 221 chambering of 227 charging of 240, 249-251 depth of 229-235 at various tunnels, table showing 235 method of firing 122 number of 219 placing of 221-229 position of primer in 249-251 Blasting cap. See Detonator Blasting powder, black, gaseous products of 238 Blasts, effectiveness of, factors affecting 227 Blisworth tunnel (England), mention of 13 Blowers, comparison with fans for ventilation 122 pressure, figure showing 1 1 1 relative merits of 1 1 1 , 122 Boilers 558 Bonticou tunnel, Catskill Aqueduct, features of 37 Bottom cut, arrangement of holes in 224, 228 description of 224 figure showing 225 Brick work (lining) 436, 531-532 Brunton & Trier rotary tunneling machine 508 Buffalo Water tunnel (N. Y.) blast holes in, arrangement of 222 depth of 235 cars used in 1 69 features of 49 quantity of explosives used in 243 INDEX 587 PAGE Buffalo Water Tunnel (N. V.), wedge cut at, figure showing 223 Buildings, surface, fire in, danger of 313 Bureau of Mines, officials of, acknowledgments to 3 Burleigh drills, use of, in Hoosac tunnel 25 Burleigh tunnel (Colo.) 35 features of blast holes in 219 Burnettizing timber, method of 272 Busk-Ivanhoe tunnel (Colo.), details of 30 C Caisson method 554-557 Call bell, for underground telephones 207 Camp 479-48 1 Canal tunnels, American 13 English 13 French 12 Candles, dangers in use of 203, 315 for illumination, merits of 203 Cap, blasting. See Detonator Capacity of ventilating pipe, table showing 120 Carbon dioxide, flows of, in Los Angeles Aqueduct 305 from gasoline locomotives, method of handling 178 in rocks, dangers from encountering 305 properties of 303 Carriage mounting for drills, merits of , 214, 217 Cars, size of 471-473, 475 tunnel, derailments of, delays from 292 desirable features of 163, 265 handling of, method of 262-265 size of 163 Carter tunnel (Colo.), air pressures used at 103 blast holes used in heading of 219 blast holes in, depth of 235 bottom cut in, figure showing 225 cars used at, features of 169 consumption of air by drills in 83 cost of drill repairs at 154 direction of air current in 1 14 drilling speed at 151 features of 35 grade of dynamite used at 241 power plant at, water supply for 66 pressure required for ventilating current 120 system of lighting in 202 Catskill Aqueduct tunnels (N. Y.), cars used at, features of 169 depth of blast holes in 235 features of 36 588 INDEX PAGE Catskill Aqueduct tunnels (N. Y.), grade of dynamite used in 241 quantity of explosives used 243 siphons of, linings of 287 speed of drilling in 151 system of lighting in 202 Caved ground, timbering for 280 Caves, water-filled, danger from 316 Cement gun 532-533 Central power stations, economy of 66 Central tunnel (Colo.), air pressures used at 103 cars used at, features of 169 depth of blast holes in 235 direction of air current in 114 drilling speed at 151 features of 39 grade of dynamite used in 241 pressure required for ventilation current at 120 system of lighting at 202 Chambering of blast holes, comment on 227 Chipeta adit (Colo.), blast holes in face of '. . . . 219 cars used at, features of 169 features of 49 Choice of power for tunnel work, factors governing 65 Clearance, automobiles 430 standard 429 Cofiferdam methods ' 557-558 Column mounting for drills, methods of 213-216 Comparison of fans and blowers for ventilation 122 Compressed air, hours of work in 561 meters for, value of 127 pipe lines, drains for 108 leakage in, method of testing for 84 plant 559-561 . power transmission by 64 removal of moisture from 105 thermal losses in loi transmission of, cost of 70» 73 use of, for ventilation 148, 305 working pressure of 103 See also, Air, compressed Compressed air locomotives, use of 173 Compressors, air, reliablity of prime importance 468 Compressors, See Air compressors Concrete, mass (lining) 436 precast (lining) 437 pneumatic placement 527~53i Conemaugh tunnel (Pa.), mention of < . . , 14 INDEX 580 I'AC.li Construction 461-481 Consumption of fuel, influence of, on choice of power 74 Contract bids 458-460 Coquitlam tunnel (B. C), mention of 23 Corbett tunnel (Wyo.), features of 22 Cornelius Gap tunnel (Ore.), car used at 169 features of 49 Coronado tunnel (Ariz.), cost of driving 329 features of 39 Cost, excavation in hard rock 486-490 shield driven iron-lined tunnels 564-566 soft ground 542-543 trench type 566-567 Cost of railway tunnels 25 Cost of tunneling 328-359 See also various tunnels named Cowenhoven tunnel (Colo.), caves in 317 timbering in, method of 282 Creosote, use of, for preserving timber 271, 272 Crimping tool, for explosives, use of 301 Cross-section, factors controlling 429 independent of span 544 Current, electric, purchased, as source of power 76 D Delia S. mine (Colo.) cave in, flow of water from 317 Depreciation, charges for 77 Depth of drill holes 229 at various tunnels, table showing 235 Design of tunnels 426-460 Detonator, amount of explosives contained in, table showing 248 definition of 247 delay-action, features of 255 electric, figure showing 247 grades of, rating of 248 ignition of 247 position of, in primer 310 proper use of 300 strength of 301 Diesel engine, advantages of 63 as a source of power 53 characteristics of 62 Direction of holes in tunnel headings 221 Direction of ventilating current, factors influencing 1 13 Double versus single tunnels 429 Drainage and pumping 451-455, 476 Drains for compressed air pipe lines, need of 108 590 INDEX PAGE Drift, definition of 3 Drill, See Air drill. Rock drill Drill holes, depth of, at various tunnels, table showing 235 determination of 229 shallow, merits of 231 See also Blast holes Drill mounting, bar 490 column 490 travelling carriage 491 Drill mountings, adaptability of various types 217 amount of mucking required with various types 215 choice of 218 horizontal bar, method of using 213 vertical column, merits of 214 Drill sharpening machines, advantages of 125 capacity of 126 types of 125 Drill shifts per day, single, merits of 209 three, merits of 211 two, merits of 210 Drilling operations, cycle of in Simplon tunnel 28 Drilling, single shift system of 209 speed at various tunnels, table showing 151 test, advanced 509 three-shift system of 211 two-shift system of 210 typical methods 493 Drilling machines. See Air drills. Rock drills Drills 468 racks for, advantages in using 207 Drinker, H. S., on early history of explosives and rock drills 19 on early railway tunnels 14 Drivers, precautions to be taken by 310 Drunkenness, See Intoxication Dump, cradle, description of 180 for cars, types of 178 Dumping, derrick for, use of 179 Dumping device, cradle, use of 179 revolving, use of 1 79 types of 178-180 Dynamite, ammonia, composition of 237 gaseous products of 238 amount of, used at various tunnels 243 burning of, noxious gases from 303, 304 prevention of 303 charging of 295, 297 detonation of 250 INDEX 591 PAGE Dynamite, for tunneling, selection of 240 gases from 237, 249 gelatin, advantages of 239 composition of 236 gaseous products of 238, 303 rating of strength of 239 strength of detonators for 301 handling of, precautions in 293, 296, 322 misfires of 299 premature explosions of 296 proper method of storing of 257 proper method of thawing of 258 proper strength of detonators for 301 storing of 257 precautions in 294 thawing of, need of 253 precautions in 294 use of, care in 324 E Earth pressures 435 Economics 424 Efficiency, maximum obtainable from blast hole 226 thermal, influence of on choice of power 75 volumetric, of air compressors 83 Egyptians, stone-cutting tools of 5 tunnels driven by 5 Electricity, accidents from, causes of 311 prevention of 321, 323, 326 cost of 76 purchased, as source of power 76 transmission of, best voltages for 71 cost of 70, 7 1 method of 71 Electric detonator, figure showing 247 Electric drill, durability of 159 merits of 157-159 types of 141-147, 157 Electric lamp, advantages of 203 Electric locomotives, shocks from, precautions against 313 use of 174 Electric motors, types of 64 Electric plant 562-563 Electric power, advantages of 64 Electric voltages, best for transmission lines, determination of 71 Elizabeth Lake tunnel (Calif.), consumption of air by drills in 83 cost of driving 342 592 INDEX PAGE Elizabeth Lake tunnel (Calif.), features of 43 quantities of explosives used in 243 timbering in 284 timbering in, figure showing 285 Elizabethtown tunnel (Pa.), mention of 15 Engines, internal combustion 457 England, early railway tunnels in 14 English Channel, tunnel under, use of tunneling machines in 183 Equipment, haulage 470-475 loading ; 468-470 shield 550-553 surface 478-479 Ernst August StoUen (Germany), details of 16 Excavating machinery 508-553 Excavation, cost of . 486-490 disposal of 496 estimates for 489 in hard rock, methods of 482-509 in soft ground, methods of 510-543 Exhaust gases, automobiles 457 Exits, separate, need of 314 Explosive, accidents from use of 293 precautions against 293-303 charge of, determination of 241 choice of detonators for 249 chronology of 19 excessive charges of, dangers from 290 firing of, precautions in 295 gaseous products from 238, 303 handling of, precautions in 293, 296, 322 high, burning of, cause of 303 high, proper strength of detonator for 301 methods of loading 249 misfires of, causes of • • • • 299 proper method of thawing of 258 proper method of storing of 257 premature explosions of 296 rating of strength of 239 risks in loading 297 selection of, factors determining 236, 239 sensitiveness of 297 slitting of cartridges of 253 storing of, precautions in 294, 257 thawing of, methods 258 thawing of, necessity for 253 thawing of, precautions in 294 use of, precautions in 293-295, 322, 324 INDEX 593 I'AGli Explosive, use of two grades of, at headings 240 work of, factors affecting 226 F Falls of roof, causes of 290 False set, see Timbering Fans, comparison with blowers for ventilation 122 Fans, ventilating, use of 1 1 1 , 122 Fatalities in tunneling, rate of 289 Fernald, R. H., on cost of producer-gas plants 69 Ferroux drills, results with, at Arlberg tunnel 27 Fires in tunnels, causes of 314 dangers from 314 danger from, avoidance of 314, 321, 324, 327 Fire setting, method of excavation 9 Firing blasts, methods of 254 First tunnel in United States 420 Foreign systems timbering 461, 510 Foreman, suggestions for 321 Forms, collapsible 525-527 concrete 52 1-525 Forepoling, definition of 280 Fort Williams tunnel (Ontario), blast holes in face of 219 depth of blast holes in 235 drilling speed at 151 features of cars used at 169 system of lighting at 202 Fowler, tunneling machine, features of 185 France, early railway tunnels in 12, 14 Free Silver mine (Colo.), rushes of water in 317 Freiberg district (Germany), early use of pow'der in 12 Fuel consumption, influence of, on choice of power 74 Fuse, miner's, danger of lacing through cartridge 253 gases from burning of 257 handling of, precautions in 298, 299 method of lighting 254 rate of burning of 244-246 causes of variations in 246 selection of, importance of 300 storage of, precautions in 247, 299 Fuse igniter, description of 256 G Gas engines, producer, as sources of power 59 Gas, from explosives, danger of 303 harmful, precautions against 325 594 INDEX PAGE Gas, inflammable, at heading, method of burning 306 method of removing 309 See also Carbon dioxide. Carbon monoxide Gases, exhaust (automobiles) 457 Gas power, producer, selection of, conditions governing 76 Gas producer, as a source of power 53 description of principles of 60, 61 Gasoline engine, advantages of 53, 59 as sources of power 59 Gasoline locomotives, advantages of 176 cost of haulage by 177 for haulage, cost of, table showing 177 use of 59, 176, 177 Gelatin dynamite, See Dynamite Geology, study of essential in design 426 Germany, early railway tunnels in 14 Gold Links tunnel (Colo.), air pressures used at 103 blast holes in 219 depth of 235 cars used at, features of 169 direction of air current in 114 drilling speed at 151 features of 39 grade of dynamite used in 241 system of lighting used in 202 Grand Central sewer (N, Y.), blast holes used in face of 219 cars used in 169 features of 50 Grant's Hill tunnel (Pa.), mention of 14 Greeks, early tunnels driven by 6 Ground, heavy, defined 421 light, defined 42 1 prevention of movement 519-520 running 514 soft defined 42 1 treacherous defined 422 Gunnison tunnel (Colo.), air pressures used at 103 blast holes, in face of 219 depth of 169 cars used at, features of 169 cost of drill repairs at 153 cost of driving 331 depth of blast holes in 235 direction of air currents in 114 features of 39 grade of dynamite used in 241 quantity of dynamite used in 243 INDEX 595 Gunnison tunnel (Colo.), system of lighting 202 Gunpowder, early use in tunneling 11 "Guns," in blasting, definition of . 299 H Hacklebernie tunnel (Pa.), mention of 18 Handling cars in tunnels 263 Hard rock, bench drilling 494-495 disposal t 496 drill mounting, bar 490 column 490 travelling carriage 491 excavation, cost of 486-490 estimates for 489 excavation methods in 482-409 heading and bench kept close together 496 heading center 499-505 heading, size of 484-486 heading top or bottom 497-499 overbreakage 505 packing 508 rotary cutters T . . . 508 test drilling, advanced 509 typical drilling methods 493 Harecastle tunnel (England), mention of 13 Harz mines (Germany), early use of gunpowder in 12 Haulage, by gasoline locomotive, cost of, table showing cars for 163-169 data concerning, table giving 169 figure showing 164, 165, 166, 167, 168 cars, size of 471-473, 475 equipment 470-475 tipple 475 track, gage 471-472 maintenance of 473 motive power for, choice of 173-178 use of animals for 1 73 use of compressed-air locomotive for 173 use of electric motors for 173 Haulage accidents, causes of 309 precautions against 320, 323, 326 Hay, storage of, in tunnel, danger of 315 Heading, advantages of three shifts at 211 and bench kept close together 496 bottom 515 center 499-505 location 514 pioneer 499-505 596 INDEX Heading, railway tunnel, comparison with mining tunnel 24 size of 484-486 timbering for 283 top or bottom 497-499 wall plate 5i3, 5i6 Heat produced during air compression loi removal of 102 Heaters for thawing houses 259 Herrick, R.'L., on Los Angeles Aqueduct 284 Hicks, G. S., Jr., air transmission, formula of 119 Hindus, caves excavated by 6 Hole, See Blast hole Holes, direction of, in tunnel headings 221 number of, in tunnel headings 219 Hoosac tunnel (Mass.), details of . 25 progress and cost of 25 tunneling machines tried at 181 use of air drills at 25 Horizontal bar mounting for drills, method of using 213 Hose, supports for, advantages of 207 Hummingbird tunnel (Idaho), mucking machine at, figure showing 170 Hydraulic compressor, as source of power 55 Taylor, details of 56 figure showing . , 56 use of, at Mt. Cenis tunnel 55 Hydraulic drills, features of 138-141 merits of 1 56 Hydraulic power plant 563 Hydrocarbon gas, from rocks, burning of 306 in tunnels, dangers from 306 explosibility of 306 I Illumination, means of, at various tunnels, table showing. 202 Illumination of tunnels, See Lighting Impulse wheels, water, regulation of 98 India, early excavations in 6 Installation cost, influence of, on choice of power 66 Insulation of electric conductors, need of close inspection of 312 Intercooler, construction of 104 figure showing 104 need of 104 Interest on capital invested, charge for 77 Internal-combustion engines, as sources of power 59 efficiency of small sizes of 76, 76 Internal combustion engines, exhaust gases 457 INDEX 597 PAGE Intoxication, as cause of accidents 318 Iron, cast (lining) 439-444 Japanese tunnels, list of 33 Joker tunnel (Colo.), blast holes in, arrangement of 219 depth of 235 drilling speed at 151 features of 50 system of lighting 202 Joseph II Stollen, mention of 16 K Karns tunneling machine, features of 186 Kellogg tunnel (Idaho), features of 50 Kelty tunnel (Scotland) , features of 21 Labor required, influence of, on choice of power 74 Lagging, definition of 280 Lake Albanus (Italy), early drainage tunnel for 8 Lake Coxamarco (Peru), early drainage tunnel for 7 Lake Fucinus (Italy), early drainage tunnel for 8 Lamps, acetylene, merits of 204 electric, merits of 203 oil, open flame, use of 202 Laramie Poudre tunnel (Colo.), l)last holes in, arrangement of 219 depth of 235 order of 224 cars used in, features of 169 figure showing 166, 176 consumption of air by drills 83 cost of driving 332 direction of air current in 114 drilling speed at 151 exhauster used at 118 features of 40 grade of dynamite used in 241 lengths of shifts at 74 mounting of drills at 213 mucking, manner of 262 power plant, at water-supply for 66 pressure required for ventilation 120 quantity of explosives used in 243 speed of driving 233 system of lighting 202 598 INDEX PAGE Larium (Greece) tunnels, In silver mines of 7 Lausanne tunnel (Pa.), blast holes in, arrangement of 219 depth of 235 cars used at, features of 169 direction of air current in 114 dump used at 1 80 features of 40 grade of dynamite used in 241 system of lighting in 202 Leakage in compressed air pipe line, method of testing for 84 Lebanon tunnel (Pa.), mention of 13 Liberty tunnels, Pittsburg, Pa 533-542 Life of power plant, influence of, on choice of power 65 Lighting 457, 477, 478 Lighting of tunnels, method of 201 Lining, backing of 447 brick work 436 cast iron 439-444 cast steel 439 concrete, mass 436 concrete, precast 437 defined 422 earth pressures to be resisted 435 materials used 439 methods . 520-542 stone masonry 436 structural steel 444-447 timber 433 waterproofing, various methods 448-451 when required 432 wood 553 List of Japanese tunnels 33 of noted railway tunnels, table giving 32 of patents for tunneling machines 188-201 Loading blast-holes, precautions in 295 Loading equipment 468 . 470 Loading machines, figure showing 170, 172 types of 170-173 Loetschberg tunnel (Switzerland), carriage mounting for drills 214 details of 29 drills employed at '. . 29 number of muckers employed in 261 progress and cost of 25 quantity of explosives used 243 speed of mucking in 216, 263 Loose Rock, See soft ground Los Angeles Aqueduct (Calif.), air pressure used in 103 INDEX 599 PAGE Los Angeles Aqueduct (Calif.), blast holes in 219 carbon dioxide encountered in 305 cars used at 169 figure showing 167 cost of drill repairs at 154 cost of driving tunnels of 333-342 cost of electric power for 76 direction of air current in 114 drilling speed in 152 features of 41 grade of dynamite used in 241 lining of, thickness of 287 officials of, acknowledgment to 3 pressure of ventilation current 120 system of lighting 202 use of equipment in 66 Lucania tunnel (Colo.), air pressure used at 103 cars used at, features of 169 consumption of air by drills in 83 cost of drill repairs at 154 cost of driving 343 depth of blast holes in 235 direction of air current in 114 drilling speed in 151 features of 43 grade of dynamite used in 241 pressure of ventilation current 120 system of lighting 202 M Machinery for ventilation, selection of, factors determining 123 Malpas tunnel (France), mention of 12 Manager, suggestions to 319 Marshall-Russell tunnel (Colo.), air pressure used at 103 blast holes in, arrangement of 219 depth of 235 cars used in, features of 169 consumption of air by drills 83 cost of drill repairs at 154 cost of driving 344 direction of air current in 1 14 drilling speed at 151 features of 44 grade of dynamite used in 241 pressure of ventilation current 120 system of lighting 202 600 INDEX PAGE Masonry, brick and stone (lining) 436, 531-53 Mauch Chunk tunnel (Pa.), air pressure used at 102 Means of lighting at various tunnels, table showing 202 Metres for compressed air, usefulness of 121 Mine tunnels, features of 2 Miner, suggestions to 324 Misfires, causes of 299 precautions following 302, 325 Mission tunnel (Calif.), air pressure used at 103 blast holes in, depth of 235 cars used at, features of 169 consumption of air by drills in 83 cost of driving 345 direction of air current in 114 features of 44 grade of dynamite used in 241 pressure required for ventilation 120 speed of drilling 151 system of lighting 202 Moisture produced during air compression 105 Moodna Siphon, Catskill Aqueduct (N. Y.), features of 37 Motive power for tunnel haulage, choice of 173-178 Mount Cenis tunnel (France), progress and cost of 25 use of air drill at 25 use of hydraulic compressor at 55 Mount Royal tunnel (Canada), details of 51 Mountings for drills, adaptability of various types 217 amount of mucking required with 215 choice of 218 horizontal bar, method of using 213 vertical column, merits of 214 Muck, danger from explosives in 302 picking of, proper method of 302 Mucking, conditions afifecting speed of 260 importance of system in 262 number of men for 261 positions of men for ., 261 speed attainable in 216, 263 use of steel plates in 267 Mucking machine, figure showing 170 M Naples, Italy, Roman tunnel near 8 Needle beams 517 New York Board of Water Supply, acknowledgments to 3 Newhouse tunnel (Colo.), air pressure used at 103 INDEX 601 PAt.K Newhouse tunnel (Colo.), blast holes in, depth of 235 order of 219 cars used at, features of 169 direction of air current in 114 drilling speed at 151 dumping of cars at 179 features of 44 grade of dynamite used in 241 system of lighting 202 Nisqually tunnel (Wash.), air pressure used at 103 blast holes in, depth of 235 order of 219 cars used at, features of 169 direction of air current in 114 drilling speed at 151 grade of dynamite used in 241 power plant of, water-supply for 67 pressure of ventilating current 120 system of lighting 202 Nitrogen peroxide, deadliness of 304 Nitroglycerine, invention of 19 use of, in tunnels 19, 25 Nitroglycerine dynamite, gaseous products of 238 rating of strength of 239 Northwest tunnel (111.) blast holes in, depth of 23 order of 220 features of 51 Noted railway tunnels, table giving list of 32 Notre Dame tunnel (France), cost of 18 Number of holes in tunnel headings, table showing 219 O Oil engines, as sources of power 53 Ontario tunnel (Utah), features of 45 Ophelia tunnel (Colo.), blast holes in, depth of 235 order of 220 drilling speed at 151 features of 51 system of lighting 202 Outside line of tunnel not to be broken 431 Overbreakage 505 P Packing back of lining 505 Packing in hard rock 508 Patents for tunneling machines, list of 188-201 Pawpaw tunnel (Md.), mention of . 14 (302 INDEX PAGE Pelton wheel, figure showing 54 proper speed for 55 Peruvians, ancient mines and tunnels of 7 Pilot tube method 520 Pioneer heading 495-505 Pipe for ventilation, size of 121 Pipe lines, compressed air, leakage in, method of testing for 84 Plant 465-481, 558-564 Pneumatic placement of concrete 527 Positions of men for mucking 261 Powder headache, cause of 303 Powder smoke, removal of, air required for 117 Power, for tunneling, sources of 53 gas producer, selection of, conditions governing 76 most suitable, selection of 64, 65 sources of : 466-467 plant, cost of machinery for 66 depreciation of, charge for 77 fuel consumption of 74 labor requirements of 74 life of, influence of, on choice of power 65 most economical equipment for 65 producer gas for 69 steam, efficiency of 75 types of 53, 78-80 Power transmission, cost of 64, 70 electricity for 79 means of 64 Precast block lining 437, 531 Precoolers for air compressors, need of 106 Pressure of ventilating current . 1 18-120 formula for determining 119 ^, table showing 119 Pressure, loss of, in ventilating pipe 119 Pressures, earth 435 Primers, handling of 297 preparation of 301 proper place of, in charge 249 Producer gas, advantages of 64 transmission of, cost of pipe for 73 possible distance of 64 Producer-gas engines, as sources of power 59 use of in Thames River tunnel (England) 60 Producer-gas plant, selection of, conditions determining 79 thermal efficiency of 76 Producer-gas power, selection of, conditions governing 76 Progress of railway tunnels, table showing 25 INDEX ()0;i I'AtJE Pumping and drainage 451-455, 476 Purchased current, as source of power 76 Pyramid cut, figure showing 224 most effective arrangement of holes in 228 R Ragged Chutes (Ontario), hydrauHc compressor at 56 Railroad tunnels, definition 420 Railway tunnels, cost of 25 details of 32 early 14 noted, table giving list of 32 progress and cost of, table showing 25 Rand mine (So. Africa), large turbo-compressors at 94 Rawley tunnel (Colo.), air pressure used at 103 blast holes in, depth of 235 order of 220 cars used at, features of 169 consumption of air by drills in 83 cost of driving 347 drilling speed at 151 features of 45 grade of dynamite used in 241 handling of cars at 265 speed of mucking at 253 system of lighting at 202 ventilation current at 114, 118, 120 blast holes in, depth of 235 Raymond tunnel (Colo.), air pressures used at 103 order of 220 car used at, features of 169 direction of air current in 114 drilling speed at 151 grade of dynamite used in 241 system of lighting 202 Reasons for tunneling 425 Regulation of air compressors 97-100 of water wheels 98 Removal of heat produced during air compression 102 Retallack and Redfield tunneling machine, features of 186 Rix, E. A., on compressed-air calculations 81, 149 Rock-cutting tools, ancient 5 Rock drills, air, air consumption of 149 auxiliary valve for, merits of 156 merits of 147 piston type 149, 153 figure showing 132, 133, 135 604 INDEX PAGE Rock drills, air, valves for, merits of _ , 132-136 figures showing 131-136 valveless, features of 137 figure showing 137 carriage mounting for 214 choice of, factors determining 160 comparison of different types 147-160 early use of 18 electric, advantages of 157 durability of 1 59 features of 141 figure showing 143, 145, 146 power consumption of 159 electric, types of 158, 159 piston, advantages of 158 gasoline, disadvantages of 147 hammer type, advantages of 150 hydraulic, features of. 138, 157 figure showing 138 types of 138, 157 mounting of 212 selection of, factors influencing 160, 161 types of 130 comparison of 160 use of, in mine tunnels. See tunnels nam.ed in railway tunnels 25, 27, 28, 29 Rogers Pass tunnel 499~505 Roger's Pass tunnel (B. C), features cf 51 Romans, rock-cutting tools of 8 tunnels driven by 8 Rondout Siphon tunnel (N. Y.), air pressure used at 103 blast holes in, depth of 235 order of 220 cars used at, features of 169 direction of air current 114 drilling speed at 151 features of 36 grade of dynamite used in 241 power plant at, labor requirements of 74 quantity of explosives used in 243 use of central power station at 66 Roof, inspection of, need of care in 321 sound of, significance of 291 testing of, importance of 291 methods for 291, 324 Roosevelt tunnel (Colo.), air pressure used at 103 blast holes in, depth of 235 INDEX 605 I'AGli Roosevelt tunnel (Colo.), blast holes in, order of 220 car used at, features of 169 cost of driving 348 direction of air current in 114 features of 46 grade of dynamite used in 241 pressure of ventilating current at 120 system of lighting 202 Rotary tunneling machines 508 Rotschonberger Stollen (Germany), details of 16 S Saint Gothard tunnel (Switzerland), details of 26 progress and cost of 25 Samos (Greece), long mine tunnel at 7 Sapperton tunnel (England), mention of 13 Second Raton Hill tunnel (N. M.), features of 52 Selection of ventilating machinery, factors determining 123 Severn tunnel (England), details of 30 Sharpening machines, drill, types of 125 Shear zones, 'timbering for 280 Shepard's Pass tunnel (Calif.), features of 47 Shield for mine tunnels, use of 284 Shield, complete defined 431 driven iron lined tunnels, cost of 564-566 may be best method 517 roof 553-554 tunneling 545^554 Shock, electrical, danger from 311 Shoshone tunnel (Colo.), cost of 22 features of 21 Shovelers, space required by 260 use of steel plates for 267 Shovels, loading by power 469 Sigafoos tunneling machine, features of 187 Simplon tunnel (Switzerland), details of 28 flow of water in 28 hydraulic drill used at, features of 138 figure showing 138 progress and cost of 25 quantity of explosives used in 243 rock drill used at, features of 157 Single drill shift per day, merits of 209 Single versus double tunnels 429 Siwatch tunnel (Colo.), air pressure used at 103 blast holes in, arrangement of 220 depth of 235 606 -NDEX PAGE Siwatch tunnel (Colo.), car used at, features of 169 direction of air current in 114 drilling speed at 151 features of 47 grade of dynamite used in 241 pressure of ventilating current at 120 system of lighting 202 Size of tunnel cars 163 Size of ventilating pipe, formula for determining 121 table showing 122 Snake Creek tunnel (Utah), air pressure used at 103 blast holes in, depth of 235 order of 220 car used at, features of 169 concrete lining of, figure showing 288 consumption of air by drills in 83 direction of air current in 114 drilling speed at 151 features of 47 grade of dynamite used in 241 pressure of ventilating current • 120 system of lighting 202 Soft ground, American system 510-51 1 bottom heading 515 brick lining 531-532 cement gun 532-533 collapsible forms 525-527 concrete forms 521-525 excavation methods in 510-543 heading location 514 Liberty tunnels 533-542 cost of 542-543 lining methods 520-542 sequence of 521 main principle of tunneling in 422 movement of ground, prevention essential 519-520 needle beams 517 pilot tube method 520 pneumatic placement of concrete 527-531 precast block lining 531 running ground 514 shield may be best method 517 simplest instance 51 1-5 12 steel sets, advantages of 518 timbering, importance of careful work 516-517 wall plate headings 513, 516 Sommeiller, hydraulic compressor designed by 55 INDEX 607 PAGE Spain, ancient tunnels and mines in 9 ventilation of ancient tunnels in 10 Spiling, definition of 280 Spiral tunnels (B. C), blast holes in, depth of 235 order of 220 features of 52 Spitter, definition of 254 Steam engine, thermal efficiency of 75 types of 58 Steam power, selection of, conditions governing 76 Steam turbine, advantages of 58 efficiency of 58 features of 58 Steel plates, use of, in loading cars 264, 267 Steel sets, advantages of 518 Steel, cast (lining) 439 structural, lining 447 Stilwell tunnel (Colo.), air pressure used at 103 blast holes in, arrangement of 220 depth of 235 car used at, features of 169 cost of driving 352 direction of air current in 1 14 drilling speed at 151 features of . . . 47 grade of dynamite used in 241 system of lighting in 202 Stoping drills, features of 137 figure showing 137 Stone masonry lining 436 Storage battery locomotive, use of 174 Storing of explosives, proper method of 257 Strawberry tunnel (Utah), air pressure used at 103 blast holes in, arrangement of 220 depth of 235 car used at, features of 169 consumption of air by drills in 83 cost of drill repairs at 154 cost of driving 353-359 direction of air current in 114 drilling speed at 151 dumping of cars at 178 features of 48 grade of dynamite used in 241 pressure of ventilating current at 120 system of lighting 202 Subaqueous 544-567 608 INDEX PAGE Subaqueous, caisson method : 554-557 chief trunk line railway tunnels 544 cofferdam methods 557-558 compressed air — hours of work in 561 cross-section independent of span 544 plant 558-564 air locks 562 boilers 558 compressed air 559-56i electric 562-563 hydraulic power 563 miscellaneous plant 564 shields, tunneling 545-554 air pressure regulation 549 bracing face while shoving 553 compressed air first used 545 description of 547-548 doors 550 equipment 550-553 erector 552 excavating machinery 553 grouting 550 hydraulic pressure 552 inventor of 545 mud, work in 549 rams 551 rock, work in 550 roof 553-554 thrust bars for concrete lining 552 wood lining 553 trench type, cost of 566-567 Superintendent, suggestions to 319 ,Sutro tunnel (Nev.), features of 19 Swelling ground, timbering for 279 T Tailblock system, timbering for 281 Taillades tunnel (France), mention of 18 Talbot tunneling machine, mention of 181 Tamping, early use of, in tunneling 11 in tunnel work, merits of 252 proper amount of 252 proper method of .• ^ 297 reasons for using 252 Tamping bar, proper use of 297 Tappet valve rock drill, features of 132 merits of 1 55 INDEX ()09 PAGE Telephone, installation of " . . 205 type of, selection of 206 use of, reasons for 205 Temperatures, high, pro(iucecl during air compression, clangers of 101 Tenders, contract 458-460 Terry, Tench and Proctor, tunneling machine of, features of 185 Tequiquac tunnel (Mexico), details of 21 Terre-noir tunnel (France), mention of 14 Thawing of explosives, proper method of 258 Thaw houss, construction of 258 heating of 259 Thermal efficiency, influence of, on choice of power 75 Tiefe Georg StoUen (Germany), details of 15 Timber, for roof support, advantages of 270 preparation of 270 preservative treatment of 270-273 seasoned, advantages of 270 selection of 292 square versus round, choice of 271 Timbering, adequate importance of 292 American system 510-51 1 arrangement of, in tunnel 273-278 defined 42 1 delay in, danger of 292 foreign systems 461, 510 for wet tunnels, figure showing 275, 276 in soft ground; importance of careful work 516-517 materials for 270 necessity of bracing 423 needle beams 517 of heading, method of 283 of swelling ground, method o*" 279 swinging false set system of 282 tail-block system of 281 Timber lining 433 Tipple 475 Torches, danger in use of 314 Totley tunnel (England), details of 30 Track, haulage, gage 471-472 maintenance 473 Tramming, dangers in 309, 310 Transmission of power, means of 64 Transvaal, ventilation requirements in 115 Trench type, cost of 566-567 Trolley wires, danger from 311 Tsude Adit (Japan), mention of 33 Tunnel, definition of 2 610 INDEX PAGE Tunnel cars, data concerning, table giying 169 figure showing. . 164-168 types of 164-170 data, outline of (appendix) 577-582 Tunnel headings, direction of holes in 221 number of holes in, table showing 219 Tunneling machines, features of . . 181 patents for, list of 188-201 requirements of 184 types of 185-187 use of, in English Channel tunnel 183 Turbine-wheels, as sources of power 55 efficiency of 57 features of , 55 steam, efficiency of 58 features of ^ 58 Turbo-compressors, advantages of 109 effectiveness of 92 features of 91-93 figure showing 95 power required by 82 section through, figure showing 93 use of, for ventilation 112 U United States Reclamation Service, officials of, acknowledgments to 3 United States, early railway tunnels in 14 Unloaders for air compressors, use of 99 Utah Metals tunnel (Utah), air pressure used at 103 blast holes in, depth of 235 order of 220 car used at, features of 159 direction of air current in 114 drilling speed at 151 features of 48 grade of dynamite used in 241 power plant of, water supply for 66 pressure of ventilating current 120 system of lighting 202 V V-cut, arrangement of holes in 226 Valveless air drills, merits of 156 Valve, butterfly, figure showing ; 134 merits of 156 tappet, advantages of 155 INDEX 611 PAGE Ventilating current, air needed for 1 15, 1 16 arrangement of pipes for, figure showing 113 direction of, factors influencing 113 machinery for in pressure of 118, 119 size of pipe line for 121, 122 Ventilating machinery, selection of, factors determining 123 Ventilating pipe, capacity of, table showing 120 Ventilation 456, 476-477 of ancient tunnels 10 of tunnels, air required for 115, 116 Vertical column mounting for drills, merits of 214 Volumetric efficiency of air compressors 83 VV Wallkill Siphon tunnel (N. Y.), air pressure used at 103 blast holes in, depth of 235 order of 220 car used at, features of 169 direction of air current in 114 drilling speed at 151 grade of dynamite used in 241 quantity of explosives used in 243 Waterproofing cast-iron lining 442-444, 448-451 Water, rushes of, danger from 315 for fire protection, need of 314 Water power, selection of, conditions determining 78 Water wheels, cost of installation of 66 efficiency of 57 impulse type, regulation of 98 turbine type, details of 55 use of 55 Wedge cut, description of 221 figure showing 223 Welfare work in camps 481 Widest tunnel in the world 421 Wood lining 553 Woolwich tunnel (England), power plant of, fuel consumption of 75 use of gas-producers at 50 Y Yak tunnel (Colo,), air pressure at 103 blast holes in, depth of 235 order of 220 car used at, features of 169 cost of drill repairs at 153 612 INDEX PAGIE Yale tunnel (Colo.), direction of air current in 114 features of 48 grade of dynamite used in 241 pyramid cut in, figure showing 224 Yonkers Siphon tunnel (N. Y.), features of 38 Z Zinc chloride as timber preservative 271 %. ^A^ -c^^^, » '^.^ v*^ '^^ >*■ ^.-v