!ilii!lii: llM ! i:-rr=4=.-t Fig. 7. — Diagram of Polycentric Sectional Profile. 20 TUNNELING springer arcs Ga and Ea', Fig. 7, must be located on the line GE; the center of the roof arc hDh^ must be located on the axis HD) the total number of centers must be an odd number; the Fig. 8 Fig. 9 Fig. 10 Figs. 8 to 10. — Typical Sectional Profiles for Tunnel. radii of the succeeding arcs from G toward D and E toward D must decrease in length, and finally the sum of the angles subtended by the several arcs must equal 180°. Dimensions of Section. — The dimensions to be given to the cross-section of a tunnel depend upon the purpose for which it is to be used. Whatever the purpose of the tunnel, the follow- ing three points have to be considered in determining the size of its cross-section: (1) The size of clear opening required; (2) the thickness of lining masonry necessary; and (3) the decrease in the clear opening from the deformation of the lining. Railway tunnels may be built either to accommodate one or two, three and four tracks. In single-track tunnels a clear space of at least 2 J ft. on each side should be allowed for between the tunnel wall and the side of the largest standard locomotive or car, and a clear space of at least 3 ft. should be allowed for be- tween the roof and the top of the same locomotive or car. Since the roof of the tunnel is arch-shaped, to secure a clearance of 3 ft. at every point will necessitate making the clearance at the center greater than this amount. In double-track tunnels the same amounts of side and roof clearances have to be provided for, and, in addition, there has to be a clearance of at least 2 ft. between trains. On the three- and four-track tunnels only the width varies while the height remains almost equal to the two track. Referring to Fig. 7, and assuming the line AB DETERMINING THE CENTER LINE 21 to represent the level of the tracks, then the ordinary dimensions in feet required for both single- and double-track tunnels are as follows : — Height, D. F. Feet. Width, G. E. Feet. Height, C. F. Feet. Height, C. H. Feet. Single track .... Double track . . . 17.6 to 18 26.6 to 28 16.5 to 18 26.6 to 28 6 to 7.4 6.3to6.9 Ito iAB i to 1 A5 The dimensions of tunnels built for aqueduct purposes are determined so as to have an area of cross-section equal to the required waterway. In the Croton Aqueduct two different types of cross-sections were used, the circular one for tunnels through rock and the horseshoe section for tunnels through loose ma- terials. In the Catskill aqueduct three different cross-sections have been selected, the circular one for tunnels under pressure and the horseshoe for tunnels at the hydraulic gradient. These, however, through rock have a cross-section formed of a semi- circular arch and vertical side walls, while through earth the semi- circular arch is supported by skewback walls. In tunnels built for railroad aqueduct sewer and any other purpose the thickness of the masonry lining to be allowed for varies with the material penetrated, as will be explained in a succeeding chapter where the dimensions for various ordinary conditions are given in tabular form. The lining masonry is subject to deformation in three ways : by the sinking of the whole masonry structure, by the squeezing together of the side walls by the lateral pressures, and by the settling of the roof-arch. The whole masonry structure never sinks more than three or four inches, and merits little attention. The movement of the side walls towards each other, which may amount to three or four inches for each wall without endangering their stability, has, however, to be allowed for; and similar allowance must be made for the settling of the roof-arch, which may amount to from nine inches to two feet, when the arch is built first as in the Belgian system and rests for some time upon the loose soil. 22 TUNNELING CHAPTER III. EXCAVATING MACHINES AND ROCK DRILLS EXPLOSIVES AND BLASTING. Earth-Excavating Machines. — Comparatively few of the labor- saving machines employed for breaking up and removing loose soil in ordinary surface excavation are used in tunnel excava- tion through the same material. Several forms of tunnel excavating machines have been tried at various times, but only a few of them have attained any measure of success, and these have seldom been employed in more than a single work. In the Central London underground railway work through clay a continuous bucket excavator (Fig. 11) was employed with Fig. 11.— Soft Ground Bucket Excavating Macliine : Central London Underground Railway. considerable saving in time and labor over hand work. In some recent tunnel work in America the contractors made quite successful use of a modified form of steam shovel. These are the most recent attempts to use excavating machines in soft ground, and they, like all previous attempts, must be classed as experiments rather than as examples of common practice. The Thomson machine,* however, can be employed * The machine was designed by Mr. Thomas Thomson, Engineer for Messrs. Walter Scott & Co. EXCAVATING MACHINES AND ROCK DRILLS 23 in any tunnel driven through loose soil. It occupies a compara- tively small space and may easily work when the timbering is used to support the roof of the tunnel. Steam shovel instead may give efficient result only in the case that the whole section of the tunnel is open at once and there are no timbers to prevent the free swinging of the dipper handle and boom. But in tunnels through loose soils it is almost impossible to open the whole section at once without the necessity of supporting the roof. Consequently the use of steam shovel in loose tunnels is very limited. The shovel, the spade, and the pick, wielded by hand, are the standard tools now, as in the past, for excavating soft- ground tunnels. Rock-Excavating Machines. — At one period during the work of constructing the Hoosac tunnel considerable attention was devoted to the development of a rock excavating, boring, or tunneling machine. This device was designed to cut a groove around the circumference of the tunnel thirteen inches wide and twenty-four feet in diameter by means of revolving cutters. It proved a failure, as did one of smaller size, eight feet in diameter, tried subsequently. During and before the Hoosac tunnel work a number of boring-machines of similar character were experimented with at the Mont Cenis tunnel and elsewhere in Europe; but, like the American devices, they were finally abandoned as impracticable. Hand Drills. — Briefly described, a drill is a bar of steel having a chisel-shaped end or cutting-edge. The simplest form of hand drill is worked by one man, who holds the drill in one hand, and drives it with a hammer wielded by his other hand. A more efficient method of hand-drill work is, however, where one man holds the drill, and another swings the hammer or sledge. Another form of hand drill, called a churn drill, con- sists of a long, heavy bar of steel, which is alternately raised and dropped by the workman, thus cutting a hole by repeated impacts. In drilling by hand the workman holding the drill gives it a 24 TUNNELING partial turn on its axis at every stroke in order to prevent wedg- ing and to offer a fresh surface to the cutting-edge. For the same reason the chips and dust which accumulate in the drill-hole are frequently removed. The instruments used for this purpose are called scrapers or dippers, and are usually very simple in construction. A common form is a strong wire having its end bent at right angles, and flattened so as to make a sort of scoop by which the drilHngs may be scraped or hoisted out of the hole. It is generally advantageous to pour water into the drill-hole while drilling to keep the drill from heating. Power Drills. — When the conditions are such that use can be made of them, it is nearly always preferable to use power drills, on account of their greater speed of penetration and greater economy of work. Power drills are worked by direct steam pressure, or by compressed air generated by steam or water power, and stored in receivers from which it is led to the drills through iron pipes. A great variety of forms of power drills are available for tunnel work in rock, but they can nearly all be grouped in one of two classes: (1) Percussion drills, and (2) Rotary drills. Percussion Drills. — The first American percussion drill was patented by Mr. J. J. Couch of Philadelphia, Penn., in March, 1849. In May of the same year, Mr. Joseph W. Fowle, who had assisted Mr. Couch in developing his drill, patented a percussion drill of his own invention. The Fowle drill was taken up and improved by Mr. Charles Burleigh, and was first used on the Hoosac tunnel. In Europe Mr. Cave patented a percussion drill in France in October, 1851. This invention was soon followed by several others; but it was not until Som- meiller's drill, patented in 1857 and perfected in 1861, was used on the Mont Cenis tunnel, that the problem of the percussion drill was practically solved abroad. Since this time numerous percussion drill patents have been taken out in both America and Europe. EXCAVATING MACHINES AND ROCK DRILLS 25 A percussion drill consists of a cylinder, in which works a piston carrying a long piston rod, and which is supported in such a manner that the drill clamped to the end of the piston rod alternately strikes and is withdrawn from the rock as the piston reciprocates back and forth in the cylinder. Means are devised by which the piston rod and drill turn slightly on their axis after each stroke, and also by w^hich the drill is fed for- ward or advanced as the depth of the drill-hole increases. The drills of this type which are in most common use in America are the Ingersoll-Sergeant and the Rand. There are various other makes in common use, however, which differ from the two named and from each other chiefly in the methods by which the valve is operated. All of these drills work either with direct steam pressure or with compressed air. Workable percussion drills operated by electricity are built, but so far they do not seem to have been able to compete commercially with the older forms. No attempt will be made here to make a selection between the various forms of percussion drills for tunnel work, and for the differences in construction and the merits claimed for each the reader is referred to the makers of these machines. All of the leading makes will give efficient service. It goes almost without saying that a good percussion drill should operate with little waste of pressure, and should be composed of but few parts, which can be easily removed and changed. Drill Mountings. — For tunnel work the general European practice is to mount power drills upon a carriage moving on tracks in order that they be easily withdrawn during the firing of blasts. Connection is made with the steam or compressed air pipes by means of flexible hose which can easily be attached or detached as the drill advances or when it is moved for repairs or during blasts. Two, four, and sometimes more drills are mounted and work simultaneously on a single carriage. In America it has been found that column mountings have been more successful for tunnel work than any other form. The 26 TUNNELING column mounting made by the Ingersoll-Sergeant Drill Co. is shown in Fig. 12. In using this form of mounting no tracks or other special apparatus is required; it is not necessary, as Fig. 12. — Column Mounting for Percussion Drill: Ingersoll-Sergeant Drill Go. is the case with the carriage mounting, to remove the debris before resuming operations, but as soon as the blasting has been finished and the smoke has sufficiently disappeared the column can be set up and drilling resumed. EXCAVATING MACHINES AND ROCK DRILLS 27 Rotary Drills. — Rotary drilling machines, or more simply- rotary drills, were first used in 1857 in the Mont Cenis tunnel. The advantages claimed for rotary drills in comparison with percussion drills are: (1) That less power is required to drive the drill, and the power is better utihzed ; (2) once the machines work easily they do not require continual repairs, and (3) in driving holes of large size the interior nucleus is taken away intact, thus reducing work and increasing the speed of drilling. Rotary drills are extensively used for geological, mining, well- driving, and prospecting purposes; but they are very seldom employed in tunnels in America, although successfully used for this purpose in Europe. The reason they have not gained more favor among American tunnel builders is due to some extent perhaps to prejudice, but chiefly to the great cost of the machine as compared with percussion drills, and to the expense of diamonds for repairs. Those who advocate these machines for tunnel work point out, however, that under ordinary usage the diamonds have a very long hfe, — borings of 700 lin. ft. being recorded without repairs to the diamonds. The form of rotary drill used chiefly for prospecting pur- poses is the diamond drill. This machine consists of a hollow cyHndrical bit having a cutting-edge of diamonds, which is revolved at the rate of from two hundred to four hundred rev- olutions per minute by suitable machinery operated by steam or compressed air. The diamonds are set in the cutting-edge of the bit so as to project outward from its annular face and also slightly inside and outside of its cylindrical sides (Fig. 13). When the drill rod with the bit attached is rotated and fed forward the bit cuts an fig. is. -sketch of Diamond Drill Bit. annular hole into the rock ; the drillings being removed from the hole by a constant stream of water which is forced dowm through the hollow drill rod and emerges, carrying the debris with it, up through the narrow space between 28 TUNNELING the outside of the bit and the walls of the hole. There are various makes of diamond drills, but they all operate in essentially the same manner. The rotary drill principally employed in Europe in tunneHng is the Brandt. The cutting-edge of the Brandt drill consists of hardened steel teeth. The bit is pressed against the rock by hydraulic pressure, and usually makes from seven to eight revo- lutions per minute. Some of the water when freed goes through the hollow bit, keeping it cool, and cleaning the hole of debris. A w^ater pressure of from 300 to 450 lbs. per square inch is required to operate these drills. Rotary rock-drills may be mounted either on carriages or on columns for tunnel work. Several machines have recently been constructed for the pur- pose of breaking the rock in tunnels without blasting, but they did not .meet the approval of tunnel engineers. One of these machines is provided with numerous electric torches, which are applied to the rock at the front. By suddenly chilling the rock with a stream of cold water the stone will crumble away. An- other machine was tested, with little success, in the excavation for the New Grand Central Depot in New York. On the face of this machine there is a multitude of chipping drills revolving on four arms and driven by air pressure. They attack the rock and chip it into fragments, which are carried away by an endless band. EXPLOSIVES AND BLASTING. When the holes are once drilled, either by hand or power drills, they are charged with explosives. The principal explo- sives employed in tunneHng are gunpowder, nitroglycerine, and dynamite. Gunpowder. — Gunpowder is composed of charcoal, sulphur, and saltpeter in proportions varying according to the quality of the powder. For mining purposes the composition employed is 65 % saltpeter, 15 % sulphur, and 20 % charcoal. It is a black granulated powder having a specific gravity of 1.5; the black EXCAVATING MACHINES AND ROCK DRILLS 29 color is given by the charcoal; and the grains have an angular form, and vary in size from | in. to | in. Good blasting powder should contain no fine grains, which may be detected by pour- ing some of the powder upon a sheet of white paper. The force developed by the explosion of gunpowder is not accurately known; it depends upon the space in which it is confined. Dif- ferent authorities estimate the pressure at from 15,000 lbs. per sq. in. in loose blasts to 200,000 lbs. per sq. in. in gunnery. Authorities also differ in opinion as to the character of the gases developed by the explosion of gunpowder, a matter of vital concern to the tunnel engineer, since they are likely to affect the health and comfort of his workmen. It may be assumed in a general way, however, that the oxygen of the saltpeter converts nearly all of the carbon of the charcoal into carbon dioxide, a portion of which combines with the potash of the saltpeter to form carbonate of potash, the remainder con- tinuing in the form of gas. The sulphur is converted into sulphuric acid, and forms a sulphate of potash, which by reaction is decomposed into hyposulphite and sulphide. The nitrogen of the saltpeter is almost entirely evolved in a free state; and the carbon not having been wholly burnt into carbonic acid, there is a proportion of carbonic oxide. Nitroglycerine. — Nitroglycerine is one of the modern explo- sives used as a substitute for gunpowder. It is a fluid pro- duced by mixing glycerine with nitric and sulphuric acids; it freezes at +41° F., and burns very quietly, developing carbonic acid, nitrogen, oxygen, and water. By percussion or by the explosion of some substances, such as capsules of gunpowder or fulminate of mercury, nitroglycerine produces a sudden explosion in which about 1250 volumes of gases are produced. The pressure of these gases has been calculated at 26,000 at- mospheres, or 324,000 lbs. per sq. in. Nitroglycerine explodes very easily by percussion in its normal state, but with great difficulty when frozen; hence, in America, at the beginning of its use, it was transported only in a frozen state. When 30 TUNNELING dirty, nitroglycerine undergoes a spontaneous decomposition accompanied by the development of gases and the evolution of heat, which, reaching 388° F., causes it to explode. Notwith- standing the enormous pressures which nitroglycerine develops, it is very seldom used in its liquid state, but is mixed with a granular absorbent earth composed of the shells of diatoms. The fluid undergoes no chemical change by being absorbed, and explodes, freezes, and burns under the same conditions as in the fluid state. Dynamite. — The credit of rendering nitroglycerine available for the purposes of the engineer by mixing it with a granular absorbent is due to Albert Nobel of Stockholm, Sweden, who named the new material dynamite. The nitroglycerine in dynamite loses very little of its original explosive power, but is very, much less easily exploded by percussion, and can be employed in horizontal as well as vertical holes, which was, of course, not possible in its Hquid state. Dynamite must contain at least 50 % of nitroglycerine. Some manufacturers, instead of using diatomaceous earth, use other absorbents which develop gases upon explosion and increase the force of the explosion. These mixtures are classed under the general name of false dyna- mites. A great many varieties of dynamite are manufactured, and each manufacturer usually makes a number of grades to which he gives special names. Dynamite for railway work, tunnehng, and mining contains about 50 % of nitroglycerine ; for quarrying about 35 %, and for blasting soft rocks about 30 %. It is sold in cylindrical cartridges covered with paper. Storage of Explosives, — In driving tunnels through rock large quantities of explosives must be used, and it is necessary to have some safe place for storing them. In many States there are special laws governing the transportation and storage of explosives; where there is no regulation by law the engineer should take suitable precautions of his own devising. It is best to build a special house or hut in one of the most con- cealed portions of the work and away from the tunnel, and EXCAVATING MACHINES AND ROCK DRILLS 31 protect it with a lightning-rod and from fire. Strict orders should be given to the watchman in charge not to allow persons inside with lamps or fire in any form, and smoking should be prohibited. The use of hammers for opening the boxes should be prohibited; and dynamite, gunpowder, and fulminate of mercury should not be stored together in the same room. A quantity of dynamite for two or three days' consumption may be stored near the entrance of the tunnel in a locked box, the keys of which are kept by the foreman of the work. When dynamite has been frozen the engineer should provide some arrangement by which it may be heated to a temperature not exceeding 120° F., and absolutely forbid it being thawed out on a stove or by an open fire. Fuses. — When gunpowder is used in tunnehng it is ignited by the Blickford match. This match, or fuse as it is more commonly called, consists of a small rope of yarn or cotton having as a core a small continuous thread of fine gunpowder. To protect the outside of the fuse from moisture it is coated with tar or some other impervious substance. These fuses are so w^ell made that they burn very uniformly at the rate of about 1 ft. in 20 seconds, hence the moment of explosion can be pretty accurately fixed beforehand. Blickford matches have the ob- jection for tunnel work of burning with a bad odor, especially when they are coated with tar, and to remedy this many others have been invented. Those of Rzika and Franzl are the best known of these. The former has many advantages, but it burns too quickly, about 3 ft. per second, and is expensive; the latter consists of a small hollow rope filled with dynamite. Bhckford matches cannot be used to explode dynamite, the use of a cartridge being required. These cartridges are small copper cylinders containing fulminate of mercury. They may be attached to the end of the Blickford match, which being ignited the spark travels along its length until it reaches the copper cylinder, where it explodes the fulminate of mercury, which in turn explodes the dynamite. Blasts may also be fired 32 TUNNELING by electricity, which, in fact, is the most common and the preferable method, because several blasts can be fired simulta- neously, and because the current is turned on at a great dis- tance, thus affording greater safety to the workmen. The method of electric firing generally employed in America is known as the connecting series method, and consists in firing several mines simultaneously. The ends of the wdres are scraped bare, and the wire of the first hole of the series is twisted to- gether with the wire of the second hole, and so on; finally the two odd wires of the first and last holes are connected to two wires of a single cable or to two separate cables extending to some safe place to which the men can retreat. Here the two cable wires are connected by binding screws to the poles of a battery, or sometimes to a frictional electric machine. The cur- rent passes through the wires, making a spark at each break, and so fires the fulminate of mercury, which explodes the dynamite. Simultaneous firing by electricity by utilizing the united strength of the blasts at the same instant secures about 10 % greater efficiency from the explosives. Another advantage of electric firing is that in case of a missfire of any one of the holes there is slight possibility of explosion afterwards, and the place can be approached at once to discover the cause. Tamping. — Tamping is the material placed in the hole above the explosive to prevent the gases of explosion from escaping into the air. Tamping generally consists of clay. When gun- powder is used the clay must be well rammed with a wooden tool, and paper, cotton, or some other dry material must be placed betw^een the moist clay and the powder. When dyna- mite is used it is not necessary to ram the tamping, since the suddenness of the explosion shatters the rock before the clay can be driven from the hole. A few experienced men should be appointed to fire the blasts. These men should give ample warning previous to the blast in order that all machinery and tools which might be injured by fly- ing fragments may be removed out of danger, and so that the EXCAVATING MACHINES AND ROCK DRILLS 33 workmen may seek safety. When all is ready they should fire the blasts, keeping accurate count of the explosions to ensure that no holes have missed fire, and should call the work- men back when all danger is over. In case any hole has missed fire it should be marked by a red lamp or flag. Nature of Explosions. — When the explosives are ignited a sudden development of gases results, producing a sudden and violent increase of pressure, usually accompanied by a loud report. The energy of the explosion is exerted in all directions in the form of a sphere having its center at the point of explo- sion, and the waves of energy lose their force as the distance from this central point increases. The energy of the explosion at any point in the sphere of energy is, therefore, inversely proportional to the distance of this point from the center of explosion. In the vicinity of the center of explosion the gases have sufficient power to destroy the force of cohesion and shatter the rock; further on, as they lose strength, they only destroy the elasticity of the material and produce cracks; and still further away they only produce a shock, and do not affect the material. Within the sphere of energy there are, therefore, three other concentric spheres: the first one being where cohesion is destroyed, the second where elasticity is overcome, and the third where the shock is transmitted by elasticity. When the latter sphere comes below the surface, the gases remain inside the rock; but when the surface intersects either of the other two spheres, the gases blow up the rock, forming a cone or crater, whose apex is at the point of explosion, and which is called the blasting-cone. The larger the blasting-cone is, the greater is the amount of rock broken up; and .the object of the engineer should, therefore, always be so to regulate the depth of the hole and the quantity of explosive as to secure the largest possible blasting cone in each case. Experiments are required to determine the most efficient depth of hole, and quantity of explosive to be employed, since these differ in different kinds of rock, with the position of the rock strata, 34 TUNNELING etc.; but in ordinary practice, the depths of the holes are made from 2 to 3 ft. in the heading and upper portion of the tunnel, when drilled by hand; and from 6 to 8 ft. when drilled by power drills. In the lower portion of the profile, the holes are made deeper, from 3 ft. to 4 ft. when drilled by hand, and exceeding 6 ft. when drilled by power. The distance of the holes apart should be about equal to the diameter of the blasting-cone ; as a general rule it is assumed that the base of the blasting-cone has a diam- eter equal to twice the depth of the hole. The following table gives the average number of holes required in each part of the excavation for the St. Gothard tunnel in which the heading was excavated by machine drills while the other parts were excavated by hand drills : NO. OF PAKT.* NAME OF PABT. NO. OF HOLES 1. Heading 6 to 9 2. Right wing of heading 3to5 3. Left wing of heading 3 to 5 4. Shallow trench with core 2 5. Deepening of trench to floor 6 to 9 6. Narrow mass of core to left 3 7. Greater mass of core to left 6 to 9 8. Culvert J Total section 30 to 43 The quantity of explosives required for blasting depends upon the quality of the rock, since the force of the explosives must overcome the cohesion of the rock, which varies with its nature, and often differs greatly in rocks of the same kind and composition. The quantity of explosives required to secure the greatest efficiency in blasting any particular rock may be determined experimentally, but in practice it is usually deduced by the following rules: (1) The blasting force is directly pro- portional to the weight of the explosives used, and (2) the bulk of the blasted rock is proportional to the cube of the depth of the holes. It is usually assumed, also, that the explosive should fill at least one-fourth the depth of the hole. * The location of the parts numbered is shown by Fig. 14, p. 36. EXCAVATING MACHINES AND ROCK DRILLS 35 The following table gives the depth of holes and amount of dynamite used at each advance in the Fort George Tunnel illustrated on page 155. Order of Firing. Kinds of Holes. Depth. Charge. Kind of Dynamite. |-| 1 1st round «B |2nd round !>„ f3d round ^^J4th round ®K 1 5th round 4 grading 5 bench 6 trimming 8 center cut 8 side 6 dry 3' to 5' 9' 6" 3' to 9' 9' 8' 8' 50 lbs. 45 " 42 " 56 " 48 " 36 " 40% climax 40% - 40% - 60% " 40% '' 40% - 36 TUNNELING CHAPTER IV. GENERAL METHODS OF EXCAVATION: SHAFTS CLASSIFICATION OF TUNNELS. A NUMBEK of different modes of procedure are followed in excavating tunnels, and each of the more important of these will be considered in a separate chapter. There are, however, certain characteristics common to all of these methods, and these will be noted briefly here. Division of Section. — It may be asserted at the outset that the whole area of the tunnel section is not ordinarily excavated at one time, but that it is removed in sections, and as each section is excavated it is thoroughly timbered or strutted. The order in which these different sections are excavated varies with the method of excavation, and it is clearly shown for each method in succeeding chap- ters. As a single example to illus- trate the proposition just made, the division of the section and the se- quence of excavation adopted at the St. Gothard tunnel is selected (Fig. 14). The different parts of the section were excavated in the order numbered ; the names given to each part, and the number of holes employed in breaking it down, are given by the table on page 34. Whatever method is employed, the work always begins by driving a heading, which is the most difficult and expensive part of the excavation. All the other operations required in breaking down the remainder Fig. 14. — Diagram Showing Sequence of Excavation for St. Gothard Tunnel. GENERAL METHODS OF EXCAVATION 37 of the tunnel section are usually designated by the general term of enlargement of the profile. The various operations of excavation may, therefore, be classified either as excavation of the heading or enlargement of the profile. Excavation of the Heading. — There is considerable confusion among the different authorities regarding the exact definition of the term "heading" as it is used in tunnel work. Some authorities call a small passage driven at the top of the profile a heading, and a similar passage driven at the bottom of the profile a drift ; others call any passage driven parallel to the tunnel axis, whether at the top or at the bottom of the profile, a drift; and still others give the name "heading" to all such passages. For the sake of distinctness of terminology it seems preferable to call the passage a heading when it is located at the top of the profile, and a drift when it is located near the bottom. Headings and drifts are driven in advance of the general excavation for the following purposes : (1) To fix correctly the axis of the tunnel; (2) to allow the work to go on at different points without the gangs of laborers interfering with each other ; (3) to detect the nature of material to be dealt with and to be ready in any contingency to overcome any trouble eaused by a change in the soil ; and (4) to collect the water. The dimensions of headings in actual practice vary according to the nature of the soil through which they are driven. As a general rule they should not be less than 7 ft. in height, so as to allow the men to work standing, and have room left for the roof strutting. The width should not be less than 6 ft., to allow two men to work at the front, and to give room for the material cars without interfering with the wall strutting. Usually headings are made 8 ft. wide. The length of headings in practice varies according to circumstances. In very long tunnels through hard rock the headings are sometimes ex- cavated from 1000 ft. to 2000 ft. in advance, in order that they may meet as soon as possible and the ranging of the center line 38 TUNNELING be verified, and so that as great an area of rock as possible may be attacked at the same time in the work of enlarging the profile. In short tunnels, where the ranging of the center line is less liable to error, shorter headings are employed, and in soft soils they are made shorter and shorter as the cohesion of the soil decreases. When the material has too little cohesion to stand alone, the tops and sides of the heading require to be supported by strutting. To prevent caving at the front of the heading, the face of the excavation is made inclined, the inclination following as near as may be the natural slope of the material. Enlargement of the Profile. — The enlargement of the profile is accomplished by excavating in succession several small prisms parallel to the heading, and its full length, which are so located that as each one is taken out the cross-section of the original heading is enlarged. The number, location, and sequence of these prisms vary in different methods of excavation, and are explained in succeeding chapters where these methods are described. To direct the excava- tion so as to keep it always within the boundaries of the adopted pro- file, the engineer first marks the center line on the roof of the heading by wooden or metal pegs, or by some other suitable means by which a plumb line may be suspended. He next draws to a large scale a profile of the proposed section; and beginning at the top of the vertical axis he draws horizontal lines at regular intervals, as shown by Fig. 15, until they inter- sect the boundary lines of the profile, and designates on each of these lines the distance between the vertical axis and the point where it intersects the profile. It is evident that' if the foreman of excavation divides his plumb line in a manner corre- sponding to the engineer's drawing, and then measures horizon- Fig. 15 — Diagram Showing Manner of Determining Correspondence of Excavation to Sectional Profile. GENERAL METHODS OF EXCAVATION 39 tally and at right angles to the vertical center plane of the tunnel the distance designated on the horizontal lines of the drawing, he will have located points on the profile of the sec- tion, or in other words have established the limits of excava- tion. In the excavation of the Croton Aqueduct for the water supply of New York city, an instrument called a polar pro- tractor was used for determining the location of the sectional Fig. 16.— Polar Protractor for Determining Profile of Excavated Cross-Section. profile. It was invented by Mr. Alfred Craven, division engi- neer of the work. This instrument consists of a circular disk graduated to degrees, and mounted on a tripod in such a manner that it may be leveled up, and also have a vertical motion and a motion about the vertical axis. The construction is shown clearly by Fig. 16. In use the device is mounted with its center at the axis of the tunnel. A light wooden measuring- rod tapering to a point, shod with brass and graduated to feet and hundredths of a foot, lies upon the wooden arm or rest, which revolves upon the face of the disk, and slides out to 40 TUNNELING a contact with the surface of the excavation at such points as are to be determined. If the only information desired is whether or not the excavation is sufficient or beyond the es- tablished lines, the rod is set to the proper radius, and if it swings clear the fact is determined. If a true copy of the actual cross-section is desired, the rod is brought into contact with the significant points in the cross-section, and the angles and distances are recorded. The general method of directing the excavation in enlarging the profile by referring all points of the profile to the vertical axis is the one usually employed in tunneling, and gives good results. It is considered better in actual practice to have the excavation exceed the profile somewhat than to have it fall short of it, since the voids can be more easily filled in with riprap than the encroaching rock can be excavated during the building of the masonry. In tunnels where strutting is neces- sary the excavation must be made enough larger than the finished section to provide the space for it. In soft-ground tunnel's it is also usual to enlarge the excavation to allow for the probable slight sinking of the masonr}^ The proper allow- ance for strutting is usually left to the judgment of the fore- man of excavation, but the allowance for settlement must be fixed by the engineer. SHAFTS. Shafts are vertical walls or passages sunk along the line of the tunnel at one or more points between the entrances, to permit the tunnel excavation to be attacked at several different points at once, thus greatly reducing the time required for excavation. Shafts may be located directly over the center of the tunnel or to one side of it, and, while usually vertical, are sometimes inclined. During the construction of the tunnel the shafts serve the same purpose as the entrances ; hence they must afford a passageway for the excavated materials, which GENERAL METHODS OF EXCAVATION 41 have to be hoisted out, and also for the construction tools and materials which have to be lowered down them. They must also afford a passageway for workmen, draft animals, and for pipes for ventilation, water, compressed air, etc. The character of this traffic indicates the dimensions required, but these de- pend also upon the method of hoisting employed. Thus, when a vdndlass or horse gin is used, and the materials are hoisted in buckets of small dimensions, the dimensions of the shaft may also be small; but when steam elevators are employed, and the material is carried on cars run on to the platform of the elevator, large dimensions must be given to the shaft. Generally the parts of the shaft used for different purposes are separated by partitions. The elevator for workmen and the various pipes are placed in one compartment, while the elevator for hoisting the excavated material and lowering construction material is placed in another. Shafts may be either temporary or permanent. They are temporary when they are filled in after the tunnel is completed, and permanent when they are left open to supply ventilation to the tunnel. Permanent shafts are usually made circular, and lined with brick, unless excavated in very hard and durable rock. When sunk for temporary use only, shafts are usually made rectangular with the greater dimension transverse to the tunnel. They are strutted with timber. A pump is generally located at the bottom of the shaft to collect the water which seeps in from the sides of the shaft and from the tunnel excavation. The dimensions of this pump will of course vary with the amount of water encountered, as will also the capacity of the pump for forcing it up and out of the shaft, which has always to be kept dry. The majority of engineers prefer to sink shafts directly over the center line of the tunnel. Side shafts are employed chiefly by French engineers. The chief advantage of the former method is the great facility which it affords for hoisting out the materials, while in favor of the latter method is the 42 TUNNELING non-interference of the shaft with the operations inside the tunnel. Were it not that the side shaft requires the intro- duction of a transverse gallery connecting it with the tunnel, it would be on the whole superior to the center shaft ; but the side gallery necessitates turning the cars at right angles, and consequently the use of a very sharp curve or a turntable to reach the shaft bottom, which is a disadvantage that may outweigh its advantages in some other respects. It is impos- sible to state absolutely which of these methods of locating shafts is the best ; both present advantages and disadvantages, and the use of one or the other is usually determined more by the local conditions than by any general superiority of either. When side shafts are employed they are sometimes made inclined instead of vertical. This form is used when the depth of the shaft is small. By it the hauling is greatly simplified, since the cars loaded at the front with excavated material can be hauled directly out of the shaft and to the dumping-place, surmounting the inclined shaft by means of continuous cables. The short galleries connecting the side shafts with the tunnel proper usually have a smaller section than the tunnel, but are excavated in exactly the same manner. Another form of side shaft sometimes used is one reaching to the surface when the tunnel runs close to the side of cliff, as is the case with some of the Alpine railway tunnels. CLASSIFICATION OF TUNNELS. Tunnels are classified in various ways, but the most logical method would appear to be a grouping according to the quality of the material through which they are driven ; and this method will be adopted here. By this method we" have first the fol- lowing general classification : (1) Tunnels in hard rock ; (2) tunnels in ordinary loose soil; (3) tunnels in quicksand; (4) open-cut tunnels ; and (5) submarine tunnels. It is hardly necessary to say that this classification, like all others, is simply GENERAL METHODS OF EXCAVATION 43 an arbitrary arrangement adopted for the sake of order and convenience in treating the subject. Tunnels in Hard Rock. — With the numerous labor-saving methods and machines now available, hard rock is perhaps the safest and easiest of all materials through which to drive a tunnel. Tunnels through hard rock may be excavated, either by a drift or by a heading. The difference depends upon whether the advance gallery is located close to the floor or near the soffit of the section. Tunnels in Loose Soils. — In driving tunnels through loose soils many different methods have been devised, which may be grouped as follows : (1) Tunnels excavated at the soffit — Belgian method; (2) tunnels excavated along the perimeter — German method; (3) tunnels excavated in the whole section — English, Austrian and American methods; (4) tunnels exca- vated in two halves independent of each other — Italian method. (1) Excavating the tunnel by beginning at the soffit of the section, or by the Belgian method, is the method ^of tunnel- ing in loose soils most commonly employed in Europe at the present time. It consists in excavating the soffit of the section first ; then building the arch, which is supported upon the unexcavated ground ; and finally in excavating the lower portion of the section, and building the side walls and invert. (2) In excavating tunnels along the perimeter an annular excavation is made, following closely the outhne of the sec- tional profile in which the lining masonry is built, after which the center core is excavated. In the German method two drifts are opened at each side of the tunnel near the bottom. Other drifts are excavated, one above the other, on each side to extend or heighten the first two until all the perimeter is open except across the bottom. The masonry lining is then built from the bottom upwards on each side to the crown of the arch, and then the center core is removed and the invert is built. 44 TUNNELING (3) This method, as its name implies, consists in taking out short lengths of the whole sectional profile before begin- ning the building of the masonry. In the English method the invert is built first, then the side walls, and finally the arch. The excavators and masons work alternately. The Austrian method differs in two particulars from the EngHsh: the length of section opened is made great enough to allow the excavators to continue work ahead of the masons, and the side walls and roof are built before the invert. In the American method the whole section of the tunnel is open a,t once : exca- vators and masons work simultaneously, hut a very large quantity of timbering is required. / (4) The Italian method is very seldonz employed on account of its expensiveness, but it can often be used where the other methods fail. It consists in excavating the lower haK of the section, and building the invert and side walls, and then filling the space between the walls in again except for a narrow passageway for the cars ; next the upper part of the section is excavated, as in the Belgian method, and the arch is built ; and finally the soil in the lower part is permanently removed. Tunnels in Quicksand. — Tunnels through quicksand are driven by one of the ordinary soft-ground methods after drain- ing away the water, or else as submarine tunnels. Open-Cut Tunnels. — Open-cut tunnels are those driven at such a small depth under the surface that it is more convenient to excavate an open cut, build the tunnel masonry inside it, and then refill the open spaces, than it is to carry on the work entirely underground. In firm soils the usual mode of opera- tion is to excavate first two parallel trenches for the side walls, then remove the core, and build the arch and the invert. In unstable soils, since the invert must be built first, it is usual to open up a single wide trench. In infrequent cases where a tunnel is desired in a place which is to be filled in, the masonry is built as a surface structure, which in due time is covered. GENERAL METHODS OF EXCAVATION 45 Submarine Tunnels. — The mode of procedure followed in excavating submarine tunnels depends upon whether the mate- rial penetrated is pervious or impervious to water. In imper- vious material any of the ordinary methods of tunneling found suitable may be employed. In pervious material the excava- tion may be accomplished either by means of compressed air to keep the water out of the excavation, or by means of a shield closing the front of the excavation, or by a combination of these tw^o methods. Tunnels on the river bed are built by means of coffer dams which inclose alternate portions of the work, by sinking a continuous series of pneumatic caissons and opening communication between them, and by sinking the tunnel in sections constructed on land. In hard rock. In loose soil. < Methods of Excavating German method. English method. Austrian method. 1^ American method. > Italian method. In quicksand. Open-cut tunnels. Submarine tunnels. Ill resistant soils. In loose soils. ^ Built up. ' At great depths under the river bed. At small depths under the river bed. On the riverbed."^ By two lateral nar- row trenches. By one very large trench. By slices. By any method. f By shield. J By compressed air. I By shield and com- [ pressed air. f By coffer dams. J By pneumatic cais- j sons. t By built-up sections. 46 TUNNELING The above diagram gives in compact form the classifica- tion of tunnels according to materials penetrated and methods of excavation adopted, which have been described more fully in the succeeding paragraphs. It may be noted here again that this is a purely arbitrary classification, and serves mostly as a convenience in discussing the different classes of tunnels with- out confusion. TIMBERING OR STRUTTING TUNNELS 47 CHAPTER V. METHODS OF TIMBERING OR STRUTTING TUNNELS. The purpose of timbering or strutting in tunnel work is to prevent the caving-in of the roof and side walls of the exca- vation previous to the construction of the lining. As the strutting has to resist all the pressures developed in the roof and side walls, which may be exceedingly troublesome and of great intensity in loose soils, its design and erection call for particular care. The method of strutting adopted depends upon the method of excavation employed; but in every case the problem is not only to build it strong enough to withstand the pressures developed, but to do this as economically as possible, and with as little hindrance as may be to the work which is going on simultaneously and which will come later. Only the latter general problems of strutting peculiar to all methods of tunnel work will be considered here. For this consideration strutting may be classified according to the material of which it is built, under the heads of timber struc- tures and iron structures. TIMBER STRUTTING. Timber is nearly always employed for strutting in tunnel work. So long as it has the requisite strength, any kind of timber is suitable for strutting, since, it being only temporarily employed, its durability is a matter of slight importance. Timber with good elastic properties, like pine or spruce, is preferably chosen, since it yields gradually under stress, thus 48 TUNNELING warning the engineer of the approach of danger ; while oak and other strong timbers resist until the last moment, and then yield suddenly under the breaking load. Soft woods, moreover^ are usually lighter in weight than hard woods, which is a con- siderable advantage where so much handling is required in a restricted space. Round timbers are generally employed, since they are less expensive, and quite as satisfactory in other respects as sawed timbers. In the English and Austrian methods of strutting, which are described further on, a few of the principal struts are of sawed timbers. The various timbers of the strutting are seldom attached by framed joints, but wedges are used to give them the necessary bearing against each other. Where framed joints are em- FiG.iT.-joining Tunnel struts ployed the v are made of the by Halving. f J J simplest form usually by 11- -, . . . .1 1 ^ ^. ^^ FlG.18. -Round halving the joining timbers, as shown by Fig. 17. Timber post Fig. 18 shows a form of joint used where round ^^"^^capBear- posts carry beams of similar shape. The reason why it is possible to do away with jointed connections to such a great extent, is that the strains which the timbers have to resist are either compressive or bending strains, and because the timbers are so short that they do not require to be spliced. Strutting of Headings. — The method of strutting the head- ing that is employed depends upon the material through which the heading is driven. In solid rock strutting may not be required at all, or only for the purpose of preventing the fall of loose blocks from the roof, then vertical props are erected where required, or horizontal beams are inserted into the side walls, as shown by Fig. 19. These horizontal beams may be used singly at dangerous places, or they may be placed from 2 ft. to 3 ft. apart all along the heading. In the latter case they usually carry a lagging of planks, which may be placed at intervals or close together, and filled above with Tl^lBElilNG Oil STIIUTTING TUNNELS 49 stone in case the roof of the excavation is very unstable. Planks used in this manner are usually called poling-boards. Where the side walls as well as the roof require support, Fig, 19. — Ceiling Strutting for Tunnel Koofs, Fig. 20. Ceiling Strutting with Side Post Supports. vertical side posts are employed to carry the roof beams, as shown by Fig. 20; and, when necessary, poling-boards are inserted between these posts and the walls of the excavation. Frame Strutting. — In very loose soils not only the roof and side Avails, but also the floor of the heading require strutting. Fig. 21. — Sill, Side Post and Cap Cross Frame Strutting. Pig. 22. — Reinforced Cross Frame Strutting for Treacherous Materials. In these cases frame strutting is employed, as shown by Fig. 21. It consists simply of a rectangular frame; at the top there is a crown bar supported by two vertical side posts 50 TUNNELLSG setting on a sill laid across the bottom of the heading. These frames are spaced at close intervals, and carry longitudinal planks or poling-boards. The sill of the frame is sometimes omitted when the soil is stable enough to permit it, and in its place Avooden footing blocks are substituted to carry the side posts. In soils where the pressures are great enough to bend the crown bar, a secondary frame is employed, as shown by Fig. 22, the two inclined roof members, or rafters, of which support the crown bar at the center. It is the more common practice in driving headings through soft soils to use inclined poling-boards to support the roof. m!^ ^ m -^ ^^^^^^=--^= ^^ — W!^ r^ 1 M P 1 1 '-'•^ f^0^^W^ym Fig. 23. — Longitudinal Poling-Board Sys- tem of Roof Strutting. Fig. 24. — Transverse Poling-Board System of Roof Strutting. Fig. 23 shows one method of doing this. The method of operation is as follows : Assuming the poling-boards a and b to be in place, and supported by the frames A, B (7, as shown, the first step in continuation of the work is to insert the poling-board c over the crown bar of frame (7, and under the block m. Excavation is then begun at the top, and as fast as the soil is removed ahead of it the poling-board c is driven ahead until its rear end only slightly overhangs the crown bar of frame C. The remainder of the face of the heading is then excavated nearly to the front end of the poling-board c, and another frame is set up. By a succession of these operations TIMBERING OR STRUTTING TUNNELS 51 the heading is advanced. The poling-boards at the sides of the heading are placed in a similar manner to the roof poling- boards. A second method of using inclined poling-boards is shown by Fig. 24. Here the poling-boards run transversely, and are supported by the arrangement of timbering shown. The chief advantage of using these inclined poling-boards, particularly in the manner shown by Fig. 23, is that the excavators work under cover at all times, and are thus safe from falling fragments or sudden cavings. Box Strutting. — In very treacherous soils, such as quick- sand, peat, and laminated clay, box strutting is commonly em- ployed. The method of building this strutting is to set up at the face of the work a rectangular frame, and use it as a guide in driving a lagging or boxing of horizontal planks into the soft soil ahead. These planks have sharp edges, and are driven to a distance of 2 ft. or 3 ft. into the face of the heading, so as to inclose a rectangular body of earth. This earth is excavated nearly to the ends of the planks, and then another frame is inserted close up against the new face of the excavation, which supports the planks so that the remainder of the earth included by them may be removed. These two frames, with their plank lagging, constitute a " box ; " and a series of these boxes, one succeeding another, form the strutting of the heading. Strutting the Face. — In some cases it is found necessary to strut the face of the heading in order to prevent it from caving in. This is generally done by setting plank vertically, and bracing them up by means of inclined props whose feet abut against the sill of the nearest cross frame. This strutting is erected while the workmen are placing the side and roof strutting, and is removed to permit excavation. Full Section Timber Strutting. — For strutting the full section two forms of timbering are employed, known as the polygonal system and the longitudinal system. Longitudinal strutting consists of a timber structure so arranged as to have all the principal members supporting the 52 TUNNELING poling-boards parallel to the axis of the tunnel. This system of strutting is peculiar to the English method of tunneling. The longitudinal timbers rest on this finished masonry at one end, and are carried on a cross frame or by props at the other end. At intermediate points the longitudinals are braced apart by struts in planes transverse to the tunnel axis. This construction makes a very strong strutting framework, since the transverse struts act as arch ribs to stiffen the longitu- dinals ; but the use of transverse poling-boards requires the excavation of a larger cross-section than is necessary when longi- tudinal poling-boards are employed, and this increases the cost both for the amount of earth excavated and the greater quantity of filling required. In polygonal strutting the main members are in a plane normal to the axis of the tunnel. They form a polygon whose sides follow closely the sectional profile of the excavation. These polygonal frames are placed at more or less short inter- vals apart, and are braced together by short longitudinal struts lying close to the sides of the excavation, and running from one frame to the next, and also by longer longitudinal members which extend over several frames. The polygonal system of strutting is peculiar to the Austrian method of tunneling, and is fully described in a succeeding chapter. One of its distinc- tive characteristics is that the poling-boards are in- serted parallel to the tunnel axis. Polygonal strutting is generally held to be stronger than longitudinal strutting under uniform loads, but it is more liable to distortion when the loads are unsymmetrical. Strutting of Shafts. — Tunnel shafts are strutted both to prevent the caving-in of the sides and to divide them into Fig. 25,— Shaft with Single Transverse Strutting. TIMBEKING OR STRUTTING TUNNELS 53 compartments. When the material penetrated is very compact, and caving is not likely, a single series of transverse struts, one above the other, running from the top to the bottom of the shaft, as shown by Fig. 25, is used to divide it into two com- partments. In softer material, where the sides of the shaft require support, Fig. 26 shows a form of strutting commonly employed. It consists of vertical corner posts braced apart at inter- vals by four horizontal struts placed close to the walls of the shaft. The long-er side ^ Fig. 26.— Rectangular Frame Strutting for Shafts. struts are also braced apart at the center by a middle strut which divides the shaft into two compartments. A lagging of vertical plank is placed between the walls of the shaft and the horizontal side struts. In very loose soils the form of strutting shown by Fig. 27 is employed. This is practically the same construction as is shown by Fig. 26, with the addition of an interior polygonal horizontal bracing in each half of the shaft. Referring to Fig. 27, the timbers a^ «, etc., are vertical and con- tinuous from the top to the bottom of the shaft; and the horizontal timbers, 5, 5, etc., are spaced at more or less close intervals verti- cally. The lagging plank may be laid with spaces between them, or close together, or, in case of very loose material, with their edges overlapping. The manner of constructing the strutting is also governed by the stability of the soil. In firm soils it is possible to sink the shaft quite a depth vrithout timbering, and the timbering can Fig. 27. — Reinforced Rectangular Frame Strut- ting for Shafts in Treacherous Materials. 54 TUNNELING be erected in sections of considerable lengtb, which is always an advantage, but in loose soils the timbering has to follow closely the excavation. The solid wall shaft struttings which have been described are discontinued at the point where the shaft intersects the tunnel excavation ; and from this point to the floor of the tunnel an open timbering is employed, whose only duty is to support the weight of the solid strutting above. This timber- ing is made in various forms, but the most common is a timber truss or arch construction which spans the tunnel section. Quantity of Timber. — The quantity of timber employed in strutting a tunnel varies with the character of the material through which the tunnel is excavated : it is small for solid- rock tunnels, and large for soft-ground tunnels. In the Bel- gian method of excavation a smaller quantity of timber is used than in any of the other ordinary methods. For single- track tunnels excavated by this method there will be needed on an average about 3 to 3 J cu. yds. of timber per lineal foot of tunnel. Practical experience shows that about four-fifths of the timber once used can be employed for the second time. In any of the methods in which the whole tunnel section is excavated at once, the average amount of timber required per lineal foot is about 8.7 cu. yds. Of this amount about two- thirds can be used a second time. In the Italian method, in which the upper half and the lower half are excavated separately, about 5 cu. yds. of timber are required per lineal foot of tunnel, about one-half of which can be employed a second time. For qaicksand tunnels the amount of timbering required per lineal foot varies from 3 to 5 cubic yds. Shaft strutting requires from 1 to 1^ cu. yds. of timber per lineal foot. Dimensions of Timber. — The dimensions of the principal mem- bers composing the strutting of headings, full section, and shafts, are given in Table I. The planks used for lagging or the poling-boards are usually from 4 ins. to 6 ins. wide, with a length depending upon the method of strutting employed. TIMBERING OR STRUTTING TUNNELS 55 TABLE I. Showing Sizes of Various Timbers Used in Strutting Tunnels Driven Through Different Materials. Headings : Cap-pieces and vertical struts Sills Struts Distance apart of the frames in feet . . . Strutting of the tunnel, longitudinal strutting : Crown bars Props vertical or inclined supporting the crown bars Sills Cap-pieces or saddles Struts to stiffen the structure Distance apart of the frames (in feet) . . . Polygonal strutting : Cap-pieces and contour pieces Vertical struts on top Vertical struts below Intermediate sills Lower sills Raking props Distance apart of the frames (in feet) . . . Shafts : Horizontal beams forming the frame . . . . Transverse beams Vertical struts between the frames Struts to reenforce the frame Distance apart of the strutting (in feet) . . . Rock. Soft Soils. 1 1 8 I 6 3 >> «5 S '8 ins. ins. ins. ins. ins. 6 8 10 12 14 8 10 12 5 5 6 7 8 6 4.5 3 2.6 2.6 12 14 14 10 12 14 8 8 10 10 12 14 6 8 10 4.5 4 3 8 10 12 14 16 10 12 14 16 18 12 14 16 20 24 12 14 16 20 24 12 16 18 10 10 10 12 12 6 4.5 4 3 3 8 8 10 12 14 8 8 8 10 12 8 8 10 12 12 6 8 8 8 6 4.5 4 3 2.6 IRON STRUTTING. In 1862 Mr. Rziha employed old iron railway rails for strutting the IS'aensen tunnel, and his example was successfully followed in several tunnels built later where timber was scarce 66 TUNNELING Fig. 28. —Strut- ting of Timber Posts and Rail- way Rail Caps. Fig. 29. — Strutting made entirely of Railway Rails. and expensive. The advantages which iron strutting is claimed to possess over the more common wooden structure are : its greater strength ; the smaller amount of space which it takes up ; and the fact that it does not wear out, and may, therefore, be used over and over again. Iron Strutting in Headings. — In strutting the headings the cross frames have a crown bar consisting of a section of old railway rail carried either by wood or iron side posts. When wooden side posts are used their upper ends have a dovetail mor- tise, and are bound with an iron band, as shown by Fig. 28. The base of the rail crown bar is set into the dovetail mortise and fastened by wedges. When iron side posts are employed they usually consist of sections of rail- way rails, and the crown bar is attached to them by fish-plate connections, as shown by Fig. 29. The iron cross frames are set up as the heading advances, and carry the plank lagging or poling-boards, exactly in the same manner as the timber cross frames previ- ously described. Full Section Iron Strutting. — The iron strutting devised by Mr. Rziha for full section work is shown by Fig. 30. Briefly described, it consists of voussoir-shaped cast-iron segments, which are built up in arch form. Fig. 31 shows the construc- tion of one of the segments, all of which are alike, with the exception of the crown segment, which has a mortise and tenon joint which is kept open by filling the mortise with sand. The segments are bolted together by means of suitable bolt- holes in the vertical flanges, and when fully connected form an arch rib of cast iron. This arch rib, A, Fig. 30, carries a series of angle or T-iron frames bent into approximately voussoir shape, as shown at B, Fig. 30. Above these frames are inserted TIMBERING OR STRUTTING TUNNELS 57 Fig. ). — Rziha's Combined Strutting and Centering of Cast Iron. the poling-boards, running longitudinally, and spanning the distance between consecutive arch ribs. By removing the bent iron frames the cast-iron rib forms a center upon which to con- struct the masonry. Fi- nally, to remove the cast- iron rib itself, the sand is drawn out of the mor- tise and tenon joint in the crown segment, which allows the joint to close, and loosen the segments so that they are easily unbutted. The illustration. Fig. 30, shows longitudinal poling-boards ; more often longitudinal crown bars of railway rails span the space between connective arch ribs, and support transverse poUng-boards. In building the masonry, work is begun at the bottom on each side, the bent iron frames being removed one after another to give room for the masonry. As each frame is removed, it is replaced with a sort of screw- jack to support the poling-boards until the masonry is sufficiently completed to allow their removal. The interior bracing of the arch rib shown at a a and h h consists of railway rails carried by brack- ets cast on to the segments. A similar bracing of rails connects the successive arch ribs. These lines of bracing serve to carry the scaffolding upon which the masons work in building the lining. Iron Shaft Strutting. — In soft-ground shaft work, the use of an iron strutting, consisting of consecutive cast-iron rings, has Fig. 31. — Cast-iron Segment of Rziha's Strutting and Centering. 58 TUNNELING sometimes been employed to advantage. Fig. 32 shows the construction of one of these rings, which, it will be seen, is com- posed of four segments connected to each other by means of bolted flanges. The holes shown in the circumferential web of the ring are to allow for the seepage from the earth side walls. The method of placing this cylindrical strutting is to start with a ring having a cutting-edge. By means of excavation inside the ring, and by ramming, the ring is sunk into the ground a distance equal to its height. Another ring is then fastened by special hooks on top of the first one, and the sinking continued until the second ring is down flush with the surface. A third ring is then added, and so on until the entire shaft is excavated and strutted. As in timber shaft strutting, the solid iron ring strutting is carried down only to the top of the tunnel section, and below this point there is an open timber or iron supporting framework. Fig. 32. ■Cast-iron Segmental Strutting for Shafts. METHODS OF HAULING IN TUNNELS 59 CHAPTER YL METHODS OF HAULING IN TUNNELS. The transportation from one point to another within the tunnel and its shafts of any material, whether it is excavated spoil or construction material, is defined as hauling. In all engineering construction, the transportation of excavated materials, and materials for construction, constitutes a very important part of the expense of the work; but hauling in tunnels where the room is very limited, and where work is constantly in progress over and at the sides of the track, is a particularly expensive process. Hauling in tunnels may be done either by way of the entrances, or by way of the shafts, or by way of both the entrances and shafts. Hauling by Way of Entrances. — When the hauling is done by the way of the entrances, the materials to be hauled are taken directly from the point of construction to the en- trances, or in the opposite di- rection, by means of special cars of different patterns. For general purposes, these differ- ent patterns of cars may be grouped into three classes, — platform-cars, dump-cars, and box-cars. Representative ex- amples of these several classes of cars are shown in Figs. 33 to 36 * inclusive, but it will be readily understood that there are many other forms. Briefly described, platform-cars (Fig. 33) consist of a * Reproduced from catalogue of Arthur Koppel, New York. Fig. S3 — Platform Car for Tunnel Work. 60 TUNNELING Fig. 34. — Iron Dump-Car for Tunnel Work. wooden platform mounted on tracks, and they are usually em- ployed for the transportation of timber, ties, etc. Dump-cars are used in greater numbers in tunnel work than any other form. Fig. 34 shows a dump-car of metal construction, and Fig. 35 one constructed with a metal under-frame and wooden box. Ihese cars are made to run on narrow-gauge tracks, and usually liave a capacity of about one to one and one-half cubic yards. Box-cars are more extensively employed in Europe for tunnel work than in Arnerica. Fig. 36 shows a typical European box-car for tunnel work. It is made either to run on narrow-gauge or standard- gauge tracks. It is usually desirable in tunnel work to employ cars of different forms for different parts of the work. hi rock tunnels it is a common practice to use narrow-gauge cars of small size in the headings, and larger, broad-gauge cars for the enlargement of the profile. Where narrow-gauge cars are employed for all purposes, it will also be found more convenient to use platform-cars for handling the construction material, and dump-cars for removing the spoil. The extent to which it is desir- able to use cars of different forms Fia. 35. -wooden nump-Car for Tunnel Work. will depend upon the character and conditions of the work, and particularly upon how far it is possible to install the permanent track. As a general rule, it is considered preferable to lay the permanent tracks at once, and do all the hauling upon them, so that as soon as the tunnel is completed, trains may pass METHODS OF HAULING IN TUNNELS 61 through without delay. To what extent this may be done, or whether it can be done at all or not, depends upon the method of excavation and other local conditions. In soft-ground tunnels excavated by the English or Austrian methods, it is quite possible to lay the permanent tracks at first, since the whole section is excavated at once, and the excavation is kept but a little ahead of the completed tunnel. In rock tunnels, where the heading is driven far ahead of the com- pleted section, it is, of course, impossible to keep the perma- nent track close to the advance work, and narrow-gauge tracks must be laid in the heading. The same thing is true in soft^ ground tunnels driven by successive headings and drifts. In these cases, therefore, where narrow-gauge tracks have to be used for some portions of the work anyway, the question comes up whether it is preferable to use temporary narrow-gauge tracks throughout, or to lay the permanent track as far ahead as possible, and then extend narrow-gauge tracks to the advance excavation. In the latter case it will, of course, be necessary to trans-ship each load from the narrow-gauge to the standard-gauge cars, or vice versa, which means extra cost and trouble. To avoid this, the method is sometimes adopted of laying a third rail between the standard-gauge rails, so that either standard- or narrow-gauge cars may be transported over the line. Whatever form the local conditions may require the system of construction tracks to assume, it may be set down as a general rule that the permanent tracks should be kept as far advanced as possible, and temporary tracks employed only where the permanent tracks are impracticable. The motive power employed for hauling in tunnels may be furnished by animals or by mechanical motors. Animal power Fig. 36. —Box-Car for Tunnel Work. 62 TUNNELING is generally employed in short tunnels and in the advance headings and galleries. In long tunnels, or where the exca- vated material has to be transported some distance away from the tunnel, mechanical power is preferable, for obvious reasons. The motors most used are small steam locomotives, special compressed-air locomotives, and electric motors. Compressed air and electric locomotives are built in various forms, and are particularly well adapted for tunnel work because of their small dimensions, and freedom from smoke and heat. Hauling by Way of Shafts. — When the excavated material a-nd materials of construction are handled through shafts, the operation of hauling may be divided into three processes : the transportation of the materials along the floor of the tunnel, the hoisting of them through the shaft, and the sur- face transportation from and to the mouth of the shaft. These three operations should be arranged to work in harmony with each other, so as to avoid waste of time and unnecessary han- dling of the materials. An endeavor should be made to avoid, if possible, breaking or trans-shipping the load from the time it starts at the heading until it is dumped at the spoil bank. This can be accomplished in two ways. One way is to hoist the boxes of the cars from their trucks at the bottom of the shaft, and place them on similar trucks running on the surface tracks. The other way is to run the loaded cars on to the ele- vator platform at the bottom, hoist them, and then run them on to the surface tracks. If the first method is employed, the car box is usually made of metal, and is provided at its top edges with hooks or ears to which to attach the hoisting cables. When the second method is used, the elevator platform has tracks laid on it which connect with the tracks on the tunnel floor, and also with those on the surface. Hoisting Machinery. — The machines most commonly em- ployed for hoisting purposes in tunnel shafts are steam hoisting engines, horse gins, and windlasses operated by hand. Wind- lasses and horse gins are rather crude machines for hoisting METHODS OF HAULING IN TUNNELS 63 loads, and are used only in special circumstances, where the shaft is of small depth, when the amount of material to be hoisted is small, or where for any reason the use of hoisting engines is precluded. The steam hoisting engine is the stan- dard machine for the rapid lifting of heavy vertical loads. Recently oil engines and electric hoists have also come to be used to some extent, and under certain conditions these ma- chines possess notable advantages. The construction of hand windlasses is familiar to every one. In tunnel work this device is located directly over the shaft, with its axis a little more than half a man's height, so that the crank handle does not rise above the shoulder line. To develop its greatest efficiency the hoisting rope is passed around the windlass drum so that the two ends hang down the shaft, and as one end descends the other ascends. A skip, or bucket, is attached to each of the rope ends ; and by loading the descend- ing skip with construction materials and the ascending skip with spoil, the two skip loads tend to balance each other, thus increasing the capacity of the windlass, and decreasing the manual labor required to operate it. Skips varying from 0.3 cu. yd. to 0.5 cu. yd. are used. The horse gin consists of a vertical cylinder or drum provided with radial arms to which the horses are hitched, which revolve the cylinder by walking around it in a circle. The hoisting rope is rove around the drum so that the two ends extend down the shaft with skips attached, as described in speaking of the hand windlass. The power of the horse gin is, of course, much greater than that of a windlass operated by hand, skips of 1 cu. yd. capacity being commonly used. Horse gins are no longer economical hoisting machines, according to one prominent authority, when V (HH-20) > 5000, where V equals the volume of material to be hoisted, and H equals the height of the hoist, the weight of the excavated material being 2100 lbs. per cu. yd. As a gen- eral rule, however, it is assumed that it is not economical to employ horse gins with a depth of shaft exceeding 150 ft. 64 TUNNELING As already stated, the most efficient and most commonly used device for hoisting at tunnel shafts is the steam hoisting engine. There are numerous builders of hoisting engines, each of which manufactures several patterns and sizes of engines. In each case, however, the apparatus consists of a boiler supply- ing steam to a horizontal engine which operates one or more rope drums. The engines are always reversible. They may be employed to hoist the skips directly, or to operate elevators upon which the skips or cars are loaded. In either case the hoisting ropes pass from the engine drum to and around ver- tical sheaves situated directly over the shaft so as to secure the necessary vertical travel of the ropes down the shaft. Where the shaft is divided into two compartments, each having an ele- vator or hoist, double-drum engines are employed, one drum being used for the operations in one compartment, and the other for the operations in the other compartment. Where the work is to be of considerable duration, or when it is done in cold weather, more or less elaborate shelters or engine houses are built to cover and protect the machinery. Choice between the method of hoisting the skips directly, and the method of using elevators, depends upon the extent and character of the work. Where large quantities of material are to be hoisted rapidly, it is generally considered preferable to employ elevators instead of hoisting the skips directly. In direct hoisting at high speed, oscillations are likely to be pro- duced which may dash the skips against the sides of the shaft and cause accidents. The loads which can be carried in single skips are also smaller than those possible where elevators are used ; and this, combined with the slower hoisting speed required, reduces the capacity of this method, as compared with the use of elevators. Where elevators are employed, however, the plant required is much more extensive and costly ; it comprising not only the elevator cars with their safety devices, etc., but the construction of a guiding framework for these cars in the tun- nel shaft. For these various reasons the elevator becomes the METHODS OF HAULING IN TUNNELS 65 preferable hoisting device where the quantity of material to be handled is large, where the shafts are deep, and where the work will extend over a long period of time ; but when the contrary conditions are the case, direct hoisting of the skips is generally the cheaper. The engineer has to integrate the various factors in each individual case, and determine which method will best fulfill his purpose, which is to handle the material at the least cost within the given time and conditions. The construction of ele- vators for tunnel work is simple. The elevator car consists usually of an open framework box of timber and iron, having a plank floor on which car tracks are laid, and its roof arranged for connecting the hoisting cable (Fig. 37 *). Rigid construc- tion is necessary to resist the hoisting strains. The sides of the car are usually de- signed to slide against tim- ber guides on the shaft walls. Some form of safety device, of which there are several kinds, should be employed to pre- vent the fall of the elevator, in case the hoisting rope breaks, or some mishap occurs to the hoisting machinery, which en- dangers the fall of the car. Speaking tubes and electric-bell signals should also be provided to secure communication be- tween the top and bottom of the shaft. * Reproduced from the catalogue of the Ledgerwood Manufacturing Company, New York. Fig. 37, — Elevator Car for Tunnel Shafts. 66 TUNNELING CHAPTER VII. TYPES OF CENTERS AND MOLDS EMPLOYED IN CONSTRUCTING TUNNEL LININGS OF MASONRY. The masonry lining of a tunnel may be describea as con- sisting of two or more segments of circular arches combined so as to form a continuous solid ring of masonry. To direct the operations of the masons in constructing this masonry ring, templates or patterns are provided which show the exact dimensions and form of the sectional profile which it is de- sired to secure. These patterns or templates will vary in number and construction with the form of lining and the method of excavation adopted. Where the excavation is fully lined on all four sides, the masonry work is usually divided into three parts, — the invert or floor masonry, the side-wall masonry, and the roof-arch masonry. At least one separate pattern has to be employed in constructing each of these parts of the lining; and they are known respectively as ground molds, leading frames, and arch centers, or simply centers. In the following paragraphs the form and construction usually employed for each of these three kinds of patterns is de- scribed. Ground Molds. — Ground molds are employed in building the tunnel invert. They are generally constructed of 3-inch plank cut exactly to the form and dimensions of the invert masonry as shown in Fig. 38. To permit of convenience of handling in a restricted space, they are generally made in two parts, which are joined at the middle by means of iron fish-plates and bolts. Either one or two ground molds may be employed. Where two TYPES OF CENTERS AND MOLDS Q7 Fig. 38. — Ground Mold for Constructing Tunnel Invert Masonry. molds are used they are set up a short distance apart, and cords are stretched from one to the other parallel to the axis of the tunnel, by which the masons are guided in their work. Ex- treme care has to be taken in setting the molds to ensure that they are fixed at the proper grade, and are in a plane normal to the axis of the tunnel. Where only one ground mold is employed, the finished masonry is depended upon to supply the place of the second mold, cords being stretched from it to the single mold placed the requisite distance ahead. The leveling and centering of the molds is ac- complished by means of transit and level. Two modifications of the form of ground mold shown by Fig. 39 are employed. The first modification is peculiar to the English method of excavation, and consists in combining the ground mold with the leading frame for the lower part of the side walls, as shown by Fig. 39. The second modification is employed where the two halves or sides of the invert are built separately, and it consists simply in using one- half of the mold shown by Fig. 38. When the last method of constructing the invert masonry is resorted to, extreme care has to be observed in setting the half-mold in order to avoid error. Leading Frames. — As already stated, leading frames are the patterns, or molds, used in building the side walls of the lining. Like the ground mold they are usually built of plank ; one side being cut to the curve of the profile, and the other being made parallel to the vertical axis of the tunnel section. The vertical side usually has some arrangement by which a plumb Fig. 39. — Combined Ground Mold and Leading Frame for Invert and Side Wall Masonry. 68 TUNNELING bob can be attached, as shown by Fig. 40, to guide the work> men in erecting the frame. The combined leading frame and ground mold shown in Fig. 39 has already been described. The use of this frame is possible only where the masonry is begun at the invert and carried up on each side at the same time. This mode of con- struction is peculiar to the English method of tunneling; in all other methods the form of sep- arate ground frame shown by Fig. 40 is employed. Fig. 40.— Lead- 'pj-^g gfround frames are lined in and leveled up bv mg Frame for ° r j Constructing transit and level ; and, as in setting the ground Side Wall Ma- /. j i j i j^ sonry. iramcs, care must be taken to secure accuracy m both direction and elevation. Arch Centers. — The template or form upon which the roof arch is built is called a center. Unlike the ground molds and leading frames, the arch centers have to support the weight of the masonry and the roof pressures during the construction of the lining, and they, therefore, require to be made strong. Owing to the fact that the pressures are indeterminate, it is impossible to design a rational center, and resort is had to those constructions which past experience has shown to work satis- factorily under similar conditions. In a general way it can always be assumed that the construction should be as simple as possible, that the center should be so designed that it can be set up and removed with the least possible labor, and that the different pieces of the framework and lagging should be as short as possible, for convenience in handling. Tunnel centers are usually composed of two parts, — a mold or curved surface upon which the masonry rests, and a frame- work which supports the mold. The curved surface or mold consists of a lagging of narrow boards running parallel to the tunnel axis, which rests upon the arched top members of two or more consecutive supporting frames. The supporting frame is built in the form of a truss, and must be made strong enough to withstand the heavy superimposed loads, consisting of the TYPES OF CENTERS AND MOLDS 69 arch masonry during construction, and of the roof pressures which are transferred to the center when the strutting is removed to allow the masonry to be placed. The framework of the center is supported either by posts resting upon the floor of the excavation, or upon the invert masonry when this is built first, as in the Enghsh and Austrian methods, or it may be supported directly upon the ground where the arch masonry is built first, as in the Belgian method of tunneling. In describing the various methods of tunneling in succeed- ing chapters, the center construction and method of supporting the center peculiar to each will be fully explained, and only a few general remarks are necessary here. Centers may be classi- fied according to their construction and composition into plank centers, truss centers, and iron centers. One of the most common forms of plank centers is shown by Fig. 41. It consists of two half-polygons whose sides consist of 15 in. X 4 ft. planks having radial end-joints. These two half- polygons are laid one upon the other so that they break joints, as shown by the figure, and the ex- Fig. 4l.-Plank center for Construct- •^ . ing the Roof Arch. trados of the frame is cut to the true curve of the roof arch. The planks commonly used for making these centers are 4 ins. thick, making the total thick- ness of the center 8 ins. Plank centers of the construction described are suitable only for work where the pressures to be resisted are small, as in tunnels through a fairly firm rock, al- though there have been instances of their successful use in soft- ground tunnels. Where heavy loads have to be carried, trussed centers are generally employed, the trusses being composed of heavy square beams with scarfed and tenoned joints, reinforced by iron plates. Different forms of trusses are employed in each of the differ- ent methods of tunneling, and each of these is described in sue- 70 TUNNELING Fig. 42.— Trussed Center for Constructing] the Eoof Arch. ceeding chapters ; but they are generally either of the king-post or queen-post type, or some modification of them. The king- post truss may be used alone, with or without the tie-beam, as shown by Fig. 42 ; but generally a queen - post truss is made to form the base of support for a smaller king post truss mounted on its top. This arrangement gives a trape- zoidal form to the center, which approaches closely to the arch profile. Owing to the character of the pressures transmitted to the center, the usual tension members can be made very light. The combined center and strutting system devised by Mr. Rziha has already been described in a previous chapter. In recent European tunnel work quite extensive use has also been made of iron centers consisting of several segments of curved I-beams, connected by fish-plate joints so as to form a semi- circular arch rib. The ends or feet of these I-beam ribs have bearing-plates or shoes made by riveting angles to the I-beams. Centers constructed in a similar manner, but made of sections of old railway rail, were used in carrying out the tunnel work on the Rhine River Railroad in Germany. The advantages claimed for iron centers are that they take up less room, and that they can be used over and over again. Setting Up Centers. — According to the method of excava- tion followed in building the tunnel, the centers for building the roof arch may have to be supported by posts resting on the tunnel floor ; or where the arch is built first, as in the Belgian and Italian methods, they may be carried on blocking resting on the unexcavated earth below. Whichever method is em- ployed, an unyielding support is essential, and care must be taken that the centers are erected and maintained in a plane normal to the tunnel axis. To prevent deflection and twisting, the consecutive centers are usually braced together by longi- tudinal struts or by braces running to the adjacent strutting. TYPES OF CENTERS AND MOLDS 71 Only skilled and experienced workmen should be employed in erecting the centers ; and they should work under the immedi- ate direction of the engineer, who must establish the axis and level of each center by transit and level. Lagging, — By the lagging is meant the covering of narrow longitudinal boards resting upon the upper curved chords of the centers, and spanning the opening between consecutive centers. This lagging forms the curved surface or mold upon which the arch masonry is laid. When the roof arch is of ashlar masonry the strips of lagging are seldom placed nearer together than the joints of the consecutive ring stones, but in brick arches they are laid close together. Besides the weight of the arch masonry, the lagging timbers support the short props which keep the pohng-boards in place after the strutting is removed and until the arch masonry is completed. Striking the Centers. — The centers are usually brought to the proper elevation by means of wooden wedges inserted be- tween the sill of the center and its support, or between the bottom of the posts carrying the center and the tunnel floor. These wedges are usually made of hard wood, and are about 6 ins. wide by 4 ins. thick by 18 ins. long. To strike the center after the arch masonry is completed, these wedges are with- drawn, thus allowing the center to fall clear of the masonry. Usually the center is not removed immediately after striking, so that if the arch masonry fails the ruins will remain upon the center. The method of striking the iron center devised by Mr. Rziha has been described in the previous chapter on strutting. TUNNELING CHAPTER VIII. METHODS OF LINING TUNNELS, Tunnels in soft soils and in loose rock, and rock liable to disintegration, are always provided with a lining to hold the walls and roof in place. This lining may cover the entire sectional profile of the tunnel, or only a part of it, and it may be constructed of timber, iron, iron and masonry, or, more commonly, of masonry alone. Timber Lining. — Timber is seldom employed in lining tunnels except as a temporary expedient, and is replaced by masonry as soon as circumstances will permit. In the first construction of many American railways, the necessity for extreme economy in construction, and of getting the line open for traffic as soon as possible, caused the engineers to line many tunnels with timber, which was plentiful and cheap. Except for their small cost and the ease and rapidity with which they can be constructed, however, these timber linings possess few advantages. It is only the matter of a few years when the decay of the timber makes it necessary to rebuild them, and there is always the serious danger of fire. In several instances timber-lined tunnels in America have been burned out, causing serious delays in traffic, and necessitating complete reconstruction. Usually this reconstruction has con- sisted in substituting masonry in place of the original timber lining. In a succeeding chapter a description will be given of some of the methods employed in replacing timber tunnel linings with masonry. Various forms of timber lining are employed, of which Fig. 44 and the illustrations in the chapter METHODS OF LINING TUNNELS 73 discussing the methods of relining timber-lined tunnels with masonry are typical examples. Iron Lining. — The use of iron lining for tunnels was intro- duced first on a large scale by Mr. Peter William Barlow in 1869, for the second tunnel under the River Thames at London, England, and it has greatly extended since that time. The lining of the second Thames tunnel consisted of cylindrical cast-iron rings 8 ft. in diameter, the abutting edges of the successive rings being flanged and provided with holes for bolt fastenings. Each ring was made up of four segments, Cross ^Section. Longitudinal Section, Figs. 43 and 44. — A Typical Form of Timber Lining for Tunnela. three of which were longer than quadrants, and one much smaller forming the " key-stone " or closing piece. These segments were connected to each other by flanges and bolts. To make the joints tight, strips of pine or cement and hemp yarn were inserted between the flanges. Since the construc- tion of the second Thames tunnel, iron lining has been em- ployed for a great many submarine tunnels in England, Continental Europe, and America, some of them having a section over 28 ft. in diameter. Where circular iron lining is employed, the bottom part of the section is leveled up with concrete or brick masonry to carry the tracks, and the whole 74 TUNNELING interior of the ring is covered with a cement plaster lining deep enough thoroughly to embed the interior joint flanges. In the succeeding chapter describing the methods of driving tunnels by shields several forms of iron tunnel lining are fully described. Iron and Masonry Lining. — During recent years a form of combined masonry and iron lining has been extensively em- ployed in constructing city underground railways in both Europe and America. Generally this form of lining is built with a rectangular section. Two types of construction are employed. In the first, masonry side walls carry a flat roof of girders and beams, which carry a trough flooring filled with concrete, or between which are sprung concrete or brick arches. Sometimes the roof framing consists of a series of parallel I-beams laid transversely across the tunnel, and in other cases transverse plate girders carry longitudinal I-beams. In the second type of construction the roof girders are supported by columns embedded in the side walls. Where the tunnel pro- vides for two or four tracks, intermediate column supports are in some cases introduced between the side columns. In this construction the roofing consists of concrete filled troughs or of concrete or brick arches, as in the construction first described. Examples of combined masonry and iron tunnel lining are illustrated in the succeeding chapter on tunneling under city streets. Masonry Lining. — The form of tunnel lining most commonly employed is brick or stone masonry. Concrete and reinforced concrete masonry lining has been employed in several tunnels built in recent years. The masonry lining may inclose the whole section or only a part of it. The floor or invert is the part most commonly omitted ; but sometimes also the side walls and invert are both omitted, and the lining is confined simply to an arch supporting the roof. The roof arcn, the side wafls, and the invert compose the tunnel lining; and all three may consist of stone or brick alone, or stone side walls may be employed with brick invert METHODS OF LINING TUNNELS 75 and roof arch. Rubble-stone masonry is usually employed, except at the entrances, where tUe masonry is exposed to view. Here ashlar masonry is usually used. The stone selected for tunnel lining should be of a durable quality which weathers well. Where bricks are used they should be of good qual- ity. Owing to the comparative ease with which brick arches can be built, they are generally used to form the roof arch, even where the side walls are of stone masonry. Masonry lining may be built in the form of a series of separate rings, or in the form of a continuous structure extending from one end of the tunnel to the other. The latter method of construction pro- duces a stronger structure ; but in case of failure by crush- ing, the damage done is hkely to be more widespread than where separate rings are employed, one or two of which may fail without injury to the others adjacent to them. The construction is also somewhat simpler where separate rings are employed, since no provision has to be made for bonding the whole lining into a continuous structure. Where a series of separate rings is employed, the length of each ring runs from 5 ft. up to 20 ft., it depending upon the character of the material penetrated, and the method of construction employed. For the purpose of detailed discussion the construction of masonry lining may be divided into four parts, — the side-wall foundations, the side walls themselves, the roof arch, and the invert. Concrete and reinforced concrete linings are now extensively used on account of cheapness and facility of handhng, but they have the great disadvantage of resisting pressure after they become hard, which is some time after being placed. The strutting should, therefore, be left to support the roof so as to prevent direct pressure on the fresh material. The roof, as a rule, is supported by longitudinal planks held in position by five or seven segments of arched frames placed across the tunnel. A large quantity of timber and carpenter work is thus entirely wasted and these costly items, in many cases, make the concrete 76 TUNNELING lining of a tunnel more expensive than the one built of brick and stone. To avoid these inconveniences tunnels have been successfully lined with concrete on the side walls and concrete blocks in the arches. These blocks have been built by hand and molded in the shape of the arch voussoirs. Foundations. — In tunnels through rock of a hard and dur- able character the foundations for the side walls are usually laid directly on the rock. In loose rock, or rock Hable to dis- integration, this method of construction is not generally a safe one, and the foundation excavation should be sunk to a depth at which the atmospheric influences cannot affect the founda- tion bed. In either case the foundation masonry is made thicker than that of the side walls proper, so as to distribute the pressure over a greater area, and to afford more room for adjusting the side-wall masonry to the proper profile. In yielding soils a special foundation bed has to be prepared for the foundation masonry. In some instances it is found suffi- cient to lay a course of planks upon which the masonry is con- structed, but a more sohd construction is usually preferred. This is obtained by placing a concrete foot- ing from 1 ft. to 2 ft. deep all along the bottom of the foundation trench, or in some cases by sinking wells at intervals along the trench and filling them with concrete, so as to form a series of supporting pillars. The form given to the foundation courses ^. and lower portions of the side walls varies. Fig. 45. — Diagram ^ Showing Forms Where a large bearing area is required, the Adopted for Side- i i p xi n • • i <• n Wall Foundations. back of the Wall IS carried up vertically as shown by the fine AB, Fig. 45, otherwise the rear face of the wall follows the line of excavation AC. For similar reasons the front face of the wall may be made vertical, as at FG, or inclined, as at FH. The line FE indicates the shelf construction designed to support the feet of the posts used to carry the arch centers during the construction of the roof arch. METHODS OF LINING TUNNELS 77 Side Walls. — The construction of the side walls above the foundation courses is carried out as any similar piece of masonry elsewhere would be built. To direct the work and insure that the inner faces of the walls follow accurately the curve of the chosen profile, leading frames previously described are employed. Roof Arch. — For the construction of the roof arch, the centers previously described are employed. Beginning at the edges of the center on each side, the masonry is carried up a course at a time, care being taken to have it progress at the same rate on both sides, so that the load brought onto the centering is symmetrical. As soon as the centers are erected, the roof strutting is removed, and replaced by short props which rest on the lagging of the centers and support the poling- boards. These props are removed in succession as the arch masonry rises along the curve of the center, and the space between the top of the arch masonry and the ceiling of the excavation is filled with small stones packed closely. The key- stone section of the arch is built last, by inserting the stones or bricks from the front edge of the arch ring, there being no room to set them in from the top, as is the practice in ordinary open- arch construction. The keying of the arch is an especially difficult operation, and only experienced men skilled in the work should be employed to perform it. The task becomes one of unusual difficulty when it becomes necessary to join the arches coming from opposite directions. Invert. — In all but one or two methods of tunneling, the invert is the last portion of the lining to be built. In the EngHsh method of tunneling, the invert is the first portion of the hning to be built, and the same practice is sometimes necessary in soft soils where there is danger of the bottoms of the side walls being squeezed together by the lateral pressures unless the invert masonry is in place to hold them apart. The ground molds previously described are employed to direct the con- struction of the invert masonry. 78 TUNNELING General Observations. — In describing the construction of the roof arch, mention was made of the stone filling employed between the back of the masonry ring and the ceiling of the excavation. The spaces behind the side walls are filled in a similar manner. The object of this stone filling, which should be closely packed, is to distribute the vertical and lateral pres- sures in the walls of the excavation uniformly over the lining masonry. As the masonry work progresses, the strutting em- ployed previously to support the w^alls of the excavation has to be removed. This work requires care to prevent accident, and should be placed in charge of experienced mechanics who are familiar with its construction, and can remove it with the least damage to the timbers, so that they may be used again, and without causing the fall of the roof or the caving of the sides by removing too great a portion of the timbers at one time. Thickness of Lining Masonry. — It is obvious, of course, that the masonry lining must be thick enough to support the pres- sure of the earth which it sustains; but, as it is impossible to estimate these pressures at all accurately, it is difficult to say definitely just what thickness is required in any individual case. Rankine gives the following formulas for determining the depths of keystone required in different soils : For firm soils = \/o.l2-, and for soft soils. .^. y,2 48-, where d = the depth of the crown in feet, r = the rise of the arch in feet, and s = the span of the arch in feet. Other writers, among them Professor Curioni, attempt to give rational methods for calculating the thickness of tunnel fining; but they are all open to objection because of the amount of hypothesis re- METHODS OP LINING TUNNELS 79 quired concerning pressures which are of necessity indetermi- nate. Therefore, to avoid tedious and uncertain calculations, the engineer adopts dimensions which experience has proven to be ample under similar conditions in the past. Thus we have all gradations in thickness, from hard-rock tunnels requiring no lining, and tunnels through rocks which simply require a thin shell to protect them from the atmosphere, to soft-ground tunnels where a masonry lining 3 ft. or more in thickness is employed. Table II. shows the thickness of masonry lining used in tunnels through soft soils of various kinds. The thickness of the masonry lining is seldom uniform at all points, as is indicated by Table II. Figs. 46 and 47 show common methods of varying the thickness of lining at different points, and are self-explanatory. Figs. 46 and 47. — Transverse Sections of Tunnels Showing Methods of Increasing the Thick- ness of the Lining at Different Points. Side Tunnels. — When tunnels are excavated by shafts located at one side of the center line, short side tunnels or galleries are built to connect the bottoms of the shafts with the tunnel proper. These side tunnels are usually from 30 ft. to 40 ft. long, and are generally made from 12 ft. to 14 ft. high, and about 10 ft. wide. The excavation, strutting, and lining of these side tun- nels are carried on exactly as they are in the main tunnel, with 80 TUNNELING such exceptions as these short lengths make possible. Table III. gives the thickness of lining used for side tunnels, the figures being taken from European practice. Culverts. — The purpose of culverts in tunnels is to collect the water which seeps into the tunnel from the walls and shafts. The culvert is usually located along the center line of the tunnel at the bottom. In soft-ground tunnels it is built of masonry, and forms a part of the invert, but in rock tunnels it is the common practice to cut a channel in the rock floor of the excava- tion. Both box and arch sections are employed for culverts. The dimensions of the section vary, of course, with the amount of water which has to be carried away. The following are the dimensions commonly employed: Kind of Culvkrt. Height in Feet. Width in Feet. Thickness of Walls in Feet. Thickness of Covering in Feet. Box culvert .... Arch culvert . . . 1 to 1.5 1 to 1.5 1 to 1.5 1 to 1.5 0.8tol.2 0.8 to 1.2 0.3 0.4 It should be understood that the dimensions given in the table are those for ordinary conditions of leakage; where larger quantities of water are met with, the size of the culverts has, of course, to be enlarged. To permit the water to enter the culvert, openings are provided at intervals along its side; and these openings are usually provided with screens of loose stones which check the current, and cause the suspended material to be deposited before it enters the culvert. In cases where springs are encountered in excavating the tunnel, it is necessary to make special provisions for confining their outflow and con- ducting it to the culvert. In all cases the culverts should be provided with catch basins at intervals of from 150 ft. to 300 ft., in which such suspended matter as enters the culverts is deposited, and removed through covered openings over each basin. At the ends of the tunnel the culvert is usually divided METHODS OF LINING TUNNELS 81 into two branches, one running to tlie drain on each side of the track. Niches. — In short tunnels niches are employed simply as places of refuge for trackmen and others during the passing of trains, and are of small size. In long tunnels they are made 1.,^ Fig, 48. — Refuge Niche in St. Gothard Tunnel. larger, and are also employed as places for storing small tools and supplies employed in the maintenance of the tunnel. Niches are simply arched recesses built into the sides of the tunnel, and lined with masonry; Fig. 48 shows this construction quite clearly. Small refuge niches are usually built from 6 ft. to 9 ft. high, from 3 ft. to 6 ft. wide, and from 2 ft. to 3 ft. deep. Large niches designed for storing tools and supplies are made from 10 ft. to 12 ft. high, from 8 ft. to 10 ft. wide, and from 18 ft. to 24 ft. deep, and are provided with doors. Refuge niches are usually spaced from 60 ft. to 100 ft. apart, while the larger storage niches may be located as far as 3000 ft. apart. The niche construction shown by Fig. 48 is that employed on the St. Gothard tunnel. Entrances. — The entrances, or portals, of tunnels usually consist of more or less elaborate masonry structures, depending upon the nature of the material penetrated. In soft-ground tunnels extensive wing walls are often required to support the earth above and at the sides of the entrance; while in tunnels through rock, only a masonry portal is required, to give a finish to the work. Often the engineer indulges himself in an elabo- rate architectural design for the portal masonry. There is 82 TUNNELING danger of carrying such designs too far for good taste unJess care is employed; and on this matter the writer can do no better Fig. 49. — East Portal of Hoosac Tunnel. than to quote the remarks of the late Mr. Frederick W. Simms in his well-known '' Practical Tunneling ": "The designs for such constructions should be massive to be suitable as approaches to works presenting the appearance of gloom, solidity, and strength. A light and highly decorated structure, however elegant and well adapted for other purposes, would be. very unsuitable in such a situation; it is plainness combined with boldness, and massiveness without heaviness, that in a tunnel entrance constitutes elegance, and, at the same time, is the most economical." Fig. 49 is an engraving from a photograph of the east portal of the Hoosac tunnel, which is an especially good design. The portals of the Mount Cenis tunnel were built of samples of stone encountered all along the line of excavation. The stones were cut and dressed and utilized for walls and voussoirs. The only ornament that is usually allowed on the portals is the date of the opening of the tunnel prominently cut in the stone above the arch. METHODS OF LINING TUNNELS 8a TABLE n. Showing Thickness of Masonry Lining for Tunnels through Soft Ground. Character of Material. Keystone. Springers . Invert. Laminated clay, first variety. . Laminated clay, second variety Laminated clay, third variety . Quicksand Ft. 2. 15 to 3 3 to 4.5 4.5 to 6.5 2 to 3.28 Ft. 2.75 to 3.5 3.5 to5.5 5.5 to8.1 2 to 4.1 Ft. 1.6 to2.5 2.5 to 4 4 to 4.5 1.33 to 2.5 TABLE m. Showing Thickness of Masonry Lining for Side Tunnels through Soft Ground. Character op Material. Laminated clay, first variety. . Laminated clay, second variety Laminated clay, third variety . Quicksand Keystone. Ft. 1.6to2.3 2.3 to 3 3 to 4 1.6 to 2.5 Springers. Ft. 1.8 to 3 3 to 4, 4.1 to 5 1.3 to 2 Invert. Ft. 1.5to2 2 to 2.6 2.6 to 3.29 1.3 to 2 84 TUNNELING CHAPTER IX. TUNNELS THROUGH HARD ROCK; GENERAL DISCUSSION; REPRESENTATIVE MECHANICAL INSTALLATIONS FOR TUNNEL WORK. The present high development of labor-saving machinery for excavating rock makes this material one of the safest and easiest to tunnel of any with which the engineer ordinarily has to deal. To operate this machinery requires, however, the developifient of a large amount of power, its transmission to considerable distances, and, finally, its economical application to the excavating tools. The standard rock excavating ma- chine is the power drill, which requires either air or hydraulic pressure for its operation according to the special type em- ployed. Under present conditions, therefore, the engineer is limited either to air or water under compression for the trans- mission of his power. Steam-power may be employed directly to operate percussion rock drills ; but owing to the heat and humidity which it generates in the confined space where the drills work, and because of other reasons, it is seldom employed directly. Electric transmission, which offers so many advan- tages to the tunnel builder, in most respects is largely excluded from use by the failure which has so far followed all attempts to apply it to the operation of rock drills. As matters stand, therefore, the tunnel engineer is practically limited to steam and falling water for the generation of power, and to com- pressed air and hydraulic pressure for its transmission. Whether the engineer should adopt water-power or steam to generate the power required for his excavating machinery de- pends upon their relative availability, cost, and suitability to the TUNKELS THROUGH HARD ROCK 85 conditions of work in each particular case. Where fuel is plen- tiful and cheap, and where water-power is not available at a comparatively reasonable cost, steam-power will nearly always prove the more economical ; where, however, the reverse con- ditions exist, which is usually the case in a mountainous country far from the coal regions, and inadequately supplied with transportation facilities, but rich in mountain torrents, water-power will generally be the more economical. In a suc- ceeding chapter the power generating and transmission plants for a number of rock tunnels are described, and here only a general consideration of the subject will be presented. Steam-Power Plant. — A steam-power plant for tunnel work should be much the same as a similar plant elsewhere, except that in designing it the temporary character of its work must be taken into consideration. This circumstance of its tempo- rary employment prompts the omission of all construction except that necessary to the economical working of the plant during the period when its operation is required. The power- house, the foundations for the machinery, and the general con- struction and arrangement, should be the least expensive which will satisfy the requirements of economical and safe operation for the time required. It will often be found more economical as a whole to operate the machinery with some loss of economy during the short time that it is in use than to go to much greater expense to secure better economy from the machinery by design and construction, which will be of no further use after the tunnel is completed. The longer the plant is to be required, the nearer the construction may economically approach that of a permanent plant. As regards the machinery itself, whose further usefulness is not limited by the duration of any single piece of work, true economy always dictates the purchase of the best quality. Speaking in a general way, a steam-power plant for tunnel work comprises a boiler plant, a plant of air compressors with their receivers, and an electric light dynamo. When hydraulic transmission of power is employed, the air 86 TUNNELING compressors are replaced by high-pressure pumps ; and when electric hauling is employed, one or more dynamos may be re- quired to generate electricity for power purposes, as well as for lighting. In addition to the power generating machines proper, there must be the necessary piping and wiring for transmitting this power, and, of course, the equipment of drills and other machines for doing the actual excavating, hauling, etc. Reservoirs. — When water-power is employed, a reservoir has to be formed by damming some near-by mountain stream at a point as high as practicable above the tunnel. The provision of a reservoir, instead of drawing the water directly from the stream, serves two important purposes. It insures a continuous supply and constant head of water in case of drought, and also permits the water to deposit its sediment before it is delivered to the turbines. The construction of these reservoirs may be of a temporary character, or they may be made permanent structures, and utilized after construction is completed to sup- ply power for ventilation and other necessary purposes. In the first case they are usually destroyed after construction is fin- ished. In either case, it is almost unnecessary to say, they should be built amply safe and strong according to good engi- neering practice in such works, for the duration of time which they are expected to exist. Canals and Pipe Lines. — For conveying the water from the reservoirs to the turbines, canals or pipe lines are employed. The latter form of conduit is generally preferable, it being both less expensive and more easily constructed than the former. It is advisable also to have duplicate lines of pipe to reduce the possibility of delay by accident or while necessary repairs are being made to one of the pipes. The pipe lines terminate in a penstock leading into the turbine chamber, and provided with the necessary valves for controlling the admis- sion of water to the turbines. Turbines. — There are numerous forms of turbines on the market, but they may all be classed either as impulse turbines TUNNELS THKOUGH HAKD PvOCK 87 or as reaction turbines. Impulse turbines are those in which the whole available energy of the water is converted into kinetic energy before the water acts on the moving part of the turbine, lieaction turbines are those in which only a part of the available energy of the water is converted into kinetic energy before the water acts on the moving vanes. Impulse turbines give efficient results with any head and quantity of water, but they give better results when the quantity of water varies and the head remains constant. Reaction turbines, on the contrary, give better results when the quantity of water remains constant and the head varies. These observations indicate in a general way the form of turbine which will best meet the particular conditions in each case. The number of turbines required, and their dimensions, will be determined in each case by the number of horse-power required and the quantity of water available. The power of the turbines is transmitted to the air compressors or pumps by shafting and gearing. Air Compressors. — An air compressor is a machine — usually driven by steam, although any other power may be used — by which air is compressed into a receiver from which it may be piped for use. For a detailed description of the various forms of air compressors the reader should consult the catalogues of the several makers and the various text-books relating to air compression and compressed air. Air compressors, like other machines, suffer a loss of power by friction. The greatest loss of power, however, results from the heat of compression. When air is compressed, it is heated, and its relative volume is increased. Therefore, a cubic foot of hot air in the com- pressor cylinder, at say, 60 lbs. pressure, does not make a cubic foot of air at 60 lbs. pressure after cooling in the receiver. In other words, assuming pressure to be constant, a loss of volume results due to the extraction of the heat of compression after the air leaves the compressor cylinder. To reduce the amount of this loss, air compressors are designed with means 88 TUNNELING to extract the heat from the air before it leaves the com- pressor cylinder. Air compressors may first be divided into two classes, according to the means employed for cooling the air, as follows: (1) Wet compressors, and (2) dry compress- ors. A wet compressor is one which introduces water directly into the cylinder during compression, and a dry compressor is one which admits no water to the air during compression. Wet compressors may be subdivided into two classes : (1) Those which inject water in the form of spray into the cylinder during compression, and (2) those which use a water piston for forcing the air into confinement. The following brief discussion of these various types of compressors is based on the concise practical discussion of Mr. W. L. Saunders, M. Am. Soc. C. E., in " Compressed Air Production." The highest isothermal results are obtained by the injection of water into the cylinders, since it is plain that the injection of cold water, in the shape of a finely divided spray, directly into the air during compression will lower the temperature to a greater degree than simply to surround the cylinder and parts by water jackets which is the means of cool- ing adopted with dry compressors. A serious obstacle to water injection, and that which condemns this type of compressor, is the influence of the injected water upon the air cylinder and parts. Even when pure water is used, the cylinders wear to such an extent as to produce leakage and to require reboring. The limitation to the speed of a compressor is also an important objection. The chief claim for the water piston compressor is that its piston is also its cooling device, and that the heat of compression is absorbed by the water. Water is so poor a conductor of heat, however, that without the addition of sprays it is safe to say that this compressor has scarcely any cooling advantages at all so far as the cooling of the air during com- pression is concerned. The water piston compressor operates at slow speed and is expensive. Its only advantage is that it has no dead spaces. In the dry compressor a sacrifice is made TUNNELS THROUGH HARD ROCK 89 in the efficiency of the cooHng device to obtain low first cost, economy in space, light weight, higher speed, greater durability, and greater general availability. Air compressors are also distinguished as double acting and simple acting. They are simple acting when the cylinder is arranged to take in air at one stroke and force it out at the next, and they are double acting when they take in and force out air at each stroke. In form compressors may be simple or duplex. They are simple when they have but one cylinder, and duplex when they have two cylinders. A straight line or direct acting compressor is one in which the steam and air cylinders are set tandem. An indirect acting compressor is one in which the power is applied indirectly to the piston rod of the air cylinder through the medium of a crank. Mr. W. L. Saunders writes in regard to direct and indirect compression as follows : — " The experience of American manufacturers, which has been more exten- sive than that of others, has proved the value of direct compression as distin- guished from indirect. By direct compression is meant the application of power to resistance through a single straight rod. The steam and air cylinders are placed tandem. Such machines natui-ally show a low friction loss because of the direct application of power to resistance. This friction loss has been recorded as low as 5 %, while the best practice is about 10 % with the type which conveys the power through the angle of a crank shaft to a cylinder connected to the shaft through an additional rod." Receivers. — Compressed air is stored in receivers which are simply iron tanks capable of withstanding a high internal pressure. The purpose of these tanks is to provide a reservoir of compressed air, and also to allow the air to deposit its moisture. From the receivers the air is conveyed to the work- ings through iron pipes, which decrease gradually in diameter from the receivers to the front. Rock Drills. — The various forms of rock drills used in tun- neling have been described in Chapter III., and need not be considered in detail here except to say that American engi- 90 TUNNELING neers usually employ percussion drills, while European engineers also use rotary drills extensively. A comparison between these two types of drills was made in excavating the Aarlberg tunnel in Austria, where the Brandt hydraulic rotary drill was used at one end, and the Ferroux percussion drill was used at the other end. The rock was a mica-schist. The average monthly progress was 412 ft., with a maximum of 64:6 ft., with the rotary drills, and an average of 454 ft. with the percussion drill. Excavation. — Since considerable time is required to get the power plant established, the excavation of rock tunnels is often begun by hand, but hand work is usually continued for no longer a period than is necessary to get the power plant in •operation. ' Generally speaking, the greatest difficulty is encountered in excavating the advanced drift or heading. Based on the mode of blasting employed, there are two methods of driving the advanced gallery, known as the circular cut and the center cut methods. In the first method a set of holes is first drilled near the center of the front in such a manner that they inclose a cone of rock ; the holes, starting at the perimeter of the base of the cone, converge toward a junction at its apex. Seldom more than four to six holes are comprised in this first set. Around these first holes are driven a ring of holes which inclose a cylinder of rock, and if necessary succeeding rings of holes are driven outside of the first ring. These holes are blasted in the order in which they are driven, the first set taking out a cone of rock, the second set enlarg- ing this cone to a cylinder, and the other sets enlarging this cylinder to the required dimensions of the heading. The number of holes, however, varies with the quality of rock and they are seldom driven deeper than 4 or 5 ft. This method of excavating the heading, which is commonly followed by European engineers, is illustrated in Figs. 50 to 52. In these figures are indicated the number of holes in each round and the sequence of rounds for the soft, medium and hard rock, as used in the Turchino TUNNELS THROUGH HARD ROCK 91 tunnel of the Geneva Ovada Asti line of the Mediterranean Railway of Italy. The heading was about 9 ft. square, and five sets of holes w^ere used in blasting, the depths being 3.91, 4.26 In Sof+ RocK In Medium RocW \n Hard Rock Figs. 50 to 52. — Arrangement of Drill Holes in the Heading of Turchino Tunnel. and 4.6 ft. for soft, medium and hard rock, respectively, and the amount of dynamite consumed was 2.38, 3.91 and 5.1 pounds per cubic yard for the three classes of rock. In the center-cut method, which is the one commonly employed in America, the holes are arranged in vertical rows, and are driven from 8 to 10 ft. deep. Fig. 53 shows the arrangement of the holes, and the method of blasting them, as used in the excavation of the heading for the Fort George tunnel of the New York rapid transit. The two center rows of holes converge toward each other so as to take out a wedge of rock; others are bored straight, or parallel, with the vertical plane of the tunnel. Figs. 53 and 54. —Arrangement of Drill Holes rf^^ i i i j i • in the Heading of the Fort George Tunnel. Ihose bored around thepenm- eter are driven either outward or upward, according as they are located, close to the sides or roof of the tunnel. In this 92 TUNNELING case, the holes of the center cut were driven 9 ft. deep, while all the other holes were bored to a depth of 8 ft. The width of the advanced gallery or heading depends upon the quality of the rock. In hard rock American engineers give it the full width of the tunnel section; but this cannot be done in loose or fissured rock, which has to be supported, the headings here being usually made about 8 X 8 ft. The wider heading is always preferable, where it is possible, since more room is available for removing the rock, and deeper holes can be bored and blasted. The important role played by the power plant and other mechanical installations in constructing tunnels through rock has already been mentioned. In some methods of soft-ground tunneling, and particularly in soft-ground subaqueous tunnel- ing, it is also often necessary to employ a mechanical installa- tion but slightly inferior in size and cost to those used in tunnel- ing rock. It is proposed to describe very briefly here a few typical individual plants of this character, which will in some respects give a better idea of this phase of tunnel work than the more general descriptions. Rock Tunnels. — The tunnels selected to illustrate the me- chanical installations employed in tunneling through rock are: The Mont Cenis, Hoosac Tunnel, the Cascade Tunnel, the Niagara Falls Power Tunnel, the Pahsades Tunnel, the Croton Aqueduct Tunnel, the Strickler Tunnel in America, and the Graveholz Tunnel and the Sonnstein Tunnel in Europe. In addition there will be found in another chapter of this book a description of the mechanical installations at the St. Gothard, Pennsylvania and other tunnels. Mont Cenis Power Plant. — The mechanical installation con- sisted of the Sommeilier air compressors built near the portals. The Sommeilier compressors, Mr. W. L. Saunders says, were operated as a ram, utilizing a natural head of water to force air at 80 lbs. pressure into a receiver. The column of water con- tained in the long pipe on the side of the hill was started and TUNNELS THROUGH HARD ROCK 93 stopped automatically by valves controlled by engines. The weight and momentum of the water forced a volume of air with such a shock against the discharge valve that it was opened, and the air was discharged into the tank; the valve was then closed, the water checked; a portion of it was allowed to dis- charge, and the space was filled with air, which was in turn forced into the tank. Only 73 % of the power of the water was available, 27 % being lost by the friction of the water in the pipes, valves, bends, etc. Of the 73 % of net work, 49.4 was consumed in the perforators, and 23.6 in a dummy engine for working the valves of the compressors and for special venti- lation. The compressed air was conveyed from each end through a cast-iron pipe 7f in. in diameter, up to the front of the excava- tion. The joints of the pipes were made with turned faces, grooved to receive a ring of oakum which was tightly screwed and compressed into the joint. To ascertain the amount of leakage of the pipes, they and the tanks were filled with air compressed to 6 atmospheres, and the machines stopped; after 12 hours the pressure was reduced to 5.7 atmospheres, or to 95 % of the original pressure. Sommeiher's percussion drilling machines were used in the excavation of this tunnel. They were provided with 8 or 10 drills acting at the same time, and mounted on carriages running on tracks. These were withdrawn to a safe place during the blasting, and advanced again after the broken rock was removed from the front and the new tracks laid. Machine shops were built at both ends of the tunnel for build- ing and repairing the drilHng machines, bits, tools, etc. A gas factory was built at each end for lighting purpose. Hoosac Tunnel. — The Hoosac tunnel on the Fitchburg R.R. in Massachusetts is 25,000 ft. long, and the longest tunnel in America. The material through which the tunnel was driven was chiefly hard granitic gneiss, conglomerate, and mica-schist rock. The excavation was conducted from the entrances and 94 TUNNELING one shaft, the wide heading and single-bench method being employed, with the center-cut system of blasting which was here used for the first time. The tunnel was begun in 1854, and continued by hand until 1866, when the mechanical plant was installed. Most of the particular machines employed have now become obsolete, but as they were the first machines used for rock tunneling in America they deserve mention. The drills used were Burleigh percussion drills, operated by com- pressed air. Six of these drills were mounted on a single car- riage, and two carriages were used at each fronts The air to operate these drills was supphed by air compressors operated by water-power at the portals and steam-power at the shaft. The air compressors consisted of four horizontal single-acting air cyhnders with poppet valves and water injection. The compressors were designed by Mr. Thomas Deane, the chief engineer of the tunnel. Palisades Tunnel. — The Palisades tunnel was constructed to carry a double track railway line through the ridge of rocks bordering the west bank of the Hudson River and known as the Palisades. It was located about opposite 116th St. in New York City. The material penetrated was a hard trap rock very full of seams in places, which caused large fragments to fall from the roof. The excavation was made by a single wide heading and bench, employing the center-cut method of blast- ing with eight center holes and 16 side holes for the 7 X 18 ft. heading. Ingersoll-Sergeant 2J in. drills were used, four in each heading and six on each bench, and 30 ft. per 10 hours was considered good work for one drill. The power-plant was situated at the west portal of the tun- nel, and the power was transmitted by electricity and com- pressed air to the middle shaft and east portal workings. The plant consisted of eight 100 H. P. boilers, furnishing steam to four Rand duplex 18 X 22 in. air compressors, and an engine running a 30 arc light dynamo. The compressed air was carried over the ridge by pipes, varying from 10 ins. to 5 ins. in diam- TUNNELS THROUGH HARD ROCK 95 eter, to the shaft and to the east portal, and was used for operat- ing the hoisting engines as well as the drills at these workings. Inside the tunnel, specially designed derrick cars were employed to handle large stones, they being also operated by compressed air. This car ran on a center track, while the mucking cars ran on side tracks, and it was employed to lift the bodies of the cars from the trucks, place them close to the front, being worked where large stone could be rolled into them, and return them to the trucks for removal. In addition to handling the car bodies the derrick was used to lift heavy stones. The haul- ing was done first by horse-power, and later by dummy locomotives. Croton Aqueduct Tunnel. — In the construction of the Croton Aqueduct for the water supply of New York City, a tunnel 31 miles long was built, running from the Croton Dam to the Gate House at 135th St. in New^ York City. The section of the tun- nel varies in form, but is generally either a circular or a horse- shoe section. In all cases the section was designed to have a capacity for the flow of water equal to a cyHnder 14 ft. in diameter. To drive the tunnel, 40 shafts w^ere employed. The material penetrated was of almost every character, from quicksand to granitic rock, but the bulk of the work was in rock of some character. The excavation in rock was conducted by the wide heading and bench method, employing the center-cut method of blasting. Four air drills, mounted on two double-arm columns were employed in the heading. The drills for the bench work were mounted on tripods. Steam-power was used exclusively for operating the compressors, hoisting engines, ventilating fans and pumps; but the size and kind of boilers used, as well as the kind and capacity of the machines w^hich they operated, varied greatly, since a separate power-plant was employed for each shaft with a few exceptions. A description of the plant at one of the shafts will give an indication of the size and character of those at the other shafts, and for this purpose the plant at shaft 10 has been selected. 96 TUNNELING At shaft 10 steam was provided by two Ingersoll boilers of 80 H. P. each, and by a small upright boiler of 8 H. P. There were two 18 X 30 in. Ingersoll air compressors pumping into two 42 in. X 10 ft. and two 42 in. x 12 ft. Ingersoll receivers. In the excavation there were twelve 3J in. and six 3J in. Inger- soll drills, four drills mounted on two double arm columns being used on each heading, and the remainder mounted on tripods being used on the bench. Two Dickson cages operated by one 12 X 12 in. Dickson reversible double hoisting engine provided transportation for material and supplies up and down the shaft. A Thomson-Houston ten-light dynamo operated by a Lidgerwood engine provided light. Drainage was effected by means of two No. 9 and one No. 6 Cameron pumps. At this particular shaft the air exhausted from the drills gave ample ventilation, especially when after each blast the smoke was cleared away by a jet of compressed air. In other workings, however, where this means of ventilation was not sufficient, Baker blowers were generally employed. Strickler Tunnel. — The Strickler tunnel for the water supply of Colorado Springs, Col., is 6441 ft. long with a section of 4 ft. X 7 ft. It penetrates the ridge connecting Pike's Peak and the Big Horn Mountains, at an elevation of 11,540 ft. above sea level. The material penetrated is a coarse porphyritic granite and morainal debris, the portion through the latter material being lined. The mechanical installation consisted of a water-power electric plant operating air compressors. The water from Buxton Creek having a fall of 2400 ft. was utilized to operate a 36 in. 220 H. P. Pelton water-wheel, which operated a 150 K. W. three-phase generator. From this gener- ator a 3500 volt current was transmitted to the east portal of the tunnel, where a step-down transformer reduced it to a 220 volt current to the motor. The transmission line consisted of three No. 5 wires carried on cross-arm poles and provided with lightning arresters at intervals. The plant at the east portal of the tunnel consisted of a 75 H. P. electric motor, driving TUNNELS THROUGH HARD ROCK 97 a 75 H. P. air compressor, and of small motors to drive a Sturte- vant blower for ventilation, to run the blacksmith shop, and to light the tunnel, shop, and yards. From the compressor air was piped into the tunnel at the east end, and also over the mountain to the west portal workings. Two drills were used at each end, and the air was also used for operating derricks and other machinery. For removing the spoil a trolley carrier system was employed. A longitudinal timber was fastened to the tunnel roof, directly in the apex of the roof arch. This timber carried by means of hangers a steel bar trolley rail on which the carriages ran. Outside of the portal this rail formed a loop, so that the carriage could pass around the loop and be taken back to the working face. Each carriage carried a steel span of 1} cu. ft. capacity, so suspended that by means of a tripping device it was automatically dumped when the proper point on the loop was reached. Niagara Falls Power Tunnel. — The tail-race tunnel built to carry away the water discharged from the turbines of the Niagara Falls Power Co., has a horse-shoe section 19 X 21 ft. and a length of 6700 ft. It was driven through rock from three shafts by the center-cut method of blasting. In sink- ing shaft No. very little water was encountered, but at shafts Nos. 1 and 2 an inflow of 800 gallons and 600 gallons per minute, respectively, was encountered. The principal plant was located at shaft No. 2, and consisted of eight 100 H.P. boilers, three 18 X 30 in. Rand duplex air compressors, a Thomson-Houston electric-light plant, and a sawmill with a capacity of 20,000 ft. B. M. per day. The shafts were fitted with Otis automatic hoisting engines, with double cages at shafts Nos. 1 and 2, and a single cage at shaft No. 0. The drills used were 25 Rand drills and three Ingersoll-Sergeant drills. The pumping plant at shaft No. 2 consisted of four No. 7 and one No. 9 Cameron pumps, and that at shaft No. 2 consisted of two No. 7 and two No. 9 Cameron pumps and three Snow pumps. An auxihary boiler plant consisting of two 60 H. P. boilers was located at 98 TUNNELING shaft No. 1, and another, consisting of one 75 H. P. boiler, was located at shaft No. 0. Cascade Tunnel. — The Cascade tunnel was built in 1886-88 to carry the double tracks of the Northern Pacific Ry. through the Cascade Mountains in Washington. It is 9850 ft. long with a cross-section 16 J ft. wide and 22 ft. high, and is lined with masonry. The material penetrated was a basaltic rock, with a dip of the strata of about 5°. The rock was excavated by a wide heading and one bench, using the center-cut system of blasting. A strutting consisting of five-segment timber arches carried on side posts, spaced from 2 ft. to 4 ft. apart, and having a roof lagging of 4 X 6 in. timbers packed above with cord-wood. The mechanical plant of the tunnel is of particular interest, because of the fact that all the machinery and supplies had to be hauled from 82 to 87 miles by teams, over a road cut through the forests covering the mountain slopes. This work required from Feb.- 22 to July 15, 1886, to perform. In many places the grades were so steep that the wagons had to be hauled by block and tackle. The plant con- sisted of five engines, two water-wheels, five air compressors, eight 70 H. P. steam-boilers, four large exhaust fans, two com- plete electric arc-lighting plants, two fully equipped machine- shop outfits, 36 air drills, two locomotives, 60 dump cars, and two sawmill outfits, with the necessary accessories for these vari- ous machines. This plant was divided about equally between the two ends of the tunnel. The cost of the plant and of the work of getting it into position was S125,000. Graveholz Tunnel. — The Graveholz tunnel on the Bergen Railway in Norway is notable as being the longest tunnel in northern Europe, and also as being built for a single-track narrow-gauge railway. This tunnel is 17,400 feet long, and is located at an elevation of 2900 feet above sea-level. Only about 3 % of the length of the tunnel is lined. The mechani- cal installation consists of a turbine plant operating the various machines. There are two turbines of 100 H. P. and 120 H. P. TUNNELS THROUGH HARD ROCK 9& taking water from a reservoir on the mountain slope, and fur- nishing 220 H. P., which is distributed about as follows: Boring- machines, 60 H. P.; ventilation, 30 to 40 H. P.; electric loco- motives, 15 H. P.; machine shop, 15 H. P.; electric-lighting dynamo, 25 H. P. ; electric drills, the surplus, or some 40 H. P. The boring-machines and electric drills will be operated by the smaller 100 H. P. turbine. Sonnstein Tunnel. — The Sonnstein tunnel in Germany is particularly interesting because of the exclusive use of Brandt rotary drills. The tunnel was driven through dolomite and hard limestone by means of a drift and two side galleries. The dimensions of the drift were 7 J X 7 J ft. The power plant con- sisted of two steam pressure pumps, one accumulator, and four drills. The steam-boiler plant, in addition to operating the pumps, also supplied power for operating a rotary pump for drainage and a blower for ventilation. The hydraulic pressure required was 75 atmospheres in the dolomite, and from 85 to 100 atmospheres in the limestone. The drift was excavated with five 3 J in. holes, one being placed at the center and driven parallel to the axis of the tunnel, and four being placed at the corners of a rectangle corresponding to the sides of the drift, and driven at an angle diverging from the center hole. The average depths of the holes were 4.3 ft., and the efficiency of the drills was 1 in. per minute. One drill was employed at each fronts and was operated by a machinist and two helpers, who worked eight-hour shifts, with a blast between shifts at first, and later twelve-hour shifts, with a blast between shifts. The 24 hours of the two shifts were divided as follows: boring the holes, 10.7 hours; charging the holes, 1.1 hours; removing the spoil, 11.7 hours; changing shifts, 0.5 hour. The average progress per day for each machine was 6.7 ft. The total cost of the plant was $17,450. St. Clair River Tunnel. — The submarine double-track rail- way tunnel under the St. Clair River for the Grand Trunk Ry. is 8500 ft. long, and was driven through clay by means of a 100 TUNNELING shield, as described in the succeeding chapter on the shield system of tunneling. The mechanical plant installed for prose- cuting the work was very complete. To furnish steam to the air compressors, pumps, electric-hght engines, hoisting-engines, etc., a steam-plant was provided on each side of the river, con- sisting of three 70 H. P. and four 80 H. P. Scotch portable boilers. The air-compressor plant at each end consisted of two 20 X 24 in. Ingersoll air compressors. To furnish light to the workings, two 100 candle-power Edison dynamos were in- stalled on the American side, and two Ball dynamos of the same size were installed on the Canadian side. The dynamos on both sides were driven by Armington & Sims engines. These dynamos furnished light to the tunnel workings and to the machine-shops and power-plant at each end. Root blowers of 10,000 cu. ft. per minute capacity provided ventilation. The pumping plant consisted of one set of pumps installed for per- manent drainage, and another set installed for drainage during construction, and also to remain in place as a part of the per- manent plant. The latter set consisted of two 500 gallon Worth- ington duplex pumps set first outside of each air lock, closing the ends of the river portion of the tunnel. For permanent drainage, a drainage shaft was sunk on the Canadian side of the river, and connected with a pump at the bottom of the open-cut approach. In this shaft were placed a vertical, direct-acting, compound-condensing pumping engine with two lOJ in. high- pressure and two 33| in. low-pressure cylinders of 24 in. stroke, connected to double-acting pumps with a capacity of 3000 gallons per minute, and also two duplex pumps of 500 gallons capacity per minute. For permanent drainage on the American side, four Worthington pumps of 3000 gallons' capacity were installed in a pump-house set back into the slope of the open- cut approach. For the permai^^nt drainage of the tunnel proper two 400 gallon pumps were placed at the lowest point of the tunnel grade. Spoil coming from the tunnel proper was hoisted to the top of the open cut by derricks operated by two TUNNELS THROUGH HARD ROCK 101 50 H. P. Lidgerwood hoisting-engines. The pressure pumping plant for supplying water to the hydraulic shield-jacks at each end of the tunnel consisted of duplex direct-acting engines with 12 in. steam cylinders and 1 in. water cylinders, supply- ing water at a pressure of 2000 lbs. per sq. in. 102 TUNNELING CHAPTER X. TUNNELS THROUGH HARD ROCK (Continued). EXCAVATION BY DRIFTS: THE SIMPLON AND MURRAY HILL TUNNELS. General Description. — The method of tunneling through hard rock by drifts is preferred by European engineers. All the great Alpine tunnels, from the Mont Cenis tunnel to the Simplon, are examples of tunnehng by drifts. In this method the se- quence of excavation is shown diagrammatically by Fig. 55. The work begins by excavating a drift close to the floor of the pro- posed tunnel (as shown in the center of the figure) and far in advance of the excavation of any other part. The section marked 2 is next re- moved and still later the portions marked 3. Then with the removal of the parts marked 4 the whole section of the tunnel will be open. The drift is usually strutted by means of side posts carrying a cap- piece placed at intervals, and hav- ing a ceiling of longitudinal planks resting on the successive caps. In hard rock the roof of the section does not, as a rule, require regular strutting, occasional supports being placed at intervals to prevent the fall of isolated fragments: When the rock is dis- integrated or full of seams, a regular strutting may be necessary, and this may be either longitudinal or polygonal in type. When longitudinal strutting is employed, a sill is laid across the roof of / ^ 2 3 \ b i \ \ 1 1 \ 1 \ 4 1 4/ \ / \ ; / \ / \ i , / / 1 L 1 Fig. 55. — Diagram Showing Se- quence of Excavations in Drift Method of Tunneling Rock. TUNNELS THROUGH HARD ROCK 103 the drift, and upon this are set up two struts converging toward the top and supporting a cap-piece close to the roof. On this cap-piece are placed the first longitudinal crown bars carrying transverse poling-boards. Additional props standing on the sill and radiating outward are inserted as parts No. 3 are excavated. These radial props carry longitudinal bars which in turn support transverse poling-boards. When polygonal strutting is used, it may take the form of three or five segment arches of heavy timbers. In hard rock tunnels, as a rule, there is no danger of caving in because of heavy pressures, and the whole section is left open for some time before it is lined. The lining may be of concrete masonry, but in many long tunnels, excavated through hard rock, the side walls are lined with rubble masonry and the arch with brick, and, in some instances, even the arch has been hned with rubble masonry. With skilful laborers at hand the rubble masonry lining has proved most efficient and economical, be- cause the rock is utilized as it is excavated without any further operation. Concrete, however, is more extensively employed for lining tunnels than any other material. Tunnels excavated by drifts enable simple means of hauling to be employed, and this is one of the reasons why the method finds so much favor with European engineers. The tracks are laid along the floor of the drift, and carry all the spoil from parts Nos. 2, 3, and 4, as well as from the front of the drift itself. As fast as the full section is completed, this single track in the drift is replaced by two tracks running close to the sides of the tunnel, or by a broad-gauge track with a third rail. THE SIMPLON TUNNEL.* Before entering upon a description of the constructive de- tails of this, the longest railway tunnel in the world, it may be well to give a general idea of the undertaking. Many schemes * Abstract from a paper read before the Institution of Civil Engineers by Charles B. Fox, Jan. 26, 1900. 104 TUNNELING for the connection of Italy and Switzerland by a railway near the Simplon Road Pass have been devised, including one in- volving no great length of underground work, the line mounting by steep gradients and sharp curves. The present scheme, put forward in 1881 by the Jura-Simplon Ry. Co., consists broadly of piercing the Alps between Brigue, the present rail- way terminus in the Rhone Valley, and Iselle, in the gorge of the Diveria, on the Italian side, from which village the railway will descend to the existing southern terminus at Domo d'Ossola, a distance of about 11 miles. In conjunction with this scheme a second tunnel is pro- posed, to pierce the Bernese Alps under the Lotschen Pass from Mittholz to a point near Turtman in the Rhone Valley; and thus, instead of the long detour by Lausanne and the Lake of Geneva, there will be an almost direct line from Berne to Milan via Thun, Brigue, and Domo d'Ossola. Starting from Brigue, the new line, running gently up the valley for IJ miles, will, on account of the proximity of the Rhone, which has already been slightly diverted, enter the tunnels on a curve to the right of 1050 ft. radius. At a dis- tance of 153 yards from the entrance, the straight portion of the tunnel commences, and extends for 12 miles. The line then curves to the left with a radius of 1311 ft. before emerging on the left bank of the Diveria. Commencing at the northern entrance, a gradient of 1 in 500 (the minimum for efficient drainage) rises for a length of 5^ miles to a level length of 550 yards in the center, and then a gradient of 1 in 143 descends to the Itahan side. On the way to Domo d'Ossola one helical tunnel will be necessary, as has been carried out on the St. Gothard. There will be eventually two parallel tunnels having their centers 56 ft. apart, each carrying one fine of way; but at the present time only one heading, that known as No. 1, is being excavated to full size. No. 2 being left, masonry lined where necessary, for future developments. By means of cross headings every 220 yds. the problems of transport and ventila- TUNNELS THROUGH HARD ROCK 105 tion are greatly facilitated, as will be seen- later. As both entrances are on curves, a small " gallery of direction " is neces- sary, to allow corrections of alinement to be made direct from the two observatories on the axis of the tunnel. The outside installations are as nearly in duplicate as cir- cumstances will allow, and consist of the necessary offices, workshops, engine-sheds, power-houses, smithies, and the nu- merous buildings entailed by an important engineering scheme. Great care is taken that the miners and men working in the tunnel shall not suffer from the sudden change from the warm headings to the cold Alpine air outside; and for this purpose a large building is in course of erection, where they will be able to take off their damp working clothes, have a hot and cold douche, put on a warm dry suit, and obtain refreshments at a moderate cost before returning to their homes. Instead of each man having a locker in which to stow his clothes, a perfect forest of cords hangs down from the wooden ceiling, 25 ft. above floor-level, each cord passing over its own pulleys and down the wall to a numbered belaying-pin. Each cord supports three hooks and a soap-dish, which, when loaded with their owner's property, are hauled up to the ceiling out of the way. There are 2000 of these cords, spaced 1 ft. 6 ins. apart, one to each man. The engineers and foremen are more privi- leged, being provided with dressing-rooms and baths, partitioned off from the two main halls. An extensive clothes washing and drying plant has been laid down, and also a large restau- rant and canteen. At Iselle, a magazine holding 2200 lbs. of dynamite is surrounded and divided into two separate parts by earth-banks, 16 ft. high. The two wooden houses, in which the explosive is stored, are warmed by hot-water pipes to a temperature between 61° F. and 77° F., and are watched by a military patrol; but at Brigue a dynamite manufactory, started by an enterprising company at the time of the com- mencement of the works, suppHes this commodity at frequent intervals, thereby avoiding the necessity of storing in such 106 TUNNELING large quantities. This dynamite factory has been largely in- creased, and supplies dynamite to nearly all the mining and tunneling enterprises in Switzerland. Geological Conditions. — Before the Simplon tunnel was au- thorized, expert evidence was taken as to the feasibility of the project. The forecasts of the three engineers chosen, in reference to the rock to be encountered and its probable tem- perature, have, as far as the galleries have gone ( an aggregate distance of nearly 2 J miles), generally been found correct. At the north end, a dark argillaceous schist veined with quartz was met with, and from time to time beds of gypsum and dolomite have been traversed, the dip of the strata being on the whole favorable to progress, though timbering is resorted to at danger- ous places. Water was plentiful at the- commencement ; in fact, one inrush has not been stopped, and is still flowing down the heading. The total quantity of water flowing from the tunnel mouth is 16 gallons per second, of which 2 gallons per second are accounted for by the drilling machines. At Iselle, how- ever, a very hard antigorio gneiss obtains, and is likely to extend for 4 miles. Very dry and very compact, it requires no timbering, and represents no great difflculty to the powerful Brandt rock-drills, which work under a head of 3280 ft. of water. The temperature of the rock depends not only on the depth from the surface, but largely upon the general form of that sur- face combined with the conductivity of the rock. Taking these points into consideration with the experience gained from the construction of the St. Gothard tunnel, 95° F. was esti- mated as the probable maximum temperature, owing to the height of Monte Leone (11,660 ft.), which lies almost directly over the tunnel axis. Survey. — After having determined upon the general position of the tunnels, taking into consideration the necessary gradi- ents, the temperature of the rock, and a large bed of trouble- some gypsum on the north side, two fixed points on the pro- TUNNELS THROUGH HARD ROCK 107 posed center line were taken, one at each entrance of tunnel No. 1, and the bearings of these two points, with reference to a triangulation survey made in 1876, were calculated sufficiently accurately to determine, for the time being, the direction of the tunnel. In 1898, a new triangulation survey was made, taking in eleven summits, Monte Leone holding the central position. This survey was tied into that of the Wasenhorn and Faulhorn, made by the Swiss Government, and the accuracy was such that the probable error in the meeting of the two headings is only 6 cms. or 2^ ins. On the top of each summit is placed a signal, consisting of a small pillar of masonry founded on rock, and capped with a sharp pointed cone of zinc, 1 ft. 6 ins. high. An observatory was built at each end of the tunnel in such a position that three of the summits could be seen, a condition very difficult to fulfill on the south side owing to the depth of the gorge, the moun- tains on either side being over 7000 ft. high. Having taken the angles to and from each visible signal, and therefrom having calculated the direction of the tunnel, it was necessary to fix, with extreme accuracy, sighting-points on the axis of the tunnel, in order to avoid sighting on to the surrounding peaks for each subsequent correction of the alinement of the galleries. To do this, a theodolite 24 ins. long and 2f ins. in diameter, with a magnifying pow^r of 40 times, was set up in the observatory, and about 100 readings were taken of the angles between the surrounding signals and the required sighting-points. In this manner the error fikely to occur was diminished to less than 1^ Thus at the north end two points were found about 550 yds. before and behind the observatory, while on the south side, owing to the narrowness of the gorge, the points could only be placed at 82 yds. and 126 yds. in front. One of these sighting- points consists of a fine scratch ruled on a piece of glass fixed in an iron frame, behind which is placed an acetylene lamp, — - corrections of alinement are always done by night, — the whole being rigidly fixed into a niche cut in the rock and pro- 108 TUNNELING tected from climatic and other disturbing agencies by an iron plate. Method of Checking Alinement. — The direction of heading No. 1 is checked by experts from the Government Survey De- partment at Lausanne about three times a year, and for this purpose a transit instrument is set up in the observatory. A number of three-legged iron tables are placed at intervals of 1 mile or 2 miles along the axis of tunnel No. 1, and upon each of these is placed a horizontal plane, movable by means of an adjusting screw, in a direction at right angles to the axis, along a graduated scale. On this plane are small sockets, into which the legs of an acetylene lamp and screen, or of the transit instrument, can be quickly and accurately placed. The screen has a vertical slit, 3 ins. in height, and, variable between i| in. and T^6 in.. in breadth, according to the state of the atmosphere, and at a distance shows a fine thread of light. The instrument, having first been sighted on to the illuminated scratch of the sighting-point, is directed up the tunnel, where a thread of light is shown from the first table. With the aid of a telephone this light is adjusted so that its image is exactly coincident with the cross hairs, and the reading on the graduated scale is noted. This is done four or five times, the average of these readings being taken as correct, and the plane is clamped to that average. The instrument is then taken to the first table and is placed quickly and accurately over the point just found (by means of the sockets), and the lamp is carried to the observa- tory. After first sighting back, a second point is given on the second table, and so on. These points are marked either tem- porarily in the roof of the heading by a short piece of cord hanging down, or permanently by a brass point held by a small steel cylinder, 8 ins. long and 3 ins. in diameter, embedded in concrete in the rock floor, and protected by a circular casting, also sunk in cement concrete, holding an iron cover resembling that of a small manhole. From time to time the alinement is checked from these points by the engineers, and after each blast the TUNNELS THROUGH HARD ROCK 10& general direction is given by the hand from the temporary points. To check the results of the triangulation survey, astro- nomical observations have been taken simultaneously at each end. With regard to the levels, those given on the excellent Government surveys have been taken as correct, but they have also been checked over the pass. Details of Tunnels. — In cross-section, tunnel No. 1 is 13 ft. 7 ins. wide at formation level, increasing to 16 ft. 5 ins., with a total height of 18 ft. above rail-level, and a cross-sectional area of about 250 sq. ft. This large section will allow of small repairs being executed in the roof without interruption of the traffic, and will also allow of strengthening the walls by addi- tional masonry on the inside. The thickness of the lining, never wholly absent, and the material of which it is composed, depend upon the pressure to be resisted, and only in the worst case is an invert resorted to. The side drain, to which the rock floor is made to slope, will be composed of half-pipes of 7 to 1 cement concrete. The roof is constructed of radial stones. Tunnel No. 2, being left as a heading, is driven on that side nearest to No. 1, to minimize the length of the cross-headings, and measures 10 ft. 2 ins. wide by 6 ft. 7 ins. high. Masonry is used only where necessary, and in that case is so built as to form part of the lining of the tunnel when eventually com- pleted. Concrete is put in to form a foundation for the side wall, and a w^ater channel. The cross-headings, connecting the two parallel headings, occur every 220 yds., and are placed at an angle of 56° to the axis of the tunnel, to avoid sharp curves in the contractors' railway Hues. They will eventually be used as much as possible for refuges, chambers for storing the tools and equipment of the platelayers, and signal-cabins. The ref- uges, 6 ft. 7 ins. wide by 6 ft. 7 ins. high and 3 ft. 3 ins. deep, occur every 110 yards, every tenth being enlarged to 9 ft. 10 ins. wide by 9 ft. 10 ins. deep and 10 ft. 2 ins. high, still larger chambers being constructed at greater intervals. 110 TUNNELING Method of Excavation. — The work at each end of the tunnel is carried on quite independently, consequently, though similar in principle, the methods vary in detail, apart from the fact that different geological strata require different treatment. Broadly speaking, the two parallel headings, each 59 sq. ft. in section, are first driven by means of drilHng-machines and the use of dynamite, this work being carried on day and night, seven days in the week; No. 1 heading is then enlarged to full size by hand- drilling and dynamite. On the Itahan side, where the rock is hard and compact, breakups are made at intervals of 50 yds., and a top gallery is driven in both directions, but, for venti- lation reasons, is never allowed to get more than 4 yds. ahead of the break-up, which is gradually lengthened and widened to the required section. No timbering is required, except to facilitate the excavation and the construction of the side walls. Steel centers are employed for the arch; they entail fewer sup- ports, give more room, and are capable of being used over again more frequently without damage. They consist of two I-beams bent to a template and riveted together at the crown, resting at either side on scaffolding at intervals of 6 ft. ; longitudinals 12 ft. by 4 ins. by 4 ins. support the roof. Hand rock-drilHng is carried out in the ordinary way, one man holding the tool and a second striking; measurements of excavation are taken every 2 or 3 yds., a plumb-line is suspended from the center of the roof, and at every half-meter (20 ins.) of height horizontal measurements are taken to each side. At the Brigue end a softer rock is encountered, necessitat- ing at times heavy timbering in the heading, and especially in the final excavation to full size, Fig. 56. The bottom heading, 6 ft. 6 in. high, is driven in the center, and the heading is then widened to the full extent and timbered; the concrete forming the water channel and the foundation for one side wall is put in; the side walls are built to a height of 6 ft. 6 ins., and the tunnel is fully excavated to a further height of 6 ft. 6 ins. from the first staging. The side walls are then continued up for the TUNNELS THROUGH HARD ROCK 111 second 6 ft. 6 ins., and from the second floor a third height of 6 ft. 6 ins. is excavated and timbered. Finally the crown is cleared out, heavy wooden centers are put in, the arch is turned and all tim- bers are withdrawn except the top pohng- boards, supporting the loose rock. The masonry for the side walls is ob- tained either from the tunnel itself or from a neighboring quarry, and varies in charac- ter according to the pressure ; but the face of the arch is always of cut or artificial stones, the latter be- ing 7 to 1 cement concrete. Where the alinement heading, or the " gallery of direc- tion," joins the curv- ing portion of tunnel No. 1, the section is very much greater, and necessitates special timbering. Transport (Italian Side). — A small line of railway, 2 ft. 7J ins. gauge, with 40-lb. rails, enters all three portals; but since the con-struction of a wooden bridge over the Diveria, the route Fig. 56. — Sketches Showing Sequence of Work in Excavating and Lining the Simplon Tunnel. ' 112 TUNNELING through the '' gallery of direction/' across heading No. 2, to tunnel No. 1, is used exclusively; this railway leads to the face in both headings, and, where convenient, from one heading to the other by the cross-galleries. Different types of wagons are in use; but in general they are four-wheeled, non-tipping box wagons, supplied with brakes and holding 2 cu. yds. of debris. A special type of locomotive is used, designed to pass round curves of 50 ft. radius, and supplied with a specially large boiler to avoid firing in the tunnel. Method of Working. — The drilling-machines employed are of the' Brandt type. Fig. 57, and are mounted in the following manner: A small four-wheeled carriage supports at its center Fig. 57. — General Details of the Brandt Rotary Drills Employed at the Simplon Tunnel. a beam, the shorter arm of which carries the boring mechanism and the longer a counterpoise ; near its center is the distributor. In the short arm is a clamp holding the rack-bar or butting column, which is a wrought-iron cylinder with a plunger con- stituting a ram, and is jammed by hydraulic pressure betweea the walls of the heading, thus forming a rigid support for the boring-machine, and an efficient abutment against the reaction of the drill. This rack-bar can be rotated on its clamp in a» TUNNELS THROUGH HAKD ROCK 113 plane parallel to the axis of the beam. Three or four separate boring-machines can be mounted on the rack-bar, and can be adjusted in any reasonable position. The boring-machine performs the double function of con- tinually pressing the drill into the rock by means of a hollow ram (1) and of imparting to the drill and ram a uniform rotary motion. This rotary motion is given by a twin cyHnder single- acting hydraulic motor (E), the two pistons, of 2| ins. stroke, acting reciprocally as valves. The cranks are fixed at an angle of 90° to each other on the shaft, which carries a worm, gearing with a worm-wheel (Q) mounted upon the shell (R) of the hollow ram (1), and this shell in turn engages the ram by a long feather, leaving it free to slide axially to or from the face of the rock. The average speed of the motor is 150 revolutions to 200 revolutions per minute, the maximum speed being 300 revolutions per minute. The loss of power between the worm and worm-wheel is only 15 % at the most; the worm being of hardened steel and the wheel of gun-metal, the two surfaces in contact acquire a high degree of pohsh, resulting in little wear- ing or heating. Taking into consideration all other sources of loss, 70 % of the total power is utilized. The pressure on the drill is exerted by a cyhnder and hollow ram (/), which revolves about the differential piston {S), which is fixed to the envelope holding the shell (R). This envelope is rigidly connected to the bed-plate of the motor, and, by means of the vertical hinge and pin (T), is held by the clamp (F) embracing the rack-bar. \Vhen water is admitted to the space in front of the differential piston the ram carrying the drilling-tool is thrust forward, and when admitted to the annular space behind the piston, the ram recedes, withdrawing the tool from the blast-hole. The drill proper is a hollow tube of tough steel 2| ins. in external diame- ter, armed with three or four sharp and hardened teeth, and makes from five to ten revolutions per minute, according to the nature of the rock. When the ram has reached the end of its stroke of 2 ft. 2 J ins., the tool is quickly withdrawn from the 114 TUNNELING hole and unscrewed from the ram; an extension rod is then screwed into the tool and into the ram, and the boring is con- tinued, additional lengths being added as the tool grinds for- ward; each change of tool or rod takes about 15 sees, to 25 sees, to perform. The extension rods are forged steel tubes, fitted with four-threaded screws, and having the same external diameter as the drill. They are made in standard lengths of 2 ft. 8 ins., 1 ft. 10 ins., and 11| ins. The total weight of the drilling-machine is 264 lbs., and that of the rack-bar when full of water is 308 lbs. The exhaust water from the two motor cylinders escapes through a tube in the center of the ram and along the bore of the extension rods and drill, thereby scouring away the debris and keeping the drill cool; any superfluous w^ater finds an exit through a hose below the motors and thence away down the heading. The distributor, already mentioned, supplies each boring-machine and the rack-bar with hydraulic pressure from the mains, with which connection is effected by means of flexible or articulated pipe connections, allowing free- dom in all directions. The area of the piston for advancing the tool is 15 J sq. ins., which, under a pressure of 1470 lbs. per sq. in., gives a pressure of over 10 tons on the tool, while for withdrawing the tool 2 J tons is available. In the rock found at Iselle, namely, antigorio gneiss, a hole 2| ins. in diameter and 3 ft. 3 ins. in length is drilled, normally, in 12 mins. to 25 mins.; a daily rate of advance of 18 ft. to 19 ft. 6 ins. is made in a head- ing having a minimum cross-section of 59 sq. ft.; the time taken to drill ten to twelve holes, 4 ft. 7 ins. deep, is 2J hrs. When the debris resulting from one operation has been suffi- ciently cleared away, a steel flooring, which is provided near the face to enable shoveling to be more easily done, and to give an even floor for the wheels of the drilHng-carriage, is laid bare at the head of the line of rails, and the drilling-machines are brought up on their carriage by eight or ten men. When advanced sufficiently close to the face, the rack-bar is slewed round across the gallery and is wedged up against the rock TUNNELS THROUGH HARD ROCK 115 sides; connection is made between the distributor and the hydrauHc main, by means of the flexible pipe, and pressure is suppHed by a small copper tube to the rack-bar ram, thereby rigidly holding the machine. Next, connections are made be- tween the three drilling-machines and the distributor, and in 20 mins. from the time the machine was brought up all three drills are hard at work, water pouring from the holes. The noise of the motors and grinding-tools is sufficient to drown all but shouts; and where the extension rods do not fit tightly, small jets of water play in all directions, necessitating the wearing of tarpaulins by the men directing the tools. Light- ing is done wholly by small oil-lamps, provided with a hook to facilitate fixing in any crack in the rock; electricity will probably be used to fight that portion of the tunnel which is completed. Two men are alloted to each drill, one to drive the motor, the other to direct and replenish the tool, one foreman and two' men in reserve completing the gang. A small hammer is freely used to loosen the screw joints of the extension rods and drill. A hole is usuafiy commenced by a two-edged flat-pointed tool, until a sufficient depth is reached to prevent the circular tool from wandering over the face of the rock, but in many instances the hole is commenced with a circular tool. The exhaust water during this period flows away by the hose underneath the motor. In the antigorio gneiss, ten to twelve holes are drilled for each attack, three to four in the center to a depth of 3 ft. 3 ins., the remainder, disposed round the outside of the face, having a depth of 4 ft. 7 ins. The average time taken to complete the holes is If hr. to 2 J hrs. Instead of pulverizing the rock, as do the diamond drills, it is found that the rock is crushed, and that headway is gained somewhat in the manner of a circular saw through wood. The core of rock inside the tool breaks up into smafi pieces, and can be taken out if necessary when the drill requires lengthening. The lowest holes, incHned downwards, are full of water; 116 ^ TUNNELING consequently two detonators and two fuses are inserted, but apart from this, water has little effect on the charge. The fuses of the central holes are brought together and cut off shorter than those of the outer holes, in order that they may explode first to increase the effect of the outer charges. All portable objects, such as drills, pipe connections, tools, etc., have mean- while been carried back; the steel flooring is covered over with a layer of debris to prevent injury from falling rock, and to the end of the hydraulic main is screwed a brass plug pierced by five holes; and immediately the explosions occur a valve is opened in the tunnel, and five jets of water play upon the rock, laying the dust and clearing the air. The necessity for this was shown on one occasion when this nozzle was broken by the explosion and the water had to be turned off immediately to avoid useless waste; on reaching the face, the atmosphere was found to be so highly charged with dust and smoke that it was impossible to distinguish the stones at the feet, although a lamp had been placed on the ground; and despite the fact that the air tube was in full blast, the men experienced great difficulty in breathing. A truck is now brought up, and four men clear a passage in front, through the heap of debris, two with picks and two with shovels, while on either side and behind are as many men as space will permit. The stone is thrown either to the sides of the heading or into the wagon, shoveling being greatly aided by the steel flooring, which, before the explosion, had been laid over the rails for nearly 10 yds. down the tunnel to receive the falHng rock. These steel plates are taken up when cleared, and the wagon is pushed forward until the drilling-machine can be brought up again, leaving the remaining debris at the sides to be handled at leisure during the next attack. The roof and side walls are, of course, carefully examined with the pick, to discover and detach any loose or hanging rock. The times taken for each portion of the attack in this particular antigorio gneiss are as follows: Bringing up and adjustment of drills, 20 mins.; drill- ing, between If hr. and 2 J hrs.; charging and firing, 15 mins.; TUNNELS THROUGH HARD ROCK 117 clearing away debris, 2 hrs.; or for one whole a,ttack, between 4i hrs. and 5 J hrs., resulting in an advance of 3 ft. 9 in., or a daily advance of nearly 18 ft. From this it appears that the time spent in clearing away the debris equals that taken up in drilling, and it in this clear- ing that a saving of time is likely to be effected rather than in the process of drilling. Many schemes have been tried, such as a mechanical plow for making a passage; at Brigue, " marin- age," or clearing by means of powerful high-pressure water-jets, directed down the tunnel, was tried, but the idea is not yet sufficiently developed. Another series of experiments has been tried at Brigue with regard to the utilization of liquid air as an explosive agent instead of dynamite; and for this purpose a plant has been laid down, consisting of one ammonia-compressor, two air-com- pressors, and two refrigerators, furnishing j\ gallon of liquid air per hour at an expenditure of 17 H. P. The system used is that of Professor Linde, who himself directs the experiments. The great difficulty experienced is that of shortening the interval of time that must elapse between the manufacture of the cart- ridge and its explosion. The liquid oxygen, with which the cartridge, containing kieselguhr (silicious earth) and paraffin, is saturated, evaporates very readily, losing power every moment; hence the effect of each cartridge cannot be guaranteed, and though it is an exceedingly powerful explosive when used im- mediately after manufacture, no practical result has yet been obtained. Power Station. — Water is abundant at either end, and there- fore hydraulic power is the motive force employed. On the Italian side, a dam 5 ft. high has been thrown across the Diveria at a point near the Swiss frontier, about 3 miles above the site of the installations. A portion of the water thus held back enters, through regulating doors and gratings, a masonry channel leading to two parallel settling tanks, each 111 ft. by 16 ft., whence, after dropping all its sand and solid matter, the now 118 TUNNELING pure water passes into the water-house, and, after flowing over a dam, through a grating and past the admission doors, enters a metallic conduit of 3-ft. pipes. Each of the settling tanks and the approach canal are provided with doors at the lower end leading direct to the river, through which all the sand and solid matter deposited can be scoured naturally by allowing the river- water to rush freely through. For this purpose the floor of the basins is on an average gradient of 1 in 30. For a similar reason the river-bed just outside the entrance to the approach canal is lined with wooden planks, from which the stones collecting behind the dam can be scoured by allowing an iron flap, hinged at the bottom, to change its position from the vertical to the horizontal in a gap left purposely in the dam, so causing a rushing torrent to sweep it clean. The chief levels are : Level of water at dam 794 . 00 meters above sea level. " in water-house 793.70 " " " " " at turbines 618.50 " " " " giving a total fall of 175.20 ms. or 570 ft., and a pressure of 17.52 atmospheres. The quantity of water capable of being taken from the Diveria in winter, when the rivers which are dependent upon the moun- tain snows for their supply are at their lowest, is calculated to be 352 gallons per second. Thus, taking the fall to be diminished by friction, etc., to 440 ft., and the useful effect at 70 %, there is obtained 2000 H. P. on the turbine shaft. The metallic conduit varies in material according to the pressure; thus cast-iron pipes 3 ft. in diameter and |f in. thick are used up to a pressure of 2 atmospheres, from which point they are of wrought-iron. The cast-iron portion has of late caused a good deal of trouble, owing to settlement of the piers causing occasional bursts, consequently a masonry pier has been placed under each joint of this portion. The following table gives the thicknesses and diameters, varjdng with the pressure : TUNNELS THEOUGH HARD ROCK 119 Water Pressure. Thickness. Diameter. , Weight per Yard. Head in Feet. Milli- meters. Inch. Feet. Inches. Lbs. 246 311 360 393 426 476 590 6 7 8 9 10 12 16 1 3 3 3 3 3 3 3 31 326 383 431 483 556 651 977 This pipe is supported every 30 ft. on small masonry piers, on the top of which is placed a block of wood hollowed out to receive the pipe, thus allowing any movement due to the con- traction and expansion of the conduit. However, to prevent this movement becoming excessive, the pipe is passed at intervals of 300 yds. to 500 yds. through a cubical block of masonry of 13 ft. side, strengthened by longitudinal tie-bars. Five bands of angle-bar riveted round the pipe, with their flanges embedded in the masonry, constitute a rigid fixed point. Straw mats are thrown over the pipe where it is exposed to the sun. The tem- perature of the conduit is not, however, found to vary greatly, since the pipe is kept full of water. To supply the rock-drills with water at a maximum pressure of 100 atmospheres, or 1470 lbs. per sq. in., a plant of four pairs of high-pressure pumps has been laid down, and a still larger addition is in course of erection. At present, two Pelton turbines of 250 H.P. each, running at 170 revolutions per minute, drive the pumps, by means of toothed gearing, at 63 revolutions per minute. These pumps are of very simple but strong construction, single suction and double delivery, entailing one suction and one delivery-valve, both heavy and both of small lift. The larger portion of the plunger has exactly double the cross-sectional area of the smaller portion, so that in the forward stroke half of the water taken in at the last admission is pumped into the high-pressure mains, and at the same time a fresh supply of water is sucked in. During the 120 TUNNELING backward stroke half of this new supply is pumped into the mains, and the remainder enters the second chamber, to be pumped during the next forward stroke. Thus the work done in the two strokes is practically the same. The pumps are in pairs, and are set at an angle of 90°, to insure uniform pressure and uniform delivery in the mains. Their size varies; but at Iselle there are three pairs, with a stroke of 2 ft. 2J ins., and the plungers of 2{^ in. and 1| ins. (approximately) in diameter, supplying 1.32 gallons per second. To avoid injury to the valves, the water to be pumped is taken from a stream up the mountain side, and is passed through filter screens. The high-pressure water, after passing an ac- cumulator, enters the tunnel in solid drawn wrought-iron tubes, SJ ins. in internal diameter, ^^ in. thick, and in lengths of 26 ft. The diameter of these mains varies with their length, so as to avoid loss of pressure. With the 1250 yds. of tunnel now driven 10 atmospheres are lost. At Brigue the installations are, as far as possible, identical. The Rhone water, however, before reaching the water-house, is carried from the filter basins, a distance of 2 miles, in an armored canal built upon the Hennebique system,* the walls and supporting beams, of cement concrete, being strengthened by internal tie-bars of steel. The concrete struts, resembling balks of timber at a distance, are occasionally 35 ft. high and 1 ft. 7J ins. square. The metallic conduit is 5 ft. in diameter, with a minimum flow of 176 cu. ft. per second and a total fall of 185 ft. In case water-power should be unavailable, three semi-portable steam engines, two of 80 H.P. and one of 60 H.P., are always kept in readiness at each end of the tunnel, and are geared by belts to the turbine shaft. Ventilation. — In tunneling, one of the most important prob- lems to be solved is that of ventilation, and it is for this reason that the Simplon tunnel consists of two parallel headings with cross cuts at intervals of 220 yds. At Brigue, a shaft 164 ft. * Network of steel rods embedded in concrete. TUNNELS THBOUGH HARD ROCK 121 deep was sunk through the overlying rock until the '' gallery of direction " was encountered. Up this chimney the foul air is drawn by wood fires, the fresh air — a volume of 19,000,000 cu. ft. per day, or 13,200 cu. ft. per minute — entering by head- ing No. 2, penetrating up to the last cross gallery, and returning by tunnel No. 1. The entrances of No. 1 and the '' gallery of direction," besides those of all the intermediate cross galleries, are closed by doors. By this arrangement, however, fresh air does not reach the working faces; therefore a pipe, 8 ins. in diameter, is led from the fresh air in No. 2 to within 15 yds. of the face of each heading, and up this pipe a draft of air is induced by means of a jet of water, the volume to each face being 800 cu. ft. per minute. One single jet of water from the high-pressure mains, with a diameter of ^\ in., is capable of supplying over 1000 cu. ft. of air per minute at the end of 160 yds. of pipe, and during the attack the men at the drills are in a constant breeze with the thermometer standing at 70° F. At Iselle, air is blown into the entrance of heading No. 2 at the rate of 14,100 cu. ft. per minute by two fans driven from the turbine shaft. This air travels from the fans along a pipe 18 ins. in diameter, till a point 15 yds. up the tunnel is reached, where beyond a door the pipe narrows to form a nozzle 10 ins. in diameter. This door is kept open to allow the outside air to be induced up the tunnel, as the headings are at present only 2500 yds. long, giving a resistance of not quite sufficient power to cause the air to return. The fresh air then travels up No. 2, crossing over the top of the " gallery of direction," from which it is shut off by doors, to the last cross gallery, returning by No. 1, and finally leaving either by the ''gallery of direction" or by No. 1. A system of cooling the air and driving it on by means of a large number of water- jets will be installed in No. 2 where that heading crosses over the " gallery of direction," but at present there is no need for it. The average temperature at the face is 73° F. during the drilling operation, 76° F. after firing the charges, and a max- 122 TUNNELING imum of 80° F., lately attaining to 86° F. on the south side, with 80° F. and 85° F. before and after firing. The tempera- ture of the rock is taken at every 110 yds. in holes 5 ft. deep, and shows a gradual increase according to the depth of over- laying rock, to the conductivity of the rock, and to the form of the mountain surface. The maximum hitherto reached on the north side is 68° F., w^hile on the south side, although a smaller distance has been traversed, it attains to 79° F., due to the more rapid increase in depth. Moreover, the temperature of the rock is observed at the permanent stations, 550 yds. from the entrances, in its relation to that of the tunnel and outside air, and though on the north side that of the rock varies almost as quickly as that of the tunnel air, on the south it is influenced very much less. A few statistics may be of interest with regard to the prog- ress of the last three months (taken from the trimestrial report of January, 1900). At Brigue, where there are three drilhng- machines in No. 1 and two in the parallel heading, the total length excavated was 995 yds. or 6409 cu. yds. in 89 working days, the average cross-sectional area being 57 sq. ft. This re- quired 507 attacks and 3066 holes, which had a total depth of 26,600 ft. and 14,700 re-sharpenings of the driUing-tool, with 44,000 lbs. of dynamite. The average time occupied in drilHng was 2 hrs. 45 mins., while charging, firing, and clearing away the debris took 6 hrs., 35 mins. At Brigue 648 men and 29 horses were employed at one time in the tunnel. At Iselle the numbers were 496 men and 16 horses, working in shifts of 8 hrs. Outside the tunnel, in the shops, forges^ etc., the men work 8 hrs. to 11 hrs. per day, the total being 541 men at Brigue and 346 men at Iselle. On the Italian side, where the rock is very much harder, there were three drilHng-machines in each heading; the total length excavated, with a cross-sectional area of 62 sq. ft., was 960 yds. or 6700 cu. yds. in 91 working days. This required 61,293 re-sharpened tools, 758 attacks, 7940 holes with a total depth TUNNELS THROUGH HARD ROCK 123 of 33,000 ft., and 56,000 lbs. of dynamite. The average time spent in drilling was 2 hrs. 55 mins., and in charging and clear- ing 2 hrs. 36 mins. Thus, in the hard gneiss, to excavate 1 cu. yd. of rock required 8J lbs. of dynamite, and each tool pierced 6 J ins. of rock before it required re-sharpening. THE MURRAY HILL TUNNEL The drift method of excavating tunnels was followed in Section IV of the New York Subway, under Park Avenue between 33rd and 41st Streets. At this point the four tracks of the subway pass under a rocky elevation, known as Murray Hill, in two double track parallel tunnels, 43 ft. apart, center to center. Here already existed a double track tunnel which was built many years ago by the New York Central and Hudson River R.R., and is now used by the Madison Avenue surface cars. The two subway tunnels were driven close below the existing tunnel and also very near the foundations of expensive residences along Park Avenue, particularly on Murray Hill, one of the best residential sections of the city. Material Penetrated. — The material penetrated by the exca- vation consisted chiefly of a surface outcrop of the mica-schist rock which underlies Manhattan Island. The rock was for the most part in compact strata, dipping at about 45° from East to West, but at intervals an unstable stratum was encountered which when free slid on the underlying stratum. Troubles from such slides were experienced during the construction of the tunnel. Cross-Section. — The cross-section selected for the tunnels had vertical side walls and a three-centered roof arch with the flattest curve at the crown. The interior dimensions were 25 ft. wide and 16 ft. high. The selected cross-section was not the best suited for a tunnel to be driven through rock, where the sharpest curve should be at the top, but in this case the flattened curve was chosen because of local conditions; chiefly, the presence of the existing tunnel and the consequent neces- 124 TUNNELING sity of leaving a certain thickness of rock between it and the new tunnel, without depressing very much the grade of the subway. Excavation. — The two parallel tunnels were driven exclu- sively from the ends reached by shafts; thus the tunnels were attacked at four parts. It was in these tunnels that a compara- tive test was made of the different methods of driving tunnels through rock. The contractor applied the heading and drift method at the southern ends of the tunnels, the eastern tunnel being driven by means of a drift while in the western tunnel the usual heading method was followed. This latter method is illustrated in the chapter following and the eastern tunnel at 33rd Street, excavated by means of a drift, is here considered. Fig. 58 shows the sequence of cuts adopted for this tunnel. It was begun by a bottom drift, about 10 ft high, 8 ft. wide and 7 ft. deep, which was located at one side of the axis of the tunnel, as indicated in the figure. This drift was imme- diately widened by removing the portions marked 2. About 50 ft. in the rear the part marked 3 was taken away, thus clearing the entire lower portion of the tun- nel. Section 4, about 50 ft. to the rear of section 3, was then broken down and removed. The methods of drilling and blasting were as follows: In taking out the original drift, a wedge-shaped center cut was made and then enlarged to the full size of the drift by drilling parallel holes. The succeeding sections, 2 and 3, were removed by driving parallel holes, while the top section, 4, was taken away by a center cut and parallel holes. The drills were mounted on columns, two drills to a column, and the holes were usually drilled about 7 ft. deep, starting with a diameter of 2f in. and ending with a diameter of If in. They were blasted with 40% Fig. 58. — 'Sequence of Excavation in the Murray Hill Tunnel. TUNNELS THROUGH HARD ROCK 125 Fig. 59. — Traveling Platform for the Excavation of the Upper Side of the Murray Hill Tunnel. dynamite in light charges, only a few holes being fired at a time, usually not more than three or four. To remove section 4, a traveling platform 10 J ft. long and 25 ft. wide was used. This platform, as shown in Fig. 59, con- sisted of two longitudinal beams mounted on four double flanged wheels which wTre running on tracks laid 23 ft. apart. Resting on top of these beams were four 12 in. X 12 in. uprights braced in every direction against the framework of the platform. This frame was built of 12 in. X 12 in. beams laid longitudinally, the transverse beams being 12 in. X 14 ins. The platform proper was made of 3 in. planks, and was set 9 ft. above the tunnel floor. The columns supporting the drills for the exca- vation of the upper section 4, were set up above the platform which was then reinforced by other vertical props, as indicated by the dotted lines in the figure. These props, however, were placed so as to leave a clearance beneath the platform for the cars to carry away the debris from the front. During the blasting the platform was moved back so that the blasted rock fell to the floor of the tunnel, whence it was loaded into boxes on the cars. Strutting. — When the rock was seamy and full of fissures, running in every direction, it was necessary to support the roof of the excavation. This was done in the following manner : After part 4 was removed the timbers supporting the roof of the excavation were set up. In this case, the polygonal strutting was used. This consisted of heavy timber frames placed trans- versely to the axis of the tunnel and supporting the planks or poling-boards which ran longitudinally against the roof of the 126 TUNNELING excavation. The seven-segment arch frame was used in the Murray Hill tunnel. At the bottom of part 4 were placed longitudinally 12 X 16 in. beams and upon them rested the inchned segments which, with a horizontal one, formed the arch frame as shown in Fig. 60. When the pressures were too heavy the crown segment was reinforced by a 6 X 12 in. beam, kept in place by two 12 X 12 in. inchned props which rested on the templates. As the tunnel was lined with concrete, the tim- bering was left in place and it Fig. 60. -Timberin^g^Used in the Murray ^^g ^^-j^ OUtslde the Me of the extrados of the concrete lining. Timbering was only used for a short distance but it necessitated a larger amount, of rock excavation when it was required. Hauling. — Great efficiency was shown in the method of hauling away the excavated materials. Three narrow-gauge parallel tracks were laid on the floor of the tunnel and extended to the faces of the advance drifts. Small flat cars were run on these tracks. They carried steel boxes, 5 ft. square and 15 ins. deep, fitted with three lifting rings and chains. AVhen filled, the cars were run to the bottom of the shaft, the boxes were hoisted by a stiff-legged derrick placed at the shaft head, and the debris was dumped into storage bins of 300 cu. yds. capacity. These bins were elevated 8 ft. above the street so that the wagons could be driven under it to take loads of spoil by means of chutes. The broken rock was loaded into the boxes by hand. Concrete Lining. — The tunnel was lined with concrete which was manufactured by a quite elaborate plant. A stone crushing plant, consisting of bins for raw and crushed stone, was erected at the shaft head and a mixing plant was suspended from the shaft. On the platform of the shaft head were two bins side TUNNELS THROUGH HARD ROCK 127 by side, one for crushed stone, the other for sand; both of which communicated, by means of trap doors, with a hopper chute. The materials from the hopper were dehvered into a measuring box where cement was laid on top of the other ingredients by hand. They were then conveyed through a canvas chute into a cubical mixer operated by an engine. The mixer discharged its contents into skips set on cars at the bottom of the shaft and the concrete was hauled inside the tunnel ready for use. The construction of the lining was accomplished by means of traveling platforms. The footing courses were laid first. Be- cause these projected inward about 18 ins. from the faces of the finished sidewalks it was possible to lay a track rail on their top inner edges on each side of the tunnel. These track rails carried the traveling platforms. There were three of these platforms; the forward one was used for building the side walls; the center one, for carrying a derrick; the last one, for building the roof arch. The side wall platform was mounted on six wheels. On each side there was mounted an adjustable lagging which was curved to conform to the inside profile of the side wall. In operation this platform was run to the point where the side walls were to be constructed and the lagging was adjusted to position and fastened. Skips of concrete were then hoisted on its top, their contents were shoveled into the space between the lagging and the wall of the excavation and were there rammed into place until the finished concrete had reached the top of the lagging. When the concrete had set, the wedges holding the lagging in place were loosened and the platform was moved ahead and adjusted for building a new section of wall. The derrick plat- form was 23J ft. wide and 18 ft. long. Transversely, it had three bays, two of which were floored over and one was left without flooring to allow passage for the concrete skips to and from the cars, on the tunnel floor beneath. At the center of the floored area was mounted a derrick to handle the skips. In operation, the derrick platform came between the side wall 128 TUNNELING platform ahead and the roof platform behind. The construction of the roof platform was practically the same as the side wall platform with the addition of roof arch centers at each bent on which lagging could be placed. The mode of procedure was to erect the form for a small space between the side walls already built and the haunches of the center, to shovel concrete from the skips and to run it into place. Then the roof lagging, a part at a time, was placed upward from the haunches and the concrete was filled and rammed behind it. The lining was built from the haunches upward until the two sides approached within a distance of about 5 ft. from each other at the crown. This 5 ft. crown strip or key was built by working from the rear toward the front end of the platform. Plant. — The plant used by the contractors for Section IV. of the subway comprised a central power plant located, about 4000 ft. from the work. This was on 42nd Street near the East River and furnished power for the work on both Sections IV. and V. The buildings consisted of an engine room 63 X 30 ft. and a boiler room, 42 X 28 ft. In the former room was located one Rand-Corliss air compressor, 22 X 40 X 48 ins., having a capacity of 5000 cu. ft. of free air per minute; in the latter room there were two 200 H.P. water tube boilers. There were also the necessary equipment of feed water pump, air condenser pump, etc. The compressors discharged into a 20 X SJ ft. receiver of riveted steel through a 7 in. pipe. The air from the receiver was carried by a 10 in. pipe 3.277 ft. to the corner of Park Avenue and 41st Street, and was thence run south along Park Avenue in an 8 in. pipe, from which 3 in. branches led to the four headings of the work. Ventilation. — The ventilation of the tunnel caused very little trouble. In cool weather the natural draft of the shafts and the air discharged from the drills served to keep the at- mosphere wholesome. In warm weather, artificial means were necessary to clear the workings of foul air, particularly after blasting. They comprised at each end a 4 ft. American exhaust TUNNELS THROUGH HARD ROCK 129 fan drawing air from a 12 in. riveted galvanized iron pipe, which extended to the working faces. lUumination. — The tunnel was lighted by electric lamps which extended even to the working face. During the blasting, how- ever, all the lamps and wires within 100 ft. from the front were removed and gasoline torches were used; they were also em- ployed before the electric lamps and wires could be replaced, to light the tunnel during the operation of clearing the debris. 130 TUNNELING CHAPTER XI. TUNNELS THROUGH HARD ROCK (Continued). EXCAVATION BY HEADINGS. EUROPEAN AND AMERICAN METHODS. The more common method of tunneling through hard rock is to begin the work by a heading, instead of by a drift. This heading may be of small dimensions, and the remainder of the section may also be removed in successive small parts, or it may be the full width of the section, and the enlargement of the section be made in one other cut. General Discussion. — When the tunnel is excavated by means, of several cuts, which is the method usually employed in Europe, the sequence of work is as indicated by Fig. 58. Work is begun by driving the center top heading No 1, whose floor is at the level of the bottom of the roof arch, and which is usually excavated by the circular cut method. This heading is widened by removing parts Nos. 2 and 3 until the top part of the section is removed, then the roof arch is built with its feet rest- ing on the unexcavated rock below. The lower portion of the section or bench is removed by first sinking the trench No. 4, after which part No. 5 is taken out, and then parts Nos. 6 and 7, and the side walls built. Part No. 8 for the culvert is finally opened. The heading is, as a rule, driven far in advance, but the excavation of each of the other parts follows the preceding one at a distance behind of about 300 ft. The strutting, when any is required, is usually the typical radial strutting of the Belgian method of tunneling. The masonry lining is constructed practically the same as in tunnels excavated by a drift. The hauling is done on a single track laid in the heading No. 1, which separates into double tracks. TUNNELS THROUGH HARD ROCK 131 where the full top section has been excavated by the removal of parts No. 2. These two tracks are again combined and form a single track along the top of part No. 5, which has been left wider than part No. 4 for this particular purpose. When part No. 3 is excavated a standard-gauge track is laid on its floor ; and as the full section of the tunnel is completed by taking out parts Nos. 4 and 5, this single track is replaced by two standard- gauge tracks, into which it switches. Spoil is transferred from the narrow-gauge tracks on the upper level, to the standard- gauge tracks on the tunnel floor, by means of chutes, and build- ing material is transferred in the opposite direction by means of hoisting apparatus. When the excavation is made by a single wide heading, and a single other cut for removing the bench, which is the method preferred by American engineers, it is called the Heading and Bench method. The work begins by removing a top heading the full width of the section; this heading is usually made 7 ft. or 8 ft. high, and is excavated by the center cut method. The method of strutting usually employed is to erect successive three- or five-segment timber arches, whose feet rest on the top of the bench; when the bench is removed, posts are inserted under the feet of each arch. These arches are covered with a lagging of plank. In America it has often been the practice to let this strutting serve as a temporary lining, and to replace it only after some time, often after years, with a permanent lining of masonry. In a succeeding chapter, some of the methods adopted in relining timber-lined arches with masonry are de- scribed. The hauling is done by either narrow or broad gauge tracks laid on the floor of the completed section below. A device called a bench carriage is often employed to enable the cars running on the heading tracks to dump their loads into the cars below, without interfering with the work on the bench front. This device consists of a wide platform carried on trucks, running on rails at the sides of the tunnel floor, so that it is level with the floor of the heading. The front of this platform carries a 132 TUNNELING hinged leaf which may be raised and lowered, and which forms a sort of gang-plank reaching to the floor of the heading. By running the heading cars out on to this traveling platform, they can be dumped into the cars below entirely clear of the work in progress on the bench front. For the purpose of illustrating the two methods of driving tunnels by a heading, which have been briefly described, the St. Gothard and the Fort George tunnels have been selected. The St. Gothard tunnel is selected, as being one of the longest tunnels in the world, and because it was excavated by a number of small parts ; and the Fort George tunnel, as being a double-track tunnel, driven by a heading, and bench, and having a concrete lining. ST. GOTHARD TUNNEL. The -St. Gothard tunnel penetrates the Alps between Italy and France, and is 9^ miles long. It was constructed in 1872-82. Material Penetrated. — The St. Gothard tunnel was excavated through rock, consisting chiefly of gneiss, mica-schist, serpen- tine, and hornblende, the strata having an inclination of from 45° to 90°. At many points the rock was fissured, and disintegrated easily, and water was encountered in large quantities, causing much trouble. Excavation. — The sequence of ex- cavation is shown by Fig. 14, p. 36. First the top center heading, No. 1, whose dimensions varied from 8.25 X 8.6 ft. to 8.5X9 ft., according to the quality of the rock, was driven never less than 1000 ft. and some- times over 3000 ft. in advance of parts No. 2. The exca- vation of parts No. 2 opened up the full top section, and parts Nos. 3, 4, 5, 6, and 7, were removed in the order numbered. Strntting. — Where regular strutting was required, the con- struction shown in Fig. 62 was adopted. 5 2 4r- Fig. 61. — Diagram Showing Se- quence of Excavation in Heading Method of Tunneling Rock. TUNNELS THROUGH HARD ROCK 133 Masonry. — The St. Gothard tunnel is lined throughout with masonry. After the upper portion of the section was fully excavated, the roof arch was built with its feet resting upon short planks on the top of the bench. Plank centers were used in constructing the arch. For the arch brick masonry was employed, but the side walls were built of rubble masonry. Shelter niches, about 3 ft. deep, were built into the side walls at intervals, and about every 3,000 ft. storage niches about 10 ft. deep, and closed with a door, were constructed. The cul- vert was of brick masonry. Mechanical Installation. — Water-power was used exclusively in driving the St. Gothard tunnel. At the north end, the Reuss, and at the south end, the Tessin and the Tremola, rivers or torrents were dammed, and their waters conducted to tur- bine plants at the opposite ends of the tunnel. The power thus furnished by the Reuss was about 1,500 H.P., and the power furnished by the combined supply of the Tessin and Tremola was 1,220 H.P. The turbine plant at both ends at first con- sisted of four horizontal impulse turbines, but later, two more turbiues were added at the south end. Each of the two sets of four turbines first installed drove five groups of three compres- sors each, and the two supplementary turbines drove two groups of four compressors each. The compressors were of the Colladon type with water injection, and four groups of three compressors each were capable of furnishing 1,000 cu. yds. of air compressed to between seven and eight atmospheres every hour, or about 100 H.P. per hour, delivered to the drills at the front. This air when exhausted provided about 8,000 cu. yds. of fresh air per hour for ventilation. The compressors at each entrance discharged into a group of four cylindrical receivers of wrought-iron each 5.3 ft. in diameter by 29.5 ft. long, and having a capacity of 593 cu. ft. The cylinders were placed horizontally, the first one receiving the air at one end and discharging it at the other end into the next cylinder, and so on. By this arrangement the air was 134 TUNNELU^TG drained of its moisture, and the discharge from the end receiver into the tunnel delivery pipes was not affected by the pulsations of the compressors. The delivery pipe decreased from 8 in. in diameter at the receiver to 4 ins. in diameter, and finally to 2i. ins. in diameter, at the front. The drills employed were of various patterns. The first one employed was the Dubois & Frangois " perforator," in which the drill-bit was fed forward by hand. This was replaced by Fer- roux drills having an automatic feed. Jules McKean's "perfo- rator " was employed at the north end of the tunnel. All of these drills were of the percussion type, and were mounted on carriages running on tracks. Their comparative efficiency was. officially tested in drilling granitic gneiss with an operating air pressure of 5.5 atmospheres with the following results : Name of Drill. Penetration Ins. per Min. Ferroux 1.6 McKean 1.4 Dubois & Frangois 1.04 Soummelier 0.85 The heading was excavated by the circular cut method, the holes being driven as follows : Near the center of the heading three holes were first drilled, converging so as to inclose a pyramid with a triangular base. Around these center holes. from 9 to 13 others were driven parallel to the tunnel axis. The center holes were blasted first, and then the surrounding holes. From 3 to 5 hours were required to drill the two sets of holes, and from three to four hours were required to remove the blasted rock. The number of holes drilled in removing each of the various parts was as follows : Part No. 1 6 to 9 Part No. 2 6 to 10 Part No. 3 ^ 2 Part No. 4 . . . . . . . ' 6 to 9 Part No. 5 3 Part No. 6 6 to 9 Part No. 7 1 Total for full section 36 to 40 TUNNELS THROUGH HARD ROCK 135 Hauling. — Two different systems were employed for haul- ing the spoil and construction material in the St. Gothard tunnel. To remove the spoil from parts Nos. 1 and 2 a narrow- gauge track was laid on the floor of the heading, and the cars were hauled by horses, the grade being descending from the fronts. These narrow-gauge cars were dumped into larger broad-gauge cars running on the track laid on the floor of the completed section and hauled by compressed air locomotives (Fig. 63). To raise the incoming structural material from the broad-gauge cars to the narrow-gauge cars running on the level above, hoisting devices were employed. Fig. 62. — Method of Strutting Roof, St. Gothard Tunnel. ■Fig. 63. — Sketch Showing Arrangement of Car Tracks, St. Gothard Tunnel. FORT GEORGE TUNNEL.* From a point north of 157th Street and Broadway almost to Dyckman Street, that is, a distance of nearly two miles, the New York Subway passes under an elevation known as Fort Washing- ton Heights, which almost bounds Manhattan Island at its upper end near the Harlem Ship Canal. Under this elevation the rapid transit railroad was constructed in tunnel. The tunnel was driven from two intermediate shafts over 110 ft. deep, located one at 169th Street and the other at 181st Street and * Condensed from a paper by Stephen W. Hopkins in Harvard Engineering Journal, April, '08. 136 TUNNELING Broadway. Both shafts were sunk at one side of the center line of the tunnel. After these shafts had been utiUzed for working purposes during the construction of the tunnel, they were equipped with electric elevators to carry passengers from the streets to the deep station. Material. — The material encountered in the excavation of the Fort George tunnel was the usual mica schist met everywhere on Manhattan Island. It was full of seams with strata running in every direction to such an extent that at many points the roof of the tunnel had to be supported by timbers; at other parts along the Hne the rock was so disintegrated that it was considered a very loose and treacherous soil. Two serious accidents, each accompanied by loss of life, occurred during the construction of this tunnel. Both of them were caused by the sudden fall of a large ledge of rock which, after the tunnel had been excavated to the full section, remained hanging on the roof, deprived of any support and held in place by the little cohesion of the material packing the seams. Excavation. — The tunnel was excavated by the heading method in only two cuts, viz., the heading and bench as indicated in the Fig. 63. The heading, almost as wide as the upper portion of the tunnel section, was excavated in the manner explained on page 91. After the heading was removed, the enlargement of the entire upper section of the tunnel was accomphshed by driving three inclined holes at each side of the heading. They were driven at different depths and inchnations, as shown in the figure and were called trimming holes. At the same time the bench was removed by means of five holes — three vertical and two inclined. The line of subgrade was reached by means of five grading holes driven almost horizontal with a shght inclination downward. The air drills for the heading were mounted on columns, all the others on tripods. The blasting was done in the following order: the grading holes were blasted in the first round, the bench and trimming in the second, the center cut of the heading in the third, the sides in the fourth TUNNELS THROUGH HARD ROCK 137 and the dry holes in the last. Thus each advance of 7 ft. of the whole tunnel section was made by means of forty holes fired in five rounds which consumed 277 lbs. of dynamite with an Cross. Section. Fig. 64. — Arrangement of Drill Holes in the Fort George Tunnel. Longitudinal Section. Fig. 65. — Longitudinal Section of the Heading and Bench Excavation at the Fort George Tunnel. average additional quantity of 76 lbs., making a total of 353 lbs. With the exception of the center cut, where 60% dynamite was used, all the other holes were discharged with 40% dynamite. Strutting. — When the rock was of such a character as to be dangerous and required permanent timber support, until the masonry lining was in place, the method employed was as follows : a top heading was first excavated about 10 ft. deep and from 10 ft. to 12 ft. wide for some distance, 100 ft. to 500 ft., the dangerous rock being supported by 10 X 10 in. yellow pine plumb or raking posts and sometimes by timber bents {" caps and legs "). The next process was to widen the heading to the full width of 30 ft. for a length of about 20 ft., placing timber supports under the dangerous rock as the widening-out progressed. The excava- tion was deepened a little at the sides to 9.5 ft. below the roof grade (ordered line of excavation) or about 11 ft. below the roof grade, which was necessary when segmental timbering was to be used, to allow for placing a 12 X 12 in. " wall plate " (timber sill) along each side. These wall plates, generally 20 ft. long, were set to the correct elevation and were leveled by blocking and wedging. As soon as the wall plates were set, 138 TUNNELING the work of erecting the segmental timber sets, one set at a time, was begun by starting from the wall plates and supporting the timber on scaffolding until keyed in, then it was blocked up to the rock at each joint and at other necessary points. When two or more sets were erected, lagging, made of boards 2 ins. thick by 6 to 10 ins. wide, was placed over the segmental timber " sets '' and the space above the timber dry packed with small stone placed by hand. Sometimes there was enough room between the timber and the rock to do all the dry packing after the full number of sets, generally six, had been placed on the two wall plates. The temporary timber posts and braces were taken out as the segmental timber sets were erected. The seven timbers that made up a timber set were of yellow pine each 10 X 10 ins., 5 ft. 2 ins. long at the intrados and 5 ft. 6 ins. at the extrados. The sets were spaced from 3 ft. to 5 ft. apart, but generally 3.5 ft. and braced to each other at each joint of the segmental timbers by 6 X 8 in. spreaders which were wedged against the joint sphces. When the timbers w^ere all erected on a set of wall plates (20 ft.) and the lagging and dry packing were completed the work of taking out the bench, which had been partly drilled as the timber sets were erected, was resumed. The face of the bench, which had been left about 4 ft. from the end of the pre- vious set of wall plates, was brought forward slowly by placing 10 X 10 in. plumb posts which extended below subgrade under the wall plates. These posts were generally spaced the same as the timber sets above and directly under them. When the face of the bench had been brought to within 3 or 4 ft. of the forward end of the wall plate, the process of widening out and timbering another 20 ft. length of heading was begun. In some places the rock, though needing permanent support, was such that the work of taking out the bench and widening the heading was carried on simultaneously without increasing the danger; but the greater portion of the work, when strutting was required, was done as has been described. TUNNELS THROUGH HARD ROCK 139 Hauling. — The excavated material was loaded at the foot of the bench in dump cars which were run by mule power to the portal or the shaft according to location, on 36 in. gauge-service tracks. Inclines at 159th Street were graded from the portal at 158th Street to the street surface. The cars were formed at this portal into a train and were taken up the incHne to the dump at 162nd Street and the North River by construction locomotives. At the 168th Street and 181st Street shafts, the cars were hoisted to the surface in cages (elevators). In the former case, they were taken to the dump at 165th Street and the North River by mules and gravity; in the latter case, to various dumps by teams. At both shafts, stone crushers were located, therefore a great part of the material did not have to be hauled to the dumps or even taken to the surface as a great deal of stone was used in dry packing over the concrete arch. The material from the portal at Fort George was hauled by mules directly to the dump near by. Lining. — The entire tunnel was lined with concrete, consisting of a floor 4 ins. thick and vertical side walls 18 ins. thick and 25 ft. apart, which carried a semicircular arch 18 ins. thick except in the timbered portions where the thickness was in- creased to 21 ins. and to 24 and 27 ins. in some places. The springing line of the arch is 6 ft. 2 ins. above the concrete floor (5 ft. 6 ins. above the base of rail), hence the maximum clearance above the base of rail is 18 ft. The side walls and arch were built solid of rock to a height of 8 ft. above springing hne and the space above that point between the concrete and the rock was packed by hand with small stones. The concrete of the arch was laid on timber centers erected for that purpose. The heading and bench method of excavating rock tunnels is not always followed in the manner just described but is em- ployed with slight modifications. There is a large variety of modifications but only the two most commonly used in practical works are given here. The heading and bench method illus- trated in Fig. 66 was used, among others, on the Gallitsin 140 TUNNELING tunnel along the Pennsylvania R.R. at the summit of the Alleghenies near Altoona, Pa., and more recently in the tunnels constructed by the same company under Bergen Hill, N. J., for the entrance to New York City. The shape of the cross-section of these tunnels was semicircular arch on vertical side walls. The excavation was made in three consecutive cuts, viz., the heading marked 1 in the figure, the top bench 2, and the lower bench 3. A heading 7 ft. high and 10 ft. wide was attached near the crown of the arch and the rock was removed by means of a center cut and parallel side Fig. 66.- Diagram Showing holes, the number of holes depending upon HoiefTnThTHeadtg^and ^he cousisteucy of the rock. The part Bench of the Gaiiitsin Tun- ;^q^ 2 was excavatcd by drilling holes at nel. *^ ° each side to cUfferent depths and at dif- ferent inclinations in order to reach the Hne of the profile as well as the springing line of the proposed tunnel. The central part of the top bench was excavated by means of holes driven vertically from the floor of the heachng. The bottom bench No. 3, included between the spring- ing hne of the arch and subgrade, was removed by means of five ver- tical holes driven from the floor of the top bench. The three different working parts were kept nearly 10 ft. apart. Blasting was effected in reversed order to the figures marked in the diagram, viz., the bottom bench first and the heading last. Still another modification of the heading and bench method, commonly followed by American engineers, is the one shown in Fig. 67. This consists in dividing the tunnel section in three Fig. 67. — Diagram Showing a 'Modi- fication of the [Heading and Bench Method. TUNNELS THROUGH HARD ROCK 141 parts by horizontal lines. The resultant parts are first the heading excavated close to the roof, and as wide as the whole section of the tunnel; second, the top bench in the middle, and lastly the bottom bench excavated to the depth of the pro- posed tunnel floor. The excavation proceeds in the numerical order, beginning at the heading which was excavated, as usual, by means of a center cut and side holes to the full width of the proposed tunnel. First the top bench, then the bottom bench, are removed by means of vertical holes driven from the floor of the heading and the floor of the top bench, respectively. COMPARISON OF METHODS. The differences between the drift and heading methods of excavating tunnels through rock, consist chiefly in the excava- tions, strutting, and hauling. When the drift method is em- ployed an advanced gallery is opened along the floor of the tunnel before the upper part of the section is removed, and when the heading method is employed the upper part of the section is completely excavated before any part of the section below is excavated. When the drift method of driving is em- ployed polygonal strutting is usually used, and longitudinal strutting is employed with the heading method of driving. In the drift method the hauling is done by one system of tracks at the same level, while in the heading method two systems of tracks are employed at different levels. It is, perhaps, impossible to state without qualification which method is the better. European engineers who have been con- nected with both the Mont Cenis and St. Gothard tunnels, driven by the drift and heading methods respectively, had the oppor- tunity to practically observe the advantages and disadvantages of these two methods. Their conclusion was that the drift method was more convenient for tunnels driven through hard and compact rock, and that the heading method was better for tunnels of fissured and disintegrated rocks. To prove this opinion, experiments were made in one of the tunnels approach- 142 TUNNELING ing the great St. Gothard tunnel. On a short tunnel the exca- vation was made by the drift method from one portal, while at the other, the heading method was followed. Although the general rule was fully confirmed still the conditions at the portals were not identical. More conclusive experiments were made by Mr. Ira A. Shaler, the contractor for Section IV., of New York Rapid Transit Railway. He had the opportunity of driving two parallel tunnels under Murray Hill only 17 ft. apart. The eastern tunnel was driven by the drift method, the western one by the heading method. After the work had proceeded for a few months, Mr. Shaler stated that in his case the drift method was more convenient. He could spare drilling several holes at each advance, thus obtaining economy in time, labor and material without considering the advantage of a simpler trans- portation- of the debris. He promised to pubhsh his results for the benefit of the profession, but, unfortunately, lost his life in an accident in the tunnel before the completion of the work. An advantage that the drift method affords in long tunnels is, that the water, which is usually found in large quantities under high mountains, is easily collected in the drift and conveyed to the culvert, while in the heading method the water from the advance gallery, before being collected into the culvert built on the floor of the tunnel, must pass through all the workings. This may be a serious inconvenience when water is found in large quantities, as, for instance, was the case in the St. Gothard tunnel, where the stream amounted to 57 gallons per second. TUNNELS THROUGH SOFT GROUND 143 CHAPTER XIL EXCAVATING TUNNELS THROUGH SOFT GROUND ; GENERAL DISCUSSION ; THE BELGIAN METHOD. GENERAL DISCUSSION. It may be set down as a general truth that the excavation of tunnels through soft ground is the most difficult task which confronts the tunnel engineer. Under the general term of soft ground, however, a great variety of materials is included, be- ginning with stratified soft rock and the most stable sands and clays, and ending with laminated clay of the worst character. From this it is evident that certain kinds of soft-ground tunneling may be less difficult than the tunneling of rock, and that other kinds may present almost insurmountable dif- ficulties. Classing both the easy and the difficult materials together, however, the accuracy of the statement first made holds good in a general way. Whatever the opinion may be in regard to this point, however, there is no chance for dispute in the statement that the difficulty of tunneling the softer and more treacherous clays, peats, and sands is greater than that of tunneling firm soils and rock ; and if we describe the methods which are used successfully in tunneling very unstable materials, no difficulty need be experienced in modifying them to handle stable materials. Characteristics of Soft-Ground Tunneling. — The principal char- acteristics which distinguish soft-ground tunneling are, first, that the material is excavated without the use of explosives, and second, that the excavation has to be strutted practically 144 TUNNELING as fast as it is completed. In treacherous soils the excavation also presents other characteristic phenomena: The material forming the walls of the excavation tends to cave and slide. This tendency may develop immediately upon excavation, or it may be of slower growth, due to weathering and other nat- ural causes. In either case the roof of the excavations tends to fall, the sides tend to cave inward and squeeze together, and the bottom tends to bulge or swell upward. In materials of very unstable character these movements exert enormous pres- sures upon the timbering or strutting, and in especially bad cases may destroy and crush the strutting completely. Out- side the tunnel the surface of the ground above sinks for a con- siderable distance on each side of the line of the tunnel. Methods of Soft-Ground Tunneling. — There are a variety of methods of tunneling through soft ground. Some of tjiese, like the quicksand method and the shield method, differ in char- acter entirely, while in others, like the Belgian, German, Eng- lish, Austrian, and Italian methods, the difference consists simply in the different order in which the drifts and headings are driven, in the difference in the number and size of these advance galleries, and in the different forms of strutting frame- work employed. In this book the shield method is considered individually ; but the description of the Belgian, German, Eng- lish, Austrian, Italian, and quicksand methods are grouped together in this and the three succeeding chapters to permit of easy comparison. THE BELGIAN METHOD OF TUNNELING THROUGH SOFT GROUND. The Belgian method of tunneling through soft ground was first employed in 1828 in excavating the Charleroy tunnel of the Brussels-Charleroy Canal in Belgium, and it takes its name from the country in which it originated. The distinctive char- acteristic of the method is the construction of the roof arcb TUNNELS THROUGH SOFT GROUND 145 before the side walls and invert are built. The excavation, therefore, begins with the driving of a top center heading which is enlarged until the whole of the section above the springing lines of the arch is opened. Various modifications of the method have been developed, and some of the more important of these will be described farther on, but we shall begin its consideration here by describing first the original and usual mode of procedure. Excavation. — Fig. 68 is the excavation diagram of the Bel- gian method of tunneling. The excavation is begun by open- ing the center top heading No. 1, which is carried ahead a greater or less distance, depending upon the nature of the soil, and is immediately strutted. This heading is then deepened \ / 2 Z 2 \ I 5 4 5 4 3 4 Figs. 68 and 68A. — Diagrams Showing Sequence of Excavations in the Belgian Method. by excavating part No. 2, to a depth corresponding to the springing lines of the roof arch. The next step is to remove the two side sections No. 3, by attacking them at the two fronts and at the sides with four gangs of excavators. The regularity and efficiency of the mode of procedure described consist in adopting such dimensions for these several parts of the section that each will be excavated at the same rate of speed. When the upper part of the section has been excavated as described, the roof arch is built, with its feet supported by the unexca- vated earth below. This portion of the section is excavated by taking out first the central trench No. 4 to the depth of the bottom of the tunnel, and then by removing the two side parts No. 5. As these side parts No. 5 have to support the arch, 146 TUNNELING they have to be excavated in such a way as not to endanger it. At intervals along the central trench No. 4, transverse or side trenches about 2 ft. wide are excavated on both sides, and struts are inserted to support the masonry previously supported by the earth which has been removed. The next step is to widen these side trenches, and insert struts until all of the material in parts No. 5 is taken out. When the material penetrated is firm enough to permit, the plan of excavation illustrated by the diagram, Fig. 68A, is substi- tuted for the more typical one just described. The only differ- ence in the two methods consists in the plan of excavating the upper part of the profile, which in the second method consists in driving first the center top heading No. 1, and then in tak- ing out the remainder of the section above the springing hues of the arch in one operation, while in the first method it is done in two operations. The distance ahead of the masonry to which the various parts can be driven varies from 10 ft. to, in some cases, 100 ft., being very short in treacherous ground, and longer the more stable the material is. Strutting The longitudinal method of strutting, with the poling-boards running transversely of the tunnel, is always employed in the Belgian method of tunneling. In driving the first center top heading, pairs of vertical posts carrying a trans- verse cap-piece are erected at intervals. On these cap-pieces are carried two longitudinal bars, which in turn support the saddle planks. As fast as part No. 2, Fig. 68, is excavated, the vertical posts are replaced by the batter posts A and B, Fig. 69. The excavation of parts No. 3 is begun at the top, the poling-boards a and b being inserted as the work pro- gresses. To support the outer ends of these poling-boards, the longitudinals X and Y are inserted and supported by the batter posts O and D. In exactly the same way the poling-boards c and dy the longitudinals V and W, and the struts U and F, are placed in position ; and this procedure is repeated until the whole top part of the section is strutted, as shown by Fig. 63, TUNNELS THROUGH SOFT GROUND 147 the cross struts x^ y, 2, etc., being inserted to hold the radial struts firmly in position. The feet of the various radial props rest on the sill M N. These fan-like timber structures are set up at intervals of from 3 ft. to 6 ft., depending upon the quality of the soil penetrated. Fig. 69.— Sketch Showing Radial Roof Strutting, Belgian Method. Centers. — Either plank or trussed centers may be employed in laying the roof arch in the Belgian method, but the form of center commonly employed is a trussed center constructed as shown by Fig. 70. It may be said to consist of a king-post truss carried on top of a modified form of queen-post truss. The collar-beam and the tie-beam of the queen-post truss are spaced about 7 ft. apart, and the posts themselves are left far enough apart to allow the pas- sage of workmen and cars be- tween them. The tie beam of the king-post truss is clamped to the collar-beam of the queen- post truss by iron bands. On the rafters of the two trusses are fastened timbers, with their outer edges cut to the curve of the roof arch. These centers are set up midway between the fan-like strutting frames previ- ously described. They are usually built of square timbers. The tie beams are usually Q x ^ in., and the struts and posts 4 X 4 in. timbers. Tlie reason for giving the larger sectional Fig. 70. —Sketch Showing Roof Arch Center, Belgian Method. 148 TUNNELING dimensions to the tie beams, contrary to the usual practice in constructing centers, is that it has to serve as a sill for distrib- uting the pressure to the foundation of unexcavated soil which supports the center. Sometimes a sub-sill is used to support the center upon the soil ; and in any case wedges are employed to carry it, which can be removed for the purpose of striking the center. After the arch is completed, the centers may be removed immediately, or may be left in position until the masonry has thoroughly set. In either case the leading center over which the arch masonry terminates temporarily is left in position until the next section of the arch is built. Masonry. — The masonry of the roof arch, which is the first part built, is of necessity begun at the springing lines, and the first course rests on short lengths of heavy planks. These planks, besides giving an even surface upon which to begin the masonry, are essential in furnishing a bearing to the struts inserted to support the arch while the earth below them, part No. 5, Fig. 68, is being excavated. As the arch masonry progresses from the springing lines upward, the radial posts of the strutting are removed, and replaced by short struts rest- ing on the lagging of the centers, which support the crown bars or longitudinals until the masonry is in place, when they and the poling-boards are removed, and the space between the arch masonry and walls of the excavation is filled with stone or well-rammed earth. Considering now the side wall masonry, it will be re- membered that in excavating the part No. 5, Fig. 68, of the section, frequent side trenches were excavated, and struts inserted to take the weight of the masonry. These struts are inserted on a batter, with their feet near the center of the tunnel floor, so that the side wall masonry may be carried up behind them to a height as near as possible to the springing lines of the arch. When this is done the struts are removed, and the space remaining between the top of the partly fin- ished side wall and the arch is filled in. This leaves the arch TUNNELS THROUGH SOFT GROUND U9 supported by alternate lengths or pillars of unexcavated earth and completed side wall. The next step is to remove the remaining sections of earth between the sections of side wall, and fill in the space with masonry. Fig. 71 is a cross-section, showing the masonry completed for one-half and the inclined props in position for the other half; and Fig. 72 is a longitudinal section showing the pillars of unexcavated earth be- tween the consecutive sets of in- clined struts and several other details of the lining, strutting, and excavating work. The invert masonry is built after the side walls are completed. This is regarded as a defect of this method of tunneling, since the lateral pressures may squeeze the side walls together and dis- tort the arch before the invert is in place to brace them apart. Fig. 71. — Sketcli Showing Method of Underpining Koof Arch with the Side Wall Masonry, To prevent as much as possible the distortion of the arch after the centers are removed, it is considered good practice to shore the masonry with hori- zontal beams having their ends abutting against plank, as shown by Fig. 71. These hori- zontal beams should be placed at close intervals, and be supported at intermediate points by vertical posts, as shown Fig. 72.— Longitudinal Section Showing Construction by the Belgian Method. 150 TUNNELING by the illustration. Since the roof arch rests for some time supported directly by the unexcavated earth below, settle- ment is liable, particularly in working through soft ground. This fact may not be very important so long as the settle- ment is uniform, and is not enough to encroach on the space necessary for the safe passage of tra^'el. To prevent the latter possibility the centers are placed from 9 ins. to 15 ins. higher than their true positions, depending upon the nature of the soil, so that considerable settlement is possible without any danger of the necessary cross-section being infringed upon. In conclusion it may be noted that the lining may be con- structed in a series of consecutive rings, or as a single cylin- drical mass. Hauling. — Since in this method of tunneling the upper part of the section is excavated and lined before the excavation of the lower part is begun, the upper portion is always more ad- vanced than the lower. To carry away the earth excavated at the front, therefore, an elevation has to be surmounted; and this is usually done by constructing an inclined plane rising from the floor of the tunnel to the floor of the heading, as shown by Fig. 66. This inclined plane has, of course, to be moved ahead as the work advances, and to permit of this movement with as little interruption of the other work as possible, two planes are employed. One is erected at the right-hand side of the section, and serves to carry the traffic while the left-hand side of the lower section is being removed some distance ahead and the other plane is being erected. The inclination given to these planes depends upon the size of the loads to be hauled, but they should always have as shght a grade as practicable. Narrow- gauge tracks are laid on these planes and along the floor of the upper part of the section passing through the center opening mentioned before as being left in the centers and strutting. In excavating the top center heading there is, of course, an- other rise to its floor from the floor of the upper part of the section. Where, as is usually the case in soft soils, this top TUNNELS THliOUGH SOFT GROUND 151 heading is not driven very far in advance, the earth from tiie front is usually conveyed to the rear in wheelbarrows, and dumped into the cars standing on the tracks below. In firm soils, where the heading is driven too far in advance to make this method of conveyance adequate, tracks are also laid on the floor of the heading, and an inclined plane is built connect- ing it with the tracks on the next level below. In place of these inclined planes, and also in place of those between the floor of the tunnel and the level above, some form of hoisting device is sometimes employed to lift the cars from one level to the other. There are some advantages to this method in point of economy, but the hoisting-machines are not easily worked in the darkness, and accidents are likely to occur. In the advanced top heading and in the upper part of the section narrow-gauge tracks are necessarily employed, and these may be continued along the floor of the finished section, or the permanent broad-gauge railway tracks may be laid as fast as the full section is completed. In the former case the perma- nent tracks are not laid until the entire tunnel is practically completed ; and in the latter case, unless a third rail is laid, the loads have to be transshipped from the broad- to the narrow- gauge tracks or vice versa. It is the more general practice to use a third rail rather than to transship every load. Modifications. — Considering the extent to which the Belgian method of tunneling has been employed, it is not surprising that many modifications of the standard mode of procedure have been developed. The modification which differs most from the standard form is, perhaps, that adopted in excavating the Roosebeck tunnel in Germany. This method preserves the principal characteristic of the Belgian method, which is the construction of the upper part of the section first ; but instead of building the side walls from the bottom upward, they are built in small sections from the top downward. The excavation begins by driving the center top heading No. 1, Fig. 73, whose floor is at the level of the springing lines of the roof arch, and 152 TUNNELING then the two side parts No. 2 are excavated, opening up the entire upper portion of the section in which the roof arch is built, as in the regular Belgian method. The next step is to excavate part No. 3, shoring up the arch at frequent intervals. Between these sets of shoring the side walls are built, resting on planks on the floor of part No. 3, and then the sets of shores are removed and re- placed by masonry. Next part No. 4 is excavated, shored, and filled with masonry as was part No. 3. In exactly the same way parts 5, 6, 7, and 8 are constructed in the order numbered. To prevent the distortion of the arch during the side-wall braced by horizontal struts, as radicated / 2 \ Z \ 4. 3 6 5 8 7 Fig. 73. —Diagram Show- ing Sequence of Excava- tion in Modified Belgian Method. construction it is above in Fig. 71. Advantages. — The advantages of the Belgian method of tunneling may be summarized as follows : (1) The excavation progresses simultaneously at several points without the differ- ent gangs of excavators interfering with each other, thus secur- ing rapidity and efficiency of work ; (2) the excavation is done by driving a number of drifts or parts of small section, which are immediately strutted, thus causing the minimum disturb- ance of the surrounding material ; (3) the roof of the tunnel, which is the part of the lining exposed to the greatest pressures, is built first. Disadvantages. — The disadvantages of the Belgian method of tunneling may be summarized as follows : (1) The roof arch which rests at first on compressible soil is liable to sink ; (2) before the invert is built there is danger of the arch and side walls being distorted or sliding under the lateral pressures ; (3) the masonry of the side walls has to be underpinned to the arch masonry. Accidents and Repairs.— One of the most frequent accidents in the Belgian method of tunneling is the sinking of the roof TUNNELS THROUGH SOFT GliOUND 153 arch owing to its unstable foundation on the unexcavated soil of the lower portion of the section. The amount of settlement may vary from a few inches in firm soil to over 2 ft. in loose soils. To counteract the effect of this settlement it is the gene- ral practice to build the arch some inches higher than its nor- mal position. When the settlement is great enough to infringe seriously upon the tunnel section, repairs have to be made ; and the only way of accomphshing them is to demolish the arch and rebuild it from the side walls. It is usually considered best not to demohsh the arch until the invert has been placed, so that no further disturbance is hkely to occur once the lining is completed anew. The rotation of the arch about its keystone, or the opening of the arch at the crown, by the squeezing inward of the haunches by the lateral pressures, is another characteristic accident. Fig. 74 shows the nature of the distortion produced ; the segments of the arch move toward each other by revolving on the intradosal edges of the keystone, which are broken away and crushed together with the operation, while the extradosal \ h 3 y] 8 \ ■ 7 / f 2 ^ 3 6 ! 6 Figs. 93 and 94. — Diagrams Showing Sequence of Excavation in Austrian Method of Tunneling. Strutting. — Each part of the section is strutted as fast as it is excavated. The center bottom drift first excavated is strutted by laying a transverse sill across the floor, raising two side posts from it, and capping them with a transverse timber having its ends projecting beyond the side posts and halved as shown by Fig. 95. The top center heading No. 2, which is next excavated, is strutted by means of two side posts resting on blocking and carrying a transverse cap as also shown by Fig. 95. Sometimes the side posts in the heading strutting- frames are also carried on a transverse sill as are those of the bottom drift. This construction is usually adopted in loose soils. When the sill is employed, the middle part. No. 3, is strutted by inserting side posts between the bottom of the top sill and the cap of the frame in the drift below. When, how- ever, the posts of the top heading frame f^.re carried on blocking, it is the practice to replace them with long posts rising from the cap of the bottom drift frame to the cap of the top heading frame. Further, when the intermediate sill is employed at the bottom level of the top heading it projects beyond the side posts and has its ends halved. After the completion of the center trench strutting the next 178 TUNNELING task is to strut parts Nos. 4 and 5. This is done by continu- ing the upper sill by means of a timber having one end halved to join with the projecting end of the sill in position. This extension timber is shown at a, Fig. 96. The next operation is to place the timber h, having one end resting on the cap-piece of the top heading frame and the other beveled and resting on the top of the sill a near the end. The timber h is laid tangent to the curve of the roof arch, and to support it against flexure the strut c is inserted as shown. To sup- port the thrust of this strut the additional post d is in- serted and the original bottom heading frame is reinforced as shown. The next step is to insert the strut e, and when this and the previous construction are duplicated on the oppo- site side of the tunnel section we have the strutting of the parts Nos. 1 to 5, inclusive; complete. Part No. 6 is then removed and Figs. 95 to 97. — Sketches Showing Construc- tion of Strutting, Austrian Method. THE FULL SECTION METHOD 179 strutted by extending the bottom drift cap-piece by a timber similar to timber a above, and then by inserting a side strut between the outer ends of these two timbers, as indicated by Fig. 97. As the final parts, Nos. 7 and 8, are removed, the in- clined prop a, Fig. 97, is inserted as shown. When the soil is loose some of the members of the framework are doubled and additional bracing is introduced as shown by Fig. 97. The frames just described are placed at intervals of about 4 ft. along the excavation, and are braced apart by horizontal struts. Some of the longitudi- nal bearing beams, as at h, Fig. 90, also extend through two or three frames, and help to tie them together. Finally, the longitudinal poling-boards ex- tending from one frame to the next along the walls of the ex- cavation serve to connect them together. The short transverse beam c. Fig. 90, located just above the floor of the invert, serves to carry the planking upon which the train car tracks are laid. Besides the timber strutting peculiar to the Aus- trian method, the Rziha iron strutting described in a pre- vious chapter is frequently used in tunneling by the Austrian process. Centers. — The two forms of centers used in the English method of tunneling are also used in the Austrian method. One of the methods of supporting these centers is shown by Fig. 98. The tie-beam of the center rests on longitudinal tim- bers carried by the strutting frames and intermediate props. In single-track tunnels it is the frequent practice also to carry the ends of the tie-beams in recesses left in the side wall Fig. 98. — Sketch Showing Manner of Constructing the Lining Masonry, Austrian Method. 180 TUNNELING masonry, with intermediate props inserted to prevent flexure at the center. When the Rziha iron strutting is employed, it also serves for the centering upon which the arch mas.onry is built. Masonry. — In the Austrian system of tunneling, the lining is built from the foundations of the side walls upward to the crown of the roof arch in lengths in consecutive rings equal to the lengths of the consecutive openings of the full section, or from 12 ft. to 20 ft. long. Except in infrequent cases in very loose materials the invert is the last part of the masonry to be built, since to build it first requires the removal of the strutting which cannot easily or safely be accomplished until the side walls and roof arch are completed. As the side wall foundations are built, however, their interior faces are left inclined, as shown by Figs. -97 and 98, ready for the insertion of the invert, and are meanwhile kept from sliding inward by the insertion of blocking between them and the bottom of the strutting. Fig. 98 shows the nature of this blocking, and also the manner in which the side wall and roof arch masonry is carried upward. Finally when the roof arch is keyed and the centers are struck, the strutting is taken down and the invert is built. Advantages and Disadvantages. — The principal advantages claimed for the Austrian method of tunneling are: (1) The excavation being conducted by driving a large number of con- secutive small galleries, which are immediately strutted, there is little disturbance of the surrounding material; (2) the polyg- onal type of strutting adopted is easily erected and of great strength against symmetrical pressures; (3) the masonry, being built from the foundations up, is a single homogeneous structure, and is thus better able to withstand dangerous pressures; (4) the excavation is so conducted that the masons and excavators do not interfere, and both can work at the same time. The disadvantages which the method possesses are: (1) The strutting while very strong under symmetrical pressures, either vertical or lateral, is distorted easily by unsymmetrical vertical or lateral THE FULL SECTION METHOD 181 pressures, and by pressure in the direction of the axis of the tunnel; (2) the construction of the invert last exposes the side walls to the danger of being squeezed together, causing a rotation of the arch of the nature discussed in describing the Belgian method of tunneling. 182 TUNNELING CHAPTER XV. SPECIAL TREACHEROUS GROUND METHOD; ITALIAN METHOD; QUICKSAND TUN- NELING; PILOT METHOD. ITALIAN METHOD. The Italian method of tunneling was first employed in con- structing the Cristina tunnel on the Foggia & Benevento R.R. in Italy. ' This tunnel penetrated a laminated clay of the most treacherous character, and after various other soft-ground methods of tunneling had been tried and had failed, Mr. Procke, the engineer, devised and used successfully the method which is now known as the Italian or Cristina method. The Itahan method is essentially a treacherous soil method. It consists in excavating the bottom half of the section by means of several successive drifts, and building the invert and side walls ; the space is then refilled and the upper half of the section is exca- vated, and the remainder of the side walls and the roof arch are built ; finally, the earth filling in the lower half of the section is re-excavated and the tunnel completed. The method is an expensive one, but it has proved remarkably successful in treacherous soils such as those of the Apennine Mountains, in which some of the most notable Italian tunnels are located. It is, moreover, a single-track tunnel method, since any soil which is so treacherous as to warrant its use is too treacherous to permit an opening to be excavated of sufficient size for a double- track railway, except by the use of shields. Excavation. — The plan of excavation in the Italian method is shown by the diagram Fig. 99. Work is begun by driving SPECIAL TREACHEROUS GROUND METHOD 183 Fig. 99, —Diagram Show- iug Sequence of Excava- tion in Italian Method of Tunneling. the center bottom heading No. 1, and this is widened by taking out parts No. 2. Finally part No. 3 is removed, and the lower half of the section is open. As soon as the invert and side wall masonry has been built in this excavation, parts No. 2 are filled in again with earth. The exca- vation of the center top heading No. 4 is then begun, and is enlarged by removing the earth of part No. 5. The faces of this last part are inclined so as to reduce their tendency to slide, and to permit of a greater number of radial struts to be placed. Next, parts No. 6 are excavated, and when this is done the entire section, except for the thin strip No. 7, has been opened. At the ends of part No. 7 nar- row trenches are sunk to reach the tops of the side walls already constructed in the lower half of the section. The masonry is then completed for the upper half of the section, and part No. 7 and the filling in parts No. 2 are removed. The various drifts and headings and ^^ — ^^ the parts excavated to enlarge them /^ are seldom excavated more than from 6 ft. to 10 ft. ahead of the lining. / Strutting. — The bottom center drift, which is first driven, is strutted by means of frames consisting of side posts resting on floor blocks and car- rying a cap-piece. Poling-boards are placed around the walls, stretching from one frame to the next. As soon as the invert is sufficiently completed to permit it, the side posts of the strutting frames are replaced by short struts resting on the invert masonry as shown by Fig. 100. To permit the old side posts to be removed and the new shorter ones to be inserted, the cap-piece of the frame is temporarily supported Fig. 100.— Sketch Showing Strut- ting for Lower Part of Section. 184 TUNNELING by inclined props arranged as shown by Fig. 103. When parts No. 2 are excavated the roof is strutted by inserting the trans- verse caps a, Fig. 100, the outer ends of which are carried by the system of struts 6, c^ d, and e. The longitudinal poling-boards supporting the ceiling and walls are held in place by the cap a and the side timber e. To stiffen the frames longitudinally of the tunnel, horizontal longitudinal struts are inserted between them. The excavation of the upper half of the tunnel section is strutted as in the Belgian method, with radial struts carrying longitudinal roof bars and transverse poling-boards. On ac- count of the enormous pressures developed by the treacherous soils in which only is the Italian method employed, the radial strutting frames and crown bars must be of great strength, Figs. 101 and lOlA. — Sketches Showing Construction of Centers, Italian Method. while the successive frames must be placed at frequent intervals, usually not more than 3 ft. After the masonry side walls have been built in the lower part of the excavation, longitudinal planks are laid against the side posts of the center bottom drift frames, to form an enclosure for the filling-in of parts No. 2. The object of this filling is principally to prevent the squeezing-in of the side walls. Centers. — Owing to the great pressures to be resisted in the treacherous soils in which the Italian method is used, the con- struction of the centers has to be very strong and rigid. Figs. 101 and 10 lA show two common types of center construction used with this method. The construction shown in Fig. 101 is a strong one where only pressures normal to the axis of the tunnel have to be withstood, but it is likely to twist under SPECIAL TKEACHEROUS GROUND METHOD 185 pressures parallel to the axis of the tunnel. In the construc- tion shown by Fig. lOlA, special provision is made to resist pressures normal to the plane of the center or twisting pres- sures, by the strength of the transverse bracing extending hori- zontally across the center. Masonry. — The construction of the masonry lining begins with the invert, as indicated by Fig. 100, and is carried up to the roof of parts No. 2, as already indicated, and is then discon- tinued until the upper parts Nos. 4, 5, and 6 are excavated. The next step is to sink side trenches at the ends of part No. 7, which reach to the top of the completed side walls. This operation leaves the way clear to finish the side walls and to construct the roof arch in the ordinary manner of such work in tunneling. Since this method of tunneling is used only in very soft ground which yields under load, the usual practice is to construct the in- vert and side walls on a continuous Fig. 102. -Sketch Showing Invert foundation COUrSC of COUCretC aS iu- and Foundation Masonry, Italian dicatcd by Fis;. 102. The liuinpf is Method. n u -1^ • • • A usually built m successive rings, and the usual precautions are taken with respect to filling in the voids behind the lining. The thickness of the lining is based upon the figures for laminated clay of the third variety given in Table II. Hauling The system of hauling adopted with this method of tunneling is very simple, since the excavation of the various parts is driven only from 6 ft. to 10 ft. ahead, and the work pro- gresses slowly to allow for the construction of the heavy strutting required. To take away the material from the center bottom drift, narrow-gauge tracks carried by cross-beams between the side posts above the floor line are employed. This same narrow-gauge line is employed to take away a portion of parts No. 2, the remaining portion being left and used for the refill- ing after the bottom portion of the lining has been built, as 186 TUNNELING previously described. The upper half of the section being ex- cavated, as in the Belgian method, the system of hauling with inclined planes to the tunnel floor below, which is a character- istic of that method, may be employed. It is the more usual Fig. 103. — Sketch ShoAying Longitudinal Section of a Tunnel under Construction, Italian Method. practice, however, since the excavation is carried so little a dis- tance ahead and progresses so slowly, to handle the spoil from the upper part of the section by wheelbarrows which dump it into the cars running on the tunnel floor below. Hand labor is also used to raise the construction materials used in building the upper sec- tion. The tracks on the tunnel floor, besides extending to the front of the ad- vanced bottom center ^drift, have right and left switches to be employed in removing the refilling in parts No. 2, the spoil from the upper part of the section, and the material of part No. 7. Fig. 103 is a longi- tudinal section showing the plan of exca- vation and strutting adopted wdth the Italian method. Modifications. — It often happens that the filling placed be- tween the side walls and the planking, which is practically the space comprised by parts No. 2, is not sufficient to resist the inward pressure of the walls, and they tip inward. In these cases a common expedient is to substitute for the earth filling Fig. 104.— Sketch Showing Sequence of Excavation, Stazza TunneL SPECIAL TREACHEROUS GROUND METHOD 187 a temporary masonry arch sprung between the side walls with its feet near the bottom of the walls, and its crown, just below the level of their tops, as shown by Fig. 107. This construction was employed in the Stazza tunnel in Italy. In this tunnel the excavation was begun by driving the center drift, No. 1, Fig. 104, and immedi- ately strutting it as shown by Fig. 105. The other parts, Nos. 2 and 3, completing the lower portion of the section, were then taken out and strutted. While part No. 2 Fig. 105. — Sketch Showing was being cxcavatcd at the bottom, and Metlied of strutting First .-i , j. r l^ • j. i •^l -i Drift, Stazza Tunnel. ^hc ccutcr part of the luvcrt built, the longitudinal crown bars carrying the roof of the excavation were carried temporarily by the inclined props shown by Fig. 106. After completing the invert and the side walls to a height of 2 or 3 ft., a thick masonry arch was sprung between the side walls, as shown in transverse section by Fig. 107, and in longitudinal section by Fig. 106. This arch braced the side walls against tipping inward, and Figs. 106 and 107. — Sketches Showing Temporary Strutting Arch Construction, Stazza Tunnel. carried short struts to support the crown bars. The haunches of the arch were also filled in with rammed earth. The upper half of the section was excavated, strutted, and lined as in the standard Italian method previously described. When the lining was completed, the arch inserted between the side walls was broken down and removed. 188 TUNNELING Advantages and Disadvantages, — The great advantage claimed for the Italian method of tunneling is that it is built in two separate parts, each of which is separately excavated, strutted, and lined, and thus can be employed successfully in very treacherous soils. Its chief disadvantage is its excessive cost, which limits its use to tunnels through treacherous soils where other methods of timbering cannot be used. QUICKSAND TUNNELING. When an underground stream of water passes with force through a bed of sand it produces the phenomenon known as quicksand. This phenomenon is due to the fineness of the particles of sand and to the force of the water, and its activity is directly proportional to them. When sand is confined it furnishes a good foundation bed, since it is practically incom- pressible. To work successfully in quicksand, therefore, it is necessary to drain it and to confine the particles of sand so that they cannot flow away with the water. This observation suggests the mode of procedure adopted in excavating tunnels through quicksand, which is to drain the tunnel section by opening a gallery at its bottom to collect and carry away the water, and to prevent the movement or flowing of the sand by strutting the sides of the excavation with a tight planking. The sand having to be drained and confined as described, the ordinary methods of soft-ground tunneling must be employed, with the following modifications : (1) The first work to be performed is to open a bottom gallery to drain the tunnel. This gallery should be lined with boards laid close and braced sufficiently by interior frames to prevent distortion of the lining. The interstices or seams be- tween the lining boards should be packed with straw so as to permit the percolation of water and yet prevent the movement of the sand. (2) As fast as the excavation progresses its walls should SPECIAL TREACHEROUS GROUND METHOD 189 be strutted by planks laid close, and held in position by interior framework; the seams between the plank should be packed with straw. (3) The masonry lining should be built in successive rings, and the work so arranged that the water seeping in at the sides and roof is collected and removed from the tunnel immediately. Excavation. — The best and most commonly employed meth( d of driving tunnels through quicksand is a modificauon of the Belgian method. At first sight it may appear a hazardous work to support the roof arch, as is the characteristic of this method, on the unexcavated soil below, when this soil is quicksand, but if the sand is well confined and drained the risk is really not very great. Next to the Belgian method the German method is perhaps the best for tunneling quicksand. In these compari- sons the shield system of tunneling is for the time being left out of consideration. This method will be described in suc- ceeding chapters. Whenever any of the systems of tunneling previously described are employed, the first task is always to open a drainage gallery at the bottom of the section. Assuming the Belgian method is to be the one adopted, the first work is to drive a center bottom drift, the floor of which is at the level of the extrados of the invert. This drift is im- mediately strutted by successive transverse frames made up of a sill, side posts, and a cap which support a close plank strut- ting or lining, with its joints packed with straw. Between the side posts of each cross-frame, at about the height of the intrados of the invert, a cross-beam is placed ; and on these cross- beams a plank flooring is laid, w^hich divides the drift horizon- tally into two sections, as shown by Fig. 108 ; the lower section forming a covered drain for the seepage water, and the upper providing a passageway for workmen and cars. The bottom drift is driven as far ahead as practicable, in order to drain the sand for as great a distance in advance of the work as possible. After the construction of the bottom drainage drift the excava- tion proper is begun, as it ordinarily is in the Belgian method 190 TUNNELING Fig, 108,— Sketch Showing Preliminary Drainage Gal- leries, Quicksand Method. by driving a top center heading, as shown by Fig. 108. This heading is deepened and widened after the manner usual to the Belgian method, until the top of the sec- tion is open down to the springing lines of the roof arch. To collect the seepage water from the center top heading it is provided with a center bottom drain con- structed like the drain in the bottom drift, as shown by Fig. 108. When the top heading is deepened to the level of the springing lines of the roof arch, its bottom drain is reconstructed at the new level, and serves to drain the full top section opened for the construction of the roof arch. This top drain is usually con- structed to empty into the drain in the bottom drift. Strutting. — The method of strutting the bottom drift has already been described. For the remainder of the excavation the regular Belgian method of radial roof strutting-frames is employed, as shown by Fig. 109. Contrary to what might be expected, the number of radial struts required is not usually greater than would be used in many other soils besides quicksand. Single-track railway tun- nels have been constructed through quicksand in several instances where the number of radial props required on each side of the center did not exceed four or five. It is necessary, however, to place the poling-boards very close together, and to pack the joints between them to prevent the inflow of the fine sand. In strutting the lower part of the section it is also necessary to support the sides with tight planking. This is usually held in place by longitudinal Fig. 109.— Sketch Showing Con- struction of Hoof Strutting Quicksand Method, SPECIAL TREACHEKOUS GROUND METHOD 191 Fig. 1 10. — Sketch Showing Construc- tion of Masonry Lining, Quicksand Method. bars braced by short struts against the inclined props employed to carry the roof arch when the material on which they origi- nally rested is removed. This side strutting is shown at the right hand of Fig. 110. Masonry. — As soon as the upper part of the section has been opened the roof arch is built with its feet resting on planks laid on the unex- cavated material below. This arch is built exactly as in the regular Belgian method previously de- scribed, using the same forms of centers and the same methods throughout, except that the poling- boards of the strutting are usually left remaining above the arch masonry. To prevent the possibility of water percolating through the arch masonry, many engineers also advise the plastering of the extrados of the arch with a layer of cement mortar. This plastering is designed to lead the water along the haunches of the arch and down behind the side walls. In constructing the masonry below the roof arch the invert is built first, contrary to the regular Belgian method, and the side walls are carried up on each side from the invert ma- sonry. Seepage holes are left in the invert masonry, and also in the side walls just above the intrados of the invert. At the center of the invert a culvert or drain is constructed, as shown by Fig. 110; inside the invert masonry. This culvert is com- monly made with an elliptical section with its major axis hori- zontal, and having openings at frequent intervals at its top. The thickness of the lining masonry required in quicksand is shown by Table II. Removing the Seepage Water. — After the tunnel is completed the water which seeps in through the weep-holes left in the ma- sonry passes out of the tunnel, following the direction of the 192 TUNNELING descending grades. During construction, however, special means will have to be provided for removing the water from the excavation, their character depending upon the method of excavation and upon the grades of the tunnel bottom. When the excavation is carried on from the entrances only, unless the tunnel has a descendmg grade from the center toward each end, the tunnel floor in one heading will be below the level of the en- trance, or, in other words, the descending grade will be toward the point where Avork is going on, while at the opposite entrance the grade will be descending from the work. In the latter case the removal of the seepage water is easily accomphshed by means of a drainage channel along the bottom of the excavation. In the former case the water which drains toward the front is collected in a sump, and if there is not too great a difference in level between this sump and the entrance, a siphon may be used to remove it. Where the siphon cannot be used, pumps are installed to remove the water. When the tunnel is excavated by shafts the condition of one high and one low front, as com- pared with the level at the shaft, is had at each shaft. Gene- rally, therefore, a sump is constructed at the bottom of the shaft; the culvert from the high front drains directly to the shaft sump, while the water from the low-front sump is either siphoned or pumped to the shaft sump. From the shaft sump the water is forced up the shaft to the surface by pumps. THE PILOT METHOD. The pilot system of tunneling has been successfully em- ployed in constructing soft-ground sewer tunnels in America by the firm of Anderson & Barr, which controls the patents. The most important work on which the system has been em- ployed is the m^ain relief sewer tunnel built in Brooklyn, N.Y., in 1892. This work comprised 800 ft. of circular tunnel 15 ft. in diameter, 4400 ft. 14 ft. in diameter, 3200 ft. 12 ft. in diameter, and 1000 ft. 10 ft. in diameter, or 9400 ft. of tunnel SPECIAL TEEACHEROUS GROUND METHOD 193 altogether. The method of construction by the pilot system is as follows : Shafts large enough for the proper conveyance of materials from and into the tunnel are sunk at such places on the line of work as are most convenient for the purpose. From these shafts a small tunnel, technically a pilot, about 6 ft. in diameter, composed of rolled boiler iron plates riveted to light angle irons on four sides, perforated for bolts, and bent to the required radius of the pilot, is built into the central part of the excavation on the axis of the tunnel. This pilot is generally kept about 30 ft. in advance of the completed excavation, as shown by Fig. 111. The material around the exterior of the pilot is then excavated, using the pilot as a support for braces which radiate from it and Bracing." ' Arch ConstrOction. Fig. 111. — Sketch Showing Pilot Method of Tunneling. secure in position the plates of the outside shell which holds the sand, gravel, or other material in place until the concentric rings of brick masonry are built. Ribs of T-iron bent to the radius of the interior of the brick work, and supported by the braces radiating from the pilot, are used as centering supports for the masonry. On these ribs narrow lagging-boards are laid as the construction of the arch proceeds, the braces holding the shell plates and the superincumbent mass being removed as the masonry progresses. The key bricks of the arches are placed in position on ingeniously contrived key-boards, about 12 ins. in width, which are fitted into rabbeted lagging-boards one after another as the key bricks are laid in place. After the masonry has been in place at least twenty-four hours, allowing the cement 194 TUNNELING mortar time to set, the braces, ribs, and lagging which support it are removed. In the meantime the excavation, bracing, pilot, and exterior shell have been carried forward, preparing the way for more masonry. The top plates of the shell are first placed in position, the material being excavated in advance and sup- ported by light poling-boards ; then the side-plates are butted to the top and the adjoining side-plates. In the pilot the plates are united continuously around the perimeter of the circle, while in the exterior shell the plates are used for about one- third of the perimeter on top, unless treacherous material is encountered, when the plates are continued down to the spring- ing lines of the arch. This iron lining is left in place. The bottom is excavated so as to conform to the exterior hues of the masonry. The excavation follows so closely to the outer lines of the normal section of the tunnel that very little loss occurs, even in bad material ; and there is no loss where suffi- cient bond exists in the material to hold it in place until the poling-boards are in position. In the Brooklyn sewer tunnel work, previously mentioned, the pilot was built of steel plates | in. thick, 12 ins. wide, and 37^ ins. long, rolled to a radius of 3 ft. Steel angles 4x4^ ins. were riveted along all four sides of each plate, and the plates were bolted together by |-in. machine-bolts. The plates weighed 136 lbs. each, and six of them were required to make one com- plete ring 6 ft. in diameter. In bolting them together, iron shims were placed between the horizontal joints to form a footing for the wooden braces for the shell, which radiate from the pilot. The shell plates of the 15-ft. section of the tunnel were of No. 10 steel 12 ins. wide and 37 ins. long, with steel angles 2^ x 2i^ x f ins., riveted around the edges the same as for the pilot, and put together with |-in. bolts. These plates weighed 61 lbs. each, and eighteen of them were required to make one complete ring 15 ft. in diameter. The plates for the 12-ft. section were No. 12 steel 12 ins. wide with 2x 2 x i-in. angles. Seventeen plates were required to make a complete ring. OPEN-CUT TUNNELING METHODS 195 CHAPTER XVI. OPEN-CUT TUNNELING METHODS; TUNNELS UNDER CITY STREETS; BOSTON SUBWAY AND NE^V YORK RAPID TRANSIT. OPEN-CUT TUNNELING. When a tunnel or rapid-transit subway has to be constructed at a small depth below the surface, the excavation is generally performed more economically by making an open cut than by subterranean tunneling proper. The necessary condition of small depth which makes open-cut tunneling desirable is most generally found in constructing rapid-transit subways or tun- nels under city streets. This fact introduces the chief difficul- ties encountered in such work, since the surface traffic makes it necessary to obstruct the streets as little as possible, and has led to the development of the several special methods commonly employed in performing it. Subways are usually constructed under and along important streets where electric cars are running. The engineers have taken advantage of the presence of these hnes to facilitate the construction of subways. In New York, for instance, the tracks of the electric Hnes were supported by cast-iron yokes 4 or 5 ft. apart and were surrounded by concrete, leaving only a large hollow space in the middle for the wires and trolleys. The rails from 40 to 60 ft. long formed almost a soHd concrete structure for their entire length. The tracks and the street surface were supported by horizontal beams inserted underneath the tracks. These were the caps of bents constructed underground whose rafters were finally resting on the subgrade of the proposed subway. 196 TUNNELING The various methods for constructing the subways may be classified as follows: (1) The single wide trench method; (2) the single narrow longitudinal trench method; (3) the parallel longi- tudinal trench method; (4) the shce method. Single Longitudinal Trench. — The simplest manner by which to construct open-cut tunnels is to open a single cut or trench the full width of the tunnel masonry. This trench is strutted by means of side sheetings of vertical planks, held in place by transverse braces extending across the trench and abutting against longitudinal timbers laid against the sheeting plank. The lining is built in this trench, and is then filled around and above with well-rammed earth, after which the surface of the ground is restored. An especial merit of the single longitudinal trench method of open-cut tunneling is that it permits the construction of the lining in a single piece from the bottom up, thus enabhng better workmanship and stronger construction than when the separate parts are built at different times. The great objection to the method w^hen it is used for building sub- ways under city streets is, that it occupies so much room that the street usually has to be closed to regular traffic. For this reason the single longitudinal trench method is seldom employed, except in those portions of city subways which pass under public squares or parks where room is plenty. This method was followed in the construction of the New York subway, Section 2, along Elm St., a new street to be opened to traffic after the subway had been completed, and at other points where local conditions allowed it. A modification of this method was used in Contract Section 6, on upper Broadway. The street at this point is very wide, so by opening a trench as wide as the proposed four-track line of the subway there still remained room enough for ordinary traffic. The electric car tracks were supported by means of trusses 60 or 70 ft. long, which were laid in couples parallel to the tracks and which rested on firm soil. The soil under the car tracks was removed, beginning with transversal cuts to OPEN-CUT TUNNELING METHODS 19T receive the needles which were tied to the lower chord of the trusses by means of iron stirrups. After the excavation had reached the subgrade, posts were erected to support the needles thus forming bents upon which the tracks rested. The trusses were removed and advanced to another section of the tunnel, and, in the clear space left, the subway was built from founda- tion up. The Single Narrow Longitudinal Trench. — This method was used on Contract Section 5, of the New York subway in order to comply with the peculiar conditions of the traffic along 42nd St. On this street, on account of the New York Central Station, there is a constant heavy traffic, while pedestrians use the northern sidewalks almost exclusively. A single longitudinal trench was then opened along the south side, and from this trench all the work of excavation and construction was carried on. At first the steel structure of the subway was erected in the trench and then a small heading was driven and strutted under and across the surface-car tracks. Afterward heavy I-beams were inserted, which rested with one end on top of the steel bents and the other end blocked to the floor of the excavation. These I-beams were located 5 ft. apart and they supported the surface of the street by means of longitudi- nal planks. The soil was removed from the wide space underneath the I-beams and the subway was con- structed from the foundation up. When the structure had been com- pleted, the packing was placed be- tween the roof of the structure and the surface of the street, the I-beams withdrawn and the voids filled in. Parallel Longitudinal Trenches. — The parallel longitudinal trench method of open-cut tunneling consists in excavating two Fig. 112. — Diagram Showing Se- quence of Construction in Open- Cut Tunnels. 198 TUNNELING Fig. 113. — Sketch Showing Method of Timbering Open- Cut Tunnels, Double Parallel Trench Method. narrow parallel trenches for the side walls, leaving the center core to be removed after the side walls have been built. The diagram, Fig. 112, shows the sequence of operations in this method. The two ULLIliillJJJiJiJiliilimuillM trenches No. 1 are first excavated a little wider than the side wall masonry, and strutted as show^n by Fig. 113. At the bot- toms of these trenches a foundation course of concrete is laid, as shown by Fig. 114, if the ground is soft; or the masonry is started directly on the natural material, if it is rock. From the foundations the walls are carried up to the level of the springing lines of the roof arch, if an arch is used; or to the level of its ceiling, if a flat roof is used. After the completion of the side walls, the portion of the exca- vation shown at No. 2, Fig. 112, is removed a sufficient depth to enable the roof arch to be built. When the arch is completed, it is filled above with well-rammed earth, and the surface is restored. The excavation of part No. 3 inclosed by the side walls and roof arch is carried on from the en- trances and from shafts left at intervals along the line. A modification of the method just de- scribed was employed in constructing the Paris underground railways. It consists in excavating a single longitudinal trench along one side of the street, and building the side wall in it as previously described. When this side wall is completed to Fig. 114. — Side-Wall Foundation Con- struction Open-Cut Tunnels. OPEN-CUT TUNNELING METHODS 199 the roof, the right half of part No. 2, Fig. 112, is excavated to the line AB, and the right-hand half of the roof arch is built. The space above the arch is then refilled and the surface of the street restored, after which the left-hand trench is dug and the side wall and roof-arch masonry is built just as in the opposite half. Generally the work is prosecuted by opening up lengths of trench at considerable intervals along the street and alternately on the left- and right-hand sides. By this method one-half of the street width is everywhere open to traffic, the travel simply passing from one side of the street to the other to avoid the excavation. When the Hning has been completed,, the center core of earth inclosed by it is removed from the entrances and shafts, leaving the tunnel finished except for the invert and track construction, etc. Another modification of the parallel longitudinal trenches method was used in the construction of the New York subway. A narrow longitudinal trench was excavated on one side of the street near the sidewalk. Meanwhile the pavement of half of the street was removed and a wooden platform of heavy planks, supported by longitudinal beams which were buried in the ground, was substituted. Then small cuts underneath the car tracks were directed from the side trench and heavy beams or needles were placed in these cuts, which also reached the longi- tudinal beams of the wooden platform. The needles were wedged and blocked to the car track structure and the beams. They were temporarily supported by cribs built from under- neath as the excavation progressed. AVhen the subgrade was reached, vertical and batter posts were inserted to support the needles, thus forming regular timber bents underground. In the space thus left open the subway was constructed to the middle of the street. While the work was going on as described, another longitudinal narrow trench was excavated at some distance on the other side of the street. From this trench, the work of constructing the other half of the subway was carried on in the manner just described. After the work had been 200 TUNNELING completed, the timbers removed, the voids filled in and the pavement of the street restored, another equal section was at- tacked on both sides of the street. Transverse Trenches. — The transverse trench or ^' slice " method of open-cut tunneling has been employed in one work, the Boston Subway. This method is described in the specifica- tions for the work prepared by the chief engineer, Mr. H. A. Carson, M. Am. Soc. C. E., as follows: — ''Trenches about 12 ft. wide shall be excavated across the street to as great a distance and depth as is necessary for the construction of the subway. The top of this excavation shall be bridged during the night by strong beams and timbering, whose upper surface is flush with the surface of the street. These beams shall be used to support the railway tracks as well as the ordinary traffic. In each trench a small portion or slice of the subway shall be constructed. Each slice of the subway thus built is to be properly joined in due time to the contiguous shces. The contractor shall at all times have as many slice- trenches in process of excavation, in process of being filled with masonry, and in process of being back-filled with earth above the completed masonry, as is necessary for the even and steady progress of the work towards completion at the time named in the contract." In regard to the success of this method Mr. Carson, in his fourth annual report on the Boston Subway work, says : '' The method was such that the street railway tracks were not disturbed at all, and the whole surface of the street, if de- sired, was left in daytime wholly free for the normal traffic." Tunnels on the Surface. — It occasionally happens when filling-in is to take place in the future, or where landslides are liable to bury the tracks, that a railway tunnel has to be built on the surface of the ground. In such cases the construc- tion of the tunnel consists simply in building the lining of the section on the ground surface with just enough excavation to secure the proper grade and foundation. Generally the lining OPEN-CUT TUNNELING METHODS 201 is finished on the outside with a waterproof coating, and is sometimes banked and partly covered with earth to protect the masonry from falHng stones and similar shocks from other causes. A recent example of tunnel construction of this char- acter was described in " Engineering News "of Sept. 8, 1898. In constructing the Golden Circle Railroad, in the Cripple Creek mining district of Colorado, the line had to be carried across a valley used as a dumping-ground for the refuse of the surround- ing mines. To protect the line from this refuse, the engineer constructed a tunnel lining consisting of successive steel ribs, filled between with masonry. Concluding Remarks. — From the fact that the open-cut method of tunneling consists first in excavating a cut, and sec- ond in covering this cut to form an underground passageway, it has been named the '' cut-and-cover " method of tunneling. The cut-and-cover method of tunnehng is almost never employed elsewhere than in cities, or where the surface of the ground has to be restored for the accommodation of traffic and business. When it is not necessary to restore the original surface, as is usually the case with tunnels built in the ordinary course of railway work, it would obviously be absurd to do so except in extraordinary cases. In a general way, therefore, it may be said that the cut-and-cover method of construction is confined to the building of tunnels under city streets; and the discussion of this kind of tunnels follows logically the general description of the open-cut method of tunneling which has been given. TUNNELS UNDER CITY STREETS. The three most common purposes of tunnels under city streets are : to provide for the removal of railway tracks from the street surface, and separate the street railway traffic from the vehicular and pedestrian traffic; to provide for rapid transit railways from the business section to the outlying residence districts of the city; and to provide conduits for sewage or subways for water and gas mains, sewers, wires, etc. Within recent years 202 TUNNELING the greatest works of tunneling under city streets have been designed and carried out to furnish improved transit facilities. Conditions of Work. — The construction of tunnels under city streets may be divided into two classes, which may be briefly defined as shallow tunnels and deep tunnels. Shallow tunnels, or those constructed at a small depth beneath the surface, are usually built by one of the cut-and-cover methods; deep tun- nels, or those built at a great depth, beneath the surface are constructed by any of the various methods of tunneling de- scribed in this book, the choice of the method depending upon the character of the material penetrated, and the local conditions. In building tunnels under city streets the first duty of the engineer is to disturb as little as possible the various existing structures and the activities for which these structures and the street are designed. The character of the difficulties encoun- tered in performing this duty will depend upon the depth at which the tunnel is driven.. In constructing shallow tunnels by the cut-and-cover method care has to be taken first of all not to disturb the street traffic any more than is absolutely necessary. This condition precludes the single trench method of open cut tunneling in all places where the street traffic is at all dense, and compels the engineer to use the methods employed in Paris and New York, as previously described, or else the transverse trench or slice method employed in the Boston Subway. These methods have to be modified when the work is done on streets having underground trolley and cable roads, and in v/hich are located gas and water pipes, conduits for wires, etc. Where underground trolley or cable railways are encountered, a common mode of procedure is to excavate parallel side trenches for the side walls, and turn the roof arch until it reaches the conduit carrying the cables or wires. The earth is then removed from beneath the conduit structure in small sections, and the arch completed as each section is opened. As fast as the arch is completed the conduit' structure is supported on it. Where OPEN-CUT TUNNELING METHODS 203 pipes are encountered they may be supported by means of chains, suspending them from heavy cross-beams, or by means of strutting, or they may be removed and rebuilt at a new level. Generally the conditions require a different solution of this problem at different points. Another serious difficulty of tunneling under city streets arises from the danger of disturbing the foundations of the adjacent buildings. This danger exists only where the depth of the tunnel excavation extends below the depth of the build- ing foundations, and where the material penetrated is soft ground. Where the tunnel penetrates rock there is no danger of disturbing the building foundations. To prevent trouble of this character requires simply that the excavation of the tunnel be so conducted that there is no inflow of the surrounding mate- rial, which may, by causing a settlement of the neighboring material, allow the foundations resting on it to sink. The Baltimore Belt tunnel, described in a preceding chap- ter, is an example of the method of work adopted in construct- ing a tunnel under city streets through very soft ground. This may be classed as a deep tunnel. Another method of deep tunneling under city streets is the shield method, examples of which are given in a succeeding chapter. Two notable examples of cut-and-cover methods of tunnehng are the Boston Subway and the New York Rapid Transit Ry., a description of which follows. Boston Subway. — The Boston Subway may be defined as the underground terminal system of the surface street railway system of the city, and as such it comprises various branches, loops, and stations. The subway begins at the Public Garden on Boylston St., near Charles St., and passes with double tracks under Boylston St. to its intersection with Tremont St., where it meets the other double-track branch, passing under Tremont St. and beginning at its intersection with Shawmut Ave. From their intersection at Tremont and Boylston streets the two double-track branches proceed under Tremont St. with four 204 TUNNELING tracks to Scollay Square. At ScoUay Square the subway divides again into two double-track branches, one passing under Hanover St., and the other under Washington St. At the intersection of Hanover and Washington streets the two double- track branches combine again into a four-track line, which runs under Washington St. to its terminus at Haymarket Square, where it comes to the surface by means of an incline. The sub- way, therefore, has three portals or entrances, located respec- tively at Boylston St., Shawmut Ave., and Haymarket Square. It also has five stations and two loops, the former being located at Boylston St., Park St., Scollay Square, Adams Square, and Haymarket Square, and the latter at Park St. and Adams Square. The total length of the subway is 10,810 ft. Material Penetrated. — The material met with in construct- ing the subway was alluvial in character, the lower strata being generally composed of blue clay and sand, and the upper strata of more loose soil, such as loam, oyster shells, gravel, and peat. At many points the material was so stable that the walls of the excavation would stand vertical for some time after excava- tion. Surface water was encountered, but generally in small quantities, except near the Boylston St. portal, where it was so plentiful as to cause some trouble. Cross-Section. — The subway being built for two tracks in some places and for four tracks in other places, it was necessary to vary the form and dimensions of the cross- section. The cross-sections actually adopted are of three types. Fig. 115 shows the section known as the wide- arch type, in which the lining is solid masonry. The second type was known as the double- barrel section, and is shown by Fig. 116. The third type of section is shown by Fig. 116. The lining consists of steel col- FiG. 115. — Wide Arch Section, Boston Subway. OPEN-CUT TUNNELING METHODS 206 umns carrying transverse roof girders, the roof girders being filled between with arches, and the wall columns having concrete walls between them. The wide-arch type and the double-barrel type of sections were employed in some portions of the Tremont St. line, where the traffic was very dense, since it was possible to construct them without opening the street. Much of the wide-arch line was constructed by the use of the roof shield, w^hich is described in the succeeding chapter on the shield system of tunneling. Methods of Construction. — Several different methods were Fig. 116. — Double-Barrel Section, Boston Subway. employed in constructing the subway. Where ample space was available, the single wide trench method of cut-and-cover construction was employed, the earth being removed as fast as excavated. In the streets, except where regular tunneling was resorted to, the parallel trench or transverse trench cut-and- cover methods were employed. In the transverse trench method, trenches about 12 ft. wide 206 TUNNELING were excavated across the street, their length being equal to the extreme transverse width of the tunnel lining, and their depth being equal to the depth of the tunnel floor. These trenches were begun during the night, and immediately roofed Concrei Cross Section ctf Side Wall, 'i-Concrefe ^"- WaterproofinaSrPtastei ' ''Ribbed Tile ^, Tar Contrets-'%^ 'Fine Brohen Snne--:^ W.proofing'S Plaster HAYMARKET SQUARE Cross Section of Roof, CofKPfff ■Brick nibbed Tile- li!^^<^0^:^^::'i^M I 'Drain Fig. 117. — Four-Track Rectangular Section, Boston Subway. over with a timber platform flush with the street surface. Under these platforms the excavation was completed and the lining built. As each trench or '' slice " was completed, the street above it was restored and the platform reconstructed over the succeeding trench or slice. During the construction of Fig. 118. — Section Showing Slice Method of Construction, Boston Subway. each slice the street traffic, including the street cars, was carried by the timber platform. In the parallel trench method, short parallel trenches were dug for the opposite side walls, and also for the intermediate columns, and completely roofed over during the night. Under OPEN-CUT TUNNELING METHODS 207 this roofing the masonry of the side walls and column founda- tions and the columns themselves were erected. When the side walls and columns had been erected, the surface of the street between them was removed, the roof beams laid, and a platform covering erected, as shown by Fig. 118. This roofing work was also done at night. The subsequent work of build- ing the roof arches, removing the remainder of the earth, and constructing the invert, was carried on underneath the plat- form covering which carried the street traffic in the meantime. The successive repetition of the processes described constructed the subway. Where the traffic was very dense on the street above, tunnel- ing was resorted to. For small portions of this work the ex- cavation was done in the ordinary way, using timber strutting, but much the greater portion of the tunnel work was performed by means of a roof shield. In the latter case, the side walls were first built in small bottom side drifts and were fitted with tracks on top to carry the roof shield. The construction and operation of this shield are described fully in the succeeding chapter on the shield system of tunneling. Masonry. — The masonry of the inclined approaches to the subway consists simply of two parallel stone masonry retaining walls. In the wide-arch and double-barrel tunnel sections, the side walls are of concrete and the roof arches are of brick masonry. In the other parts of the subway the masonry consists of brick jack arches sprung between the roof beams and covered with concrete, of concrete walls embedding the side columns, and of the concrete invert and foundations for the columns. Figs. 115 to 118 inclusive show the general details of the masonry work for each of the three sections. The inside of the lining masonry is painted throughout with white paint. Stations. ^^ The design and construction of the stations for the Boston Subway were made the subjects of considerable thought. All the stations consist of two island platforms of artificial stone having stairways leading to the street above. 208 TUNNELING The platforms are made 1 ft. higher than the rails. The station structure itself is built of steel columns and roof beams with brick roof arches and concrete side walls. Its interior is lined with white enameled tiles. The intermediate columns are cased with wood, and have circular wooden seats at their bottoms. Each stairway is covered by a light housing, consisting of a steel framework with a copper covering and an interior wood and tile finish. Ventilation. — The subway is ventilated by means of exhaust fans located in seven fan chambers, some of which contain two fans, and others only one fan. Each of the fans has a capacity of from 30,000 to 37,000 cu. ft. of air per minute, and is driven by electric motor, taking current from the trolley wires. This system of ventilation has worked satisfactorily. Disposal of Rain Water. — The rain water which enters the subway from the inclined entrances, together with that from leakage, is lifted from 12 ft. to 18 ft. by automatic electric pumps to the city sewers. The subway has pump-wells at the Public Garden, at Eliot St., Adams Square, and Haymarket Square. In each of these wells are two vertical submerged centrifugal pumps made entirely of composition metal. In each chamber above, are two electric motors operating the pumps. Each motor is started and stopped according to the height of water by means of a float and an automatic release starting box. The floats are so placed that only one pump is usually brought into use. The other, however, comes into service in case the first pump is out of order or the water enters more rapidly than one pump can dispose of it. In the latter case, both motors continue to run until the same low level has been reached. Very little dampness except from atmospheric condensation is to be found on the interior walls or roof of the subway, al- though numerous discolored patches, caused by dampness and dust, may be seen on some parts of the walls. Substantially all of the leakage comes through the small drains in the invert leading from hollows left in the side walls. Careful measure- OPEN-CUT TUNNELING METHODS 209 ment was taken at the end of an unusually wet season to de- termine the actual amount of leakage, and the total amount for the entire subway was found to be about 81 gallons per minute. Estimated Quantities. — The estimated quantities of material used in constructing the subway were as follows : Excavation 369,450 cu. yds. Concrete 75,660 " " Brick 11,105 " " Steel 8,105 tons Granite 2,285 cu. yds. Piles 117,925 lin. ft. Ribbed tiles 12,440 sq. yds. Plaster 88,190 " " Waterproofing (asphalt coating) .... 117,980 " " Artificial stone 6,790 " " Enameled brick 2,210 " " Enameled tiles 2,855 " " Cost of the Subway. — The estimated cost of the subway made before the work was begun was approximately $4,000,000, and the cost of construction did not exceed $3,700,000. This in- cludes ventilating and pump chambers, changes of water and gas pipes, sewers and other structures, administration, engineer- ing, interest on bonds, and all cost whatsoever. Dividing this number by the total length we obtain a cost per linear foot of $342.30. New York Rapid Transit Railway. — The project of an under- ground rapid transit railway to run the entire length of Man- hattan Island was originated some years previous to 1890. In 1894, however, a Rapid Transit Commission was appointed to prepare plans for such a road, and after a large amount of trouble and delay this commission awarded the contract for construction to Mr. John B. McDonald of New York City, on Jan. 15, 1900. Route. — The road starts from a loop which encircles the City Hall Park. Within this loop the tunnel construction is two-track; but where the main line leaves the loop, all four tracks come to the same level, and continue side by side thereafter 210 TUNNELING except at the points which will be noted as the description proceeds. Proceeding from the loop, the four-track line passes under Center and Elm Streets. It continues under Lafayette Place, across Astor Place and private property between Astor Place and Ninth St. to Fourth Ave. The road then passes under Fourth and Park Avenues until 42d St. is reached. At this point the Hne turns west along 42d St., which it follows to Broadway. It turns northward again under Broadway to the boulevard, crossing the Circle at 59th St. The road then follows the boulevard until 97th St. is reached, where the four-track line is separated into two double-track lines. At a suitable point north of 96th St. the outside tracks rise so as to permit the inside tracks, on reaching a point near 103d St., to curve to the right, passing under the north-bound track, and to continue thence across and under private property to 104th St. From there the two-track tunnel goes under 104th St. and Central Park to 110th St., near Lenox Ave.; thence under Lenox Ave to a point near 142d St.; thence across and under private property and the intervening streets to the Harlem River. The road passes under the Harlem River and across and under private property to 149th St., which street it follows to Third Ave., and then passes under Westchester Ave., where, at a con- venient point, the tracks emerge from the tunnel and are carried on a viaduct along and over Westchester Ave., Southern Boule- vard, and Boston Road to Bronx Park. This portion of the line, from 96th St. to Bronx Park, is known as the East Side Line. From the northern side of 96th St. the outside tracks rise and after crossing over the inside tracks they are brought to- gether on a location under the center line of the street and pro- ceed along under the boulevard to a point between 122d and 123d Streets. At this point the tracks commence to emerge from the tunnel, and are carried on a \daduct along and over the boulevard at a point* between 134th and 135th Streets, where they again pass into the tunnel under and along the boulevard and Eleventh Ave. to a point about 1350 ft. north of the center OPEN-CUT TUNNELING METHODS 211 line of 190th St. There the tracks again emerge from the tunnel, and are carried on a viaduct across and over private property to El wood St., and over and along El wood St. to Kingsbridge St. to Kingsbridge Ave., private property, the Harlem Ship Canal and Spuyten Duyvil Creek, private property, Riverdale Ave., and Broadway to a terminus near Van Cortland Park. That portion of the line from 96th St. to the above-mentioned ter- minus at Van Cortland Park is known as the West Side Line. The total length of the rapid transit road, including the parts above and below the surface ground of the streets, as well as both the East and West Side Lines, is about 22^ miles. Material Penetrated. — The soil through which the road was excavated was a varied one. The lower portion of the road, or the part including the loop up to nearly Fourth St., was excavated through loose soil, but from Fourth St. to the ends it was ex- cavated in rock. The loose soil forming the southern part of Manhattan Island is chiefly composed of clay, sand, and old rubbish — a soil very easy to excavate. Water was met at some points, but not in such quantities as to be a serious in- convenience. From Fourth St. to the ends of both the east and west side lines, the soil was chiefly composed of rock of gneissoid and mica-schistose character, these rocks prevailing nearly throughout the whole of Manhattan Island. The rock, as a rule, was not compact, but full of seams and fissures, and at many points it was found disintegrated and alternated with strata of loose soils, and even pockets of quicksand were met with along the line of the road. Cross-Sections. — The section of the underground road is of three different types, — the rectangular, the barrel-vault, and the circular. The rectangular section. Fig. 119, is used for the greater part of the road, of which a portion is for four tracks and a portion for two tracks. The dimensions adopted for the four tracks are 50 X 13 ft., and for the double tracks 25 X 13 ft. The barrel-vault section, composed of a polycentric arch, having the flattest curve at the crown, has been adopted for the tunnels 212 TUNNELING under Park Avenue — while the semicircular arch is used for all the other portions of the road to be tunneled. The circular section of 15-ft. diameter is used under the Harlem River, and being for single track, two parallel tunnels were built side by side. The main line from the City Hall loop to about 102d St. con- sists of four tracks built side by side in one conduit, except for that portion under the present Fourth Ave. tunnel where two parallel double-track tunnels are employed. The West Side Line will consist of double tracks laid in one conduit, except across Manhattan St. and beyond 190th St., where it is carried Water Dvofinq MMmumThi'c/iness iobe 8.' ' Thichness Increased in Bad &round Fig. 119. — Double-Track Section, New York Rapid Transit Railway. on an elevated structure. The East Side Line consists of a double-track tunnel driven from 102d St., and the boulevard under Central Park to 110th St. and Lenox Ave., and two parallel circular tunnels excavated under the Harlem River, — the other portions of the road being double-track, subway and elevated structure. Methods of Excavation. — Both the double- and four-track subway were built by using the different varieties of the cut-and- cover method. The single wide-trench method was used for the construction of the double-track line and also for the con- struction of the four-track line where the local conditions allowed OPEN-CUT TUNNELING METHODS 213 it. The single narrow-trench method was used for the con- struction of the four-track subway at 42d St., to meet with the pecuHar conditions of the traffic. Almost the total length of the four-track line of the subway was built by means of the two parallel side trenches. The slice method, so successfully em- ployed in the Boston Subway, was used only on 42d St. west of 6th Avenue. Lining. — The lining of the subway is of concrete, carried by a framework of steel. The floor consists of a foundation layer of concrete at least eight inches thick on good founda- tion, but thicker, according to conditions, where the foundation is bad. On top of this is placed another layer of concrete, with a layer of waterproofing between the two. In this top layer are set the stone pedestals for the steel columns, and the mem- bers making up the tracks. In the four-track subway, the steel framework consists of transverse bents of columns, and I-beams spaced about five feet apart along the tunnel. The three interior columns of each bent are built-up bulb-angle and plate columns of H-section. The wall columns are I-beams, as are also the roof beams; be- tween the I-beams, wall columns, and roof beams there is a concrete filling, so that the roof of the subway will be made up of concrete arches resting on the flanges of the I-beams of the roof. The concrete used is of one part Portland cement, two parts sand, and four parts broken stones. The double- track subway is built in the -same way, except that only one column is placed between the tracks for the support of the roof. ^All the concrete masonry of the roof, foundations, and side walls contains a layer of waterproofing, so as to keep perfectly dry the underground road, and prevent the percolation of water. This waterproofing is made up as follows : On the lowest stratum of concrete, whose surface is made as smooth as possible, a layer of hot asphalt is spread. On this asphalt are immediately laid sheets or rolls of felt ; another layer of hot asphalt is then spread 214 TUNNELING over the felt, and then another layer of felt laid, and so on, until no less than two, and no more than six, layers of felt are laid, with the felt between layers of asphalt. On top of the upper surface of asphalt the remainder of the concrete is put in place so as to reach the required thickness of the concrete wall. Tunnels. — When the distance between the roof of the pro- posed structure and the street was 20 ft. or over, the Standard Subway construction was replaced by tunnels. Three important tunnels have been constructed along the line of the New York Rapid Transit and these are located between 33d and 42d Streets on Park Ave., under Central Park northeast of 104th St. and under Broadway north of 152d St. The Park Ave. construction (Fig. 120) consists of two parallel double-track tunnels, located - /7'(7' Fig. 120. — Park Avenue Deep Tunnel Construction, New York Rapid Transit Railway. on each side of the street, and about 10 ft. below the present tunnel. The soil being composed of good rock, the tunnels were driven by a wide heading, and one bench, since no strutting was required, and the masonry lining, even of the roof, was left far behind the front of the excavation. The masonry lining consists of concrete walls and brick arches. The tunnels under Central Park and under Broadway being driven through a similar rock, the same method of excavation and the same manner of lining was used. The tunnel under the Harlem River was driven through soft ground; and it was constructed as a submarine tunnel, according to the caisson process. The tunnels were lined with iron made OPEN-CUT TUNNELING METHODS 215 up of segments, with radial and circumferential flanges. Con- crete was placed inside and flush with the flanges. The tracks, both in the subway and tunnels, are an intimate part of the concrete flooring. The rail rests on a continuous bearing of wooden blocks, laid with the grain running transversely with respect to the line of the rail, and held in place by two channel iron guard rails. The guard rails are bolted to metal cross-ties embedded in the concrete. Viaduct. — A considerable portion of the double-track branch lines north of 103d St. is viaduct, or elevated structure. The Fig. 121. — Harlem River Tunnel, New York Rapid Transit Railway. viaduct construction on the West Side Line extends, including approaches, from 122d St. to very near 135th St. Of this dis- tance, 2018 ft. 8 ins. are viaduct proper, consisting of plate girder spans carried by trestle bents at the ends, and by trestle towers for the central portion. The columns of the bents and towers are built-up bulb-angle and plate columns of H-section of the same form as those used in the bents inside the subway. The approaches proper are built of masonry. The elevated line proper consists of plate girder spans, supported on plate cross girders carried by columns. 216 TUNNELING Stations. — Many stations are built along the line. These are located on each side of the street. The entrances at the stations consist of iron framework, with glass roofs covering the descending stairways. The passageways leading down are walled with w^hite enameled bricks and wainscoted with slabs of marble. The stations for the local trains are located on each side of the road close to the walls, since the outside tracks are reserved for the local trains, w^hile the middle ones are reserved for the ex- presses. The few stations for the express trains are located between the middle and outside tracks. Stations are provided with all the conveniences required, having toilet rooms, news stands, benches, etc., and are lighted day and night by numerous arc lamps. General. — The contractor completed the work in four years. No difficulty was encountered in doing this, since the great extension of the road and the great width of the avenues under which it runs allowed work all along the line at the same time. The work, briefly summarized, comprises the following items : — Length of all sections, ft 109,570 Total excavation of earth, cu. yds 1,700,228 Earth to be filled back, cu. yds 773,093 Rock excavated, cu. yds 921,128 Rock tunneled, cu. yds 368,606 Steel used in structure, tons 65,044 Cast iron used, tons 7,901 Concrete, cu. yds 489,122 Brick, cu. yds 18,519 Waterproofing, sq. yds. 775,795 Vault lights, sq. yds 6,640 Local stations, number 43 Express stations, number 5 Station elevators, number 10 Track total, Un. ft 305,380 " underground, lin. ft 245,514 " elevated, fin. ft 59,766 In addition to the construction of the railway itself, it was necessarv to construct or reconstruct certain sewers, and to OPEN-CUT TUNNELING METHODS 217 adjust, readjust, and maintain street railway lines, water pipes, subways, and other surface and subsurface structures, and to relay street pavements. The total cost of the work, according to the contract signed by Mr. McDonald, was 135,000,000. Dividing this amount by the total length of the road, which is 109,570 lineal feet, we have the unit cost a lineal foot $315, or a little less than unit of cost of the Boston Subway, which was 1342 per lineal foot. The road belongs to the city. The contractor acts as an agent for the city in carrying out the work, and he is the leaser of the road for fifty years. The work was paid for as soon as the various parts of the road were completed, and the money was obtained from an issue of city bonds. During the fifty years' lease the contractor will pay the interest plus 1% of the face value of the bonds. This 1% goes to the sinking-fund, which within the fifty years at compound interest forms the total sum required for the redemption of bonds. This first New York Subway has been extended to Brooklyn, and more lines will be built so as to form a complete underground railway system to accommodate the ever-increasing traveling crowd of the American metropolis. No new method of con- struction has been devised yet. The only variation from the illustrated methods has been where the subway is built under- neath the Elevated Road which had to be strongly supported during the construction of the subway. This has been done in two different ways, either by supporting the columns of the Elevated Road by means of two wooden A-frames abutting at the top and leaving a large space close to the foot of the column where a pit was excavated to the required depth of the subway, or by attaching the columns to long iron girders placed longitudinally and resting with both ends in firm soil. 218 TUNNELING CHAPTER XVII, SUBMARINE TUNNELING: GENERAL DISCUS- SIGN. — THE SEVERN TUNNEL. GENERAL DISCUSSION. Submarine tunnels, or tunnels excavated under the beds of rivers, lakes, etc., have been constructed in large numbers during the last quarter of a century, and the projects for such tunnels, which have not yet been carried to completion, are still more numerous. Among the more notable completed works of this character may be noted the tunnel under the River Severn and those under the River Thames in England, the one under the River Seine in France, those under the St. Clair, Detroit, Hudson, Harlem and East Rivers, and the one under the Boston Harbor for railways, that under the East River for gas mains, that under Dorchester Bay, Boston, for sewage, and those under Lakes Michigan and Erie for the water supply of Milwaukee, Chicago, Buffalo, and Cleveland in America. For the details of the various projected submarine tunnels of note, which include tunnels under the English and Irish Chan- nels, under the Straits of Gibraltar, under the sound between Copenhagen in Denmark and Malino in Sweden, under the Messina Straits between Italy and Sicily, and under the Straits of Northumberland between New Brunswick and Prince Edward Island, and those connecting the various islands of the Straits of Behring, the reader is referred to the periodical literature of the last few years. Previous to attempting the driving of a submarine tunnel it is necessary to ascertain the character of the material it will SUBMARINE TUNNELING 219 penetrate. This fact is generally determined by making dia- mond-drill borings along the line, and the object of ascertaining it is to determine the method of excavation to be adopted. If the material is permeable and the tunnel must pass at a small depth below the river bed, a method will have to be adopted which provides for handling the difficulty of inflowing water. If, on the other hand, the tunnel passes through impermeable material at a great depth, there will be no unusual trouble from water, and almost any of the ordinary methods of tun- neling such materials may be employed. Shallow submarine tunnels through permeable material are usually driven by the shield method or by the compressed air method, or by a method which is a combination of the first and second. It is not an uncommon experience for a submarine tun- nel to start out in firm soil and unexpectedly to find that this material becomes soft and treacherous as the work proceeds, or that it is intersected by strata of soft material. The method of deaUng with this condition will vary with the cir- cumstances, but generally if any considerable amount of soft material has to be penetrated, or if the inflow of water is very large, the firm-ground system of work is changed to one of the methods employed for excavating soft-ground sub- marine tunnels. The Milwaukee water supply tunnel, de- scribed elsewhere, is a notable example of submarine tunnels, began in firm material which unexpectedly developed a treacher- ous character after the work had proceeded some distance. Occasionally the task of building a submarine tunnel in the river bed arises. In such cases the tunnel is usually built by means of cofferdams in shaUow water, and by means of caissons in deep water. Submarine tunnels under rivers are usually built with a de- scending grade from each end which terminates in a level middle position, the longitudinal profile of the tunnel corresponding to the transverse profile of the river bottom. Where, however, such tunnels pass under the water with one end submerged, and 220 TUNNELING the other end rising to land like the water supply tunnels of Chicago, Milwaukee, and Cleveland, the longitudinal profile is commonly level, or else descends from the shore to a level position reaching out under the water. The drainage of submarine tunnels during construction is one of the most serious problems with which the engineer has to deal in such works. This arises from the fact that, since the entrances of the tunnel are higher than the other parts, all of the seepage water remains in the tunnel unless pumped out, and from the possibility of encountering faults or permeable strata, which reach to the stream bed and give access to water in greater or less quantities. Generally, therefore, the excavation is conducted in such a manner that the inflowing water is led directly to sumps. To drain these sumps pumping stations are necessary at the shore shafts, and they should have ample capacity to handle the ordinary amount of seepage, and enough surplus capacity to meet probable increases in the inflow. For extraordinary emergencies this plant may have to be greatly enlarged, but it is not usual to provide for these at the outset imless their likelihood is obvious from the start. The character and size of the pumping plants used in constructing a number of well-known tunnels are described in Chapter XII. In this book submarine tunnels will be classified as follows : (1) Tunnels in rock or very compact soils, which are driven by any of the ordinary methods of tunneling similar materials on land; (2) tunnels in loose soils, which may be driven, (; Fig. 128. — Beach's Shield Used on Broadway Pneumatic Railway Tunnel. 246 TUNNELING for this work a special crane to be used in erecting the cast-iron segments of the hning. AVhile these works had been progressing in England, Mr. Beach, an American, received a patent in the United States for a tunnel shield of the construction shown by Fig. 128, which was first tried practically in constructing a short length of tunnel under Broadway for the nearly forgotten Broadway Pneumatic Underground Railway. This shield, as is indicated by Fig. 129. — Shield for City and South London Railway. the illustration, consisted of a cylinder of wood with an iron- cutting-edge and an iron tail-ring. Extending transversely across the shield at the front end were a number of horizontal iron plates or shelves with cutting-edges, as shown clearly by the drawing. The shield was moved ahead by means of a number of hydraulic jacks supplied with power by a hand pump attached to the shield. By means of suitable valves all or any lesser number of these jacks could be operated, and by thus regulating the action of the motive power the direction of SUBMARINE TUNNELING I r * ♦ t ^ - • • Tit: ^Holesforp.bolrs' .f..-.p/:'/2'f-''3'6ff- ?-. ..,_. SECTION SHOWING HALF OF WALL F. ^rrr: -^>^SECnON SHOWING HALF OF WALL E. ^u. 248 TUNNELING the shield could be altered at will. Work was abandoned on the Broadway tunnel in 1870. In 1871-2 Beach's shield was used in building a short circular tunnel 8 ft. in diameter in Cincinnati, and a little later it was introduced into the Cleve- land water-works tunnel 8 ft. in diameter. In this latter work, which was through a very treacherous soil, the shield gave a great deal of trouble, and was finally so flattened by the pressures that it was abandoned. The obviously defective features of Longitudinal Section. Cross Section. Fig. 131. — Shield for Blackwall Tunnel. this shield were its want of vertical bracing and the lack of any means of closing the front in soft soil. With the foregoing brief review of the early development of the shield system of tunneling, we have arrived at a point where the methods of modern practice can be studied intelligently. In the pages which follow we shall first illustrate fully the con- struction of a number of shields of typical and special construc- tion, and follow these illustrations with a general discussion of present practice in the various details of shield construction. Mr. Raynald Legouez, in his excellent book upon the shield system of tunneling, considers that tunnel shields may be di- SUBMARINE TUNNELING 249 Transverse Section. - 7zji Longitudinal Section. Fig. 132. — Elliptical Shield for Clichy Sewer Tunnel, Paris. vided into three classes structurally, according to the character of the material which they are designed to penetrate. In the first class he places shields designed to work in a stiff and com- 250 TUNNELING paratively stable soil, like the well-known London clay; in the second class are placed those constructed to work in soft clays and silts; and in the third class those intended for soils of an unstable granular nature. This classification will, in a general way, be kept by the writer. As a representative shield of Longitudi na\ Section ._> Cross Section. Fig. 133. — Semi-elliptical Shield for Clichy Sewer Tunnel. the first class, the one designed for the City and South London Railway is illustrated in Fig. 129. The shields for the London Tower tunnel, the AVaterloo and City Railway, the Glasgow Dis- trict Subway, the Siphons of Clichy and Concorde in Paris, and the Glasgow Port tunnel, are of the same general design and construction. To represent shields of the second class, the St. SUBMARINE TUNNELING 251 Clair River and Blackwall shields are shown in Figs. 130 and 131. The shields for the Mersey River, the Hudson River, and the East River tunnels also belong to this class. To repre- sent shields of the third class, the elHptical and semi-elliptical shields of the Clichy tunnel work in Paris are shown by Figs. 132 Details of Casting Supporting Ends of Jacks. Details of Casting under Ends Longitudinal Section C-Q. of Girders. Fig. 134. — Roof Shield for Boston Subway, and 133. The semi-circular shield of the Boston Subway is illustrated by Fig. 134. Prelini's Shield. — In closing this short review mention will be made of a new shield designed and patented by the Author and shown in Fig. 135. It is an articulated shield composed of two separated shields whose outer shells overlap each other. The shields are connected together by means of hydraulic jacks attached all around the two diaphragms. Between these dia- phragms is a large inclosed space called a safety chamber, where the men can withdraw in case of accidents and where the air can be immediately raised to the required pressure. This is 252 TUNNELING an advantage in case of blow-outs, because the flooding of the tunnel is prevented, while the accident is Hmited to only a few feet from the front. On account of the shield being advanced Fig. 135. — Transversal and Longitudinal Section of Prelini's Shield. half at a time it is always under control and is thus better directed through grade and alignment. Besides, this shield will not rotate around its axis and consequently it can be built of any shape, thus permitting the construction of subaqueous tun- nels of any cross-section and even with a wider foundation, which is impossible to-day with the ordinary rotating shields of circu- lar cross-section. SHIELD CONSTRUCTION. General Form. — Tunnel shields are usually cylindrical or semi-cylindrical in cross-section. The cylinder may be circular, elliptical, or oval in section. Far the greater number of shields used in the past have been circular cylinders; but in one part of the sewer tunnel of Clichy, in Paris, an elliptical shield with its major axis horizontal, was used, and the German engineer, Herr Mackensen, has designed an oval shield, with its major axis vertical. A semi-elHptical shield was employed on the Clichy tunnel, and semi-circular shields were used on the Bal- timore Belt Line tunnel and the Boston Subway in America. Generally, also, tunnel shields are right cylinders; that is, the SUBMARINE TUNNELING 253 front and rear edges are in vertical planes perpendicular to the axis of the cylinder. Occasionally, however, they are oblique cylinders; that is, the front or rear edges, or both, are in planes oblique to the axis of the cylinder. One of these visor-shaped shields was employed on the Clichy tunnel. The Shell. — It is absolutely necessary that the exterior sur- face of the shell should be smooth, and for this reason the ex- terior rivet heads must be countersunk. It is generally admitted, also, that the shell should be perfectly cylindrical, and not conical. The conical form has some advantage in reducing the frictional resistance to the advance of the shield; but this is generally considered to be more than counterbalanced by the danger of subsidence of the earth, caused by the excessive void which it leaves behind the iron tunnel lining. For the same reason the shell plate, which overlaps the forward ring of the lining, should be as thin as practicable, but its thickness should not be reduced so that it will deflect under the earth pressure from above. Generally the shell is made of at least two thick- nesses of plating, the plates being arranged so as to break joints, and, thus, to avoid the use of cover joints, to interrupt the smooth surface which is so essential, particularly on the exterior. The thickness of the shell required will vary with the diameter of the shield, and the character and strength of the diametrical bracing. Mr. Raynald Legouez suggests as a rule for determin- ing the thickness of the shell, that, to a minimum thickness of 2 mm., should be added 1 mm. for every meter of diameter over 4 meters. Referring to the illustrations. Figs. 128 to 132 inclusive, it will be noted that the St. Clair tunnel shield, 21J ft. in diameter, had a shell of 1-in. steel plates with cover-plate joints and interior angle stiff eners; the shell of the East River tunnel shield, 11 ft. in diameter, was made up of one J-in. and one f-in. plate; the Blackwall tunnel shield, 27 ft. 9 ins. in diam- eter, had a shell consisting of four thicknesses of |-in. plates; and the Clichy tunnel shield, with a diameter of 2.06 meters, had a shell 2 milHmeters thick. 254 TUNNELING Front-End Construction. — By the front end is meant that portion of the shield between the cutting-edge and the vertical diaphragm. The length of this portion of the shield was formerly made quite small, and where the material penetrated is very soft, a short front-end construction yet has many advocates; but the general tendency now is to extend the cutting-edge far enough ahead of the diaphragm to form a fair-sized working chamber. Excavation is far more easy and rapid when the face can be attacked directly from in front of the diaphragm than where the work has to be done from behind through the apertures in the diaphragm. So long as the roof of the excava- tion is supported from falling, experience has shown that it is easily possible to extend the excavation safely some distance ahead of the diaphragm. In reasonably stable material, like compact -clay, the front face will usually stand alone for the short time necessary to excavate the section and advance the shield one stage. In softer material the face can usually be sustained for the same short period by means of compressed air; or the face of the excavation, instead of being made vertical, can be allowed to assume its natural slope. In the latter case a visor-shaped front -end construction, such as was used on some portions of the Clichy tunnel, is particularly advantageous. The following figures show the lengths of the front ends of a number of representative tunnel shields. City and South London . 1 ft. Mersey River .... 3 ft. St. Clair River 11.25" East River 3f " Hudson River 5| " BlackwaU 6.5" Two general types of construction are employed for the cutting-edge. The first type consists of a cast-iron or cast-steel ring, beveled to form a chisel-like cutting-edge and bolted to the ends of the forward shell plates. This construction was first employed in the shield for the London Tower tunnel, and has since been used on the City and South London, Waterloo and City, and the Clichy tunnels. The second construction consists in bracing the forward shell plates by means of right SUBMARINE TUNNELING 255 triangular brackets, whose perpendicular sides are riveted re- spectively to the shell plates and the diaphragm, and whose inclined sides slant backward and downward from the front edge, and carry a conical ring of plating. The shields for the St. Clair River, East River, and Blackwall tunnels show forms of this type of cutting-edge construction. A modification of the second type of construction, which consists in omitting the conical plating, was employed on some of the shields for the Clichy tunnel. This modification is generally considered to be allowable only in materials which have little stability, and which crumble down before the advance of the cutting-edge. Where the material is of a sticky or compact nature, into which the shield in advancing must actually cut, the beveled plating is necessary to insure a clean cutting action without wedging or jamming of the material. Cellular Division. — It is necessary in shields of large diam- eter to brace the shell horizontally and vertically against dis- tortion. This bracing also serves to form stagings for the workmen, and to divide the shield into cells. The following table shows the arrangement of the vertical and transverse bracing in several representative tunnel shields. Name of Tunnel. Diameter. Hori- zontal. Plates, DiST. Apart. Vert. Braces. Hudson River Clichy Ft. 19 19.4 21 24 27 11 In. 11 6 m 8 3 4 No. 2 2 2 2 2 None Ft. 6.54 6.54 6.98 7.12 6.0 No. 2 None 3 None 3 1 St. Clair River Waterloo (Station) Blackwall East River Referring first to the horizontal divisions, it may be noted that they serve different purposes in different instances. In the Clichy tunnel shield the horizontal divisions formed simply working platforms; in the Waterloo tunnel shield they were designed to abut closely against the working face by means of special jacks, and so to divide it into three separate divisions; in 256 TUNNELING the St. Clair tunnel they served as working platforms, and also had cutting-edges for penetrating the material ahead; and in the Blackwall tunnel shield they served as working platforms, and had cutting-edges as in the St. Clair tunnel shield, and in addition the middle division was so devised that the two lower chambers of the shield could be kept under a higher pressure of air than the two upper chambers. Passing now to the vertical divisions, they serve to brace the shell of the shield against ver- tical pressures, and also to divide the horizontal chambers into cells; but unlike the horizontal plates they are not provided with cutting-edges. The St. Clair, Hudson River, and Black- wall tunnel shields illustrate the use of the vertical bracing for the double purpose of vertical bracing and of dividing the hori- zontal chambers into cells. The Waterloo tunnel shield is an example, of vertical bracing employed solely as bracing. The vertical division of the East River tunnel shield was employed in order to allow the shield to be dissembled in quadrants. The Diaphragm. — The purpose of the shield diaphragm is to close the rear end of the shield and the tunnel behind from an inrush of water and earth from the face of the excavation. It also serves the secondary purpose of stiffening the shell diamet- rically. Structurally the diaphragm separates the front-end con- struction previously described from the rear-end construction, which will be described farther on; and it is usually composed of iron or steel plating reinforced by beams or girders, and pierced with one or several openings by which access is had to the working face. In stable material, where caving or an inrush of water and earth is not likely, the diaphragm is omitted. The shield of the Waterloo tunnel is an example of this con- .struction. In more treacherous materials, however, not only is a diaphragm necessary, but it is also necessary to diminish the size of the openings through it, and to provide means for closing them entirely. Sometimes only one or two openings are left near the bottom of the diaphragm, as in the St. Clair and Mersey tunnel shields; and sometimes a number of smaller SUBMARINE TUNNELING 257 openings are provided, as in the East River and Hudson River tunnel shields. In highly treacherous materials subject to sudden and violent irruptions of earth from the excavation face, it sometimes is the case that openings, however small, closed in the ordinary manner, are impracticable, and special construction has to be adopted to deal with the difficulty. The shields for the Mersey and for the Blackwall tunnels are examples of such special devices. In the Mersey tunnel a second diaphragm was built behind the first, extending from the bottom of the shield upward to about half its total height. The aperture in the first dia- phragm being near the bottom, the space between the second and first diaphragms formed a trap to hold the inflowing material. The Blackwall tunnel shield, as previously indicated, had its front end divided into cells. Ordinarily the face of the excava- tion in front of each cell was left open, but where material was encountered which irrupted into these cells a special means of closing the face was necessary. This consisted of three poling- boards or shutters of iron held one above the other against the face of the excavation. These shutters were supported by means of strong threaded rods passing through nuts fastened to the vertical frames, which permitted each shutter to be ad- vanced against or withdrawn from the face of the excavation independently of the others. Various other constructions have been devised to retain the face of the excavation in highly treacherous soils, but few of them have been subjected to conclusive tests, and they do not therefore justify consid- eration. Rear-end Construction. — By the rear end of the shield is meant that portion at the rear of the diaphragm. It may be divided into two parts, called respectively the body and the tail of the shield. The chief purpose of the body of the shield is to furnish a place for the location of the jacks, pumps, motors, etc., employed in manipulating the shield. It also serves a purpose in distributing the weight of the shield over a large 258 TUNNELING area. To facilitate the passage of the shield around curves, or in changing from one grade to another, it is desirable to make the body of the shield as short as possible. In the Mersey, Clichy, and Waterloo tunnel shields, and, in fact, in most others which have been employed, the shell plates of the body have been reinforced by a heavy cast-iron ring, within and to which are attached the jacks and other apparatus. The latest opinion, however, seems to point to the use of brackets and beams for strengthening the shell for the purpose named, rather than to this heavy cast-iron construction. In the Hudson River, St. Clair River, and East River tunnel shields, with their long and strongly braced front-end construction to carry the jacks, the body of the shield, so to speak, is omitted and the rear-end con- struction consists simply of the tail plating. In the Blackwall shield, the body of the shield shell provides the space necessary for the double diaphragms and the cells which they inclose. In a general way, it may be said that the present tendency of engineers is to favor as short and as hght a body construction as can be secured. The tail of the shield serves to support the earth while the lining is being erected; and for this reason it overlaps the for- ward ring of the lining, as shown clearly by most of the shields illustrated. To fulfill this purpose, the tail-plates should be perfectly smooth inside and outside, so as to slide easily between the outside of the hning plates and the earth, and should also be as thin as practicable, in order not to leave a large void behind the lining to be filled in. In soils which are fairly stable, the tail construction is often visor-shaped; that is, the tail-plates overlap the lining only for, say, the roof from the springing lines up, as in one of the shields for the Clichy tunnel. In unstable materials the tail-plating extends entirely around the shield and excava- tion. The length of the tail-plating is usually sufficient to over- lap two rings of the lining, but in one of the Clichy tunnel shields it will be noticed that it extended over three rings of lining. This seemingly considerable space for thin steel plates is made SUBMAEINE TUNNELING 259 possible by the fact that the extreme rear end of the tail always rests upon the last completed ring of lining. In closing these remarks concerning the rear-end construction, the accompanying table, prepared by Mr. Raynald Legouez, will be of interest, as a general summary of principal dimensions of most of the important tunnel shields which have been built. The figures in this table have been converted from metric to English measure, and some slight variation from the exact di- mensions necessarily exists. The different columns of the table show the diameter, total length, and the length of each of the three principal parts into which tunnel shields are ordinarily divided in construction as previously described : Name of Shield. Concorde Siphon . . . Clichy Siphon .... Mersey East River City and South London Glasgow District . . . Waterloo and City . . Glasgow Harbor . . . Hudson River .... St. Clair River .... Clichy Tunnel .... Clichy Tunnel .... Blackwall Waterloo Station . . . Length in Feet. DLA.METER. Tail. Body. Front. Total. 6.75 2.51 2.55 1.16 6.67 8.39 2.51 2.55 1.16 6.16 9.97 5.61 2.98 2.98 11.58 10.99 3.51 0.32 3.67 7.51 10.99 2.65 2.82 1.01 6.49 12.07 2.65 2.82 1.01 6.49 12.99 2.75 2.98 1.24 6.98 17.25 2.75 2.98 1.08 8.49 19.91 4.82 2.98 5.67 10.49 21.52 4.00 2.98 11.25 15.25 23.7-19.8 4.00 2.98 6.88 17.22 23.8-19.4 7.44 11.90 4.46 23.65 27.00 6.98 5.90 6.59 19.48 24.86 3.34 5.51 1.14 10.00 A shield of 60 or 100 tons weight can hardly be directed along the line of the proposed tunnel and also through curves and grades, especially when driven through loose or muddy soils. The tunnels of the New York and Hudson River Railroad under the Hudson, and the tunnel of the New York Rapid Transit Railway under the East River, show marked evidence of how troublesome this work is. To avoid these and other incon- veniences encountered in every shield, the Author has designed a new shield which was briefly described at page 251. 260 TUNNELING Jacks. — The motive power usually employed in driving modern tunnel shields is hydraulic jacks. In some of the earlier shields screw-jacks were used, but these soon gave way to the more powerful hydraulic device. The manner of attaching the hydraulic jacks to the shield is always to fasten the cylinder castings at regular intervals around the ins de of the shell, with the piston rods extending backward to a bearing against the forward edge of the lining. In the older forms of shield, having an interior cast-iron reinforcing ring construction, the jack cylinder castings were always attached to this cast-iron ring; but in many of the later shields constructed without this cast- iron reinforcing ring, the cylinder castings are attached to the shell by means of bracket and gusset connections. The number and size of the jacks employed, and the distance apart at which they are spaced, depend upon the size of the shield and the character of the material in which it is designed to work. In stiff and comparatively stable clays, the skin friction of the shield is comparatively small, and an aggregate jack-power of from 4 to 5 tons per square yard of the exterior friction surface of the shield has usually been found ample. The cylinders are spaced about 5| ft. apart, and have a working diameter of from 5 to 6 ins., with a water pressure of about 1000 lbs. per sq. in. In soft, sticky material, giving a high skin friction, the aggregate jack- power required per square yard of exterior shell surface rises to from 18 to 24 tons; the jacks are spaced about 3 ft. apart; and the working cylinder diameter and water pressure are, re- spectively, about 6 or 7 ins., and from 4000 lbs. to 6000 lbs. per sq. in. With these high pressures, power pumps are necessary to give the required water pressure; Fig. 136. — Elevation and Section of Hydraulic Jack, East River Gas Tunnel. SUBMARINE TUNNELING 261 but where the pressure required does not exceed 1000 lbs. per sq. in.; hand pumps may be, and usually are, employed. Fig. 118 shows the hydrauHc jacks used in the East River Gas Tun- nel at New York. The number of jacks required depends upon the diameter of the shield, and, of course, upon the distance apart which they are placed. In the City and South London tunnel shield six jacks were used, and in the Blackwall shield 24 were used. The mechanical construction of the jacks for tun- nel shields presents no features out of the usual lines of such devices used elsewhere. The jacks used on the East River tun- nel shield are shown by Fig. 136. Two general methods are employed for transmitting the thrust of the piston rods against the tunnel lining. The object sought in each is to distribute the thrust in such a manner that there is no danger of bending the thin front flange of the forward lining ring. In English practice the plan usually adopted is to attach a shoe or bearing casting to the end of the piston rod, which will distribute the pressure over a considerable area. An example of this construction is the shield for the City and South London tunnel. In the East River and St. Clair River tunnels built in America, the tail of the piston rod is so constructed that the thrust is carried directly to the shell of the lining. LINING. Either iron or masonry may be used for lining shield-driven tunnels but present practice is almost universally in favor of iron lining. As usually built, iron lining consists of a series of successive cast-iron rings, the abutting edges of which are pro- vided with flanges. These flanges are connected by means of butts, the joints being packed with thin strips of wood, oakum, cement, or some other material to make them water-tight. Each lining ring is made up of four or more segments, which are provided with flanges for bolted connections similar to those fastening the successive rings. Generally the crown seg- ment is made considerably shorter than those forming the sides 262 TUNNELING and bottom of the ring. The erection of the iron segments forming the successive rings of the Hning may be done by hand in tunnels of small diameter where the weights to be handled are comparatively light, but in tunnels of large size special Part Transverse Section. Longitudinal Section. Fig. 137. — Cast-iron Lining, St. Clair River Tunnel. cranes attached to the shield or carried by the finished lining are employed. The construction of the iron lining for the Hudson River tunnel is illustrated in Chapter XX., and that for the St. Clair River tunnel is shown by Fig. 137. SUBMARINE TUNNELING 263 CHAPTER XX. SUBMARINE TUNNELING (Continued). THE SHIELD AND COMPRESSED AIR METHOD. THE HUDSON RIVER TUNNEL OF THE PENNSYLVANIA RAILROAD. The shield and compressed air method of excavating sub- aqueous tunnels is used when the distance is small between the roof of the tunnel and the bed of the river. These tunnels are usually driven from the shafts sunk from each shore. It is very seldom they can be driven also by an intermediate shaft. This, however, was done in the case of the Belmont tunnel under the East River. Here the tunnels passed under the man-of-war reef where a working shaft was sunk. The plant is located at some convenient point near the head shaft. It consists of a set of boilers to provide the power for the different machines. They are low and high pressure com- pressors, the former supply the air through the tunnel; the latter, the air for working the drills, in case rock is encountered, and power for hauling and hoisting purposes. The various pumps force the water for the hydraulic rams that drive the shield and work the erector. They also remove the water from the tunnel which always collects in variable quantities at the bottom of the excavation. Besides the machines for light and ventilation purposes, the head shaft is provided with an overhead con- stmction where are housed the hoisting machines, the telephone and other means of communication with the work at the front. Usually a long trestle is built in connection with the head shaft, leading to the dumping place and yard. On this inclined elevated structure are located, also, the tracks upon which will run the small cars used inside the tunnel for hauling purposes. 264 TUNNELING The shafts are excavated on a square, rectangular or circular plan and are usually lined with masonry. It is only recently that shafts excavated through loose soils have been lined with the same cast-iron lining used in the tunnels, the only difference being that the rings were laid flat on the ground and attached to those already sunk. After the shaft has been sunk to the required level, the tunnel is driven toward the river by any one of the methods used for land work. At some convenient distance from the shaft, the dimensions of the tunnel are enlarged for a length of 20 or 30 ft. In this larger space, called the shield chamber, the shield is assembled, mounted, and, when completed, it is slowly pushed toward the river. The tunnel is excavated from the shield chamber on, with dimensions equal to the exterior shell of the shield. . The construction of the shield and the hydraulic jacks used for its advance are explained in a preceding chap+er. In very loose soils, a solid bulkhead of masonry is built across the tunnel, after the shield has advanced to a certain distance and some rings of the cast-iron lining have been erected. The bulkhead is provided with three air locks — two near the floor of the tunnel, for working purposes, and one near the roof, called the emergency lock, which, as the name suggests, is used only in case of danger. The air locks are steel cylinders from 10 to 15 ft. long and 6 ft. in diameter, made up of boiler plates. They are provided with doors at each end, besides the pipes for the admission and exit of compressed air. The working locks also have narrow-gauge tracks for hauHng purposes. In rock or more consistent soil the bulkhead is constructed after the shield is far ahead, since there is no immediate necessity, under these conditions, to use the compressed air. In both the loose and good soils, when the shield has been advanced over 500 ft. from the bulkhead, a second bulkhead, with air locks, is erected in the tunnel. The first is left in place but used only in case of emergency. SUBMARINE TUNNELING 265 To direct the shield along the center Hne and through curves and grades, accurate measurements are taken, and the distance between the shield and the last ring inserted in the iron lining is regulated accordingly. The alignment inside the tunnel is maintained in a very simple way. For this purpose, points corresponding to the center line are marked on the roof at distances of 100 ft. Nearly 100 ft. from the shield, a transit is set up on a strong scaffold spanning the tunnel, and it is sup- ported by the flanges of the iron lining. A plumb-line is hung from one of the points of the roof already determined, as indicat- ing the center line; and the transit man aligns his instrument with this plumb-line; after this he " plunges " his telescope. A rodman next places a horizontal rod of special construction between the flanges of the last ring of the lining. This rod has in the center an open slot which carries a glass with a black vertical line. The slot is graduated, the zero of graduation remains in the center while the vertical line is moved right and left. The rodman places a lamp behind the slot and the transit- man tells him how to move the dark line until it coincides with the axis of the tunnel. If the ring, just erected, be a little out of alignment, it is readjusted by pushing the shield a little more on the side that has swerved from the axis of the tunnel. As the shield is pushed forward, it is kept in place by four men with graduated rods, one man on each side of the shield, one on top and the other on the floor. As the shield progresses, they repeat aloud in succession, the distance indicated on the rods, which is the distance from the shield to the outer circumferential flange of the last ring of the lining. When an advance of one foot has been made, readings are taken at every inch ; and when very near the required distance, they are taken at every quarter of an inch. In this way it is not difficult to bring the shield back into line, in case it may have shifted a little to the right or left. AATien curves are met, the rings are no longer cylindrical segments but tores, so that the segments at one side are longer than those on the other. In this case, the shield is advanced more 266 TUNNELING on one side by a quantity equal to the difference of the two sides of the ring to be erected. At each advance the shield is moved 2 ft. or 2 J ft. ahead, the distance corresponding to the length of the cast-iron rings of the lining. Within the space now open between the shield and the lining another ring is inserted. The ring is composed of different segments provided with flanges and holes bored so they can be bolted together. The segments of the lining are very heavy and diflScult to handle but they are easily set by means of the erector. When the erector is not mounted on the shield, it is located in the middle of a girder placed across the iron rings of the lining and just at the rear end of the shield. The girder, at both extremities, has flanged wheels resting on rails which are placed on brackets. These brackets are attached temporarily to the flanges of. the iron lining. The erector is provided with an arm capable to swing in a full circle. Its movements are regulated by two hydraulic jacks, located horizontally on the spanning girder. On the extreme end of the revolving arm are projections with holes for the bolts. Each segmental plate of the lining has a kind of plug in the center which is cast together with the plate and is provided with holes for the bolt. In placing the segmental plates of the lining, the arm of the erector is swung over the plate to be lifted, then two bolts are passed through the holes in the projection of the erector, and through those in the plug. The arm of the erector is then moved upwards until the plate, free from all obstacles, is swung very near its intended position. There it is adjusted and held until bolts are inserted to fix it to the plates of the preceding ring. In connection with the method of excavating submarine tunnels by means of shield and compressed air, the excavation varies with the quality of soil encountered. In compact rock the usual heading and bench method, so common in land tunnels, is also employed in this case. The shield is left behind in presence of good rock. The men at the front attack the rock with air drilling machines SUBMARINE TUNNELING 267 and charges of dynamite. The holes are driven at a smaller depth than in land work; very light charges of dynamite are used and only a few holes fired at each round. Every precaution is taken in order not to disturb the shield and the bed of the river any more than is possible, because at a shallow depth the blast would tend to widen the existing crevices in the rock and thus permit an inflow of water. When the rock is fissured or dis- integrated and the roof of the excavation at the front requires timbering, the shield should be kept closer to the front. In this way the quantity of timber for strutting is greatly reduced, so lessening the probabilities of fires. It is very difficult, in com- pressed air, to extinguish fires and in almost every instance the only way is to flood the tunnel. This was done at the Manhattan end of the tunnel under the East River for the extension to Brooklyn of the New York Subway. The excavation is made by hand in loose but compact soils such as clay. The men work on platforms located at the front of the shield and they are protected from the caving-in of the roof by a hood added for working through loose soils. The men excavate the material which is shoveled inside the tunnel and is carried away in small cars. The shield is very close to the front of the excavation in loose soil. The East Boston tunnel, under Boston Harbor, connecting with the Boston Subway, was excavated through blue clay. The minimum distance between the bottom of the water and the roof of the excavation was 18 ft. The tunnel was excavated by means of compressed air and the shield which was only used for the roof. It slid on top of concrete side walls built in two drifts which were excavated nearly 100 ft. ahead of the shield. The tunnel was lined with concrete, the arch being reinforced by longitudinal steel rods which received the thrust of jacks used for advancing the shield. The material in the drifts under the shield and the bench was removed by hand and carried away in small cars. Subaqueous tunnels driven through very loose soils can be excavated by simply leaving the doors open while the shield is 268 TUNNELING pushed ahead. The material, dislodged by the cutting edge of the shield, is forced through the doors and falls on the floor whence it is removed in small cars. In very loose soils the excavation has been made in a still more economic way; the shield with closed doors is simply squeezed through the soil. This method is financially convenient, because all the excavating and hauling operations are eliminated and the tunnel progresses from 40 to 50 ft. per day, but clearly indicates a lack of stability. In this manner, the Hudson River tunnel of the New York and New Jersey Railroad was constructed. The pressure of the air in the tunnel depends upon the depth and as a rule it varies between 20 and 40 or even more pounds per square inch above atmospheric pressure. Working in com- pressed air causes a peculiar disease commonly known as ^^ bends " or '' caisson disease " often proving fatal. To prevent and remedy the disease, the engineers should order a set of rules to be strictly observed. The preventative measures should be, first, to employ only sober, strong and healthy men, never one who has not successfully passed the examination of the attending physician; second, to order the lock tenders never to allow any man in or out of the tunnel unless he has spent at least ten minutes within the locks. Both compression and decompression should be thorough and it cannot be in less than this time. A stop of only a few minutes in the locks is not sufficient and this incomplete compression or decompression is the real cause of the bends. The men become careless after they have been in the compressed air for some time, and they try to reduce this tire- some operation to a minimum, hence the duty of the engineer to strictly enforce this rule. The remedial measures should consist of constant medical attendance near the shafts and the erection of a compressed air hospital where the men affected by bends for lack of decompression may be attended and cured. SUBMARINE TUNNELING 269 THE HUDSON RIVER TUNNELS OF THEj PENNSYLVANIA RAILROAD.* The tunnels constructed under the Hudson River for the Penn- sylvania Railroad, consist of two parallel tubes driven side by side 14 ft. apart. The tubes are of circular cross-section, 23 ft. exterior diameter, and are lined with cast-iron rings. The tunnels were driven from two shafts, one on the eastern shore of the Hudson River near 32nd St. and 11th Ave., New York; the other at Weehawken, New Jersey, near the piers of the Erie Railroad. The horizontal distance between the shafts was 6550 ft. The permanent one at Weehawken was built on a square plan, 130 ft. to a side. It was lined with concrete masonry and the walls were battered in such a way as to become the shape of an inverted frustum of a pyramid. It was provided with five openings at the bottom, four of these are used by trains that run in the open, the fifth one leads to a power house near by. During the con- struction of the tunnels one-third of this shaft was used for the land portion of the tunnel under Bergen Hill, while the remaining two-thirds were devoted to the construction of the tunnel under the river. The working shaft on Manhattan Island was a side shaft of rectangular plan 30 ft. by 22 ft., the tunnel proper being connected by two drifts 10 ft. by 10 ft. each. The shield rooms 23 ft. long, were situated on both sides of the river just in front of the shafts. On the New York side, the shields, one for each tube, were built inside the iron lining of the shield chamber, and the hoisting tackle was slung from the iron lining. The erection on the Weehawken side was done in the bare rock excavation where timber falsework was used. After the shields were finished and in position, the first two rings of the lining were erected in the tail of the shield. These rings were firmly braced to the rock and the chamber lining; then the shields were shoved ahead by their own jacks, another ring was built and so on. * Condensed from paper by James Forgie, " Eng. News," Vol. LVI, and by H. B. Hewett and W. L. Brown, " Proc. Am. Soc. C. E.", Vol. XXXVI. 270 TUNNELING Shield. — The shields used in these tunnels were designed by Mr. James Forgie, M. Inst. C. E. and M. Am. Soc. C. E., and were provided with three innovations : the segmental doors, the sliding platforms and the removable hood. The shields, Fig. 138, Half -jecrion A- Horizontol S€ci-lon. Fig. 138. — General Elevations and Sections of Shield. were circular, 23 ft. 6i ins. in external diameter, and were 16 ft. long, exclusive of the hood. The tail of the shield overlapped the lining, the maximum being 6 ft. 4 J ins. during ordinaiy working; the minimum, 2 ft. during the operation of taking any SUBMARINE TUNNELING 271 ram out for repairing. The shields had only one transverse bulkhead made up of two continuous horizontal platforms and three vertical partitions stiffening angular web plates fore and aft the ram chambers. They were connected by angles and skin plates which formed a ring-shaped frame 25 ins. thick radially and nearly 5 ft. long. Between the vertical and horizontal partitions were left openings which either were partially or entirely closed by segmental doors pivoted on an axis parallel to the face of the shield bulkhead. There were nine of such openings on each shield, the clear width being 2 ft. 7 ins., the height varying from 2 ft. 2 ins. to 3 ft. 4 ins., according to the location. The hood at the front of the shield was designed so as to be detached underground and was made of complete segments to permit easy erection or detachment. The hood was extended as far as the upper platform, thus protecting only the roof of the excavation. It was attached to the shield by means of bolts, and, when removed, it was replaced by the cast- steel cutting-edge, built in 24 sections and placed all around the shield. The eight sliding platforms, another characteristic of this shield, could be extended 2 ft. 9 ins. in front of the shield by means of hydraulic rams, and, when so extended, were able to stand a pressure of 7900 lbs. per sq. ft. These sliding plat- forms w^ere used as hoods for the protection of the men working through loose soils, while in rock they enabled the drilling and blasting to be carried on at three levels. A water trap or bird fountain was constructed, at the rear of the bulkhead of the shield, by means of angle irons to which steel plates were bolted. The opening to the face was so spacious that in an emergency the men could readily escape by getting over this trap into safety. Besides, with the assistance of compressed air, it was sufficient to perfectly trap the water-bearing ground, in case the face collapsed. Including rams and erector, the total weight of the shield was 193 tons. Hydraulic Rams. — The shield w^as operated by hydraulic pressure. The machines were designed for a maximum pressure 272 TUNNELING of 5000 lbs., to a minimum of 2000 lbs., while the average work- ing pressure was 3500 lbs. per sq. in. The forward movement of the shield was obtained by means of 24 single-acting rams 8J in. in diameter and with 38 in. stroke. Each ram exerted a pressure of nearly 100 tons, so that the combined action of the 24 rams was equal to 2400 tons. Each sliding platform was operated by two single-acting rams 3 J ins. in diameter and with 2 ft. 9 in. stroke. The rams were attached to the rear face of the shield and the front ends of the cylinders to the front ends of the sliding platforms, and since the cylinders were movable and free-sliding so also were the platforms. Erector. — The erector, a box-shaped frame mounted on a central shaft, revolved in bearings attached to the shield. Inside this frame there was a differential hydraulic plunger of 4 in. and 3 in. diameters and 48 in. stroke. To the plunger head were attached two channels which slide inside the box frame and to the projecting ends of which the grip was attached. At the opposite end of the box frame was attached a counter-weight which balances about 700 lbs. of the tunnel segment at 11 ft. radius. The erector was revolved by two single-acting rams fixed horizontally to the back of the shield, above the erector pivot, through double chains and chain wheels which were keyed to the erector shaft. Air Locks. — Two bulkhead walls, forming the rear closure of the pneumatic sections, were built in each end of each tunnel, one just ahead of the shield chamber, the other about 1200 ft. ahead of the first. The walls were built of Portland concrete 10 ft. thick, and they were grouted with Portland cement, under a pressure of nearly 100 lbs. per sq. in., to make them thoroughly air-tight. Each wall had in it three locks; for man, material and emergency. Each was equipped with hand valves arranged to be operated from either outer end or from within. The floors of the man and material locks were on a level with the working platform of the tunnel, about 3 ft. 6 ins. above the invert; the floor of the emergency lock was about 5 ft. above the horizontal SUBMARINE TUNNELING 273 Sec+jonal £ E30 ^^Hiqh Pressuf>e^Air^ [. .i ; .-^ ." ■ ■ i; ji :T| 'j . V *.■ flrv jlll axis of the tunnel. The locks were made of steel plates and shapes, with iron fittings riveted and bolted together. The man lock was 11 ft. long of ellip- tical cross-section, 6 ft. vertical diameter and 5 ft. horizontal ; the material lock was 25 ft. long, with circular cross-section, 7 ft. diameter, and the emer- gency lock was 20 ft. long, of elliptical cross-section, 4 ft. vertical and 3 ft. hori- zontal diameters. Fig. 139 shows the elevation of the air lock used in the Penn- sylvania tunnel. Excavation. — In driv- ing these tunnels almost any kind of material was encountered, viz., rock, partly rock, and partly loose soil, sand and gravel, and finally silt. Rock. — Much of the rock excavation was made before the shields were erected in orderto avoid the handling of rock through the narrow openings of the shield doors. Throughout the cross-section the shield traveled on a cradle of concrete in which 2 or 3 steel rails were imbedded. At the points where the excavation had been made for the full tell I :i?fl::■^^^^^l;v■^;!-:|:v|^^ ,i[ 1 ;t i; Man Lock y\ \-%.\-[' \ :.-:[' ' H 'vi- rll If:':: Fig. Horizontal ' Section 139. — Plan and Elevation of First Bulkhead Wall in South Tube Manhattan. 274 TUNNELING section of the tunnel, it was only necessary to trim off the projecting corners of rock. Where only the bottom heading had been driven the excavation was completed just in front of the shield; the drilling below the axis level being done from the heading itself, and above that from the front sliding plat- forms of the shield. The holes were placed near together and were drilled short; very light charges of powder were used in order to lessen the chance of knocking the shield about too much. Mixed Face. — When the rock dipped to such an extent that the front of the tunnel was excavated partly in rock and partly in loose soil, the compressed air was turned on, starting with a pressure varying from 12 to 18 lbs. When the surface of the rock was penetrated, the soft face was held up at first by hori- zontal boards braced from the shield until the shield was shoved. The braces were then taken out and, after the shield had been shoved, were replaced by others. As the amount of soft ground in the surface increased, the system of timbering was gradually changed to one of 2-in. poling-boards. These rested on top of the shield and were supported by vertical breast-boards which in turn were held by 6-in. by 6-in. walings, braced through the upper doors to the iron lining and from the sliding platforms of the shield. Sand and Gravel. — Sand and gravel were only met at Wee- hawken, where two different methods were used. The first method was employed when the roof of the excavation was through sand. It consisted of excavating the ground 2 ft. 6 ins. ahead of the cutting-edge, the roof being held in place by longi- tudinal poling-boards. These boards rested on the outside of the skin at their back end, and at the forward end on vertical breast-boards, braced from the sliding platforms and through the shield doors to cross timbers in the tunnel. The second method of timbering was used in the presence of gravel at the upper part of the excavation. In such a case, the excavation was only carried 1 ft. 3 ins. (half a shove) ahead of SUBMARINE TUNNELING 275 the cutting-edge, the roof being supported by transverse boards held by pipes which rested in holes left in the shield. After a small section of the ground had been excavated a board supported by a pipe that was inserted underneath and wedged to it was placed against the ground. These polings were kept below the level of the hood, so that when the shield was shoved, they would come inside of it ; in addition they were braced with vertical posts from the sliding platform. The upper part of the face was held by longitudinal breast-boards braced from the sliding plat- form by vertical pieces. The lower part of the face was supported by vertical sheeted poling, braced to the tunnel through the lower doors. Straw and clay were used in front of the boards to prevent the escape of air which was very large, when the tunnel was excavated through sand and gravel. The average rate of progress in these materials was 5.1 ft. per day. Silt. — When silt was encountered, the shield was shoved into the ground without any excavation being done by hand ahead of the diaphragm. As the shield advanced the silt was forced through the doors into the tunnel. Forcing the shield through the silt resulted in raising the bed of the river, the amount that the bed was raised depending on the quantity of material brought into the shield. When the whole volume of the excava- tion was brought in, the surface of the bed was not affected; when about 50% was taken in, the surface was raised about 3 ft.; if the shield was driven blind, the bed was raised about 7 ft. When the shield was driven bhnd, the tunnel began to rise for about 2 ins., and the iron lining was distorted, the vertical diameter increasing and the horizontal one decreasing by about IJ ins. It was found, however, that the tunnel was not affected when part of the excavation was taken, but if all of it was taken in or the shield was shoved with open doors, the tunnel was lowered. A powerful aid was thus found for the guidance of the shield; for, if high, the shield could be brought down by increasing the quantity of muck taken in, if low, by decreasing it. The junction of the shields under the river was made as 276 TUNNELING follows: When the two shields of one tunnel, which had been driven from opposite sides of the river, approached within 10 ft. of each other, they were stopped; a 10-in. pipe was driven be- tween them, and a final check of lines and levels was made through the pipe. One shield was then started up with all doors closed, while the doors of the stationary shield were opened for the muck driven ahead by the moving shield. This was con- tinued until the cutting-edges came together. All doors in both shields were then opened and the shield mucked out. The cutting-edges were taken off and the shields moved together again, edge of skin to edge of skin. As the sections of the cutting-edges were taken off, the space between the skin edges was poled with 3-in. stuff. ^Vhen everything except the skin had been removed, iron lining was built up inside the skins ; the gap at the junction was filled with concrete and long bolts were used from ring to ring on the circumferential joint. Lining. — The tunnels were lined with cast-iron circular rings of the segmental bolted type. In some special cases, cast steel was used instead of cast iron. The rings were made 30 ins. long, with an internal diameter of 21 ft. 2 ins. and an external one of 23 ft. The rings were composed of nine equal segments of 77 J ins. external circumferential length each, except the two segments adjoining the key which were equal to the other segments with the difference, that one end joint was not radial but formed so as to make an opening 12.25 ins. wide at the outside and 12.60 ins. at the inside, which was closed by the key segment. Each seg- ment had six bolts in the circumferential joint, the key had one, so that there were 67 bolts in one circumferential joint. Each of the twelve longitudinal or radial joints had five bolts, in all 127 bolts per ring. The circumferential flanges of each plate were strengthened by two transverse webs or feathers on each flange. Each segment was provided with a IJ-in. grout hole closed with a screw plug. In order to pass around curves, whether horizontal or vertical, or to correct deviation from the line or grade, tapering was used ; by this is meant the placing of SUBMAEINE TUNNELING 277 rings in the tunnels which were wider than the standard rings, either at one side (horizontal tapers or liners), or at the top (depressors), or at the bottom (elevators). Tapers J, f or even 1 in. were used. The taper rings were made by casting a ring with one circumferential flange much thicker than usual and then machining it off to the taper. Grouting^. — From the exterior of the tunnel already lined with cast-iron rings, grout was forced through the holes closed by screw-plugs, at a pressure of 90 lbs. per sq. in. The grout was composed of 1 Portland cement and 1 sand by volume and was forced in by a specially constructed machine, so it formed a shell of cement nearly 3 ins. thick around the exterior of the iron lining. The grouting began at the lower segment; the cement was forced in until it reached the hole above, then the hole was plugged, and the grouting was carried on from the consecutive hole and so on until all the tunnel was finally encased in grout, as it filled every crevice between the outside of the lining and the ground as excavated. The cast-iron rings of the tunnel were covered with a concrete lining which was placed in the following order: First, on the invert; second, on the duct benches; third, on the arch; fourth, on the ducts; fifth, on the face of the bench. Before any concrete was placed, the surface of the iron was cleaned by scrapers and wire brushes and by washing it with water. The invert was built in sections 30 ft. long and the duct benches were constructed soon after. These duct benches were built with several steps for the ducts to be laid later. They were built by means of a traveling stage on wheels which ran on tracks on the working platform of the tunnel. The arch was constructed soon after. First the portion from the duct benches to the haunches, then the arch proper, was built on traveling centers on tracks laid on the steps of the duct benches. The concrete was received in |-cu.-yd. dumping buckets, from the flat cars on which they were run; the buckets were hoisted to the level of the lower platform of the arch by a small Lidgerwood compressed air hoister. At this level the concrete was dumped 278 TUNNELING on a traveling car or stage and moved in that to the point on the form where it was to be placed. For the lower part of the arch the concrete was thrown directly into the form from this travel- ing part of the stage. Fig. 140 shows the cross-section of the tunnel with the iron lining and concrete. Hauling. — A working platform, made up of 5-ft. sections, was built inside the tunnel and kept close to the shield. On this platform two lines of industrial railway tracks with switches and sidings at the locks, and a heading, were laid for hauling materials and spoils. These lines converged into a single track Sc^fTTfffTtS^ W^||_5^5ft^5g-V._ Section to Sand and Gravel or Kock Section In Hudson Jliver Silt, with foundatlona Fig. 140. — Typical Cross-Sections of One Tube of Pennsylvania Railroad Tunnel Under the Hudson River. in passing through the air locks. At the shaft elevators, they terminated in a steel plate floor to avoid switches. Between the locks of the bulkheads was installed an electrically driven cable system, to haul the loaded muck up grade and to empty the flat cars. From the first bulkhead to the shaft, the cars were hauled up grade by a steam hauling engine. At the Manliattan end there was one 10-H.P. engine for each tunnel, while at Wee- hawken one 25-H.P. engine served for both tunnels. Each shaft contained two elevators driven by a double-cable, reversible single-drum steam-hoisting engine. A grouty frame was built SUBMARINE TUNNELING 279 over the shafts, and on the platforms over this frame were narrow- gauge tracks, extending from the elevators to the muck-chutes and to points where the lining segments were loaded on the cars. The elevators were arranged to stop at both the ground and the grouty platform levels. The rolHng-stock at each of the tunnels consisted of 75 flat cars for moving the tunnel segments, and of about 50 muck cars, each of IJ cu. yd. capacity. Plant. — The plants located at each end of the tunnel near the shafts were almost identical. Each consisted of three 500-H.P. Stirtling boilers, which supplied steam at 150 lbs. pressure. Feed water was supplied by three 13^ metropolitan injectors, and two Blake duplex pumps. Two Worthington surface condensers, each of 2250 sq. ft. condensing surface, took care of the exhaust from the engines and compressors. Condensing water was pumped from the river through a 16-in. pipe. The high-pressure air was supplied by a duplex Ingersoll-Sergeant compressor, with cross-compound steam end 14 X 26 X 30 ins. and simple water-jacket air cylinders 13J X 36 ins. Its capacity at 100 r.p.m. was 1085 cu. ft. free air per minute. The maximum pressure was 130 lbs. per sq. in. The air for the pneumatic working was supplied by three 14x26x30 in. duplex Ingersoll-Sergeant compressors. The maximum capacity of the three was 12,000 cu. ft. free air per minute at 125 r.p.m. and a discharge pressure of 50 lbs. per sq. in. The suction air was taken from the outside about 10 ft. above the roof of the engine house. Three after- coolers, 32J ins. X 11 ft. 4 ins., each having 809 sq. ft. cooling surface of tinned brass tubes, cooled the low-pressure discharge to within 10° F. of the temperature of the cooling- water. From the aftercoolers, the air passed into three steel receivers each 54 X 12 ft., placed outside the engine room and fitted with weigh- ing safety valves. The receivers were connected to two 10-in. mains; one serving the north, the other the south tunnel. A fourth receiver of the same size was built to receive the discharge of the high-pressure compressor, through a 4-in. pipe. The high-pressure water required for the shield was furnished by 280 TUNNELING three Blake direct-acting, duplex pumps with outside packed plungers- The steam end was 16 X 18 ins., the water end 2tV X 18 ins. At 55 r.p.m. pumping against 5000 lbs. per sq. in., the capacity of each pump was 57 gals, per minute. Two of them, one on each tunnel, were sufficient to run the shields and the third was held in reserve. The high-pressure water was conveyed to the front by means of a 2-in. double, extra strong pipe which was buried between the engine room and the shaft, in a trench, to prevent freezing in cold weather. The electric current for light and power was supplied by two 100-K.W. 250-volt G.E. direct- current generators directly connected to Ball & Wood high-speed engines running at 250 r.p.m. The switchboard had two machine panels, two distributing panels and one panel carrying a circuit breaker for the traction circuit. niumination. — The tunnel was lighted by electricity, there being two rows of lamps, one in the crown and one in the south axial line. The lamps were 16-c.p., 240-volt, two-wire system, and were spaced 35 ft. apart in the crown and 12 J ft. apart on the axial line. In addition, five nests of 5 lamps each were used at the front. Candles were supplied for miscellaneous and emergency uses. The sockets for electric globes were fitted to a wooden reflector^ coated with white enamel paint on the inside. SUBMAKINE TUJSNELING 281 CHAPTER XXI. SUBMARINE TUNNELING (Continued); TUNNELS AT VERY SHALLOW DEPTH. THE COFFER- DAM METHOD. THE PNEUMATIC CAISSON METHOD. THE JOINING TOGETHER SEC- TIONS OF TUNNELS BUILT ON LAND. The tunnels on the river bed or at such a shallow depth that only a few feet of material will remain between the bottom of the river and the roof of the tunnel can be built in three different ways, viz., (1) by a cofferdam; (2) by pneumatic caissons; (3) by sinking and joining together whole sections of tunnels that were built on land. The Cofferdam Method. — The Van Buren Street Tunnel, Chicago River. — According to the cofferdam method, the work is at- tacked at one of the shores, and the tunnel built in sections of such length as not to interfere with the flow of water or the navigation of the river. Round the entire exterior line of the first section a double-walled cofferdam is built, and strongly braced transversely, so as to withstand the pressure of the water. When the water is pumped out, a single-walled cofferdam is built within the first, leaving sufficient distance between the two to allow of the construction of the masonry. The soil is then removed within the inner cofferdam, and the tunnel constructed from the foundation. When the end of the tunnel reaches the channel end of the cofferdam, a crib-wall is erected over the end of the completed tunnel. This crib, in turn, forms the end wall of another cofferdam, built in continuation of the first, so as to allow the second section to be proceeded with, and at the same time to facilitate the removal of the cofferdams of the first 282 TUNNELING section. The work goes on continuously in this way until the distant shore is reached. VAN BUREN STREET TUNNEL, CHICAGO. The Van Buren Street tunnel, built to carry a double-track street railway under the Chicago River, was completed in 1894 by the cofferdam method. The special features of the tunnel* are: (1) the unusually large dimensions of the cross-section of 30 ft. X 15 ft. 9 ins.; (2) its construction inside of cofferdams of great length and width; (3) the construction under some very high buildings calling for great care and very strong tem- porary and permanent supports. The special feature of the work for our present purpose was the construction of the tunnel across the river. To accomplish this a cofferdam was built out from the west shore of the river to its middle, and the tunnel constructed within it like the building of any other structure within a cofferdam. Trans- verse and longitudinal sections of this cofferdam are shown by Fig. 119. As will be seen, it was a simple double-wall coffer- dam, with a clear width between the walls of 58 ft., and braced transversely as shown. Inside of this a single-wall cofferdam of piles was constructed, with a clear width just sufficient to allow the construction of the masonry within it. When the tunnel end reached the channel end of the cofferdam, a crib-wall was built over the end of the completed tunnel, as shown by the drawings. This crib-wall was intended to form the end wall of another cofferdam, which was built out from the east shore, and within which the remaining half of the tunnel was built as the first half had been. The drawings show the character of the tunnel masonry and of the centering upon which it was built. The Van Buren Street tunnel was the last of the three tunnels under the Chicago River, constructed according to the cofferdam method. At the time the tunnels were constructed the bed of *" Eng. News," April 12, 1892. SUBMARINE TUNNELING 283 284 TUNNELING the river was 17 ft. deep. In connection with the harbor and river improvements, the Federal Government ordered the Chicago River to be lowered so as to give a depth of 26 ft. of water. This necessitated the lowering of the tunnel roof and the excavation for a deeper floor which was a very difficult operation. This work was described in ^'Eng. News/' Sept., 1906. THE PNEUMATIC CAISSON METHOD. — THE TUNNEL UNDER THE HARLEM RIVER. In the early seventies Prof. Winkler proposed to construct a tunnel under the River Danube to connect the various por- tions of the Vienna, Austria, underground railway, and to use caissons in the construction. Prof. Winkler proposed to build caissons from 30 ft. to 45 ft. long, with a width depending upon the lateral dimensions adopted for the tunnel masonry. The caisson was to be made of metal plates and angle iron with riveted connections on all sides except those running vertically transverse to the tunnel axis, whose connections were to be bolted. In the middle of the roof an opening was to be left; this was for the shaft having the air-locks to allow the passage of men, materials, and compressed air. Across the river two parallel rows of piles were to be driven into the river bed, to fix the place where the caisson was to be sunk. Then the first caisson near the shore was to be lowered in the ordinary way, and a second caisson was to be immediately sunk very close to the first one. When both caissons had reached the plane of the tunnel floor, the sides which were in contact were to be unbolted and removed, and the small space between made water-tight. The chambers of the two caissons were to be opened into a single large one communicating above by means of two shafts. At the same time that the masonry was being built in the first two caissons, from the inverted arch up, a third caisson was to be sunk; and when by excavation it had reached the plane of the projected tunnel floor, the partitions were to be removed so that the three caissons were in communi- SUBMARINE TUNNELING 285 cation, forming a large single caisson. Then the outer partition of the first caisson was to be removed, and the masonry of the submarine tunnel connected with the portion of the tunnel built on land. In a similar manner all the caissons were to be sunk; and when the last one was placed, and the masonry lining con- structed, and connected with the portion of the tunnel built on the other shore of the river, the partition walls were to be battered down, and the submarine tunnel completely constructed and open to traffic. The Harlem River Tunnel. — The pneumatic caissons method was employed in the construction of the tunnel under the Harlem River for the New York Rapid Transit Railway. The tunnel proper consisted of two parallel tubes riveted to each other and surrounded by a cradle of concrete as shown in Fig. 121, page 216. The tunnel was built in three sections : — The first, from the Manhattan shore well towards the middle of the river; the second, from the shore of the Bronx towards the middle of the river; and the last, the section uniting the other two and completing the tunnel. Each section was built within a specially constructed working- chamber, consisting of timber side walls forming a wooden caisson, so constructed that compressed air could be used. This working-chamber of Mr. McBean presented some novel features, inasmuch as the caisson was not built on land, but under water. In building the tunnel, the Harlem River was dredged to a certain depth, so as to leave only 6 ft. or 8 ft. of excavation to be done before reaching the line of sub-grade of the proposed structure. Two service platforms were built on piles 10 ft. apart longitudinally, and cut off at a point above mean high- water mark, braced in the usual manner, and covered with heavy planks, to serve as the floor of the platform. On this platform were placed rails for the trains used in the transportation of materials. These platforms were also used in maintaining the perfect alignment of the caissons. Within the platforms and along the dredged channel four 286 TUNNELING Fig. 142. — Showing Working Platforms and Piles Sunk in the Dredged Channel. longitudinal rows of piles were sunk. These piles were accurately brought to line by beams bolted together, and placed across and above the water-level. A few beams were also added for the purpose of bracing the piles transversely, after which they were cut off under water and capped. Fig. 142 shows the manner in which the working platforms were constructed, and also the rows of piles sunk in the dredged channel. Between the piles a very '^ strong frame was placed, made up of waling pieces and two trans- verse beams 14 ins. by 14 ins. each, placed one below the other at a distance of 5 ft. 8 ins., and strongly braced together. Guiding-beams were fixed on each side of the frame for the sheeting piles. The frames were built in sections of different lengths, and placed directly above the cap-pieces of the pile-bents sunk in the dredged channel. The longitudinal sides of the caisson were constructed by sinking two rows of sheeting piles, each row being close to a service platform. The sheeting piles were made up of yellow- pine timbers 12 ins. by 12 ins.; three piles bolted together formed a section 3 ft. wide. Each section was grooved and tongued, so as to be firmly connected with the adjacent sections to be sunk. The lower ends of the piles were cut wedge-shaped, with a sharp edge to offer a small resistance while penetrating the soil. The sheeting-piles were then cut off under water, which operation was successfully carried out by means of a circular saw operated by a pile-driving machine. The sheeting was also extended between two platforms to make a bulkhead, and in this way the four sides of the caisson were built up. Particular attention was always given to the alignment of the sheeting piles, which was obtained by guiding the piles with the timbers placed longi- SUBMARINE TUNNELING 287 \, mi :y / Fig. 143. — Showing Sheeting-Piles for the Sides of the Caisson and Trussed Beam for theRoof. tudinally, one below the water-line in connection with the frames located between the pile-bents, and the second along the inner edge of the service platform, as shown in Fig. 143. The caisson was completed by placing a roof covering the sides. This roof was 40 ins. thick, made up of three layers of 12-in. beams placed trans- versely to the axis of the cais- son, while between the beams planks 2 ins. thick were placed lengthwise and bolted together, so as to make a firm, solid structure. The roof was built ashore, in sections each varying from 39 ft. to 130 ft. long. The edges of the roof fitted the sides of the caisson perfectly; and when each section was towed to the proper spot, it was sunk and made secure. Under the roof were placed six longitudinal beams, 12 ins. by 14 ins., called '' rangers," resting on the cap- pieces of the pile-bents that were laid across the space of the proposed tunnel; while the extreme rangers were used for the purpose of fitting above the sheeting-piles of the cais- son, in order to make the lat- ter water-tight. The two ex- treme rangers were provided with T-irons, the flat side being laid on the sheeting-piles, while the web penetrated the ranger by reason of the weight of the load resting on the roof, for the purpose of sinking it to the required point. Earth was next heaped on the roof, and in this way a large working-chamber was prepared, as shown in Fig. 144. The working-chamber built on the Manhattan side of the Fig. 144. — Showing the Caisson with the Work- ing-Chamber. 288 TUNNELING Harlem River was 216 ft. long, provided with two rectangular shafts 7 ft. by 17 ft., rendered water-tight, and rising above the high-water mark of the river. Within these shafts the air-locks of the tunnel tubes were placed, so that the work could be carried on by means of compressed air. The pressure of the air was used to expel the water, being sufficiently intense to equilibrate a column of water equal to the depth of the lowest point of the roof of the caisson. "When the working-chamber was constructed, the tunnel proper was begun by excavating the soil down to the required level; the concrete was then laid on. It was just at this point, when a large part of the roof was constructed and supported only by the sheeting-piles of the sides of the caisson, that the writer of this article feared that this novel method of tunneling would prove a failure. The tendency of the timber to float, aided as it was by the air pressure within the caisson, was counteracted only by the weight of the earth heaped on the roof, and by the friction of the soil against the feet of the sheeting-piles. This friction was only a small quantity, as the soil was loose, so that it was considered rather risky and dangerous to place reliance on such a feeble quantity. This fear was, unfortunately, justified on two occasions, when on cutting off a portion of the pile-bents some of the sheeting-piles got loose and water flooded the whole chamber, but, happily, without loss of life. As the chamber was one of large dimensions, the workmen had time enough to effect their escape. It may be remarked that during these troubles only a few of the sheeting-piles were displaced, while the caisson itself offered a stout and successful resistance, due to its being strongly braced transversely. The accidents were, therefore, limited to a few piles, instead of affecting the entire caisson. On the occasion of the first, the repairs were effected by sinking the piles to a greater depth, continuing down until rock was encoun- tered. After that, the water was pumped out and the work resumed. In repairing the second accident, the sheeting-piles were driven down to bed-rock, and the surrounding soil strength- SUBMARINE TUNNELING 289 Fig. 145. ■Showing the Tunnel Constructed within the Caisson. ened by cement forced through the loose soil around the piles. This remedy proved effective, and no further trouble occurred to delay the work on the Manhattan side of the Harlem River. On the concrete bed of the tunnel the segments of the metal lining were placed and sur- rounded by concrete, as re- quired by the plans and speci- fications (Fig. 145). The con- tractors had planned to unbolt the roof from its holdings, to remove by means of dredgers the earth which had been heaped on it, and thus set the roof afloat, after which it was to be towed within the two working platforms already erected on the Bronx shore. But Mr. McBean devised a simpler and more economic, but at the same time more dangerous, way of constructing this second section of the tunnel. He thought that the upper half of the tunnel proper could be used instead of the timber roof, thereby reducing the capacity of the working chariiber, and limiting the use of compressed air. In this way he dispensed with the removal of timber, and also of the earth heaped on the roof. In building this Bronx section, a channel was dredged along the line of the tunnel to a depth of 5 ft. from the foundation-bed of the proposed tunnel . The working platforms were constructed on both sides of this channel, quite similar to those erected on the other half of the tunnel; and between them pile-bents were sunk, capped with 12-in. by 12-in. beams. Over the cap-pieces rangers were placed longitudinally, which also rested on the sides of the wooden working caisson. Fig. 146. The sheeting-piles were cut off at level, but much lower down than in the first half of the tunnel. The roof was built on floats made of 12-in. by 12-in. timber laid transversely 4 ft. apart and supporting a floor of 3-in. by 12-in. 290 TUNNELING Fig. 146. — Showing Sides of the Caisson and Supports for the Roof. planks rendered water-tight. The sides of the floats were made by verticals, 4 ins. by 6 ins., and planks, 3 ins. by 12 ins., care- fully caulked. A temporary floor was built on the base of the float, consisting of transverse beams, 16 ins. by 16 ins., placed 8 ft. apart. A center piece, 10 ins. by 16 ins., was laid so as to correspond with the axis of the tunnel; and on each side of it, other parallel beams, 16 ins. by 16 ins., corresponding to each center of the circular metal lining of the tunnel; the beams, longitudinal and transversal, were strongly bolted to- gether. The temporary floor was completed by boarding the spaces left between the various beams. On this float, the upper half of the tunnel was constructed by erecting the segments of the metal lining, which were strongly supported, so as to prevent any settling or distortion; the con- crete was then built up in a large flange with vertical suspension rods, four to each bar. The rings of the tunnel were 6 ft. each, the weight of each lining being 41,000 lbs., the concrete covering 618 cubic feet. The second part of the tunnel was 300 ft. long, with roof constructed in three sections — two of 90 ft. in length each and the third of 84 ft. Each of these sections alternated with a smaller section, 12 ft. long, provided with air-locks. The shortest of the three sections was the first one set up, and was constructed close to the Bronx side of the Harlem River. For this purpose the two extreme ends of the section were closed by means of steel plates forming diaphragms, built 6 ft. inward, thus leaving one ring projecting out at each end. Openings were left on the top of these projecting rings for access by divers. The exterior of the upper half section of the permanent tunnel was filled with water until it was lowered into position. It was SUBMARINE TUNNELING 291 directed by means of tackles attached to vertical eye-bars, which were strongly fixed to the flanges of the springing line of the arch, and bolted to the beams of the temporary floor. In this way the roof was towed into place, and lowered by means of stone ballast, until it rested on the cap-pieces and frames of the pile abutments, the sides of the roof remaining just on top of the sheeting-piles that formed the sides of the caisson, as shown in Fig. 147. Per- fect alignment was obtained by wires strung at each end and along the side of the roof, corresponding to points fixed on the working platforms and sighted with transits. Such accuracy was obtained that the circumferential flanges of the outer 6-ft. ring were brought into contact with those of the 12-ft. section already constructed. A diver then entered by the opening left in the projecting ring, and bolted this section of the roof to the preceding one. By removing the iron diaphragm, the consecutive sections were united into one. When the diver completed his work, the opening was closed up, and compressed air used to keep the water out of the box included between the roof and the temporary flooring. The remaining sections of the tunnel roof were built in the same w^ay, until the last abutted against the part of the work constructed within the caisson under the high wooden roof on the Manhattan side of the river. The following method was adopted for the purpose of connecting the few parts of the tunnel which had been differently constructed. The diaphragm at the end of the last section of the tunnel roof was constructed so as to abut against the last circumferential flanges of the iron lining without leaving a projecting ring. It was continued above the metal and concrete lining of the roof in a rectangular form, and Fig. 147. — Showing the Roof of the Caisson Formed by the Upper Half of the Tunnel. 292 TUNNELING of the same height and width as the wooden bulkhead of the working-chamber on the Manhattan side of the river. The diaphragm was made of riveted plates and angles, with an open- ing 20 ins. by 30 ins., bolted so as to be removable at will. The diaphragm was of the same height as the roof and was connected with a roof-plate to the rangers supporting the thick wooden roof. Other steel plates, placed vertically, were riveted to the diaphragm and bolted to the caisson. All this work was carried on by divers. The wooden bulkhead was cut to the springing- hne of the arch; and between the two parts of the tunnel, built- by different methods, a bulkhead was placed, made of steel plates 14 ins. long, which prevented the entrance of water into the working-chamber. When the different sections were joined together, and all the openings closed and made water-tight, cement-grout was poured on the roof, and earth was heaped up to a height of 5 ft. The 300 ft. of the roof, resting on sheeting-piles and provided with diaphragms at the ex- treme ends, formed a water- tight working-chamber, or cais- son, communicating with the exterior by means of the shafts and air-locks. The lower por- tion of the tunnel was built under air-pressure. The pile- bents were first cut off at the plane of the tunnel sub-grade, after which the foundation-bed of concrete was laid. The lower segments of the iron Hning were then placed in position, and the structure made continuous by building up the lateral walls, consisting of concrete (Fig. 148). No accidents occurred while building the second part of the tunnel. The Harlem River tunnel was completed in contract time, although the opening of the subway was delayed by difficulties Fig. 148. — Showing the Tunnel Completed by Building the Lower Half within the Caisson. SUBMARINE TUNNELING 293 encountered in tunneling through rock in the borough of the Bronx. The writer endeavored to obtain information regarding the expense per Hnear foot, but all his efforts were rewarded with a general assurance that it proved to be the cheapest method. SINKING AND JOINING TOGETHER SECTIONS OF TUNNELS BUILT ON LAND. THE SEINE. THE DETROIT RIVER TUNNELS. In the year 1896, Mr. Erastus Wyman secured a patent for building subaqueous tunnels close to the river, by sinking and joining together small sections of tunnels previously built on land. Each section would have been provided with a long vertical tube for the air-lock when compressed air was to be admitted to expel the water and permit the construction of the lining within the sunken shell. Thus each section of the tunnel would have acted as a pneumatic caisson; being, however, an improvement on Professor Winkler's suggestion inasmuch as the caisson was a portion of the tunnel itself, instead of a simple inclosure for facilitating the construction of the shield. Mr. Wyman proposed to use this method in the construction of a tunnel between South Brooklyn and Stapleton, Staten Island; a charter was granted him but the tunnel was never built. The Tunnel under the Seine River. — The caisson method of building tunnels under water was used at Paris, France, in the construction of the Metropolitan Railroad under the Seine River. The caissons designed by Mr. L. Chagnaud were for a double track line. They were sunk, ends to ends, and formed a portion of the tunnel lining which was enveloped by a framework of metal embedded in concrete. Built-up frames carried a shell of steel plating on the sides, from toes to springing hues, and on the sides and roof of the working-chamber. A temporary plate diaphragm closed the open ends. This construction formed a vessel capable of floating with a very light draft. The method of sinking the caissons was as follows : The cais- son was erected on the river bank and when completed it was 294 TUNNELING launched and towed into position between pile stagings which served the double purpose of guiding the descent at the beginning of the sinking and of forming a working platform. The caisson when launched and, consequently, before the cast-iron hning had been put in place within it, weighed 280 metric tons; but, beyond some difficulty in taking it under the bridges in the way, the towing was accomplished without serious trouble. i Working \ Chamber Fig. 149. — Transversal Section of the Caissons for the Tunnel under the Seine River. Previous to placing the caisson in position between the stagings, the portion of the river bed it was to rest upon had been leveled by dredging. Once in position, the first work was the erecting of the cast-iron lining segments within the frame- work. Work was then begun by filling the annular space between the lining and the shell with concrete; this additional weight gradually sunk the caisson to the river bottom. The working shafts, made up of steel cylinders, were placed as the sinking progressed to this point. After the caissons had been sunk to the required place and in continuation of one another, a space of nearly 5 ft. was left between them. The construction of the tunnel within the bank SUBMARINE TUNNELING 295 of earth separating the two caissons was as follows : A cofferdam was built around this space. It was formed by two diaphragms closing the ends of the tunnel, and by two longitudinal walls sunk as temporary caissons, one on each side of the tunnel SEINE RIVER Surface of Wafer Working Chamber Section' C>"-'A-B ' " Caisson No. 4. Ene ^ News. Fia. 150. Section C-D. Caisson No. 5. Plan at Joint. Showing the Joining of the Caissons at the Pont Mirabeau Tunnel under the Seine River. ^ and inclosing their ends. This cofferdam was covered with a metal working-chamber whose lower edges rested on top of the four walls of the cofferdam. The joints were made tight by means of rubber or packed clay. The water in the cofferdam was then pumped out, the earth excavated, and the masonry built in continuation of the two ends of the tunnel sections. The submerged sections of the tunnel which were allowed to 296 TUNNELING remain full of water to render them more stable and to save effort in pumping them, were now made dry; the diaphragms were removed from the ends of the caisson tunnels and the work made continuous. Fig. 149 shows the cross-section of the caissons. At the Pont Mirabeau crossing of the Seine, a slightly differ- ent method was used, described in ''Eng. News," May 18, 1911. The caissons were sunk to the required line and grade with an intervening longitudinal space of 15f ins. between two adjoining caissons. At each end of this space, which was filled with the river marl, was sunk against the edges of the caissons a hollow cylinder 20 ins. outside diameter. The interior of these cyl- inders was excavated and filled with concrete, thus forming a continuous wall on both sides of the two adjoining caissons. The earth from the intervening space was then removed and concrete deposited from bottom opening tremies up to the level of the top of the caisson. After nearly one month the tunnel was entered from the shaft and an opening the shape and size of the tunnel section cut through the diaphragms of the 15f-in. wall and the concrete tunnel lining made continuous between the two sections. Fig. 150 shows the method of joining the caissons. The Detroit River Tunnel.* — With some modifications which permitted dispensing with compressed air, the tunnel under the Detroit River was built for the Michigan Central Railroad, con- necting Detroit with Windsor, Canada. The tunnel is 6625 ft. long; of this, however, only 2625 ft. are under the river, while the approach on the American side is 2000 ft. long and that on the Canadian side, 4000 ft. The tunnel consists of two parallel circular tubes 23 ft. in diameter, built up of |-in. steel plate. They are placed 26 ft. apart, center to center, and are connected by diaphragms at 12-foot intervals. Each section of the subaqueous tunnel is approximately 262 ft. long. There are ten of these sections and an eleventh a little over 60 ft. long. These tubes were built at the shipyards * Condensed from a paper by B. H. Ryder. SUBMARINE TUNNELING 297 of the Great Lakes Engineering Works at St. Clair, about 30 miles from Detroit. After the assembling was completed, the ends of each tube were closed by temporary wooden bulkheads to make them float, and the outside sheathed horizontally with heavy timbers bolted to the diaphragms. This sheathing running lengthwise of the tube made a form or pocket, into which the inclosing jacket of concrete was placed. The sections were then launched and towed down to the tunnel side and sunk separately in a trench on the river bottom that had been previously dredged to receive them. This trench was dug to a width of 50 ft. and depth varying from 25 to 50 ft. by clamshell buckets, swung from a scow, working to a depth below the water level of 60 to 90 ft. As a foundation for the sections, a grillage was constructed on the surface and sunk in place in the trench by derricks swung from a scow. The grillage was placed underneath each joint between the sections and built up of I-beams imbedded in con- crete. This grillage is the width of the trench and about 30 ft, long, with posts projecting downward from the four corners, and these were seated into the river bottom, by means of pile drivers, to the desired grade. Then the eleven sections of the tunnel were lowered and con- nected, one at a time. By the aid of air tanks placed on each section the movement was controlled until the final sinking upon the grillage in the trench. This operation called into play the greatest engineering skill and ingenuity. When it is considered that the current velocity at the river bed is about 2 ft. per second and much higher along the surface, some idea can be gained of the problems to be overcome. The movement of the enormous sections must be absolutely under control. Thirty-five-ton blocks of concrete were sunk in the river bottom up and down stream to act as anchors, and through them cables were rigged and connected back to the hoisting engines on the derrick scows. These were prevented from moving by spuds at each corner, securely driven into the river bottom at depths sometimes as 298 TUNNELING great as 90 ft. Controlling cables were also run from the sections to the tremie scow to pull one structure close to the adjoining section previously sunk, and the divers made the necessary con- nection. Fig. 151 shows cross-sections and plans of the tunnel as given in ''Eng. Record/' March 2, 1907. . 55-8- HAUF HORIZONTAL SECTION X-X HALF TOP VIEW Fig. 151. — Cross-Sections and Plans of the Detroit River Tunnel. Steel masts had been previously attached to each end of the sections to enable the engineers on shore to determine the align- ment and locate the exact position during the sinking. Concrete was then deposited in the pockets, completely sur- SUBMARINE TUNNELING 299 rounding the tubes, forming a solid monolithic structure from end to end. This was done by means of the tremie process. A 32-ft. by 160-ft. scow was equipped with a concrete mixing plant and the tremie pipes, three in number, through which the concrete was deposited. Each pipe is 12 ins. in diameter, of spiral riveted steel, 80 ft. long. These pipes could be raised or lowered, reaching from the receiving hoppers on the scow to the bottom of the trench. When the pipes were filled with concrete and lowered into position, a continuous flow was maintained. As fast as the concrete escaped at the bottom end of the pipe it was replenished at the top ; this process continuing until the entire space surrounding the section was filled to the desired level, and under the pressure produced not only by the depth of water under which it was submerged, but also by the weight of the long column of concrete contained in the tubes. It is interesting to note that this is the first time a large amount of concrete has been deposited at a depth of 70 ft. by this method, and upon the accomplishment of this task in a measure depended the success- ful building of the tunnel. Inside the tubes was placed a lining of reinforced concrete 20 ins. thick. Side walls were built up from this ring to provide ducts, which carry the electrical cables for the distribution of power, lighting, signal and telegraph wires. They also serve to provide a footwalk along the side of the tunnel. There are cross passages in the tunnel every 200 ft., and also various niches for the different equipment needed in connec- tion with the signaling, telephone and fire alarm system. The tunnel is lighted with 800 16-candle-power incandescent lights. The track construction is new. There is no ballast used, the ties being laid in concrete. A ditch in the center of each track carries the rainfall that will flow down from the summits to sumps which are drained by centrifugal pumps. One remarkable feature of its construction is that com- pressed air was not used in the building of the subaqueous 300 TUNNELING tunnel, but it was necessary in building the approach tunnels. This is contrary to the usual program where compressed air is required in subaqueous work, and not ordinarily used in approach or land tunnel construction. The trains are operated by very heavy electric locomotives, operated by the third-rail system. The tunnel was constructed under the supervision of W. S. Kinnear, Chief Engineer of the Detroit River Tunnel Co. ; Butler Bros, of New York were the general contractors. ACCIDENTS AND REPAIRS IN TUNNELS 301 CHAPTER XXII. ACCIDENTS AND REPAIRS IN TUNNELS DURING AND AFTER CONSTRUCTION. In the excavation of tunnels it often happens that the dis- turbance of the equilibrium of the surrounding material by the excavation develops forces of such intensity that the timbering or lining is crushed and the tunnel destroyed. To provide against accidents of this kind in a theoretically perfect manner would require the engineer to have an accurate knowledge of the character, direction and intensity of the forces developed, and this is practically impossible, since all of these factors differ with the nature and structure of the material penetrated. The best that can be done, therefore, is to determine the general character and structure of the material penetrated, as fully as practicable, by means of borings and geological surveys, and then to employ timbering and masonry of such dimensions and character as have withstood successfully the pressures devel- oped in previous tunnels excavated through similar material. If, despite these precautions, accidents occur, the engineer is compelled to devise methods of checking and repairing them, and it is the purpose of this chapter to point out briefly the most common kinds of accidents, their causes, and the usual methods of repairing them. Accidents During Construction. — Accidents may happen both during or after construction, but it is during construction, when the equilibrium of the surrounding material is first disturbed, and when the only support of the pressures developed is the timber strutting that they most commonly occur. 302 TUNNELING Causes of Collapse. — Collapse in tunnels may be caused : (1) by the weight of the earth overhead, which is left unsupported by the excavation ; (2) by defective or insufficient strutting ; and (3) by defective or weak masonry. (1) The danger of collapse of the roof of the excavation is influenced by several conditions. One of these is the method of excavation adopted. It is obvious that the larger the volume of the supporting earth is, which is removed, the greater will be the tendency of the roof to fall, and the more intense will be the pressures which the strutting will be called upon to support. Thus the English and Austrian methods of tunneling, where the full section is excavated before any of the lining is placed, and where, as the consequence, the strutting has to sustain all of the pressures, present more likehhood of the roof caving in than any of the other common methods. The character and structure of the material penetrated also influence the danger of a collapse. A loose soil with little cohesion is of course more likely to cave than one which is more stable. Rock where strata are horizontal, or which is seamy and fissured, is more likely to break down under the roof pressures than one with vertical strata and of homogeneous structure. Soft sod containing boulders whose weight develops local stresses in the roof timbering is likely to be more danger- ous than one which is more homogeneous. A factor which greatly increases the danger of collapse, especially in soft soils, is the presence of water. This element often changes a soil which is comparatively stable, when dry, into one which is highly unstable and treacherous. The liability of the material to disintegration by atmospheric influences and various other conditions, which will occur to the reader, may influence its stability to a dangerous extent, and result in collapse. (2) Collapse is often the result of using defective or insuf- ficient strutting. Of course, in one sense, any strutting which fails under the pressures developed, however enormous they may be, can be said to be insufficient, but as used here the term ACCIDENTS AND REPAIRS IN TUNNELS 303 means a strutting with an insufficient factor of safety to meet probable increases or variations in pressure. Insufficient strut- ting may be due to the use of too light timbers, to the spacing of the roof timbers too far apart, to the yielding of the founda- tions, to insufficient bearing surface at the joints, etc. Collapse is often caused by the premature removal of the strutting dur- ing the construction of the masonry. The masons, to secure more free space in which to work, are very likely, unless watched, to remove too many of the timbers and seriously weaken the strutting. (3) The third cause of collapse is badly built masonry. Poor masonry may be due to the use of defective stone or brick, to the thinness of the lining, to poor mortar, to weak centers which allow the arch to become distorted during construction, to poor bonding of the stone or bricks, to the premature removal of the centers, to driving some of the roof timbers inside it, etc. Prevention of Collapse. — Tunnels very seldom collapse with- out giving some previous warning of the possible failure, and also of the manner in which the failure is likely to occur. From these indications the engineer is often able to foresee the nature of the danger and take steps to check it. The danger may occur either during excavation or after the lining is built. During excavation the danger of collapse is indicated before- hand by the partial crushing or deflection of the strutting tim- bers. If the timbers are too light or the bearing surfaces are too small, crushing takes place where the pressures are the greatest, and the timbers bend, burst, or crack in places, and the joints open in other places. The remedy in such cases is to in- sert additional timbers to strengthen the weak points, or it may be necessary to construct a double strutting throughout. When the distance spanned by the roof timbers is too great, failure is generally indicated by the excessive deflection of these timbers, and this may often be remedied by inserting intermediate struts or props. In some respects the best remedy 304 TUNNELING under any of these conditions is to construct the masonry as soon as possible. When collapse is likely to occur after the masonry is com- pleted, its probability is generally indicated by the cracking and distortion of the lining. A study of the cause is quite likely to show that it is the percolation of water through the material surrounding the lining which causes cavities behind the lining in some places, and an increase of the pressures in other places. When it is certain that this water comes from the surface streams above, these streams may often be diverted or have their beds lined with concrete to prevent further perco- lation. When percolating water is not the cause of the trouble, a usually efficient remedy is to sink a shaft over the weak point, and refill it with material of more stable character. These, and the remedies previously suggested, are designed to prevent failure without resorting to reconstruction. When they or similar means prove insufficient, reconstruction or repairs have to be resorted to. Repairing Failures. — Tunnels may collapse in several ways : (1) The front and sides of the excavation may cave in; (2) the floor or bottom may bulge or sink ; (3) the roof may fall in; (4) the material above the entrances may slide and fill them up. (1) One of the most common accidents is the caving of the front and sides of the excavation. This may often be prevented by taking care that the face of the excavation follows the natu- ral slope of the material instead of being more or less nearly vertical. When, however, caving does occur it may usually be repaired by removing the fallen material, strongly shoring the cavity, and filling in behind with stone, timber, or fascines. (2) The bulging or rising of the bottom of the tunnel may usually be considered as a consequence of the squeezing together of the side walls. It usually occurs in very loose soils, and is chiefly important from the fact that the reconstruction of the side walls is made necessary. The sinking of the tunnel bot- ACCIDENTS AND REPAIRS IN TUNNELS 305 torn is a more serious occurrence. It seldom happens unless there is a cavity beneath the floor, due either to natural causes or to the fact that mining operations have gone on in the hill or mountain penetrated by the tunnel. When the bottom of the tunnel sinks, three cases may be considered : (a) when the sinking is limited to the middle of the tunnel floor ; (6) when only a portion of the foundation masonry is affected ; and, ((?) when the entire lining is disturbed. In the first case repairs are easily made by filling in the cavity with new material. In the second case the unimpaired portion of the masonry is tem- porarily supported by shoring while the injured portion is re- moved and rebuilt on a firm foundation. The remaining cavity is then filled. In the case of the complete failure of the lining, the method of repairing employed when the roof falls, and described below, is usually adopted. (3) The most dangerous of all failures is the falling of the tunnel roof. In such casualties two cases may be considered : (a) When the falling mass completely fills the tunnel section, and (5) when it fills only a portion of the section. When the whole section is filled by the fallen material, the problem may be considered as the excavation of a new tunnel of short length inside the old tunnel, and under rather more difficult conditions. The first task, particularly if men have been imprisoned behind the fallen material, is to open com- munication through it between the two uninjured portions of the tunnel. It is advisable to do tliis even when there is no danger to life because of imprisoned workmen, since it enables the work of repairing to be conducted from both directions. The excavation of a passageway through the fallen material is rendered difficult, both because the fallen material is of an unstable character, and also because it is usually filled with the hning masonry, timbering, etc. When, therefore, the accident has happened before the full section of the original material has been removed, the first heading or drift is driven through this original material rather than through the fallen debris. 306 TUNNELING Any of the regular soft-ground methods of tunneling may be employed, but it is usually better to select one which allows the masonry to be built with as little excavation as possible at first. For this reason the German method of tunneling is par- ticularly suited to repair work of this nature. The Belgian method may also be used to advantage, particularly w^hen the caving extends to the surface of the ground above, and the upper portion of the debris is, therefore, practically the same material as that through which the original tunnel was driven. The greatest defect of the Belgian method for making repairs is that the roof arch is supported by a rather unstable mass of Fig. 152.— Tunneling tlirougli Caved Material by Heading. mingled earth, stone, and timber, which constitutes the bottom layer of the fallen material. The method of strutting the work when the German or Belgian method is used is shown by Fig. 152. It sometimes happens that the fallen debris is so un- stable that it will not carry safely the arch masonry in the Belgian method or the strutting in the German method, and in these cases one of the full-section methods of excavation is usually adopted. The nature of the strutting employed is shown by Fig. 153. When the section has been opened and the new masonry built, great care should be taken to fill the ca\dty behind the masonry with timber or stone ; and should ACCIDENTS AND REPAIRS IN TUNNELS 307 the disturbance reach to the ground surface it is often a good plan to sink a shaft through the disturbed material, and fill it with more stable material. Fig. 153. —Tunneling through Caved Material by Drifts. When the fallen debris fills only a part of the section, the first thing to provide against is the occurrence of any further caving ; and this is usually done by building a protecting roof above the line of the future roof masonry. Figs. 154 and 155 Figs. 154 and 155. —Filling in "Roof Cavity Formed by Falling Material, show two methods of constructing this temporary roof, which it will be noticed is filled above with cordwood packing. As soon as the temporary roof is completed, the lining masonry is. constructed. 308 TUNNELING (4) Landslides which close the tunnel entrance are repaired in a variety of ways. Fig. 156 shows a common method of preventing the extension of a landslide which has been started Fig. 156. —Timbering to Prevent Landslides at Portal. by the excavation for the entrance masonry. Fig. 157 shows a method often adopted when the slope is quite flat and the amount of sliding material is small. It consists essentially of removing the fallen material and building a new portal farther back ; that is, the open cut is extended and the tunnel is shortened. When the amount of the sliding material is very large, the contrary practice of lengthening the tunnel and shorten- ing the open cut, as shown by Fig. 158, may be adopted. Accidents After Construction. — Accidents after the comple- tion of the tunnel may be divided into two classes: first, those which entirely obstruct the passage of trains, of which the collapse of the roof is the most common ; and second, those which allow traffic to be continued while the repairs are being made, Fig. 157. •Shortening Tunnel Cruslied by Landslide at Portal. ACCIDENTS AND REPAIRS IN TUNNELS 309 such as the bulging inward of a portion of the lining without total collapse. In the first case the first duty of the engineer is to open communication through the fallen debris, so that passengers at least may be transferred from one part of the tunnel to the other and proceed on their way. This is done by driving a heading, and strongly timbering it to serve as a passageway. If the tunnel is single tracked this heading is afterwards enlarged until the whole section is opened. In double-track tunnels the method generally adopted is to open first one side of the section and timber it strongly, so as to clear one track for traffic. While the trains are run- ning through this temporary passageway the other half of the section is opened and re- paired ; the traffic is then shifted to the new permanent track, and the temporary structure first employed is replaced with a permanent When the accident is that the repairs can b made without ob- structing traffic en- tirely, various -p^^ jgg — Extending Tunnel through Landslide at Portal. modes of procedure are followed. In all cases great care has to be exercised to prevent accident to the trains and to the tunnel workmen. The work should be done in small sections so as to disturb as little as possible the already troubled equilibrium of the soil ; the strutting should be placed so as to give ample clearing space to passing trains, and the trains themselves should be run at slow speeds past the site of the repairs. To illustrate the two kinds of accidents and the methods of repairing them, which have been mentioned, the accidents at the Giovi tunnel in Italy and at the Chattanooga tunnel in America have been selected. Giovi Tunnel Accident. — In September, 1869, at a point about 310 TUNNELING 220 ft. from the south portal of the Giovi tunnel, a disturbance of the masonry linmg for a length of about 52 ft. was observed. Accurate measurements showed that the lining was not sym- metrical with respect to the vertical axis of the sectional profile. It was concluded that omng to some disturbance of the sur- rounding soil unsymmetrical vertical and lateral pressures were acting on the masonry. Close watch was kept of the dis- torted masonry, which for some time remained unchanged in position. In 1872, however, new crevices were observed to have developed, and shortly afterwards, in January, 1873, the injured portion of the masonry caved in, obstructing the whole tunnel section. The fallen material consisted chiefly of clay in a nearly plastic state. The surface of the ground above was observed to have settled. Investigation showed also that the cause of the caving was the percolation of water from a nearby creek. The water had soaked the ground, and decreased its stability to such an extent that the masonry lining was unable to withstand the increased vertical and lateral pressures. The mode of procedure decided upon for repairing the damage was : (1) To open at least one track for the temporary accommodation of traffic ; (2) To remove permanently the causes which had produced the collapse ; (3) To build a new and much stronger lining. Close to the western side wall, which was still standing, the debris was removed, and the opening strongly strutted in order to allow the laying of a single track to reestablish communication. At the same time a shaft was sunk from the surface above the caved portion of the tunnel, for the double purpose of facilitating the removal of the fallen material and of affording ventilation. The depth of the surface above the tunnel was 41.6 ft., which made the construc- tion of the shaft a comparatively easy matter. The shaft itself was 6^ ft. wide and 18 ft. long, with its longer dimensions parallel to the tunnel, and it was lined with a rectangular horizontal frame and vertical-poling board construction. After tem- ACCIDENTS AND REPAIRS IN TUNNELS 311 porary communication had been opened on the western track of the tunnel, the remainder of the fallen earth was removed and the excavation strutted. The new masonry lining was then built. To remove permanently the cause of the cave-in, which was the percolation of water from a close-by stream, this stream was diverted to a new channel constructed with a concrete bed and side walls. The failure of the original lining occurred by cracks develop- ing at the crown, haunches, and springing lines. The new lining was made considerably thicker than the original lining, and at the points where failure had first occurred in the original arch cut-stone voussoirs were inserted in the brickwork of the new arch as described in Chapter XIII. Chattanooga Tunnel. — The Western & Atlantic Ry. passes through the Chattanooga mountains by means of a single-track tunnel 1,477 ft. long, constructed in 1848-49. The lining con- sisted of a brickwork roof arch and stone masonry side walls. After the tunnel had been opened to traffic, this lining bulged inward at places, contracting the tunnel section to such an ex- tent that it was decided to reconstruct the distorted portions. After careful surveys and calculations had been made, it was decided to take down and reconstruct about 170 ft. of the lining. Owing to contracted space in the tunnel, it was necessary to remove all men, tools, and material, whenever trains were to pass through ; and in order to do this a work-train of three cars was fitted up with necessary scaffolds, and supplied with gasoline torches for lighting purposes. Mortar was mixed on the cars, and all material remained on them until used. Debris torn out of the old wall was loaded on the cars, and hauled to the waste dump. A siding was built near the West end of the tunnel for the use of this train, and a telephone sys- tem was installed between the entrances and the working-train. On account of the contracted working-space and the greater 312 TUNNELING ease with which brick could be handled, it was decided to re- build the walls out of brick instead of stone. In tearing out the old wall a hole was first cut through the three bottom courses of the arch and gradually widened. When the opening became four or five feet long, a small jack was placed near the center of it and brought to a bearing against the arch to sustain it. After cutting the opening to a length of from 7 to 10 ft. depending on the stability of the earth backing, the jack was removed and a piece of 8x16 in. timber placed under the arch and brought up to a bearing with jacks. One end of the timber rested on the old wall, the other on a seat built into the adjoining section of new wall. Wedges were then driven under the ends of timber and the jacks removed. With this timber in place, the old wall could be taken down with ea§e, the only trouble being that small stones and earth fell in from above and behind the arch. This was obviated by placing a 2 in. plank across the opening and just back of the 8x16 in. timber. At several points, however, the earth backing was saturated with water, and it became necessary to put in lagging as the old wall was removed. This timbering would be taken out as the new work was built up. A suitable foundation for the new wall was secured at a depth from 2 to 4 ft., and a concrete footing was used. The section of the new wall was then built up as near as possible to the 8x16 in. timber; the timber was then removed and the new wall built up and keyed under the arch. The new wall had a minimum width of 2^ ft. at the top, and 4 ft. at the base of rail, and was provided with weep holes at intervals. To facilitate matters, work was carried on simul- taneously at two or three different places, the intention being to get one place torn out and ready for the bricklayers by the time they completed a section of the new wall at another place. In rebuilding the arch, sections extending from the spring- ing line up as far as was necessary to obtain the desired clear- ACCIDENTS AND REPAIRS IN TUNNELS 313 ance, and from 2i to 4 ft. in length, were removed. Near the sides, the earth above the arch was a stiff clay, which was self- sustaining; but near the center there occurred a stratum of gravel and clay saturated with water. This gave considerable trouble, falling through almost continuously until timbering could be placed. One end of this timber rested on the old arch, the other on the adjoining section of the new work. As the new work was to be set 6 to 13 ins. back from the old, it was necessary to block up this distance on top of the old arch, to carry the end of the lagging timber, in order that the timber should be clear of the new arch. Owing to the small clearance between the car roof and the arch, a special form of centering was required, one that would occupy as small space as possible. Bar iron 1 in. thick, 4 ins. wide, and 20 ft. long was curved to a radius of 6i ft., and on the underside of this was riveted a 6-in. plate i in thick. This plate projected 1 in. on the sides of the centering, and carried the ends of the 1 in. boards used for lagging. The rivets were counter-sunk on the outside of the centering to present a smooth surface next the arch. In keying up a section of the new work, a space about 18 ins. square had to be left open for the use of the workmen. As soon as the next section had been torn out, this space was built up. In building up the last section, this space had to be filled from below, which proved to be a tedious undertaking. The opening was gradually reduced to a size of 10 x 18 in., and the top ring then completed and keyed up, the adhesion of mortar holding the bricks in place until the key could be driven home. The next ring was treated in a similar manner, and so on to the face ring. Altogether 412 lin. ft. of the walls and 178 lin. ft. of the arch were taken down and rebuilt, amounting in all to 607 cu. yds. of masonry at the total cost of 17,440, or about 112.25 per cu. yds. The regular trains arrived so frequently at the tunnel that slightly over two hours was the longest working-time between 314 TUNNELING any two trains, and usually less than one hour at a time was all that it could be worked. In addition to the regular trains, a large number of extra trains, moving troops, had to be accom- modated. Work was in progress eight months, and during that time there was no delay to a passenger train. The repairs were completed in August, 1899. The work was under the direction of Mr. W. H. Whorley, engineer of the Western & Atlantic R. R., and foreman of construction, A. H. Richards. A recent examination failed to reveal any sign of settlement cracks at the junction points of the new and old work. RELINING TIMBER-LINED TUNNELS WITH MASONRY 315 CHAPTER XXIII. RELINING TIMBER-LINED TUNNELS WITH MASONRY. The original construction of many American railway tunnels with a timber lining to reduce the cost and hasten the work has made it necessary to reline them, as time has passed, with some more permanent material. In most cases the work of removing the old lining and replacing it with the new masonry has had to be done without interfering with the running of trains, and a number of ingenious methods have been developed by engineers for accomplishing this task. Three of these methods which have been employed, respectively, in relining the Boulder tunnel on the Montana Central Ry., in Montana, the MuUan tunnel on the Northern Pacific Ry., in Montana, and the Little Tom tunnel on the Norfolk & Western R. R., in Virginia, have been selected as fairly representative of this class of tunnel work. Boulder Tunnel. — This tunnel penetrates a spur of the main range of the Rocky Mountains, at an elevation at the summit of grade of 5,454 ft., and is 6,112 ft. in length. Its alignment is a tangent, with the exception of 150 ft. of 30' curve at the north end. The material penetrated is blue trap-rock with seams for 4,950 ft. from the north end, and syenitic boulders with the intervening spaces filled with disintegrated material for the remaining 1,160 ft. The dimensions and character of the old timber lining and of the new masonry lining replacing it are shown in Figs. 141 and 142. The form of masonry adopted consisted of coarse rubble side walls of granite, 13 ft. 8 ins. high, and generally 20 ins. thick, 316 TUNNELING with a full center circular arch of four rings of brick laid in rowlock form. When greater strength was needed the thick- ness of the side walls was increased to 30 ins. and that of the arch to six rings of brick. The first plan adopted in putting in the masonry was to remove all the timbering ; but owing to the large number of falls and slides this was abandoned, and the plan followed was to leave in the three roof segments of the timbering with the over- lying cord-wood packing and debris. In carrying on the work the first step was to remove the side timbers. This was done by supporting the roof timbers, as shown in Fig. 159 ; that is, the first and fourth arch rib of an 8-ft. section containing four Cross Sertion. Uinaitudinal Section. Cross Section. Figs. 159 and 160.— Relining Timber-Lined Tunnel. Cross Section. arch ribs were supported by temporary posts. The intermedi- ate arch ribs were supported against the downward pressure by 6 X 6 in. timbers, extending from the side ribs near the tops of the temporary posts to the opposite sides of the intermediate roof segments, as shown in the longitudinal section. Fig. 160. To resist the pressure from the sides, 4 X 6 in. braces were placed across the tunnel from near the center of the intermedi- ate segments to the upper ends of the hip segments, as shown in the cross-section. Fig. 159. The hip segments were then sawed off below the notch, and the side timbering removed and the masonry built. The stone was conveyed into the tunnel on flat cars, and laid by means of small derricks located on the cars. Two derricks EELINING TIMBER-LINED TUNNELS WITH MASONRY 317 were used, one for each side wall, and the work on both walls was carried on simultaneously. The arch was built upon a centering, the ribs of which were 5i ins. less in diameter than the distance between the side walls, so as to permit the use of 2| ins. lagging. Each center had three ribs, made in 1-in. or 2-in. board segments, 10 ins. thick and 14 ins. deep. These ribs were mounted on frames, which followed the opposite walls, and were 4 ft. apart, making the total length of the center out to out about 9 ft. The frames, upon which the ribs were supported, are shown in Fig. 161. As will be seen, they were mounted on dollys to enable the center to be moved from one section to another. Jacks were used to raise and lower the center into its proper position. The arch was built up from the springing lines on both sides at the same time, four masons being employed. The rings were built beginning with the intrados, which was brought up, say, a dis- tance of about 2 ft. from the springing line. Then the back of the ring was well plastered with from | in. to i in. of mortar, and the second ring brought up to the same height and plastered on the back, and so on until the last ring was laid. After bringing the full width of the arch up some distance, new laggings were placed on the ribs for an additional height of 2 ft. and the same process was repeated. All the space between the extrados of the masonry arch and the old lining was compactly filled with dry rubble. When high enough so that the hip segments had a foot or more bearing on the masonry the segments were securely wedged and blocked up against the brickwork, and the longitudinal 4 X 6 in. timbers Cross Section. longitudinal Section. «»«• Fig. 161.— Relining Timber-Lined Tunnel, Great Northern Ry. 318 TUNNELING removed. The remaining space was now clear for completion of the arch, and both sides were brought up until there was not sufficient space for four masons to work, when the keying was completed by two masons beginning at the completed and working back toward the toothed end. The brickwork was built from the top of a staging-car. In a few instances where slides occurred after the removal of the slide timbering, the method of re timbering the tunnel shown in Fig. 162 was adopted. Two side drifts were first run 2i ft. wide by 4 ft. high, and the plate timbers placed in position and blocked. Cross drifts were then run, and the roof segments placed, and the core down to the level of the bottoms of the side drifts taken out. The lower wall plates were then placed and the hip segments inserted. The bench was then taken down by degrees, the side plates being held by jacks, and the posts placed one at a time. As the masonry at the points where slides occur consists of 30-in. walls and six-ring arch, the timbering was 22 ft. wide in the clear, with other dimensions as shown in Fig. 162. Only a single crew of brick and stone masons was employed. In order to prepare the sections for these masons it was necessary to have timber and trimming crews at work through- out the whole day of 24 hours, so that an engine and two train crews were in constant attendance. The single mason crews were able to complete 8 ft. of side wall and arch in 24 hours. The number of men actually employed at the tunnel was 35. This included electric-light maintenance, and all other labor pertaining to the work. The tunnel was lighted by an Edison Cross Section Fig. 162. Longitudinal Section. Relining Timber-Lined Tunnel, Great Northern Ey. RELINING TIMBER-LINED TUNNELS WITH MASONRY 319 dyiiamo of 20 arc light capacity, one arc light being placed on each side of the tunnel at all working-places. Each lamp carried a coil of wire 20 or 30 ft. long to allow it to be shifted from place to place without delay. Mullan Tunnel. — This tunnel is 3,850 ft. long, and crosses the main range of the Rocky Mountains, about 20 miles west of Helena, Mont. The tunnel is on a tangent throughout, and has a grade of 20 % falling toward the east. The summit of the grade, west of the tun- nel, is 5,5^8 ft. above sea level, and the mountain above the line of the tunnel rises to an elevation of 5,855 ft. Owing to the treacherous nature of the material through which the tunnel passed, it had been a constant menace to traffic ever since its con- struction in 1883, and numer- ous delays to trains had been caused by the- falls of rock and fires in the timber lin- ing. For these reasons it was finally decided to build a per- manent masonry lining, and work on this was begun in July, 1892. The original timbering consisted of sets spaced 4 ft. apart c. to c, with 12 X 12 in. posts supporting wall plates, and a five-segment arch of 12 x 12 in. timbers joined by li-in. dowels. The arch was covered with 4-in. lagging, and the space between this and the roof was filled with cordwood. Except where the width had been reduced by timbering placed inside the original timbering to increase the strength, the clear width was 16 ft., and the clear height 20 ft. above the top of the rail. Fig. 163 shows the timbering and also the form Permanent Work Fig. 163. — Reliuing Timber Lined Tunnel, Great Northern Ry. 320 TUNNELING of masonry lining adopted. The side walls are of concrete and the arch of brick. This new masonry, of course, required the removal of all the original timbering. The manner of doing this work is as follows : A 7-ft section, A B, Fig. 164, was first prepared by removing one post and supporting the arch by struts, aS' S. After clearing away any backing, and excavating for the foundation of the side wall, two temporar}^ posts, F F, were set up, and fastened by hook bolts. Fig. 146, X, and a lagging was built to form a mold for the concrete. Several of these 7-ft. sections were prepared at a time, each two being sepa- rated by a 5-ft. section of timbering. ^ f' F LassM. F 1 1 r 1 ^ m ^ Uiqqmq _ ,, , _ ~I -" "- ''■r" With Wall.Plate. _ Wirtiout Wojl Plate. SecHon ,wHh Concrete Osr^ tongitudinal Sectiorx. Fig. 164. — Construction of Centering Mullan Tunnel. The mortar car was then run along, and enough mortar (1 cement to 3 sand) was run by the chute into each section to make an 8-in. layer of concrete. As the car passed along to each section, broken stone was shoveled into the last preced- ing section until all the mortar was taken up. The walls were thus built up in 8-in. layers, and became hard enough to sup- port the arches in about 10 to 14 days. The arches were then allowed to rest on the wall, and the posts of the remaining 5-ft. sections were removed, and the concrete wall built up in the same way as before. RELINING TIMBER-LINED TUNNELS WITH MASONRY 321 The average progress per working-day was 30 ft. of side wall, or about 45 cu. yds. ; and the average cost, including all work required in removing the timber work, train service, lights and tools, engineering and superintendence, and interest on plant, was |8 per cubic yard. The centering used for putting in the brick arches is shown in Fig. 165. From 3 ft. to 9 ft. of arch was put in at a time, the length depending upon the nature of the ground. To re- move the old timber arch, one of the segments was partly sawed through; and then a small charge of giant powder was exploded in it, the resulting debris, cordwood, rock, etc., being caught by a platform car ex- tending underneath. From this car the debris was re- moved to another car, which conveyed it out of the tunnel. The center was then placed and the brickwork begun, the cement car shown in Fig. 164 being used for mixing the mortar. The size of the bricks used was 2^ + 2^ + 9 ins., four rings making a 20- in. arch and giving 1.62 cu. yds. of masonry in the arch per lin. ft. of tunnel. The bricks were laid in rowlock bond, two gangs, of three bricklayers and six helpers each, laying about 12 lin. ft. per day. The brickwork cost about |17 per cu. yd. The total cost of the new lining averaged about |50 per lin. ft. Little Tom Tunnel. — The tunnel has a total length of 1,902 ft., but only 1,410 ft. of it were originally hned with timber. This old timber lining consists of bents spaced 3 ft. apart, and located as shown by the dotted lines in the cross-section. Fig. 166. Instead of renewing this timber, it was decided to replace it with a brick lining. Although the tunnel was constructed Fig. 165.— Centering Mullan Tunnel. 322 TUNNELING RELINTNG TIMBER-LINED TUNNELS WITH MASONRY 323 through rock, this rock is of a seamy character, and in some portions of the tunnel it disintegrates on exposure to the air. In removing tlie timber to make place for the new lining some of the roof was found close to the lagging, but often also con- siderable sections siiowed breakages in the roof extending to a height varying from 1 ft. to 12 ft. above the upper side of the timbering. This dangerous condition of the roof made it neces- Fig. 167 — flelining Timber-Lined Tunnel, Norfolk and Western Ky. sary that only a small section of the timber lining should be removed at one time. It made it necessary, also, that the brick arch should be built quickly to close this opening, and finally that all details of centers, etc., should be arranged so as to furnish ample clearance to trains. The accompanying illustra- tions show the solution of the problem which was arrived at. Referring to the transverse and longitudinal sections shown 324 TUNNELING by Fig. 166, it will be seen that two side trestles were built to carry an adjustable centering for the roof arch. Two sections of these trestles and centerings were used alternately, one being carried ahead and set up to remove the timbering while the masons were at work on the other. The manner of setting up and adjusting the trestles and centerings is shown by Fig. 148 and also by Fig. 167, which is an enlarged detail drawing of the set screw and rollers for the centering ribs. The following is the bill of material required for one set of trestles and one center : Trestles : Caps and sills 8 pieces 8x8 ins. x 20 ft. Posts . 18 " 8 X 8 " X 11 " Braces 16 " 6x 4 " x 7" Centerings : Ribs 27 " 2 X 18 " X 7 " Bracing 12 " 2 x 8 " x 7 " Support to crown lagging 2 " 6 x 6 " x 10 " Crown lagging 20 " 3x 6 " X 2" Side lagging 30 " 3 x 6 " x 10 " Side strips 2 " 2 x 12 " x ^ " Blocking for rollers 1 " 5 x 8 " x 12 " 6 screw and roller castings complete with bolts and lever ; 114 bolts i-ins. in diameter ; 7? U. H. hexagonal nut and 2 cast washers each. With this arrangement the progress made per day varied from 2 lin. ft. to 3 lin. ft. of lining complete. By work com- plete is meant the entire lining, including stone packing between the brickwork and the rock. On Feb. 23, 1900, 363 ft. of lin- ing had been completed, at a cost of |33.50 per lin. ft. This cost includes the cost of removing the old timber, the loose rock above it, and all other work whatsoever. VENTILATION AND LIGHTING DURING CONSTRUCTION 325 CHAPTER XXIV. THE VENTILATION AND LIGHTING OF TUN= NELS DURING CONSTRUCTION. VENTILATION. In long tunnels, especially when excavated in hard rock, proper ventilation is of great importance, because the air cannot be easily renewed, and the amount of oxygen consumed by miners horses and lamps during construction is very large. The gases produced by blasting also tend to fill the head of ex- cavation with foul air. Pure atmospheric air contains about 21 % of oxygen and only 0.04 % of carbonic acid ; when the latter gas reaches 0.1 %, the fact is indicated by the bad odor; at 0.3 % the air is considered foul, and when it reaches 0.5 ^o it is dangerous. It is generally admitted that the standard of purity of the air is when it contains 0.08 % of carbonic acid. A large quantity of carbonic acid in the air is easily detected by observing the lamps, which then give out a dim red light and smoke perceptibly ; the workmen also suffer from headache and pains in the eyes, and breathe with difficulty. Naturally, miners cannot easily work in foul air and, therefore, make very slow progress. It is, therefore, to the interest of the engineer to afford good ventilation, not only because of his duty to care for the safety and health of his men, but also for reasons of econ= omy, so that the men may work with the greatest possible ease, thus assuring the rapid progress of the work. It would be impossible to change completely the atmosphere inside a tunnel, as the gases developed from blasting will pene- trate into all the cavities and gather there, but the fresh air 326 TUNNELING carried inside by ventilation has a very small percentage of car- bonic acid, mixes with that which contains a greater quantity, and dilutes it until the air reaches the standard of purity. We have not here considered the gases developed from the decom- position of carboniferous and sulphuric rocks, which may be met with in some tunnels, and which render ventilation still more necessary. Tunnels may be ventilated either by natu- ral or artificial means. Natural Ventilation. — It is well known that if two rooms of different temperatures are put in communication with each other, e.g., by opening a door, a draft from the colder room will enter the other from the bottom, and a similar draft at the top, but with a contrary direction, will carry the hot air into the colder room, thus producing perfect ventilation, until the two rooms have the same temperature. Now, during the construc- tion of tunnels the temperature inside may be considered as constant, or independent of the outside atmospheric variations ; hence during summer and winter, there will always be a draft affording ventilation, owing to the difference of temperature in- side and outside the tunnel. In winter time the cold air out- side will enter at the bottom of the entrances and headings, or along the sides of the shafts, and the hot air will pass out near the top of the headings or entrances or the center of the shafts ; in summer the air currents will take the contrary direction. Natural ventilation in tunnels is improved when the exca- vation of the heading reaches a shaft, because the interior air can then communicate with the exterior at two points, at dif- ferent levels. In such cases a force equal to the difference in weight between a column of air in the shaft and a similar one of different density at the entrance of the tunnel, will act upon the mass of air in the tunnel and keep it in movement, thus producing ventilation. Consequently, during winter, when the outside air has greater weight than that inside, the air will come in by the headings and go out by the shaft, and in the summer it will enter at the shaft and pass out at the entrance. VENTILATION AND LIGHTING DURING CONSTRUCTION 327 Sometimes to afford better ventilation shafts 8 or 12 in. in di- ameter are sunk exclusively for the purpose of changing the air. When the inside temperature is equal to that outside, as often happens during the spring and autumn, there are no drafts, and consequently the air in the excavation is not re- newed and becomes foul ; then fires are lighted under the shaft and a draft is artificially produced. The hot air going out through the shaft, as through a chimney, allows the fresh air to come in as in ordinary ventilation. When the head of the excavation is very far from the en- trances, or when the mountain is too high to allow excavation by shafts, it is quite impossible to secure good natural ventila- tion, especially during the spring and autumn months, and the engineer has to resort to some artificial means by which to supply fresh air to the workmen. Artificial Ventilation. — Artificial ventilation in tunnels may be obtained in two different ways, known as the vacuum and plenum methods. Their characteristic difference consists in this, that in the vacuum method the air is drawn from the in- side and the vacuum thus produced causes the fresh air from the outside to rush in, while the plenum method consists in forcing in the fresh air which dilutes the carbonic air produced inside the tunnel by workingmen and explosives. In the vac- uum method the pressure of the atmosphere inside the tunnel is always less than the pressure outside, while in the plenum method the pressure within is always greater than that outside. Ventilation is the result of this difference of pressure, as the tendency of the air toward equilibrium produces continuous drafts. Both these methods have their advantages and disad- vantages ; but in the presence of hard rock, when explosives are continually required, the vacuum method is considered the best, because the gases attracted to the exhaust pipes are expelled without passing through the whole length of the tunnel, thus avoiding the trouble that a draft of foul air will give to the workmen who are within the tunnel. In both these methods it 328 TUNNELING is necessary to separate the fresh air from the foul one ; and this is done by means of pipes which will exhaust and expel the foul air in the vacuum method, or force to the front a current of fresh air when the plenum method is used. Artificial venti- lation may also be obtained by compressed air which is set free after it has driven the machines, especially in tunnels excavated through rock, when rock drilling machines moved by com- pressed air are employed. Vacuum Method Contrivances. — The most common of the vac- uum appliances consists in the simple arrangement of a pipe leading from the head of the tunnel out through the fire of a furnace. The air in the pipe is rarefied by the heat of the fur- nace and then set free from the other end of the pipe, thus creating a partial vacuum in the pipe, into which the foul air of the head rushes, the fresh air from the entrance taking its place, and thus ventilating the tunnel. A similar arrangement may be used with shafts, and the foul air may be driven out by a furnace which is placed either at the top or bottom of the shaft. Such furnaces act the same as those commonly used for heating purposes in the houses, with this difference, that, instead of fresh air being forced in, foul air is expelled. Another simple arrangement for producing a vacuum is by means of a steam, jet which is thrown into the pipe, and which helps the expul- sion of the air by heating it, thus producing a different density which originates a draft besides that mechanically originated by the force of the steam jet, which tends to carry out the foul air of the pipes. Foul air may also be expelled by means of exhaust fans which are connected with pipes near the entrance of the tunnel. The fan consists of a box containing a kind of a paddle wheel turned by steam or water power and arranged so as to revolve at a high speed. The air inside the pipe is forced out by blades attached to the wheel, and thus the foul air of the front is driven away and fresh air from the entrance rushes in to take its place, and perfect ventilation is obtained. VENTILATION AND LIGHTING DURING CONSTRUCTION 329 The best manner of expelling foul air from tunnels, accord- ing to the vacuum method, is by means of bell exhausters. This consists of two sets of bells connected by an oscillating beam and balancing each other. Each set consists of a movable bell, which covers and surrounds a fixed bell with a water joint. In the central part of the fixed bell there are valves which open upwards, and on the bottom of each movable bell there are valves which open from the outside. When one bell ascends, the valves at the bottom are closed, the air beneath is then rarefied, and a vacuum is produced ; the valves in the central part of the fixed bell filled with water are opened, and there is an aspiratory action from the pipe leading to the headings, and the foul air is thus carried away. The apparatus makes about ten oscillations per minute, and the dimensions of the bells depend upon the quantity of air to be exhausted in a minute. In the St. Gothard tunnel, where these bell exhausters were used, they exhausted 16,500 cu. ft. of air per minute. Plenum Method Contrivances. — Fresh air may be driven into tunnels to dilute the carbonic acid by two different ways, viz., by water blast and by fans. Water when running at a great velocity produces a movement in the air which may be some- times usefully and economically employed for ventilating tunnels. Water falling vertically is let run into a large horizontal zinc pipe having a funnel at the outer end ; into this the air attracted by the velocity of the water is forced. By an opening at the bottom the water is afterward withdrawn from the pipe, and there remains only the air which is pushed for- ward by the air which is being continually sucked in by the velocity of the water. The best and most common means of ventilation by the plenum method is by fans. There are numerous varieties of these fans in the market, but they all consist of a kind of fan wheel which by rapid revolution forces the fresh air into the pipe leading to the headings of the tunnel or to the working places. Instead of a large single fan, such as is used for min- 330 TUNNELING ing purposes, it is better to have a number of small fans acting independently of each other, conveying the fresh air where it is needed through independent pipes. Saccardo's System. — A new method of ventilating tunnels was devised by Mr. Saccardo for the ventilation of the Pracchia tunnel along the Bologna and Lucca Railway in Italy. At the highest end of the tunnel the mouth was contracted inward in a funnel shaped form so as to just admit a train. Immediately at this contraction, a lateral tunnel, 50 feet long, branched off from one side of the main tunnel. At the mouth of this lateral tunnel was installed a fan which forced air into the tunnel and with 70 revolutions per minute delivered 3.532 cu. ft, of air per second at a water pressure of 1 in. This air current was directed inward through a second contraction or funnel, parallel to the 'One at the entrance and 23 ft. beyond it. In operation the action of the artificial air current was to suck in a considerable volume of outside air, while the air pressure was sufficient to counterbalance the movement of air produced by a train mov- ing at a velocity of 16.1 ft. per second. Mr. Saccardo ^s method was employed in ventilating a tunnel on the Norfolk and West- ern Railway with satisfactory results. Compressed Air. — In the excavation of tunnels in hard rock a number of rock drilling machines are employed which are moved by compressed air at a pressure of not less than five atmospheres. At each stroke about 100 cu. ins. of compressed air are set free, and at an average of 10 strokes per minute there would be 5000 cu. ins. of air at five atmospheres or 25,000 cu. ins., or a little more than 175 cu. ft. of fresh air at normal pressure set free every minute by each of the machines employed. But the air exhausted from the drilling machine is foul. Regarding ventilation by compressed air, Mr. Adolph Sutro, in a lecture delivered to the mining students of the University of Cahfornia, said: "T will note a curious fact which I have never seen explained, and which is worthy of close investigation by means of experiments. In the Sutro tunnel VENTILATION AND LIGHTING DURING CONSTRUCTION 331 we found that the compressed air used for driving the machine drills, after having been compressed and expanded and discharged from the drills, was not wholesome to breathe, and the men and mules would all crowd around the end of the blower pipe to get fresh air. Whether the air in being compressed has parted with some of its oxygen or because vitiated from some other cause, I do not know, and I Kope that this subject will at some future day be carefully examined into." In the December, 1901, number of ^^ Compressed Air,'^ a magazine especially devoted to the useful application of com- pressed air, is read : Compressed air wasted from power drills is so contaminated with oil from the cylinders that it cannot be taken into consideration as ventilation. It is as important to displace it with pure air as it is to drive out or draw off other viti- ated air. The ventilation should be an independent supply provided by fan or blower, delivering by pipe at the point where miners are working. Quantity of Air. — The quantity of air to be introduced into tunnels must be in proportion to the oxygen consumed by the men, the animals, and the explosions. It is allowed that the quantity of air required for breathing purpose and explosions is as follows: 1 workman with lamp needs 240 cu. yds. of fresh air in 24 hours. 1 horse " 850 '' " " 1 lb. gunpowder 100 " . " " 1 lb. dynamite 150 " " " In a long tunnel excavated through hard rock the number of workmen all together may be assumed at 400 at each end, and each workman is supposed to be furnished with a lamp. No less than ten horses are employed, and the average quantity of dynamite consumed is 600 lbs. per day. From the data given the consumption of air by workmen and lamps would be: 240 X 400 = 96,000 cu. yds.; the consumption of air by horses would be 850 X 10 = 8500 cu. yds.; the consumption of air by dynamite would be 150 X 600 =90,000 cu. yds.; making a total consumption of air per day of 194,500 cu. yds., or about 8000 cu. yds. per hour. To obtain good ventilation, then, it will be necessary to furnish every hour a quantity of fresh air amounting to not less 332 TUNNELING than 8000 cu. yds. Since, however, a large quantity of pure air is expelled with the foul air, it is necessary greatly to in- crease this quantity. It may be observed, in closing, that the water having its particles divided, as in a fog or mist, rapidly precipitates the gases produced by explosions. Now, when hydraulic machines are used, there is a hollow ball pierced by holes that are almost imperceptible, from which the compressed water spreads in very subtile particles, and this causes the fall of the gases from explosions. Such a method of precipitating gases is very good, but does not have the advantage of supplying new oxygen to replace that consumed by the men, animals, lamps, and ex- plosions; besides, it has the defect of increasing the quantity of water to be removed. In tunnels the pipes used either for con- veying the fresh air or for carrying away the foul air, are of iron, having a diameter of about 8 in.; they are fixed along the side walls about 3 ft. above the inverted arch. LIGHTING. The object and necessity of a perfect lighting of the tunnel- workings during construction are so obvious that they need not be enlarged upon. Comparatively few tunnels require lighting after completion; and these are generally tunnels for passenger traffic under city streets, of which the Boston Subway is a rep- resentative American example. Considering the methods of lighting tunnels during construction, we may, for sake of con- venience, chiefly, divide the means of supplying light into (1) lamps and lanterns usually burning oil; (2) coal-gas lighting; (3) acetylene gas lighting; and (4) electric lighting. Lamps and Lanterns. — Lamps and lanterns are commonly employed by engineers for making surveys inside the tunnel, and to light the instrument. For ranging in the center line, a con- venient form of lamp consists of an oil light inclosed in glass chimney covered with sheet metal, except for a slit at the front and back through which the light shines, and on which the VENTILATION AND LIGHTING DURING CONSTRUCTION 333 observer sights his instrument. To direct the operations of his rodmen the engineer usually employs a lantern, either with white or colored glass, much like the ordinary railway train- man's lantern, which he swings according to some prearranged code of signals. Lamps and lanterns are used by the workmen both for sig- naling and for lighting the workings. For signaling purposes red lanterns are usually placed to denote the presence of unex- ploded blasts or other points of possible clanger; and colored or white lights are usually placed on the front and rear of spoil and material trains. For hghting purposes, two forms of lamps are employed, which may be somewhat crudely designated as lamps for individual use and lamps for general lighting. Indi- vidual lamps are usually of small size, and burn oil; they may be carried in front of the miner's helmet, or be fixed to stand- ards, which can be set up close to the work being done by each man. Miners' safety lamps should be employed where there is danger from gas. A great variety of lamps for mining and tunneling purposes are on the market, for descriptions of which the reader is referred to the catalogues of their manu- facturers. Lamps for general lighting are always of larger size than lamps for individual use. A common form consists of a cyl- inder ten or twelve inches in diameter, provided with a hook or bail for suspension, and filled with benzine, gasolene, or other similar oil. Connected with this cylinder is a pipe of con- siderable length and small diameter through which the benzine or gasolene vapor runs, and burns when lighted with a brilliant flame. Lamps of this type burning gasolene were extensively employed in building the Croton Aqueduct tunnel. Various patented forms of lamps for burning coal-oil products are on the market, for descriptions of which the manufacturers' cata- logues may be consulted. Coal-gas Lig^hting. — A common method of Hghting tunnel workings is by piping coal-gas into the headings and drifts from 334 TUNNELING some nearby permanent gas plant, or from a special gas works constructed especially for the work. Gas lighting has the great advantage over lamps and lanterns of giving a light which is more brilliant and steady. Its great objection is the danger of explosion caused by leaks in the pipes, by breaks caused by flying fragments of rock, and by the carelessness of workmen who neglect to turn off completely the burners when they ex- tinguish the hghts. In nearly every tunnel where gas has been used for hghting, the records of the work show the occurrence of accidents which have sometimes been very serious, partic- ularly when fire has been communicated to the tunnel tim- bering. Acetylene Gas Lighting. — The comparatively recent develop- ment of acetylene gas manufactured from carbide of calcium has given little opportunity for its use in tunnel lighting, and the only instance of its use in the United States, so far as the author knows, is the water-works tunnel conduit for the city of Washington, D. C. Col. A. M. Miller, U. S. Engineer Corps, who is in charge of this work, describes the method adopted in his annual report for 1899 as follows : — "It had been the practice to do all work underground by the light of miners' lamps and torches. This means of illumination is very poor for me- chanical work. The fumes and smoke from blasting, added to the smoke from torches and lamps, render the atmosphere underground, especially when the barometer conditions were unfavorable to ventilation, very offensive and discomforting to the workmen. An investigation of the subject of lighting the tunnel by other means, more especially at the locality where the mechanics were at work, — brick and stone masons, and the workmen on the iron lining, — resulted in the selection of acetylene gas as the most available and eco- nomical in this special emergency. Accordingly, an acetylene gas plant for 300 burners was erected at Champlain- Avenue shaft, and one for 60 lights at Foundry Branch. The engine-houses at the shafts, the head-houses, and local- ities in the tunnel, when required, are lighted by these plants. ''Gas pipes were cariied down the Champlain- Avenue shaft and along the tunnel both in an easterly and westerly direction, with cocks for burners at proper intervals every 30 feet; and this system sufficed for illumination from Rock Creek to Harvard University, a distance of over two miles. The plant erected at Foundry Branch was in like manner utilized for the illumination from that point in both directions. "By connecting with the stopcocks by means of a rubber hose, a movable VENTILATION AND LIGHTING DURING CONSTRUCTION 335 light, chandelier, or 'Christmas-tree' of any required number of burners is used, thus concentrating the hght in the immediate vicinity of the work, and also enabling the illumination to be carried into the cavities or 'crow-nests,' so called, behind the defective old lining. "This method of illuminating has proved very satisfactory and quite eco- nomical. It is especially valuable as enabling good work to be done, and facilitating a thorough inspection of the same." Electric Lighting. — By far the most perfect, and at present the most commonly employed means for lighting tunnel work- ings, is electricity. The light furnished by electric lamps is steady and brilliant, and does not consume oxygen or give off offensive gases. The wires are easily removed and extended, and the lamps are easily put in place and removed. About the only objection to the method is the fragility of the lamps, which are easily broken by the flying stones and the concussion pro- duced by blasting. 336 TUNNELING CHAPTER XXV. THE COST OF TUNNEL EXCAVATION AND THE TIME REQUIRED FOR THE WORK. Cost. — The cost of a tunnel will depend upon the cost of the two principal operations required in its construction, viz., the excavation of the cross section and the lining of the exca- vation with masonry, metal, or timber. These two operations may in turn be subdivided, in respect to expense, into cost of labor and cost of materials. It is a comparatively simple mat- ter to calculate the cost of the building materials required to construct a tunnel ; but it is very difficult to estimate with accuracy what the cost of labor will be. The reason for this is that it is impossible to foresee exactly what the conditions will be ; the character of the material may change greatly as the work proceeds, increasing or decreasing the cost of excavation ; water may be encountered in quantities which will materially increase the difficulties of the work, etc. Nevertheless, while accurate preliminary estimates of cost are not practicable, it is always desirable to attempt to obtain some idea of the probable expense of the work before beginning it, and the more usual means of getting at this point will be discussed here. Two methods of estimating the cost of tunnel work are em- ployed. The first is to calculate the probable expense of the various items of work, based upon the available data, per unit of length, and then add to this a margin of at least 10% to allow for contingencies ; the second is to apply to the new work the unit cost of some previous tunnel built under substantially the same conditions. In the first method it is usual to consider the strutting and hauling as constituting a part of the work of COST OF EXCAVATION AND TIME KEQUIRED 337 excavation. To estimate the cost of excavation involves the consideration of three general items, viz., the excavation proper, the strutting of the walls of the excavation, and the hauling of the excavated materials and the materials of construction. The cost of excavating the preliminary headings or drifts is greater per unit of material removed than that of excavating the enlargement of the section. The cost of bottom drifts is also always greater than that of top headings, the material pene- trated remaining the same. Mr. Rziha gives the comparative unit costs of excavating drifts, headings, and enlargement of the profile as follows : — Bottom drifts $9.20 per cu. yd. Top headings 4.80 " " " Enlargement of profile 2-84 "" " The cost of hauling increases with the length of the tunnel. This fact and amount of this increase are indicated by the following actual prices for the Arlberg tunnel : — Top heading $6.76 per cu. yd., increasing 37 cts. per mile Bottom drift 7.40 " " " " 26 " " " Enlargement of profile . . . 2.70 " " " " 10 " " " In all the prices given above, the cost of strutting and haul- ing is included in the cost of excavation. The cost of excavation is not always the same for the same character of materials in different tunnels. The following figures show the prices paid for the excavation of calcareous rock in four different German tunnels : — Berliner Nordhausen Wetzler R.K f 1.24 per cu. yd. Ofen 1.30 " " " Staffiach 2.76 " " " - Gries 1.92 " " '« The method of tunneling has little influence upon the cost of the work, as shown by the following figures from tunnels excavated through calcareous rock by different methods : — 338 TUNNELING Ofen tunnel Austrian method .|93.19 per lin. ft. Dorremberg tunnel Belgian method 86.08 " " " Stafflach tunnel English method 91.69 " " " The Martha and Merten tunnels, excavated through soft ground by the Austrian and Gerroan methods respectively, cost 187.95 and $87.55 per hn. ft. respectively. In the exca- vation of the various sections of the tunnel for the new Croton Aqueduct in America, the following prices were paid : — Excavation of heading -f 8 to $10.00 per cu. yd. Tunnel in soft ground 8 to 9.00 " " " Tunnel in rock 7 to 8.50 " " " Brick masonry 10.00 " " " Timber in place $40 per M. ft. B. M. It is the practice in America to include the work of hauling under excavation, but not to include the strutting, which is paid for separately. In some cases only the market price of the timber is paid for separately, the cost of setting up being included in the price of excavation. The writer prefers the European practice of including the total cost of timbering under excavation, since the two operations are so closely con- nected, and since the contractor employs the same timber over and over again. Knowing the dimensions of the several mem- bers of the strutting, it is a simple, although somewhat tedious, process to calculate the total quantity required. An idea of the quantity of timber required for stratting in soft ground may be had from the data given on page 50. The quantity will decrease as the cohesion of the material penetrated in- creases, until it becomes so small in hard rock-tunnels as to cut very little figure in the total cost. The cost of hoisting excavated materials through shafts depends upon the depth from which it is hoisted, and upon the character of hoisting apparatus employed. The following table, showing the cost of hoisting for different lifts and by different methods, is given by Rziha, the cost being in francs per cubic meter : — COST OF EXCAVATION AND TIME REQUIRED 339 Height tn Windlass. HOKSE Gins. Steam Hoists. Metrks. Francs per Cu.M. One Horse. Francs per Cu. M. Two Horses. Francs per Cu. M. Francs per Cu. M. 15 0.172 0.077 0.062 0.035 30 0.212 0.087 0.070 0.045 45 0.257 0.100 0.080 0.050 60 0.305 0.112 0.092 0.082 90 0.410 0.152 0.110 0.087 120 0.535 0.195 0.135 0.092 150 0.722 0.240 0.157 0.112 Mr. Sejourne, a French engineer, who has been connected with the construction of numerous tunnels by the Belgian method where he was in position to secure comparative figures, has given the following rules for calculating the cost of tunnels. Assuming A to represent the cost of excavating a cu. yd. in the open air, the cost of excavating the same quantity underground in driving headings will be from 9 A to 11 A, and in enlarging the profile it will be about 5 A. The cost of constructing single-track tunnels varies with the thick- ness of the lining, and may be calculated by the following formulas : Without lining, C = 5.5 A. With roof arch only, C = 6.4 + 6.4 A. With lining 18 in. thick, C = 9.4 + 7 A. With lining 2 ft. thick, C = 11 + S A. In these formulas C is the cost per cu. yd. of excavation, including the masonry. For double-track tunnels the amounts given by the above formulas may be used by reducing them about 7i % or 8 %. The second method of estimating the cost of tunnel work consists in assuming as a unit the unit cost of tunnels pre- viously excavated under similar conditions. Mr. La Dame gives the following unit prices for a number of tunnels driven through different materials ; 340 TUNNELING Nature of Soil. EXCAV. PER Cu. Yd, Cost per Lin. Ft. Max. and Min. per Lin. Ft. Granite-gneiss . . Schist Triassic Jm-assic .... Cretaceous .... Tertiary and modern 56 39 3 69 34 39 $3.07 @$3.85 1.38 @ 1.53 1.23 @" l!38 0.61 @ 0.77 0.33 @ 0.61 $100. 75.42 90.85 77.86 59.60 105.80 $61.46 @ $190.40 43.11 @ 70.68 84.75 @ 93.33 35.24 @ 157.2 27.37 @ 92.25 51.52 @ 188.36 In the following table is given a list of tunnels excavated through different soils, from the most compact to very loose DOUBLE-TRACK TUNNELS. Name of Tunnels, Quality of Soil. Cost per Lin. Ft. Method of Tunneling. Mt. Cenis St. Gothard Stammerich italic . Bothenfels Dorremberg .... Stafflach Ofen Wartha Mertin Scloss Matrei .... Trietbitte Granitic, Granitic, Broken schist, Dolomite, Calcareous, Calcareous, Calcareous, Grewack, Grewack, Clay schist, Clay and sand. $273.73 ] 93.63 157.90 290.58 115.64 86.08 91.69 93.19 87.95 87.55 94.25 229.0 69.50 178.0 182.31 Drift. Heading. English. Austrian. English. Belgian. English. Austrian. Austrian. German. English. German. Wide heading. Canaan Church-Hill .... Bergen No. 1 . . . . Clay-slate, Clay with shells, Trap rock. SINGLE-TRACK TUNNELS. Name of Tunnels. Quality of Soil. Cost per Lin. Ft. Method of Tunneling. Mt. Cenis Stalletti Marein Welsberg Sancina Starre Cristina Burk Brafford Ridge . . . . Dunbeithe Fergusson Port Henry Points Gneiss, Granite and quartz, Clay schist. Gravel, Clay of 1st variety, Clay of 2d variety. Clay of 3d variety, Limestone, Sandstone, Limestone, Granite, $82.27 62.75 64.36 165.07 129.40 191.61 307.42 83.90 85.33 70.47 37.46* so.oot 72.00* Heading. Austrian. English. Austrian. Belgian. Belgian. Italian. Wide heading. Wide heading. Wide heading. Wide heading. Wide heading. Wide heading. * Are unlined. t Lined with timber. COST OF EXCAVATION AND TIME REQUIRED 341 materials, and driven according to the various methods v^hich have been illustrated. The Habas tunnel through quicksand, between Dax and Ramoux, France, cost 1118.50 per lin. ft. The cost of the Boston subway was 1342.40 per lin. ft. The Severn and Mersey tunnels, constructed through rock under water, cost respectively 1208.33 and |263 per lin. ft. The First Thames Tunnel, driven by Brunei's shield, cost $1661.66 per lin. ft. The Hudson River and St. Clair River tunnels, exca- vated through soft ground by means of shields and compressed air, cost respectively 1305 and |315 per lin. ft. The Black- wall double-track tunnel under the River Thames, which is the largest tunnel ever built by the shield system, cost $600 per lin. ft. In making estimates of the cost of projected tunnel work based on the cost of tunnels previously constructed through similar materials, it is important to keep in mind the date and location of the work used as the basis for calculations. For example, a tunnel excavated in Italy, where labor is very cheap^ will cost less than one excavated in America, where labor is dear, all other conditions being the same. Other reasons for variation in cost due to difference of date and location of con- struction will suggest themselves, and should be taken into full consideration in estimating the cost of the new work. Time. — The time required to excavate a tunnel depends upon the character of the material penetrated and upon the method of work adopted. Tunnels driven through soft ground by hand require about the same time to construct as tunnels driven through hard rock by the aid of machinery. Tunnels can be driven through hard rock at about as great a speed as through soft or fissured rock, chiefly because the work of blasting is more efficient in hard rock, and because no time is required in timbering. The following table shows the average rate of progress in different parts of the tunnel excava- tion through both hard and soft materials in feet per month : — 342 TUNNELING Quality of Soil. Headikg. Excavation of Shafts. Enlarge- ment OF Profile. By hand. By macliine. By hand. By machine. By hand. Very loose soil . Loose soil . . Soft rock . . . Hard rock . . Very hard rock. 16.7 -26.8 33.4 -100 66.8 50 -66.8 33.4 233.8-334 233.8-334 233.8-334 6.6-16.7 16.7-33.4 33.4-66.8 33.4-50 16.7-33.4 66.8-132.6 66.8-132.6 66.8-132.6 6.6-16.7 16.7-33.4 33.4-50 66.8-100 66.8-100 The following tables showing the average rate of progress have been compiled from the actual records made in the tunnels named : Name of Tunnel. DlxMENSIONS IN Feet. pi Character of Material. Observations. Excavation of headings by hand: Mount Cenis . . 10X10 65.8 Schist, Bottom drift. Sutro 6.7 X5.7 70.14 Quartzose, St. Gothard . . . 8.4x8.7 70.14 Granite, Top heading. Excavation of headings by machine: Mount Cenis 10 X 10 188.7 Calcareous schist, Bottom drift. Sutro .... 8.15X10 227.45 Quartzose, St. Gothard 8.4X8.7 339.45 Granite, Top heading. Trari . . 8 X 9.35 167 Gneiss, Top heading. Arlberg . 8.35 X 9.35 474.2 Mica schist, Bottom drift. Palisades . 16x7 160 Trap rock. Top heading. Busk . . 15x7 126 Granite, Top heading. Cascade . 16 X 8 180 Basaltic rock. Top heading. Franklin . 15 X 7 240 Top heading. The following table shows the monthly progress of com- pleted tunnel in feet excavated through rock : Name of Tunnel. Progress IN Feet. Material. Method. Cascade Palisades Busk Tennessee Pass 207 186 190 169.5 Basalt, Trap rock, Granite, Granite, Top heading. Top heading. Top heading. Top heading. COST OF EXCAVATION AND TIME REQUIRED 343 The average monthly progress in feet of excavating tunnels through treacherous ground may be quite generally assumed to be for: (1) clay of the first variety from 43.4 ft. to 60 ft. ; for clay of the second variety from 33.4 ft. to 43.4 ft. ; for clay of the third variety from 23.3 ft. to 33.4 ft., and for quicksand from 30 ft. to 50 ft. The monthly progress in feet made in sinking the shafts of the Hoosac and Musconetcong tunnels in America was as follows : — Name of Tunnkl. DiMENSIOKS IN Feet. Depth IN Feet. Pbogkess IN Feet. Character OF Material. Hoosac: East shaft West shaft Musconetcong: Vertical shaft .... 15.4X27.7 8X16 8.35 X 16.7 1035 267 113.5 304. 21.7 16.7 100 32 Mica schist. Gneiss. Loose rock. Loose rock. Inclined, shaft .... 8 35 X 26 The average monthly progress of sinking shafts in treach- erous soils may be assumed to be as follows : clay of first variety, 50 ft. to 75 ft. ; clay of second variety, 36.75 to 50 ft; clay of third variety, 23.4 ft. to 36.75 ft. ; quicksand, 16.7 ft. to 33.4 ft. For the reason that the details change with the various conditions encountered in every work, all the tunnel operations have been treated in a general way, purposely avoiding to give any detail. Also the rate of progress and items of cost of tun- nels have been given in a broad manner because they greatly vary in the different works. This information, however, can be easily obtained by consulting the Engineering Magazines, where are reported all the tunnel works of America and Europe, and where are given so many details which are very valuable to expert engineers in charge of similar works, but not to stu- dents and people who are looking only for general knowledge. INDEX Accidents and Repairs in the Belgian Method, 152 Accidents in Tunnels: After Construction, 308 Baltimore Belt Line, 165 Chattanooga Tunnel, 311 During Construction, 301 General Discussion, 301 Giovi Tunnel, 309 Repairing of, 304 Acetylene Gas Lighting, 334 Air Compressors, Description of, 87 Air Locks, 264-272 Air Pressure, 268 American Method : General Description, 172 Excavation, 172 Strutting, 174 Hauling, 175 Arrangement of Drill Holes, 90 Artificial Ventilation, 327 Austrian Method of Tunneling: Advantages and Disadvantages, 180 Excavation, 176 General Description, 176 Lining, 180 Strutting, 177 Average Progress in Tunnels, 342 Baltimore Belt Line Tunnel, General Description, 160 Barlow's Shield, 242 Beach's Shield, 246 Belgian Method: Accidents and Repairs, 152 Advantages and Disadvantages, 152 Excavation, 145 General Description, 144 Lining, 148 Hauling, 150 Strutting, 146 Bench, 131 Bends, 268 Blackwall's Tunnel Shield, 248 Blasting-cone, 33 Bhckford Match, 31 Boston Subway: General Descriptions, 203 Roof Shield, 251 Boulder Tunnel Relined, 315 Box-cars, 61 Box Strutting, 51 Brandt DrilHng Machine, 28, 112 Brown, W. L., 269 Brunei's Shield, 240 Caissons, 293 Canals and Pipe Lines, 86 Cascade Tunnel, 98 Center-cut, 91 Center Line: Curvilinear Tunnels, 14 Determination of, 9 Rectihnear Tunnels, 9 Simplon Tunnel, 106 Submarine Tunnels, 265 Triangulation, 12 Transferred through Center Shafts, 13 Transferred through Side Shafts, 14 Value's Device, 10 Centers : For Arches, 68 EngHsh Method, 169 Ground Molds, 66 Itahan Method, 184 Lagging, 71 Leading Frames, 67 Setting Up, 70 Striking, 71 Chattanooga Tunnel, Accident, 311 City and South London Railway Shield, 250 Classification of Tunnels, 42 Coal-gas Lighting, 333 Cofferdam Method of Tunneling, 281 Van Buren Street Tunnel, Chicago, 282 Collapse of Tunnels, 302 345 346 INDEX Compressed Air: For Power, 87 For Ventilation, 330 Concrete Lining, 75 Fort George Tunnel, 139 Murray Hill Tunnel, 126 Cost of: Double-track Tunnels, 340 Hauling, 338 Headings, 337 Hoisting, 338 Single-track Tunnel, 340 Submarine Tunnels, 341 Subways, 209-217 Tunnels, 336 Craven, Alfred, 39 Craven's Sunflower, 39 Cross-section : Dimensions of, 20 Form of, 18 Hudson River Tunnel Pennsyl- vania Railroad, 277 Crown-bar (see American Method). Subways, 204-211 Croton Aqueduct Tunnel, 95 Culverts, 80 Detroit River Tunnel, 296 Diamond Drilling Machine, 27 Directing the Shield, 265 Drift, 37 Drift Method: General Discussion, 102 Murray Hill Tunnel, 123 Simplon Tunnel, 103 DriJhng Machines: Brandt, 112 Ingersoll, 26 Drills: Diamond, 27 Hand, 23 Mountings for, 25 Percussion, 24 Power, 24 Rotary, 27 Dumping Cars, 60 Electric Firing, 32 Electric Lighting, 335 EngHsh Method: Advantages and Disadvantages, 171 Centers, 169 Excavation, 166 General Discussion, 166 Lining, 170 Strutting, 167 Enlargement of the Profile, 38 Entrances, 81 Erector, 272 Excavation : American Method, 172 Arrangement of Drill Holes, 90 Austrian Method, 176 Belgian Method, 145 Center-cut, 91 Enlargement of Profile, 38 English Method, 166 Fort George Tunnel, 136 German Method, 155 Headings, 37, 91 Hudson River Tunnel of Pennsyl- vania Railroad, 273 Itahan Method, 182 Murray Hill Tunnel, 124 Quicksand Method. 189 Pilot Method, 193 Shield and Compressed Air Method, 267 Simplon Tunnel, 110 Excavating Machines: For Earth, 22 For Rock, 23 Explosions, 33 Dynamite, 30 Gunpowder, 28 Nitroglycerine, 29 Quantity of, 34 Storage of, 30 Failure of Tunnel Roof, 305 Forgie, James, 269 Fort George Tunnel, 135 Foundations for Lining, 76 Fox, Charles B., 103 Frame Strutting, 49 Fuses, 31 Geological Survey, 3 German Method: Advantages and Disadvantages, 159 Excavation, 155 General Description, 155 HauHng, 158 Strutting, 156 Giovi Tunnel Accident, 309 Graveholz Tunnel, 98 Greathead's Shield, 245 Hand Drills, 23 Harlem River Tunnel, 285 HauUng: American Method, 175 INDEX 347 Hauling: Continued Belgian Method, 150 Italian Method, 185 German Method, 158 Hudson River Tunnel of Penn- sylvania Raihoad, 278 Motive Power, 61 By Way of Entrances, 59 Simplon Tunnel, 111 By Way of Shafts, 62 Heading and Bench Method: Fort George Tunnel, 135 General Discussion, 130 St. Gothard Tunnel, 1 Headings, 37, 91 Hewett, H. B., 269 History of Tunnels, xiii Hoisting Machines: General Discussion, 62 Elevators, 64 Horse Gins, 63 Windlass, 63 Hoosac Tunnel, 93 Hopkins, Stephen W., 135 Hudson River Tunnel of Pennsyl- vania Railroad, 269 HydrauHc Jacks, 260, 271 Hydraulic Rams, 271 Illumination : Acetylene Gas, 334 Coal-gas, 333 Electric, 335 Hudson River Tunnel of Pennsyl- vania Railroad, 280 Lamps and Lanterns, 330 Inclination of Strata, 6 IngersoU Drilling Machine, 26 Inverted Arch Lining, 77 Iron and Masonry Lining, 74 Iron Lining, 73, 261, 276 Iron Strutting, 55 Full Section, 56 Headings, 56 Shafts, 57 Itahan Method: Advantages and Disadvantages, 188 Excavation, 182 General Description, 182 Modifications, 186 Strutting, 183 Jacks, 260, 271 Joining the Caissons, 295 Lagging, 71 Lamps and Lanterns, 330 Lighting (see Illumination). Lining: Austrian Method, 180 Belgian Method, 148 Concrete, 126, 139 Enghsh Method, 170 Foundations, 76 General Observations, 78 German Method, 158 Hudson River Tunnel Pennsyl- vania Railroad, 276 Invert, 77 Iron, 73, 261, 276 Iron and Masonry, 74 Itahan Method, 185 Masonry, 74 Quicksand Method, 191 Roof Arch, 77 Side Tunnels, 79, 83 Side WaUs, 77 Subways, 207-213 Timber, 72 Thickness of Masonry, 78, 83 Little Tom Tunnel Relined, 321 Loose Soil (see Soft Ground). Masonry (see Centers) . Masonry Culverts, 80 Masonry (see Lining). Masonry Lining, 74 Masonry Niches, 81 McBean, Daniel, 285 Mechanical Installations for Tunnel Work, 84 Milwaukee Tunnel, 226 Mont Cenis Tunnel, 92 Monthly Progress of Tunnels, 342 Mullan Tunnel ReUned 319 Murray HiU Tunnel, 123 Natural Ventilation, 326 New York Rapid Transit Subway, 209 Niagara Falls Power Tunnel, 97 Niches, 81 Open Cut or Tunnel, 1 Open-cut Tunneling: General Discussion, 195 Parallel Longitudinal Trenches, 197 Single Trench, 196 Single Narrow Trench, 197 Transverse Trenches, 200 Tunnels on the Surface, 200 348 INDEX Palisade Tunnel, 94 Pennsylvania Railroad Shield, 270 Percussion Drills, 24 PUot Method of Tunneling, 192 Plank Centers, 69 Platform Cars, 59 Plenum Method of Ventilation, 329 Pneumatic Caissons, 287 Polar Protractor, 39 Portals, 81 Power Drills, 24 Power Plants: Air Compressors, 87 Canals and Pipe Lines, 86 Cascade Tunnel. 98 Croton Aqueduct Tunnel, 95 General Description, 84 Graveholz Tunnel, 98 Hoosac Tunnel, 93 Hudson River Tunnel Pennsyl- vania Railroad, 279 Mont Cenis Tunnel, 92 Murray Hill Tunnel, 128 Niagara Falls Power Tunnel, 97 PaHsades Tunnel, 94 Receivers, 89 Reservoirs, 86 Simplon Tunnel, 117 Sounstein Tunnel, 99 St. Clair River Tunnel, 99 St. Gothard Tunnel, 133 Steam, 85 Strickler Tunnel, 96 Turbines, 86 PreUni's Shield, 251 Presence of Water, 7 Prevention of Collapse, 303 Progress in Sinking Shafts, 343 Progress of Excavation, 342 Progress of the Work, 342 Progress in Simplon Tunnel, 122 Quantity of Air for Ventilation, 331 Quicksand Tunneling: General Discussion, 188 Removing the Seepage Water, 191 Quantity of Timber in Strutting, 54 Receivers, 89 Rehning Tunnels, 315 Boulder Tunnel, 315 Little Tom Tunnel, 321 MuUan Tunnel, 319 Repairing of Accidents in Tunnels, 308 Reservoirs, 86 Roof Arch Lining, 77 Roof Shield for Boston Subway, 251 Roof of Caissons, 287-291 Rotary Drills, 27 Ryder, B. H. Saccardo System of Ventilation, 330 Saunders, W. L., 88 Seepage Water, 191 Seine River Tunnel, 293 Setting up Centers, 70 Severn Tunnel, 221 Shafts, Description of, 40 Shaler, Ira A, 142 Shield and Compressed Air Method, 263 Shield Construction: Diaphragm, 256 Cellular Division, 255 Dimensions of Shields, 259 Front End, 254 General Form, 252 Rear End, 257 SheU, 253 Shield Method: Barlow Shield, 242 Beach's Shield, 245 Blackwall Tunnel Shield, 248 Brunei Shield, 240 City and South London Railway Shield, 250 Greathead's Shield, 245 History, 238 Prelini's Shield, 251 St. Clair River Tunnel Shield, 247 Side Shafts, 41 Side Tunnels Lining, 79 Side WaUs Lining, 77 Simplon Tunnel, 103 Soils Encountered in Tunnels, 3 Sounstein Tunnel, 99 Stations of Subways, 207-216 St. Clair River Tunnel Shield, 247 St. Gothard Tunnel, 132 Steam Power Plant, 85 Stratification of the Soils, 6 Strickler Tunnel, 96 Striking the Centers, 71 Strutting: American Method, 174 Austrian Method, 177 Belgian Method, 146 Dimensions of Timber, 54 Pnghsh Method, 167 Fort George Tunnel, 137 Full Section, 51 German Method, 156 Headings, 48 Italian Method, 183 INDEX 349 Strutting: Continued Murray HiU Tunnel, 125 Pilot Method, 193 Quantity of Timber, 54 Shafts, 52 Iron: Full Section, 56 Headings, 56 Shafts, 57 Submarine Tunneling: Cofferdam Method, 281 Compressed Air Method, 225 Detroit River Tunnel, 296 General Discussion, 218 Harlem River Tunnel, 285 Hudson River Tunnel Pennsyl- vania Railroad, 269 Lining, 261 Milwaukee Water-Works Tunnel, 226 Pneumatic Caisson Method, 284 Seine River Tunnel, 293 Severn Tunnel, 221 Shield and Compressed Air Method, 263 Shield System, 238 Sinking and Joining Sections Built on Land, 293 Van Buren Street Tunnel, 282 Subways : Boston, 203 Cost of, 209-217 Cross-sections, 204-211 General Discussion, 195-202 Lining, 207-213 New York Rapid Transit Railway, 209 Stations, 207-216 Sutro, Adolph, 330 Tamping, 32 Thickness of Lining Masonry, 78, 83 Thomson Excavating Machine, 22 Timber Lining, 72 Timbering (see Strutting). Tremies, 299 Trussed Centers, 70 Tunnel or Open Cut, 1 Tunnels : Baltimore Belt Line, 160 Classification of, 42 Tunnels: Continued Fort George, 135 Murray HiU, 123 Simplon, 103 St. Gothard, 132 Hard Rock, 84 Drift Method, 102 Comparison of Methods, 141 Heading and Bench Method, 152 Heading Method, 130 Soft Ground: American Method, 172 Austrian Method, 176 Belgian Method, 144 Enghsh Method, 166 German Method, 155 Itahan Method, 182 Pilot Method, 192 Quicksand Method, 188 Submarine : Detroit River Tunnel, 296 Harlem River Tunnel, 285 Hudson River Tunnel of Penn- sylvania Railroad, 269 Milwaukee Tunnel, 226 Seine River Tunnel, 293 Severn Tunnel, 221 Van Buren Street Tunnel, Chi- cago, 282 Under City Streets: General Description, 201 Boston Subway, 203 Turbines, 86 Vacuum Method of Ventilation, 328 Value, Beverley R. 10 Van Buren Street Tunnel, 282 Ventilation, 325 Artificial, 327 Compressed Air, 330 Natural, 326 Plenum Method, 329 Quantity of Air, 331 Saccardo's System, 330 Simplon Tunnel, 120 Vacuum Method, 328 Vernon-Har court, L. F., 221 Working Platforms, 286 Wyman, Erastus, 293 D. VAN NOSTRAND COMPANY 2 5 PARK PLAGE New York SHORT=TITLE CATALOG OF OF SCIENTIFIC AND ENGINEERING BOOKS This list includes the technical publications of the following English publishers: SCOTT, GREENWOOD & CO. CROSBY LOCKWOOD & SON CONSTABLE & COMPANY, Ltd. TECHNICAL PUBLISHING CO. ELECTRICIAN PRINTING & PUBLISHING CO. for whom D. Van Nostrand Company are American agents. March, 1912 Short-Title Catalog OF THE Publications and Importations OF D. VAN NOSTRAND COMPANY . 25 PARK PLACE, NEW YORK "Prices marhed with an asterisk (*) are NET, All bindings are in cloth unless otherwise noted. ABC Code. (See Clausen-Thue.) Abbott, A. V. The Electrical Transmission of Energy. 8vo, *$5 oo A Treatise on Fuel. (Science Series No. 9.) i6mo, o 50 Testing Machines. (Science Series No. 74.) i6mo, o 50 Adam, P. Practical Bookbinding. Trans, by T. E. Maw i2mo, *2 50 Adams, H. C Sewage of Sea Coast Towns 8vo, *2 00 Adams, H. Theory and Practice in Designing 8vo, *2 50 Adams, J. W. Sewers and Drains for Populous Districts Svo, 2 50 Addyman, F. T. Practical X-Ray Work Svo, *4 00 Ai Code. (See Clausen-Thue.) Aikman, C. M. Manures and the Principles of Manuring Svo, 2 50 Aitken, W. Manual of the Telephone. Two Volimies d'Albe, E. E. F., Contemporary Chemistry i2mo, *i 25 Alexander, J. H. Elementary Electrical Engineering i2mo, 2 00 Universal Dictionary of Weights and Measures 8vo, 3 50 " Alfrec.'* Wireless Telegraph Designs Allan, W. Strength of Beams Under Transverse Loads. (Science Series No. 19.) i6mo, o 50 Theory of Arches. (Science Series No. 11.) i6mo, Allen, H. Modern Power Gas Producer Practice and Applications.. i2mo, *2 50 Gas and Oil Engines Svo, *4 50 Anderson, F. A. Boiler Feed Water Svo, *2 50 Anderson, Capt. G. L. Handbook for the Use of Electricians Svo, 3 00 Anderson, J. W. Prospector's Handbook i2mo, i 50 And€s, L. Vegetable Fats and Oils Svo, *4 00 Animal Fats and Oils. Trans, by C. Salter Svo, *4 00 Drying Oils, Boiled Oil, and Solid and Liquid Driers Svo, *5 00 Iron Corrosion, Anti-fouling and Anti-corrosive Paints. Trans, by C. Salter Svo, *4 00 Oil Colors, and Printers' Ink. Trans, by A. Morris and H. Robson Svo, *2 50 D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 3 And^s, L. Treatment of Paper for Special Purposes. Trans, by C. Salter i2mo, *2 50 Annual Reports on the Progress of Chemistry. Vol. I. (1904) 8vo, *2 00 Vol. IL (1005) 8vo, *2 00 Vol. III. (1906) 8vo, *2 00 Vol. IV. (1907) 8vo, *2 00 Vol. V. (1908) 8vo, *2 00 Vol. VI. (1909) 8vo, *2 00 Vol. Vn. (1910) 8vo, *2 00 Argand, M. Imaginary Quantities. Translated from the French by A. S. Hardy. (Science Series No. 52.) i6mo, o 50 Armstrong, R., and Idell, F. E. Chimneys for Furnaces and Steam Boilers. (Science Series No. i.) i6mo, o 50 Arnold, E. Armature Windings of Direct-Current Dynamos. Trans, by F. B. DeGress 8vo, *2 00 Ashe, S. W., and Keiley, J. D. Electric Railways. Theoretically and Practically Treated. Vol. I. Rolling Stock i2mo, *2 50 Ashe, S. W. Electric Railways. Vol. II. Engineering Preliminaries and Direct Current Sub-Stations i2mo, *2 50 ■ Electricity: Experimentally and Practically Applied i2mo, *2 00 Atkinson, A. A. Electrical and Magnetic Calculations 8vo, *i 50 Atkinson, J. J. Friction of Air in Mines. (Science Series No. 14.) . . i6mo, o 50 Atkinson, J. J., and Williams, Jr., E. H. Gases Met with in Coal Mines. (Science Series No. 13.) i6mo, o 50 Atkinson, P. The Elements of Electric Lighting.. i2mo, i 50 The Elements of Dynamic Electricity and Magnetism i2mo, 2 00 Power Transmitted by Electricity i2mo, 2 00 Auchincloss, W. S. Link and Valve Motions Simplified 8vo, *i 50 Ayrton, H. The Electric Arc 8vo, *5 00 Bacon, F. W. Treatise on the Richards Steam-Engine Indicator . . i2mo, i 00 Bailes, G. M. Modern Mining Practice. Five Volumes 8vo, each, 3 50 Bailey, R. D. The Brewers' Analyst 8vo, *5 00 Baker, A. L. Quaternions 8vo, *i 25 Thick-Lens Optics {In Press.) Baker, Ben j. Pressure of Earthwork. (Science Series No. 56.)... i6mo, Baker, I. 0. Levelling. (Science Series No. 91.) i6mo, o 50 Baker, M. N. Potable Water. (Science Series No. 61.) i6mo, o 50 Sewerage and Sewage Purification. (Science Series No. 18.).. i6mo, o 50 Baker, T. T. Telegraphic Transmission of Photographs i2mc, *i 25 Bale, G. R. Modern Iron Foundry Practice. Two Volumes. i2mo. Vol. I. Foundry Equipment, Materials Used *2 50 Vol. IL Machine Moulding and Moulding Machines *i 50 Bale, M. P. Pumps and Pumping i2mo, i 50 Ball, R. S. Popular Guide to the Heavens 8vo, *4 50 Natural Sources of Power. (Westminster Series.) 8vo, *2 00 Ball, W. V. Law Affecting Engineers 8vo, *3 50 Bankson, Lloyd. Slide Valve Diagrams. (Science Series No. 108.) . i6mo, o 50 Barba, J. Use of Steel for Constructive Purposes i2mo, i 00 Barham, G. B. Development of the Incandescent Electric Lamp. . . .(In Press.) 4 D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG Barker, A. Textiles and Their Manufacture. (Westminster Series.) . . 8vo, 2 00 Barker, A. H. Graphic Methods of Engine Design. i2mo, *i 50 Barnard, F. A. P. Report on Machinery and Processes of the Industrial Arts and Apparatus of the Exact Sciences at the Paris Universal Exposition, 1867 8vo, 5 00 Barnard, J. H. The Naval Militiaman's Guide i6mo, leather i 25 Barnard, Major J. G. Rotary Motion. (Science Series No. 90.) i6mo, o 50 Barrus, G. H. Boiler Tests 8vo, *3 00 Engine Tests 8vo, *4 00 The above two purchased together *6 00 Barwise, S. The Purification of Sewage i2mo, 3 50 Baterden, J. R. Timber. (Westminster Series.) 8vo, *2 00 Bates, E. L., and Charlesworth, F. Practical Mathematics 1 2 mo. Part I. Preliminary and Elementary Course *i 50 Part II. Advanced Course *i 50 Beadle, C. Chapters on Papermaking. Five Volumes i2mo, each, *2 00 Beaumont, R. Color in Woven Design 8vo, *6 00 Finishing of Textile Fabrics. 8vo, *4 00 Beaumont, W. W. The Steam-Engine Indicator .8vo, 2 50 Bedell, F., and Pierce, C. A. Direct and Alternating Current Manual.8vo, *2 00 Beech, F. Dyeing of Cotton Fabrics 8vo, *3 00 Dyeing of Woolen Fabrics 8vo, *3 50 Beckwith, A. Pottery 8vo, paper, o 60 Begtrup, J. The Slide Valve 8vo, *2 00 Beggs, G. E. Stresses in Railway Girders and Bridges (In Press.) Bender, C. E. Continuous Bridges. (Science Series No. 26.) i6mo, o 50 Proportions of Piers used in Bridges. (Science Series No. 4.) i6mo, o 50 Bennett, H. G. The Manufacture of Leather 8vo, *4 50 Bernthsen, A. A Text - book of Organic Chemistry. Trans, by G. M'Gowan i2mo, *2 50 Berry, W. J. Differential Equations of the First Species. i2mo (In Preparation.) Bersch, J. Manufacture of Mineral and Lake Pigments. Trans, by A. C. Wright 8vo, *5 00 Bertin, L. E. Marine Boilers. Trans, by L. S. Robertson 8vo, 5 00 Beveridge, J. Papermaker's Pocket Book i2mo, *4 00 Binns, C. F. Ceramic Technology 8vo, *5 00 Manual of Practical Potting 8vo, *7 50 The Potter's Craft -. . . i2mo, *2 00 Birchmore, W. H. How to Use a Gas Analysis i2mo, *i 25 Blaine, R. G. The Calculus and Its Applications i2mo, *i 50 Blake, W. H. Brewers' Vade Mecum 8vo, *4 00 Blake, W. P. Report upon the Precious Metals 8vo, 2 00 Bligh, W. G. The Practical Design of Irrigation Works Svo, *6 00 Bliicher, H. Modern Industrial Chemistry. Trans, by J. P. Millington Svo, *7 50 Blyth, A. W. Foods: Their Composition and Analysis Svo, 7 50 • Poisons: Their Effects and Detection Svo, 7 50 Bockmann, F. Celluloid i2mo, *2 50 Bodmer, G. R. Hydraulic Motors and Turbines i2mo, 5 00 Boileau, J. T. Traverse Tables Svo, 5 00 D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 5 Bonney, G. E. The Electro-platers' Handbook V i2mo, i 20 Booth, W. H. Water Softening and Treatment 8vo, *2 50 Superheaters and Superheating and Their Control 8vo, *i 50 Bottcher, A. Cranes: Their Construction, Mechanical Equipment and Working. Trans, by A. Tolhausen 4to, *io 00 Bottler, M. Modern Bleaching Agents. Trans, by C. Salter i2mo, *2 50 Bottone, S. R. Magnetos for Automobilists i2mo, *i 00 Boulton, S. B. Preservation of Timber, (Science Series No. 82.) . i6mo, o 50 Bourgougnon, A. Physical Problems. (Science Series No. ii3.)..i6mo, o 50 Bourry, E. Treatise on Ceramic Industries. Trans, by J. J. Sudborough. 8vo, *5 00 Bow, R. H. A Treatise on Bracing 8vo, i 50 Bowie, A. J., Jr. A Practical Treatise on Hydraulic Mining 8vo, 5 00 Bowker, W. R. Dynamo, Motor and Switchboard Circuits 8vo, *2 50 Bowles, 0. Tables of Common Rocks. (Science Series No. 125.). . i6mo, o 50 Bowser, E. A. Elementary Treatise on Analytic Geometry i2mo, i 75 Elementary Treatise on the Differential and Integral Calculus. 12 mo, 2 25 Elementary Treatise on Analytic Mechanics i2mo, 3 00 Elementary Treatise on Hydro-mechanics i2mo, 2 50 A Treatise on Roofs and Bridges i2mo, *2 25 Boycott, G. W. M. Compressed Air Work and Diving.. 8vo, *4 00 Bragg, E. M. Marine Engine Design. i2mo, *2 00 Brainard, F. R. The Sextant. (Science Series No. loi.) i6mo, Brassey's Naval Annual for 191 1 8vo, *6 00 Brew, W. Three-Phase Transmission 8vo, *2 00 Brewer, R. W. A. The Motor Car i2mo, *2 00 Briggs, R., and Wolff, A. R. Steam-Heating. (Science Series No. 67.) i6mo, o 50 Bright, C. The Life Story of Su- Charles Tilson Bright. 8vo, *4 50 British Standard Sections 8x15 *i 00 Complete list of this series (45 parts) sent on application. Broadfoot, S. K. Motors, Secondary Batteries. (Installation Manuals Series) i2mo, *o 75 Broughton, H. H. Electric Cranes and Hoists *9 00 Brown, G. Healthy Foundations. (Science Series No. 80.) i6mo, o 50 Brown, H. Irrigation 8vo, *5 00 Brown, Wm. N. The Art of Enamelling on Metal i2mo, *i 00 Handbook on Japanning and Enamelling i2mo, *i 50 • House Decorating and Painting i2mo, *i 50 History of Decorative Art i2mo, *i 25 Dipping, Burnishing, Lacquering and Bronzing Brass Ware. . . i2mo, *i 00 Workshop Wrinkles 8vo, *i 00 Browne, R. E. Water Meters. (Science Series No. 81.) i6mo, o 50 Bruce, E. M. Pure Food Tests i2mo, *i 25 Bruhns, Dr. New Manual of Logarithms 8vo, half morocco, 2 50 Brunner, R. Manufacture of Lubricants, Shoe Polishes and Leather Dressings. Trans, by C. Salter 8vo, *3 00 Buel, R. H. Safety Valves. (Science Series No. 21.) i6mo, o 50 Bulman, H. F., and Redmayne, R. S. A. Colliery Working and Manage- ment 8vo, 6 00 Burgh, N. P. Modern Marine Engineering 4to, half morocco, 10 00 6 D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG Burt, "W. A. Key to the Solar Compass i6nio, leather, 2 50 Burton, F. G. Engineering Estimates and Cost Accounts i2mo, *i 50 Buskett, E. W. Fire Assaying i2mo, *i 25 Cain, W. Brief Course in the Calculus i2mo, *i 75 Elastic Arches. (Science Series No. 48.) i6mo, o 50 Maximum Stresses. (Science Series No. 38.) i6mo, o 50 Practical Designing Retaining of Walls. (Science Series No. 3.) i6mo, o 50 Theory of Steel-concrete Arches and of Vaulted Structures. (Science Series No. 42.) i6mo, o 50 Theory of Voussoir Arches. (Science Series No. 12.) i6mo, o 50 Symbolic Algebra. (Science Series No. 73.) i6mo, o 50 Campin, F. The Construction of Iron Roofs 8vo, 2 00 Carpenter, F. D. Geographical Surveying. (Science Series No. 37.) . i6mo. Carpenter, R. C, and Diederichs, H. Internal Combustion Engines. 8vo, *$ 00 Carter, E. T. Motive Power and Gearing for Electrical Machinery . . 8vo, *5 00 Carter, H. A. Ramie (Rhea), China Grass i2mo, *2 00 Carter, H. R. Modern Flax, Hemp, and Jute Spinning 8vo, *3 00 Cathcart, W. L. Machine Design. Part I. Fastenings 8vo, *3 00 Cathcart, W. L., and Chaffee, J. I. Elements of Graphic Statics 8vo, *3 00 Short Course in Graphics i2mo, i 50 Caven, R. M., and Lander, G. D. Systematic Inorganic Chemistry. i2mo, *2 00 Chambers' Mathematical Tables 8vo, i 75 Charnock, G. F. Workshop Practice. (Westminster Series.). . . .8vo {In Press.) Charpentier, P. Timber 8vo, *6 00 Chatley, H. Principles and Designs of Aeroplanes. (Science Series.) No. 126.) i6mo, o 50 How to Use Water Power i2mo, *i 00 Child, C. T. The How and Why of Electricity i2mo, i 00 Christie, W. W. Boiler- waters. Scale, Corrosion, Foaming 8vo, *3 00 Chimney Design and Theory 8vo, *3 00 Furnace Draft. (Science Series No. 123.) i6mo, o 50 Church's Laboratory Guide. Rewritten by Edward Kinch 8vo, *2 50 Clapperton, G. Practical Papermaking 8vo, 2 50 Clark, A. G. Motor Car Engineering. Vol. 1. Construction *3 00 Clark, C. H. Marine Gas Engines i2mo, *i 50 Clark, D. K. Rules, Tables and Data for Mechanical Engineers 8vo, 5 00 Fuel: Its Combustion and Economy i2mo, i 50 The Mechanical Engineer's Pocketbook i6mo, 2 00 Tramways: Their Construction and Working 8vo, 7 50 Clark, J. M. New System of Laying Out Railway Turnouts i2mo, i 00 Clausen-Thue, W. ABC Telegraphic Code. Fourth Edition i2mo, *5 00 Fifth Edition 8vo, *7 00 The A I Telegraphic Code 8vo, *7 50 Cleemann, T. M. The Railroad Engineer's Practice 12 mo, *i 50 Clerk, D., and Idell, F. E. Theory of the Gas Engine. (Science Series No. 62.) i6mo, o 50 Clevenger, S. R. Treatise on the Method of Government Surveying. i6mo, morocco 2 50 Clouth, F. Rubber, Gutta-Percha, and Balata 8vo, *5 00 D VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 7 Coffin, J. H. C. Navigation and Nautical Astronomy i2mo, *3 50 Colburn, Z., and Thurston, R. H. Steam Boiler Explosions. (Science Series No. 2.) i6mo, o 50 Cole, R. S. Treatise on Photographic Optics i2mo, i 50 Coles-Finch, W. Water, Its Origin and Use 8vo, *5 00 Collins, J. E. Useful Alloys and Memoranda for Goldsmiths, Jewelers. i6mo o 50 Constantine, E. Marine Engineers, Their Qualifications and Duties. 8vo, *2 00 Coombs, H. A. Gear Teeth. (Science Series No. 120.) i6mo, o 50 Cooper, W. R. Primary Batteries 8vo, *4 00 " The Electrician " Primers . . . • Svo, *5 00 Part I *i 50 Part II *2 50 Part III *2 00 Copperthwaite, W. C. Tunnel Shields 4to, *9 00 Corey, H. T. Water Supply Engineering Svo (In Press.) Corfield, W. H. Dwelling Houses. (Science Series No. 50.) i6mo, o 50 Water and Water-Supply. (Science Series No. 17.) i6mo, o 50 Cornwall, H. B. Manual of Blow-pipe Analysis Svo, *2 50 Courtney, C. F. Masonry Dams Svo, 3 50 Cowell, W. B. Pure Air, Ozone, and Water i2mo, *2 00 Craig, T. Motion of a Solid in a Fuel. (Science Series No. 49.) .... i6mo, o 50 Wave and Vortex Motion. (Science Series No. 43.) i6mo, o 50 Cramp, W. Continuous Current Machine Design Svo, *2 50 Crocker, F. B. Electric Lighting. Two Volumes. Svo. Vol. I. The Generating Plant 3 00 Vol. II. Distributing Systems and Lamps 3 00 Crocker, F. B., and Arendt, M. Electric Motors Svo, *2 50 Crocker, F. B., and Wheeler, S. S. The Management of Electrical Ma- chinery i2mo, *i 00 Cross, C. F., Be van, E. J., and Sindall, R. W. Wood Pulp and Its Applica- tions. (Westminster Series.) Svo, *2 00 Crosskey, L. R. Elementary Perspective Svo, i 00 Crosskey, L. R., and Thaw, J. Advanced Perspective Svo, i 50 Culley, J. L. Theory of Arches. (Science Series No. S7.) i6mo, o 50 Davenport, C. The Book. (Westminster Series.). Svo, *2 00 Davies, D. C. Metalliferous Minerals and Mining Svo, 5 00 Earthy Minerals and Mining Svo, 5 00 Davies, E. H. Machinery for Metalliferous Mines Svo, S 00 Davies, F. H. Electric Power and Traction Svo, *2 00 Dawson, P. Electric Traction on Railways Svo, *9 00 Day, C. The Indicator and Its Diagrams i2mo, *2 00 Deerr, N. Sugar and the Sugar Cane Svo, *8 00 Deite, C. Manual of Soapmaking. Trans, by S. T. King 4to, *5 00 De la Coux, H. The Industrial Uses of Water. Trans, by A. Morris . Svo, *4 50 Del Mar, W. A. Electric Power Conductors Svo, *2 00 Denny, G. A. Deep-level Mines of the Rand 4to, *io 00 Diamond Drilling for Gold *5 00 De Roos, J. D. C. Linkages. (Science Series No. 47.) i6mo, o 50 *I 50 = 10 oo 50 *I oo *8 00 6 50 *3 50 *3 00 *2 00 8 D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG Derr, W. L. Block Signal Operation Oblong i2mo, Desaint, A. Three Hundred Shades and How to Mix Them 8vo, De Varona, A. Sewer Gases. (Science Series No. 55.) i6nio, Devey, R. G. Mill and Factory Wiring. (Installation Manuals Series.) i2nio, Dibdin, W. J. Public Lighting by Gas and Electricity 8vo, Purification of Sewage and Water Svo, Dichmann, Carl. Basic Open-Hearth Steel Process i2mo, Dieterich, K. Analysis of Resins, Balsams, and Gum Resins Svo, Dinger, Lieut. H. C. Care and Operation of Naval Machinery i2mo, Dixon, D. B. Machinist's and Steam Engineer's Practical Calculator. i6mo, morocco, i 25 Doble, W. A. Power Plant Construction on the Pacific Coast {In Press.) Dodd, G. Dictionary of Manufactures, Mining, Machinery, and the Industrial Arts i2mo, i 50 Dorr, B. F. The Surveyor's Guide and Pocket Table-book. i6mo, morocco, 2 00 Down, P. B. Handy Copper Wire Table i6mo, *i 00 Draper, C. H. Elementary Text-book of Light, Heat and Sound. . . i2mo, i 00 Heat and the Principles of Thermo-dynamics i2mo, i 50 Duckwall, E. W. Canning and Preserving of Food Products Svo, *5 00 Dumesny, P., and Noyer, J. Wood Products, Distillates, and Extracts. Svo, *4 50 Duncan, W. G., and Penman, D. The Electrical Equipment of Collieries. Svo, Duthie, A. L. Decorative Glass Processes. (Westminster Series.). .Svo, Dyson, S. S. Practical Testing of Raw Materials Svo, Dyson, S. S., and Clarkson, S. S. Chemical Works (In Press.) Eccles, R. G., and Duckwall, E. W. Food Preservatives Svo, paper Eddy, H. T. Researches in Graphical Statics Svo, Maximum Stresses under Concentrated Loads Svo, Edgcumbe, K. Industrial Electrical Measuring Instruments Svo, Eissler, M. The Metallurgy of Gold Svo, • The Hydrometallurgy of Copper Svo, The Metallurgy of Silver Svo, The Metallurgy of Argentiferous Lead Svo, Cyanide Process for the Extraction of Gold Svo, A Handbook on Modern Explosives Svo, Ekin, T. C. Water Pipe and Sewage Discharge Diagrams folio, Eliot, C. W., and Storer, F. H. Compendious Manual of Qualitative Chemical Analysis i2mo, Elliot, Major G. H. European Light-house Systems Svo, Ennis, Wm. D. Linseed Oil and Other Seed Oils Svo, Applied Thermodynamics Svo Flying Machines To-day i2mo, Vapors for Heat Engines i2mo, Erfurt, J. Dyeing of Paper Pulp. Trans, by J. Hubner Svo, Erskine-Murray, J. A Handbook of Wireless Telegraphy Svo, Evans, C. A. Macadamized Roads (In Press.) Ewing, A. J. Magnetic Induction in Iron Svo, *4 00 u 00 *2 00 *5 00 50 I 50 I 50 *2 50 7 50 *4 50 4 03 5 OD 3 00 5 00 *3 00 *i 25 5 00 *4 00 *4 50 *i 50 *i 00 *7 50 *3 50 D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 9- Fairie, J. Notes on Lead Ores i2mo, *i oo Notes on Pottery Clays i2mo, *i 50 Fairley, W., and Andre, Geo. J. Ventilation of Coal Mines. (Science Series No. 58.) i6mo, o 50 Fairweather, W. C. Foreign and Colonial Patent Laws 8vo, *3 00 Fanning, J. T. Hydraulic and Water-supply Engineering Svo, *5 00 Fauth, P. The Moon in Modern Astronomy. Trans, by J. McCabe. Svo, *2 00 Fay, I. W. The Coal-tar Colors Svo, *4 00 Fernbach, R. L. Glue and Gelatine Svo, *3 00 Chemical Aspects of Silk Manufacture i2mo, *i 00 Fischer, E. The Preparation of Organic ComprettmiSii Tjrirj. by R. V„ Stanford 121m}} *i 25 Fish, J. C. L. Lettering of Working Drawings .1 Jifelong SVji, i 00 Fisher, H. K. C, and Darby, W. C. Submarine Cable Testing Svo, *3 50 Fiske, Lieut. B. A. Electricity in Theory and Practice Svo, 2 50 Fleischmann, W. The Book of the Dairy. Trans, by C. M. Aikman. Svo, 4 00 Fleming, J. A. The Alternate-current Transformer. Two Volumes. Svo. Vol. I. The Induction of Electric Currents *S 00 Vol. II. The Utilization of Induced Currents *5 00 Propagation of Electric Currents Svo, *3 00 Centenary of the Electrical Current Svo, *o 50 Electric Lamps and Electric Lighting Svo, *3 00 Electrical Laboratory Notes and Forms 4to, *5 00 A Handbook for the Electrical Laboratory and Testing Room. Two Volumes Svo, each, *5 00 Fluery, H. The Calculus Without Limits or Infinitesimals. Trans, by C. 0. Mailloux {In Press.) Flynn, P. J. Flow of Water. (Science Series No. 84.) i6mo, o 50 Hydraulic Tables. (Science Series No. 66.) i6mo, o 50 Foley, N. British and American Customary and Metric Measures . . folio, *3 00 Foster, H. A. Electrical Engineers' Pocket-book. (Sixth Edition.) i2mo, leather, 5 00 Engineering Valuation of Public Utilities and Factories Svo, *3 00 Foster, Gen. J. G. Submarine Blasting in Boston (Mass.) Harbor.. . .4to, 3 50 Fowle, F. F. Overhead Transmission Line Crossings i2mo, *i 50 The Solution of Alternating Current Problems. Svo (In Press.) Fox, W. G. Transition Curves. (Science Series No. no.) i6mo, o 50 Fox, W., and Thomas, C. W. Practical Course in Mechanical Draw- ing i2mo, I 25 Foye, J. C. Chemical Problems. (Science Series No. 69.) i6mo, o 50 Handbook of Mineralogy. (Science Series No. 86.) i6mo, o 50 Francis, J. B. Lowell Hydraulic Experiments 4to, 15 00 Freudemacher, P. W. Electrical Mining Installations. (Installation Manuals Series ) . . . i2mo, *i 00 Fritsch, J. Manufacture of Chemical Manures. Trans, by D. Grant. Svo, *4 00 Frye, A. I. Civil Engineers' Pocket-book i2mo, leather. Fuller, G. W. Investigations into the Purification of the Ohio River. 4to. *io 00 Furnell, J. Faints, Colors, Oils, and Varnishes Svo, *i 00 10 D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG Gant, L. W. Elements of Electric Traction 8vo, *2 50 Garforth, W. E. Rules for Recovering Coal Mines after Explosions and Fires i2mo, leather, i 50 Gaudard, J. Foundations. (Science Series No. 34.) i6mo, o 50 Gear, H. B., and Williams, P. F. Electric Central Station Distribution Systems 8vo, *3 00 Geerligs, H. C. P. Cane Sugar and Its Manufacture 8vo, *5 00 Geikie, J. Structural and Field Geology ^ Svo, *4 00 Gerber, N. Analysis of Milk, Condensed Milk, and Infants' Milk-Food. Svo, i 25 Gerhard, W. P. Sanitation, Watersupply and Sewage Disposal of Country Houses i2mo, *2 00 • Gas Lighting. (Science Series No. iii.) i6mo, o 50 Household Wastes. (Science Series No. 97.) i6mo, o 50 " House Drainage. (Science Series No. 63.) i6mo, o 50 Sanitary Drainage of Buildings. (Science Series No. 93.) .... i6mo, o 50 Gerhardi, C. W. H. Electricity Meters Svo, *4 00 Geschwind, L. 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