LIBRARY OF THE UNIVERSITY OF CALIFORNIA. Class LONGMANS' CIVIL ENGINEERING SERIES CIVIL ENGINEERING LONGMANS' CIVIL ENGINEERING SERIES NOTES ON DOCKS AND DOCK CONSTRUCTION. By C. COLSON, C.B., M.Inst.C.E., Deputy Civil Engineer-in-Chief, Loan Works, Admiralty. With 365 Illustrations. Medium 8vo, 2is. net. CALCULATIONS IN HYDRAULIC ENGINEERING: a Practical Text-Book for the Use of Students, Draughtsmen, and Engineers. By T. CLAXTON FIDLER, M.I.C.E., Professor of Engineering, University College, Dundee. Part I. Fluid Pressure, and the Calculation of its Effects in Engineering Structures. With numerous Illustrations and Examples. Medium 8vo, 6.r. 6d. net. Part II. Calculations in Hydro-Kinetics. With numerous Illustra- tions and Examples. Medium 8vo, Js. 6d. net. RAILWAY CONSTRUCTION. By W. H. MILLS, M.I.C.E., Engineer-in-Chief, Great Northern Railway of Ireland. With 516 Illustrations. Medium 8vo, i&r. net. PRINCIPLES AND PRACTICE OF HARBOUR CON- STRUCTION. By WILLIAM SHIELD, F.R.S.E., M.Inst.C.E., and Executive Engineer, National Harbour of Refuge, Peterhead, N.B. With 97 Illustrations. Medium 8vo, 15-r. net. CIVIL ENGINEERING AS APPLIED IN CON- STRUCTION. By LEVESON FRANCIS VERNON-HARCOURT, M.A., M.Inst.C.E. With 368 Illustrations. Second Edition, revised by HENRY FIDLER, M.Inst.C.E., F.G.S. Medium 8vo, i6s. net. SANITARY ENGINEERING WITH RESPECT TO WATER-SUPPLY AND SEWAGE DISPOSAL. By LEVESON FRANCIS VERNON-HARCOURT, M.A., M.Inst.C.E. With 287 Illustrations. Medium 8vo, 14*. net. TIDAL RIVERS : their (1) Hydraulics, (2) Improvement, (3) Navigation. By W. H. WHEELER, M.Inst.C.E. With 75 Illustrations. Medium 8vo, i6s. net. NOTES ON CONSTRUCTION IN MILD STEEL: Arranged for the Use of Junior Draughtsmen in the Architectural and Engineering Professions. By HENRY FIDLER, M.I.C.E., Author of the Article on "Dockyards" in the Encyclopedia Britannica, and Editor of "Notes on Building Construction." With Illustrations from Working Drawings, Diagrams, and Tables. Medium 8vo, i6s. net. LONGMANS, GREEN, AND CO. LONDON, NEW YORK, BOMBAY, AND CALCUTTA LONGMAN^ CIVIL ENGINEERING SERIES CIVIL ENGINEERING AS APPLIED IN CONSTRUCTION BY LEVESON FRANCIS yERNON-HARCOURT M.A., M.lNST.C.E. AUTHOR OF " SANITARY ENGINEERING," " RIVERS AND CANALS," " HARBOURS AND DOCKS," AND "ACHIEVEMENTS IN ENGINEERING" SECOND EDITION REVISED BY HENRY FIDLER M.lNST.C.E., F.G.S. AUTHOR OF THE ARTICLE ON "DOCKYARDS" IN THE "ENCYCLOPAEDIA BRITANNICA," AND "NOTES ON CONSTRUCTION IN MILD STEEL" WITH NUMEROUS ILLUSTRATIONS OF WORKS IN THE TEXT LONGMANS, GREEN, AND CO. 39 PATERNOSTER ROW, LONDON NEW YORK, BOMBAY, AND CALCUTTA 1910 All rights reserved PREFACE CIVIL engineering, even in its more restricted signification as applied to works of construction, covers such a wide range that it might reasonably appear somewhat presumptuous for any civil engineer to endeavour to deal with so far-reaching a subject, more especially within the limits of a single volume; and my sole excuse for making the attempt is that nearly ten years ago I unexpectedly received a request from Messrs. Longmans to undertake this onerous task. Possibly the publication of "Achievements in Engineering" in 1891, may have led to the request being addressed to me ; but that book, giving descriptions, in a popular form, of some of the most notable engineering works, and only touching incidentally upon the principles involved in their con- struction for the sake of engineering students, was totally different in scope to this book, which treats primarily of the principles involved in the various branches of engineering construction, and refers to a great variety of works chiefly with the view of illustrating the methods by which these principles receive their practical application. Descriptions of a few important engineering works, in popular language, are com- paratively easy of accomplishment; and the facility with which the earlier book was carried out, led me to underrate the difficulties and labour inseparable from the aims of the present book, which, had I appreciated them at the time, would probably have decided me to decline the proposal. Moreover, the leisure at my disposal proved much less than I had anticipated ; and, owing to the various professional demands on my time, the preparation of the book has, to my regret, been greatly delayed, so that at times I almost despaired of bringing it to a conclusion ; and it was only the courteous consideration accorded me by Messrs. Longmans, and their strongly expressed wish that I should not relinquish the undertaking, that have at last led to the com- pletion of the book according to the scheme originally laid down by me. The long delay, however, has not been devoid of some com- pensating advantages, for it has enabled me to summon to my aid an extended experience of various engineering works and the conditions for their application, gained in the interval, not merely in the course of my ordinary professional avocations in England and Ireland, but also on the Continent and in distant countries. Thus a professional visit to India afforded me the opportunity of passing through the Suez Canal, of inspecting Port Said Harbour, of spending several days on the river Hiigli and its estuary and viewing the inlet from the Ganges of its 222070 VI PREFACE. principal feeder, and of studying the changes the river has undergone by a comparison of the various charts. The British Association Meet- ing at Toronto, which I attended as a member of the Council, gave me an occasion for going up the St. Lawrence to Montreal, of seeing the various bridges across the Niagara Rapids below the Falls, and of traversing the Canadian Pacific Railway from Toronto to Vancouver, and back to Montreal. Attendances, also, at four International Navi- gation Congresses, with their accompanying visits to works, within the last ten years, in France, Holland, and Belgium, have enabled me to visit several of the principal navigation and maritime works in those countries, under the most favourable conditions, in company with the engineers in charge of the works, one congress alone, held in Paris, having led to visits to various inland navigation works, the weirs on the Lower Seine, the ports of Calais and Havre, the Furens Reser- voir Dam, the Lyons Cable Railway, the Mulatiere weir on the Saone, the regulation works along the Rhone from Lyons nearly to its outlet, the St. Louis Canal forming the navigable outlet from the Rhone, Marseilles Harbour, and the Marseilles Cliff Railway. A short visit to Chamonix and Switzerland enabled me to see the Chamonix Railway then in course of construction, and specimens of the Swiss rack and cable railways; whilst my duties in 1900, as the British Member of the International Jury for Civil Engineering at the Paris Exhibition, led to my receiving particulars about several large works in progress abroad, including the actual condition of the Panama Canal Works. The experience thus gained, and the knowledge thereby acquired, together with the information derived from earlier visits to works abroad, have enabled me to deal with many foreign works in the light of the results of personal observation and intercourse with foreign engineers. In the preparation of this book, besides utilizing the above sources of information, together with a varied professional practice which has extended over a period of thirty-six years, particulars have been gathered, especially as regards details of works, from the most reliable sources available ; and in this respect, I am specially indebted to the Proceedings of the Institution of Civil Engineers and the excellent technical library of that Institution. Every endeavour has been made to acknowledge in the notes the source from which any information or illustration may have been derived ; and in many instances, owing to the necessarily concise character of the descriptions or details of works, references have been given where fuller accounts or information can be found, more with the view of assisting the reader, than because any acknowledgment is due. On account of the number of subjects which have had to be dealt with, and the restricted space available, the descriptions or details of the works selected as examples have been limited to what is necessary for the elucidation of the subject under consideration, and indications of the practice followed in actual execution. The classification of a subject under various headings, has often led to a subdivision of the descriptions of works in illustration amongst the several headings to which their different parts relate, as specially PREFACE. Vll noticeable in the chapter' on " Ship-Canals " ; and this necessary sub- division has involved the preparation of a full index, so that details of any particular work, scattered over some pages in the book, may be collected together under the heading of the work in the index, with a concise indication of the purport of each reference. Moreover, by giving the purport, as well as the page of each reference in the index, the reader is saved the trouble of a wearisome search, possibly through several pages, before the required reference is found. Care also has been taken to draw the illustrations, as far as practicable, to simple fractional scales, easily comparable with each other, so that the relative sizes of different works may be readily per- ceived ; and where several illustrations are given of works of a similar class, such, for instance, as arched, suspension, girder, and cantilever bridges respectively, and cross sections of tunnels, movable weirs, canals, dock and quay walls, breakwaters, and masonry reservoir dams, the typical examples given of each class of works are grouped as much as possible together, and drawn to the same scale for greater facility of comparison, except where unusual divergencies of size, as in the cases of the Brooklyn and Forth bridges, precluded this arrangement. The numerous illustrations distributed throughout the book will, I trust, materially aid the elucidation of the principles involved, and add to the intelligibility and interest of the descriptions of works ; . and I desire to take this opportunity of acknowledging the care my assistant, Mr. Edward Blundell, has bestowed on the preparation of these illustrations, under my direction. I now venture to submit this book, the product of much time and thought spread over some yeats, to the generous consideration of my professional brethren, both British and foreign, with the earnest hope that, in spite of many deficiencies, of which no one can be more conscious than its author, it may prove of interest, and perhaps of some service to them, in view of the concise grouping together in a single volume of the various branches of constructive civil engineering, and their illustration by numerous references to works, and may also to some extent assist the progress of engineering science, and the advance of the profession to which all engineers are so proud to belong; and in that case, I shall feel that my time and labour have not been spent in vain. I trust, moreover, that the book may be of considerable value to engineering students, in directing their attention to the principles forming the basis of design and construction in civil engineering, and in indicating the different ways in which these principles have been applied to actual practice. The book also, I venture to hope, may prove of use to many persons who, though not engineers, are concerned in some way or other with engineering undertakings, and desire to gain some insight into engineering practice, or take an interest in engineering progress. L. F. VERNON-HARCOURT. 6, QUEEN ANNE'S GATE, WESTMINSTER, S.W., \2th December > 1901. PREFACE TO THE SECOND EDITION A NEW edition of this work having been called for since the decease of its distinguished Author, it has been necessary to determine to what extent revision of the text was desirable. The descriptions of engineering works which, at the date of the publication of the first edition, were in course of construction or in an early stage of initiation, were naturally subject to such revision as the progress of events had rendered necessary ; while it was evident that works of magnitude which, during the period which has elapsed since the issue of the first edition, have been commenced, and, for the most part, brought to a successful conclusion, must receive such brief notice as the scope of this work would permit. Subject to these considerations the Author's text has been, as far as possible, left intact, while on the other hand it is hoped that the attempt which has been made to include such examples as would best illustrate the progress of Civil Engineering within the last eight or ten years will not be without advantage to the student of construction. HENRY FIDLER. January, 1910. CONTENTS PART I. MATERIALS, PRELIMINARY WORKS, FOUNDATIONS, AND ROADS. CHAPTER PAGE I. INTRODUCTION 3 II. MATERIALS EMPLOYED IN CONSTRUCTION 9 III. PRELIMINARY ARRANGEMENTS FOR CARRYING OUT WORKS . 29 IV. EXCAVATIONS, DREDGING, PILE-DRIVING, AND COFFERDAMS . . 36 V. FOUNDATIONS, AND PIERS OF BRIDGES 61 VI. ROADS, AND STREET- PAVING Si PART II. RAILWAY, BRIDGE, AND TUNNEL ENGINEERING. VII. LAYING OUT AND FORMATION OF RAILWAYS 101 VIII. ARCHED BRIDGES 120 IX. SUSPENSION BRIDGES . . . 138 X. GIRDER BRIDGES 152 XI. CANTILEVER AND MOVABLE BRIDGES 172 XII. VIADUCTS AND TUNNELS 188 XIII. SUBAQUEOUS TUNNELS 214 XIV. METROPOLITAN RAILWAYS 227 XV. PERMANENT WAY; JUNCTIONS; AND STATIONS ..... 247 XVI. LIGHT RAILWAYS . 263 XVII. MOUNTAIN RAILWAYS 274 XVIII. CABLE RAILWAYS 289 XIX. TRAMWAYS 303 l CONTENTS. PART III. RIVER AND CANAL ENGINEERING, AND IRRIGATION WORKS. CHAPTER PAGE XX. CHARACTERISTICS, FLOODS, CONTROL, AND REGULATION OF RIVERS 3 2 7 XXI. CANALIZATION OF RIVERS 340 XXII. IMPROVEMENT OF RlVER OUTLETS OBSTRUCTED BY DRIFT, AND TlDELESS DELTAIC OUTLETS 360 XXIII. THE IMPROVEMENT OF TIDAL RIVERS AND ESTUARIES . . . 370 XXIV. INLAND NAVIGATION CANALS 386 XXV. SHIP-CANALS 403 XXVI. IRRIGATION WORKS 421 PART IV. DOCK WORKS; AND MARITIME ENGINEERING. XXVII. RIVER QUAYS, BASINS, AND DOCKS . . .441 XXVIII. DOCK ENTRANCES, AND LOCKS; AND GRAVING DOCKS . . . 457 XXIX. HARBOUR WORKS 471 XXX. LIGHTING COASTS AND CHANNELS 490 XXXI. LAND RECLAMATION ; AND COAST PROTECTION 501 PART V. SANITARY ENGINEERING. XXXII. SOURCES AND STORAGE OF WATER-SUPPLY 53 XXXIII. CONVEYANCE, PURIFICATION, AND DISTRIBUTION OF WATER- SUPPLY 532 XXXIV. SEWERAGE WORKS 546 XXXV. DISPOSAL OF SEWAGE 557 INDEX 569 LIST OF ILLUSTRATIONS FIG. PAGE 1. Bucket-ladder Excavator . 38 2. Steam-navvy 39 3. Cable-way 41 4. Cantilever Crane 41 5. Bag and Spoon 43 6. Bucket-ladder Dredger 44 7, 8. Grab Buckets Semicylindrical, Hemispherical 45 9. Hydraulic Grab Dredger 46 10. Sand-pump Dredger 47 11. Appliances for Suction Dredgers 48 12. Rock-blasting Diving-bell 50 13. Rock-breaking Rams 51 14. Long Shoot for discharging Dredgings 52 15. Pile-engine 55 1 6. Nasmyth's Pile-driver 56 17. Steam Pile-driver 56 18. Cofferdam 59 19. Gatmell's "Jham" Grab '...'. 65 20. Well-foundations 65 21. Foundation of Fascines 67 22. Cylindrical Foundations 67 23. Brick Well for Pier 67 24. Screw-pile 68 25. Disc Piles . 69 26, 27. Cylindrical Bridge Piers 70 28. Cylinders for Pier 71 29, 30. Caisson for Pier 72 31. Compressed-air Foundations 75 32. Well-sinking by Compressed Air 77 33. Loops and Spirals 106 34. Loops and Switchbacks 108 35. Setting out a Railway Curve 109 36. Tangential Angle 109 37. Earthwork on Side-lying Ground in 38. Railway Cutting and Embankment 113 39. Slip in Railway Cutting 116 40. Culvert under Embankment 118 41. Pressures on Arch 123 42. Diagrams of Loaded Suspension Cables and Arch 124 Xll LIST OF ILLUSTRATIONS. FIG. P AGE 43. Bridge under Railway 125 44. Bridge across Railway Cutting 126 45. Bridge in Rock Cutting 126 46. Skew Arch, showing Lines of Courses 127 47. Large Masonry Arched Bridge 128 48. Centering for Erection of Large Masonry Arch 129 49. Distribution of Pressures in Arch 130 50-54. Arched Bridges : St. Louis, Garabit, Stony Creek, Salmon River, Niagara River 132 55. Metal Arched Bridge with Double Roadway 134 56. Steel Arched Bridge of Large Span 134 57. Building out Steel Arches from Piers 136 58. Erection of High Arch from Springings . . 136 59. Building out Large Arch from Abutments 137 60-64. Suspension Bridges: Clifton, Albert, Francis -Joseph, Pittsburg Point, Brooklyn . 141 65. Suspension Bridge with Auxiliary Cables 143 66. Cross Section of Brooklyn Bridge 145 67. Diagram of Bending Moments .153 68. Stresses in Warren Girder 156 69-72. Cross Sections of Girder Bridges . . 158 73-78. Girder Bridges : Saltash, Ribinsk, Kuilenberg, Cincinnati Southern Railway, Covington and Cincinnati, Lachine 160 79. Scaffolding for erecting Girders 165 50. Temporary Girders for Erection of Bridges 166 81. Floating out Girders 166 82. Floating out Girder . 167 83. Bending Moments of Continuous Girder 168 84. Erection by rolling out 1 70 85. Rolling out Continuous Girders 170 86-88. Diagrams of Stresses on Cantilever 173 89-94. Cantilever Bridges : Forth, Poughkeepsie, Memphis, Niagara, Sukkur, Hugli Jubilee 175 95. Continuous Girder converted into Cantilever 176 96. Building out Cantilevers 177 97. Swing Bridge in Two Halves 182 98. Swing Bridge across Two Equal Spans 183 99. Counterpoised Swing Bridge 183 100. Traversing Bridge 184 101. Bascule Bridge in Two Halves 185 102. Lift Bridge 186 103,104. Viaducts: Esk, Pecos 19 105-107. Heading, Timbering, and Lining for Tunnels : Bletchingley, Ampt- hill, Hoosac 19-1, 195 108. Central Core with Timbering 197 109. Austrian System of Timbering I9 8 110-112. Rafter Timbering, Block Arching, Arched Framing, for Tunnels . 198 113. Iron Frames for Construction of Tunnels 199 114-119. Cross Sections of Tunnels: Sydenham, Arlberg, Mont Cenis, St. Gothard 202 LIST OF ILLUSTRATIONS. Xlll FIG. PAGE 120,121. Simplon Tunnel, Cross Sections 209 122-129. Subaqueous Tunnels : Severn, Mersey, Blackwall 216 130-132. Covered Way, London Metropolitan Railway 229 133. Underpinning Houses, Metropolitan Railway 230 134, 135. Retaining Walls, Metropolitan Railway 230 136. Tubular Tunnel with Cast-iron Lining 233 137. Brick Air-lock 234 138. Covered Way, Paris Metropolitan Railway 235 139, 140. Covered Way, Tunnel, and Station, Glasgow District Railway . 237 141. Overhead Railway on Brick Viaduct 239 142-144. Elevated Railways : New York and Brooklyn 240,241 145-147. Overhead Railway, Liverpool 243 148. Overhead Railway, Berlin 244 149. Longitudinal Sleepers and Bridge Rails 250 150. Metal Bed-plate under Flange Rail 251 151, 152. Cast-iron Pot Sleepers 252 153-155. Steel Sleepers 254 156. Flange Rail with Fastenings 255 157. Bull-headed Rail with Chair 255 158-160. Fish-plates 257 161. Single-line Railway Junction 259 162. Double-line Railway Junction 260 163. Branch Line carried under Main Lines 260 164. Cross-over Road 262 165. Mono-rail Railway 269 1 66. Suspended Mono-rail Railway 271 167. Central Rail, Fell System .276 168. Ladder-rack 278 169. Double Side-rack and Train 279 170. Telfener Rack .281 171. Strub Rack 282 172. Abt Triple Rack .283 173-175. Territet-Glion Cable Railway 2 p 2 , 293 176. Clifton Cliff Cable Railway .299 177-180. Tramway Rails and Tracks: American and British Rails; Des Moines, New Orleans, Toronto, and New York Tracks . . . 305 181. Tramway Passing-place , 309 182-184. Cable Tramways : Edinburgh, Paris 311 185-187. Electric Overhead-wire Tramways 315, 316 1 88, 189. Electric Underground Cable and Connector 317 190. Seashore Railway 322 191. Suspended Travelling Car 323 192. Embanking River for preventing Inundations 333 193. Winding River Channel : 335 r 94> 1 9S- Ri ver Regulation Works 337 196. Modification of Water-level of River by submerged Dykes . . . 338 197, 198. Canalization of Rivers 341 199. Double Lock on River 343 200,201. Oblique Weir 345 202, 203. Angular Weir 345 XIV LIST OF ILLUSTRATIONS. FIG. *" AGB 204-206. Draw-door Weir 347 207-209. Movable Frame Weirs 350 210. Suspended Frame Weir with Bridge 352 211. Bear-trap Weir 354 212. Movable Shutter Weir 354 213. Drum Weir .... 357 214. River Outlet diverted by Drift 362 215-217. Straight Cut with Jetty Outlet 362 218. Deltaic Outlets of Tideless River 364 219-221. Jetties at Deltaic Outlet 368 222. Simultaneous Tidal Lines 372 223, 224. Effect of Sharp Bends in Tidal Rivers 375 225-227. Regulation and Protection of Outlet 377 228-230. Regulation and Training Works 378 231-233. Training Works in a Sandy Estuary 382 234-236. Training Works through a Sandy Estuary 383 237-240. Inland Navigation Canals, Cross Sections : Canal du Centre, Dort- mund-Ems, Merwede, Soulanges 389 241, 242. Canal Lock with Large Lift 391 243. Barge on Cradle 396 244. Barge in Caisson 30,7 245. Hydraulic Canal Lift . 390, 246. Floating Canal Lift 401 247-253. Ship-canals, Cross Sections : Terneuzen, Manchester, Baltic, Amster- dam, Panama, Corinth, Bruges 404 254. Sand-dam on Baltic Canal 406 255-260. Suez Canal, Plans and Sections 409 261. Amsterdam Canal, Plan 410 262. Panama Canal, Longitudinal Section . . . . . . . . .411 263. Manchester Canal, Longitudinal Section 412 264, 265. Holtenau Locks, Baltic Canal 413 266-268. Entrance Lock, Bruges Canal 414 269, 270. Barton Locks, Manchester Canal 415 271,272. Irrigation Reservoir Dams : Periyar, Assuan ....... 424 273. Diagram of Discharges of River Nile at Assuan 426 274. Irrigation Canals of India, Map 430 275. River Weir for Irrigation Canals 434 276. Movable Shutter with Hydraulic Brake 435 277. Irrigation Weir at Head of Delta 436 278, 279. River Quay Walls : Antwerp, Rouen . 443 280-282. River and Maritime Quay Walls : Dublin, Marseilles, Mormugao . 444 283. Basins on Seacoast 445 284. River Quays and Basins 447 285. Arrangement of Docks at a Coaling Port 448 286. Protected Approach to Port on Seacoast 449 287. Entrances, Half-tide Basin, and Branch Docks 450 288,289. Main and Branch Docks 451 290. Port with Jetty Entrance 452 291-293. Dock Walls : Liverpool, Barry, Havre 455 294. Dock Entrance 459 LIST OF ILLUSTRATIONS. XV 295. Entrance Lock to Docks 460 296-298. Dock -gates, Sections : Hull, London, Havre 464 299. Rolling Caisson 467 300-303. Graving Dock, and Ship-caisson 468 304-307. Harbours, Plans : Plymouth, Colombo, Madras, Zeebrugge . . . 474 308-315. Breakwaters, Cross Sections: Plymouth, Alexandria, Marseilles, Civita Vecchia, Colombo, Newhaven, Dover, Zeebrugge . . . 480 316. Revolving Titan laying Sloping Blocks 483 317. Revolving Titan laying Horizontal Blocks 488 318-321. Rock Lighthouses : Eddystone, Bishop Rock 491 322. Lighthouse Lenses 495 323. Screw-pile Lighthouse 497 324. Cement and Concrete Beacon 498 325. Light-ship "Snouw" 499 326, 327. Light-giving Buoys 500 328, 329. Reclamation Embankments in Estuaries 503 33> 33 ! Reclamation Embankments on Seacoasts 504 332-334. Groynes 507 335-339. Sea Banks and Walls : Ostend, Hove, Margate, Scarborough . . 509 340. Reservoir Embankment with Puddle Wall 523 341. Reservoir Embankment with Masonry Wall 524 342. Reservoir Embankment with Selected Material 525 343. Diagram of Pressures in Masonry Dam 526 344. Form of High Masonry Dam 528 345, 346. Masonry Dams : New Croton, Vyrnwy 529 347,348. Lines of Aqueducts, Thirlmere, Vyrnwy ., 535 349-352. Sections of Aqueducts, Thirlmere, Elan, Lock Katrine, New Croton 536 353-356. Branch and Main Sewers 548 357> 358. Outfall Sewers : London, Paris 550 359-364. Paris Outfall Sewers 552 365. Hydro-pneumatic Ejector 555 366. Settling and Precipitating Tank 563 367. Cylindrical Precipitating Tank 564 368. Circular Precipitating Tank with Chambers 564 LIST OF TABLES Cost of Railways of different Gauges under specified Conditions of Country traversed 264 Gauges of Railways in the United Kingdom, with their respective Lengths . . 269 Extent and recent Increase of Railways in the different Quarters of the World . 273 Lengths of Tramways in the United States and Canada, worked with different Methods of Traction 320 PART I. MATERIALS, PRELIMINARY WORKS, FOUNDATIONS, AND ROADS. CHAPTER I. INTRODUCTION. Objects of civil engineering Scope of the book Relation of civil engineering to science Mathematics as applied to civil engineering Physics as applied to civil engineering Chemistry in relation to civil engineering Geology in relation to civil engineering Meteorology in relation to civil engineering Remarks on the scientific requirements of civil engineers. CIVIL engineering was defined by Thomas Tredgold, in 1828, as "the art of directing the great sources of power in nature for the use and convenience of man." The epithet civil has been applied to this great science of construction in order to distinguish it from military engineer- ing, to which its main objects present a very striking contrast. Military engineering, indeed, is concerned with provisions for the attack and defence of fortresses, and the defeat of opposing armies ; whereas civil engineering is directed to the extension of the means of communication and commerce, and to the promotion of the well-being and prosperity of mankind. The civil engineer, by extending railways through undeveloped or barbarous countries, becomes the pioneer of progress and civilization ; and he is largely instrumental in developing the intercourse and trade of communities and nations, by improving rivers, and constructing roads, railways, canals, harbours, and docks. Moreover, the civil engineer, by carrying out irrigation works in hot, dry countries, converts arid regions into fertile plains, thereby greatly increasing the productiveness of these districts, and averting the famines resulting from a deficiency in rainfall. Furthermore, by providing an ample supply of good water, and efficient sanitary arrangements, he is enabled to preserve from ravaging epidemics and untimely death the vast populations which, in recent years, have been crowding more and more into cities and towns. Scope of the Book. Civil engineering, in its widest signification, comprises a great range of subjects, embracing not merely works for developing means of communication, for facilitating sea-going trade, and for securing water-supplies and efficient drainage for towns, but also mining and metallurgy ; the lighting of towns with gas and electricity ; telegraphic and telephonic inter-communication; the construction of 2 4 CIVIL ENGINEERING BASED ON SCIENCE. steam-engines, other forms of motors, and machinery of all kinds ; ship-, building, including ironclads and swift cruisers; and the manufacture of heavy ordnance, projectiles, and torpedoes. Such a great variety of subjects, however, could not be properly dealt with by a single author, or condensed into a single book. Moreover, the vast and increasing development of engineering science, and its numerous ramifications have necessarily led to the subdivision of engineering into different branches, such as mechanical engineering, mining engineering, electrical engineering, and naval architecture, as well as civil engineering, which is more and more being employed to denote the special constructive branch of engineering as distinguished from the other four. It is, accordingly, proposed to deal in this book with civil engineering in its modern, restricted sense; and even in this limited application of the term, it comprises some distinct branches which are often regarded as more or less subdivisions of the science, such as railway, canal, river, maritime, hydraulic, and sanitary engineering, though much less distinctly separated from one another than the five branches of engineering enumerated above. Relation of Civil Engineering to Science. In order to be able to direct rightly the forces of nature for the benefit of mankind, it is essential to possess some knowledge of the principles of these forces, which have been long studied by scientific workers, the recorded results of whose labours are termed " natural science." Civil engineer- ing is, accordingly, based primarily upon natural science ; and it may, indeed, be regarded as the practical application of the discoveries of science for industrial purposes and the general well-being of the human race. It is evident, therefore, that a scientific education should constitute an indispensable part of the preliminary training of every person who aspires to embrace the profession of a civil engineer. Some branches of science, however, are more intimately connected with the problems involved in civil engineering than others ; and their relative importance depends upon the special branch of the subject to which a civil engineer may have occasion to devote his attention. Mathematics, physics, chemistry, geology, and meteorology find practical applications in the designs and works of civil engineers ; and a knowledge of the general principles of some of these sciences is an invaluable assistance in the succcessful practice of civil engineering. 1 The aims, however, and the requisite knowledge of the man of science, and of the civil engineer, are essentially different. The man of science generally devotes himself to the minute investigation of some special branch of one of these sciences, with which long study has rendered him intimately familiar. The civil engineer, on the contrary, merely needs an adequate general acquaintance with these sciences to be enabled to select those portions of the discoveries of the great body of scientific investigators, which are capable of useful application to the requirements of his pro- fession. 1 Report of the British Association, 1895, Ipswich Meeting, President's Address to the Mechanical Science Section, pp. 782-788. CIVIL ENGINEERING AND MATHEMATICS. 5 Mathematics as applied to Civil Engineering. Trigonometry constitutes the basis of surveying and tacheometry, which are employed for the preliminary examination of sites before works are undertaken ; and it is also made use of in setting out the lines of works about to be carried out. Logarithms, moreover, are useful in simplifying the calculations required in triangulation, and the ranging of railway curves. Statics supply the groundwork for the design of bridges and other structures, by determining the direction and amount of the strains at different parts of the structure, which would result from the loads liable to be imposed on the structures after their erection. Graphic statics, however, in which the strains are represented in magnitude and direction by lines on a diagram, have to a great extent advantageously superseded analytical methods. Hydrostatics serve for the calculation of the pressures to which reservoir dams, lock-gates, and weirs are exposed when supporting given heads of water ; and hydrodynamics deal with the general laws of fluid motion, which, however, require to be sup- plemented by experiment in order to determine with accuracy the flow of water in pipes and open channels, points of great importance in hydraulic engineering. Geometrical optics are utilized in determining the forms to be given to the lenses for concentrating the rays of the lamps of a lighthouse into a single beam of parallel rays, directed to the required quarter of the sea for giving due warning to vessels. Astronomical observations have also been employed to enable surveyors to determine directions when traversing unexplored regions. Mathematics, indeed, enter so largely into the solution of problems presented in the various branches of civil engineering, that no engineer would be justified in dispensing with their aid. Physics as applied to Civil Engineering. The researches of physics have such an intimate connection with civil engineering, that they in reality occupy as important a position in relation to it as mathematics. The physical properties of matter, indeed, cannot be disregarded by the civil engineer. He has to provide, in his designs of large structures, for expansion by heat and contraction by cold. The feasibility of constructing long tunnels under high mountains, depends upon the heat which is liable to be encountered at great depths below the surface ; whilst the adoption of compressed air in the advanced headings of such tunnels has greatly facilitated their con- struction, by serving to drive the perforators for drilling holes in the hard rock, and by the improved ventilation from the supply of air thereby afforded. Compressed air has also been employed for many years past in executing subaqueous foundations with the same security as on dry land ; and this system has been more recently applied to the driving of tubular tunnels through water-bearing strata. Congelation of the soil is another process which has been used for sinking wells through soils charged with water and running sand. The properties of light as regards its visibility at considerable distances, and the relative penetration of different kinds of light through 6 CIVIL ENGINEERING AND CHEMISTRY. fog, have to be considered by the civil engineer with reference to light- - house illumination ; and investigations in acoustics have to be made for determining the best kind of sonorous signal for giving warning of danger in foggy weather. A just appreciation, indeed, of general physical considerations, in relation to civil engineering, appears to be indispensable for the satisfactory prosecution of large under- takings. Chemistry in Relation to Civil Engineering. The chemical constitution of various materials employed in construction by civil engineers, furnishes in some instances important evidence as to their soundness. The elements of arsenic, silicon, sulphur, phosphorus, and manganese in iron and steel each exert an important influence on the strength and other qualities of the metal, while the percentage of carbon largely determines the quality and grade of the material. The strength and durability of mortar and concrete depend greatly upon the chemical composition of the lime or cement with which they are made, more especially when employed in structures in the sea. The powerful explosives, also, used in carrying tunnels through hard rock, and in blasting rocky shoals under water, are chemical compounds, and are comparatively recent discoveries as compared with gun- powder. Chemical processes have been employed in the numerous efforts to utilize sewage economically for agricultural purposes; and chemical analysis has to be resorted to for determining to what extent the effluent water, from land irrigated with sewage, has been rendered innocuous. Recourse, moreover, is had to chemical analysis for deciding as to the adequate purity of any proposed source of supply, and in the periodical testing of the state and due filtration of the potable waters supplied to towns. Geology in Relation to Civil Engineering. The nature of the ground to be excavated in ordinary cuttings for railways or canals, is generally adequately indicated by borings or trial pits; but where the cuttings to be executed are very deep and extensive, and rock or treacherous strata are liable to be met with at some depth below the surface, as happens occasionally in railway works, and more commonly in the construction of large ship-canals, some knowledge of the general geology of the district is valuable. Such knowledge becomes of much greater importance in driving long tunnels at a considerable depth below the surface, where the difficulties to be encountered, the possible influx of large volumes of water during construction, and the cost and period required for the work greatly depend upon the nature and dip of the strata to be traversed. Geological considerations are also important in judging as to the impermeability of a site proposed for a reservoir, and the adequate stability of the foundation for a reservoir dam ; and indications of the thickness of water-bearing strata, their depth below the surface, their dip, and the extent and position of their outcrop, as well as the prospect of fissures,, and the possibility of faults, are of the utmost importance in determining the position where a deep well for water-supply should be sunk, the depth to which it would CIVIL ENGINEERING AND METEOROLOGY. J require to be carried, and the probability of obtaining a suitable supply of water. Meteorology in Relation to Civil Engineering. Gales exert a considerable pressure against high walls, bridges, and roofs; and therefore a knowledge of the maximum force of the wind in different localities is important in designing structures, so as to ensure their stability during exceptional storms. The maritime engineer has to ascertain the direction and prevalence of the strongest gales to which his works on the sea-coast are liable to be exposed, so as to provide shelter from the worst quarters by works of requisite stability ; and he should also know the general direction and average force of the wind at different periods of the year, in order to select the calmest period of the year for the prosecution of his works. In localities visited periodically by cyclones or earthquakes, special precautions have to be adopted to prevent the structures erected from succumbing to these calamitous visitations. Observations of the amount and distribution of rainfall are very valuable for hydraulic engineers, to enable them to determine the minimum flow available in rivers for navigation or irrigation in the summer or the dry season, and the maximum discharge for which an adequate channel has to be provided to prevent inundations. The varying influences of evaporation and percolation in reducing the actual amount of rainfall available, and the equalizing effect of forests and vegetation on the flow of mountain streams, are of considerable interest to engineers concerned in water-supply and river works ; and meteoro- logical considerations are essential for forming a reliable estimate of the average amount of water that can be collected for distribution from a given catchment area. Remarks on the Scientific Requirements of Civil En- gineers. The foregoing observations indicate that engineers have numerous opportunities for utilizing the researches of science in the practice of their profession, and show how intimately science is bound up with civil engineering, which is its practical exponent. It is, more- over, evident that a fair knowledge of mathematics and pbysics, in their practical aspects, should constitute a recognized necessary portion of the professional equipment of every civil engineer ; whilst some acquaintance with chemistry, geology, and meteorology is desirable, and in some branches essential, for the intelligent and systematic carrying out of civil engineering works. An engineer cannot devote sufficient time to become very proficient in one or more of the sciences enumerated, except under exceptionally favourable conditions in his preliminary education ; but a general scientific training furnishes the most valuable preparation for a profession which deals with the practical applications of science ; and, other conditions being equal, those civil engineers will be the best qualified for the successful pursuit of their profession, and the advancement of the science of civil engineering, who have been most thoroughly trained in the principles of science, and have become imbued with scientific methods of observation and inquiry. In com- plicated or abstruse cases, a civil engineer should necessarily seek 8 CIVIL ENGINEERING AND SCIENCE. the assistance of a scientific expert ; but it is necessary that he should understand the principles of the particular science involved, in order to appreciate properly the views of his adviser ; and an engineer will be less liable to errors, and better able to utilize . fully the results of scientific investigations, in proportion as he has a clear insight into the principles of the sciences which he is called upon to apply for the benefit of mankind. CHAPTER II. MATERIALS EMPLOYED IN CONSTRUCTION. Choice of materials Materials used in works Standardization Timber: nature, protection, uses, strength of various kinds Fascines : uses, construction, mattresses Building-stone : principal kinds ; from primi- tive rocks, special uses ; sandstones, nature and uses ; limestones, forms and qualities; strength of different kinds Bricks : conditions of use and advantages, composition and manufacture, form and qualities, strength Limes: ordinary, sources and uses; hydraulic, composition and advantages Cements : natural, sources ; artificial, introduction ; slag cement, composition ; Portland cement, composition, fineness, strength, tests Mortars : proportions of ingredients, manufacture, strength, remarks Concrete: importance, composition, proportions in blocks, bags, and mass ; forms and uses, mixing and depositing, advantages of, in mass, effect of sea-water Iron and Steel : differences in composition ; cast iron, uses and strength, disadvantages ; wrought iron, uses and advantages ; steel, manufacture, advantages, strength, uses Safe Strains on Materials : limit of elasticity ; dead and moving loads ; stresses allowed on structures ; wind-pressure and snow. THE duty of a civil engineer is to carry out the works entrusted to him with the most suitable materials, and in as economical a manner as practicable, consistently with efficiency and stability. The materials employed should therefore depend, not merely on the nature of the work, but also on the conditions of the site, and the materials most readily available in the locality. Materials used in Works. The materials commonly employed by civil engineers are timber, fascines, stone, bricks, lime, cement, mortar, concrete, iron, and steel, as well as various substances in their natural condition, such as sand, gravel, shingle, rubble stone of different kinds, chalk, and clay. In some cases, inspection by an experienced person is sufficient to determine whether the materials are suitable for the particular purpose. Mechanical tests, however, and in some instances chemical tests also, are required to secure that materials employed in construction are up to the required standard of strength and durability, as in the case of cement, iron, and steel ; whilst where high pressures are liable to be reached, and the slightest failure might lead to disastrous results, as for instance in high reservoir dams, the stone, bricks, mortar, and concrete have to be subjected to tests. The important question of the standardization of the tests of materials employed in Engineering Construction has received much attention in recent years, and the student will do well to carefully study the reports and specifications issued and revised from time to time by the Engineer- ing Standards Committee, more especially those dealing with Portland 10 TIMBER EMPLOYED IN CONSTRUCTION. Cement, Structural Steel, Railway and Tramway Rails, the Properties of British Standard Sections, Test Pieces, Nuts and Bolt Heads, etc. TIMBER. The timber usually employed in permanent, as well as temporary, works is fir, obtained from the large forests of Northern Europe and America, as it is generally the cheapest wood of adequate size, and is more easily worked than hard wood. Where, however, hard-wood trees abound, or in positions where the timber is specially exposed to wear and tear, or to other sources of injury or decay, hard woods are adopted. Thus fenders put along jetties, piers, and quays, against which vessels rub, and the wedges used for fixing rails in chairs, are made of hard wood; and greenheart, from British Guiana, has been extensively employed for dock-gates and jetties exposed to the ravages of the teredo, which is found in salt water, and soon honeycombs most sorts of timber when immersed in sea-water. Nature of Timber. Timber should be compact, free from cracks, shakes, hollows, knots, and other defects, and should be procured from trees cut down in their prime, and at the period of the year when most devoid of sap. Most varieties of timber, and particularly soft woods, tend gradually to decay when exposed to the weather, more especially in positions where they are alternately wet and dry, as at the surface of the ground or when standing in water varying in level ; whereas timber buried in the ground, or always under water, remains sound for a long period. Sap in timber is liable to cause decay by its decomposition ; and the seasoning of timber by the removal of its moisture, can be effected either naturally by long exposure to a current of air under shelter, or artificially by subjecting it to a current of hot air. Teak, oak, greenheart, ironbark, and jarrah are some of the most durable and strongest woods ; whilst larch and pitch pine, though decidedly less durable and less strong, are superior in these respects to red pine and spruce, but more difficult to work. Protection of Timber. Timber must be thoroughly dried before being protected externally by paint or tar, otherwise the imprisoned moisture rots the wood. A more effective method, however, of pro- tecting timber exposed to the weather or damp, consists in thoroughly filling up the pores of the wood with some preservative liquid, such as creosote, mercuric or zinc chloride, or copper sulphate, thereby pre- cluding the entrance of moisture. Zinc chloride or copper sulphate is sometimes injected on the spot into recently felled trees, thus expelling the sap directly ; but by the ordinary process, the liquid is forced under pressure into the seasoned timber, for which purpose creosote is very extensively employed. Uses of Timber. Timber is largely used for jetties, landing- places, floors, roofs, and sleepers, and also for bridges and viaducts where economy is a paramount consideration, as in the extension of railways through undeveloped countries where wood is abundant ; but though numerous timber bridges were erected in the first instance on USES OF TIMBER AND FASCINES. II the Great Western Railway, timber is only now used for such structures under exceptional conditions. Owing, also, to the attacks of the white ant, wood has been abandoned for sleepers in some tropical countries. Moreover, though greenheart is found to resist successfully the attacks of the teredo in temperate seas, it is liable to be injured by them in tropical waters, as, for instance, in the River Hugli at Calcutta; and the immunity of jarrah under such conditions, which has been suggested as a substitute, has not been proved. In France, wooden dock-gates, exposed to sea-water, have been protected by studding them all over with large-headed nails. Strength of Timber. Timber possesses about double the strength in tension that it has in compression ; and most of the Australian hard woods are about twice as strong in tension as red pine and spruce, the former possessing an average tensile strength of over 9 tons per square inch, and the latter about 4^ tons. 1 The strength of timber in com- pression, being less than in tension, and influenced by the length of the specimen, is an important factor in timber construction, together with the transverse and shearing resistances. The crushing strength of white pine is between J ton and i ton per square inch; of Danzig fir and yellow pine, f ton to 2 tons; of P^nglish oak, ij tons; of pitch pine, about 2 tons; of Norway spruce, nearly 2\ tons; of Oregon pine, nearly 3 tons ; of Australian hard woods, from 2 to 4 tons ; 2 and of greenheart, about 4 tons per square inch. The shearing strength along the fibres has been found to range, in American timbers, from between 253 and 374 Ibs. per square inch for spruce, up to between 726 and 999 Ibs. for red oak; and in Australian timbers, from between 700 and 1400 Ibs. per square inch for gum, up to between noo and 1400 Ibs. for ironbark. The coefficient of the bending strength, or modulus of rupture of timber beams, is about 2 tons per square inch for Danzig fir, Baltic red pine, and American spruce and white pine ; 3 tons per square inch for Swedish and Russian pine, and American yellow pine; about 4j tons for English oak ; and it ranges, in the hard woods of Australia, from about 3 tons for the red gum of Victoria, up to 8 tons per square inch for ironbark and 9 tons in the salmon gum of West Australia. 3 FASCINES. Uses of Fascines. When a road or railway has to be carried across a soft marsh or a bog, or when protection works, training works, or dams have to be carried out in rivers at places where stone is difficult to procure, faggots of wood or fascines are employed. For instance, the Liverpool and Manchester Railway was carried across Chat Moss by laying a number of bundles of brushwood across the bog along the line of the railway, which served to support the railway in crossing the soft marshy ground ; 4 and fascines are extensively used in river works in Holland and the United States. 1 " Engineering Construction in Steel and Timber," W. H. Warren, p, 60. \Jbid., p. 73. 3 7^.,p. 73. " Lives of the Engineers," Samuel Smiles, vol. iii. p. 224. 12 FASCINE MATTRESSES AND BUILDING-STONE. Construction of Fascines and Mattresses. Fascines are ordinarily formed of a bundle of five or six sticks or pieces of brush- wood, about 7 to 1 1 feet long, bound firmly together near each end by an osier. Recently-cut willow furnishes the best material; but the brushwood of other trees, such as oak, hazel, ash, and alder, is also employed. The fascines are fixed in position by pegs or stakes, and are weighted with stones, bricks, or clay. For large works in rivers, the fascines are laid together in rows for three or more layers, connected together by strong intertwined bands of fascines to form a large mattress, the layers being fastened together by stakes driven down through the interstices of the upper network and round the edges of the mattress, and joined together by bands of interwoven sticks. The mattress, on completion, is launched from the bank, towed into position, and sunk by being loaded with rubble stone thrown out from boats alongside. In constructing dams, training walls, or jetties, several rows of mattresses are laid one over the other till the desired height is reached, the mound thus formed being capped with stone pitching or concrete blocks. The silt deposited by the river in the interstices of the mattresses, and over the surface of the mound, protects the fascines from decay. BUILDING-STONE. The employment of stone in engineering works depends on the accessibility and nature of the stone in the neighbourhood of the works. If stone is readily available, is durable, and fairly easily dressed, it is naturally used extensively ; but when the stone is very hard, or has to be procured from a distance, in the first case it is only used for special purposes, or as rough walling or backing, and in the second case brickwork or concrete generally proves preferable. Granite, sandstone, and limestone are the principal kinds of stone used in construction. Stones from Primitive Rocks. Granite, though very valuable for certain classes of work where great hardness and durability are essential, as for the sills and hollow quoins of large locks, the coping of docks, the voussoirs of large arched bridges, and the bed stones of large girders or columns, the difficulty of working it and its consequent cost render it unsuitable for ordinary masonry. Other igneous rocks, such as gneiss, whinstone, trap, and basalt, are used to some extent for masonry in the districts where they are found; but gneiss is more specially suited for flagstones, and the others for paving and metalling roads, on account of their hardness and durability, and the small blocks in which they are generally found. The igneous rocks are particularly durable, owing to their compactness and consequent imperviousness to water and they are specially adapted for bearing high pressures, heavy weights, and great wear and tear. Sandstones. Sandstones consist of grains of quartz cemented together into a solid mass by a substance of variable composition, upon the durability of which the value of the stone depends. When the BUILDING-STONE AND BRICKS. 13 cementing substance consists mainly of silica, mica, or hard felspar, the sandstone is hard and durable ; but when it is composed of alumina or oxides of iron, the sandstone is softer and more liable to disintegration. When calcium carbonate forms the cementing material, the sandstone can be easily sawn and worked, but it is somewhat readily injured by the weather. 1 Sandstones, accordingly, vary considerably in their qualities, some of the best for building being the millstone grit, the sandstones of the coat-measures, and the red sandstones. They are largely used for facework and ashlar masonry, on account of the facility with which they are dressed. Limestones. Calcium carbonate forms the main ingredient of limestones, which vary considerably both in composition and quality, the hardest forms being marble, which is an almost pure crystallized calcium carbonate, and dolomite, which is a double carbonate of calcium and magnesium. Oolitic limestones vary greatly in durability, some forms being subject to rapid decay ; whereas Portland stone is durable, and also some varieties of Bath stone, which are easily worked and harden by exposure to the air, though others readily disintegrate. There are also shelly limestones, of which Purbeck limestone is an instance, being largely composed of small shells. As a rule, limestones are softer, absorb more water, and are more subject to injury from the weather than sandstones. Strength of Building-stones. In practice, masonry, brickwork, and concrete are almost always wholly subjected to compressive strains, for mortar is incapable of undergoing tensional strains of any impor- tance; and therefore only the crushing strength of stone has to be ascertained, as well as its relative impermeability to the absorption of water, which furnishes some measure of its durability, though this and its rate of wear are matters which are largely based on experience. Granite and Italian white marble possess a very similar compressive strength of about 1400 tons per square foot, whilst in basalt and slate it averages about 1200 tons; whereas the compressive strength of sand- stones ranges from about 700 "to 260 tons, and of the better class of limestones, from about 600 to 200 tons per square foot. 2 The per- centage of water absorbed, which is under i per cent, for granite, whin- stone, slate, and marble, amounts to between 3^ and 10 per cent, for sandstones, and between 5 \ and i2j- per cent, for limestones. BRICKS. When a district is devoid of stone, and clay is obtainable, brick- work is commonly employed in place of masonry for constructive pur- poses. Brickwork possesses the advantages of being carried out with less skilled labour, and with lighter staging, termed scaffolding, than masonry, as no dressing is required, and no heavy weights have to be lifted and put in position. On the other hand, there are many more 1 "Chemistry for Engineers and Manufacturers," B. Blount and A. G. Bloxam, vol. i. p. 2. 2 " Notes on Building Construction," Part iii. 14 CONSTITUTION AND QUALITIES OF BRICKS. joints in brickwork than in masonry, necessitating the use of more mortar, and affording much less bond in the work, which is sometimes compensated for by the insertion of long strips of iron at intervals along some of the joints, an arrangement known as hoop-iron bond. Composition of Bricks. Clay containing some sand, or pure clay mixed with about a fourth of its volume of sand, is used for the manufacture of bricks, the usual composition of the material being chiefly silicate of alumina and silica in the form of sand, combined generally with lime, potash, and magnesia, together with some ferric oxide, which, when present in a fair proportion, gives a red colour to the bricks. The bricks are manufactured by making the mixture of clay and sand into a paste with water, which is then moulded into bricks ; and the bricks are burnt in clamps or stacks, or in kilns. There are various .kinds of bricks, as their colour, porosity, weight, and strength depend upon the composition of clay, loam, or marl from which they are manufactured. Gault clay, containing 25 per cent, of calcium carbonate, forms a close, light-coloured brick, suitable for facework; and pressed bricks are also used for the same purpose. The hardest and strongest bricks are made from a highly ferruginous clay, and are generally known as Staffordshire blue bricks, which are much less porous than ordinary bricks. Form and Qualities of Bricks. The dimensions of ordinary bricks, including the thickness of the joints, are 9 inches long, 4^ inches wide, and 3 inches high. They are generally laid in alternate rows of headers and stretchers on the outside in large engineering structures, for the sake of bond ; and the best bricks, or sometimes special bricks, are laid along the face. Hand-made bricks are generally formed with a hollow in the top, which keys the bricks into the mortar. Bricks when knocked together should give a sort of metallic ring, and when broken across should exhibit a compact uniform texture, quite free from iron pyrites, and any lumps of lime, which in slaking would crack the brick. Bricks weigh from about 6 to 10 Ibs., according to their quality, some being so porous as to absorb a fifth of their weight of water whilst others, such as blue bricks, are so compact that they absorb hardly any water. Ordinary bricks in hot, dry weather should be wetted just before being laid, as this promotes the adherence of the mortar. Smooth, compact, non-porous bricks, like blue bricks, should be laid in cement mortar or neat cement, as ordinary lime mortar does not adhere firmly enough to their smooth, impervious surfaces. Strength of Bricks. London stock bricks have a crushing strength when tested singly of from 80 to 180 tons per square foot ; gault bricks from 100 to 180 tons; Leicester red, 380 tons ; Stafford- shire blue from 400 to 700 tons; but the compressive resistance of brickwork in the form of piers is much below the above figures, being influenced by the nature of the mortar and other conditions. LIMES. Limes employed with sand for making mortar, may be divided into two classes, namely, ordinary lime obtained by calcining pure LIMES AND CEMENTS. 15 limestones, and hydraulic lime made from limestones containing clay or other substances, such as are found in the Lias formation. Ordinary Lime. Common lime is obtained by calcining limestone composed almost wholly of calcium carbonate, such as chalk, marble, and some oolites, resulting in the expulsion of the carbonic acid and water. The quicklime thus formed slakes when mixed with water, producing calcium hydrate, which gradually hardens in the air by drying and the absorption of carbonic acid, a change termed setting. This class of lime, however, does not set at all under water, and is therefore only suitable for structures out of the reach of water. It is largely used for ordinary building operations, owing to its furnishing the cheapest form of mortar, such as greystone lime mortar in London ; and the addition of sand to the lime in making mortar, by exposing a much larger surface of lime, facilitates the absorption of carbonic acid from the air, and consequently hastens the setting. Hydraulic Lime. Lias lime in England, Aberthaw lime in Wales, Theil lime in France, and other limes of similar character, con- taining 10 to 30 per cent, of clay, other silicates, and sometimes certain other substances, in addition to calcium carbonate, are able to set under water, and have therefore been employed for hydraulic works. These limes, accordingly, are more generally serviceable than ordinary limes, but they are also usually somewhat more costly. CEMENTS. When water-tightness, rapid setting, or special strength are requisite, cements are employed instead of lime. Some cements are obtained from limestones containing between 20 and 40 per cent, of clay; whilst other cements are manufactured by mixing the suitable ingredients before burning, in the proportions which experience has shown to be satisfactory. There are, therefore, natural and artificial cements. Natural Cements. The materials from which natural hydraulic cements are obtained, consist of nodules found in the London clay and other beds, and thin strata interspersed amongst hydraulic limestone beds. Roman cement, the best known of these natural cements, was dis- covered in 1796, and is formed by calcining nodules found on the island of Sheppey, at Harwich, and other places, containing about 66 per cent, of calcium carbonate, 25 per cent, of clay, and some ferrous oxide. It sets quickly, and therefore is very useful as a protection for the face-joints of tidal work in exposed situations ; but its ultimate strength is only between one- half and one-third that of Portland cement. 1 The cement should be used soon after its manufacture, for exposure to the air soon reduces its strength. Medina cement, another quick-setting hydraulic cement, obtained from septaria procured from the Isle of Wight, the bed of the Solent, and Hampshire, has been used for tidal work. It is very similar to 1 Proceedings Inst. C-E., vol. xxxii. pp. 280 and 281. 1 6 VARIETIES OF CEMENTS. Roman cement, but contains rather more lime ; and though it apparently reaches its maximum strength somewhat sooner than Roman cement, it is liable to deteriorate in course of time, which is a fatal objection to its use in permanent works exposed to the sea. Certain volcanic earths, consisting very largely of clay which has been subjected at some period to heat, possess the property of con- verting ordinary limes into a sort of hydraulic cement when mixed with them ; such, for instance, as pozzolana, found at Pozzuoli near Vesuvius, and trass, obtained on the sites of extinct volcanoes. Artificial Cements. In 1824 it appears to have been first dis- covered that a cement could be manufactured from a mixture of chalk and clay, which was called Portland, from the supposed resemblance of the blocks made with it to Portland stone. Portland cement, how- ever, was not extensively used for many years after its discovery, being only gradually adopted for dock and harbour works on the south coast of England and on the continent, till numerous systematic tests, commenced in 1858, led to its use for the main drainage works of London ; and these trials having resulted in great improvements in the quality of the cement, aifd increased reliance in its soundness, its employment has been extended to most classes of works where Roman cement and hydraulic limes were formerly used. Slag cement is another artificial cement which has occasionally been used. It is made by granulating slag from the blast furnaces by chilling it in water, and then grinding it with lime, to which it imparts hydraulic properties. Slag cement contains rather less than 50 per cent, of lime, in place of about 60 per cent, contained in Portland cement ; but it contains rather more silica, and considerably more alumina and oxide of iron than Portland cement. Slag cement, how- ever, though it has been used for concrete deposited under water in some harbour works, 1 sets slowly as compared with Portland cement, and does not increase in strength as quickly. More uncertainty, more- over, has been experienced hitherto as to the quality of the cement produced by this process, than in the now well-understood manufacture of Portland cement. Portland Cement. Great attention has been paid to the manu- facture of Portland cement for many years past, and to the tests requisite to ensure that any unsoundness or deficiency in strength of the cement shall be detected before it is used. Portland cement is commonly made by an intimate mixture of clay and chalk, varying in proportion from about 3 of clay and 7 of chalk, to i of clay and 4 of chalk, according to the differences in constitution of these substances, which is afterwards burnt in a kiln, whereby the water and car- bonic acid are driven off, and the calcium carbonate is converted into quicklime, which, decomposing the clay, forms calcium silicate and calc'um aluminate, of which the clinkered cement should chiefly consist. 2 Clay consists almost wholly of silicate of alumina, and chalk of calcium 1 Proceedings fnst, C.., vol. cv. pp. 234 and 235. 2 lbid. t vol. cvii. p. 32. MANUFACTURE AND TESTING PORTLAND CEMENT. 1 7 carbonate, which together, after burning, form Portland cement, which should be composed of about 62 per cent, of lime, 22 per cent, of silica, 9 per cent, of alumina, 2 to 3 per cent, of oxide of iron, and not more than 2 to 3 per cent, of magnesia. Similar cements can also be made from various other substances, provided they contain the necessary ingredients in the requisite proportions when mixed together. 1 The presence of free lime or magnesia is liable in time to injure works, by the swelling of these substances in combining with water, though free lime in a cement increases its strength in the first instance. The adequate burning of the cement is tested by its specific gravity, which should not be less than 3*1, as a lower specific gravity shows that the cement is underburnt. The value of any cement largely depends upon the fineness to which the clinker is ground ; for the extent to which the cement can coat over, and consequently cement together a certain quantity of sand of definite size, depends upon its fineness. Samples of the cement supplied are, accordingly, passed through a very fine sieve, having 76 meshes of wire, 0^0044 inch diameter, or 5776 meshes per square inch, leaving not more than 3 per cent, residue, and through a finer sieve of 32,400 meshes per square inch, with a residue of not more than 18 per cent. The coarser cement left on the sieve has little cementing value, and should be treated as so much sand in determining the proportion of cement to be used. The strength of Portland cement is almost always tested in tension, as the most convenient method, owing to its compressive strength averaging about nine times its tensile strength. The cement is formed into a paste with water, and moulded into briquettes contracted in the middle to a sectional area of z\ square inches, 2 or more recently i square inch, immersed in water when one day old, and taken out and tested seven days after manufacture. The standard tensile breaking strain of the cement under these conditions has been gradually raised, with improvements in manufacture, to not less than 400 Ibs. per square inch at seven days. A much lower breaking strain indicates that the cement is comparatively weak ; and a much higher breaking strain points to the probable presence of free lime, which is liable to be a source of subsequent injury, especially in sea- water. The test after seven days is the regulation one, in order to avoid delay in using the cement ; but later tests are expedient to prove a due increase in the strength of the cement with age; and a breaking strain of 500 Ibs. on the square inch 28 days after the making of the briquettes, has been included as a standard qualification. 3 Tests, however, of cement in tension do not furnish quite exact indications of the strength of a substance subjected in practice to compressive strains, as the strength in compression does not always bear the same relation to the tensile strength in different samples of Portland cement. The soundness, or prospect of durability, of cement is tested by forming small pats of cement with water on a glass plate, and then, when set, immersing them in water for seven days, at the end of which 1 Proceedings Lust. C.J5., vol. cvii. p. 118. 2 Ibid,, vol. xxv. plates 3 and 5, 3 bee British Standard Specification for Port, and Cement. C 1 8 COMPOSITION AND MIXING OF MORTARS. time reliable cement should show no signs of disintegration or cracks. The tests for the strength of cement mortar prepared with standard sand, for the expansion of the cement by the Le Chatelier method, and for the determination of the setting period by means of the " needle," are all included among the standard qualifications. 1 MORTARS. Mortar is made by mixing lime or cement with a definite proportion of clean, sharp sand, which is determined according to the quality of the lime or cement, and the position in which the mortar is to be used. The choice of proportions should also be guided by the quality of the sand available for making mortar. Proportions of Sand in Mortars. Under favourable conditions, the highest proportions of sand generally used for mortar, are 3 parts of sand to i part of lime, and 5 parts of sand to i part of Portland cement ; whilst 2 of sand to i of lime, and 3 of sand to i of Portland cement, are proportions often used under ordinary conditions. Roman cement, however, is so much weakened by admixture with sand, that equal proportions of sand and cement are commonly adopted in this case. When the work in which the mortar is to be used is liable to be exposed to water, the proportions should be reduced to equal quantities of sand and hydraulic lime, and 2 of sand to i of Portland cement ; and where the work is actually exposed to water, i of sand to i of Portland cement may become necessary, the face joints being protected by a coating of neat Portland or Roman cement when the work is subject to the wash of the sea shortly after construction. In important sea-works, the actual proportion of sand chosen for the mortar should be regulated by the coarseness or fineness of the sand to be employed ; for it has been found by experiment that fine sand requires to be mixed with about twice as much cement as coarse sand to attain the same strength, owing to the much larger surface needing coating with cement in the case of fine sand, than of coarse sand, to cement the particles together. 2 On the other hand, mortar made with very coarse sand, though needing less cement, is not so compact as mortar made with finer sand, and consequently is not so suitable for a work subject to a pressure of water ; and the admixture of some fine sand with the coarse becomes necessary to ensure the impermeability of the work. Manufacture of Mortars. In making lime mortars, the lime has to be slaked with water before it is mixed with sand; whereas finely-ground Portland cement can be mixed at once with sand, and made into mortar by the addition of water and turning the materials over sufficiently to ensure thorough admixture. Ordinary lime mortar is mixed in large quantities in a mortar-mill, the measured ingredients being placed in the revolving pan, and guided by iron scrapers under 1 British Standard Specification for Portland Cement. 2 " International Maritime Congress, London, 1893, Proceedings of Section I," p. 91. MIXING AND STRENGTH OF MORTARS. 19 a pair of heavy rollers, which grind any lumps of lime, as well as assist in mixing the ingredients. With finely-ground hydraulic lime or cement, the mixing machine is only required to ensure the complete incorporation of the materials. Where fine sand is used for the mortar, a more thorough mixing, as well as a larger proportion of lime or cement, is required than with coarse sand, owing to the far greater number of particles of sand which have to be coated with cement. The amount of water used should be just sufficient to make the materials into a paste, and must necessarily vary according to the condition of the materials and the state of the weather; whilst an excess of water washes fine lime or cement away from the sand, and delays the setting of hydraulic limes and cements. Ordinary lime mortar can be safely used some hours after manufacture, on account of its slowness in setting ; but hydraulic lime mortars, and especially quick-setting cement mortars, should be used as soon as possible after mixing, for their strength is considerably impaired by disturbance after setting has commenced. Strength of Mortars. The strength of mortars depends, not merely upon the strength and soundness of the lime and cement used, but also upon the quality of the sand and the thoroughness of the mixing. Accordingly, in important works, tests are made of cement mortars as well as of neat cement. Except in the case of certain substances, such as the volcanic earths already alluded to, the materials mixed with the lime or cement are simply inert substances, added for the sake of economy, and reducing the strength of the lime or cement. One of the advantages of Portland cement is that, owing to its strength and fineness, it can form an adequately strong mortar with a considerably larger proportion of sand than lime can, and still more than Roman cement. In this respect, some experiments seem to indicate that the best slag cement is even superior to Portland cement, on account of its still greater fineness ; l but a greater reliability in the manufacture of slag cement, and much more extended experience of its qualities and durability will be needed, before it can have any prospect of competing successfully with Portland cement. To make comparable tests of Portland cement mortars, sand of similar quality and size must be used in the experiments. It has been found that the tensile strength of Portland cement mortar at the end of a year, when mixed with equal quantities of sand and cement, is about three-fourths that of neat cement ; and with larger proportions of sand, from 2 of sand to i of cement up to 4 of sand to i of cement, the tensile strength of the mortar varies approximately according to the ratio of cement to sand as compared with neat cement, having about one-half the strength of neat cement in the first case, and one-fourth in the latter case. 2 Beyond this limit, however, the strength appears to diminish more rapidly with an increase in the proportion of sand, since mortar with 5 of sand to i of cement has only one-sixth the tensile strength of neat cement. 1 Proceedings Inst. C.. s vol. cv, p. 225. * Jbid., vol. xxv. pp, 77 and 88. 20 STRENGTH AND PROPORTIONS OF MORTARS. The strength of Portland cement mortars in compression, though much greater than in tension, diminishes more rapidly with an increase in the proportion of sand ; for the crushing strength, at the end of a year, of a mortar made with equal quantities of sand and cement, was found to be rather more than half the crushing strength of neat cement, a 2 to i mortar one-third, a 3 to i mortar one-fifth, a 4 to i mortar one- eighth, and a 5 to i mortar only one-thirteenth that of neat cement. 1 The strength of mortars is greatly affected by the nature, as well as the size of the sand, the mortar made with clean, sharp, or angular sand being muctr stronger than mortar made with dirty sand with rounded grains. The presence of loam, silt, or clay in sand can be detected by taking up a handful of moist sand, and closing one's hand on it with a little pressure, as dirty sand will bind together, instead of falling to pieces, when the grasp is relaxed. Dirty sand must be washed by a stream of water before being used for mortar. The increase in the strength of cement mortar is slower and more prolonged than that of neat cement ; and the increase, which is fairly rapid during the first two or three years, gradually decreases in amount, till at last, after the lapse of several years, the ultimate strength is reached, and a slight tendency to deteriorate is exhibited by the mortar. 2 Remarks on Mortars. The strength and permanence of any structure depends so largely upon the strength and durability of the mortar which binds the stones or bricks together, that the utmost care is needed in selecting the most suitable materials for the mortar, in mixing it, and in laying it in the work. As frost injures newly laid mortar, building has to be discontinued during frosty weather. The proportion of cement to sand must be regulated by the required strength and the exposure of the work, as well as by the strength and fineness of the cementing material ; and where the best class of sand is not procurable at a reasonable cost, compensation must be made for the poorer quality of sand available, by an increased proportion of lime or cement. Portland cement has been so much improved in quality in recent years, and cheapened in cost, that it is very generally used now for mortar in important works ; and it is regarded by most engineers as almost indispensable in works exposed to water or the sea, not merely on account of its strength and quick setting under water, but also owing to the preservation of its strength during storage on a long voyage if not exposed to damp, and the maintenance of its qualities when mixed with salt water or made into mortar with sea-sand. CONCRETE. Concrete has gradually become one of the most important materials of construction at the disposal of the civil engineer, on account of its cheapness, the facility with which materials for it are often procured where ordinary building materials are scarce, the ease with which it 1 Proceedings Inst. C.E., vol. xxxii. pp. 288-291. 2 Ibid,, vol. cvii. p. 388. MATERIALS AND THEIR PROPORTIONS IN CONCRETE. 21 is manufactured, its adaptability to various situations, and its good strength and durability when carefully made. Composition of Concrete. Concrete is generally formed of sand mixed with gravel, small rubble stone, broken bricks, slag, or other inert hard materials cemented together into a solid mass by lime or cement; and it may be regarded as composed of lime or cement mortar filling up the spaces between, and connecting together the larger hard materials, which take the place of stone or bricks in ordinary constructions. The materials should be so proportioned according to their size, that the whole, when thoroughly mixed with water, may harden gradually into a solid, impervious mass. A large proportion of the big materials expedites the work, whilst strengthening it by causing it to approximate to rubble masonry; it involves less labour in mixing ; and it reduces the amount of mortar required, and the quantity of the cementing material, which is the most costly item. Large materials, however, must only be introducedMn the proportions, and in the class of work, in which an adequate thickness of mortar can be ensured between every large piece. The proportion of sand to the lime or cement, and its quality, must be determined by the same considerations as the formation of any strong, impervious mortar referred to above. The smallest proportion of cement is allowable in the manufacture of concrete blocks, which can be left to harden for some time before being used ; and a specially large proportion of cement is necessary when concrete is deposited under water, and more particularly where it is likely to be partially exposed, before becoming set, to a current of water or the wash of the sea. Proportions employed for Concrete. The actual proportions of the materials used in making concrete vary considerably according to the quality and accessibility of the materials, the form in which the concrete is placed in the work, and the conditions of the site. Thus concrete made into blocks has been formed in proportions ranging between 3! of sand to i of Theil lime at Port Said harbour, 1 and 2 of sand, 6 of broken stone, and i of Portland cement in sloping and horizontal blocks in various recent breakwaters. The proportions adopted for concrete in bags deposited under water, were 3 of sand, 4 of shingle, and i of Portland cement at the north breakwater of Aberdeen harbour, and 2 of sand, 5 of shingle, and i of Portland cement at Newhaven breakwater, or 7 of materials to i of cement in both cases. The concrete-in- mass deposited below low water, was composed of 7 of gravel and sand to i of Portland cement at Wicklow harbour, 2 2 of sand, 4 of stone, and i of Portland cement for Babba- combe fishery pier, and 4 of sand and stone to i of Portland cement at Buckie harbour ; whilst the concrete-in-mass above low water, was formed of 3 of sand, 4 of shingle, and i of Portland cement at the north pier of Aberdeen harbour, about n of sand and stone to i of Portland cement at Buckie, and 2 of sand, 5 of shingle, and i of 1 " Harbours and Docks," L. F. Vernon-Harcourt, p. 642. * Proceedings Inst. C.E., vol. Ixxxvii. p. 118. 22 COMPOSITION AND WAYS OF USING CONCRETE. Portland cement at Newhaven. The proportions of concrete-in-mass in recent important clockworks have been as follows : Dock floors and walls below low water, i Portland cement, i J sand, 5 broken stone ; dock and basin walls between high and low water, i Portland cement, 2 sand, 6 broken stone ; above high water, i Portland cement, 3 sand, 8 broken stone. 1 The proportion of stone in concrete-in-mass above low water, or in very large blocks, can be advantageously increased by embedding large blocks of rubble stone at intervals in the concrete, provided these blocks are kept away from the face ; but it is not safe to introduce such blocks in concrete deposited under water, as their proper bedding in the concrete, apart from one another, cannot be secured. Cement and mortar naturally adhere more firmly to angular, rough, clean surfaces than to smooth or dirty surfaces ; and therefore, just as a stronger mortar is formed by sharp sand than by rounded sand, so angular or broken stones make a stronger concrete than smooth shingle or boulders; and in concrete, as in mortar, all the materials composing it should be perfectly clean. Forms and Uses of Concrete. One of the earliest applications of concrete to engineering works was in the form of blocks, where stone was scarce or difficult to dress, and where close-fitting work was required. Concrete blocks are made within timber frames to the required size ; and when the concrete has set sufficiently, the frames are taken off to form other blocks, and the blocks are left to harden in the open air for a month or more before they are placed in the work, holes having been left in forming the blocks, by the insertion of pieces of wood in suitable positions inside the frames, for the introduction of long iron bolts when the blocks have to be lifted. These blocks are very commonly used in the construction of breakwaters under water, where the blocks have to be laid as close together as possible, in a position in which the joints cannot be filled with mortar. The advantages of this form of concrete are, that the blocks being made beforehand, and given ample time to set hard, the work can be conducted rapidly, and with certainty 'as to the condition of the concrete when immersed in water, and that a smaller proportion of cement can be safely used than in concrete work executed under less favourable conditions. Concrete has been employed enclosed in very large bags for the portions of some breakwaters below low water, as the yielding nature of the bag-work enables the bottom bags to adapt themselves to the irregularities of a hard chalk or rocky bottom ; whilst the covering provided by the bag prevents the concrete being injured by the sea when being deposited, and after it has been put in position. Moreover, a sufficient portion of the finest part of the concrete oozes through the jute sacking forming the bag, under pressure, to unite the heap of bags into a solid mass. This system, though involving the use of large plant of a special character for the deposit of the bags, as in the case where large concrete blocks have to be handled, has the advantages of 1 Proceedings Inst. C.., vol. clxxii. CONCRETE IN BAGS AND IN MASS. 23 obviating the great cost of levelling a rocky bottom under water, and of requiring only a moderate amount of cement in making the concrete, owing to the protection afforded by the bag. Concrete in bags has also been used, like concrete blocks, as an apron for protecting the upper exposed surface of the rubble mound of a breakwater, near the sea-face of the superstructure resting on the mound, and also in filling up hollows in foundations exposed to a current of water. Concrete-in-mass has been very extensively used in foundations, dock walls, retaining walls, and the portions of breakwaters above low water, and occasionally for reservoir dams, lighthouse towers, and arched bridges. The reliance, moreover, felt of late years in Portland cement, has led to the use of concrete-in-mass for breakwaters and other work under water, deposited within framing lined with jute canvas, by closed skips with movable bottoms. The mixing of the concrete deposited in mass or into large bags, has to be very efficiently performed, either by hand for small quantities, or by mixing machines for large amounts. In making concrete by hand, the measured materials are turned twice over when dry, on a clean floor, and then again after admixture of water. Concrete-mixing machines consist of revolving boxes or cylinders worked by steam-power, in which the materials are turned over several times, and thoroughly mixed, before being discharged ready for use. The concrete should not, if possible, be deposited from a height, or through a long shoot, for the stones, descending faster than the rest, tend to form a heap by themselves ; and the deposited concrete needs somewhat mixing again. The greatest care is required in deposit- ing concrete under water, to prevent the concrete losing a portion of its cement by falling through the water ; and the concrete must not be disturbed when once deposited. Concrete has sometimes been allowed to set partially before being deposited under water, with the view of preventing the washing out of the cement from the concrete in its passage through the water; but it is probable that the concrete loses as much strength by the disturbance of its setting when in what is termed the plastic state, as by the loss of cement under ordinary conditions. Concrete deposited under water must be given an ample proportion of cement ; it must be protected from any wash or current ; and it must be lowered in a closed skip as near the bottom as practicable, before being deposited. When concrete-in-mass is deposited in large amounts in successive layers, the top surface of the layer of the previous day's work must be cleaned from any coating of silt before the next layer is commenced ; and in the case of concrete out of water, the surface should be moistened, and roughened when necessary, to ensure the adherence of the succeeding layer. Concrete-in-mass possesses several advantages. It furnishes a cheap method for forming broad foundations for heavy structures, and readily fills up hollows or other irregularities in its excavated foundations ; and it can easily be finished ofif to a level surface at the top, for the structure to be erected upon it. Moreover, though requiring constant care and supervision in its mixing and deposit, concrete-in-mass can be carried out with very little plant, and without skilled labour. This system of 24 PORTLAND CEMENT CONCRETE, IRON, AND STEEL. construction has been resorted to in dock walls and graving docks from economical considerations. For breakwaters, however, concrete- in-mass possesses the additional advantage that it forms the structure into a huge monolith, not liable to disturbance by the sea; though its deposit under water in such conditions needs very special precautions. On the other hand, porous concrete, subject to the percolation of sea- water under pressure, has in some instances become disintegrated, in consequence, apparently, of the substitution of magnesia from sea-water for the lime in the cement, which has led to the expression of doubts as to the permanence of structures exposed to sea-water, which have been formed with Portland cement. 1 The durability, however, of many break- waters, docks, and basin walls of Portland cement concrete, and exposed to the action of sea-water, indicates that Portland cement in concrete properly proportioned and mixed so as to form an impervious mass, and devoid of free lime and magnesia, is not liable to decomposition by the sea-water, which merely comes in contact with the face of the work. IRON AND STEEL. Iron is used in three forms in construction, namely, as cast iron, wrought iron, and steel. Cast iron contains between 90 and 95 per cent, of pure iron, the remaining constituents being from 2 to 4 per cent, of carbon, mainly in the form of graphite, together with small amounts of silicon, manganese, phosphorus, and sulphur, in variable proportions according to the nature of the ore from which the iron is obtained. Wrought iron is the purer, malleable metal obtained from molten cast iron in the puddling process, by which the greater portions of the impurities are removed, so that their combined residues form less than i per cent, of the mass, the rest consisting of pure iron. Steel, which is of various grades of tensile strength and hardness according to its chemical composition, contains proportions of carbon ranging from about the same minute percentage in mild steel as in wrought iron, up to between i and 2 per cent, in hard-tool steel ; whilst the quantities of silicon, sulphur, and phosphorus, are decidedly less in steel than in wrought iron, and the amount of manganese is greater. Cast Iron. Towards the close of the eighteenth century, and in the earlier half of the nineteenth century, cast iron was the form of metal almost wholly employed for bridges, the use of wrought iron having been confined to suspension bridges, as, for instance, the Menai Suspension Bridge, where the strains are entirely tensile. Cast iron was, indeed, very naturally adopted for arches, as the strains in these structures are wholly compressive, which cast iron is specially suited to sustain, as its crushing strength is about 40 to 45 tons per square inch, whereas its tensile strength only amounts to between 7 and 10 tons per square inch. Accordingly, cast iron has been successfully employed for arched bridges of considerable span, as, for example, 1 Proceedings List. .., vol. cvii. pp. 74-77 ; and "Report on the Causes of Damage to the Aberdeen Graving Dock," 1887, P. J. Messent. CAST IRON, WROUGHT IRON, AND STEEL. 25 South wark Bridge over the Thames in London, erected in 1819, with a central span of 240 feet; but it was ill adapted for the small girder bridges constructed with it in the early days of railway enterprise, on account of the tensile strains on the bottom flange, which had to be made considerably larger in area than the top flange subject only to compression. It was not, however, till after the successful completion, in 1850, of the Britannia Tubular Bridge across the Menai Straits, made of wrought iron, that cast iron was abandoned in favour of wrought iron for girder bridges. The use of cast iron has been gradually relinquished, even in arched bridges, for railways, for cast iron is liable to be fractured by sudden, severe shocks ; and serious flaws have been discovered in some of the castings forming the ribs of old railway bridges, when taken down owing to their proving unsafe under the increased strains due to the heavier locomotives and higher speeds of the present cfciy. Cast iron, however, is still very largely employed for columns, cylinders, tubes, and pipes, bed-plates, chairs for rails, and various other purposes. Wrought Iron. The use of wrought iron in construction, which was at first mainly employed for suspension bridges, in the form of link chains, suspending rods, and bolts, and later on in wire cables, and also for rails, was extended to large-span bridges in the case of the Britannia and Conway tubular bridges, and the Saltash Bridge over the Tamar, after it had been proved by experiments that wrought-iron plates and angle-irons riveted together could form beams capable of sustaining heavy loads over wide spans. Wrought iron was subsequently adopted for girders of various forms for. many years, and has occasionally been used for arched bridges ; but it has, in its turn, been gradually super- seded by steel, owing to the greatly cheapened production of this stronger metal, especially for rails and bridges of large span. Wrought iron possesses the advantage over cast iron that its strength in compres- sion is not much less than its strength in tension, the crushing strength of wrought iron being between one-half and one-third that of cast iron, and its tensile strength being about three times that of cast iron. More- over, wrought iron is not liable to fracture or to have flaws like cast iron ; and whereas the joining of several castings together by bolts only forms a thoroughly satisfactory connection when the strains on the structure are wholly compressive, the riveting together of plates and angle-irons, forming a wrought-iron girder, rigidly connects the different parts for resisting tensile as well as compressive strains. Steel. The old method of making steel from wrought iron manufactured from the purest Swedish or other ores, by combining it with carbon in the cementation process, rendered steel a costly product. The introduction, however, of the Bessemer process, in which mild steel, approximating in composition to wrought iron, can be manufactured more directly in large quantities from impure ores, resulting in a very great reduction in cost, opened out a wide field for steel as a material for engineering construction. The original aim of the Bessemer process was to arrest the removal of carbon from cast iron at the intermediate stage, when steel might be 26 PROCESSES USED FOR MAKING STEEL. assumed to have been produced, instead of first removing almost all the carbon so as to form wrought iron, and then adding carbon, in a second process, to wrought iron in order to make steel. Owing, however, to the presence of phosphorus, silicon, and sometimes sulphur in the iron obtained from impure ores, it proved impracticable, except in the case of the purest iron, to stop the blast of air through the molten metal, in the Bessemer converter, at the stage when the carbon originally existing in the cast iron has been reduced by the blast to the proportion forming steel; and the carbon has to be restored to the molten metal by the addition of the requisite proportion of the pure iron ore, rich in carbon, known as spiegeleisen, after the other impurities have been removed by the prolongation of the blast. The Thomas-Gilchrist process introduces a basic lining into the converter, which, entering into combination with the impurities in the molten metal, especially phosphorus, removes them from the steel, which is thereby procured in an adequately pure condi- tion. In the Siemens-Martin process, a bath of molten pig-iron mixed with more or less wrought iron, steel, or similar iron products with the addition of manganese or spiegeleisen is converted into steel by exposure to the direct action of the flame in a regenerative gas furnace, the operation being so conducted that the final product is entirely fluid. Various modifications of the open hearth process, which may be acid or basic, are in operation. Steel manufactured by the above processes has been fused, and more effectually freed from impurities than wrought iron, and steel formed from puddled iron, which are never wholly freed from the impurities of the slag in which they have been immersed. The tensile strength of steel varies with the proportion of carbon in its composition, ranging from that of wrought iron in very mild steel, up to a maximum with about 1*5 per cent, of carbon, when it attains more than double that strength, its breaking strain sometimes reaching about 60 tons on the square inch. The strength, moreover, of steel is very similar in tension and compres- sion. Cast steel, much used for special purposes, is generally considered to have three times the strength of cast iron ; but owing to its much higher fusing point, its contraction in cooling is nearly double that of cast iron. Mild steel, owing to its greater strength and elasticity, has practically superseded wrought iron not only in bridge work but in most other branches of iron construction, but is, like its predecessor, open to the destructive effects of corrosion, unless carefully and efficiently pro- tected against rusting. 1 Steel has also been very advantageously adopted for rails, which are now exposed to increased strains and wear by the augmented weight of locomotives and the use of continuous brakes; and as rails must be both tough and hard, to sustain the shocks of heavy trains travelling at a high speed and to support the wear of the brakes, they are tested for toughness by the impact of a falling weight, and for hardness by their breaking strain. 1 "Notes on Construction in Mild Steel," Longmans' Civil Engineering Series. LIMIT OF ELASTICITY ; LOADS ON STRUCTURES. 27 SAFE STRAINS ON MATERIALS. In all structures, it is of the utmost importance that none of the materials of which they are formed should ever be strained to an extent liable to produce any permanent injury. In certain materials, such, for instance, as wrought iron and steel, there is a limit, varying with the nature of the material, up to which changes in form are proportionate to the load imposed ; and the original form is gradually regained on the removal of the load. When, however, this //;;/// of elasticity is excee.ded, the change in form becomes greater than in proportion to the increase of load; and the material no longer returns to its original condition after the withdrawal of the load, but acquires a permanent set. It would be unsafe to strain materials close up to this limit ; for repeated applica- tions of such a load, causing fatigue of the metal, is liable to lower the elastic limit, and may eventually even produce fracture. Factors of safety have, accordingly, been deduced from the results of experiments for various materials, representing the relation between the breaking load and the stresses to which the different materials may be safely subjected, which are considerably below the elastic limit. Dead and Moving Loads. The loads which some structures have to bear, such as bridges, floors, and roofs, are of two kinds, namely, the dead or permanent load, and the live or moving load. The dead load consists of the roadway or other permanent weight borne by the structure, together with the weight of the supporting structure itself between the points of support. The moving or variable load comprises trains, vehicles, and foot-passengers crossing over bridges, and wind, and in some countries snow, especially on roofs. The moving load imposes a more severe strain upon a structure than the dead load, owing to its frequently rapid and unequal application, the shocks with which it is often accompanied in the case of a train going at a high speed, and the alteration sometimes produced in the nature of the stress, putting certain portions into tension and compression alternately, a change which is much more trying to materials than similar stresses of unvarying kind. The greater strain, however, produced by the moving load is to some extent compensated for, in actual practice, by the structure being designed to bear the maximum moving load possible, which may, indeed, be imposed in the testing of the strength of the structure before its opening for traffic, but which is rarely, if ever, attained in actual working. The ordinary allowances for the moving loads on bridges are i to i tons per lineal foot per line of way for railway bridges, i cwt. per square foot for roadways, and 70 Ibs. per square foot for footways. Stresses allowable on Structures. Certain general rules have been framed for ensuring the stability of structures, some of which are enforced by the Board of Trade with regard to railway bridges in the United Kingdom. In timber structures, the dead load, together with twice the maximum moving load, should not produce a stress in any part of the structure exceeding one-fifth of the breaking stress of the 28 SAFE STRESSES, WIND-PRESSURE, AND SNOW. timber employed. Masonry and brickwork should only be weighted to the extent of about one-eighth of their crushing strength on the average. Cast iron should be only used in compression ; and the stress due to the dead load, together with twice the maximum moving load, should not exceed one-third to one-fourth of the breaking stress in any part of a cast-iron structure. The standard maximum working stresses on metal structures allowed by the Board of Trade, are 5 tons per square inch in tension, and 4 tons per square inch in compression for wrought iron, and 6J tons per square inch for steel ; whereas the elastic limit has been found to average about 1 2 tons per square inch for wrought iron, and 1 8 tons per square inch for mild steel. In the above limits of safe stresses, no distinction is made between the dead and moving loads ; and the limits are somewhat low 7 for the large members of a girder of large span, and high for the small members subjected to shocks and to alternate tensile and compressive stresses. Moreover, the load which can be safely borne by a steel structure, varies considerably according to the nature of the steel employed. Wind-pressure, and Snow. In addition to the dead and moving loads, allowance has to be made, in designing railway bridges, for a wind-pressure against the exposed surfaces, of 56 Ibs. per square foot a condition imposed by the Board of Trade after the overthrow of the Tay Bridge during a gale in December, 1879. Tne pressure of wind has also to be considered in the case of roofs, and the occasional additional load due to snow in cold countries. The wind-pressure, however, is greater in proportion to the pitch of the roof; whereas the depth of snow which may accumulate, increases in proportion to the flatness of the roof; but the pressure imposed on a roof by these two influences, constitutes a considerable portion of the stresses which have to be borne by a roof. The weight or compactness of the snow is in inverse proportion to the size of the flakes, and may be assumed to amount to from 5 to 10 Ibs. per cubic foot; but the weight of snow on bridges in North America, has been estimated to attain 30 Ibs. per square foot under unfavourable conditions. The subject of wind-pressure and its influence on the design of roofs and bridges has received much attention in recent years, and the experimental investigations which have been carried out on the influence of the pitch of roofs, negative wind-pressure, the results of wind- pressure on lattice girders, and the sheltering influence of the wind- ward girder should be carefully studied. 1 CHAPTER III. PRELIMINARY ARRANGEMENTS FOR CARRYING OUT WORKS. Surveys Investigations of physical conditions Borings, and trial pits ; methods and objects Parliamentary plans and sections ; objects, and general conditions Working or contract drawings Methods of carry- ing out works ; with, and without a contractor Specification ; general description, and forms appended Tenders ; contents and stipulations Lump-sum contract ; based on schedule of prices, extras Progress of the works ; conditions, inspection of materials, supervision of works, stipulations as to plant and materials Payments for works ; arrange- ments, retentions Completion of the works ; stipulations, variable competency of contractors Remarks on the carrying out of works ; relative efficiency and cost of methods, importance of supervision. BEFORE any work is designed, a careful survey of the site has to be made, with a longitudinal section along the line of the work, and often cross-sections as well^ so that the levels of the ground to be traversed or built upon may be accurately known, the best position for the work may be selected, and the amount of earthwork to be carried out may be ascertained. Reference should be made to any previous survey of the locality, to facilitate the execution of the more detailed, and generally larger survey required, on which the general plan of the proposed work is laid down. Moreover, if a geological map of the district has been made, it is very desirable to consult it, in order to obtain a general idea of the strata through which excavations will have to be carried, or on which foundations for structures will have to be laid. More particular information as to the nature of the soil in which the works are to be carried out, should be procured by borings and trial pits ; and some data as to the rainfall of the locality, and the height of the floods of the streams and rivers to be traversed or dealt with by the works, should be obtained. In fact, as intimate a knowledge as practicable of the physical characteristics of the district in which the works are to be carried out is most desirable, for enabling engineers to prepare suitable designs and reliable estimates of cost, the importance of special branches of information varying with the nature and object of the work. Thus the nature and dip of the strata, and the existence of underground springs, exercise an important influence on the design and cost of deep cuttings and tunnels ; the rainfall, the catchment area, and the presence 30 DATA FOR WORKS ; BORINGS, AND TRIAL PITS. of faults or fissures, are additional essential factors in the provision of water-supplies for towns ; the maximum and minimum discharge of rivers, the nature of their bed, their fall, and the amount of detritus they bring down, determine to a great extent their capability for improvement, and the works that should be carried out ; whilst the direction of the strongest and prevailing winds, the drift of sand or shingle along the coast, the rise of tide, and the slope of the sea-bottom, are of paramount importance in the design of works for the formation of harbours, the improvement of river outlets, and the protection of coasts. Borings, and Trial Pits. Ordinary borings furnish the cheapest and most expeditious means of ascertaining the nature of the strata below the surface for a considerable depth. The bore-hole is excavated through soft soil by turning round in it a hollow cylindrical auger, somewhat pointed at the lower end, which collects and brings up the material when lifted ; and as the bore-hole is carried down, it is lined by thin wrought-iron pipes. When rock or other hard material is encountered, it has to be broken up by the blows of a jumper before it can be raised by the auger. The nature, thickness, and position of the several strata are thus readily indicated ; and by the aid of a series of borings, a sort of geological section of the ground can be drawn out. The process of sinking the boring, however, so disintegrates the more compact materials, such as indurated silt, clay, or rock, that it is impossible to form an accurate opinion of the condition of the materials in position ; and in this respect, diamond boring machines, which bring up a complete core of the strata traversed, afford much more satisfactory indications of the actual condition of the materials, but the method is considerably more expensive than the ordinary prpcess. Trial pits enable a far more correct idea to be formed of the exact con- dition of the soil at the various depths, and are not subject, like borings, to the error of mistaking a chance solitary boulder for a stratum of rock ; but these pits occupy a much longer time in excavating, and are considerably more costly; and, moreover, their excavation, even at moderate depths below the surface, is liable to be impeded by the influx of water directly the line of saturation of the soil is reached. Accordingly, the number and depth of the trial pits have generally to be strictly limited, and are confined to the most important spots ; whilst extended investigations of the nature of the ground are commonly effected by borings. These preliminary investigations of the strata are not merely needed for determining the proper side slopes for the cuttings, the nature, and consequently the cost, of the excavations, and the depth to which the foundations of bridges, walls, and buildings, will have to be carried, but they are also very valuable in indicating to what extent the materials obtained from the excavations may be suitable for the purposes of the works, such, for instance, as masonry, pitching, ballast, or concrete, which has an important bearing on the cost of the works. Parliamentary Plans and Sections. Except where the works are kept within the property of a single landowner, it is generally necessary, in the United Kingdom, to obtain parliamentary sanction for the works, so as to secure the compulsory purchase of the land PARLIAMENTARY PLANS, AND CONTRACT DRAWINGS. 31 required for the undertaking. In the case of large works, this is accomplished by means of a private Bill in Parliament ; and often, for small works, the cost is notably reduced by applying for a " Provisional Order," with the sanction and aid of the Board of Trade. In return for the privileges conferred on the promoters of the scheme, when the Bill, after passing through both Houses of Parliament, is con- verted into an Act on receiving the Royal assent, certain preliminary conditions have to be complied with, in order to safeguard the interests of the public, and to give due notice to the owners and occupiers of the lands proposed to be taken for the works. Plans and sections of the proposed works, drawn up in accordance with the " Standing Orders " of Parliament published each year, have to be deposited before the 3