UC-NRLF \\ GIFT OF MICHAEL REE&E J X MODERN TUNNEL PRACTICE ILLUSTRATED BY EXAMPLES TAKEN FROM ACTUAL RECENT WORK IN THE UNITED STATES AND IN FOREIGN COUNTRIES BY DAVID McNEELY STAUFFER r. Member American Society of Civil Engineers; Member Institution of Civil Engineers; Vice- President Engineering News Publishing Co. (i?8 ILLUSTRATIONS) NEW YORK ENGINEERING NEWS PUBLISHING CO. 1906 Copyright, 1905, by THE ENGINEERING NEWS PUBLISHING COMPANY Entered at Stationers' Hall, London, England 1906 "j. : Ft VALLEY- CO. PRINTERS AND BINDERS New York, U. S. A. CONTENTS PAGE PREFACE vii CHAPTER I TUNNEL LOCATION AND SURVEYING General rules for location Geological considerations Alignment of tunnels Station points Producing line from portal into tunnel Instrumental work at the Cascade tunnel Carrying center-line down a shaft Use of electric light in producing center-line I CHAPTER II EXPLOSIVES Gunpowder; its composition, reaction, measure of force, tempera- ture, etc. Nitroglycerine; its composition and appearance, action, original method of use Nitro-gelatine, as used in blasting opera- tions Dynamite; its action, etc. Lithofracteur, Forcite, Atlas powder, Hercules powder, Judson powder, Joveite The Sprengel class of explosives Safety or time fuses The primer Electric firing Cautions to be observed in firing high explosives The handling and storing of explosives Frozen dynamite and its treatment Powder magazines 14 CHAPTER III BLASTING General principles to be observed in proportioning depth and diameter of holes to the work to be done The line of least resistance in blasting The location of bore-holes The square and the V-shaped center cut The consumption of explosives Method pursued on the New York Subway work Testing the blasting qualities of rock Loading with black powder Loading with dynamite Effect of nitroglycerine fumes and precautions to be observed Hints on power-drilling Device for preventing the crushing of shaft-timbers by the flying rock 34 iii 146242 IV CONTENTS CHAPTER IV NOTES ON SHAFT-SINKING PAGE Location of a shaft Dimensions Relation of shaft-work to tunneling proper General conditions of shaft-sinking Forces exerted and precautions to be observed in framing A steel shaft-house Cages and skips A cheap hoisting-cage and head-house Shaft- sinking in wet gravel and quicksand Sheet-piling shaft 47 CHAPTER V ,4 PRINCIPLES OF TUNNEL TIMBERING AND DRIVING General rules Choice of timber English method of timbering as ap- plied in the United States Belgian and Belgian-French systems German S3'stem Austrian system American system Driving through loose gravel Crutch system Timbering a sand tunnel Meem poling-board system Iron crown-bar system Old rail crown-bars, their advantages and disadvantages Steel-lined tunnel Sand-chamber and caisson method Pilot-tunnel system Sewer tunnel in quicksand Dry-sand tunneling Enlarging tun- nel in soft grounds Sewer tunnel in dry sand 65 CHAPTER VI TUNNEL ARCH CENTERS Requisites of a good arch center Methods of framing centers Adjust- able or moving centers Steel-rib .centers Concrete-form for small tunnels Placing concrete lining in tunnels 99 CHAPTER VII SUB-AQUEOUS TUNNELS AND TUNNEL SHIELDS Form of shield and methods pursued at East Boston Subway East River gas tunnel Massachusetts pipe line Blackwell tunnel St. Clair tunnel Berlin-Spree tunnel Harlem River tunnel Penna. R. R. Hudson River tunnel Screw-jack shield Shankland shield Metropolitan Railway in Paris 112 CHAPTER VIII SUBWAYS, OR UNDERGROUND RAILWAYS General notes on location Orleans Railway in Paris Boston Subway East Boston tunnel Buda-Pest Subway New York Rapid Transit Subway Atlantic Avenue Subway in Brooklyn 144 CONTENTS V CHAPTER IX SPECIAL TUNNEL-BUILDING PLANT PAGE Cascade tunnel plant Scraper-loading Automatic dump at shafts Dumping-wagon Cement-mortar car Walker's detaching hoist- hook Concrete-mixer I7 1 CHAPTER X SOME DATA UPON THE COST OF TUNNELING Cost of hand-drilling in shaft-sinking Cost of power-drilling in shaft- work Cost of drifting and cross-cutting Cost of diamond-drill work Cost of square-set mine timbering Cost of mine hauling by compressed air Cost of concrete tunnel lining Cost of water- hauling vs. pumping in mines Cost of driving a mine-heading Cost of tunnel driving and steam-shovel work 186 CHAPTER XI THE VENTILATION OF TUNNELS The principles of artificial ventilation The Saccardo system Ventila- tion methods in the Boston Subway The East Boston tunnel, the Baltimore and Potomac tunnel, the Paris-Orleans Railway, the Pennsylvania Avenue Subway, the Simplon tunnel 201 CHAPTER XII AIR-LOCKS The general purpose of air-locks Their location The limits of human endurance under compressed air Effect of compressed air upon the workman Compressed-air hospital locks The O'Rourke air- lock Mirabeau bridge air-lock The Hughes air-lock Hyde Park tunnel air-lock Morison air-lock Victoria bridge air-lock Air- locks at Kiel dry-dock 213 CHAPTER XIII TUNNEL NOTES The freezing process for shaft-sinking in wet ground Its application at Ronnenberg and Iron Mountain Tunnel rock temperatures Definition of quicksand Making water-tight concrete The hand- auger in prospecting work Tunnel cross-section instrument Coxe plummet lamp 236 VI CONTENTS CHAPTER XIV PAGE The construction of the Simplon tunnel Water-works tunnel at Cin- cinnati, Ohio Telephone and freight transportation tunnels in Chicago 250 APPENDIX Glossary of some of the more unusual terms used in tunneling 301 PREFACE The practice of tunneling, in many of its important features, has been radically changed within a comparatively short period by the introduction of high explosives, by the use of machine drills, by special appliances for handling the debris or pro- tecting the roof of the tunnel, and by the employment of electric power and light. As a consequence of these innovations, much that was useful to the engineer and to the contractor in the older works upon tunneling is now out of date ; and with this in view, the present work has been compiled. As to methods to be pursued, it is unnecessary to tell the practicing engineer that each piece of tunnel work is prac- tically a problem calling for individual solution. No broad rules can be laid down which will cover all possible conditions, though some general principles for guidance can be formulated. In the arrangement of this work, therefore, especial effort has been made to present modern practice in tunneling under as many varying conditions as possible, and to clearly and con- cisely describe the methods actually adopted in carrying on the work under certain controlling conditions. The material used is very largely taken from the detailed descriptions of modern tunnel work as these are found in the pages of technical journals and in the proceedings of engineer- ing societies, supplementing this by the personal experience of engineers and contractors who do not usually make a formal record of this experience. Illustration is very freely employed, because it frequently tells more than can be expressed in the text alone. And in every case the description of any especial method is prefaced by a brief statement of the physical condi- tions which called for some particular treatment. It is believed that the examples selected cover a wide range of practice. As Vlll PREFACE only typical modern cases have been cited, no attempt has been made to include every important tunnel. The field is too wide, in fact, to be intelligently covered in any one book. The instrumental work, or surveying, connected with tunnel- ing, differs very little from that common to all larger public works, and as many special textbooks are devoted solely to the use and care of engineering instruments, what is here said upon that subject is intended simply as a general statement of the processes involved and of their sequence. The composition, nature and use of modern explosives have been treated at considerable length ; but here again, much has been left out that was considered as having little or no useful bearing upon modern practice in tunnel building. The writer acknowledges his indebtedness for some of the material here used, to Mr. Drinker's monumental work upon tunneling, published in 1878. And he has also freely used the comprehensive handbook upon explosives, written by Mr. M. Eisler, and the excellent manual on the care and handling of ex- plosives prepared by Prof. Courtenay De Kalb, for the Ontario Bureau of Mines. D. McN. STAUFFER. New York City, Dec. i, 1905. CHAPTER I TUNNEL LOCATION AND SURVEYING Selection of a tunnel route General rules for location Geological con- siderations Alignment of tunnels Station points The Cascade tunnel Carrying the center-line down a shaft Tunnel-targets. The route selected for a tunnel depends somewhat upon the end in view. If the tunnel is intended to meet the demands of modern rapid-transit in a great city, or if it is proposed to- connect two parts of a city separated by a waterway, the lines of traffic as indicated by existing streets will very generally control the location. In such cases the engineer has a com- paratively narrow choice of routes ; and he must deal with the problem as he finds it. Railway tunnels, other than the rapid-transit tunnels re- ferred to, have for their chief objects the reduction of grades .and the shortening of distance between given points separated by a dividing mountain or ridge, or a projecting spur. In such cases the surface conditions may be so complex as to ad- mit of several distinct tunnel lines between the terminal points ; and it is the business of the engineer to find the one line best adapted to the proposed traffic and the most economical in con- struction and operation. No fixed laws can be laid down for the engineer that will cover every possible contingency of tunnel location. The ex- perience of the locating engineer in similar work and his good judgment as based upon this experience can alone produce suc- cessful results. There are, however, some general points that must be care- fully weighed by the engineer as these are presented in his study of the actual topography of the country to be traversed. A tunnel is always an expensive and troublesome piece of >. . I , ,. ,. . - " , v I ".. C t. v V J- cC V" v - i.^iO'lijAD, 2 MODERN TUNNEL PRACTICE construction; and it should be avoided if conditions of traffic and the economic operation of this traffic will warrant any other solution of the problem. But it should not be forgotten that there are cases where a tunnel is safer and is really more economical in the end than an apparently cheaper open cut or a longer and curved line passing around some natural obstruction. In the case of the open cut, the material may show a tendency to slide, and the volume that ultimately may have to be removed, to provide a stable slope, may be so great as closely to approximate if not exceed the estimated cost of a tunnel. On the other hand, tunneling through ground of this description is expensive work ; and the utmost care and experience are necessary in deciding upon the plan finally to be adopted. As the necessary slope in the sides o'f a cut can rarely be decided upon in advance, and as this slope is practically controlled by the stratification of the ground, the operated line in an open cut is subjected to positive danger from slides of earth or rock. In elevated and mountainous regions, subject to heavy snowfalls and resulting avalanches, or falls of rock loosened by frost, the open cut is especially objectionable, and the more expensive tunnel may be advisable, and really cheaper in the end. In a winding valley with relatively sharp curves a tunnel or a series of tunnels will usually reduce distance and permit of a better location and more economical operation than a curved surface line. And in such cases it is often good practice to build a tunnel rather than to erect and maintain the bridges otherwise necessary at stream crossings. Careful surveys and a close study of alternative plans can alone decide these points. In the suburbs of large cities a tunnel may, again, be a cheaper structure than a sunken way, with its many street bridges, or than an elevated structure occupying valuable land. Geological Considerations in Tunnel Location The cost of a tunnel is largely measured by the character of the material pen- etrated. A careful study of the natural formation is therefore a necessary preliminary to any intelligent estimate of this cost, or even to any final location. TUNNEL LOCATION AND SURVEYING 3 It is practically impossible to foretell with any degree of cer- tainty just what material and what stratification may be found in the interior of a mountain. And that a geological forecast of this kind should have any value at all, this work should be entrusted only to a geologist of wide experience and good judg- ment ; and even then the records of engineering are full of the mistakes of experts in this connection. In most cases borings made along the line of the work can alone be depended upon, though these borings may also deceive if read by the inexpert. There are, however, surface indications that have some value in establishing the general character of the work to be per- formed. , If the rock, in its outcroppings, is hard and relatively little affected by atmospheric conditions, it may be classed as good and probably will stand well. If, on the other hand, this surface rock is seamy, or shows a tendency to disintegrate under the effect of moisture and frost, or if it contains pyrites, heavy timbering and troublesome and expensive work may be ex- pected. The general inclination of the strata, with reference to the tunnel section, and the frequency of seams in the rock, indicate to some extent the pressures or slips to be guarded against and the amount and kind of timbering necessary. The existence of bodies of water lying above the tunnel level, taken jn connec- tion with any prevailing direction in the rock seams, affords some indication of the amount of water to be dealt with and the pressure with which it will escape into the workings. In the case of a deep and long tunnel, however, it is generally im- possible to trace underground conditions with any degree of certainty; and the safest course is to generally guard against the unexpected. Among the treacherous and difficult materials encountered in tunneling the following are probably the worst : Laminated wet clay that may exert enormous pressures by swelling:: shales liable to swell and to disintegrate Upon exposure to air or water ; small, dry, loose sand or gravel, that will run. like a fluid through a relatively small opening and bring unequal pressures upon the timbering, and water-bearing sand. Each one of these 4 MODERN TUNNEL PRACTICE materials demands special treatment, expensive timbering and heavy masonry lining, and patience. How engineers have met these problems in actual practice will be seen in following chapters of this work. Tunnel Surveying. When the general location of a tunnel route has been definitely fixed, the points to be next considered are : The exact alignment, the gradients to be adopted, the final length of the tunnel, and the establishment of permanent sta- tions marking the line. Wherever possible the alignment should be a tangent. A straight line is the shortest line between two points, and it is most easily and certainly carried through the workings. In very mountainous regions, however, and especially where a line has to follow a deep and crooked gorge with precipitous sides, curvature in the tunnel or tunnels may be absolutely un- avoidable. And in great tunnels, like the St. Gothard, for ex- ample, spiral and looped tunnels are employed for the purpose of obtaining distance and consequently easier grades, in a line run between two points that are horizontally near each other, but vary greatly in relative elevations. Unless the grade is a continuous one, which is rarely the case, the summit or highest point in the tunnel should be as near to the center of the tunnel as possible. By this disposition of the summit natural drainage is secured toward the two portals. Except in very long tunnels, or in tunnels having a compara- tively small depth of ground overlying them, intermediate shafts have been largely eliminated by the introduction of high explosives and modern machinery, which vastly shorten the time of completion and do away with the necessity of increas- ing the number of working faces by multiplying shafts. This absence of shafts has a direct effect upon the drainage problem and decreases pumping. The final length of a tunnel is generally fixed by the most economical limits of the open-cut approaches; and this length cannot be definitely known until the approaches are actually completed. The instrumental work of a tunnel survey is largely that of TUNNEL LOCATION AND SURVEYING 5 any other important survey ; the chief requisites being first-class instruments and experience, care and patience on the part of the observers. Assuming that the line is a tangent, the problem to be solved is the laying down of this line across the mountain to be pierced, extending this line beyond both portals and then permanently marking the established line in such manner that it can be pro- duced into each portal. If the tunnel is surmounted by a single peak or ridge, from which both ends of the tunnel can. be seen, the problem is presented in its simplest form. The preliminary line, or a special survey, will approximately fix the summit point; but this point must then be tested and adjusted by a patient series of sights and reversed sights taken upon stations assumed to mark the ends of the line, and the necessary shifting laterally of the transit instrument. With the mean of many sights finally adopted as indicating the correct line, a perma- nent sighting station is fixed upon this summit which serves as a forward sight for each portal station, in prolonging the line into the tunnel as work progresses. If the tunnel is very long, or the summit of the mountain is broken into several ridges and the ends of the tunnel cannot be seen from a single middle station, then triangulation becomes necessary, with all the skill and careful work that this process implies. For shorter tunnels any standard work on surveying will indicate the triangulation methods employed; and for the greater tunnels, like those penetrating the Alps, the reader is referred to the history of these tunnels. In whatever manner the main station points have been es- tablished, they must be repeatedly and carefully tested under all atmospheric conditions; in winter and in summer, and by day and by night. Experience proves that the best time for sighting is about sunrise, before the heat of the sun can cause atmospheric disturbances. A plummet-lamp, used on a clear, calm night, is* usually found to give more accurate results than other forms of targets sighted upon in the daytime. The permanent station points should be very solidly con- structed, with stone foundations laid deep enough to be unaf- 6 MODERN TUNNEL PRACTICE fected by frost. And in the case of the summit station, sighting conditions may demand that the line point be transferred to the top of a strong and rigidly braced wooden structure, sur- mounted by a platform about 8 feet square. Especial care must be exercised in locating and in preserving the portal stations from all danger of interference; for it is from these stations that the line is prolonged into the tunnel. AVorkmen are proverbially careless in the matter of preserving "points," either inside or outside of the tunnel, and it remains to the engineer to devise means of minimizing danger in this connection. To diminish some of the difficulties encountered in preserv- FlG. I. Dunham Method of Tunnel Alignment. ing the tunnel points, Mr. H. F. Dunham, M. Am. Soc. C. E., suggests the following mode of procedure.* In the first place, he removes his line from the center of the tunnel approach, where it is always in trouble, to one side of this approach. At a point about 50 feet from the tunnel portal, and against one side of the approach, he built a strong timber platform, supported by 8 x 12-inch posts set 3 feet into the rock. As the alignment "Trans. Am. Soc. C. E.; Vol. XXVII, p. 453. TUNNEL LOCATION AND SURVEYING / of a timbered tunnel is generally established by the lining-up of the wall-plates, the level of this platform was such that when an ordinary wye-level was set upon it the line of sight would strike a little above and inside the line of the wall-plates on that side of the tunnel. To enable the instrument to be quickly set in position small holes were made in the platform and-pro- tected by iron washers, marking the position of the three legs. The distance between the center-line of the tunnel and the center-line of the instrument and the height of the instrument were carefully measured and noted; and these measurements were used in fixing a permanent target back of the portal and about 1,000 feet away. A gage-board of convenient form was then made, which would rest upon the corner of the wall-plate and also support a plummet-lamp. A larger board was pro- vided that would span one-half the distance between the wall- plates; and in both gages the parts liable to wear were pro- tected with iron. The work of alignment was then conducted as follows : The instrument was set upon the platform, sighted upon the rear target, and securely clamped. The level was next carefully re- versed in the wyes and used to line-in the plummet-lamp at- tached to the smaller gage-board, this board being held upon the wall-plate and the plate moved laterally, or raised and low- ered, as the rodman might direct. With the wall-plate on one side of the tunnel fixed in place, the longer gage, with a spirit- level placed upon it, was employed in determining the posi- tion of the opposite wall-plate. To carry out this method a space 2 feet wide and 2 feet high must be kept cleared of all timber and broken stone across the floor of the heading. Mr. Dunham, in describing this method, says that the neces- sary instrumental work can be done in one-fourth the time de- manded in the older methods. The work performed by the level was checked up at intervals by running-in the center line with a transit. Under conditions under which men could work, the plummet-lamp could be sighted upon up to about 1,000 feet. The Cascade Tunnel. The following account of instru- 8 MODERN TUNNEL PRACTICE mental work done at the Cascade tunnel of the Great Northern Railway is condensed from an article written by the then chief engineer, John F. Stevens, M. Am. Soc. C. E.,* now chief en- gineer of the Panama Canal. As shown by the map presented, we here have in concrete form the economic gain of a tunnel over surface crossing of this same mountain, the surface line in this case, however, being represented by a temporary switch- back used during the construction of the tunnel. This switch- back represents the cheapest location across the ridge. To have flattened out the curves and to have reduced the gradients by FIG. 2. Map, Showing Cascade Tunnel Location and the Temporary Switchback. the necessary loops would have made the contrast still more striking between, the surface and the tunnel lines. As compared with the switchback, the construction of the tunnel saved 9 miles in distance, 2,332 of curvature, and 700 feet in rise and fall. Aside from these considerations of construction and decrease in time of crossing the summit, the building of this straight tunnel vastly decreased the mainte- nance-of-way expenses. Mr. Stevens points out that the snow- fall in the Cascade Range is excessive, and in the winter of 1897-98 the aggregate snowfall at the summit of the switch- *Engincering News, Jan. 10, 1901. TUNNEL LOCATION AND SURVEYING Q back was 140 feet, with 20 feet of snow on the level at times. The removal of this snow from the switchback tracks was very difficult and costly; and this factor of expense, and also the delay in traffic, were the determining factors in deciding upon the tunnel line. The accompanying map shows that the mountain overlying the tunnel line has two peaks, the western or highest peak hav- ing an elevation of 2,150 feet above the portal at that end, and the eastern peak lying 1,750 feet above the east portal. By many trials transit points were established on each of these peaks, each commanding the other, as well as points just out- side the two portals. These points were carefully checked by observations, repeated many times under the most favorable atmospheric conditions. Timber towers 16 feet high were erected at each of these summit stations, and in the center of each tower gas-pipe tar- gets were secured ; each pipe was 2 inches in diameter and 20 feet long, so as to be seen above the deep snow ; and whenever the opportunity offered these pipe targets were tested by drop- ping a plumb-line through them to a tack below them. Inter- mediate fore-sights were also located on the mountainside, to be used when the summit targets were obscured by clouds. At each portal permanent transit stations were made by building a strong elevated structure, spanning the working tracks and roofed over. The length of the tunnel was obtained by direct measure- ments, this method being preferred to any system of triangu- lation possible on that ground. Measurements were made with a 400- foot steel tape, on measurement points previously established as nearly 400 feet apart as the nature of the ground would permit. These "points" were located on high stumps, on braces nailed to trees, or on plugs driven into holes drilled in the rock; the elevations of these points were carefully taken with the level. In measuring, the tension of the steel tape was regulated by a spring balance, and the tempera- ture was noted at each end of the steel tape. Work was usu- ally done on cloudy days and when there was little wind ; and TO MODERN TUNNEL PRACTICE as a preliminary a base-line had been laid out with a loo-foot standard tape, and with this the proper tension to apply to the 400- foot tape was fixed, 62 Fahr. being assumed as the nor- mal temperature. From the slope measurements, corrected for temperature and vertical measurements, the horizontal dis- tances were calculated. Inside the tunnel the measurements were carried along- the plumb-posts, and after the concrete lining had been completed each station was marked on plugs driven into holes drilled in the concrete. Bench-marks for the levelman were made in a similar manner. In prolonging the center-line, transit sights were placed in the key-segment of the timber arch ; and at intervals of about 800 feet platforms were erected at the elevation, of the wall- plates, with two independent floors, one to support the transit, and the other to hold the observer. Electric lights, carefully cen- tered, served as back-sights. By this arrangement of transit platforms the muck and concrete cars passed beneath them without interfering with the work of the engineering party. Carrying a Center-line Down a Shaft. While modern methods of tunnel-driving have eliminated shaft-work to a considerabl e extent, it is still necessary at times to transfer the center-line of a tunnel down a shaft, the difficulties of the problem increasing with the depth of the shaft. To do this the center-line must be carried to the mouth of the shaft, and marked upon permanent station-points located on either side of the shaft and about 25 feet away from the shaft. While the shaft timbers themselves may now be used for the prolongation of the center-line, it is better to place these marks on solid supports near to, but independent of the shaft lining. With these shaft points fixed, two horizontal steel wires, about one-sixteenth inch apart, are stretched between the points, with the space between the wires coinciding with the center-line. These steel wires are usually kept tightly stretched by means of a small drum and ratchet. To transfer to the bottom the line thus established over the mouth of the shaft, two wires of steel or copper, strong and as TUNNEL LOCATION AND SURVEYING II small as possible, are passed between the horizontal wires and as far apart as the dimensions of the shaft will permit. To the bottom of these wires two plummets, weighing 15 pounds or more, are attached. If the shaft is deep the suspended wires are liable to disturbance by air currents, or by falling water, and in such cases the wires are often protected by passing them through light pine boxes, about 6 inches square, attached to the floor of the shaft. To check oscillation in the plummet-wires the plummets themselves are allowed to swing in buckets of water, oil, or some other fluid, placed in the bottom of the shaft. The final operation is to determine, from the position of the two plummet-wires at the bottom of the shaft, the correct cen- ter-line ; to permanently mark this center-line at the bottom, and to prolong this line into the tunnel in both directions as the headings progress. As the base-line thus transferred is neces- sarily very short, an exceedingly small error is rapidly multi- plied in the prolongation, and the utmost care and patience must be observed throughout. To fix the line below, two beams are securely fastened just above the roof of the tunnel and close to the two plummet- wires. To these beams brass scales are attached, and the oscil- lation of the wires before these scales is patiently watched and noted. The mean of hundreds of these oscillations is finally assumed as marking the true line, and this mean is marked upon the scales. From these latter marks two other plummets are suspended, and from these thin wires the tunnel line is pro- longed by a transit, in the usual manner of shifting and check- ing. If the tunnel has a firm rock roof, the line of prolonga- tion is marked by driving plugs into holes drilled in the roof, and from small hooks in these plugs plummet-lamps are sus- pended for sights. The device shown in Fig. 3 is the scale used in marking the center-line at the bottom of the shaft on the Central Park tun- nel of the New York Rapid Transit Railway. In this case the distance between the wires was only 7.9 feet ; and fine piano wire was used for suspending 25-pound plummets, hanging freely in a tub of water. The brass bars were fixed in the 12 MODERN TUNNEL PRACTICE roof as shown, and the center part was graduated in tenths and hundredths of a foot. A vernier, reading to two-thousandths, slides over the top of the bar, with its zero intersected by the plummet-line. One of the most notable cases of alignment transfer down a deep shaft is the work of this class done at the Hoosac tunnel. This shaft was 1,030 feet deep, and it was encumbered by sixty-four separate floors. The base available at the bottom of the shaft was 23 feet long, and to this the line was transferred from the surface practically in the manner described above. But from this base of 23 feet the engineers prolonged the cen- i , '-Graduation \J Divided Into Tenths of Inches CM. \Plumb .- "** I Un Line Elvotlon. Cross Section. F IGt 3_Device Used for Marking the Center-line of a Tunnel, at the Foot of a Shaft. ter-line 1,563 feet east and 2,056 feet west, with errors of align- ment- of only 5-16 inch and 9-16 inch respectively. In this Hoosac tunnel the ordinary distant target was a dark- lantern with a small parabolic reflector and a panel of ground glass on the side facing the transit. In front of this panel the plummet was hung, this being sometimes a ^-inch turned, black rod forming part of the suspending line. At other times a brass plate was employed; this plate was 4 inches wide, and had in it a vertical slit from J to J inch wide, the slit coinciding with the plumb-line. With good air in the tunnel these sights were plainly seen at distances of 1,000 to 1,500 feet. At the present time electric lights are largely used in tun- nels for sighting purposes, and this light is so penetrating that TUNNEL LOCATION AND SURVEYING 13 it can be successfully used, even under somewhat foggy condi- tions. Kerosene lamps, which are easily handled by unskilled labor, also furnish excellent results; and in geodetic work an 8-inch reflector attached to a lamp of this kind enabled the light to be bisected at a distance of forty miles. CHAPTER II EXPLOSIVES Gunpowder; its composition, reaction, measure of force, temperature, etc. Nitro-glycerine ; its composition, action, and original method of use Nitro-gelatine, as employed in blasting operations Dynamite ; its action, etc. Lithofracteur, Forcite, Atlas powder, Hercules pow- der, Judson powder, Joveite The Sprengel class of explosives Safety or time fuses The primer Electric firing Cautions to be observed in firing high explosives The handling and storing of explosives Frozen dynamite and its treatment Powder magazines. A variety of explosive compounds are now employed in blast- ing operations, though the so-called modern high explosives have largely supplanted the old black powder for all tunneling work. But for purpose of information, the various explos- ive agents coming within the scope of this work are here briefly described. Gunpowder. This oldest of explosives is made of various percentages of nitre, sulphur and charcoal, according to the purpose intended. For military use, the proportions adopted by the War Department of the United States are: 75 parts nitre, 10 parts sulphur, and 15 parts charcoal. But, while this is the standard composition, for certain blasting operations, as in coal mining where a heaving, or rending, rather than a shattering effect is desirable a weaker composition is fre- quently employed, the proportions being as low as 65 parts nitre, 15 parts sulphur, and 20 parts charcoal. Good gunpowder should show hard, angular grains which do not soil the fingers, and the grains should have a perfectly uniform dark-gray color. If the color is bluish or jet-black, the powder contains an excess either of charcoal or of water. The appearance of bluish-white specks indicates that the nitre has effervesced in drying, or that the powder has absorbed suffi- 14 EXPLOSIVES 15 cient water to partially dissolve the nitre. In either case the mixture is no longer uniform. When gunpowder is new it should be free from dust, and it should leave no residuum or stain when flashed on a copper or porcelain plate. Probably the best summary of the results of the primary and secondary reactions that occur in the explosion of gunpowder is that given by Dr. Debus, as follows : "The combustion of gunpowder consists of two distinct stages : a pro- cess of oxidation, which is finished in a very short time, occupying only a very small fraction of a second, and causing the explosion, and during which potassium carbonate and sulphate, carbonic acid, and some car- bonic oxide and nitrogen are produced ; and a process of reduction, which succeeds the process of oxidation and requires a comparatively long time for its completion. "As the oxygen of the saltpeter is not sufficient to oxidize all the carbon to carbonic acid, and all the sulphur to sul- phuric acid, a portion of the carbon and a portion of the sul- phur are left free at the end of the process of oxidation. The carbon so left reduces, during the second stage of the combustion, potassic sulphate, and the free sulphur decomposes potassic carbonate. Hydrogen and marsh- gas, which are formed by the action of heat upon charcoal, likewise re- duce potassic sulphate, and some hydrogen combines with sulphur and forms sulphureted hydrogen."' The force of the blasting powder is measured either by the pressure of the gases given off or by the work done. The pressure of the gases depends upon the nature, volume and temperature; while the work performed depends upon the amount of heat given off. It is practically impossible, however, to exactly determine the potential energy of the explosion of gunpowder, owing to the fact that its rate of explosion is slow as compared with modern compounds ; and as nearly all rock is more or less seamy or loose, the gas escapes at every crack, and with this gas we also lose heat that would otherwise perform work. For these reasons the force resulting from the explosion of gunpowder cannot be even closely determined. Various au- thorities figure it from 15,000 pounds per square inch in loose rock, to about 200,000 pounds per square inch in the case of a modern type of gun, carefully loaded with the best and strong- est powder. 1 6 MODERN TUNNEL PRACTICE Sir Frederick A. Abel is quoted as stating that gunpowder yields upon explosion 43% by weight of permanent gases, and 57% of matter which is solid at ordinary temperatures; but part of the latter may exist as vapor when the powder is ex- ploded under pressure. At o Cent., and ordinary barometric pressure, the permanent gases generated by gunpowder occupy about 280 times the volume of the original powder. The tem- perature of the explosion is about 2,000 Cent., and these gases consequently exert a pressure, when developed in a confined space, which amounts to 6,400 atmospheres, or about 42 tons per square inch, if the powder completely fills the space in which it is exploded. Sir Frederick concludes that the total theoretic work which gunpowder is capable of performing, in expanding indefinitely, is about 486 foot-tons per pound of powder. Nitroglycerine. Nitroglycerine was discovered by Sobrero, in 1847, an d> generally speaking, it is the product of the action of concentrated nitric acid upon glycerine, though the processes of manufacture vary. At ordinary temperatures nitroglycerine is an oily liquid, clear and colorless, or yellowish ; it refracts light, has a sweet- ish and burning taste, is without odor, and has a specific grav- ity of 1.6. At lower temperatures it becomes solid. It is in- soluble in water, but dissolves easily in ether, wood spirit, ben- zol, chloroform, and hot alcohol. When taken into the human system it causes vertigo, weakening of sight, stupor, and pains in the cardiac region; and in larger doses it acts like strych- nine, over ten grains being fatal. Even mere contact with the skin produces serious symptoms, though workmen get used to it in time. Pure nitroglycerine does not decompose spontaneously at ordinary temperatures; it may be gradually heated to 100 Cent, without explosion, but it is then very sensitive to slight shocks. At 185 Cent., Champion says that 'it evaporates, boil- ing and evolving red fumes ; at 217 Cent, it burns briskly, and at 257 Cent, it detonates with violence. Alfred Nobel, the discoverer of dynamite, figures that one EXPLOSIVES 17 volume of nitroglycerine disengages 1,298 volumes 01 gas at 100 Cent, at ordinary barometric pressure; Dr. List estimates the bulk of the liberated gas at 1,505 volumes. At the lowest estimate, however, nitroglycerine evolves nearly six times as much gas as gunpowder at 100 Cent. But, as a far higher degree of heat is produced by the instantaneous combustion-of nitroglycerine, Nobel claims that this heat expands the bulk of the free gases to eight times the original 1,298 volumes, while the gas of gunpowder would not be trebled at the same temperature. According to volume, then, the explosive force of nitroglycerine compares with that of gunpowder as thirteeen to one. Nitroglycerine cannot be detonated by the simple application to it of a flame or heated iron ; in a thin sheet the liquid simply burns away like gunpowder. It is only when heated to 257 Cent, in a closed space, that the entire mass explodes. A sud- den blow will evolve heat enough to explode it ; but in this case only the portion of the liquid actually struck will detonate. If the nitroglycerine is frozen, however, a blow given, to a part of the mass is at once transmitted to the remaining portion, and accidents occur from this cause. The sun's rays also transform nitroglycerine into a very unstable, easily exploded substance. In practice, nitroglycerine is exploded by the detonation of an adjacent volume of gunpowder, guncotton, or fulminates; and this occurs whether the nitroglycerine is loose or under confinement. As at first used in blasting operations, nitroglycerine was employed in conjunction with gunpowder. A tin cartridge tube was filled first with gunpowder, and then nitroglycerine was poured in. The tube was closed by a cork and placed in a bore- hole, made somewhat larger in diameter than the cartridge, and the annular space was filled with a coarse-grained gun- powder, which covered the cartridge about one inch in depth. A fuse was inserted, the bore-hole was tamped with sand, and then fired. Nobel, later, poured the nitroglycerine directly into the bore-hole, and exploded it by a special black-powder de- tonator and a fuse. !g MODERN TUNNEL PRACTICE The efficiency of the new explosive was at once recognized, and a great demand for it arose. But the liquid explosive leaked away into seams, parts did not explode and lay hidden in pockets, that were later liable to detonation under the action of a drill. Many fatal accidents occurred, and the blowing up of ships at Colon and San Francisco, about 1866, stopped the transport of the new explosive. Attempts were made to render nitroglycerine non-explosive by adding methylic alcohol, that could be removed by shaking in water ; but the invention of dynamite, a comparatively solid form of nitroglycerine, caused the liquid compound to be abandoned except for some special use, as in increasing the flow of sluggish oil wells, etc. Nitrogelatine. The first marked improvement on the liquid form of nitroglycerine was the invention, by Nobel, of nitrogel- atine, or nitroglycerine solidified by means of guncotton collo- dion. This compound was a solid jelly, and its inventor claimed that it was very safe and highly suitable for every purpose to which a very powerful explosive could be applied. This explo- sive jelly was pressed into cartridges, and exploded either by a strong fuse or, preferably, by a powerful detonator charged with fulminate. As described by Gen. Abbot, nitrogelatine No. i, or blasting gelatine, contained 92% nitroglycerine and 8% nitro-cotton. It is straw-colored, quite elastic to the touch, has a density of 1.6, and it can be cut with a knife. It softens a little at a tem- perature of 122 to J4O Fahr., and when inflamed in the open it burns like dynamite, or dry compressed guncotton. Pure explosive gelatine, slowly heated, detonates at 400 Fahr. When mixed with 4 to 10% of camphor it simply burns with- out exploding at 570 to 600 Fahr., or the temperature at which gunpowder explodes. Nitrogelatine was one time quite extensively used in blast- ing rock under water, and is still useful in military operations. Dynamite. In attempting to render nitroglycerine less dan- gerous and better adapted to the uses of the engineer, Alfred Nobel finally invented dynamite. This is simply a combination of nitroglycerine with some porous and more or less inert sub- EXPLOSIVES IQ stance that will absorb and hold the liquid without leakage. Many materials were tried before Nobel adopted for this pur- pose kieselguhr, an infusorial earth, chiefly found in Hanover, and made up of very minute siliceous plant skeletons, that hold the liquid within their recesses. The great success attending the employment of this kieselguhr dynamite led to the inven- tion of a number of nitroglycerine compounds, all having for their main purpose the substitution of the solid for the liquid form, and some adding other ingredients intended to render the compound either more powerful or safer. The action and effect of dynamite proper are practically stated under the head of Nitroglycerine. Mr. M. Eissler, in his "Handbook on Modern Explosives," gives a useful table comparing the power which various explosives are capable of exercising, bulk for bulk. This table is of far greater import- ance in its application to blasting than any comparison of the relative power of explosive substances, weight for weight, and is as follows : Power of Explosives, Bulk for Bulk. Nitroglycerine 100.0 Ammonia powder 80.0 Dynamite, No. I, 75% nitroglycerine 74.0 Lithofracteur 53.0 Guncotton 60.0 Lithofracteur. This compound is made of 55% nitroglycer- ine, 21% kieselguhr, 6% charcoal, 15% barium nitrate and carbonate of soda, or either of them, and 3% sulphur and man- ganese oxide, or either of them. Forcite. Forcite was invented by Capt. J. M. Lewin, of the Swedish army. It is a mixture of nitroglycerine with cellu- lose, the latter being gelatinized by heating in water under con- siderable pressure. As manufactured in America and Belgium, forcite is a thin blasting gelatine, or nitro-cotton, incorporated with a mixture of nitrate of soda, coated with molten sulphur and wood tar. 20 MODERN TUNNEL PRACTICE To counteract the stickiness of the tar, i% of wood pulp is added. Atlas Powder. This is a composition of nitroglycerine, wood fibre, nitrate of soda, and 2% to 3% of carbonate of magnesia. It is made in various grades, containing from 20% to 75% of nitroglycerine. American Hercules Powder. In the No. I grade of this powder the proportions and ingredients are stated to be 75% nitroglycerine, 20% carbonate of magnesia, 2.1% nitrate of soda, 1.05% chlorate of potash, i% white sugar. The carbonate of magnesia is here employed as the absorb- ent. The claim is made that the resultant fumes from explosion are not so bad in their effect upon the miners as those arising from dynamite. Mr. Eissler says that this advantage may be due to the presence of the alkaline absorbent, which gives off gases which contain no carbonic oxide. Judson Powder. In this powder, instead of absorbing the nitroglycerine, as in the case of dynamite, a thin film of $% to 15% of nitroglycerine is used as a final operation to coat grains of non-absorbent and non-hygroscopic oxidizing salts. This process is carried out in various ways. One example of the oxidizing salts mentioned by Eissler is made up, by weight, of 15 parts sulphur, 3 parts resin, 2 parts asphalt, 70 parts nitrate of soda, 10 parts anthracite coal. The sulphur, resin and asphalt are melted together and well stirred ; and to this melted mixture are added the nitrate of soda and the coal, both pulverized and thoroughly dry. The mixture is then gently stirred until so cool that the grains cease to ad- here together, and these grains are thoroughly varnished. The nitroglycerine is added when the explosive is to be used. This powder is extensively used, is cheap, and is more powerful than common mining powder, depending for its strength on the per- centage of nitroglycerine. Joveite This substitute for dynamite belongs to the picric- acid class of powders. It is made by melting crystals 'of solid nitronaphthaline and solid picric acid in a steam- jacketed kettle or mixer, after which solid nitrate of soda is added. The prod- EXPLOSIVES 21 uct is a yellow, granular substance resembling sawdust or cornmeal. This product is sold either in the granulated state or is made up into cartridges, resembling outwardly "sticks" of dynamite. Joveite is fired with a cap, either with a fuse or with an elec- tric battery. If the cap, however, is not thrust into the~end of the stick, but placed about f of an inch away from It, the joveite will not explode. In a test held in 1903 one capped stick was placed within 2 inches of the other sticks lying around it, and fired. The capped stick exploded, but the others did not. As joveite contains no liquid in its original composition, it is a solid, and should not freeze any more than black powder. And as it is made at a high temperature, Charles E. Munroe, Ph.D., of Columbian University, states that it is not subject to changes of condition or alternating heat and cold. He says that the powder showed no change after being exposed in open boxes in a room for four years. Its makers also claim that the fumes of burnt joveite produce no ill effect upon the work- men. It can be used in wet holes or under water, though it should not be left there long enough for the nitrate of soda to leak out. This difficulty is overcome by its makers, by put- ting it into cloth-covered wrappers entirely impervious to water. The explosive power of joveite, as compared with nitro- .glycerine powders, is not stated ; but as tested in a steel mortar, is over three times stronger in projectile force than black powder. As made in three grades, joveite No. i is said to be equivalent to 20% dynamite ; No. 2 is equivalent to 40% dyna- mite, and No. 3XX is the equivalent of 60% dynamite. Bulk for bulk, joveite weighs fully one-third less than most dyna- mites of equal grade. It was patented in 1894. Sprengel Class of Explosives. In 1873 Dr. Hermann Sprengel introduced a type of explosive which had for its char- acteristic feature the admixture of an oxidizing with a com- bustible agent, at the time or just before it was to be used, the separate constituents of the mixture being non-explosive. Dr. Sprengel originally used substances one or all of which would be liquid, as liquids better assured a speedy and' intimate 22 MODERN TUNNEL PRACTICE mixture. But it was found by experience that there was too much danger attending the mixture of liquids by ordinary workmen, and other substances were discovered which were safer- and still retained the advantages of the Sprengel prin- ciple, so far as transportation and mixing were concerned. Rack-a-Rock. This is the most widely known of the Spren- gel mixtures. Gen. Abbot says that the best results are secured when rack-a-rock is made of 79 parts of potassium chlorate and 21 parts of mono-nitrobenzene. These ingredients may be safely transported and stored separately. When required for use the chlorite cartridges are placed in a special wire basket and dipped into a vessel holding the liquid mono-nitrobenzene for three to six seconds, depending on the size of the cartridges. The cartridges are then allowed to drain, and in ten minutes they are ready for use. According to Gen. Abbot, rack-a-rock has a specific gravity of 1.7, and is a compact solid. It requires a very powerful de- tonator to explode it, and it decrepitates with difficulty when hammered on an anvil. Gen. John Newton, Corps of Engi- neers, U. S. A., employed 240,399 pounds of this explosive in blowing up Flood Rock, in the East River, New York. Hellhoffite. This compound was invented in 1885 by Hell- hoff and Gruson. It is made of approximately 47 parts of meta-di-nitrobenzene and 53 parts of nitric acid. On mixture it appears as a dark-brown liquid. If mixed, and not immediately wanted for use, the di-nitrobenzene can be recrystallized by gradually adding water to the mixture, the acid being wasted. To develop the full force of this compound a detonator is required that is twice as powerful as that used with dynamite. It is more powerful than nitroglycerine in the ratio of 106 to 100; and it can be stored and transported with perfect safety. But it is a liquid ; the acid is volatile and can only be stored in perfectly tight vessels ; it cannot be used for submarine work, as water renders it completely inexplosive; and the acid acts injuriously on the copper casing of the detonators. Other Sprengel Compounds. Other explosives of this type are known as Oxonite, Plancastite, Romite, etc. But, while EXPLOSIVES 23 their great power as explosive agents is undoubted, their prac- tical value is greatly diminished by reason of the relatively high degree of intelligence required in their proper admixture; by the fact that they are liquids; by the serious objection made to the fumes of the exploded ingredients in confined places, and by the fact that they cannot be used under water. They Thay have value for military operations, as their proper manipula- tion would be thus generally assured. Safety or Time Fuses. The ordinary or Bickford fuse includes a core o meal-powder, tightly compressed and en- closed in a wrapper of spun yarn impregnated with a water- proof composition. These fuses are made in various forms, with "single" and "double" tape, etc., the thicker wrapping be- ing employed in damp places. In using any make of safety fuse it is well to carefully deter- mine the rate of burning. This is simply done by attaching different lengths of fuse to blasting caps and noting the time necessary for the powder to explode the cap. With the rate of burning known, the miner can cut a sufficient length of fuse to allow him ample time to retire to a place of safety before the charge is exploded. In capping a fuse, examine the cap carefully to see 'that no particle of the sawdust in which the caps are packed remains inside. Cut the end of the fuse cleanly and squarely, and insert it in the cap until it is in close contact with the upper surface of the fulminate. The fuse must fit the cap snugly. If the fuse is too large, pare it down ; if it is too small, wrap it with paper until it fits snugly. When this is all done the free end of the cap is tightly crimped to the fuse, so that it cannot be detached. If the charge to be fired is in a very damp place, or under water, the joining of the cap and the fuse should be made watertight by a coating of paraffine, tar, shellac, or some such substance. Primer. The primer is the cartridge to which the cap and fuse are attached. This primer is completed and the cap at- tached to the cartridge as follows : One end of the wrapper of the cartridge is opened in the case of a dynamite cartridge 24 MODERN TUNNEL PRACTICE and a smooth, round stick, slightly larger in diameter than the cap, is used to make a hole in the center of the cartridge. In this hole the cap is inserted ; the cartridge is compressed by the hand so as to come in contact with the cap, and the end of the paper wrapper is then drawn around the fuse and tied tightly with a string. The cap should only have two-thirds of its length inserted into the cartridge; otherwise, the burning fuse might set fire to the cartridge before igniting the fulminate in the cap. The completed primer is preferably placed in the center of the charge to be fired, and always in contact with the charge. The object of the blast in each individual case must determine the placing of the charge itself. If only one cartridge is used in a hole, it is still advisable to use a primer, using for this purpose a piece of cartridge about two inches long, to which the fuse and cap are attached as described above. Electric Firing. The ordinary safety fuse has several serious disadvantages when employed to explode dynamite cartridges. It is liable to "miss fire," and to "hang fire," the last of these be- ing the cause of innumerable accidents. It is also impossible to secure simultaneous action in the explosion of several charges, and there is a consequent loss of effect in the explosion. In using the electric system of firing dynamite cartridges, the electric cap is entirely buried in the primer-cartridge ; and, instead of tying the paper wrapper around the fuse, the fuse wires are doubled back and fastened to the primer by two half- hitches. Electric Fuse. The so-called low, medium and high-tension electric fuses only differ essentially in the manner of igniting them. The low-tension type acts by the heating of a very fine wire, imbedded in a proper priming, and the uniting of insu- lated conductors. The medium and high-tension fuses are fired by the passage of the electric spark over a break in the me- tallic circuit, this spark igniting a suitable priming. Each electric fuse has two insulated conductors, a plug to receive and firmly hold the ends of the conductors near EXPLOSIVES 25 to, but not touching each other ; a small, sensitive priming prop- erly arranged at the plug for firing, and a metallic cup or cap, usually containing fulminating mercury, representing the de- tonating charge. The so-called fuse-wires, extending out from the cap, must always be well insulated, and should not be less than two feet long. Connecting or Lead Wires These two wires conduct the electric current from the igniting apparatus to the primer-car- tridge. One of these wires conducts the electricity to the cap, and is known as the "conducting wire" ; the other completes the circuit back to the igniter, and is known as the "return wire." These wires should both be well insulated, for should bare wires touch each other or the ground a "short circuit" may be formed and the firing of the charge prevented. Bare wires can be used in special cases by placing them on poles and insulators. The best connecting wires are made of perfectly clean copper wire covered with india rubber insulation. For short distances wires may be insulated with paraffined cotton yarn, and these answer fairly well. Firing Apparatus. Various forms of igniting apparatus are employed in connection with the use of electric fuses. But the favorite machine and one that is compact, strong and reliable is the magneto-electric apparatus. This machine, as usually supplied, is contained in a wooden box about 16x8x5 inches, and weighs about eighteen pounds. Outwardly, this box shows a strap-handle, two brass binding-posts for the lead wires, and a central firing-bar working vertically. Without entering into the detail of the inner mechanism, it is sufficient to say that the novelty of this device lies in the method adopted for ro- tating a Siemens armature between the soft iron prolongations of the cores of an electro-magnet. The brass firing-bar has a wooden handle at the top, and one side of the bar has rack teeth cut upon it, engaging in a loose pinion fitting over the armature spindle prolonged. When the bar is descending a clutch holds the spindle to the pinion, the pinion rotates, and a strong electrical current is produced; as 2 6 MODERN TUNNEL PRACTICE the bar ascends the clutch releases the spindle ; there is no ro- tation, and action is thus restricted to the one downward move- ment of the bar. The purpose of this one-direction action is to avoid possible accidents in manipulating the machine. To use this igniter, the ends of the two connecting wires are well cleaned, inserted in the two binding-posts on the box, and firmly held in position by the binding screws. The firing-bar is then pulled up to its full length, and when all is ready the bar is pushed down with a quick, uniform motion. Electricity is thus generated, transmitted by the wires to the cap, and the charge is exploded. This machine may be temporarily disabled by two causes: ( i ) Dust or dirt may get between the platinum contact-points inside the box. To remedy this, remove the rear of the case and use a piece of fine emery-cloth on the contact-points. (2) The surface of the transformer or commutator may become tarnished. In this case open the rear of the box as before, and withdraw the firing-bar by first taking out a small pin at the bottom of the bar. The shelf holding the internal mechanism can now be partially withdrawn ; the springs pressing upon the commutator and the spindle-yoke can be disconnected, and the face of the commutator can then be cleaned with emery-cloth. Precautions to be Observed in Firing -High Explosives. In his lectures on explosives, delivered before the U. S. Artillery School, Lieut. W. Walke, U. S. A., gives some general advice upon the use of electricity in firing high explosives. This ma- terial is here condensed, with some additional matter added. To reap the full benefit of this method especial attention must be paid to the preparation of the connecting wires. To pre- vent the ends of the leading wires from being constantly blown off, the "fuse wires" and the "connecting wires" should be con- nected by a coupling of two short wires. And, if practicable, the fuse wires should be long enough to extend at least six or eight inches outside of the bore-hole. To connect the fuse and leading wires, pare off two to three inches of the insulating material from the ends of the wires and clean these ends with sand-paper. To join the wires, bend EXPLOSIVES 27 back the ends of the wires to form hooks; hook the wires to- gether, and then twist the ends of the wires closely and firmly around the hooks. Some old miners recommend as a better method the crossing of the ends of the wire, and then making about six close twists about the standing parts of the wires. In either case a close, tight twist is necessary, as a slack joint makes a bad connection. In very damp ground this joint may be protected by slip- ping a small piece of thin rubber tubing over one wire before joining, and when the connection is made the tubing can be slipped over it and tightly tied at the ends. A rule of great importance is : Never connect the fuse and the connecting wires until you are absolutely sure that one, at least, of the leading wires is disconnected from the igniting apparatus. The very last thing to be done before actually firing the charge is the connecting of the leading wires with the firing apparatus. All other connections must be made before this is done, and every precaution taken to see that the charge is ready for explosion. All bare joints in connecting wires should be kept off the ground and out of the water; if this cannot be done, protect the joints as described above. Special reels are made for handling the leading wires, and their use will be found to be economical. By proper attention to all these details, Lieut. Walke says that it is possible to simultaneously fire fifteen charges in the same circuit. Handling and Storing of Explosives In his "Handbook on Modern Explosives" Mr. M. Eissler gives some excellent ad- vice in this direction, summarized as follows : 1. Put dynamite into close quarters, and hold it there by the most unyielding method of confinement at command. Let there be no vacancies about the charge of any kind or degree. 2. Always tamp if you can. But use a wooden rammer; never use an iron or steel bar with any explosive. 3. If you value your fingers, do not fool with the cap "to see what is in it." * 28 MODERN TUNNEL PRACTICE 4. The charge must fit and fill the bottom of the bore-hole, and be packed solid. 5. Never pick out a "miss fire" of powder or dynamite, but gently clear out the hole to within about eight inches of the old charge. Then place a fresh cartridge, or a piece of one, in the hole, and fill it up again as before. Fire this, and it will explode the original charge below. 6. Never attempt to roast, toast or bake frozen dynamite, and never put it into heated vessels or on boilers. The only absolutely safe method of thawing out frozen dynamite is to keep it in a room at summer heat and away from the fire until it is soft. 7. Never put a cap into a charge or a primer until you are ready to use it. And after the charge or primer is capped never let it leave your hands until it is put into the hole. Keep all caps away from the dynamite until the charge is to be fired. Invariably prepare your primer away from the explosive. 8. Never allow smoking, or other forms of fire, near the ex- plosive. Powder and other explosives burn rapidly, especially when loose; and if any caps are incautiously left near by they may be fired and a dangerous explosion result. 9. Do not get nitroglycerine upon your fingers. It will be absorbed by the skin and cause headache, or worse. 10. For powder, use the best quality of double-tape fuse; it is always the cheapest and best in securing results. When you know that the ground is almost dry you can use single- tape fuse. Frozen Dynamite When dynamite and other nitroglycerine compounds are frozen they can only be exploded by very strong primers; but the effect of the explosion is more violent than when exploded in a soft state. As a rule, the frozen mass does not become uniformly hard throughout, because of slight variations in the proportions of nitroglycerine in different parts of the mixture, and partly be- cause the external portion of the cartridge will be more thor- oughly frozen than the interior, unless the exposure to cold is very prolonged. It may happen that partly frozen or wholly EXPLOSIVES 2 9 unfrozen dynamite may be more or less completely enclosed in a strong crust of perfectly frozen, and comparatively very cold dynamite. On exposure to considerable heat, rapidly applied, some part of the cartridge may be ignited and the unfrozen portion exploded. In such a case the hard, frozen dynamite practically acts as the metal envelope of a detonator ; the ex- plosive is confined and in a condition to exert extreme violence. The explosion of the unfrozen dynamite acts as a detonator or primer, and explodes the remainder of the dynamite. For the reasons given above, Sir F. A. Abel points out the danger of assuming that because frozen dynamite is less sen- sitive to the effect of a blow, or to initiative detonation, than is the thawed material, it may be submitted to the action of heat, for the purpose of thawing it, without using special care. Thawing Frozen Dynamite There are only two ways of safely thawing out frozen dynamite : ( i ) By placing the frozen FIG. 4. Dynamite Thawer: Hamilton Powder Co. cartridges in a room heated to a summer heat by steam pipes, being careful to keep the explosive away from the pipes them- selves. (2) By placing the cartridges in a suitably constructed vessel surrounded by water heated to 125 Fahr. The water should be heated separately and poured into the thawer. Sheet zinc is the best material for this thawer, though galvanized iron is largely used. A form of thawer is sold which is built somewhat upon the model of a glue-pot. It has a hot-water receptacle, into which 30 MODERN TUNNEL PRACTICE fits another annular vessel for holding the cartridges. The water space between the inner vessel and the outer wall should be at least two inches wide. For thawing large quantities of dynamite at a time, the following plan is shown in Mr. De Kalb's "Manual," as recommended by the Hamilton Powder Company : A barrel has fitted into it a circulating hot-water system of pipes, with an expansion pipe. This pipe system passes through a wall, and is heated by a stove. The barrel is filled with water, which is heated by the hot water circulating in the pipes, and kept hot. The frozen dynamite is put into the zinc or gal- vanized iron receptacle suspended in the barrel. In using any kind of thawer, the only way of being sure that there are no accumulations of nitroglycerine in the thawer is to wash the thawer out after each thawing with a strong solu- tion of washing soda, best applied warm. To the same end, all sawdust should be removed from the cartridges before they are put into the thawer. As long as the dynamite feels lumpy in the cartridges it is not properly thawed. It should be uniformly pliable through- out. Aside from the danger in loading, partially thawed dyna- mite is less powerful in exploding, and it gives off particularly noxious fumes. Dynamite-thawing House The dynamite-thawing house shown in Fig. 5 is one recommended by the commissioners ap- pointed to investigate the explosion of dynamite on the Fourth Avenue section of the New York Rapid Transit Railway, on January 27, 1902. It is intended to hold 500 pounds of dyna- mite. The special feature of the design is the arrangement of the drawers immediately back of folding doors, leaving no space for a man to stand inside the magazine; and making it unnecessary to use any form of artificial light in handling the dynamite. An experimental house built on this plan cost $200. Magazine. In the storage of ordinary black powder, im- munity from fire is a first consideration. As it is assumed in this work that the powder magazine is a more or less temporary structure, the more permanent forms of magazines are not here EXPLOSIVES 3 T discussed or described; and in general the form recommended is suitable for storing gunpowder or dynamite. The Austrian law on. the storage of all explosives requires that the structure used for this purpose should be as light as Sheet Iron or Tin covering throughout K -4'7- - -> Vertical Section. Hot . Water Pipe leaves Top of Heatfr Lnc, ' NE.WS. FIG. 5. Dynamite-Thawing House. possible. The purpose of this law is that, in case of explosion, the building may be completely disintegrated and no pieces of any size be thrown to a distance, thus reducing the radius of the danger zone to a minimum. In England the law demands 32 MODERN TUNNEL PRACTICE a more substantial structure, as a precaution against fire and burglars. But in a comparatively open country the light struc- ture is preferable. Storage in a tunnel, cave, or other similar place should never be permitted, as such places are almost in- variably damp, and any powder containing nitrates will be damaged. A suitable structure for the storage of explosives on ordi- nary contract work may be described as follows : Use a 2 x 4- inch frame, and cover with weather boarding. Put in a tongue- and-grooved tight floor, blind-nailed, and the inside walls and ceiling may be sheathed with the same stuff. The roof should be A-form, and a covering of strong tar paper will make it tight. When there is danger from fire the roof and the outside walls may be covered with the lightest kind of steel shingles. A structure of this kind, 6x6 feet on the base, and 6 feet high, will hold about 216 kegs of powder. As a further precaution, bottom ventilators should be put in, with the openings covered with wire to keep out vermin ; and a hooded ventilator pipe should be extended from the ceiling through the roof. In a region where there is danger from rifle balls, the magazine may be built with a 6-inch space, enclosing fine, dry sand, extending upward as high as the kegs or cases of explosives are to be piled. Prof. Courtenay De Kalb, in a "Manual of Explosives," issued by the Ontario Bureau of Mines, says that, by actual experiment, the ball from a Lee- Metford rifle, at a range of twenty-four feet, only penetrated five inches into a sand protection of this type. Storing In magazines, kegs of powder should be kept slightly inclined on suitable racks. Dynamite, when stored in tiers of cases, should have wooden battens between the tiers to insure ventilation and to lessen danger from friction. No fulminates, or caps, and no loose coils of fuse should be stored in the same building with powder or dynamite. The building should be kept very clean, and no fires or smoking permitted in or near it. Gunpowder kegs should be rolled over every two or three days, to prevent caking. Cases of dynamite should be turned EXPLOSIVES 33 over every two weeks. This tends to keep the dynamite homo- geneous in composition and is economical. No keg of powder or case of dynamite should be opened inside the magazine. This should be done in a distant and special small building, never containing at one time more than 200 pounds of an explosive. Keep kegs closed after taking out what powder is wanted. In the case of dynamite^ unpack the cartridges and wipe off the sawdust, which usually contains some nitroglycerine. Carefully remove this sawdust and the boxes and burn them at some convenient distant point Lay the cartridges on their sides on planed boards, and keep these boards clean at all times by removing oily stains with washing soda. CHAPTER III BLASTING General principles to be observed in proportioning the depth and diameter of the holes to the work to be done The line of least resistance The location of bore-holes The square and the V-shaped cut The con- sumption of explosives Method followed on the New York Subway Testing the blasting properties of rock Loading with black powder Effect of nitro-glycerine fumes, and precautions to be observed Hints on power-drilling To prevent the crushing of shaft-timbers by flying rock. No rigid rules can. be laid down for the diameter and depth of holes, the direction these holes should take, the distance apart of holes, or the amount of the charge placed in each hole. The character of the material, the purpose of the blast, and a number of other and varying conditions will here control. Effi- cient work in blasting is a matter of experience and good judg- ment on the part of the miner, and this cannot be gained from books. But writers on this subject lay down some general and fundamental rules which must be observed in the interest of systematic, economical work. Prof. De Kalb, in his "Manual," quoting from the works of Daw, Oscar Guttmann and others, lays down the following points of prime importance and general application : 1. The strength and quantity of the explosive should be prop- erly proportioned to the cohesive strength or resistance of the rock. 2. The "burden," or line of least resistance (i. e., the shortest line that can be drawn from the charge in the bore-hole to the outer free face of the rock), should bear a proper relation to the strength of the explosive and the resistance of the rock. 3. If the working face of the rock is so blasted as to leave two or more free faces, instead of one, for further blasts, the 34 BLASTING 35 power required to overcome the resistance of the rock will be reduced, and explosives can be economized. 4. A seam or fissure is a valuable aid in blasting if the hole is so located as to take advantage of this weakness ; on the other hand the power of the explosive may be expended along such a seam without doing useful work, if the hole is improperly located. 5. Breaking to regular benches and faces is more economical than irregular breaking, because the condition of the rock can be more carefully observed, the subsequent bore-holes can be more intelligently placed, and it facilitates the setting up and handling of machine drills. It is also more convenient for hand-drilling. 6. Simultaneous firing of charges is more economical, in general, than single or series shots; for the adjacent charges assist each other, reducing the amount of explosive required and the total length of holes drilled for removing any given volume of rock. 7. Careful charging greatly increases the efficiency of the explosion. 8. In the case of high explosives a well prepared primer is the key to a successful detonation of the charge. Other things being equal, all efficiency depends on this. 9. The efficiency of all explosives, including high explosives, depends to a considerable extent upon the kind, length and de- gree of compactness of the tamping. 10. The object of blasting in a tunnel, quarry or mine is to rupture the rock so that it may be removed ; hence only enough explosive should be used to do this. When fragments are thrown more than a few feet by a blast, it is generally an evi- dence that too large a charge was used for the length of the line of least resistance. In the accompanying illustration, Fig. 6, B N is the bore- hole, W L is the shortest line measured from the center of the charge to the free face A K. M is the charge, which should be about twelve times as long as the diameter of the bore at the bottom ; R S K is the outline of the new face after blasting. 36 MODERN TUNNEL PRACTICE To obtain the best results the line of least resistance W L should be perpendicular to the bore-hole and shorter than the bore-hole. If it is not shorter the force of the explosion will exert itself in the direction of the bore-hole, and the result will be a crater, or a so-called "gun," with relatively little effect. In very strong, compact rock the distance between holes, in simultaneous firing, should be at least twice the length of the line of least resistance; for average strong rock, ij to 2 times; FIG. 6. Blasting Nomenclature. for moderately strong rock, i to i^ times, and for weak rock this distance should not exceed the length of the line of least resistance. The lines of least resistance should be proportional in length to the diameter of the bore-holes, and Mr. Eissler gives the following table on this head : No. i. " 2. " 3- DIAMETER OF BORE HOLES. 1^4 in. iK in. LINES OF LEAST RESISTANCE. 3Y 2 feet. 4 feet. 3 3 A " 5 " 5 " 6 " 5 feet. 7 " Mr. Eissler gives the corresponding depth of the bore-holes as: No. i, equal to line of least resistance; No. 2, i| times that length ; No. 3, twice that length. BLASTING 37 The economy in simultaneous firing varies with the strength of the rock ; but it may be stated as an average, that there is a saving of about 25% in the explosives used. Under the best conditions there is also an economy of about 24% in the boring, depending on the distance apart of bore-holes. Locating Bore-holes In tunnel driving or shaft-sinking, the first holes are drilled for the purpose of "unkeying" the face. If there is a persistent joint or seam, advantage should be taken of this seam, and the "key" may be thus broken out to the full depth of the cut with a minimum of explosive. In homogeneous rock a square of V-shaped center cut is generally adopted. Square Center Cut Again quoting fromDeKalb's "Manual," we have the plan and elevation of a square center cut (Fig. 7) FIG. 7. The Square Center-cut. in a rock heading 7 feet high and 6 feet wide. The small cir- cles in the plan indicate the commencement of the holes, and the parallel lines show their projection, or direction. The sectional elevation on the line A B shows this further, though hole No. 1 8 is only approximately accurate. In this heading 20 holes have been bored reaching to a dis- tance of 3 feet 3 inches from the face, which is the depth of the cut. Nos. i, 2, 3, and 4 are the "unkeying" shots, converging 38 MODERN TUNNEL PRACTICE to a point ; these holes preferably unite at the point, and they must be fired simultaneously. The remaining 16 holes are for the "enlarging" shots, to be fired in two or three successive volleys. The plan most economical of powder would be to fire 5, 7, 9, ii in a second volley; 6, 8, 10, 12 in the third; 13, 14, 15, 16, 17, 1 8, 19, 20 in the fourth and last volley. Conditions, however, might make it more economical to use larger charges in 6, 8, 10, 12 and include them in the same volley with 5, 7, 9, ii. The last is one of the trimming-up shots; and to avoid irregularities in the rock it is essential to start the holes as close to the walls as possible, and to give them very little inclination. V-shaped Center Cut In this form of cut (Fig. 8) there are fewer dry holes to be bored, and the "key" can be broken out fo'M, End Elevation. Cross Section* FIG. 8. The V-Shaped Center-cut. with smaller charges, as I, 2, 3, 4 are short holes, with corre- spondingly short lines of resistance. There are 22 holes in this heading. Nos. i, 2, 3, 4 constitute the first volley, and provide shorter lines of resistance for the next shots 5, 6, 7, 8; holes 9, 10, n, 12, 13, 14 make the third volley ; and the trimming volley includes 15, 16, 17, 18, 19, 20, 21, 22. In the case of both types of cut here described, the methods of procedure are given as suggestions for economical work under normal conditions. They must be suitably modified as these conditions vary. An example of drilling and blasting methods is here taken BLASTING 39 from the work performed on the New York Rapid Transit tun- nel. The diagrams (Fig. 9) further illustrate the remarks already made on pointing and firing holes, and also note the usual nomenclature for the various holes. The method of excavating the tunnel is substantially the sin- gle top-heading and bench method commonly employed in The United States. Both heading and bench, however, were un- keyed, or broken out by an opening and a trimming cut. Alto- gether 40 holes were drilled and blasted in opening up the full tunnel secticrn. The approximate location and depth of these holes is shown in the diagrams, and with the work well under way, the sequence of firing is given in the table below : BENCH HOLES. Order of firing. I. II. Kind of holes, No. 7 grading. 5 bench. Depth, feet. 3 to 5 9-5 Charge, pounds. 50 45 Climax, Dynamite, per cent. 40 40 HEADING HOLES. II. 6 trimming. 3 to 9 42 40 III. 8 center cut. 9 56 60 IV. 8 side. 8 48 40 V. 6 dry. 8 36 40 NOTE All holes taper from 3 to 2% in. diameter. Consumption of Explosives. The amount of explosive re- quired can only be determined by intelligent experiment under actual conditions present. But as a general guide one authority approximately estimates this consumption as follows : For small blasts in open workings, J to \ Ib. of black powder, and i- 1 6 to -J Ib. of dynamite, per ton of rock. For large blasts, in open workings, \ to \ Ib. of black powder, and \ to -J Ib. of dynamite, per ton of rock. For headings, tunnels and shafts, ^ to 2 Ibs. of dynamite per ton of rock. In his "Handbook of Modern Explosives/' Mr. Eissler gives a table of the quantity of explosives actually used in the course of tunneling work executed for the Glasgow Corporation Water Works. The average quantity of explosives, etc., used is given for each cubic yard in the several tunnels. 40 MODERN TUNNEL PRACTICE ER CUBIC YARD OF EXCAVATION; REDUCED . LINEAL YARDS OF TUNNEL. gall's. Remarks. rt Q bb rt ffi | rt b cu o CO d CJ rt O CJ CO bb G G E 1 I O Q bb G 1 U 2 1 1 1 CJ I 1 43 3 CO c/} cu C IS CJ rt S jj 2 1 d CJ rt "c O CJ I 3 CO c/j CU _c IS CJ rt 1 rt HH d 0.050 Dry red sandstone. Hand drilling. Sub-contract. O rt Q bb *o T3 C rt cu C O 1/0 T3 C rt C/3 W 1 d & 8 USED TT Candles Longitudinal Section. B.H. "Bench Holes 6. H. Grading Hole* C.H. - Cut 5.H. - Sic/9 n Q.H. " Dry n T,H. Trimming FIG. 9. Drilling and Blasting Methods on the New York Rapid Transit Tunnel. holes of the standard diameter, 3 feet deep, thus giving a line of least resistance equal in each case to 2 feet. The distance be- tween these holes should be at least three times the length of the line of least resistance, so that one shot shall not influence another by opening up seams. Now charge* the several holes with different weights of the explosive, beginning with a quan- tity so small as not to effect rupture, and increasing by regular amounts to a charge that will be more than sufficient. Select the blast which has produced the desired effect as the one deter- mining the coefficient. 42 MODERN TUNNEL PRACTICE For example: If this hole were charged with f Ib. (0.625 Ib.) of dynamite, then the rock coefficient is 0.625 = 0.0781 2 3 (=8) The charge for future blasts is then found by multiplying the cube of the length in feet of the line of least resistance by this coefficient. Thus : If this line is 2f feet, the amount of dynamite necessary would be 2.75 3 (=20.797 X 0.0781 = 1.624 Ib. As the specific gravity of well compacted, high- grade dynamite is about 1.6, and as the bore-hole has a diameter of 1 1 inches, the charge will occupy a length of 1.25 feet in the hole. This is approximately correct also as to the length of charge in the bore-hole, which should have been 1.5 X 12 = 18 inches. Guttmann recommends that where there are more than two free faces the proper charge will be as follows : For 3 free sides, f of the calculated charge. For 4 free sides, -J of the calculated charge. For 5 free sides, 2-5 of the calculated charge. For 6 free sides, \ of the calculated charge. Loading with Black Powder The ordinary practice in load- ing a hole with black powder may be outlined as follows : Re- move the sludge and dry out the hole by any proper material tied to the end of a long rod. Pour in the powder so that it does not touch the sides of the hole above the charge ; for horizontal or inclined holes, the powder may be deposited in small paper bags, closely pressed home by a wooden rod. Special water- proof cartridges are supplied for wet holes. The fuse is now put in place, or tied to the last bag of powder, if bags are used. Dry clay is next pressed over the charge, followed by 3 inches of ordinary wet clay pressed in firmly. After this further tamping may be rammed by tapping the end of the tamping stick with a hammer. Practice shows that the amount of tamping desirable is determined by the diameter of the hole and not by the volume of the charge. The least depths of tamp- ing material admissible are : For a hole 2 inches in diameter,. BLASTING 43 7 inches of tamping; for a 2^-inch hole, 18 inches ; for a 3-inch hole, 20 inches. The depth of tamping should always be some- what in excess of these figures. When Dynamite Is Used. Mr. Eissler gives some useful gen- eral directions relating to the drilling and loading of holes with dynamite, condensed as follows : As a general rule the drill holes and charges for dynamite can be and should be comparatively small. In heavy work r however, the holes should be larger in size and less in number, and the amount of dynamite should be proportioned to the work to be done. A general rule applicable to all explosives is : That the quantity of explosive should not only be proportionate to the resistance, but the hole should be proportionate to the explosive, or the explosive to the hole. Tamping dynamite is of great importance. Mr. Eissler says that it is a fallacy to suppose that dynamite "strikes down- ward" more than upward, and that tamping is thus useless. By reason of its quickness of action dynamite, without tamp- ing, will do much work where gunpowder would do nothing; but the former will do much more effective work when tamped. In deep and down holes a sufficient amount of water makes a good tamping, but sand, brick dust or clay are much better. A shallow tamping of water has little effect. In a fissured rock the charge should be surrounded with mud, clay, sand or water, when possible. In tamping dynamite use the same precaution for putting in the first portion of the tamping as specified for black powder. As a precautionary measure, it is well to push a ball of old newspaper just over the primer and under the tamping. If the shot misses fire this paper will indicate the nearness of the explosive, in removing the tamping for putting in another car- tridge, as before described. The paper also prevents the scraper from coming in contact with the fulminating cap. To insure effective work the dynamite must not be frozen; the fuse must be good and properly fitted and kept in the cap ; the cap must be kept dry, and must not be withdrawn from the explosive. 44 MODERN TUNNEL PRACTICE Dynamite, as a rule, throws rock less and breaks it more, and extends its effects much deeper than ordinary gunpowder. The great advantages of modern explosives, says Mr. Eissler, consist not so much in diminishing the cost of explosives, as in increasing the amount of work done. The difference in the cost of high explosives and gunpowder is trifling in comparison with the difference in cost of drilling, charging, tamping, con- venience in wet work and effectiveness of blasts. Effect of Nitroglycerine Fumes. The best account of the effect of nitroglycerine fumes upon workmen exposed to them is probably found in a paper presented to the Medical Rec- ord, in 1890, by Thomas Darlington, M.D., of New York. Dr. Darlington bases his article upon 1,300 cases of asphyxia, partial asphyxia and poisoning resulting from the product of dynamite combustion, and treated by him during the construc- tion of the new Croton Aqueduct for New York City. He divides his cases into two classes ; acute cases, where the men inhaled considerable quantities of the gas at one time ; and chronic cases, where the men constantly breathed a small amount of the gases. In the acute cases, the symptoms are : giddiness, a trembling sensation, frequently nausea, sometimes vomiting, a fullness in the head, and intense headache; the heart's action is increased and the pulse is full and round. If the man is brought into sudden contact with a large percentage of the poisonous fumes as just after a blast the giddiness is immediately followed by unconsciousness, and the patient pre- sents the usual appearance of asphyxia. The comatose condi- tion soon passes away and is succeeded by drowsiness, languor, cold perspiration, intermittent pulse, and generally nausea and vomiting. Nearly all the cases mentioned recovered, no matter how serious they seemed at the time. In the chronic cases the four prominent symptoms are : head- ache, cough, indigestion, and disturbance of the nervous system. The cough is similar in character to that of pertussis, or ma- laria. In nearly all cases there is a continuing headache and neuralgia. As soon as the patient is removed from the tunnel and put to work above ground, he steadily improves and will BLASTING 45 finally recover entirely. Men who previously suffered from dyspepsia or neuralgia are made much worse by dynamite smoke. In treating these cases, Dr. Darlington proceeded as in cases of asphyxia, adding to this treatment cold applications to the head; and he administered subcutaneously atropine, ergotme, or other vaso-motor stimulants. He recommends that work- men carry small vials of aromatic spirits of ammonia for imme- diate use, in case of necessity, as he believes that a nitrate is formed in the blood from the decomposition of nitroglycerine. The inhaling of ammonia also has a beneficial effect. Hints in Power Drilling. In seamy rock, drills mounted on a bar are apt to bind in a hole, and much time is lost in pounding them loose. Instead of discarding the power for a hand-drill, some miners advise the use of the tripod as a mounting in such cases. The whole machine can then be moved slightly by rais- ing or lowering one of the legs, and the trouble due to binding is entirely done away with. In overhead stoping, however, a tripod cannot be so readily set up or moved, because of the irregularity of the broken rock on, which it stands. But in such case a rough platform of lag- ging can be used to advantage. Or a small wooden triangle answers even better than the platform, as it holds the tripod and is readily blocked up. To facilitate drilling in seamy ground it is recommended to make the short bits, used first, larger in diameter than the long ones. And another expedient is to use drills having four shoulders or wings, extending 6 or 8 inches up the drill-shank from the cutting edge, and only a trifle less in diameter than the drill. These wings check the tendency of the cutting edge to follow the slant of a seam. To Prevent Crushing of Shaft Timbers by Blasting. Mr. C. K. Colvin, M. E., of Denver, Colo., describes a "float," or a device used to prevent the crushing of the bottom timbering of a shaft by blasts. This consists of two thicknesses of i-inch boards laid crosswise and faced on each side with ^-inch boiler-iron, well bolted. 46 MODERN TUNNEL PRACTICE The wood center acts as a cushion to protect the plates. This float is built at the bottom of the shaft, and is large enough to extend at least 2 inches beyond the timbers. It is supported at the four corners by 2-ton chain blocks, and just before firing it is pulled up tight against the bottom timbers. There is a "bucket-hole" through the center of the float and this is closed by a chain net. After some months' use the float is usually battered into a cup shape ; it is then turned over so that it will be battered back again. CHAPTER IV SHAFT-SINKING Location of shafts Dimensions Relation of shaft-work to tunneling proper General conditions of shaft-sinking Forces exerted on tim- bers and precautions to be observed Steel shaft-house Cages and skips Cheap form of hoisting-cage and head-house Shaft-sinking in wet gravel and quicksand Sheet-piling shaft. At the present time shaft-sinking is largely confined to the extraction of minerals of various kinds and to the exploitation of city subways, or subaqueous tunnels. In the days of black powder and hand-drilling, shafts were sunk at frequent inter- vals on railway tunnels of any considerable length, for the pur- pose of providing a greater number of working faces and thus hastening the completion of the work. The use of high explo- sives, power drills and improved machinery for removing the debris have so increased the rate of progress in tunneling work that the old-time necessity for a number of shafts has largely disappeared. Location of the Shaft. Where a shaft is necessary it may be located directly upon the center line, or to one side and outside the width of the tunnel. In the United States the former posi- tion is very generally preferred. The shaft on the center line is better adapted to transferring the alignment to the tunnel below; it is more convenient for the laying of track and the handling of cars at the foot of the shaft ; and the center shaft costs less than one for which a cross-cut has to be made. In treacherous soil the side shaft may also bring about a disturb- ance of the material at the side of the tunnel and lead to a dangerous slip. Dimensions. The horizontal dimensions of a shaft must be carefully proportioned to the character and amount of material to be hoisted, and to the pumping and ventilating plant that 47 48 MODERN TUNNEL PRACTICE may possibly be needed. A shaft that is too small for the work proposed is an endless source of trouble and expense, for the shaft is the neck of the bottle through which everything must pass in and out, and its dimensions are thus the controlling factor. The usual shaft is rectangular in plan and nearly twice as long as it is wide. This form permits of the establishment of separate compartments for hoisting and for the pumping and ventilating pipes, and provides means for the constant inspec- tion and repair of the pipe system without interfering with the regular hoisting work. Unless the shaft is a permanent one ladders or a stairway are seldom provided. Square or circular shafts are badly adapted to the disposition of the plant. Shaft Sinking. Owing to its vertical or sharply inclined position and the consequent collection of water on the bottom, or working face ; to its limited dimensions ; to the extraction of the material by a bucket-hoist, and to the necessary shifting of pumps and pipes, competent authorities estimate that it re- quires, from 1 5 to 20% more time to sink a shaft per lineal foot of advance than to drive a tunnel heading of similar dimen- sions. The cost is also much greater owing to the conditions cited. The method adopted for sinking any shaft depends entirely upon the character of the material to be penetrated. If this material is fairly solid and homogeneous rock, with little water, the task is a comparatively simple one. But if the material is water-bearing, is soft or liable to run into the bottom of the shaft as it is being excavated, it is only a question, of time when the ground about the shaft will be "moving" and exerting unequal and destructive pressures upon the shaft timbering, tending to tear these timbers apart vertically. Every precau- tion must be taken to prevent this movement in the adjacent soil by careful timbering, and by floors, if the soil is very soft. In very bad soil iron cylinders are sometimes employed, either sunk in solid rings added from above and forced down, or by segmental rings bolted into place at the bottom. In loose or running ground, with any system of timbering SHAFT-SINKING 49 that may be adopted, the important precautions to be observed by the timber-men are the following : Make the timbers heavy enough to resist all lateral pressures. To guard against the horizontal separation of the sets, or timbers, see that these sets are securely tied together vertically, thus anchoring them to timbers on firm ground above if such ground exists ; and in any event, hang the timber together as the shaft is built down- ward. Above all, prevent, if possible, the removal of any ground outside the cube of the shaft itself ; any space thus left outside the timbers by careless excavation will be filled up by pressure from above and gradually start a dangerous movement in the soil about the shaft. In very soft ground the material in the bottom may have a tendency to swell, or "rise" in the shaft. This is an exceedingly troublesome problem to deal with, and is overcome usually by flooring the bottom of the shaft and strongly bracing from above, and sinking this floor in sections made as small as possible. As a rule, in bad ground, all open- ings made in the sides for new timbers, or in the bottom for sinking, should be so small as to be always under control, care- fully "poling" the space to be finally provided for a new timber, in such manner as to prevent a "run" of soil from without. In sinking a shaft or in driving a tunnel too much stress can- not be laid upon the importance of adhering as closely as possi- ble to the true section of the excavation. As remarked before, voids outside this section inevitably invite and bring about pres- sure, and the final amount of this stress cannot be even esti- mated. If such voids are unavoidable, as is often the case in tunnel driving, they should be carefully and completely filled by masonry or by packing of loose stone. And it is the duty of the engineer to see that this is done. With the purpose of hasten- ing the completion of a certain piece of masonry careless work- men are too prone to scamp this packing, with the impression that it will never be discovered. This is especially the case in tunnel lining ; and the writer has personally known cases where a man could stand upright in the space left over a tunnel arch, and where empty cement barrels were substituted for the stone packing called for in the specifications. As a matter of fact, 50 MODERN TUNNEL PRACTICE few tunnel linings fail under direct pressure upon this lining; in nearly all cases failure can be directly traced to unfilled voids. Various methods are employed for sinking a shaft through sand or other water-bearing material of a comparatively homo- geneous nature; and some of these methods are described in more detail in succeeding pages. Among these methods may be noted the plenum pneumatic, or compressed-air process, oper- ated either in iron cylinders bolted together by horizontal flanges, or in caissons connected with the part above the water level by cylindrical shafts. The use of compressed air in this connection is practically limited to a depth of about no feet, by its effect upon the human organism, and it is generally em- ployed in foundation work for piers in bridges or building construction. The freezing process is employed under circumstances which warrant the necessary expenditure, in sinking a shaft through w r ater-bearing material. In this process the ground and the contained water is frozen to a solid mass for some distance out- side the limits of the shaft, by first sinking vertically a circle of special double pipes, penetrating to the full depth of the pro- posed shaft, and then circulating through these pipes brine or other freezing compounds. When the ground is sufficiently solid the shaft is excavated and lined in the usual manner. This process is described in more detail in a following portion of this book. The Kind-Chaudron method of shaft-sinking had its origin in Belgium and has had a limited use in sinking shafts in the coal regions of that country. Briefly stated, the process con- sists in sinking iron cylinders by using heavy and specially de- vised cutters for breaking tin the bottom material ; these being operated from the top of the shaft and through any depth of water in the shaft. The material thus broken up is removed by dredging through the water, and as the cylinder sinks, its length is increased by adding sections at the top. It is an ex- pensive method, slow in operation, and is liable to fail from the difficulty of keeping the cylinder in a vertical line, and its con- sequent jamming. SHAFT-SINKING p" .!.*< n i 1 1: | (L o 1 Z JE } a Q. , 4 -7T 1 - CLL/i::^ A 1 I I I O I jj 'H, c c/5 52 MODERN TUNNEL PRACTICE In his monumental work on tunneling* Mr. Drinker gives the following general precautions to be observed in sinking a shaft through treacherous ground. These precautions amplify some of the remarks made above. 1. Regular and constant examination of the shaft-timbering ; so that all wedges, bolts, props, joints, etc., may be kept tight. 2. All holes must be quickly stopped, and even small cracks should be at once plugged with straw or similar material. 3. Careful, tight connection must be maintained between the inner and outer timbering. If wedging does not suffice, use props, or spikes and clamps. 4. Where there is wrenching and distortion, connect the sets by longitudinal "bars," or put in rakers or bearing beams, when the ground at the bottom of the shaft is solid enough for this purpose. 5. Do not forget that all pressure is intensified by neglect, and that this pressure tends to increase in considerably more than a direct proportion. After a shaft is sunk to the tunnel or mine level, it must be operated; and for this purpose a hoisting plant is necessary, proportioned according to the amount of hoisting work to be performed and the temporary or permanent character of the work itself. The shaft-house, or head-house, contains the steam- generating plant, the hoisting engines, drying-rooms, etc. ; and the head of the shaft must be equipped with the proper railway tracks leading to the dumping ground, or to storage or load- ing bins. A Simple Hoisting Cage. The tunnel elevator, or cage, here illustrated is intended to show a cheap and easily constructed hoisting appliance that has been thoroughly tested by long and hard service. In the particular case referred to, the timber used in its construction was hard pine, though other strong wood can be employed. It was entirely made upon the works, and its detail and dimensions are fully shown in Fig. 10. The shaft-guides were 4 x 4-inch yellow pine sticks, planed *"Tunneling, Explosive Compounds and Rock Drills," by Henry S. Drinker, E.M. ; New York, 1878, John Wiley & Sons. SHAFT-SINKING 53 on three sides and secured by f-inch counter-sunk bolts to a 4 x lo-inch timber as shown. These guides were kept well oiled. The safety appliance was made of a pair of steel-pointed chisel- arms, secured at the elbow by a i^-inch pin passing through the uprights of the cage ; and these pins practically carried the whole weight of the cage and its load. On the bottom of the cross-head of the cage frame an iron plate, ^-inch thick, was secured; and against this plate reacted a strong, three-leaf spring, passing through the bottom of the bar carrying the hoisting rope. The inside ends of the chisel-bars worked in a box secured to the bottom of this suspension-bar. The spring was adjusted so as to resist the weight of the empty cage ; and so long as the hoisting rope was intact the vertical part of the chisel-arm lay inside the socket provided in the uprights. But, should the rope break from any cause, the spring was re- leased, and the horizontal arm was pushed downward by it; the vertical or chisel-arm was thus pushed outward and into a position to cut into the 4 x 4-inch guide member as the cage de- scended. In this particular cage the safety device was severely tested several times by the breaking of the hoisting rope, with a full load on the cage. In each case the cage was brought to a standstill with a maximum fall of 20 inches ; the guides were badly cut up in the operation, but their construction permitted the rapid replacement of the damaged portion. The "cage-stop," for holding in adjustment the platform track and the track leading to the dump, was effective and eas- ily handled. The cage in ascending opened the stops ; and these fell- into place by gravity as the cage passed through them. In sending the cage down, the latter was hoisted a little, and the stops were thrown back and out of its way by the hand- lever shown. As an open shaft-mouth is a source of frequent danger to the top-men, this shaft was always closed at the top, either by the cage itself or by a grillage made as shown. This grillage was long enough to extend over the sides of the opening and strong enough to support a car. When the cage came up it lifted the grillage with it on the cross-head of the 54 MODERN TUNNEL PRACTICE cage. The hoisting frame is sufficiently well shown in the illustration. Steel Shaft-house. During 1902 the Oliver Iron Mining Company, of Duluth, Minn., put down two shafts at Ely, Minn., 1,500 feet apart, but both operated by a single hoisting plant. As the house at each shaft is constructed of steel, a brief description of the plant is here given, as showing the latest practice in this direction.* The shaft-house here shown (Figs, n and na) was built by the American Bridge Company at its Minneapolis shops, and is 30 feet wide on the face, 75 feet deep on the ground level, FIG. na. Foundation Plan of Steel Shaft-house, Ely, Minn. and is 158 feet high from the collar of the shaft. About 265 tons of structural steel were used in its erection. The main frame is made of columns composed of pairs of steel channels, with horizontal lines of steel channel-framing be- tween them. As it is not advisable to build column foundations close to the shaft, the first columns are supported on a heavy box girder. The two heavy, inclined columns at the rear of the *For a detailed description of this plant, by Mr. Frank Drake, M. Am. Inst. M. E., Chief Engineer of the company, see Engineering News, Nov. 19, 1903. SHAFT-SINKING 55 house act as braces to resist the pull of the hoisting ropes, which pass over the 1 2-inch grooved sheaves near the top of the house. At a height of 33 feet above. the shaft is a projec- Half front Elevation. .' Half Reor ElevOT FIG. ii. Steel Shaft-house: Oliver Iron Mining Co., Ely, Minn. tion enclosing the guides and cages, this projection being sup- ported by cantilever girders with latticed webs. At the level of the first floor is a line of 36-inch plate-girders and lattice-. MODERN TUNNEL PRACTICE girders between the outer columns, instead of the 1 5-inch chan- nels between the inner columns, as shown in the section. The fine and lump ores are dumped from the cages through separate hoppers into bins; from the latter it is discharged as Front Elevation. FIG. 12. Cage for Sibley Shaft : Oliver Iron Mining Co., Ely, Minn. required into cars standing on tracks which pass through the shaft-house. These hoppers are made of 5-16 inch steel plate; while the bins have plank lining attached to the structural framework. The whole shaft-house is sheathed with corru- SHAFT-SINKING 57 gated steel, painted with two coats of iron-ore paint on all its members, excepting only the interior of the hoppers and the lining woodwork. Cages and Skips. As one shaft is vertical and the other in- clined, the cages and skips used differ in design ; and both types are here shown in all their dimensions. All of the structural material is soft, open-hearth steel ; the floor is 2-inch plank cov- ered with ^-inch steel plate. The two draw-bar springs are . .^_ FIG. I2a. Skip Used in the Sibley Shaft. made of square steel, and they have an outside diameter of 6^ inches, and a length of 7 inches when free. Under 10,000 pounds load the compression is ij inches. The skip for the vertical shaft weighs 4,678 pounds, or 4,935 pounds with a lip. The construction is plainly shown in the illustrations. Shaft-sinking in Wet Gravel and Quicksand. The Penn Min- ing Company, of Norway, Mich., in 1890 found it necessary to sink a shaft through 60 feet of glacial drift very heavily 50 MODERN TUNNEL PRACTICE charged with water. It was decided to sink a caisson, or drop- shaft, to reach the underlying impermeable stratum. The top of the shaft (Fig. 14) was 6x 13 feet inside; the bottom was made 4 feet larger each way, or lox 17 feet in- side; and to within. 12 feet of the bottom the shaft was divided into three compartments, the middle one being uniformly 4 feet Anachmenr TO Cage I A \. j. v & " " ~ " Front Elevation. yfaaanr 1 1 | '* i n Ii . i i, ^: |j g ^ Bottom Plan ife Side Elevation N tws. Section of Guide Shoe on Line A- B. FIG. 13. Skip for Savoy Shaft. wide. As shown in Fig. 15, the pumps were placed in the two end compartments, and these were covered over to admit of sand for loading the caisson. The middle compartment was used for hoisting, the pipes, etc. A ventilating box was put in one corner of the shaft. SHAFT-SINKING 59 The bottom timbers of the shaft were oak, 15 inches square, beveled to 6 inches. Above these came white pine sticks 12 inches square, framed in sets and bolted together and to the shoe with eight bolts each 5 feet long. The successive sets were reduced i inch in width and length, until at 48 feet above the bottom the dimensions corresponded with the top set. The corner-posts were 12 inches square, and broke joints with each other. They were bolted to every other side and end piece. The bolts were put in from the inside, with the nuts counter- sunk; they were thus easily recovered when the corner-posts were removed. The side-posts were secured in a similar man- 4..-. v ,8'.... FIG. 14. Top and Bottom Sets: Harrison Shaft, Norway, Mich. ner, one at each corner of the middle compartment. At every 5 feet 12-inch dividers were used. After the ground had been leveled the caisson was built up and bolted to a height of about 30 feet. The seams were care- fully caulked outside, and 3-inch plank was spiked on vertically to protect the 'caulking and still further strengthen the caisson. Steam hose, and later elbowed pipe, were used to connect the pump with the boilers. The quantity of water to be pumped was estimated at 1,500 gallons a minute ; and this water was charged with fine, sharp sand, that rapidly wore out the pump-linings, causing delay. The shaft was sunk the 60 feet in sixty-three days, including all delays. The flow of water at the bottom was stopped as follows: The corner-posts were taken out, the bolt-holes were plugged, 6o MODERN TUNNEL PRACTICE and the inside of the shaft was caulked. Then the shaft was sunk 1 1 feet into the ledge. To seal the bottom of the drop- shaft, a set of 12 xi 2-inch timbers, 6x13 feet inside, was carefully placed in line with the top set, as shown in Fig. 16, and extending about 6J feet below the shoe. This set was FIG. 15. Harrison Shaft: Longitudinal Section. thoroughly blocked against the rock by wedges, and six other sets were built upon it, each being bolted to the one below. A thin layer of clay was put over the wedges, and, as the suc- cessive sets were put in, a concrete of equal parts of sand and cement was packed between the timbers and the rock. Through the top set, which was about on the level of the shoe, SHAFT-SINKING 6l twenty 2-inch holes had been bored ; and behind these holes was laid a 4-inch layer of broken stone. Three other sets were laid on this last set, gradually widening out, with the top set bolted to the sides of the caisson. The space behind these was also filled with concrete, and this was allowed to set. The holes FIG. 16. Method of Closing the Bottom of the Harrison Shaft, Norway, Michigan. in the special set were finally plugged, and the inflow of water at once dropped to 200 gallons per minute. Thorough inside caulking further reduced this flow to 90 gallons. Sheet-piling Shaft.* The Brooklyn shafts for the extension *For a detailed description of this work see Engineering Record, Oct. 3i, 1903- 62 MODERN TUNNEL PRACTICE of the New York Rapid Transit Railway under the East River are made of sheet-piling, as here shown. The two shafts are 50 feet apart on centers, and each one is 23 feet 1 1 inches by 20 feet 2 inches in inside dimensions, and is 65 feet deep. The ma- terial penetrated is as follows: Ten feet of loam, 35 feet of boulders and gravel, and the remainder is in sharp, fine sand that runs quite freely. The water level is about 60 feet below the street surface. The shafts (Fig. 17) were sunk by open excavation inside sheet piling driven down as the work progressed. An outer vertical Boards M'Lbncf . Plon of Shof* Timbering Section thr FIG. 17. Sheet-piling shaft: New York Rapid Transit Railway, Brook- lyn Extension. guide frame of 12 x 1 2-inch timbers was first- laid down on the ground; and inside of this were placed the 12 x 1 2-inch rangers, braced as shown. In the 4-inch space between these sets the 4 x lo-inch tongued and grooved braced sheet-piling was driven. These piles were cut at the lower end to an angle of 60, and shod with a thin, bent steel plate 7 inches wide. The sheet-piling was driven by a steam hammer, commencing at one corner of the shaft and driving successively around the four sides, driving each pile uniformly one to two feet at a time. A gang of ten men, working ten hours per day. exca- vated 15 feet of shaft in one week. The sheet-piling was 65 feet long; and each pile was made SHAFT-SINKING In five sections with a halved butt and lap-joint, each joint secured by eight or more 5-inch wire nails. The excavation was kept just above the bottom of the sheeting. The corner sheeting was dovetailed and bolted together, and driven as one pile. The bottom ranger set was braced up horizontally from ta z i \u _ Sheet Pile Driver, suspended from Derrick Boom. PiG. I7a. Device for Cushioning the Blow of the Hammer on Sheet-piling. the bottom of the pit, while the piles were driven against it. After the excavation had been carried about 2 feet below this set a second ranger set was put together at the bottom of the pit, and lo-ton hydraulic jacks were set up at each corner of the shaft reacting upon the frame above. As the digging pro- ceeded these jacks drove the bottom set downward, and this 6 4 MODERN TUNNEL PRACTICE was continued until there was a space of 6 feet between the sets. The upper frame was now temporarily supported on cleats nailed to sheeting, and the jacks were removed. Dig- ging was resumed, and as soon as 2 feet had been gained the above operation was repeated. The ranger sets were hung to each other by a pair of vertical planks nailed in each corner. The pile-driver had special wooden leads, made as shown FIG. 18. Plan and Elevation of Shaft at Aspen Tunnel. (Fig. 173), and arranged in such manner that the 2,ooo-pound hammer struck this wooden packing and thoroughly drove the piles. The accompanying illustration (Fig. 18) shows the method adopted for timbering a shaft on the Aspen tunnel of the Union Pacific Railway. This shaft was 331 feet deep, and penetrated hard but seamy sandstone, carrying very much water below the 257-foot level. CHAPTER V PRINCIPLES OF TUNNEL TIMBERING AND DRIVING General rules Choice of timber English method of timbering as applied in the United States Belgian and Belgian-German system German system Austrian system American system Driving through loose gravel Crutch system Timbering a sand tunnel Meem paling-board system Iron crown-bar system Old rail crown-bars, their advantages and disadvantages Steel-lined, tunnel Sand-chamber and caisson method Pilot-tunnel system Sewer tunnel in quicksand Dry-sand tunneling Enlarging tunnel in soft ground Sewer tunnel in dry sand. The particular manner of timbering a tunnel will depend upon the nature of the material and the experience and choice of the miner conducting the work. But some of the funda- mental principles underlying work of this character may be noted as follows : Compression is very largely the force against which the miner has to contend. Therefore, all joints should be of the simplest character, as all notching, mortising, dovetailing, etc.. tends to weaken and split timbers under pressure; and where angles are necessary flat surfaces and wide angles only can be used with any safety for abutting timbers. The pressure itself tends to tighten the joints ; and, to avoid slipping, heavy spikes driven outside of the upright timbers are most satisfactory. In nearly every system of timbering, wedges are an important factor in securing tightness between surfaces. Wedges are em- ployed to tighten joints and to lengthen timbers that are too short ; and as they may be cut out, they permit the removal of timbers in heavy ground and under pressure. As a rule, spikes and nails should not be driven into the timbering proper, the one exception being the heavy spikes, or "brobs," referred to above, to keep the foot of a post from slipping, or the top of a post from coming out from under a 65 66 MODERN TUNNEL PRACTICE cap. But in both of these cases the spikes are driven outside of the post or strut, and not into it. A great part of the tim- bering used in a tunnel must come down again, and it may be essential to remove it as quickly as possible. Hence, any spik- ing of timbers delays and makes more difficult the work of removal or shifting. Screw-bolts are made to fasten together English System. Belgian System. German System. Austrian System. FIG. i8a. Diagrams Illustrating Four Systems of Tunnel Attack; the Numerals Showing the General Sequence of Excavation. the segments of arch-centering, in making fish- joints, etc., but these are easily removed. Where the risk will warrant the cost, rings or bands may be employed to prevent timbers from splitting ; and in shaft-sinking, iron hangers, heavy steel cables or tie-rods may be necessary to hold the sets together vertically. PRINCIPLES OF TUNNEL TIMBERING AND DRIVING 67 Another very useful appliance in tunnel-timbering is a screw- jack fastened to one end of a heavy timber. These jack-timbers save time, and are economical of timber in special cases ; and as they are quickly adjusted to length and applied, they may be very useful in an emergency. - Tunnel-timbering is a temporary means of supporting the roof or sides until the tunnel section can be excavated and the permanent masonry lining can be put in place. As timber is perishable in any but very wet tunnels, it should be removed wherever this is possible; and it is economy to use the timbers over again where this can be safely done. The best system of timbering, therefore, is one that permits proper drainage and the maximum of room to handle the material ; that is, suf- ficiently strong for the forces to be contended with, and that permits ready handling of the separate members and the re-use of the bulk of the timbers. For timbering purposes a soft, elastic evergreen wood is gen- erally preferable to oak or other hard woods. Pine wood is straight of grain, lighter and easier to handle; it is soft enough to cushion a sudden thrust in bad ground ; and as it will bend before breaking, it gives warning of coming danger. The methods of tunnel attack, timbering, sequence of lining, etc., as generally illustrated in Fig. i8a, vary widely in different countries ; and, mainly for purposes of general reference, the essential features of the principal methods are briefly described. English Method as Applied in the United States. The main features of this system of tunneling are the driving of a top- heading ; the widening out laterally from this- heading and the excavation of the full section of the arch ; the removal of the bench immediately ; and, particularly, the use of heavy crown- bars of timber to hold up the roof timbers, and the withdrawal of these crown-bars as the work progresses, whenever this can be safely clone. The advantages of this 'system are summarized by its ad- vocates as follows : The large, free space provided facilitates drainage, ventilation, and the easy and economical removal of the debris, this debris being either taken directly from the 68 MODERN TUNNEL PRACTICE bench, or run into cars in a bottom heading. Where the crown- bars can be withdrawn and re-used there is a saving of time, material and labor in bringing down new sets. As the crown- bars are drawn after the arch is in place, this system does not interfere with the masons as tnuch as a system requiring the timbers to be removed as the arch is built. The objection is made that this system requires the miners FIG. 19. English-American Tunnel System; as Applied at the Musconet- cong Tunnel. to be idle while the masons are at work; but the work can be so arranged that other work can be found for the miners. The English system has been successfully used, with various modifications, for over fifty years in England, in America, and on the Continent; and even in earth and comparatively soft ground it can be safely and economically applied. The two cases (Figs. 19 and iQa) used for illustration are taken from the Musconetcong and the Hoosac tunnels. PRINCIPLES OF TUNNEL TIMBERING AND DRIVING 6 9 Belgian and Belgian-German System. The Belgian engineers were the first to build the arch first, underpin this arch and build the side walls last, this process being illustrated in Figs. 20 and 21. It commences with a top-heading, which is en- larged laterally until it includes the whole arch area. The_ underpinning of the completed arch, preparatory to building FIG. iQa. English- American Tunnel System; as Applied at the Hoosac Tunnel. one of the side walls, is shown in the illustration. Both illustra- tions are taken from Mr. Drinker's description of the St. Cloud tunnel. In the German modification of the Belgian system the cen- tral core is left to support the roof timbering; but the side drifts are excavated, and in these the side walls are built, the arch being constructed last. French engineers have also adopted the central core system for some of their tunnels, but they build the arch first, as in the original Belgian system. 70 MODERN TUNNEL PRACTICE The claimed advantage of the Belgian system is that it pro- vides a speedy and secure roof under which to carry on the rest of the work of excavation and masonry. But this con- tention is only true when, the roof is a loose rock, demanding some, but comparatively little, support. The disadvantages are many. In the first place the main FIG. 20. The Belgian Tunnel System : St. Cloud Tunnel. cross-sectional area of the tunnel is not at once accessible ; and the successive removal of comparatively small sections at a time is very uneconomical. The underpinning of the arch is also very objectionable to English and American engineers; though Continental engineers have done some good work in this direction, notably in the St. Gothard tunnel. In this Belgian system the handling of the material and removal of the debris are difficult and costly in the small openings provided; and this is especially true in building the arch and the side PRINCIPLES OF TUNNEL TIMBERING AND DRIVING JI walls. The tunnel is also drained at a disadvantage, as a bot- tom heading driven for this purpose tends to loosen the sides and weaken the temporary supports of the completed arch. And under a common arrangement of the timbering support- ing the arch there is a decided tendency to concentrate the load on a single part of the central core. This is contrary to all good tunnel practice. German System. While modified in a number of ways, and as conditions may dictate, the essential feature of this system, as FIG. 21. Belgian System; Showing Centers and Method of Underpinning the Arch. shown in Figs. 22 and 22a, is a central core used for support- ing the roof. A top-heading is usually driven first, and this is gradually widened laterally until it includes the entire arch section. The excavation for the side walls is then made from the top down, and the building o>f the side walls precedes arch construction. In some cases, however, the side walls are started in two bottom drifts, which meet the top-heading enlargement. The German engineers claim that this central core provides 72 MODERN TUNNEL PRACTICE cheap working in hard ground ; and as the system is based upon relatively small openings, in soft ground the pressures can be better met. The use of the core is also supposed to save much timbering. But even in Germany the system is now practically aban- doned because of its defects. Owing to these small openings the work is inconvenient and costly; the ventilation is bad; bad bonding is apt to result from the cramped space in which FIG. 22. German System: Triebitz Tunnel. the masonry of the side walls has to be laid ; it is very difficult to preserve the alignment in a tunnel so constructed, and the arrangement of the timbering tends to a dangerous concentra- tion of load and pressure. Austrian System. In its final development this system is char- acterized by a very strong timber support during exploitation. PRINCIPLES OF TUNNEL TIMBERING AND DRIVING 73 It commences with a central bottom-heading-; immediately above this is driven, a second heading extending to the top of the arch masonry; this last heading is enlarged laterally until it takes in the whole arch area ; and finally the bottom- heading is enlarged laterally until it includes the side-wall area. - side walls are built first, and the arch is then made. The completed timbering arrangement is here shown from FIG. 22a. German System: Ozernitz Tunnel. illustrations taken from Drinker's "Tunneling." The Aus- trian engineer, Rziha, advocates this system for all kinds of ground, from loose rock to quicksands. In this Austrian system the central bottom-heading is a good feature, as it well provides for ventilation and drainage. The general arrangement of the supporting timbers, though some- times crowded, is effective as a rule. All cross and longitudinal 74 MODERN TUNNEL PRACTICE connections are well designed ; there is no undue concentration of load at any one point, and the space left for the removal of the debris and the work of the masons is ample, as compared with the preceding systems. The one marked disadvantage of the system is the over- crowding of the timbers, requiring a large amount of material and handling, and to that extent decreasing the room available for work. American System. The so-called American system, as shown FIG. 23. Austrian System; Advance Heading and Top Enlargement. in Fig. 24, is a development, and it had its origin in the condi- tions imposed by the character of the rock through which a number of the earlier American tunnels were driven. These tunnels were largely located in the coal regions, in slates, shales, and other weak rock requiring ample support. The system it- PRINCIPLES OF TUNNEL TIMBERING AND DRIVING 75 self more nearly resembles the Austrian method than it does others described ; but it is much more economical of timber. In this manner of driving a tunnel a central top-heading is usually first driven, and this is enlarged sideways so as to in- clude the full arch area. The bottom is' taken out m 4wa benches as the work progresses. But the essential feature of the system is the construction of the roof support. This is made of nine or more arch blocks, FIG. 233. Austrian System; Arch Area Enlargement. or wooden voussoirs, well jointed and connected, carried upon longitudinal wall plates resting upon posts, the latter either with or without a sill. In the earlier, and in some of the later Western American tunnels, this timber lining was lagged and left in place, well packed outside with broken stone. This was simply a measure of original economy of construction, as the rotting of the tim- 7 6 MODERN TUNNEL PRACTICE bers and the danger from fire sooner or later demanded a more permanent lining of brick, stone or concrete. A simple application of the American system of timbering is here shown in an illustration of the Little Tom tunnel, on the Norfolk & Western Railway, built in 1888-90. The ma- terial penetrated was a gray sandstone, in approximately hori- zontal beds, and cut at times by the coal seams of that section. These rock beds varied in thickness from a few inches to sev- FIG. 23b. Austrian System ; Section Completely Excavated. eral feet; and the rock itself disintegrated upon exposure to the air, and thus required ample timbering. The dimensions, location and form of the timbers are shown in Fig. 24. The wood used was first-class white-oak, and originally it was left in the tunnel as a protection against fall- ing rock during the early operation of the road. Where the rock was comparatively sound the three roof-segments were alone used, supported in "niches" cut in the rock; but as a rule PRINCIPLES OF TUNNEL TIMBERING AND DRIVING 77 the 3-inch lagging shown was laid on these segments, forming a continuous protection. In a letter to Engineering News* Mr. Emile Lowe, C.E., gives the cost of this work as follows: The amount of timber-- ing per lineal foot approximated 250 feet board measure, _A part of this timbering was done by day labor, and the remainder under a contract of $60 per thousand feet board measure. The timbering actually cost about $15 per lineal foot. The area of the rock section was 263.66 square feet, equivalent to 9.765 cubic yards per lineal foot. The area of the timbered section Cross Section. Longitudinal Section. FIG. 24. American Tunnel System: Little Tom Tunnel, Norfolk & Western Railroad. of the tunnel was 314.16 square feet, or 11.635 cubic yards per lineal foot. The contract price for excavation was $3.50 per cubic yard ; so that the respective costs of the two sections for excavation were $34.17 and $40.72 per lineal foot. Some allowance was made for breakage outside of the theoretical sec- tion of the tunnel, and for this outside work the contractor was allowed $1.50 per cubic yard. Stone packing over the timbers was paid for at the rate of $1.50. The total cost of the tunnel was thus about $115,000, divided about as follows in relative cost : Excavation, per lineal foot $43.00 Timbering, per lineal foot 16.00 Packing, per lineal foot i.oo Total cost per lineal foot ^Engineering News, April 19, 1900. $60.00 7 MODERN TUNNEL PRACTICE This tunnel was driven partly by hand and partly by ma- chine drills; and the daily progress ranged from 2 feet to 6 feet in the heading, and from 2 feet to 4 feet in the bench. Driving Through Loose Gravel. A good example of the American method of driving a tunnel through loose gravel is here taken from an article on the tunnel on the Crow's Nest Pass line, Canadian Pacific Railway, written by C. R. Coutlee, C.E., of Vancouver, B. C.* This tunnel was only 900 feet long, but it passed through a loose and comparatively dry gravel for its entire length. The Chute Cross Brace Car-^L \Cribhing of 2" Planks ' ':"' EX- for Post Chambers Longitudinal Section. 5 VL ti ff Diagram Plan. FIG. 25. Crow's Nest Pass Tunnel ; Longitudinal Section and Plan. Show- ing Method of Driving. method adopted for driving was practically as follows, the di- mensions of the tunnel being indicated on the accompanying illustration (Fig. 26) : In the arch area of the tunnel two side drifts, 8 feet high and 6 feet wide, were driven, leaving about 8 feet of material between them. The frames of these drifts were made of 8-inch round mountain fir. A sill-piece 6 feet long^ was first set accu- rately to the elevation of the under side of the wall plate; on ^Engineering News, April 2, 1903. PRINCIPLES OF TUNNEL TIMBERING AND DRIVING. 79 this were set up the posts ; and the cap, 4 feet long, was flatted and gained down i inch upon the posts to form a small shoulder and prevent squeezing in. With the drift-frame in place the face in front was walled with i -inch breast-boards, braced with inclined struts. ^All around the outside of the frame close lagging was entered and driven forward by sledges. This lagging was made of 2x4- inch mountain fir, in 5-foot lengths. Each piece was first driven about half way, with an upward and outward lead, mak- ing as close joints with its neighbor as possible. With a 2-foot hood thus secured, the miner carefully removed the top breast- FIG. 26. Transverse Section ; Showing Method of Excavating and Timbering. board, and was met with a flow of gravel. But he stopped this flow by pushing the board ahead about 2 feet and wedging it in place. The next board was removed and pushed forward in like manner, and the operation was repeated until the whole breast of the drift had been advanced about 2 feet. As the advanced lagging was subjected to side and top pres- sures, and only held by the precarious support given by the breast-boards advanced, to secure a better support a false frame of lighter timber was now 7 set up. With the latter in place the lagging was driven forward its full length, and the breast- 8O MODERN TUNNEL PRACTICE boards were separately advanced as before ; and finally a second true frame was erected about 4 feet from the first one. The almost fluid pressure of the gravel was too great to allow the insertion of a new set of lagging to wedge out the lagging already in place. But the upward and outward flare given the lagging brought the points about 4 inches outside the second frame. This space, outside the posts and cap, was bridged by 2-inch scantling, blocked off from the frame by 2-inch blocks ; and beneath this bridge the new lengths of lag- ging were driven. As it was, considerable friction was en- countered. After the side drifts had advanced about 20 feet, the top- heading was driven in a similar manner, though this was only 4 feet high, and the 8-foot cap required a middle prop. This top-heading connected the side drifts at the top ; the top lagging of the side galleries was broken through, and the block arch of five 12 x 1 2-inch timbers was set up on the wall plates, the latter being also 12 x 1 2-inch sticks, shaped on top to fit a "crow- foot" or V-shaped notch on the arch timber, and bored at 15-inch intervals for dowels. At each joint of the arch f-inch round iron dowels, 6 inches long, were inserted. In this tunnel the arch sets and vertical posts were placed only 3 inches apart. As the lower bench was excavated the two sides were breast- boarded with 2-inch plank ; but the central part was allowed to assume a slope. Round, 6-inch timbers were placed hori- zontally, as the digging progressed, across the tunnel at the level of the wall plates and at 5-foot intervals ; and another tier of the same bracing was located 7 feet lower down. Against these struts the lower boarding was braced. In excavating the post-chambers the top breast-board was re- moved and the gravel scraped away sufficiently to allow this board to be set forward 3 feet. A side-board was then in- serted parallel to and just outside the wall plate to prevent side- runs. In this manner a chamber was cribbed down to grade at each side; and at grade a 12 x 1 2-inch sill 2 feet long was set. A post was then entered under the wall plate and resting PRINCIPLES OF TUNNEL TIMBERING AND DRIVING 8l on the sill, and the bottom of the post was pushed outward by a jack until the post was plumb. Great force was required to do this, but a tight fit .was secured. While excavating the post-chambers the unsupported wall plate formed a bridge, about 3 feet long, from the gravel of the bench to the posts already in; the drift-frames assisted in holding up these plates. When the ground would permit it, a space for two posts was excavated at one time. At this tunnel an advance of about 21 feet per week was made, and the cost amounted to about $77 per lineal foot for labor, timber and supplies. The timber lining was left in the tunnel permanently. Crutch System. The Lake View tunnel, under Lake Michi- In Good Ground. . - . , , . . ... in weroanaand Loam. FIG. 27. The Crutch System of Tunnel Driving. gan at Chicago, 111., is two and two-thirds miles long, and it was driven through different grades of clay, with occasional pockets of sand. The standard section was circular, 8 feet and 10 feet in diameter inside. Owing to excessive excavation resulting from methods pre- viously followed, Mr. Paul G. Brown, engineer in charge, adopted the so-called crutch and crown-bar system of timber- ing, here shown in Fig. 27. In this system horizontal wall plates were first let into the sides of the excavation about on the line of the horizontal diam- eter. Upon these plates rested pairs of 6 x 8-inch timbers, form- 82 MODERN TUNNEL PRACTICE ing inverted V's, with the apex supporting a longitudinal tim- ,ber. Upon the outside of the V's, or crutches, blocking was placed to hold other longitudinals supporting the sides. The number of these latter timbers varied with the character of the soil. A 6 x 8-inch sill was placed at the face, and the face was bulkheaded to form a bearing for the sill. One set of crutches tross '^SectilorC" Longitudi FIG. 28. Tunneling Through Sand: Brooklyn, N. Y. was used to support the bars, midway between the face and the finished masonry, the rear end of the bars being carried by the masonry, and the front end by posts at the face. All of the timbers were set up by wedges. The progress made was about 14 feet per day; costing $24.41 per lineal foot in clay, and $38 in rock. Timbering a Sand Tunnel. The timbering here described was used in building a circular sewer, 13 feet 6 inches clear diam- eter, in Brooklyn, N. Y. ; the work was designed by, and was executed under, the direction of Henry R. Asserson, Chief En- gineer of Sewers. This sewer tunnel was lined with 16 inches of brickwork, with a granite block invert. The "tunnel was driven through fine sand carrying considerable water. This sand would not stand up during excavation, but was hardly PRINCIPLES OF TUNNEL TIMBERING AND DRIVING 83 unstable enough to be classed as quicksand. The work was car- ried on from two shafts. In excavating this tunnel (Fig. 28) a drift 6 feet wide and 7 feet high was first driven at the bottom center of the sec- tion. The primary purpose of this drift was to drain the sand, and to facilitate this a tile sub-drain was laid about 2 feet be- FIG. 29. Meem Peking-board System. low the bottom of the invert and left in place. Almost simul- taneously with the bottom drift, another drift was driven at the top of the section, 8 feet wide and 7 feet high ; and both drifts were kept about 50 feet ahead of the full section work. As they were driven, these drifts were held by the usual frame and FIG. 30. Detail of Meem Poling-board. poling-boards, with the face bulkheaded and held up by struts, or rakers. The section, was enlarged from the heading by excavating on each side, inserting the roof-bars, radial struts and poling- boards one after the other, as shown in the illustration. The radial struts were removed as the lining was built ; but all other timbering was left in place, with all the interstices rilled with concrete. 8 4 MODERN TUNNEL PRACTICE Meem Poling-board Method. For another sewer tunnel in Brooklyn, driven, through the same water-bearing fine sand, Mr. J. C. Meem, C.E., devised the plan here shown in Fig. 29. In this method a top-heading was first taken out, embracing about one-quarter of the perimeter of a circular section 17 feet 8 inches diameter. The segment guide- frame A B C D E was then erected, and over the top of this was slipped the ends of five special iron poling-boards (Fig. 30) . These boards were gradually pushed forward as the excavation progressed beneath them, and other guide-frames were successively set up, until there were five of these frames under the boards. To next carry down the excavation on each side the roof was temporarily braced by the struts E F G supporting lag- ging. As soon as the side cuts were completed the segmental FIG. 31. Iron Crown-bar System of Tunneling. frame H I J K was set up, and struts were inserted to relieve the poling-boards and temporary timbering. The excavation was carried on down the sides by lagging and radial struts, until the section had been sufficiently opened to permit the building of a portion of the invert. The timber frame L M N O was then built, and the weight of the segmental timbering was transferred to the invert. The excavation was now ready for the completion of the lining masonry. To build this masonry segmental centers were used, with the frames erected PRINCIPLES OF TUNNEL TIMBERING AND DRIVING 85 between the timbering sets, the latter being removed as the masonry progressed. As shown in the cut, the poling-boards used at the top have steel-shod cutting edges and a steel-plate tail-piece with small I-beam stiffeners beneath. In operation the tail-piece over- lapped the roof-lagging. The poling-boards were driven ahead by 30 and 6o-ton hydraulic jacks, operated by a hand pump. The face of the heading was generally kept about 30 feet ahead of the brickwork. Iron Crown-bar System. The King's Cross Station tunnel, driven in 1890 in London, England, is only 1,590 feet long, FIG. 3ia. Needles Used in Iron Crown-bar System. but it passes under the Regent's Canal, with only 6 feet of earth above the tunnel at some places. The tunnel is generally circu- lar, with a clear diameter of 26 feet, and is lined with brick throughout. In this case and especially to reduce the head room required by timber the ordinary timber crown-bars were replaced by a series of iron and steel "needles," grooved longitudinally so that the bars link together and yet have sufficient play to allow them to take the form of the arch. As it was difficult to roll the double-needle, two ordinary needles were joined by counter- sunk rivets, as shown in Fig. 31 a. The needles here used are 10 feet long, 6 inches wide and 2 inches deep. As soon as the brickwork is built under their protection, the needles are pushed forward in sets of 86 MODERN TUNNEL PRACTICE three, until only one or two feet of the needles rest upon the brickwork; and as the needles are pushed forward by screw- jacks, they are held up by successive segmental frames of the ordinary type. To facilitate the forward motion of the needles, holes are drilled at intervals along each needle; into these holes the two bosses of a bracket are set, and against this bracket the screw-jack pushes. Crown-bars of Old Rails. The Marsden tunnel on the Lon- don & Northwestern Railway, in England, was driven, in 1893, by tne English method of timbering. Wooden crown- bars were used in part of the tunnel; but, to decrease the amount of excavation and packing, Mr. A. A. Macgregor, Resident Engineer, suggested the method described in Fig. 32. E NO. NEW: FIG. 32. Crown-bar of Old Rails. To each side of a 3 x5^-inch timber he through-bolted two 75-pound bullhead steel rails, worn out in service. The crown- bars thus made were cheaper than the all-timber bars, saved one-half or more in excavation and packing and were easier to handle. Tests made showed that this crown-bar was equal in strength to a round larch bar 1 1 inches in diameter, under similar conditions of loading. The chief objection to the rail-bars is their stiffness. Their maximum deflection is about one-half that of the larch bars; and they are somewhat treacherous and have to be carefully watched against undue stress. They do not give warning by bending to the same extent as the all-wood bar. Steel-lined Tunnel While not properly coming under the head of tunnel timbering or driving, the tunnel here described PRINCIPLES OF TUNNEL TIMBERING AND DRIVING / is sufficiently curious to be noted. In the Cripple Creek mining" region it was necessary to extend the line of the Golden Circle Railway through the dumping ground of the Portland mine; and to meet the conditions a steel covered way was constructed which would be gradually converted into a tunnel by the opesa-- tion of dumping the waste from the mine. This way was 242 feet long, 14 feet wide inside, 10 feet high to the springing line, and was roofed with a semicircular arch of 7-foot radius. It was made of steel posts and arches resting on soft cast-iron piles. These piles were hollow, 12 inches in diameter outside and i inch thick; they averaged 8 feet in length and were spaced 8 feet between centers. The point of the pile was solid for half its length and a timber core was used in driving them. After the tops had been cut to a level by pipe- cutting machines, a cast-iron cap was put on each pile ; and on these caps, on lead plates, were laid two sets of 12-inch 31- pound longitudinal I-beams. The calculated load on each pile was 56 tons ; and the pile foundation cost $7 per lineal foot of tunnel. Each post was made of two 1 2-inch 31 -pound I-beams, hav- ing a bearing surface of 12 x 14 inches on each pile; the posts being spaced 2 feet apart, center to center. Attempts were first made to bend the tops of the posts so as to form a half arch. But this failed, and each half arch was made of web and angles in three 4- foot sections, spliced with f-inch plates; a ^-inch plate was used for a connection with the posts. For lateral bracing an 8-inch I-beam crosses under the track and connects the longitudinals at each set of piles. At the top of the arch another 8-inch longitudinal ties each arch to its neighbor, and 8-inch channel irons connect the sets at the springing-lines on each side and outside the posts. The roof covering and siding is made of 3-inch red spruce timber; but as this rots away it will be replaced with two rings of brick. The cost of the steel work and planking amounted to about $50 per lineal foot of tunnel, in 1898. Sand-chamber and Caisson Method.* The Meudon tunnel, on ^Engineering News, Sept. n, 1902. 88 MODERN TUNNEL PRACTICE the new line between Paris and Versailles, was completed in 1902, after encountering difficulties which were surmounted in the following manner : The tunnel penetrates a marl formation overlaid by water- bearing sands. Work was commenced with a Clichy-type of Fkj.3. FIG. 33. Meudon Tunnel : Sections Showing Temporary Interior Walls, and the Transverse Gallery at the Point of Commencing Attack on the Debri's near the Top of the Tunnel. shield; but this was soon deformed and heavy and careful tim- bering was resorted to. At one point the marl very closely approached the sand ; the marl swelled on exposure to the air, and water finally broke through from above, and a serious cave-in occurred when only 115 feet of the side walls remained Oevrion. S ectional Pla n . FIG. 33a. Meudon Tunnel : Detail Showing the Construction of a "Sand- chamber." to be built. The difficult work lay in tunneling through this mass of marl, sand, water and broken masonry. The first operation was to build strong masonry bulkheads across the tunnel to confine the cave-in, leaving small passages through these bulkheads that could be quickly closed. Then a PRINCIPLES OF TUNNEL TIMBERING AND DRIVING 8 9 small gallery was driven outside the masonry standing, with the view of draining the cave down grade toward Paris. Two temporary walls were then built inside and parallel to the axis of the tunnel to better support the arch-centers, and this was done in ordinary drifts and without great trouble. (See Fig. 33). The Versailles end of the cave was soon reached ; and as the central part of the mass was relatively free from quicksand, a cross-heading was driven through it and Fourth Stage. FIG. 34. The Four Successive Stages of Emptying 1 a Sand-chamber: a = roof of pieces 13x13 cm., raking and jointed ; b = transverse poling- boards 13x13 cm., with a jog; c = horizontal pieces 6x18 cm.; d = ad- vance poling in pieces 20x25 cm. centers were erected upon the temporary longitudinal and the side walls for building the arch. But the building of this arch proved to be a long, difficult and costly operation. The fine sand, carrying water, was almost fluid ; the use of compressed air was impossible owing to the enormous water pressure, and the freezing process could not be resorted to, owing to the im- possibility of driving pipes horizontally through the broken arch masonry imbedded in the sand. 9 o MODERN TUNNEL PRACTICE In this emergency the engineers devised the "sand-chamber" method (Fig. 34). The advance was made in a concave form and maintained by a system of small boxes formed with poling- boards, completely stopping off the face. This was done by forcing forward, for sides and roof, a series of 6 x 6-inch squared sticks, as closely jointed as possible and sometimes caulked. The size of these chambers never exceeded one cubic metre in volume, and in each the face was bulkheaded. The 6 x 6-inch timbers were forced through this bulkhead by 3<>ton hydraulic jacks, by first boring holes around a place 6 inches square and then forcing the enclosed block ahead of the timber. To decrease the hydraulic pressure encountered, the timbers were sometimes bored on their axis, thus permitting the sand and water to flow through the sticks as these advanced. Fin- ally the pressure became so great that beams (Fig. 35) 6x6 Interior Caisson. 1 Section C-D. FIG. 35. Detail of Metal Beams, or "Caissons," at Versailles End. inches, outside, were made with two channel bars and two plates. These iron beams were open at the forward end and closed at the rear, with an opening in the plugged end that could be closed if necessary. After each main chamber had been divided by the above de- scribed means into four secondary chambers of not more than one cubic yard capacity, each new chamber had to be emptied of sand and the bulkhead pushed forward. This was very slow and dangerous work, and it is only necessary to say that to empty one chamber, or to take out a little over one cubic yard of sand, required one week's time. When the arch work thus constructed approached within 6J feet of the crushed end of the standing arch, a metallic roof was pushed forward from the top of the advance gallery to the top of the arch still in place. This roof was of so-called iron PRINCIPLES OF TUNNEL TIMBERING AND DRIVING QI "caissons/' 6 inches square and 10 feet long, pushed forward by 7O-ton rams (Fig. 36). Though the new arch throughout the renewal was 5.24 feet thick, water filtered through it owing to the enormous pressure. To stop this a waterproof tunnel lining was put in. A steel_ sheet lining imm. thick, was made into a ring im. wide by soldering the joints, and these rings were also soldered to- gether. This sheet lining was secured to oak pegs driven in holes drilled in the masonry, and a space of about i^ inches was left between the lining on the masonry, which was filled by injecting cement mortar. To hold this steel shell against the outside pressure a concrete steel lining was put inside of it and secured to bolts passing through the steel shell to the masonry This concrete steel lining was about 13 inches thick at the Cross Section A-B. Longitudinal Section. FIG. 36. Method of Using "Caissons," at Versailles End. crown, 9 inches at the spring and 1 1 inches thick at the base, and imbedded in the concrete was a network of round longitudi- nal, transverse and diagonal rods, of varying diameters. Pilot-tunnel System This system was first devised and used at the old Hudson River tunnel by Mr. John Anderson, general manager for the contractor. It was later successfully employed by the contracting firm of Anderson & Barr in building a sec- tion of the Brooklyn relief sewer, 10 to 15 feet diameter, run- ning through fine sand and loose, dry gravel. The pilot-system is especially devised for tunneling through soft and uncertain material, the pilot itself furnishing a sup- port for holding the roof, as well as the centering for masonry. The "pilot" is a cylinder, usually 6 feet in diameter, made up. 92 MODERN TUNNEL PRACTICE of curved plates of boiler iron riveted on the four sides to light angle-irons pierced with holes for bolts. The pilot is located on the axis of the tunnel (See Fig. 37) and the segments are bolted up, commencing with the roof -plates, as the excavation is made from within the pilot, which is thus pushed forward and kept about 30 feet in advance of the completed section. The rear end of the pilot is supported by timbering, and the cylinder itself acts as a truss over the short invert space. In operation the material is carefully removed from about FIG. 37. The Anderson Pilot-tunnel System. the center-plane of the pilot; the material in the roof and sides being held up by an outer plate-iron shell, made of flanged seg- ments and supported by radial struts abutting upon the shell of the pilot tube. The masonry lining is put in place by setting up ribs of T-iron, curved to fit the intrados of the arch and with al- lowance made for the lagging. These center-ribs are also sup- ported by struts leading to the pilot, and the roof-struts are removed as these are put in place. In putting in the outer shell-plates, work is commenced at the top and the material is PRINCIPLES OF TUNNEL TIMBERING AND DRIVING 93 held back by light poling-boards until the plates can be bolted to the completed shell. This outer shell, which is extended over one-third, or a little more, of the perimeter of the tunnel, is left in place. Sewer Tunnel in Quicksand In building a sewer in Roches^ ter, N. Y., the contractor found it necessary to drive a 500- foot tunnel through quicksand. W. D. Lockwood, M. Am. Soc. C.E., describes as follows the method pursued:* The heading was only 6x6 feet and this was timbered as shown. In the breast a center leg was sometimes employed, and in other cases a false cap and raker was put in, tying up the completed work with stretchers. The sets were placed about 4^ feet, c. to c., using 8 x 8-inch hemlock, with 6-foot oak lagging, 2 inches thick on the top, and 2-inch hemlock lagging on the sides. Two miners in the Longitudinal Section, Showing Methods of Timbering. FIG. 38. Sewer-tunnel in Quicksand: Rochester, N. Y. breast and two muckers constituted the working force, and the average progress made was 4^ feet per shift. The miners were paid $2.50 per day and the muckers $2.00. The work of driv- ing and timbering the tunnel complete cost $5 per lineal foot, $3 of this being for labor. ^Engineering News, Feb. 21, 1895. 94 MODERN TUNNEL PRACTICE Dry Sand Tunneling. Dry sand will run almost like a fluid ; and as a consequence tunneling through it is slow and danger- ous work, requiring the utmost care and patience in timbering to prevent a run of sand. Small, loose, dry gravel acts in much -the same way. In the case of a large sewer tunnel through very dry sand, built some years ago in Brooklyn, the sand flowing into the ex- cavation undermined adjoining houses, and the job was aban- doned by several contractors in succession. The then firm of '- ** f ; i 3f //4 t x > 5'*' -- !t| > !.... \l " ._ ., , M~~ ~~^7v~\ a / / 5ect/bns ra/yanq \ \ / Iron Bracesare 'made ; V.\ / to ao in any Section. ' \ ^ r5w^ !/2i'/2 Longitudinal Section. Cross Section. FIG. 39. Temporary Bracing of Old Tunnel. Anderson & Barr, of New York, carried out the work success- fully as follows : A connection was made with the city water distribution sys- tem, and a large pipe was carried into the tunnel and near the working face of the tunnel. To this water pipe was connected by a flexible hose a section of 2-inch pipe, about 16 feet long, plugged at the end and perforated at the sides for a length of about 10 feet. By means of this simple apparatus the dry sand in the advance heading was made wet enough to stand during excavation; and a wall of wet sand was thus continually kept between the dry, running sand and the finished tunnel. PRINCIPLES OF TUNNEL TIMBERING AND DRIVING 95 Enlarging Tunnel in Soft Ground. In 1894 the Boston, Revere Beach and Lynn Railroad Company was forced to re- place an old and narrow single-track tunnel by a twin tunnel adapted to the requirements of modern traffic. The old tunnel was 471 feet long, 12^ feet wide and 14 feet high in the clear, and the material penetrated by it was a clay hardpan of IT treacherous nature. Mr. George M. Tompson, M. Am. Soc. C.E., Chief Engineer, devised the plan of reconstruction here briefly described : Though the three-ring brick arch of the old tunnel had been badly squeezed out of shape by the ground pressure, it was determined to build the new north tunnel parallel to the old .* r.r , FIG. 40. Section of New Tunnel Excavation, Showing Drifts and Bracing. tunnel, complete the new tunnel and turn the traffic into it while building the new south tunnel. The old tunnel was first braced up with old rails bent to form as shown in Fig. 39. This work was done at night, and the upper sections were forced and held up by a hydraulic jack placed on a flat-car, while the men were bolting on the leg sec- tions. The whole form was then lowered to a bearing and lagging was driven in to fill the space between the iron rails and 9 6 MODERN TUNNEL PRACTICE the brickwork. To provide clearance this frame had to be sunk into the brickwork in some places. The new tunnel was commenced from shafts sunk near each end, and the material was found to be badly ruptured, requir- ing the heavy timbering shown in Fig. 40. Work was com- menced at each end at the top of the high side or south drift, and carried down 3 or 4 feet by driving sheeting and poling- boards. The short temporary timbers were put in and the drift was closed by a bulkhead to prevent caving. The excavation in this drift was then carried down to a point just below the base 1~ ~: . _J_J iCff Diortt ' tT^./i Klevuc. "already inPiace'-'' FIG. 41. Timber-core Used in Rebuilding Old Tunnel. of the rail and the long side timber was set. The north drift was then driven and timbered, and the arch area was enlarged from the upper central drift shown. The timber sets were spaced 3 feet, c. to c. After the north tunnel had been completed, a heavy timber center platform was built (Fig. 41) to replace the earth core used in the new tunnel and not removed until the arch had been PRINCIPLES OF TUNNEL TIMBERING AND DRIVING 97 built. A drift was then run over the old brickwork and the arch was broken through from above. The new lining was five rings thick. Sewer Tunnel in Sand In connection with the construction of the New York Rapid Transit Railway a sewer tunnel harhto be driven under Chatham Square. The depth below the surface a. "Jacking in" of Lagging. W "Tile Drain ** FIG. 47. Musconetcong Tunnel : Traveling Arch-center. the side walls. The timber was hard pine, and the wheels were double-flanged. The cross-beam indicated carried the wofking floor for the men, and was sufficiently high to permit the pass- age of trains beneath. To put in the concrete arch the rock roof was hand-drilled and blasted; the sides were blasted out ahead of the traveler, 40% dynamite being used, so as not to shake up the rock any more than was necessary. In the case of heavy roof shots, the traveler was run out of the way and the track was protected by ties. In from 10 to 20 minutes after a shot the track was cleared of all debris and the traffic was never delayed. The side walls were built by first setting up the temporary posts, then lagging up for a few feet, and depositing the con- crete in the space behind. When the concreting had reached the springing lines, and was set, the posts and lagging were re- moved and thinner posts were substituted; on the latter were laid the wall-plates for supporting the iron ribs and the 2-inch IO6 MODERN TUNNEL PRACTICE lagging. These iron ribs were made in halves, bolted together at the crown, and the foot of each rested on a cast-iron sand-box fitted with a screw plug. A 1 6- foot section was concreted at one time at the sides, and a lo-foot section at the roof. As the arch concreting approached the crown, stiff struts were put in between the ribs and the rock roof to keep the sides from rising at the key, owing to the heavy load on the haunches. Where the drip of water from the roof, or the flow of water from the sides, was heavy, a 3-inch pipe was buried in the concrete ex- tending clear through to the rock. The cost of this re-lining was $54 per lineal foot of tunnel lined, including blasting, mucking, concreting, handling ma- terials, supplies and workmen. To this must be added $29.91 FIG. 48. New York Subway : Method of Roof-timbering. per lineal foot for a charge for temporary spur, gauntlet track, shanties, platform, train service, etc., making a total cost of $83.91 per lineal foot of tunnel lined. In placing the concrete lining in the New York Rapid Tran- sit tunnel, traveling forms and centers were used as shown in Figs- 5 5 1 - The general section of the tunnel, and the method of timber- ing the roof in the Park Avenue tunnel, is shown in Fig. 48. The concrete footing courses of the side walls were first laid, these projecting inward about 18 inches from the face of the wall. On these projections track rails were laid on each side of the tunnel for carrying traveling platforms. There were three of these platforms; the forward one (Fig. 49) was made for TUNNEL ARCH CENTERING 107 building the side walls, a center one carried a derrick, and the third (Fig. 50) was employed in building the arch. Fig. 49 shows the construction of the traveler used in build- ing the side walls. This platform was mounted on. six wheels in. all, and on each side there was mounted an adjustable lag^ ging, curved to fit the profile of the wall. In operation this platform was rolled to place, and the lagging adjusted to posi- tion and held by wedges. Skips of concrete were then hoisted onto the platform and the concrete was shoveled into the space between the lagging and the rock and rammed until it reached the top of the lagging. When the concrete had set, the wedges were loosened and the platform was moved ahead and ad- justed for building a new section. The derrick platform was 22^ feet wide between center of Part Side Elevation. Half Cross Section. FIG. 49. New York Subway : Platform for Building Side-walls. track wheels and was 18 feet long over all. Transversely it was divided into three bays, the center bay being unfloored so that concrete skips could be hoisted through it from the cars run- ning on a track beneath the platform. A derrick was mounted at the center of one of the floored bays, and this derrick served both the side wall and the arch platforms. The roof-arch platform is shown in Fig. 50. It was practi- cally the same as the side wall platform, with the addition of roof-arch centers at each bent. The top of the completed side walls reached the point B, while the roof-lagging commenced at A. The space A B was bridged by using special sector-like forms. The concrete was shoveled into the arch, commencing at the spring on both sides, until the arch was too high for con- venient handling from the platform. When the throw became loS MODERN TUNNEL PRACTICE TUNNEL ARCH CENTERING IOQ excessive, the concrete was shoveled from the skip onto the small platform C D, and then into the arch. When the two sides approached within 5 feet of each other FIG. 51. New York Subway: Side-wall Mold. at the crown, this key was built in by working from the rear forward. In certain sections of the New York Subway the side wall FIG. 52. Steel Arch-center: East Boston Tunnel. mold was made as shown in Fig. 51. This was mounted on the traveling platform already described in Fig. 50. Steel-rib Center In building the East Boston tunnel, an ex- tension of the Boston Subway, a steel rib was employed to sup- 110 MODERN TUNNEL PRACTICE port the lagging used in building, the concrete-steel lining. The clear dimensions of this tunnel were 20.5 feet high by 23.3 feet wide, and the steel-rib support was devised to facilitate the rapid transport of all debris out of the tunnel, and concrete into it. The ribs were made of curved steel beams riveted and braced together, and on the cross tie-beams provided a platform was laid containing a track for the concrete cars. The muck cars ran on the two lower tracks. Steel Traveling Shields The Moncreiffe Tunnel,* England, has been recently enlarged from a single to a double track sec- tion, the traffic being meanwhile maintained on the single-track line in the center of the tunnel. The work of reconstruction was done by means of four steel traveling shields, designed as follows : Each shield was 32 feet long, divided into 9 ribs, and each rib was made of a curved channel (9x4 inches) shaped to fit the inner section of the new masonry. Inside this channel member were two vertical posts and a horizontal top beam arranged to leave a clear rectangular space for the passage of trains, 13 feet 8 inches wide and 13 feet 6 inches high. The external width of the shield itself was 22 feet, and the height was 16 feet 8 inches. The vertical posts and the outer channels were latticed together, and two inclined members, reaching from the crown point to the springing point on each side, tied the posts, horizon- tal beam and outer channels together. The shield was tied to- gether longitudinally by beams and cross braces between the ribs. The feet of the outer channel and the inner posts were car- ried on four sets of longitudinal steel beams ; under these beams were four sets of cast-iron wheels, and between these beams, on each side, was a clear space of 2 feet 3 inches to permit the passage of narrow iron cars running on a separate track of 13-inch gage and used for bringing in supplies and transport- ing waste material. In operating this shield the side rock was excavated and the ^Proceedings of The Institution of Civil Engineers ; Vol. CLXI, Sep- tember, 1905. TUNNEL ARCH CENTERING lit side walls were built in advance. The shield was then used as a staging for the workmen for dealing with the arch portion, and as a protection to the traffic on the railway. The unlined por- tions of the old tunnel were reconstructed in lengths of 12 feet, so that the 32-foot shield projected 5 feet under the previously- built new arch and 15 feet under the old arch, thus giving an ample margin of protection. Where crown-bars had to be used to prevent the fall of large pieces of loose rock in the roof, these bars were supported by posts resting upon the steel ribs. When the necessary rock excavation had been completed, ordinary FIG. 53. Method of Setting Form for 'Concrete Invert. wooden tunnel centers were used for building the new arch, located in the rear of the steel shield. Concrete Form for Small Tunnel The form illustrated in Fig. 53 was used in laying the concrete invert foundation in the Cin- cinnati Water Works tunnel. The concrete was laid in 1 6-foot sections, the forms being set 4 feet apart. The interest in this form chiefly lies in the simple manner devised for holding the form in place. After the brick invert had been laid on this concrete founda- tion, the brick arch was built on lagging supported on ribs made of two 3 x 4 x f -inch angles, bent to form and riveted. CHAPTER VII . . \ SUB-AQUEOUS TUNNELS AND TUNNEL SHIELDS Introduction Form of shield and method of driving at East Boston Sub- way The East River gas tunnel Massachusetts pipe-line tunnel Blackwell tunnel St. Clair tunnel Berlin-Spree tunnel Harlem River tunnel Pennsylvania R. R. Hudson River tunnel Screw-jack shield Shankland shield. Tunnels of the type here discussed are usually located under a waterway separating parts of one city, or are found on lines of railway where it is deemed more economical and as better meet- ing the demands of general traffic, to tunnel under the water- way rather than to bridge it. Where rock is found in tunnels of this description, the line of the tunnel is necessarily so near to the surface of the rock that the work is liable to be seriously interfered with by the occurrence of vertical seams filled with decomposed rock and communicating with the water above. And when the material penetrated is other than rock it is an alluvial deposit also more or less water-bearing. Conditions of traffic as well as those of construction re- quire that these sub-aqueous tunnels be located as near to the water-level as the depth of water in the channel and the nature of the material penetrated will permit ; otherwise, the gradients or the length of the tunnel may be excessive for the purposes of construction or operation. Owing to these facts tunnels of this nature are usually difficult to build, costly and more or less dan- gerous to the working force; and various methods have been devised to minimize the dangers to be encountered and to facil- itate the work of driving the tunnel. Chief among these is the use of shields and compressed air, employed together or sepa- rately. As shields for supporting the face and roof and guard- ing against the inrush of material or water, are an essential 112 SUB-AQUEOUS TUNNELS AND TUNNEL SHIELDS 113 feature of sub-aqueous tunneling, this chapter deals largely with this engineering device. Historically considered, the first sub-aqueous tunnel of any importance, and through soft ground, is that under the River Thames, in London. This tunnel was first proposed in 1798, by Ralph Dodd; and in 1807 work was actually commenced upon it by the Cornish engineer, Trevithick, and a small drift was run under the river for a length of 1,046 feet. But as some doubt had been raised as to the accuracy of this line in direction, Trevithick made an opening in the top to test his position, with the result that he let in the water and nearly drowned himself and his party. The project was taken up in 1824 by Mark Isambard Brunei; but again the water broke in and the tunnel was abandoned for a time. Brunei then devised a sectional shield for protecting the ad- vance working, the first shield of record, and by its use the tunnel was opened to foot passengers in 1843. This original Brunei shield was made up of a strong iron framework built in horizontal sections of a comparatively small depth that could be advanced separately, and cut vertically into three compart- ments. The sections were advanced by powerful screw-jacks, and the vertical face was protected by horizontal poling-boards that could be handled separately and pushed forward as the ground was excavated. The brickwork, covering two arches of 1 4- foot span each, was built behind the shield as this ad- vanced. This Thames tunnel was 1,300 feet long, and in its extreme dimensions it was 35 feet wide and 20 feet high. Hydraulic rams for pushing forward the shields, and a per- manent iron lining in which to lay the masonry, were probably first used in 1868-69 m building an 8- foot tunnel under the Thames ; the next prominent use of the hydraulic jack was in the 10- foot tunnel of the City and South London Subway, com- pleted in 1890; and jacks of this type were used on a large scale on the Blackwell tunnel of 1890, and the 20- foot St. Clair tunnel of 1892, and in the Paris sewer tunnels of 1896. Since these dates the use of shields has been extended in many coun- tries, and the development of this process of excavation is best 114 MODERN TUNNEL PRACTICE noted by the description of typical actual modern work of this class. Blackwell Tunnel This tunnel under the Thames, completed in 1895, is 27 feet diameter, making it the largest sub-aqueous tunnel built to that date. The material penetrated was chiefly water-bearing sand, loose gravefand some good clay. At one point in its length only 5 feet of so-called "ballast," or small water- worn stone, covered the roof of the tunnel ; and at this point clay was dumped to a depth of 10 feet and 150 feet in width, to protect the workmen from an inrush of water. The river portion of the Blackwell tunnel is 1,212 feet long. The shield here used was chiefly remarkable for its unusual size and its somewhat complicated design. As shown in Fig, 54, this shield was circular in form, 28 feet 8 inches in outside diameter and it was 19 feet 6 inches long over all; it weighed 230 tons. The outside shell was made of four f-inch steel plates, and the interior was divided and the shell stiffened by two vertical diaphragms, 25^- inches apart. The space between these diaphragms was to be used as an air-lock should condi- tions demand a greater air-pressure at the working face than at the rear of the shield ; but there was no occasion to employ this differential pressure. The material excavated at the face was passed through these diaphragms by chutes provided with doors at each end and acting as air-locks. Horizontally, the forward part of the shield .was divided by three platforms, forming four working stages for the men. The three longitudinal and vertical partitions cut the face into twelve compartments and also acted as stiffeners. About 6^ feet back from the cutting edge, in each one of these twelve compartments, a vertical cross screen was introduced, about 30 inches in depth from the top; these screens being intended to form a place of refuge for the men in case of an inrush of water, as the air in these closed places would keep them from filling with water. The shield was pushed forward by 28 loo-ton hydraulic jacks abutting against the cast-iron tunnel lining inside the rear hood. This tunnel lining was very heavy, each segment weigh- 7, if*/ < e j f+ ^ 6 m ^ ?^> 'p'.-ft- SUB-AQUEOUS TUNNELS AND TUNNEL SHIELDS I 15 FIG. 54. Hydraulic Shield and Lock : Blackwell Tunnel Under the Thames. Il6 MODERN TUNNEL PRACTICE ing about one ton and two hydraulic "erectors" were used to lift and hold up a segment until it could be bolted to the seg- ments in place. This shield proved unwieldy, and after about 125 feet of the tunnel had been driven with it the cutting edge encountered a boulder in the sand and was bent upward at the bottom. The shield was pushed forward about 192 feet further, but it then became so damaged as to be useless. As it could not be with- drawn, it was forced forward to the next shaft by driving a timber advance bottom-heading, and laying down in this a concrete bed upon which the shield could slide, the injured part being thus relieved of strain. St. Clair Tunnel. This tunnel passes under the river of the same name connecting Lakes Huron and Erie. The tunnel is 2,465 feet long between centers of shore shafts, and is 21 feet 6 inches in outside diameter. It is located in a bed of blue clay, with the bottom of the tunnel about 60 feet below water level, and was built inside a circular cast-iron lining by means of a shield designed by Joseph Hobson, the Chief Engineer.* The chief interest lies in the size and form of the shield used. As here shown, this shield consisted of a cylindrical shell, 21 feet 6 inches in external diameter and 15 feet 3 inches long over all. The shell was made of i-inch steel plates butt- jointed with plain joints; and the segments forming the shield were united by double angles on the interior face, riveted to the shell and together. The shield bulkhead was placed four feet back of the rear end. It was made of -|-inch plate, with seven hori- zontal and three vertical stiffening members. In the lower-- part of this opening were two openings, 6 feet high by 4^ feet wide, passing the material excavated; these openings were closed by sliding doors suspended by chains. But, as a matter of fact, these doors were never closed throughout the execution of the work. To push the shield forward twenty-four hydraulic jacks were installed in the outer ring. Each jack had two cylinders : *For a detailed history of this tunnel see Engineering News, Oct. 4, Nov. 8 and Dec. 20, 1890. SUB-AQUEOUS TUNNELS AND TUNNEL SHIELDS FIG. 55. Longitudinal and Transverse Sections of the Shield Used at the St. Clair Tunnel. n8 MODERN TUNNEL PRACTICE one 8 inches in diameter, to push the shield forward ; the other, 2 inches in diameter, used in drawing back the large plunger to make room for a new set of lining rings. With a hydraulic pressure of 2,000 pounds per square inch, the first set of jacks exerted a force of 99,000 pounds, and the second 7,250 pounds. The arrangement of these jacks is shown in the illustration. In front of the bulkhead three vertical and two horizontal partitions were built, to stiffen the shell and to serve as plat- forms for the workmen. Both sets of partitions stopped within 4 feet of the bulkhead, or diaphragm, thus leaving abundant room to throw the clay down before the bottom open- ings ; these partitions were sloped back from the face, as shown. Mr. Hobson made some calculations on the friction of the FIG. 56. Shield Used at Spree Tunnel, Berlin. cylinder in moving through fairly homogeneous clay. The pressure used to drive the cylinder forward varied from 450 to 2,000 tons, and the area of skin of the cylinder was 1,030 square feet in contact with the clay. The theoretical friction was, therefore, about 875 to 3,880 pounds per square foot, or 6 to 27 pounds per square inch. Berlin Tunnel Under the Spree. This tunnel is 1,490 feet long under the River Spree, and is 13.12 feet in outside diameter, lined with cast-steel flanged rings, coated inside and out with cement mortar. The tunnel bottom lies about 40 feet below the mean water level, with a least thickness of 10 feet of soil above the shell. The material penetrated was mud and sand, heavily charged with water. The steel cylinder rings are 2.13 and 1.64 feet wide, and each ring is made of nine segments SUB-AQUEOUS TUNNELS AND TUNNEL SHIELDS I IQ fitted with inside flanges. Between these rings, during erec- tion, flat steel circles were bolted, extending outside the shell and increasing the rigidity of the tube. FIG. 57. Boston Subway : East Boston Extension, Showing Standard Con- crete Lining and Steel Ribs Imbedded in Concrete. The actual excavation was conducted under compressed air and with a shield. As shown in. Fig. 56, this shield had a I2O MODERN TUNNEL PRACTICE double bulkhead, with an air-lock passing through both; and in the rear of this transverse partition were the hydraulic jacks. In front of the bulkhead was a hood, cut away at an angle of 45, with this oblique face closed by hinged doors, which may be opened at will. The material removed through the doors was thrown to the bottom of the hood, where it was removed by a sand-pump ex- tending through the bulkhead. The advance hood was perma- nently closed at the top, providing a space filled with air, which could be used as a refuge by the workmen in case of a sudden rush of sand and water. The air-lock, placed in the bulkhead, is intended for similar use. The actual construction chamber lay between this shield and a temporary transverse wall, built at some distance to the rear and fitted with two air-locks, one for men and the other for materials. The steel rings were mounted under the rear of the shield, with some space left between the lining and the rear hood of the shield. In this annular space cement was rammed in place ; this cement acting as a protection to the metal shell and also as a seal against sand and water from without. In pushing- forward the shield the sixteen hydraulic jacks acted against the steel lining ring. This tunnel was completed in 1899. East Boston Extension : Boston Subway This tunnel for about 2,250 feet of its length passes under an arm of Boston Harbor, with 1 6 to 1 8 feet of earth over the outside of the tunnel roof at the deepest part of the harbor, where there is 35^ feet of water at mean low tide. The material being generally clay, but somewhat treacherous, the construction called for a roof-shield. A horse-shoe section was adopted for the tunnel, (Fig- 57) with a clear width of 23 feet 4 inches, and a clear height of 20 feet 6 inches. Owing mainly to the high cost of iron, a concrete shell was built about this tunnel, 2 feet 9 inches thick at crown and sides, and 2 feet thick in. the invert. In water-bearing material this shell was tightened and reinforced by a cast-iron shell of flanged and bolted segments, having steel plate ribs imbedded in the concrete, with cement grout forced SUB- AQUEOUS TUNNELS AND TUNNEL SHIELDS 121 between the cast-iron shell and the grout. This construction is also shown in Fig-. 57. The roof-shield actually used on this extension was semi- FIG. 58. Roof-shield, Boston Subway, East Boston Extension; Front Rear Rib and Longitudinal Section. and 122 MODERN TUNNEL PRACTICE circular, tied together at the base by a transverse girder and stiffened by vertical and diagonal riveted plate and angles. It is shown in Figs. 58 and 59. East River Gas Tunnel This tunnel is used for piping gas under the East River, and serves as a typical illustration of tunneling in a treacherous, water-bearing material ; it was built in 1894 by the East River Gas Company, under Mr. C. M. Jacobs as Chief Engineer. From center to center of shore shafts the tunnel is 2,516 feet FIG. 59. Roof-shield: Boston Subway; Half Front Elevation and Jack- connection. long; the center of the tunnel is 107 and 119 feet below mean low tide, giving a drainage toward the Long Island side. In the solid rock the section is 10 feet wide by 8J feet high at the crown, and in soft ground a cast-iron shell (Fig. 60) is used, 10 feet 2 inches in diameter clear of flanges. The material penetrated was hard gneiss rock for the lower part of the tun- nel ; but for something over 200 feet the tunnel passed through almost vertical layers of decomposed felspar, a 'greenish, marl- like formation that ran like paint when wet, and loose rock. All of this material was water-bearing, the vertical seams com- municating with the river above. SUB-AQUEOUS TUNNELS AND TUNNEL SHIELDS I2J The hard rock portion was tunneled in the usual manner without difficulty; but for the soft ground part a shield and iron lining were required, operated along with compressed air. The and Go Section. Long, Section. FIG. 60. East River Gas Tunnel : Cast-iron Lining. cast-iron lining was 10 feet 10 inches in outside diameter was made in rings 16 inches wide, and in nine flanged seg- Longitudinal Section., End View of Head. FIG. 61. Shield : East River Gas Tunnel. I2 4 MODERN TUNNEL PRACTICE ments with a key-piece 8 9-32 inches long. Every segment was drilled for a i^-inch pipe nipple for hose attachment to grout- pump. This iron lining was chiefly adopted because it was found that water was forced through the brickwork first tried. The shield is shown in Fig. 61, planned by Mr. W. I. Aims, the engineer in charge. It weighed about twelve tons, and was 10 feet f inches in external diameter and 7 feet 2.\ inches long: its general arrangement is shown in the cut. In the annular space indicated twelve 5-inch hydraulic jacks were located, each designed to work under a hydraulic pressure of 5,000 pounds per square inch, making it possible to exert a force of 600 tons FIG. 62. Twin-tube Tunnel Under Harlem River. in pushing the shield forward. The shield and heading were lighted by incandescent lamps, and were connected with the office above ground by a telephone. As the axis of the tunnel was 120 feet below mean low tide, the air pressure required ran from 48 to 52 pounds per square inch, a record surpassing that of any other known work con- ducted by the plenum-pneumatic process. Notwithstanding careful physical examination of the workmen, and the use of every precaution, in leaving or entering the air-lock, there were SUB-AQUEOUS TUNNELS AND TUNNEL SHIELDS four fatal cases, due to carelessness in entering or leaving the lock. The air-lock was of the ordinary construction. Harlem River Tunnel This tunnel forms part of the New York Subway system, and it passes under the Harlem River, with the rail-base 44.66 feet below mean high water ; the depth of the river is about 26 feet, with a range of tide of about 5 feet. The material penetrated by the tunnel is mud, silt and sand, the latter flowing with remarkable ease when wet. Be- tween the bulkhead lines the river is 400 feet wide; but for 610 feet the tunnel is made of two cast-iron cylinders, im- bedded in concrete, as shown in Fig. 62. To build this section of tunnel Mr. D. D. McBean, of the sub-contracting firm, devised the following plan : He proposed to enclose the space to be occupied by the tunnel by two lines of specially constructed 1 2-inch tight sheet-piling; upon these lines of piling, carefully cut off at the proper level, he would lay a timber roof made of three layers of 1 2-inch timbers, with courses of 2-inch plank running at right angles between the heavy courses, all well caulked, and making a roof 40 inches thick. Under the protection of the box so made, he proposed to excavate the material, either with or without the use of com- pressed air. Before driving the sheeting the river had been dredged to such an extent as to leave an average depth of 7 or 8 feet of material to be removed in the chamber to be formed. Then four longitudinal rows of piles were driven under the proposed tunnel, 6 feet 4 inches apart, c. to c. transversely, and 8 feet apart longitudinally. These piles were cut off and capped as shown in Fig. 64, their office being to support the heavy timber roof ; to support the interior bracing system ; and to be eventu- ally cut off at sub-grade and further support the finished tunnel. A substantial pile service platform, 20 feet wide, placed paral- lel to the tunnel line and on both sides of it, aided materially in the accurate alignment of the bearing piles and the placing of the bracing. To accurately align the two rows of sheet piling, a timber frame was constructed to fit closely between the two lines of 126 MODERN TUNNEL PRACTICE io SUB-AQUEOUS TUNNELS AND TUNNEL SHIELDS I2/ sheet piling to be driven, with the center of this frame exactly over the center line of the tunnel. This frame, shown in part in Fig. 64, was built in lengths of 216 feet, and floated between the service platforms, accurately aligned and sunk. As this frame was now exactly opposite another frame bolted to the pile platform, the space between them formed a true guide on either side for driving the sheet piling. The sheet piling (Fig. 65) was made of 12 x 1 2-inch long- leaf yellow pine, in sticks usually 65 feet long. Three of these sticks were bolted together so as to form a single unit 36 x 12 inches; and these were "tongued and grooved" by spiking 3 x 4-inch pieces on each edge, suitably arranged. To further insure accuracy in the driving of this sheet piling, FIG. 65. Sheet-piling Used at the Harlem River Tunnel. pilot-piles were employed with great advantage. These were made of steel channels and plates, forming a 12 x 1 2-inch pile 60 feet long. They were fitted with pipes running down through the pile point so that a water-jet could be used in washing away the material. Three of these piles were very carefully driven on the spot to be occupied by the sheet piling; they were then withdrawn and the timber sheeting at once in- serted in the hole and driven to refusal with a 6,ooo-pound hammer. The advantage of the pilot-pile was that by its use boulders and other obstructions could be detected and removed before the permanent piling was driven. The sheeting, when 128 MODERN TUNNEL PRACTICE driven, was carefully cut off by a circular saw to the exact level required by the plans. With the sheeting in place, and the roof described thoroughly bolted together and caulked, lengths of this roof, varying from 39 to 130 feet in length, were floated into place. Previous to this six lines of 12 x 1 4-inch range timbers had been bolted to the bottom of this roof ; and when the latter was sunk these timbers rested exactly upon the two rows of sheet piling and the four inner rows of piles. To the outer lines of rangers bolted under the roof system T-irons had been fastened, and the vertical web of these irons cut into the sheet piling under the weight of the roof. This T-iron was intended to assist in making a tight joint between the roof and the lines of the sheeting; but as the silt soon washed in and closed any small crevice, they were unnecessary. The sunken roof was next overlaid with about 5 feet of earth or mud, dredged from the immediate vicinity, to bring the tim- ber roof to a firm bearing and also to provide weight against the uplifting tendency of compressed air used within the work- ing chamber. Each end of this chamber was closed by a suit- able bulkhead, making the length of the chamber 216 feet, or about half the width of the river. The other half of the river was left unobstructed for traffic. In the center of this length a timber air-shaft was built, 7x17 feet, fitted with an air-lock of the usual type. Inside were placed a rotary and direct- acting pump for jetting out the soft material excavated. A material shaft, large enough to take in the segments of the iron lining, was placed near the center, and two smaller shafts were located between the center and the two ends. When the water was driven from the working chamber by the compressed air, the leakage of air from under the edge of the roof was found to be small, considering the length of the sides, and the sheeting was found to be in excellent alignment. The preliminary work had evidently been done with the great- est accuracy and care. The material inside was excavated with little trouble, and the tunnel lined and concreted. In building the shore sections of the tunnel the roof was SUB-AQUEOUS TUNNELS AND TUNNEL SHIELDS 129 130 MODERN TUNNEL PRACTICE omitted altogether, the heavy sheet piling being considered a sufficient protection when suitably braced inside. The coffer- dam was successfully pumped, and the space inside was nearly completed when water broke into the enclosure. It was found that some of the sheeting had stopped 5 to 8 feet above the rock ; and the pressure of water in this soft material was suffi- cient to force its way under the sheeting. Further driving of the sheeting and the use of filling, cement, etc., outside stopped this and a second similar break that occurred. For the building of the second half of the tunnel, Mr. Mc- Bean was convinced that he could introduce greater economy by substituting the upper half of the tunnel itself for the heavy timber roof described, especially as this timber roof had no function to perform after the tunnel was completed, and a sec- tion of it actually had to be removed later to provide the re- quisite depth of channel. This new plan was carried out as follows : As before, the site was dredged to nearly sub-grade, and the double line of 12 x 1 2-inch sheeting w r as driven for the sides and ends of the submarine box, with inside bearing piles and guide and bracing frames as in the western half. But the sheet- ing was now cut off at the springing line of the proposed tun- nel, instead of on a line considerably above the top of the iron- concrete structure to be built. The box thus made by the sheet- ing was about 300 feet long. The roof was built in three sections, two 90 feet long, and one section 84 feet long. To erect this iron-concrete roof a floating box was first constructed, 106 feet long, 35 feet wide, and 12 feet deep. The bottom was made of 12 x 1 2-inch trans- verse timbers laid 4 feet apart, and floored with 3 x 1 2-inch planks ; the vertical side sticks were 4x6 inches, and to these were spiked 3-inch planks. All joints in the bottom and sides were well caulked. On three 4xi2-inch longitudinals fas- tened to the floor of this box was then built a false floor for the upper half of the tunnel. This floor was made of 16 x 16- inch transverse timbers, 8 feet apart, and on these were placed a center longitudinal of 10 x 1 6-inch timber, and two 16 x 16- SUB-AQUEOUS TUNNELS AND TUNNEL SHIELDS 13! inch timbers laid 6 feet 3 inches each side of the box-center. The space between these longitudinals was floored with 2-inch plank, spiked to the 16 x 1 6-inch transverse sticks and well caulked. Bolts held this flooring firmly bound together. - Upon this false floor the cast-iron tunnel lining was erected, in 6- foot rings; and, as shown in the illustration, rods and braces were introduced as precautions against any possible de- formation, and suspension bars were built in for use in sinking this roof. The skewbacks are especially heavy, and have a wide horizontal flange, with an outside vertical guide-flange. It might be mentioned here that this flange was drift-bolted to the top of the sheeting after the roof was sunk. This was done by leaving openings in the concrete covering this flange ; and the bolts were then set by a diver and driven by using a guide-pipe and a heavy "follower." To close the ends of this roof-box, and yet to permit con- nection with an adjoining section, a vertical diaphragm of J- inch iron plate was so bolted over the ends as to leave a 6-foot shell-ring outside of the diaphragm. In the center of the top of the projecting ring was a specially provided opening for the use of the diver who was to enter this section and do the con- necting of two main tunnel sections. The cover was left off this opening until the diver had finished his work inside. Each 6- foot ring of the iron shell weighed about 41,000 pounds, and it carried 618 cubic feet of concrete. As calculated, the total weight of the iron, concrete floor, etc., was about 50 pounds less per lineal foot than the estimated buoyancy of the empty roof-chamber. The concreting having been completed according to plan, the roof was now ready to be lowered down upon the sheeting sides. The Bronx shore section, 84 feet long, was the first to be sunk. But before this was done, a short section of the tun- nel had been built in an open cut on the shore, provided with horizontal air-locks, and presenting a completed ring for con- nection, a tight bulkhead having been built over it some little distance inshore of the end before the end of the original cof- ferdam was removed. 132 MODERN TUNNEL PRACTICE When all was ready for sinking, and suspension tackle had been attached to the eye-bars noted and to heavy beams rest- ing on the surface platforms, water was pumped into the box in which the roof had been built until its floor sunk below the false floor of the tunnel-roof chamber, the buoyancy of the latter having arrested any further sinking of this roof portion. When the clearance was sufficient, one end of the box was re- moved, and it was pulled out lengthwise from under the roof portion, and was used in building another roof section. Com- pressed air was meanwhile pumped into the roof to decrease any leakage through the false floor and to maintain the water displacement. To aid in locating the roof on the sheeting, fine wires were set up at each end of the tunnel section and aligned by a transit, and other tag-lines fastened to the tunnel roof were set for longitudinal and transverse adjustment. With these guides the roof was carefully moved longitudinally until the flanges in the projecting 6-foot ring coincided vertically with the ending of the shore section; the roof was then weighted with stone to overcome its buoyancy, and was sunk and connected by a diver, as already described. As showing the care taken, the flanges were bolted together by i-inch bolts entering i i-i6-inch holes. This section was now ready for excavation, the separating diaphragm being cut, and after the diver had closed the opening by which he entered the project- ing ring. The other two roof sections were assembled and sunk on the sheeting in a similar manner; but the connection of the last section with the river end of the old western tunnel section required some special provisions. As already noted, the timber roof of this first section was placed so high that the entire tunnel section could be built under it, and the lines of the sheet- ing were cut off at a correspondingly higher level. Under this roof a section of the tunnel, about 47 feet long, was left un- built. The problem was to connect the lower iron-concrete roof section with the high-roof section of the first, or western, half of the tunnel. The outside transverse bulkhead of the high-roof section SUB- AQUEOUS TUNNELS AND TUNNEL SHIELDS 133 was first cut off to the level of the springing line of the tunnel, or to correspond with the sheeting under the new roof. The river end of the last section of the new roof sunk had been closed by a special diaphragm, which had a flanged base at the springing line, which permitted it to rest upon and be lag- screwed to the transverse sheeting mentioned. But the dia- phragm itself, instead of conforming in shape to the line of the twin-tunnel section, as before, was now a rectangular plate lo# Roof Tunnel-- >[< -High Roof Tunnel Connecting Roof f/afe. Longitudinal Section. Sheeting --^.High Side Sheeting ' a*"*" m T Jhee^ ENS. NEVVS. Part Sectional Plan A~D. FIG. 67. Manner of Connecting Old and New Work. extending to the full width of the transverse sheeting, or 32 feet 2 inches, and it was 8 feet 4 inches high. To the top of this plate was connected by plates and angles another plate of the same width and almost 5 feet high. In the lower plate was a manhole, 20 x 30 inches, and angle irons were riveted to 134 MODERN TUNNEL PRACTICE both sides and the top of the diaphragm plates, to receive the side plates to be put on after the section was sunk. After the last section had been sunk into place with the dia- phragm attached, the latter was first connected by a diver to the line of transverse sheeting by lag screws. Then, to close a space of about 14 inches between the line of the diaphragm and the sheeting of the high-roof section, two side plates and a horizontal roof plate were lowered into position, fitted by a diver against the sides and over the top of the roof-rangers and the bolt-holes marked. These plates were then taken up, drilled to correspond with the holes in the diaphragm flanges, and fin- ally bolted to the timber sides and roof by divers. In this man- ner a water-tight connection was made between the two sec- tions of the tunnel built on different plans, and with this con- nection complete the water was expelled by compressed air from the old completed tunnel, and the connecting link of the tunnel was built as in the original plan. In the diaphragm as erected, holes had been drilled for the bolts that were finally to connect the flanges of the abutting tunnel shells, and other holes carried anchor-bolts for connecting this diaphragm with the concrete backing. Penna. R. R. Hudson River Tunnel This novel tunnel, for which the contract is let at this date, is intended to connect Manhattan Island, or New York City, with the Pennsylvania Railway System. The Hudson River section of the tunnel is 5,502 feet long; though with its land terminal connections it will be eventually 5.7 miles long. Under the river the tunnel will be laid in two parallel concrete-lined tubes, each supported on a row of 27-inch screw-piles spaced 15 feet apart. The con- struction shown in Fig. 68 is made necessary by the unstable character of the fine silt forming the larger part of the bed of the Hudson River at New York. The cast-iron lining, 23 feet in diameter, is of the usual type, except that a special segment is inserted at the point where the screw-pile occurs. Each lining-ring is 30 inches long and is made in twelve segments, one of the latter being a key-segment 12! inches long. These segments have flanges n inches deep SUB-AQUEOUS TUNNELS AND TUNNEL SHIELDS 135 Leave Concrete rough as shown until Track System is ready to be put in place, when invert of Tunnel can be completed. FIG. 68. Hudson River Tunnel of the Pennsylvania R. R. Co.: Typical Section of One of the Tubes Supported by Screw-piles. MODERN TUNNEL PRACTICE 136 on all edges of the segment ; they break joints longitudinally, and the key segment is thus alternately right and left of the crown-line of the tunnel. Section KK FlG. 69. Details of Bore-segments of Tube Lining. SUB-AQUEOUS TUNNELS AND TUNNEL SHIELDS 137 The segments through which the screw-pile passes are of spe- cial construction, and are made of cast steel, and in pairs occu- pying the width of two rings. Their construction is shown in Fig. 69. The circular opening in the plates is intended for the shaft of the screw-pile ; and to permit the passage of the bladt* of the screw a slot is left in the casting, as shown. A tempo- rary collar and cast-iron plug close the hole in the lining until the pile is put down; and cast-iron fillers similarly close the slot referred to. The screw-piles are in general of the usual construction. The helix has one turn, with the usual lap, and a pitch of 21 inches. The shaft is 27 inches in outside diameter and is made in 7- foot lengths, connected by inside flanged joints, with four flange bolts and twelve steel dowels fitting into adjoining circu- lar mortices. These dowels take the torsional strains resulting FIG. 70. Detail of Dowel and Bolt for Screw-pile Shaft. from the screwing-down of the piles, while the bolts clamp the adjoining sections together, as shown in Fig. 70. As shown in the general cross-section, the upper part of the pile is enclosed in a sleeve. This is simply a sheet steel cylinder placed as shown, when the pile has been driven down sufficiently to permit it. Its purpose is to provide a sort of cofferdam, in which the final 7-foot length of pile can be disconnected and lifted out, and in which another pile section of the exact re- quired length can be inserted and connected up. The top 12 feet of the pile shaft is filled with concrete. At or near the intersection of grades and the rock, where some distortion may occur owing to the difference in support- 138 MODERN TUNNEL PRACTICE ing quality in the ground, an expansion- joint construction will be used. This joint ( Fig. 71) will consist of a ring within a ring, and these rings will be made of wrought steel instead of cast-iron. The figure shows a section through the rings paral- lel to the axis of the tunnel. Quoting here from the specifications, we find that the tun- nel portion under the river is to be built by means of a shield and compressed air. Bulkheads and safety screens are to be built across the tube at intervals not exceeding 1,000 feet. These bulkheads shall be constructed of concrete, or brick set in Portland cement ; and each shall have two air-locks not less than 6 feet in diameter and 20 feet long one near the roof, as an emergency lock for the men ; and one at the bottom, for pass- ing material, pipes, rails, etc. An air pressure of 55 pounds NHWS. ''-Temporary C.I. Block to take the. Reaction of the Shield. FIG. 71. Expansion- joint for Tube-tunnel Lining. per square inch is to be provided for in designing these bulk- heads. A safety screen, extending from the roof downward into the tunnel, is to be maintained within 100 feet of each working face. The contractor is to design his own shield, under certain specifications ; and, of course, this cannot be now described. Screw-jack Shield. In constructing the water-works at Rip- ley, N. Y., Mr. E. A. Wilder, C. E., devised a simple shield for use in driving a 700- foot tunnel through clay and a material closely approaching quicksand. The tunnel was circular, 42 inches in diameter, lined with two rings of brick. As hydraulic jacks would require a special plant for their operation, screw-jacks were employed to push the shield forward. This shield (Fig. 72) was made of f-inch plates, connected by 3 x 4-inch angles. As the circular angle was cut away en- SUB-AQUEOUS TUNNELS AND TUNNEL SHIELDS 139 tirely for the pockets for the screws, the engineer advises the use of a 3 x 5 x ^-inch angle for this purpose. The steel jack- screws were i^ x 16 inches, and brass nuts were used, with a convex bearing seated on a thin concave plate bolted to the cir- cular flange, but not rigidly. This arrangement held the screws"" always in place, and at the same time permitted a slight move- ment that prevented binding of the screw. The pockets en- tirely enclosing the screws answered as brackets, transmitting .-Screw K - 56" - FIG. 72. Screw-jack Tunnel Shield. the thrust of the screw to the cutting edge, and prevented sand from coming in contact with the screw. This shield was built by the Erie City Iron Works, and cost $140 f. o. b. at Erie, Pa. Shankland Shield In constructing the Chicago Intercepting System, in 1902-03, a shield was employed that was practically designed by E. C. Shankland for the contractor. This shield (Fig. 73) was 24 feet 10 inches outside diameter, and the forward 10 feet of hood was made of i-inch steel plates. At the middle of this hood is an inside ring made of two 12-inch channels set back to back and 12 inches apart. From the rear of this ring a series of 1 2-inch horizontal I-beams are spaced 15 inches apart, forming a series of chambers for the hydraulic jacks. The rear ends of these I-beams rest upon another ring of two 1 2-inch channels. The front part of the I4O MODERN TUNNEL PRACTICE hood is stiffened by eight deep gusset plates, forming exten- sions of the central, vertical and three horizontal partitions. At the intermediate points there are shallower gusset plates; and all these plates are riveted to horizontal steel angles inside the shell, and to other angles against the 1 2-inch channel ring. The partitions, dividing the shell into sixteen compartments, are made of f-inch steel plate, stiffened by double rows of 12- inch steel channels. The shield was fitted with thirty 65-ton hydraulic jacks, the 5-inch plunger of each jack having an end bearing plate, 8 x 26 4b Skw,. {"Steel KM K'1,401^ Half Rear Elevation. Half Front Elevation. Longitudinal Section. FIG. 73. Chicago Sewer Tunnel : The Shankland Shield. inches, butted against the 8-inch circular wooden tunnel lining projecting into the tail of the shield. The brickwork is built inside this lining, the latter being left in place. The average rate of progress with this shield, in 93 days, was 8.74 feet of tunnel in 24 hours. Timber-lined Subaqueous Tunnel In 1901 the Massachusetts Pipe Line Gas Company was compelled to carry its pipe system under the Mystic and Charles rivers, near Boston. Subaqueous tunnel siphons were built for this purpose ; and the 42 and 54- SUB-AQUEOUS TUNNELS AND TUNNEL SHIELDS 141 inch cast-iron pipes were protected against corrosion by con- creting them inside a wood-lined shaft and tunnel, as here described. The shafts were sunk by using an ordinary air-lock sur- mounting a riveted steel caisson. This caisson was sunk in the_ usual way and extended in lo-foot sections, until material was reached sufficiently compact to prevent the escape of air. The steel caisson was then stopped, and a segmental plank lining was put in. This lagging consisted of circular segments 6 inches wide, sawed from 2-inch plank, and the circle had an outer diameter of 7 feet. There were eight segments to a ring, Detail of Cutting Edg< FIG. 74. Details of Shankland Shield. and these were spiked together with 7-inch spikes, each ring breaking joint with the one below it. This construction was found to be exceedingly rigid, and it was used in building the tunnel proper. The curved connection between the shaft and the tunnel was made by successively lengthening the diameter of each ring in the direction of the axis of the tunnel, as shown in Fig. 743. In driving the tunnels a simple shield of the Greathead type was employed. The excavation was carried two feet ahead of 142 MODERN TUNNEL PRACTICE this shield by placing boards and posts ; and the shield was then pushed forward by six hydraulic jacks abutting directly against the wood lining. This operation also tended to close up the joints in the lagging; though, as the timber was thor- oughly dry when put in, the swelling of this timber usually f ; '. i-7.--, ~-T.,V- /TvJA ft^g-*-v.^>--.-ft**fti PIG. 74a. Charlestown Siphon Tunnel : Showing Method of Grouting Cast-iron Pipe. made very tight work. The lining was given a wash of thin cement after it was in place ; and any special leaks were plugged by wooden wedges and caulked, or dry cement was fed into the holes and carried outward by the air pressure. To preserve the cast-iron pipes from corrosion, and espe- cially to avoid any opportunity for gas-pockets due to leakage, SUB-AQUEOUS TUNNELS AND TUNNEL SHIELDS 143 the space between the pipes and the wooden lining was filled with concrete where space permitted, or with injected grout. In the latter case the grout was run in pipes to holes drilled in the top of each length of cast-iron pipe ; and, after various de- vices had been tried and abandoned, owing to clogging, the pressure due to the height of the mixing trough at the surface was alone used. But the grout pipe leading through the large gas pipe was washed out with clean water after every run. The cost of this work is given for the several tunnels as follows:* The Maiden tunnel, here illustrated, cost $55.64 per Alter i End Elevation. Section A~B. FIG. 74b. Shield Used by Massachusetts Pipe Line Gas Co. lineal foot complete; or $35.34 per foot for driving the tunnel, $15.50 per foot for the 54-inch pipe, and $4.80 per foot for laying and grouting. The Charleston tunnel was built without a shield, but under air pressure. The total cost was $101.40 per lineal foot; or, driving $87.45, 42-inch pipe $4.35 per foot, laying and concreting $9.60 per foot. The River Street tunnel was 90 feet below the water level ; it was also built without a shield and under great difficulties. It cost $99.65 per lineal foot; or, driving $/i8.8/t per foot, 48-inch pipe $5.36 per foot, laying and concreting $45.45 per foot. The cost of labor on the concrete was about $5 per cubic yard ; and the concrete complete in the tunnel cost about $9 per cubic yard. ^Engineering News, Oct. 3, 1901 ; p. 229. CHAPTER VIII SUBWAYS, OR UNDERGROUND RAILWAYS Location of Orleans Railway in Paris Metropolitan Railway of Paris- Boston Subway East Boston tunnel Buda-Pest Subway New York Rapid Transit Subway Atlantic Avenue Subway in Brooklyn. Subways, or railways of this type, are comparatively very modern in their application. They have for their object the shortening of time of transit between given points in a great city, and the relief of the surface streets from congestion of traffic. Subways are constructed both in tunnels and in open cuts; and they may be combined with the elevated roads where the conditions demand such a combination. The extensions of these subways may be carried under rivers separating parts of a great city; but in such cases these extensions are properly classed as subaqueous tunnels, and they are here treated under that head. Subways are usually located as near to the general street surface as conditions will warrant, for the convenience of the people using them, or to avoid as much as possible the use of long flights of stairs, or elevators, at the stations. At the same time, provision must be made in this location and con- struction for all existing sewers, water and gas mains, electrical conduits, and other underground pipe or conduit systems. The sewers and water and gas mains are usually carried over the subway; and wire conduits are provided for in the construc- tion of the abutment walls. Tunneling close to the street surface involves open-cut work, with all its obstruction to street traffic; or the use of some form of roof-shield, when the soil conditions and the depth 144 SUBWAYS, OR UNDERGROUND RAILWAYS 145 of the covering will permit. In solid rock, and at a sufficient depth, the usual method of rock-tunneling is resorted to. In some of the original London subways, driven through a practically homogeneous clay formation, the tunnels are cir- cular in section, with one tunnel devoted to each of the two - tracks. The advantages claimed by the advocates of this twin- tunnel system are: That this arrangement results in a lower initial cost, as the section of the separate tunnels is less than that of a double-track tunnel ; and, as these separate tunnels can be arranged side by side, or one over the other, the double line can be kept below a comparatively narrow street. There, are also advantages in the ventilation of a single tunnel, by means of the continuous passage of trains in one direction ; and the possibility of collision in meeting trains is eliminated. But there are also objections to this twin-tunnel plan, espe- cially from the point of view of operation; and the cost of maintenance of way is relatively increased, as is that of in- spection and signaling. The stations on the twin-tunnel sys- tem cost more, as they are necessarily more complicated in the arrangements for entrance and exit. The inability to switch over from one line to another is also objectionable, and special cross-overs must be provided. Orleans Railway Tunnel in Paris This extension of the Or- leans railway system into the heart of Paris comes properly under the head of subways in the method of its construction. The execution of the work presented exceptional difficulties : The extrados of the arch was very near the street surface, while the foundation was at times below the water level; the alignment was a succession of curves of large radius; many sewers were cut ; and the abutments of bridges, quay walls, old masonry and other obstructions were constantly encountered. The soil itself was made up of the rubbish of many epochs; and the contract demanded that traffic should not be interrupted on the streets above. The standard section, inside the masonry arch and side walls, is as follows : Span at springing line, 29.52 feet ; level of rail to springing line, 6 feet; rise of arch, 10.38 feet. The side walls 146 MODERN TUNNEL PRACTICE are 2.62 feet thick throughout, and the arch is 2 feet thick at the crown, increasing to 2.62 feet at the spring. The conditions noted, and especially the unreliable character of the soil, necessitated the shield method of execution. The plan of attack adopted was to drive the side galleries, and in these timbered galleries to erect the masonry side walls as a support for the roof-shield to be used in excavating the remain- ing section. These side galleries were 6.6 feet wide at the top, and this top extended 2.3 feet above the springing line of the arch. The roof-shield was practically the same in design as the one previously used so successfully at Clichy, in Paris. But in this case the shield was guided around the numerous curves by lateral rollers ; and an important modification was made in the method of sustaining the soil behind the shield. As shown in Fig. 75, the shield included a steel skin A, made of two plates each f inch thick. This skin was supported by a double-latticed truss, with the ten hydraulic jacks located in the lower truss. It was provided with the usual front hood, cut away at an angle of about 45. The latticed beam H tied the trusses together and formed the floor of the shield. As compressed air was not used, the shield was not fitted with a transverse bulkhead. To guide the shield laterally in its forward motion, side rollers were provided, running upon planks of hardwood cov- ered with steel plates, and attached to the masonry inside the side walls. These are shown in Fig. 75. The method of sustaining the earth behind the shield was novel. Upon special latticed centering trusses provided, and held up by posts and braces leading to the center core of soil, latticed beams e (Fig. 76) were placed longitudinally and held in place by angle irons on the centering trusses. These longitudinal beams carried a series of small hydraulic presses u, with the upper end of the press buried in a timber / (Fig. 75b), which was about 8 inches thick and sheeted with steel plate on the soil side. These beams e were of different lengths, corresponding to the stage of construction in the arch SUBWAYS, OR UNDERGROUND RAILWAYS I 148 MODERN TUNNEL PRACTICE masonry the longest, 26.24 feet, being at the key; and the shortest, 9.84 feet, at the springing line. Small screws g running in the space between the latticed shield trusses were used in. separately pulling forward the latticed beams e and the 8-inch timbers / attached to them, the beams slipping in the angle-iron guides. The greatest difficulty in using this method lay in the great friction encountered in hauling these members forward ; but the French engineer believed, neverthe- less, that this system possessed important advantages over the old method of building the masonry under a rear shield, as all necessary openings in the arch work are made easily. The ten hydraulic jacks used in forcing the shield forward exerted a combined force of 1,000 metric tons. These jacks, instead of reacting upon the finished masonry, as usual, abutted against solid continuing struts passing through the centering system, as shown at h (Fig. 76). In operating this roof shield, the shield was first advanced its length by the push of the jacks; the shield rolling on the rollers b placed under the beam C at the base of the shield. The sills and wedges are then laid for the new center which is erected to take the place vacated by the shield. The beams e and the 8-inch timbers f are pulled forward as the masonry advances; the small hydraulic presses u being operated to push up the timbers / into the space left by the advancing shield. The arch masonry is built up at the haunches on small steel forms, and is continued on lagging held up by the same cen- tering truss that holds the longitudinal beams e. The arch was constructed of beton blocks, molded and thoroughly set before they were brought to the work. Masonry was laid con- tinuously, day and night. Roof -shield of the Paris Metropolitan Railway This shield is interesting as embodying the latest practice of the French engi- neers in shield construction. The roof of the Metropolitan Railway of Paris is but little below the surface of the street; and the tunnel is a double-track structure with a clear span of SUBWAYS, OR UNDERGROUND RAILWAYS P4 149 b II bfi C o JZ in 150 MODERN TUNNEL PRACTICE 23.29 feet and a rise of 6.79 feet in the arch. The arch, abut- ments and floor are all in masonry. The first, or Vincennes-Maillot portion of this railway was partly constructed in 1898 by means of a modification of the Clichy sewer shield, previously here described. This was a half-section shield, on which the arch was built and the abut- ments constructed last, though in some cases the abutments were built in advance and the shield pushed forward on them. But the results were not satisfactory on the Metropolitan line, and much of the work was really done by ordinary methods of timbering. The failure of the shield was largely due to the fact that the soil penetrated was not homogeneous, being largely filled ground, with old foundation walls and broken masses of masonry interspersed through it. Then, too, in moving for- ward, the shield carried with it, around its outer surface, a cer- tain thickness of earth which caused undulations in the surface ground, and by its broken condition threw too much weight on the tail-end of the shield. There was thus a tendency in the shield to rise at the forward end, while the fresh arch masonry was damaged under the friction of the shield when this was moved forward. The shield here shown was devised by the engineers, Radenac and Raguet, especially to avoid these troubles, and in actual use it has been advanced as much as 20 feet in 24 hours' work. The characteristic features of this new roof-shield are : Its length and the more stable support provided for the shield-roll- ers when the shield is moved forward. Instead of operating the rollers on top of freshly laid masonry, as is often done, the steel centers here employed are firmly braced together, and they are so supported and tied together at the bottom that they are prac- tically immovable. As these centers carry the tracks on which the shield moves forward, this forward movement is steady and the surface settlements or undulations do not exceed three inches. The shield is made of an outer sheet-steel shell, ismm. thick and shaped to the extrados of the arch, and the total length of this shell is 7. 5m. (24.6 feet). The shell is supported by four SUBWAYS, OR UNDERGROUND RAILWAYS 152 MODERN TUNNEL PRACTICE cross-beams shaped to the shell and connected by 38 longitudi- nal girders, of which 20 extend forward to support the forward end, and 14 carry the rear end. As arranged the bottom of the shell is o.68m. (2.23 feet) above the springing line of the tun- nel and the forward end of the shell is shaped like a hood with four set-backs of about one foot each on each side of the axis. The shell is fastened to the girders by countersunk bolts, pre- senting a smooth surface outside. The webs of the girders are stiffened with angle-iron, making a box-beam of each pair of girders, or 19 in all. Ten of these box-beams support the rollers, and the 9 beams coming between them carry the hydraulic jacks. All of the members of this shield are connected by bolts in such manner that it can be readily taken apart after use, and the total weight of the shell and its framework is 67,540 pounds. The cast-steel cutters on the front of the hood are 8 in number, each about 3^ inches thick by 6 inches wide, and these are bolted to the shield by f-inch bolts. The centers upon which the rollers operate are built beams shaped to the arch and divided into two equal parts connected by means of bolts. The foot of this center extends about 18 inches below the spring of the arch, and it there rests upon a cross-tie made of two steel plates and angles. This tie is put in to obviate a tendency in the center to spread, and the whole center is carried on longitudinal sills supported by posts driven into the undisturbed ground of the lower advance gallery. There are usually 30 of these centers under the shield and the finished masonry at one time; each center weighs about 1,980 Ibs., and they are spaced one metre (3.28 feet) apart, c. to c. On top of this series of centers there is a projection in the axis of each of the 19 box-beams carried by these centers, and each center is connected to its mate by a series of cast-iron beams fitted with shoes and bolt-holes. The top of each of these connecting beams carries a rail 2.56 inches high, which is also the depth of the lagging to be used in lay- ing the masonry on these centers. Arrangement is also made on these connecting beams for attaching the thrust-blocks of the hydraulic jacks. SUBWAYS, OR UNDERGROUND RAILWAYS 153 The rollers are attached to the framework of the shell, and are set in 10 rows; the 6 rows in the middle having 6 rollers each, and the 2 rows on each side having 5 rollers. These rollers are made of cast-iron, double-flanged to prevent them running off the tracks, and with an extra width between the flanges so as to permit the guiding of the shield in its forward movement. Each roller is mounted on a 3! -inch soft-steel axle, 16.34 inches long, supported in castings bolted to the frame. The hydraulic jacks are each 8.8 feet long over all, and they have a stroke of 3.7 feet. While place was made for 9 hy- draulic jacks, only 7 were actually installed, and 4 do all the work required. Each jack exerts a maximum pressure of 50 tons. In operating this shield a bottom gallery is first pushed forward, and into this gallery is thrown the material exca- vated at the front of the shield. Before the shield is advanced, a new center-rib is set up and securely bolted to its predeces- sors, the roller-track for the shield being also lengthened by the span of the new center, or by one meter. The hydraulic jacks are fastened to the shell framework, and the pistons of the jacks act upon thrust-blocks set between the center-ribs. As these ribs are theoretically immovable, the shield-shell and its framework advance. As the shield moves forward, sheets of thin steel replace it and prevent the earth from falling in, and these plates are held in place by temporary timbering until the masonry is completed, the plates remaining in the ground. The masonry is thus actually built behind the shield and not under it. The rear of the shield is shaped with two off-sets on each side, and the arch masonry is thus being laid with the abutment portions continually in advance of the crown of the arch. The masonry is built on wooden lagging laid upon the steel centers, and it completely fills the space between this lagging and the steel top-plates, the temporary props under these plates being removed as far as possible. The crew for this shield work was made up as follows : One foreman and one machinist; 4 carpenters and i helper, to take down and put up centers ; 4 miners, working at the face ; 154 MODERN TUNNEL PRACTICE 8 laborers, 6 shoveling and 2 attending to cars in the advance, lower gallery. In addition to these, 5 masons and 5 helpers were at work on the masonry ; the masons working on the low wall that lies under the shield and along the springing-line on both sides in the intervals between advances of the shield. With the arch masonry complete, the two side walls and the floor of the tunnel are built by underpinning the arch as the bottom material is excavated. Boston Subway System Boston, a few years ago, had proba- bly a more complicated and congested electric street-railway system than any other in the United States, and these condi- tions resulted in Boston being the first of our cities to construct a regular system of underground lines for its electric street- railway service. Without entering intq^the detail of routes, it is sufficient to say the plan adopted by the Boston Rapid Transit Commission of 1895 contemplated the construction of about 5,600 feet of double-track subways, and about 3,500 feet of four-track sub- ways. These subways were to be ventilated by fans driven by electric motors, and well lighted by electric lights. The chief engineer was Mr. Howard A. Carson, M. Am. Soc. C. E. The material to be penetrated was mainly earth, sand and gravel, and the conditions were generally favorable, the maxi- mum depth of excavation being 38 feet. The grades were 3% and 5%, and changes in direction, were made by curves of 700-foot radius on the center line. As shown in Fig. 77, the general construction consisted of a concrete invert, side walls of steel columns with concrete filled between, and a roof of plate-girders or I-beams, with brick jack-arches between them, the whole covered by concrete. In the four-track lines a middle column supported the roof. The detailed dimensions are given in the illustration. The steel columns were spaced 6 feet apart, with a V-brace of 3 x f -inch angle-iron in each panel and a longitudinal tie at the base of the post made of a similar angle. One of the ventilating chambers is shown in Fig. 78. It is a concrete chamber fitted with a ventilating fan driven by an SUBWAYS, OR UNDERGROUND RAILWAYS 155 . . uoiuuoy sfuuHQj. pis 156 MODERN TUNNEL PRACTICE electric motor, the air exhausted being discharged through an air-duct 6^ feet in diameter. This subway was largely built in open cut, and this portion of the work requires no special explanation. About one-third of the length of this subway is tunnel, with a concrete invert, side walls and haunching, and a brick arch, as shown in Fig. 79. The peculiar feature of this system of construction is the use of the tie-rods through the crown of the arch, intended to prevent any deformation of the arch due Section F-F FIG. 78. Boston Subway : Ventilating Chamber. to eccentric loading, as the street surface is very near at some points. In tunneling, the two side walls were built in advanced head- ings ; the arch was then built by means of a shield supported on the side walls, and the center core of material was removed later. The concrete side walls are double. The outer wall, 6 to 12 inches thick, is backed directly against the sides of the ex- cavation, and the inner face is then plastered with an asphalt composition to make it watertight. SUBWAYS, OR UNDERGROUND RAILWAYS 157 For the tunnel section a roof-shield was employed of the type here shown. The position of the shield in relation to the tunnel section is shown in Fig 1 . 80. The shield weighed about 22 tons and cost about $6,000. It was calculated to sustain an approximate load of 640,000 pounds. It was 29 feet 4 inches wide over all, and had a rise of 4 feet 45-16 inches. The shield is composed of two plate-girders 3 feet 8 inches deep and 4 feet apart, with cover plates extending 4 feet beyond the girder, while an additional top-plate extends 2 feet to the rear. Under each foot of each girder is an iron casting with a spherical pro- jection on the under side, which fits into a recess in a cast-steel shoe, the surface in contact being planed to a truly spherical FIG. 79. Typical Section of the Boston Subway, in Concrete and Brick Work ; Double-track. surface. These shoes rest upon two lines of lo-inch steel I-beams imbedded in the tops of the concrete side walls, form- ing a track upon which the roof-shield slides as it is pushed forward. The girders are divided into 10 panels by transverse f-inch webs, and a 6-inch hydraulic jack is located between the girders in each panel. The closed ends of these jacks are supported by the castings shown in the figure. The 6-inch plungers of the jacks pass through loj-inch holes in the web of the rear girder, the outer ends of the plungers being fitted with collars, which latter abut upon 2^-inch cast-iron round bars, about 2 feet 10 158 MODERN TUNNEL PRACTICE inches long, with 2|-inch pipe-sleeves at the joints. These iron bars are built into the brickwork of the arch and form continu- ous lines of metal to resist the thrust of the jacks ; a device ap- parently first used by Mr. Walton I. Aims in the East River gas tunnel, at New York. In moving the shield forward the pipes leading to the jacks are brought under the rear of the shield, and they are fitted with valves, so that a man at this point can direct and regulate the direction of the advance by varying the pressure on each jack; men stationed at each jack watching and measuring the Details of Casting Supporting Ends of Jar Details of Casting under Ends of Girders. Longitudinal Section C-Q. FIG. 80. Detail of Roof-shield, Boston Subway. advance simultaneously. As soon as the shield has been pushed forward about 3 feet the timber centering is erected behind it and the brick arch is built. During this time a heading 6 feet high and the whole width of the tunnel is excavated ahead of the shield and supported by posts and poling-boards, which are removed as the shield reaches them. In the subway work in Boston the material was mainly gravel and stiff clay ; the depth of earth above the tunnel SUBWAYS, OR UNDERGROUND RAILWAYS 159 roof varying from 6 feet 9 inches to 13 feet. A progress of about 50 feet per week was made. East Boston Tunnel The construction of the Atlantic Ave- nue station of the Boston Subway Extension, to East Boston, furnishes an interesting example of wide-arch, soft-ground tun- neling. As shown in Fig. 82, this station is deep under ground and below the water-level, and at each end it connects with a standard double-track tunnel which is 23 feet 8 inches wide by 20 feet 8 inches high. The entrance shaft to the station is Surfact of Strut. , r^T'^ 4 . Qa9 ' ' f.T.C.Ct Q QlS'Stwtr HgW* if n g;|~ 5- ' 20' T >i 1 5 R FIG. 82. East Boston Tunnel ; Atlantic Avenue Station. 40 x 57^ feet in plan, and will contain elevators, stairways, etc., and this was built by sinking pits from the surface. The station portion proper is 150 feet long. This station tunnel comes entirely within a blueTclay stra- tum, with occasional pockets of sandy clay. The side walls were built first, as shown in Fig. 83. A bottom drift was first opened and timbered as at a; the side boarding was then replaced by a lagging of corrugated boards, and behind this was built a 6-inch concrete wall, as shown at b. A portion i6o MODERN TUNNEL PRACTICE of the side wall and invert were then laid, as in b and c; and a second drift was started above the first and timbered, as shown by e, and in this drift the 6-inch concrete wall was carried up as before; the side wall was next carried up, as at /. This operation completes the wall to the springing line of the arch, both side walls being constructed simultaneously. It is understood that this side-wall work is a continuous operation. And it will be noted that the bottom drift at track level has a spoil-car platform. The construction of the roof-arch follows close behind the FIG. 83. Sequence of Operations in Building the Side-walls at the Atlantic Avenue Station. completed side walls, and the method of procedure is shown in Fig. 84. A crown heading A, 8 feet wide and ?J feet high, is driven and timbered, and over the caps are inserted four sheet- steel poling-boards. Ahead of A and below it, is driven a sec- ond heading B, 8 x 6 feet ; this latter heading serves for the removal of the soil. From heading A a drift is carried right SUBWAYS, OR UNDERGROUND RAILWAYS 161 and left toward the haunches, steel poling-boards being- inserted and braced by radial struts from the core below. On each haunch and at the same time the drifts D are driven and roofed in a similar manner, working toward the springing lines. When drifts C and D meet an annular space is dug out, 30 inches deep^ or the width of the poling-boards; in this space the concrete arch is built on centers in 3O-inch sections. The steel poling-boards referred to are made of No. 12 plate, 2 feet by 2 feet 6 inches in plan, and on each of the four sides is riveted a 2 x 2 x ^-inch angle, each drilled for four bolt-holes, used in connecting the plates. -In operation, four crown-plates Longitudinal Section of Heading. Cross Section. FIG. 84. East Boston Tunnel ; Atlantic Avenue Station : Method of Building Roof-arch. are inserted endwise at the top of heading A and bolted to- gether and to the rear plates. The lateral enlargement, 5 feet high and 30 inches wide, is roofed in a similar way for every 2 feet gained. Normally, the advance heading is kept about 10 feet in advance of the arch ring. All the material from the headings A and B and the lateral drifts C is removed on muck cars running in the heading B ; the spoil from the drifts D is passed down to cars in the bottom side drifts. The arch-ring centers were built in 3O-inch sections, and the lagging is left off the ribs at the crown. A special floor is con- 162 MODERN TUNNEL PRACTICE SUBWAYS, OR UNDERGROUND RAILWAYS 163 structed for the concrete cars, as the arch work progresses, and at the level of the top deck of the shield through which the cars must pass on their way through the standard tunnel section. This is about 2 feet below the floor of heading A. The cars were dumped on this floor and the concrete was shoveled 4n by hand, working from the springing line to the crown. The key was built by passing the concrete in endwise over the for- ward center-rib. The steel plates were left in place. A 5-foot section of arch was constructed every 24 hours. The earth core was removed as a final operation, from several benches ; taking the material out under air-pressure and passing it through the air-locks. The invert was built in sections as this core was removed. Buda-Pest Subway This line is historically interesting as being the first underground city railway operated by electricity. This double-track railway is about two miles long and runs under the center of a broad street. It was, consequently, con- structed in an open cut in 1895; Siemens & Halske, of Berlin, designing the electrical equipment. The typical cross-sections shown in Fig. 85 are those of a dry-ground section and a deeper section where the excavation penetrates below the water-line in the ground. In the latter case every precaution has been taken to exclude water from the subway. The asphalt felt employed for this purpose was ap- plied in sheets in two layers, each sheet being about 31 J inches wide and laid to break joints. On the under side these sheets were painted with a sticky natural asphalt, and the upper side was coated with fluid asphalt. The invert shown was only used for a short distance, where ground-water was encountered. The drain-pipes under the center of each track drain into small reservoirs at each station, where the water is pumped from them by small electric pumps. New York Rapid Transit. Without entering into the detail of the history, route, etc., of the Rapid Transit Railway now nearing completion in New York, some of the standard cross- sections are here given. The plan and section of the four-track subway shown in Fig. 164 MODERN TUNNEL PRACTICE 86 requires little explanation. The same type of construction applies to the bulk of the two and three-track sections. The form is rectangular, and it is made up of transverse bents of steel columns and roof beams, with side walls, roof and floor of concrete. The interior columns are built up, while the side Waltr Proofing... ..:-.. 777/s Roof Construct/on if to be used where extra h is required topers} s across Top of Structure. Part Plan. FIG. 86. New York Subway : Plan and Section, Four-track Line. columns are I-beams; the roof is supported by rolled I-beams. The entire four sides of the section are preserved from seepage by a layer of waterproof material imbedded in the concrete. The double-track rock and earth sections are 25 feet wide SUBWAYS, OR UNDERGROUND RAILWAYS in the clear and 18 feet high at the crown, as shown in Fig. 87. In each case the tunnel is lined with concrete. Open-cut Work, New York Rapid Transit Railway. As an illustration of deep open-cut work in subway construction, a sketch plan is here given showing the method adopted in build- ing a portion of the New York Rapid Transit Railway. In this section the subway excavation had to be made unus- ually wide to provide for the station and a fifth or switching- track. The excavation extended to a depth of about 35 feet, with the bottom 10 to 15 feet in rock. The sequence of operation was as follows : The trench A FIG. 87. New York Subway : Standard Earth and Rock Sections. was first opened on the south side of the street down to sub- grade and wide enough to permit the erection of two bays of the steel work. This trench was sheeted and braced in the usual manner, and the two bays of the tunnel were completed. The next step was to start the transverse drifts B, each about 12 feet wide and 50 feet apart, and long enough to reach beyond the column of the fourth bent of steel work. The top of these drifts was kept well above the subway roof line and the bottom was carried to the rock, each drift being well timbered and sheeted. When a number of these drifts had been completed the north ends were connected by the longitudinal drift C with 1 66 MODERN TUNNEL PRACTICE the same top and bottom level as the transverse drift. Then these drifts B and C were deepened through the rock to sub- grade, and the concrete floor was laid in C, and on this was erected the fifth row of columns. The next operation was to widen drift B so as to permit the placing of the 25-foot roof beams connecting the third and fifth rows of columns. This widening was done by breaking down both sides of the drift under poling-boards driven ahead and supported by vertical posts until the headings met and left Section W-X. C.L. of Subway Trvrcks Core &Lf Section Y~2. C.I, of Subway Trcrcte I ^4-^-4 J ^-J,-.-_-Y|-14^1 |^inch track carrying small side-dump cars, of a capacity of 18 cubic feet each. The mixer itself consisted of a heavy cast-iron box, in which revolved in opposite direc- tions two mixing paddles. The dry material was shoveled into the gaged hoppers and dumped directly into the mixer through bottom doors operated by levers. The sand and cement came from the material yard in skips, these latter being rilled from the cars by a 3-ton American hoist traveling derrick. This derrick was also used for lifting the bricks required and hand- Plan. /\ 1,000 1 3ricks I'-' g Side Elevation. Cross Section. FIG. 98. Crates for Handling Bricks. ling the heavy roof beams, which, in the larger canals, weighed one ton each. The trains to and from the work were operated by an electric trolley system. The bricks were made near Lake Ponchartrain. And as these bricks were taken from the kilns they were piled on spe- cial crates (Fig. 98) holding 1,000 bricks each. These crates, with the bricks, were picked up by a derrick and loaded upon barges, each barge carrying 100,000 bricks. This barge was towed to a city landing, and the crates and bricks were again picked up and deposited directly on the material cars, each SPECIAL TUNNEL-BUILDING PLANT 185 car carrying 4,000 bricks. The bricks were finally dumped on the work within reach of the bricklayers. This method saved much time and expense in avoiding rehandling, and materially reduced the percentage of breakage. CHAPTER X SOME DATA UPON THE COST OF TUNNELING Cost of hand-drilling in shaft-sinking Cost of power-drilling in shaft- work Cost of drifting and cross-cutting Hand-work in tunnel driv- ing Diamond-drill work Cost of square-set mine timbering Cost of mine-hauling by compressed air Cost of concrete tunnel-lining Water-hauling vs. pumping in mines Cost of driving a mine-heading Cost of tunnel-driving and steam-shovel work. While the probable cost of performing work is of the utmost importance to the bidder upon public works, for reasons easily guessed at, reliable data as to this cost is a valuable asset to the individual contractor, and, as a rule, he .is not willing to publish it for the benefit of others. So many varying factors also enter into this cost that experience on one piece of work is not always a safe guide for the cost of other and seemingly similar work. But, from returns of cost carefully made by engineers, a few cases have been here selected, chiefly for the purpose of showing how such records should be kept. Hand-drilling in Shaft Sinking. The following detailed record of shaft sinking at the Golden Eagle Mine, Lassen Co., CaL, is given by Mr. E. H. Benjamin, M. Am. Inst. M. E. This shaft was commenced at the 4OO-foot level, and was sunk 150 feet below that point. The rock was hard andesite, with no water. The shaft was /x 12 feet in the clear; timbered by 10 x lo-inch sawed timbers, plates and center-braces dove- tailed in, and center and corner posts gained in. The sets were 5 feet apart c. to c., filled and lagged with 12 x 1 2-inch lining set 3 feet apart. The work was completed in forty-seven 8-hour shifts, work- ing three shifts a day with three men on a shift. This makes an average of 3.2 feet per shift, hoisting by bucket 20 tons of material per shift, besides timbering. 1 86 SOME DATA UPON THE COST OF TUNNELING l8/ For each round 18 holes were drilled; each hole 3^ to 4 feet deep, using j-inch steel; No. 2 Giant powder was used for blasting; and the ground drilled hard, but broke well. Mr. Benjamin says that he does not know of a better record for hand-drilling in a shaft. This detailed record is useful for purposes of comparison, and as showing how complete a record of this kind can be made. DETAILED RECORD OF SINKING 150 FEET OF SHAFT AT THE GOLDEN EAGLE MINE, LASSEN COUNTY, CAL., 1902. Detail. Shifts. Miners (9) 423 Topmen (2) 94 Engineers (2) 94 Blacksmith (i) 47 Foreman (i) 47 Wages, or Price. $3.00 per shift. 2.50 3-00 3-50 $100.00 per month. Totals. Ci $1,269.00 235-00 282.00 164.50 172.30 jst per ft. $8.460 1.566 1.880 1.096 1.149 Total labor .... 705 Timber 10,976 feet B. M. Lagging 2,250 feet B. M. Lining 2,270 feet B. M. Cord wood, block G 5 cords Wedges 3,000 QUANTITY. $13.00 per M. 0.035 per piece 14.00 per M. 3.00 per cord o.oi per piece $2,122.80 $142.69 88.20 31-78 15.00 30.00 $14.151 $0.951 .588 .212 .100 .2OO Total timber $7Q7 67 $2 O^I Wood, Fuel 25 cords Oil and incidentals $3.00 per cord $75-00 15.00 $0.500 .IOO Total power cost $QO OO $O600 Coal oil 6 cases Candles 6 cases $4.15 per case 6.40 per case $44.90 38.40 $0.166 .256 Total illumination $6? to $O 422 Powder 600 Ibs. Fuse 2,500 ft. Caps 550 $0.14 per Ib. 3.70 per M. 6.25 per M. $84.00 9-25 344 $0.560 .O6l 023 Total explosives $9669 $0644 Total cost of mo feet of shaft. . $2.680.46 $17.868 Power Drilling in Shaft Sinking Mr. E. C. Voorheis, Super- intendent of the Lincoln Gold Mine Development Company, Amador Co., CaL, gives the following data in power drilling in shaft work, in 1902. 1 88 MODERN TUNNEL PRACTICE The Lincoln shaft was sunk from the 1,260- foot level to the 2,ooo-foot level, a depth of 740 feet. The ground was green- stone and hard, black slate, and the size of the excavation was 8x 17 feet. The men worked in 8-hour shifts. The drilling was done by means of the "Baby" giant drill; the average depth of each hole in the shaft being 6 feet. Hercules powder, 40% nitroglycerine, was employed; and crude oil, at $1.50 per barrel of 42 gallons, was used for steaming. To sink the shaft 3.864 blasting holes were required, or 5.2 per foot of shaft. During the sinking of the shaft 60,025 tons of water were hoisted; adding to this 9,456 tons of waste makes a total of 69,481 tons hoisted to the surface. The following table gives the labor cost of sinking the shaft and putting in the timbers : COST OF SINKING 740 FEET OF SHAFT. Cost per ft. Quantity. Class. Wages, or Item Cost. Total Cost, of Shaft. 2,956 days Labor $2.75 per 8 hours $7,129.00 350 days Day foreman 4.00 per 8 hours 1,400.00 282 days Night foreman 3.25 per 8 hours 916.50 Total labor cost, sinking and timbering $9,445.50 $12.76 12,450 Ibs. Hercules powder (16.8 Ibs. per ft. shaft) 1,307.25 1.76 35,800 ft. Fuse 125.30 .17 46 boxes Lion caps 46.00 .06 2,400 Ibs. Candles 288.00 .39 148 sets Timbers 207,200 ft. at $18 per M -3,729.60 5.04 Total cost labor, lumber, powder, etc $14,941.65 $20.18 Total labor engineers, blacksmiths, framers, etc. 6,224.00 8.41 Total cost fuel 5,893.50 7.96 Total cost, all expenses except office $27,059.15 $36.56 Drifting and Cross-cutting From this same shaft a cross-cut was extended 642 feet, passing through 40 to 60 feet of black slate, with considerable water; and then two drifts were driven, aggregating 483 feet in length. This work was done with the "Baby" giant, and the average depth of each drill hole was 5 feet. The following table of cost was furnished by Mr. Voorheis : SOME DATA UPON THE COST OF TUNNELING 189 COST OF RUNNING 1,125 FEET OF DRIFTS AND CROSS-CUTS. Total Cost Quantity. Class. Wages, or Item Cost. Cost. Per Ft. 1,428 days Labor Miners, $2.75 ; car men, $2.50 $3,772.50 168 days Day foreman $4.00 per lo-hour day 672.00 134 days Night foreman 3.25 per lo-hour day 435-5O Total labor cost $4,880.00 $4.153 11,150 Ibs. Powder 1,226.50 1.043 26,500 ft. Fuse 79-50 .068 35 boxes Lion caps 35-QO .030 800 Ibs. Candles 96.00 .082 Total cost $6,317.00 $5.376 3,258 holes drilled, or 2.77 per foot ; using average of 3.42 pounds of powder for each blasting hole. Hand Work in Tunnel-driving The following cost data re- fer to a short tunnel on the W. Va. & P. R. R., driven in 1891. The tunnel was only 624 feet long, and was driven through a soft blue-clay shale, showing little stratification and practically dry. The tunnel had a span of 23 feet, was 13 feet from the floor to springing line, and the arch was a full center of n^ feet radius. The heading area was 208 square feet; bench area, 299 square feet, or 507 square feet in all. The work was done entirely by hand, with the following force: On heading, i foreman, 8 miners, 6 muckers, and one boy; on bench, I foreman, 8 miners, 10 muckers and one boy. Common laborers were paid $1.45 per day, and miners received $1.75 per day of ten hours. In the heading three sets of holes were drilled, each set consisting of 4 holes about 4 feet deep. Each hole was loaded with from 4 to 6J-pound sticks of dynamite, and an average advance of 2.\ feet was made in each blast. A derrick-car was used in handling the muck, and also for handling the timbers, lagging and packing. The bench was taken down in 4- foot lifts, two half-depth blasts being made for each hole. Each blast consisted of 4 holes, with 10 sticks of dynamite to an outside hole and 15 sticks to the center hole. The bench-progress per shift was about 2^ feet. The work was done by contract at the following cost to the railway company : I9O MODERN TUNNEL PRACTICE 11,726 cubic yards excavation at $2.85 $33>4iQ 742 cubic yards packing at $1.75 1,298 256 cubic yards fallen rock at $1.25 320 303,000 ft. B. M. timbering at $30.00 9,090 Total cost of 624 lin. feet tunnel $44 127 Cost per lin. foot $70.70 Cost of Driving Heading In 1899 the cost of driving a 7 x 8- foot heading in the Melones Mine, Calaveras Co., Cal., is given as follows by W. C. Ralston, M.E. : This heading, or adit, was 2,608 feet long, with a grade of 3 inches per 100 feet. The drilling was done by three Inger- soll Eclipse drills, run by an Ingersoll-Sargent Class B com- pressor ; the latter was operated by a 5-foot Pelton wheel under a head of 470 feet. The rock was diabase, brown slate and talc schists, requiring timbering on some lengths. The working force of 29 men was divided into three 8-hour shifts of 7 men each. No. 2 40% Hercules powder was used throughout; and after each blast water, under 200- foot head, was freely used in condensing fumes and cooling the air. After eight and a half months of almost continuous use the total cost of repairs and extras for the compressor amounted to $21.32. The total cost of extra parts for the three drills was $91.65. ACTUAL COST (EXCLUSIVE OF MANAGEMENT) OF 2,608.5 FEET OF TUNNEL AND DRIFTS, 7x8 FEET. Cost per Totals. Lin. //. Labor, including timbering $19,501.46 $7-47 2,000 Ibs. powder, No. ij at 16.6 cts 25,550 Ibs. powder, No. 2, at 11.9 cts 3,405.65 1.30 75,000 ft. fuse, at 51.7 cts ....! 200 boxes caps, at 60 cts '. 500.20 .19 333^ cords wood, at $5.00 1,667.50 .63 40 ins. water and tender, at 15 cts 828.50 .32 11,591 Ibs. coal, at $15 per ton and freight 179-43 .06 8,466 ft. timbering, at $20 per M 169.32 .06 3,040 Ibs. candles, at 7M> cts 262.04 -io 21,555 Ibs. steel rails, i l / 4 to 2^/4 cts 567-62 .22 Air pipe, n in., at 18 and 30 cts Air pipe, 3 in., at 22 cts Water pipe, 2 in., at 11^/4 cts .' 1,042.45 .45 Hay, iY 2 cts. ; barley, .019 cts 267.16 .10 Steel, drill parts, oil, tools, etc 316.92 .12 Total $28,708.25 Actual cost per lin. ft $1.1.02 The air and water pipe were in large part reused, hence comparatively small cost per lin. foot. SOME DATA UPON THE COST OF TUNNELING 19! Tunnel Work on Ohio Residency, Pittsburg, Carnegie & West- ern R. R.* This road is characterized by exceedingly heavy work in grading; and construction was still in progress in 1904. The double-track tunnel section is shown in Fig. 100. The usual method of attack adopted was to drive, at the same time, two 7 x 8-foot headings, the floor of the headings being about I2j feet above grade. As these headings advance, the material between them is blasted out and the arch area cleared through from portal to portal. The 12^-foot bench is then removed. Two steam drills are operated in each heading, without inter- ference. The excavated material is run out on small dump cars, and is dumped into a chute that leads to cars on the grade below. FIG. loo. P. C. & W. R. R. Standard Tunnel Section. The cost of driving by han<^ a 7 x 8-foot heading in sand- stone is given as follows : Labor, per shift $18.20 Explosives 3.84 Repairs 90 Light 32 Total $23.26 As each shift removed 6.2 cubic yards of heading, the cost was $3.75 per cubic yard. ^Engineering News, May 21, 1903. MODERN TUNNEL PRACTICE In another sandstone tunnel where power drills were used, the cost of driving 100 feet of a full-sized heading, running 15 cubic yards to the lineal foot, was as follows, per lineal foot of heading : Labor $2,527-45 2,000 Ibs. dynamite, 40 per cent., at 12 cts 260.00 470 gals, kerosene oil, at 12 cts 56.40 1,875 gals, gasolene, at 12 cts 225.00 3,000 bushels coal, for compressor, at 9 cts 270.00 Machine and lubricating oil 62.50 Blacksmithing 150.00 4I.6JQ ft. B. M. timber, at $23 957-93 Total cost loo lin. ft $4,509.28 Cost per lin. ft. including timber $45.09 Cost per cubic yard, including timber 3-6 The timber was in rings of 12 x 1 2-inch stuff, 4 feet c. to c., lagged with 4-inch plank. This timbering is shown in Fig. TOO. The ribs are usually spaced 3 feet c. to c. ; though this was made 2 feet in soft ground and 4 feet in hard ground. The tunnel timbering was Georgia pine, and in one tunnel the cost was as follows : Cost per iwoft.B.M. Georgia pine, f . o. b. cars $23.60 Hauling 6 miles 3.00 Cost of framing 5.00 Cost of erecting and bracing 3.00 Total cost in place $34-6o To put in the packing over the lagging cost, in some cases, 80 cents per cubic yard. The carpenters who did the fram- ing received $3.00 per lo-hour day, and the laborers who did the erecting received $1.50 for a similar day. In this case the framing and erecting cost was excessive, owing to the im- proper division of labor and doubling of "bosses." Steam Shovel Work As shovel work may be advantageously used in the approaches to tunnels, some late notes upon the cost of work of this type are here given from experience on the Ohio Residency, Pittsburg, Carnegie & Western R. R. With a 35-ton Vulcan traction shovel, with I cubic yard dipper, 1 1 minutes were consumed in loading 6 dump cars of SOME DATA UPON THE COST OF TUNNELING 3 cubic yards nominal capacity each. To haul this train 800 feet to the dump and return, by a contractor's locomotive, re- quired 6 minutes. Dumping one car at a time through a trestle took 3 men 3 minutes for the 6 cars. The force employed at the shovel was : i boss, i craneman,. I engineer on shovel, i fireman, i engineer on locomotive, I brakeman on train, i engine-driver on water-supply pump, 3, pitmen, 6 drillers, i blacksmith and 2 dumpmen. This crew averaged 500 cubic yards of material excavated in a 10-hour day, the material being mostly soft shale, with a face 10 to 15 feet high. Though the shovel is apparently standing idle one-third the time, there is not so much lost time as appears. During the absence of the cars the shovel is moved forward, requiring about 3 minutes to move 4 feet and to block up. Concrete Tunnel Lining In 1903 a double-track tunnel 275, feet long, and near Peekskill on the New York Central Rail- way, was driven and lined with concrete, and the following statement of the cost is made by George W. Lee, M. Am. Soc. C. E., engineer for the contractor. The tunnel section (Fig. 99) was enlarged from 6 inches to 3 feet outside the concrete section, the rock being the usual rock of the Hudson River valley. As soon as the foundation trenches had been excavated and concreted, platforms 25 feet square were erected at each end of the tunnel and at the level of the springing line of the arch. Near each platform a stiff-leg derrick with a 4<>foot boom was then set up, between the ma- terial track and the mixing platforms, to handle the skips. This material track ran under the platform and through the tunnel, and a turnout was laid beyond each portal for switching pur- poses. Steam was furnished to the hoisting engines by a 60 h.-p. boiler on wheels. The bench-wall forms were made in 1 2-foot sections, with plates and sills of 4 x 6 inches, and studs of 4 x 4-inch hemlock, spaced 3 feet c. to c. The sheathing was 2-inch dressed and matched spruce. Four of these forms were set in place on each foundation at the center of the tunnel length; and wheel- 194 MODERN TUNNEL PRACTICE barrow runways were laid on bents leading to both mixing platforms. These bench walls were not carried back to the rock; back forms of i-inch hemlock were used, and the space behind the walls was filled with spawls, to allow the consider- able seepage from the rock to collect and run out at the "weep- holes" provided in every 15 feet of the bottom part of the walls. While the concrete was being filled into these forms, other sections were being set up at each end of this central part. The k- si'ii" FIG. 99. Peekskill Tunnel : Concrete Lining. forms for the bench walls were removed in 24 hours after the concrete had been laid, and the surface was rubbed smooth with wooden floats. The bench walls terminated in sandstone portals. Arch forms were then erected for a distance of 96 feet in the center of the tunnel, and the lagging was laid in 1 2-foot sections, at first extending only 3 feet above the springing line. Runways were laid over the lower chords of the ribs, the latter being spaced 4 feet c. to c. On the upper portion of the ring the concrete was first shoveled on a platform laid about 2 feet below the crown, and then passed in onto the lagging, which was here in 4-foot lengths. The arch section was water- proofed by six layers of tar paper, laid in hot tar, and the space above the arch was filled in with spawls. The foundations, bench walls and arch were made of i part SOME DATA UPON THE COST OF TUNNELING IQ5 cement, 2 parts sand, and 4 parts of crusher-run stone, of a size passing through a i-inch ring. The quantities were: Foundations, 200 cubic yards; bench walls, 692 cubic yards; arch-ring, 932 cubic yards. The total cost of the concrete work is given as follows : Cement, at $i .63 $5, 755-5 Sand, at 75 cts 662.94 Crushed stone, at 80 cts 1,303.20 Lumber, total i, 497-71 Coal ii8.73 Oil 16.12 Nails, spikes, etc 224.39 Tools .... 181.10 Freight on cement, stone, etc 3,089.86 Labor, including superintendent, foreman, etc 8,036.31 $20,885.76 Average cost of concrete $10.72 per cubic yard. Water Hoisting vs. Pumping in Mines. An interesting paper on "Methods and Cost of Water Hoisting in the Pennsylvania Anthracite Region" was read before the American Institute of Mining Engineers by R. V. Norris, M. Am. Inst. M. E. This paper is very fully illustrated, and those interested are advised to read the original paper in the Proceedings of the Society, or its reprint in Engineering News of April 9, 1903. Some ab- stracts from the paper are here given, showing the general system and the results. The removal of mine water by hoisting in tanks instead p of pumping is rapidly coming into favor in the anthracite region of Pennsylvania, about fourteen large collieries being ' so equipped. Some of the shafts so cleared are 1,500 feet deep. The hoisting tanks are cylindrical or semi-cylindrical, tak- ing in water through chock-valves at the bottom and discharg- ing in various ways, usually automatically. These tanks were first attached to the bottom of the regular shaft carriages ; but the objection to this was the limiting of their use to the night shift, with a corresponding loss in capacity. The present prac- tice is to locate these tanks in a special water compartment, permitting constant service, whether in a vertical or inclined shaft. 196 MODERN TUNNEL PRACTICE Mr. Norris gives a table of capacity, cost, etc., for two of these plants, as follows : WATER HOIST. Wm. Penn Mine. Lyttle Mine. Depth of shaft 953 feet. 1,500 feet. Capacity of tanks 1,440 gals. 2,600 gals." Size of engines 32 x 48 ins. 36 x 60 ins. Size of drums * Straight 12 ft. diam. Cone 10 to 16 ft. Capacity of hoist in 24 hours. .. . 2,100,000 gals. 3,750,000 gals. Best record, 24 hours 2,291,040 gals. 3,772,600 gals. COST, SHAFT AND HOIST. Sinking and timbering $20,673.81 $22,641.63 Head frame 4,224.13 3,540.58 Water hoist, engines and house. . 15,583.64 29,653.17 Tanks and ropes 2,393.23 3,899.65 Steam line 3,726.12 16,091.76 $46,600.93 $80,777.96 Cost without shaft & steam plant. $22,201.00 $37,093.40 At these plants Mr. Norris summarizes the operating- cost of hoisting water by this method as follows, for the time noted : Fidler Mine, Wm. Penn Mine, Lyttle Mine, 3 years. 37 days. i month. Depth of shaft, feet 960 953 1,500 Water hoisted, gals 918,501,200 112,468,080 236,906,000 Average height hoisted, feet 960 727.8 740.6 Cost of labor, supplies and re- pairs per 1,000 gals $0.0114 $0.0088 $0.0071 Cost of steam per 1,000 gals. .. . 0.0192 0.0146 0.0148 Total cost per i,ooo gals. . . . $0.0306 $0.0234 $0.0219 Estimating on the above data, the author places the cost of hoisting water, per 1,000 gallons lifted i,ooo.feet vertically, at $0.032, $0.029 and $0.028 respectively. As compared with this he finds that the average cost of pumping water in the collieries of the Lykens Valley Coal Company is $0.0533 an d $0.0390 per 1,000 gallons pumped 1,000 feet vertically. Aside from any actual saving in operating cost, Mr. Norris claims that there are other decided advantages in the hoisting plan. (i) Simplicity of construction; (2) all the operating plant is on the surface, with a resulting low cost for repairs ; (3) there is an almost total absence of slip ; (4) the operating plant cannot be flooded. An automatic electric water-hoist is used at one of the anthracite mines of the Delaware. Lackawanna and Western SOME DATA UPON THE COST OF TUNNELING 197 Railroad. This hoist lifts 4,000 gallons of water per minute through a height of 550 feet. Mr. H. M. Warren, the elec- trical engineer of the company, specified an 800 horse-power induction motor to drive the hoist, running continuously in one direction, fitted with reversing clutches for driving the hoist- ing drum. The motor drives a pair of bevel-gears by means of a single bevel pinion ; and the bevel-gear shaft carries a pinion which engages the main-gear on the drum-shaft. The two drums are of the cylindro-conical type, 16 feet and 10 feet in diameter. A steel head-frame, 93 feet high, carries two steel two-inch cables terminating in two steel buckets, each 6 feet in diameter and 19 feet 6 inches long; each bucket holding 17 tons of water. These buckets have bottom lift-gates which open automatically when the buckets reach the top and dis- charge the water through two lateral spouts into concrete basins built on either side of the shaft. The hoist makes a complete round trip in I minute 50 seconds, including a stop at either^ end of the travel long enough to let the upper bucket empty. Cost of Square-set Mine Timbering. In 1902 Mr. Bernard Macdonald presented to the Canadian Mining Institute a paper on "Mine Timbering by the Square-set System at Rossland, B. C." From this the following data are taken relating to cost : The square^set is a rectangular skeleton framework of posts, silk, girts, diagonal braces and caps, all of comparatively short lengths and mortised together. Round, peeled, seasoned logs, or sawed timber, 8 to 10 inches in diameter, may be employed; though in the Rossland mine 1 6-inch round sticks, 16 feet 6 inches long, were also used. A square-set, including one post, one cap, and a girt or brace, requires 18^ lineal feet of logs, which, at 8 cents per foot in this case, cost $1.50 a set at the framing shed. The cost of framing is about $0.55 per set, framed by hand labor by carpenters receiving $3.50 for nine hours' work. The detail of this cost is : For material. For labor. One post $0.65 $0.167 One cap 43 .219 One girt 40 .187 Total $1.48 $0.573 198 MODERN TUNNEL PRACTICE The cost per set in place is : Material $1.48 Labor in framing 57 Lowering into mine, about .10 Delivering at place, about 10 Labor erecting 1.50 Wedges, nails, etc .10 Sill floor, averaged over 1 1 sets .15 Total per set, about $4-00 Segregating the labor items, we find that one set of i&J- lineal feet of timber costs $2.27, or about 12 cents per lineal foot. If the timbers were 12x12 inches the labor cost would be about $10 per 1,000 feet, board measure, which is not ex- cessive, considering the high rate of wages. Mr. Macdonald says that the average space to be excavated for each set is 5.3 feet wide, 5 feet long, and 9 feet high, or 240 cubic feet. Since the Rossland ore yields 200 pounds per cubic foot in place, the cost of timbering amounts to 17 cents per ton of ore mined. Mine Hauling by Compressed Air Mr. Richard Hirsch, in a paper upon this subject read before the Engineers' Society of Western Pennsylvania, gives some data upon the cost of haul- ing in mines by compressed air locomotives. The 30 mules formerly used were replaced by 2 compressed- air locomotives, with 7x 1 4-inch cylinders; tank capacity, 130 cubic feet; tank pressure, 500 pounds per square inch. They were built by the H. K. Porter Company, of Pittsburg. Each locomotive weighed 16,000 pounds. In 1897 this plant was operated a total of 197 days in Col- liery No. 6 of the Susquehanna Coal Company, at Lyon, Pa. The contrasted cost of operating with locomotives and mules is summarized below : Total cost of plant, except steam boilers, cars and track $15,156.00 Operating expenses, including all labor, fuel, supplies, re- pairs, etc 2,202.78 Fixed charges, including interest, depreciation and renewals... 1,776.60 Cost of mules required for same work 4,052.48 Cost of operation by mules, including labor, supplies, interest, depreciation, etc., for 179 days 11,328.63 Cost of operation by compressed air 3,979-38 Saving in cost of operation $7,349.25 SOME DATA UPON THE COST OF TUNNELING IQ9 The daily average work of these two motors for 197 days was 1,185 net ton-miles; or, the cost of hauling per net-ton mile was 1.9 cents. The corresponding cost by mule haulage was 5.34 cents. For 300 working days the contrast would have been still greater. Cost of Diamond-drill Exploration in South Africa The 1901 report of the Commissioner of Mines for Natal Colony, South Africa, gives some interesting data as to the cost of explor- ing by the diamond drill in that country. The carbons used were inferior Brazilian diamonds, costing $50 per carat, and Kimberly stones at $15 per carat. The cost of the carbons per foot of hole drilled was 20 cents for a 2.\- inch hole in the softer rock, and $1.35 for a 3-inch hole in quartzite. Both hand-driven and steam drills were used. With hand-driven drills, the cost and progress made is shown by the following table : I. 2. 3- 4- 6. 8." Sandstone. Sandstone. Shale. Sandstone. Sandstone. Whinstone. Sandstone. Shale. 2 2 2 2 2 2 3 3 78 80 28 161 34i 369 8l 116 9 9 3 35 93^ 7 8.7 8.9 9-5 ii. i 9-7 11.6 7.8 $145-54 142.15 48.95 464.55 406.35 2,146.00 197.65 240.60 $1.86 2.02 1.70 2.90 1.20 5-85 2.44 2.IO 2 IO 5 12 o 6 i For drills driven by steam power, the similar record for an- other set of holes is as follows : ^ c % I ? i S "> -si *>" 2 * ^ -^ ^ "^ ~ ~ <^H; >^- ** ** * * -5 '^ = Q * "^ O ^ Alternate Plan for Connection of Hoops Elevation. Section under Little Miami River . Detail of End* of Hoop*. FIG. 137. Water-works Tunnel: Section of Land-tunnel. voir to that at the city pumping station. It is approximately parallel with the Ohio River shore line (but from 300 to 900 feet distant) and has a down grade of i in 2,000 towards the city. Its top is 60 feet below low-water level, or 130 feet below high- water level in the river, but when in use the inside pressure will be equivalent to 90 feet head. The tunnel, Fig. 137, is 7 feet inside diameter, and lined with two rings of specially made radial pressed vitrified shale brick, laid with close joints; the inner surface is as smooth as the best pressed-brick building work. The bricks are 3 x 4 inches, 9 inches long, with bonding grooves on the sides, and the face curved to a diameter of 7 feet. The brick lining is backed with concrete, the minimum THE CONSTRUCTION OF THE SIMPLON TUNNEL 287 thickness of concrete being 6 inches. Where the tunnel crosses beneath the Little Miami River, the lining is reinforced by rings of f-inch round steel bars, 2 feet c. to c., as also shown in Fig. 137. The tunnel is completed, and in order to determine the amount of leakage, if any, it has been filled with water from the city mains. The tunnel was driven through limestone and shale rock, with about 25 feet of rock above the crown. This rock was in some places badly shattered and much water was encountered. The pneumatic or air-lock system was tried for a short distance (350 feet), but did not prove satisfactory. The successful method of dealing with the water consisted in driv- ing pipes into the seams, so as to discharge the water within the tunnel ; where the streams were too small and too numerous for this, aprons were put in to collect the water outside of the lin- ing, the apron leading to a single pipe passing through the lin- ing. In this way the brick lining and concrete backing were put in without trouble from washing, and the pipes were left projecting into the tunnel. After the work had set, the pipes were fitted with valves, and then cement grout was forced into them under 80 pounds' pressure ; when no more grouting could be pumped in, the valve was closed and the grouting machine transferred to another pipe. The grouting was found to travel considerable distances, sometimes appearing at other pipes be- yond where the grout was being forced in. The sealed pipes were left for 10 or 20 days, to insure thorough setting of the grout, and they were then cut off a little back of the tunnel face, and the recess pointed up. In one place there were 300 pipes i to 2 inches diameter in 1,000 feet of tunnel. In spite of the seamy rock, with direct connection to the river, and in spite of the amount of water encountered, the finished tunnel is very dry, the measured infiltration being only 10 gallons per minute for the entire length. Pockets of gas were encountered at several places, and sev- eral small explosions occurred ; six men were killed by gas ex- plosions. Further trouble was prevented by providing an in- crease of ventilation from the compressed-air mains which were supplying power for the rock drills. The gas was natural gas, 288 MODERN TUNNEL PRACTICE and this with a little dilution with air is less explosive than marsh gas with much dilution. The work was prosecuted by ten headings from the two per- manent shafts and four intermediate shafts, the latter being afterwards sealed and filled and the tunnel lining carried past them. As the center line of the tunnel makes one or more angles between each pair of shafts, the survey work was some- what complicated, more especially as buildings and other obsta- cles prevented direct sights on some of the tangents. The tan- gents were measured several times at different temperatures and the average distances taken. The angles were also repeated and averaged, each angle being measured no less than ten times and by at least three observers. For the levels, bench marks were established at one-half-mile intervals. The line was trans- ferred down the shafts by two wires, kept taut by 2O-pound weights in glass jars filled with glycerine. The wires being adjusted to line by the transit over the shaft, were then used by the tunnel transit to project the line upon scales set 300 feet apart and attached to anchors in the tunnel lining. The levels were transferred down the shafts by measurements with steel tapes, the measurements being repeated and averaged. The east end shaft is shown in Fig. 138, but in construction the intersection with the opening for the /-foot nozzle was fin- ished in concrete instead of with a ring of special brick as orig- inally designed. The interior lining, also, instead of being brick on edge, as shown by the drawing, was of special radial or voussoir-shaped brick laid flat. Each brick used is 3 x 4 inches, 9 inches long, with bonding grooves top and bottom, and a face radius of 5 feet. The shaft is 10 feet inside diam- eter, and the upper part is built within a shell of f-inch steel plate, 12 feet diameter, extending to the rock and having a water-tight seal. The rings are 6 feet high, with three plates to a ring and 1 6-inch triple-riveted vertical cover plates. In the lower part the rings are butt-joinied, with inside 6-inch single-riveted cover plates; but at the top the rings are lap- jointed and set alternately inside and outside. The contractors for the tunnel were W. J. Gawne & Co. THE CONSTRUCTION OF THE SIMPLON TUNNEL 289 Survey Work for the Land Tunnel The surveying methods employed for the four and one-quarter mile land tunnel to the city have been described as follows in a paper by Mr. John A. Hiller, Assoc. M. Am. Soc. C.E., who was Resident Engineer during construction : . __ Center of Tunnel , FIG. 138. Water- works Tunnel, Cincinnati, Ohio: East End Shaft. 290 MODERN TUNNEL PRACTICE "The construction was executed from the permanent shaft at each end and four working shafts, making ten headings. The alignment of the tunnel not being a continuous tangent be- tween the shafts, but being broken by one or two angles be- tween, it became necessary to make a very careful survey of the surface line to establish the true position and magnitude of the angles "The centers of the shafts and the angle points were estab- lished from the preliminary survey line, then the tangents and angles were measured. "Between shafts i and 2 the line traverses a comparatively thickly built up portion of the city. Tangent I passes through a frame dwelling; and to obtain the line between shaft i and angle i, the transit was set up on a chimney of this house, shifted into the line, and from this position permanent points were fixed on both sides and foresights established. "Tangent 2 passes through the machine shop and retort house of the East End Gas Works, and the office, stable and coke piles of the Marmet Coal Company. With these obsta- cles on the line, it was found impossible to get the instrument at any point where the two extremities of the tangent could be seen. A transverse line was run, beginning at angle i, running to angle 2 and returning by another route to angle i. This was a closed survey, which was divided by tangent 2 into two parts, which, when considered separately, gave tangent 2 as the closing line for each part. "The results obtained from three trials of this traverse are given in Table i, each result being the mean found by consider- ing each part : TABLE i. MEASUREMENTS OF TANGENT 2 No. of trial. Length of tangent 2. Size of angle i. Size of angle 2. ist 1314.5920 15 27' 32.1" 9 08' 45.9" 2d 1314-5892 15 27' 11.4" 9 08' 43.1" 3d 1314-5871 15 27' 14.6" 9 08' 49.9" Mean 1314.5895 15 27' 194" 9 08' 46.3" "On the third tangent there was one building and a pile in a tramway ; a perpendicular offset line passed these obstructions. THE CONSTRUCTION OF THE SIMPLON TUNNEL 2QI "The remainder of the tangents offered no obstacles which could not be overcome by the erection of foresights from 10 to 20 feet in height. "The crossing of the Little Miami River was made by trian- gulation, using a quadrilateral, one of whose diagonals was the tunnel line. "The measurement of all tangents was made with a 5o-foot steel tape, which was ascertained to be correct at 60 Fahr., with a pull of 14 pounds. Stakes were driven along the line every 50 feet ; and at breaks in the ground, the line was marked thereon, levels run to establish the differences of elevation of the stakes, the tape stretched, and the length and the tempera- ture of the air for each length was taken and recorded. "Each tangent was measured forward and checked backward during the summer, and the whole operation repeated later dur- ing the winter. In case of any great difference a check meas- urement was made. Thus each line was measured at least four times uncler widely different weather and temperature condi- tions, with no accepted difference greater than one in about 30,000. A mean of all measurements was taken as the length of the tangents. These mean measurements did not differ more than one in about 50,000 from any extreme. "The field data were tabulated for reduction to the horizontal distance and to a temperature of 60 Fahr. "The angles were measured by repeating each ten times, by three or more observers, and the average result of all observa- tions was accepted as the most probable. "The bench levels were run from an established bench at Cal- ifornia to near shaft i and return. Benches were established about every half mile, and in the immediate vicinity of the shafts. Such parts of the line where the differences of the two runs were greatest, a check run was made and the mean differences of elevations used to determine the elevations of the benches. "Transfer of the Alignment into the Tunnel. At each shaft an observation station was erected for each tangent and foresights built at or near the distant angle points. These stations were MODERN TUNNEL PRACTICE so built that the observer's platform was independent of the transit support, and all enclosed in a small house to protect the instrument from sun and wind. The wires used for plumbing down the shafts were No. 5 piano wire, about one-sixtieth of an inch in diameter, held in a clamp at the top of the shaft in such a manner that the wire could be moved tranversely by a slow- motion screw. The method of securing the device to top of the shaft cannot well be shown, as the local conditions at each shaft required a different arrangement. At the lower end of the wire was a hook, upon which was hung a cylindrical lead weight of 20 pounds. The weights were suspended in glass jars containing glycerine. This arrangement permitted the weights being seen at all times and afforded absolute assurance that the weights hung free. Back of each wire was a small shield or background painted white; the lower end of the wires being blackened, showed distinctly against the white ground. The jar nearer the tunnel transit was supported on a small stand about 3 feet from the floor ; the farther jar rested directly upon the floor of the tunnel. This permitted each wire being viewed separately and allowed no chance or confusion of viewing the wrong wire. An electric light was supported so as to throw light upon the wire and background. "The tunnel transit was supported on a wooden strut secured against the tunnel arching by four large set-screws. A tripod could not be used on account of the wooden floor being too springy for a secure set-up. "The tunnel transit was provided with a slow-motion ar- rangement whereby the whole transit could be moved a small distance at right angles to the tunnel line, allowing of very small changes in the position of the instrument. "The cross-hairs of the transit consisted of a diagonal cross and two vertical hairs, so spaced that they covered about one- sixteenth of an inch at a distance of about 60 feet. This made the sighting of the instrument very exact, as the cross-hairs and the plumb wire appeared white between, about equal to the diameter of the wire. THE CONSTRUCTION OF THE SIMPLON TUNNEL 2Q3 in ^^ & : : .S ;' -J j j.S : ;'.d ._d ..G ..G . ..d . e g . CO I-H 01 q ; ON IN. I-HI-H . ^ > Tf-^- OITf'VOOO t^O -O lO^O 01 ^ 01 VO Tj- to O CO CO 01 of of CO CO 5 .S I d ,d _d d d d d o o o o o o ^o ^o co 0000 vo VO 0000 VOVO "col Icol .'col Ifo- ' ^ / : 1 : ' " ' : 1 : M ' : t vo tx -00 o" * "* ; M . ; :^. ; i" ; ; R ; ibb *I^ * "cj * *cj * *G * ^ tQ2 QS 2.Q OQ.' OS' O> ON ON p\ O\. ON. ON . Suiuui&q lo d t va^ ^^ ^^ " " "^ ' d >>>> ad >>>> ^^ P SS QQ " M O 0\ "The operation of transferring the line into the tunnel con- sisted of setting a transit, in the observation station, on line by double foresights and bringing both wires to this line by means of the slow-motion clamps. The tunnel transit was then brought into the line of the two wires and the line transferred to the scales, fastened to anchors in the masonry lining of the tunnel. 294 MODERN TUNNEL PRACTICE The scales were placed about 300 feet apart and read by ver- niers to o.oi inch. "All necessary reversions of the transit were made to elimi- nate all probable errors of instrumental adjustment. Readings were made on the two scales and recorded for each position of the transit. Several independent trials were made, and in all about 50 readings were taken on each side, in each heading, and a mean accepted as the working base line inside the tunnel. This line was extended into the tunnel as the excavations were advanced, always making the necessary reversions of the in- strument and accepting the mean of all trials as the correct line. "The required distances from the shafts to the angle points were measured along the roof, using the same precautions as in the measurement of the surface line. The angles were turned by repeating several times. Afterward curves of 3O-foot radius were used for easing off the intersections. The angles being generally small, none of these curves was long, and little or no additional excavation was needed in order to place the lining on the curved line. "The levels were transferred into the tunnel by steel-tape measurements down the shafts. Four to eight trials were made at each shaft and a mean result accepted. "Table 2 shows the distances between the wires at each shaft, the lengths driven in each heading, and the errors for closing for each meeting point. "The engineering department took samples of air from each heading daily and made tests for explosive gas. The daily progress of each kind of work in each heading was measured and recorded on a progress diagram. Samples were taken from each shipment of cement and tests made for soundness and tensile strength. "Lines and levels were given in each heading for every ad- vance of about 100 feet. Holes were drilled in the roof about every 30 feet and plugs driven, containing a small staple in the true line. The distances from the plug to the axis of the tunnel were computed and a list given to the heading foreman for his guidance in pointing the holes when drilling. These same THE CONSTRUCTION OF THE SIMPLON TUNNEL 295 grades were afterwards used when setting invert forms. The spring-line grades were marked on the invert for setting the arch centers." Telephone and Freight Transportation Tunnels at Chicago. A peculiar system of tunnels exists at Chicago, consisting of a network of small tunnels under the streets (and including nearly all the principal streets in the downtown districts). These tunnels carry telephone and telegraph cables, but are also to be operated for the transportation of mails and freight, con- necting the several postoffices, warehouses, wholesale stores, etc. The tunnels were commenced in September, 1901, and were originally intended to carry the cables for the automatic tele- phone system of the Illinois Telephone Company, as it was found that the streets were so completely occupied by water and gas mains, sewers, electrical conduits, and the various man- holes, that there was no room to be found for conduits to ac- commodate cables for the proposed central exchange for 100.- ooo subscribers. It was finally determined, therefore, to build a system of tunnels, and to build these deep enough to be within the solid clay, and avoid disturbance of foundations. The city also required them to be deep enough to allow of the future con- struction of a subway system for street cars, and the level of the tunnel floor is about 30 feet below the street level. After a considerable amount of work had been done the company ob- tained permission from the city to utilize the tunnels for the transportation of mails, express matter and freight, etc., but their use for passenger traffic is specifically forbidden. In June, 1905, there were about 30 miles completed, and the entire sys- tem will aggregate about 60 or 70 miles. The tunnels are of horseshoe section, with a clear height of 7 feet 6 inches, and a width of 6 feet ; they are lined with con- crete, having a thickness of 10 inches in the sides and crown and 13 inches in the floor. They are driven in stiff blue clay, containing very little water, but occasional pockets of gas and of quicksand were encountered. As a precaution the work was all done on the pneumatic system, the air pressure being about 9 pounds per square inch. The air locks were placed near the 296 MODERN TUNNEL PRACTICE bottoms of the several shafts ; they were 23 feet long, and had doors 24 x 36 inches. No tunneling shields were used. The material was excavated with spades and draw-knives, and hauled away in small cars, 20 x 48 inches inside measurement, to the shafts. These small cars were used to facilitate handling, and to enable a double track of narrow gage (14 inches) to be laid. The shafts were sunk mainly in the basements of buildings, which were utilized also for the making of concrete and storing of cars. In some cases, however, the shafts were located in the streets (at the curb line) and were covered with tall head-houses. The method of construction was as follows : The excavation was made in the clay for a distance of about 20 feet, and about a foot larger than the completed tunnel. The 1 3-inch concrete bottom was then put in place, and upon this were placed forms made of 5-inch steel channels in two sections, curved to the contour of the inside of the tunnel, and put together with flanged and bolted joints at top and bottom. These ribs or forms were 3 feet apart, and outside of them were laid 2-inch planks to form the lagging. These planks were at first 20 feet long, but afterwards 15 feet was found more satisfactory. They were laid one at a time on each side and the concrete rammed into the space between them and the clay. When the crown, forming the key, was reached, boards 3 feet long were used. The concrete was composed of i part Portland cement, 3 parts sand and 5 parts gravel; it was mixed by machines installed in basements at the heads of the shafts, and carried to the work in the small cars on a double track of 1 4-inch gage. The con- crete was well tamped so as to fill all voids and prevent any subsequent movement in the mass of clay. The work was carried on continuously in three 8-hour shifts. The mining gang (about 7 men) worked from 4 p. m. to mid- night; this was followed by. the trimming gang (also about 7 men), which worked until 8 a. m. in trimming the excavation to proper form and dimensions and putting up the centers and lagging. The concreting gang then commenced its work, arranging it so as to complete it in time to make way for the THE CONSTRUCTION OF THE SIMPLON TUNNEL mining gang at 4 p. m. Work was carried on at about 14 headings, with 20 men to each. The first 12 miles were built in lo-J months, with an average advance of 20 to 76 feet per working day at the different headings. In April and May, 1905, the progress made was 10,105 feet (25 working days) and 12,619 feet (27 working days) respectively; or an average of 404 to 467 feet per working day. This required the excava- tion of about 60,000 cubic yards of material. The excavated material was at first carried up the shafts and dumped into wagons, this work being done only at night. When one of the tunnels approached the east side of the river an in- cline was built, up which the cars were taken by traveling chains having arms to engage the axles, and the cars were dumped into scows. Another incline was built on the lake front, where cars were taken out by electric locomotives and dumped to fill in the site for Grant Park. After this latter method of disposal had been put into service, nearly all the tunnel material was hauled out at the lake front, as well as wreckage from old buildings and the material excavated for deep foundations and basements of new buildings. The tunnel intersections above mentioned are very peculiar. The two lines intersecting at right angles and on the same level are in most cases connected by four curves of 2O-foot radius, leaving four "pillars" of the original ground. Here the roof is reinforced by steel I-beams. The sharpest curves in the main tunnels are of 1 6- foot radius. The lines are mainly level, with maximum grades of 1.75%, and inclines not exceeding 12%, Branches or spurs are run to the postoffices, stations, etc., to be served, and either enter a deep sub-basement or have a shaft and elevator to the buildings with shallow foundations. The completed tunnels have a single track of 24-inch gage, laid with 56-pound rails on cast-iron chairs imbedded in the concrete floor. Both the overhead trolley wire and central third-rail conductor system of electric traction have been tried. In the latter case, the Morgan system is used, in which the con- ductor is a slotted bar protected by side timbers and gearing with a contact or spur wheel on the locomotive. The tunnels 298 MODERN TUNNEL PRACTICE are well drained, lighted by electricity, and provided with tele- phones at frequent intervals. It is expected that this system of transporting mails, newspa- pers, parcels, coal, freight, etc., as well as wreckage from dis- mantled buildings and material for new buildings, will not only facilitate traffic, but also relieve the congestion of traffic in the busy streets and avoid much of the dirt and nuisance incident to the hauling of refuse and building material through the streets. Tunneling through soft material in the heart of a city where numerous tall and heavy buildings exist, and where many of these buildings have foundations practically on the surface of this material, is a delicate kind of work which was successfully prosecuted in these Chicago tunnels for about five years, with practically no trouble from settlement of the ground. A change from the original plans, by which the tunnels began to be car- ried under the buildings as well as under the streets, caused trouble, however, and during the spring and summer of 1905 settlements of streets and buildings occurred, with the result that the effect of city tunnel construction upon the foundations of buildings was made the subject of expert investigation. The Commissioner of Public Works appointed a committee of engi- neers to investigate the cause, and their first report stated that no settlements had occurred where the main tunnels had been built under air pressure, but that they had occurred where con- nections or spurs had been built without the use of air pressure. A later report recorded specific instances of settlement and showed that a serious problem faced the tunnel company. The main tunnels are built in the Chicago clay and at a depth of about 20 feet from the street surface to the crown of the tunnel ; as they are located under the center lines of the streets they are clear of the lines of pressure from the buildings, and are subject only to the pressure due to the overlying material. At street intersections the tunnels also have intersections, and the two lines of straight tunnel are in many cases connected by four curved tunnels, as already explained. This, of course, involves, the removal of a great mass of material, and unless the work is. THE CONSTRUCTION OF THE SIMPLON TUNNEL prosecuted very carefully there is liable to be a slip or movement of the clay. The construction of one of these intersections without sufficient care and precaution is given as the cause of one of the street settlements already referred to. But a much more serious matter is that of tunneling through clay subjected to pressure from neighboring buildings. As long as the tunnels were to be used simply as conduits for electric wires and cables, there would be very little of this class of work, but when their use for transportation purposes was planned it was proposed to build lateral branches and spurs to serve post- offices, newspapers and express offices, railway passenger and freight stations, wholesale and retail stores, warehouses, office buildings, etc. These spurs would enter the basements of modern buildings having deep basements, while in other cases they would connect with shafts having elevators to serve the build- ing above. The construction of these connections must involve the excavation of clay under varying degrees of pressure from the buildings, and when any void is left, however small and if only temporary, the clay will fill in and the movement of the clay body may extend for considerable distances. The engi- neering committee considered that the tunnel company had un- dertaken the construction of these branches without having given sufficient consideration to the special conditions affecting this phase of its work, and recommended that no more such branches should be built until the special conditions in each par- ticular case had been carefully studied and a proper course of construction planned. Whatever care is taken, however, some settlement is considered unavoidable. The use of compressed air will not suffice to sustain the material, and in fact its use in this part of the work was not considered practicable by the committee. The soil under pressure must be supported by mechanical means, and it was pointed out in the report that the case "is a building proposition, and the methods common in building practice will probably meet all the difficulties that may be encountered." The committee also recommended the adop- tion of a circular section for the spurs and branches instead of the horseshoe section of the main tunnels. 300 MODERN TUNNEL PRACTICE The work was all planned by Mr. George W. Jackson, Chief Engineer and General Manager of the Illinois Tunnel Con- struction Company, and has been executed by day labor under his direct supervision. APPENDIX GLOSSARY OF SOME OF THE MORE UNUSUAL TERMS USED IN TUNNELING ADIT. See Heading. AIR-LOCK. A device employed in connection with the use of compressed air, for permitting men and material to pass from the normal atmo- spheric pressure to a higher pressure, or the reverse, without undue loss of pressure in the working-chamber. AIR-SHAFT. In mining, a shaft used solely for ventilating purposes. ALIGNMENT. The laying-out of the axis of a tunnel by instrumental work. See Ranging. ARCH-BLOCKS. A term applied to the wooden voussoirs used in framing a timber support for the tunnel roof, when driving a tunnel on the co- called American system. These blocks are made of plank, super- imposed in three or more layers and breaking joint. BACKING. The rough masonry in a wall faced with a better class of work. BACK-JOINT. A joint-plane more or less parallel to the strike of the rock- cleavage; frequently vertical. BALLISTIC EFFECT. The throwing of rock to a distance from the exploded charge, a thing to be avoided in rock-blasting. BARS. Strong timbers placed horizontally for supporting the poling- boards in the face of the excavation. BATTERY. A magneto-electric apparatus employed in firing an explosive connected with it by a pair of insulated copper wires. BEARERS. In shaft-sinking, heavy sticks of timber, longer than the width of the shaft, set in niches cut in the rock, and used as supports for timber-sets. BEARING-IN SHOTS. Bore-holes tending to meet in the body of the rock; intended to "unkey" the face when charged and fired. BENCH. In tunnel excavation, where a top-heading is driven, the bench is the mass of rock left, extending from about the spring-line to the bottom of the tunnel. BENCH-MARK. A permanent mark of a suitable character for preserving and transferring vertical elevations in a tunnel. BIT. A piece of steel welded to the end of a drill, or the point of a pick. The horizontal section, of this cutting edge is either + or x-shaped; the edges making an angle of nearly 90. BLOCK-HOLING. The operation of drilling and blasting a detached boulder or mass of rock ; the purpose being to reduce the mass to dimensions more easily handled or transported, or cut for building purposes. BOWK. An English term fo-r an iron tub used in hoisting debris from a shaft. BREAKERS. The row of drill-holes above the mining holes in a tunnel face. BREAST-BOARD. The timbers or boards placed horizontally across the face of an excavation, or heading, to prevent the inflow of gravel or other loose or flowing material. BROB. An English term for a wrought-iron spike driven into bars and sills to steady the head or foot of a prop. 301 302 APPENDIX BULKHEADS. Masonry diaphragms built across a subaqueous tunnel where compressed air is used, as a precaution and to prevent the flooding of an entire tunnel in case of an accident. These bulkheads are usually kept some distance in the rear of the working face, and are provided with two air-locks; one of them is an emergency-lock near the roof. BULL. An iron rod used in ramming clay to line a shot-hole. BULLING. Lining a shot-hole with clay. BURDEN. In blasting, the volume of rock that should be broken by a proper charge of powder. CAGE. The elevator used in a shaft for hoisting the cars loaded with muck. The cage is generally provided with a safety device intended to hold the cage and its load in the case of a breaking hoisting-rope. CENTERS. Framed supports, usually arch-shaped, upon which are placed the lagging- boards used, in building an arch, for supporting the roof of a tunnel. CHAMBER-BLASTING. Used in very heavy blasting, where a great quantity of rock is to be thrown down at one time by a correspondingly large charge. A tunnel or drift is usually run to the site of the chamber, and the latter is excavated and charged. The drift is well packed with earth and sand before firing. In such a chamber or series of chambers as much as 7,000 Ibs. of dynamite may be placed, throwing down 350,000 tons of rock at one blast. CHAMBERING. The enlargement of the bottom of a deep drill-hole by the successive explosion of small charges. The purpose is to provide room for a final, large charge of powder to be used in throwing down a large mass of material. CHOG. English term for chocks, or blocks spiked into the corner of a shaft to form a bearing for the side-waling piece, or the blocks used in headings to separate the cap and poling-board. CHURN-DRILL. A long iron bar with a steel cutting-edge, used in quarrying or in blasting hard-pan, etc. It is worked by lifting and letting it fall. COLLAR. The bar, or cross-piece, in a framed timber set. The first wood frame in a shaft. COLUMN or BAR. This is a round column set vertically or horizontally in a heading and to it the machine-drill is clamped. This column is pro- vided with a head at one end, and a shoe at the other end provided with a screV for setting it up against the rock walls. A column gives a firmer support, as a rule, than the tripod also used for holding the drill. Blocks of tough wood are placed between the column ends and the rock. CORE. In several European methods of tunneling, the sidewalls are built first in special drifts : and the arch area is then excavated and the arch built, leaving the central mass to be removed last. This center of rock or earth is called the "core." CRATER. In blasting, the funnel of rupture, which in bad rock may have very steep sides and a relatively small volume of broken rock. CRIBBING. Close timbering in lining a shaft. A structure made of horizon- tal timbers laid one on top of the other. CRIMPER. A tool specially made for fastening a cap to a fuse. CROW-FOOT. A V-shaped notch in an arch-block; sometimes made in the bottom block where this rests upon the wall-plate. CROWN-BARS. Strong timbers, usually round, used in supporting the roof of a tunnel in the English method of driving. DOG. A round iron rod, with the pointed ends bent at right angles. DOLLY. A tool used to sharpen drills. DOWELS. Round, headless iron pins, inserted half way into each of two abutting timbers to prevent slipping. DRAG-TWIST. A spiral hook used for wiping a blast-hole with hay before charging with black powder. DRAWING. Removing or pulling out the crown-bars in a tunnel. APPENDIX 303 DRIFT. See Heeding. DRIFT-FRAME. See Square Sets. DUMP. The place of deposit of debris from an excavation. ELECTRIC FUSE. A metallic cup, usually containing fulminating mercury, in which are fixed two insulated conducting wires held by a plug, the latter holding the ends of the wires near to but not touching each other. At this plug is a small amount of a sensitive priming. When an elec- tric current is sent from the battery through these conductors, the re- sulting spark fires the priming, then the fulminate and the charge of the explosive proper. ENLARGING SHOTS. Bore- holes driven after the face of the rock has been "unkeyed," and two or three free-faces have thus been provided. FACE. The surface exposed by excavation. The "working-face" is the face at the end of a heading, or the end of a full-size tunnel excavation. FALSE SET. A temporary set of timbers, used until the work is sufficiently advanced to put the permanent set in place. FAULT. A dislocation in the natural strata. FLOAT. This is a timber platform, faced with boiler-iron on both sides and provided with rings at the corners for lifting. It is used in shaft- work to prevent the crushing of the bottom timbers by flying frag- ments of rock. FOOT BLOCKS. Flat pieces of wood placed under props, to give a broader base and distribute the weight. FOREPOLING. The act of driving the poling-boards beyond the last set of timbers, thus forming a roof for further advance. FREEZING-PROCESS. A method invented by F. A. Poetsch about 1883, for penetrating a water-bearing stratum. Circulating pipes are sunk around the site of a shaft ; and the ground and water is then frozen solid by passing thrqjugh these pipes a solution of brine. The frozen material is then extavated and the shaft linetl in the usual manner. FUSE-CAP. A small cylinder of copper, closed at one end and charged with a fulminate. The end of the fuse is inserted in this cap, for firing a charge. GAD. A small steel wedge used for loosening seamy rock. GALLERY. A drift or adit. In France it is another name for the heading of a tunnel, usually called "Advanced Gallery." GALLOWS-FRAME. The frame supporting the pulley at the head of a shaft, over which pulley the hoisting-rope runs. CANISTER. A hard, compact, exceedingly silicious fire-clay. GRAIN. As applied to rock, planes of cleavage at right angles to the rift, or bed of the rock. GUN. A term applied to the explosion of a charge in a bore-hole, which simply enlarges the hole without rending or splitting the rock. GUSSET. A V-shaped cut in the face of a heading. HANG-FIRE. A term applied to a charge which is delayed in exploding, but does eventually explode. HEAD. As applied to rock, natural planes of cleavage at right angles to the grain and the rift of the rock. HEAD-HOUSE. A covered timber framing at the top of a shaft, into which the shaft-guides are continued that carry the cage or elevator. The term is sometimes applied to the structure containing the hoisting en- gine, boilers and other machinery, in addition to the actual hoisting- cage, etc. HEADING. A smaller excavation driven in advance of the full-size section ; it may also be driven laterally, and is then called a "Cross Heading" or "Side Drift." A heading may be driven at the top or the bottom of the full-size face; it is then a "Top" or a "Bottom Heading," as the case may be. HEAD-PILES. The top poling-boards in a heading. HEAD-TREE. The cap-piece of a heading-set. 304 APPENDIX HEEL-OF-A-SHOT. In blasting, the face of a shot farthest away from the charge. HITCH. A step cut in the side of a shaft, or in other excavations, for holding timbers for various purposes. HOLING-THROUGH. Connecting two sections of a tunnel driven toward each other. HORSE-HEAD. English term for a heading-frame, of a cap and two posts. INVERT. A flat inverted arch of masonry used for the floor of the tunnel lining. JUMPER. A long iron drill, with a steel cutting-edge, worked by blows from a heavy hammer. KEY. Of an arch; the top closing-voussoir, or ring-stone. The "Key" may also be a closing section of brick masonry. KICKING-PIECES. Short struts to prevent a sill or other member from being pushed out of place. LAGGING. Narrow boards, generally planed, placed horizontally on the arch-frames of a center. On this lagging the arch of masonry is built. The term is also applied to poling-boards. LEAD-WIRES. Two insulated copper wires leading from the battery or ig- niting apparatus to the primer-cartridge in an explosive charge. These are also called "Connecting Wires." LINE OF LEAST RESISTANCE. As this term is used in blasting operations.. it indicates the shortest line that can be drawn from the charge in the bore-hole to the outer face of the rock. LINING. The lining of a tunnel may be stone, brick or concrete masonry, iron or steel rings, or concrete-steel. In the early American tunnels wood was also used for this purpose. LOOP TUNNEL. A method of gaining grade in a tunnel location by looping or folding the line back upon itself. MINERS. The row of drill-holes in a tunnel face, located below the break- ing-down holes. MISS-FIRE. A term applied to a charge which from some cause has failed to explode. MOP. A disc of some material used around a drill, to prevent water from splashing up. MUCK. The broken rock or other material coming from a tunnel exca- vation. MUD-CAPPING. A method of breaking up boulders by placing dynamite on top of the boulder and covering this with wet clay. The process is very wasteful of powder, as the powder does not do its best work. NEEDLES. An English term used for a special form of poling-boards ; they are sometimes made of iron or steel plate and may be as much as m feet long by 6 inches wide. NIPPER. A name given to the boy who carries the drills to the smithshop. OUT-CROPPINGS. Applied to a rock or ore-vein as seen exposed on the surface. OVERWINDING. A term applied to a continued pull on the hoisting rope of a cage, after the cage has reached the top of the shaft. The result of this carelessness, or accident, is a broken hoisting rope and all the danger that implies. PACKING. Any material, usually rock, packed between the rock-roof of a tunnel and the top of the arch-masonry. PIGEON-HOLE. An opening left at the meeting of two sections of arch work, permitting the workmen to close the arch and to come out. The "Pigeon-hole" itself is closed from below. PILOT-TUNNEL. See detailed description in text. PLANT. A term used to include the machinery, derricks, railway, cars, etc., employed in tunnel work. PLUG-AND-FEATHER HOLE. A hole drilled for the purpose of splitting a block of stone. These holes are usually in rows. The plug is a slightly APPENDIX 305 wedge-shaped piece of iron driven between two> L-shaped irons, or "feathers," inserted in the hole. PLUGS. Small wooden pins driven into holes driven in the rock-roof of a tunnel. The axis of the tunnel is marked on these plugs by tacks, or by small iron hooks from which a plummet-lamp may be suspended for sighting upon. PLUMB-POSTS. The vertical posts at the side of a tunnel, resting on sills and carrying the wall-plates ; the whole supporting the tunnel roof by means of centering. POLING-BOARDS. Narrow boards of varying lengths, sharpened at the front end and driven forward over the bars to support the roof or sides of a heading or of a full arch section. POP-SHOT. In blasting, when the explosion of the charge simply blows out the tamping. PORTALS. The entrance and exit of a finished tunnel, usually faced by masonry to support the loose rock or earth. PRIMER-CARTRIDGE. The cartridge to which the cap and fuse are attached, or, in electric firing, into which the electric cap is inserted. PROPS. Struts or posts, either vertical or raking, used as supports or stays in tunnel timbering. The inclined prop is usually called a "Raker." PUNCHEONS. English term for the props, or posts set up between lines of waling in shaft-sinking. See Studdle. RAKER. See Props. RANGING. The English term for aligning a tunnel. RIFLED. A term applied to the three-cornered section of a hole drilled by hand. Though the bit is supposed to be turned one-eighth after each blow, to insure a circular hole, the majority of hand-drilled holes are three-cornered. RIFT. In sedimentary rocks, the horizontal plane of stratification, or the bed of the rock. RUN. The escape of any flowing material into the tunnel-area; it may be sand, gravel, or mud. RUNNERS. English term for sheet-piling. SAFETY FUSE. The safety or time fuse is made of a core of meal-powder lightly compressed and enclosed in one or more wrappers of spun-yarn made waterproof. According to the number of wrappers and the dampness of the ground in which they are to be used, fuses are called "Single Tape," "Double Tape," etc. SCRAG. The batir of a post. SERIES SHOTS. A number of loaded holes connected and fired one after the other. In contradistinction to "Simultaneous Firing," where the charges are connected electrically, and are all exploded at one time. SETTINGS. The timber frames used at intervals in shaft-sinking, and close- poled behind. SHAFT. Temporary or permanent pits sunk to give access to an under- ground working. The shaft may be vertical or inclined, though the latter is only used in mining operations. SHIELD. A metal diaphragm used in tunneling under rivers, or in water- bearing or loose material under cities. The shield may be cylindrical and include the entire tunnel section ; or it may be a "Roof-shield" and support the roof only. SHIFT. The working hours per day of a gang of laborers. SIDE-PILES. Another term for the side poling-boards in driving a heading. SIDE-TREES. The two posts of a heading-set. SILLS. Strong timbers laid horizontally to support posts or other tunnel timbers. SKIPS. Metal buckets, usually opening at the bottom ; sometimes used for removing water from shafts. SLIP. A fault. A smooth joint where one stratum has moved on another. SOCKET. The bottom of a shot-hole, not blown away in firing. 306 APPENDIX SOLDIER-FRAME. Frames set into the inside of a shaft prior to breaking through for a heading. SOLE-PLATE. Formed of several pieces of lagging fastened together, and laid down in the bottom of an invert. It forms a base for the iron ribs used in laying a concrete invert. SPIRAL TUNNEL. A method of gaining grades in a tunnel by driving the tunnel on a constantly ascending and circular line. SPOON. A scraper, or similar instrument, for cleaning the sludge out of shallow drill-holes. This spoon is usually made of one-fourth to one- half inch iron rod, with a disc at each end. SPRAG. The horizontal member of a square set of timbers running parallel to the axis of a heading. SPRINGING A HOLE. Enlarging a drill-hole at the bottom to permit the use of a greater charge of explosive. This is usually done by ex- ploding smaller charges of dynamite at the bottom of the hole and thus pulverizing the harder rock. The process is also called "chambering," "shaking," and "bullying." SPRINGING-LINE. The horizontal line drawn at the point of origin of an arch ; or at the point where the intrados of the arch meets the interior face of the side-walls or abutments. SQUARE SETS. Timber frames used at intervals to support poling-boards, in shaft-sinking or driving a heading. STATIONS. Points on the center-line of a tunnel, permanently marked. These stations may be outside of the tunnel and used for projecting the center-line into the tunnel, or they may mark the center-line inside the tunnel. STONE-BOAT. A species of wooden sled, used for hauling large stones a comparatively short distance. STRETCHERS. In shaft-sinking, the cross-pieces holding the waling apart. STRIKING. Lowering the arch-centers, after the masonry is completed and the mortar set. STRIKING-PLATES. Two horizontal timbers separated by striking-wedges and supporting an arch-center. The latter is lowered by slacking the wedges. STRIPPING. Removing the earth, etc., overlying rock that is to be exca- vated. English miners apply the term of "over-burden" to this same overlying material. STUDDLE. A square timber, or short post, placed vertically between two sets of shaft timbers. STUMP-PROP. Short posts set under the crown-bars of a tunnel. SUMP. An excavation, usually at the bottom of a shaft, to collect water so that it may be better handled by the pumps or buckets. TAILING. Giving the proper angle, or elevation, in driving the poling- boards in a heading. TAMPING. The material placed over a charge in a bore-hole, to better confine the force of the explosion to the lower part of the hole. TENDING CHUCK. Pouring water into a drill-hole to assist in drilling. TEMPLATE. A form for building tunnel inverts. TIMBERING. A general term for the placing of timber, to support the roof or the face of a tunnel during excavation and lining. TOOTHING. In a stone or brick arch, the jogs left in the face of the arch- work, for the purpose of joining it to the following section. TRIMMERS. The top row of holes in a tunnel face. TUCKING SPACE. The space between the blocks separating the cap in a heading-set from the poling driven. This space provides for driving the second set of poling-boards. UNKEYING. In attacking a rock-face the first effort of the miner is di- rected toward making a cut that will permit the succeeding shots to exert the greatest force with the minimum charge of explosive. In do- APPENDIX 307 ing this "unkeying," he takes advantage of any persistent seam in the rock face. WALINGS. Sets of longitudinal timbers used as guides in driving sheet pil- ing, etc. Also the horizontal side-pieces in a shaft-set separated by "stretchers." WALL-PLATE. A horizontal timber supported by posts resting on "sills" and extending lengthwise on each side of the tunnel. On these wail- plates the roof-supports rest. INDEX TO CONTENTS PAGE AIR-LOCKS Their purpose 213 Kiel dry-dock 231 The Hughes 223 Hyde Park tunnel 225 Morison's 228 The O'Rourke 218 Victoria Bridge 230 Zschokke-Terrier 222 AIR-REFRIGERATION in tunnels.. 212 In Simplon tunnel 260 Air-valve Slow pressure 232 ALIGNMENT of tunnels 6.4 Transfer of line into Cin- cinnati Water Works tunnel 291 Dunham method of 6 Simplon tunnel 269 ARCH-CENTERS Requirement and form of 99 Adjustable 101 Cincinnati and Southern R. R ioo Norfolk and Western R. R. 101 Steel East Boston tunnel. 109 Battery Electric firing 25 BLASTING General principles of 34 Nomenclature 36 Square center cut 37 V-shaped center cut 38 Qualities of rock, testing. . 41 Methods on N. Y. Rapid Transit tunnel 39 To prevent crushing of shaft-timbers by 45 BORE-HOLES Diameter and length of 36 Location of 37 Brant Rotary Drill at Simplon tunnel 272 Brick-crates New Orleans drainage 184 Cement mortar car Mullan tunnel 179 COMPRESSED AIR Effect of, on human organism 216 PAGE Hospital-lock 216 Human endurance under. . 214 Limits of working in 215 CONCRETE TUNNEL LINING 107 Cascade tunnel 173 East Boston tunnel 160 N. Y. C. &H. R. R. R.... 193 Concrete invert form sewer tunnel in Concrete side walls building. . 180 Concrete and steel lining, East Boston tunnel 119 COST Concrete tunnel lining. . 193 Diamond drill work, Africa 199 Diamond drill work, Mon- tana 200 Drifting and cross-cutting. 188 Driving heading in Me- lones Mine 190 Excavation, timbering and packing Little Tom tun- nel 77 Hand-drilling at Golden Eagle Mine 186 Hand-work in W. Va. & P. R. R. tunnel 189 Mass. Pipe Line Gas Co. tunnel 143 Mine hauling by com- pressed air vs. mules. . . . 198 O. R., P. C. & W. R. R. tunnel 191 Power drilling, Lincoln Gold Mine 187 Square-set timbering 197- Steam-shovel work 192- Water-hoisting vs. pump- ing in mines 195 Crown-bars, made of old rails. . 86 Crown-bars Special iron 85 Distance targets Hoosac 12 Drifting and cross-cutting 188 Dry-sand tunneling 94 Dumping wagon The Shadbolt 178 Dunham method of tunnel alignment 6 309 310 INDEX TO CONTENTS PAGE DYNAMITE Frozen 28 Loading with 43 Thawing-house 30 ELECTRIC Firing 24 Firing apparatus 25 Power heat from, in sub- ways 203 EXPLOSIVES Atlas powder 20 Consumption of 39 Dynamite 18 Forcite 19 Gunpowder 14 Handling and storing 27 Hellhoff ite 22 Hercules powder 20 Joveite 20 Judson powder 20 Lithof racteur 19 Nitrogelatine Composi- tion and use 18 Nitroglycerine Its compo- sition, power, expansion, etc 16 Effect of fumes 44 Oxonite 22 Plancastite 22 Power of, bulk for bulk. . . 19 Rack-a-rock 22 Romite 22 Used in Simplon tunnel... 274 Sprengel class of 21 Excavation Sequence of ope- ration, Simplon tunnel. (See also tunnel timber- ing) 270 Expansion joint in tunnel lin- ing 137 FORCE of gunpowder 15 Of nitroglycerine 16 FREEZING process in shaft-sink- ing, history of 236 As applied at Iron Moun- tain 238 At Ronnenberg, Germany. 237 Frozen Soil Conductivity of. . 238 FUSE Electric 24 Safety or time 23 Geology in tunnel location 2 Grouting sub-aqueous tunnel . . 142 GUNPOWDER Composition, etc. 14 Loading with 82 Hamilton Powder Co. dyna- mite thawer 29 Hand-auger for prospecting work 244 PAGE Hand-drilling Cost of at Gol- den Eagle Mine 186 Heading timbering, Simplon tunnel 282 High explosives Precautions in firing 26 Hoisting cage Simple form of 52 Hoisting hook, Walker detach- able 181 Humidity in subways 206 Illumination in Simplon tunnel 261 Lamps for sighting in tunnels. . 13 Line of least resistance in blast- ing 34 LINING for heavy pressures Simplon tunnel 279 Timber in sub-aqueous tunnel, Boston 140 Location of tunnels I Loose gravel, driving through. 78 Magazine, powder, design of . . 31 NEEDLES Iron 85 As used on N. Y. subway. 168 Open-cut work, N. Y. subway. 165 Pilot-piles, Harlem river tunnel 127 Pilot-tunnel system 91 PLANT Brick crates, New Or- leans drainage 184 At Cascade tunnel 171 Concrete-mixing, New Or- leans ' 183 Detaching cage-hook 181 Dump-car, New Orleans drainage 182 Scraper loading 176 Simplon tunnel 252 Steam-shovel work inside tunnel, N. Y. & H. R. R. R 180 (See Ventilation.) Plummet lamps 249 Powder magazine, plan of 31 POWER DRILLING, cost of at Lin- coln Mine 187 Hints on 45 Power installation, Simplon tunnel 253 Power plant, Cascade tunnel. . 174 Primer cartridge-making 23 Prospecting work, tools for. . . . 244 QUICKSAND Definition of 239 Sewer tunnel in 93 Shaft-sinking in 57 INDEX TO CONTENTS PAGE Rock temperatures in tunnels. . 239 Rollers under arch-centers.... 102 ROOF-SHIELD, Boston subway... 157 Metropolitan Railway Paris 149, ISO Orleans Railway, Paris.... 146 (See Shields.) Scraper loading at Kellogg tunnel 176 Screw piles, used under sub- aqueous tunnel 137 SHAFT Automatic dump for. . 177 O'Rourke system of con- struction 218 Location and dimensions of 47 A sheet-piling 62 Built with segmental tim- bers 140 Simple head-house for.... 51 Stopping flow of water at bottom of 60 Transferring center line down 10, 288 Framing, Norway, Mich. . . Aspen tunnel . Shaft-house, a steel 54 SHAFT SINKING, controlling features of 48 Cost of at Golden Eagle Mine 186 At Lincoln Gold Mine, cost of 187 In wet gravel and quick- sand 57 SHEET-PILING Driving of 63 As used at Harlem tunnel. 127 SHIELDS Tunnel, history of... 113 Blackwell tunnel 114 East Boston tunnel 121 East River gas tunnel 123 Mass. Pipe Line Gas Co. . . 142 Orleans Railway, Paris 146 St. Clair tunnel 116 Friction on, at St. Clair tunnel 118 Screw-jack type 138 The Shankland 139 Spree tunnel, Berlin 118 Steel traveling no Siphon tunnel, Mass. Pipe Line Gas Co 142 Skips, for shaft work 57 Snow fall, in tunnel location. . . 8 Soap and alum solution for waterproofing concrete. . 242 Station points, preserving 5 Station towers 9 PAGE Steam-shovel work, cost data. . 192 SUBWAY Requirements and location 144 Atlantic Avenue, Brooklyn. 168 Boston system 154 Buda-Pest 163 East Boston 159 Humidity in 206 Orleans Railway, Paris.... 145 N. Y. Rapid Transit, gen- eral plan of 163 Open-cut work on 165 SURVEY WORK Cascade tunnel 9 Cincinnati W. W. tunnel.. 289 Switchback Cascade tunnel ... 8 Tamping, necessity of 27 Temperatures in deep tun- nels 211, 239 Thawing dynamite 29 TRANSPORTATION in Kellogg tunnel 177 In Simplon tunnel 265 Traveler N. Y. subway lining. 107 (See Arch-Centers.) TUNNEL Aspen, shaft lining. . 64 Boulder 102 Cascade 8 Cincinnati Southern R. R. 100 Cincinnati Water Works.. 285 Cross-section instruments.. 247 Crow's Nest Pass 78 Debris, handling in 173 East Boston 109, 159 Hoosac shafts 12 Kellogg, scraper loading at 176 King's Cross, London 85 Lake View, Chicago 81 Location of i Meudon, France 87 Moncreiffe, England no Mullan, relining 179 Musconetcong, relining 104 Norfolk & Western R. R. . 101 O. R., P. C. & W. R. R., cost data 191 Pracchia, ventilation of. ... 204 Relining 102 Revere Beach, Mass 95 Sand tunnel in Brooklyn. . 82 Simplon, detailed descrip- tion of 250 Simplon, standard sections 267 Steel-lined 86 Surveying of 4 Telephone and freight, in Chicago 293 W. Va. & P. R. R. R., cost data 189 312 INDEX TO CONTENTS PAGE TUNNEL LINING, cement mor- tar car for 179 Simplon tunnel 278 TUNNEL TIMBERING General principles of 65 American system 74 Austrian system 72 Belgian system. 69 Belgian-German system. . . 69 English- American system.. 67 German system 71 Hoosac 69 Little Tom 77 Musconetcong 68 N. Y. subway 106 Ozernitz 73 St. Cloud 70 Simplon tunnel 276 Triebitz 72 TUNNELING Under clay pres- sure 298 Crutch system 81 In dry sand 82 Through dry, running sand 94 East Boston 161 Iron crown-bar system. ... 85 In loose gravel 78 Meem poling-board system 84 With- pilot-tunnel 91 Sand-chamber and caisson method 87 With screw-pile supporting column 134 Sewer tunnel in sand, Chatham Square, N. Y. . 97 Simplon tunnel 280 In soft ground, East Bos- ton 159 Through soft ground 95 Tunneling terms (See Glos- sary in Appendix.) TUNNELS, SUBAQUEOUS Black- well, London 114 Cast-iron 123, 134 PAGE East Boston 119 East River Gas 123 Harlem River 125 McBean system of 125 Mass. Pipe Line Gas Co... 140 Pa. R. R., Hudson River. . 134 St. Clair 116 Spree, Berlin 118 VENTILATION IN TUNNELS General principles of.... 201 Volume of fresh air re- quired, formula for 202 Baltimore and Potomac tunnel 207 Boston subway 154, 205 Cascade tunnel 174 East Boston tunnel 206 Mersey tunnel 208 Pennsylvania Avenue sub- way, Philadelphia 209 Saccardo system 204 Simplon tunnel 210, 257 Required in electrically operated subways 203 Vernier scale, for transferring line down shaft 12 WATERPROOFING Concrete ex- periments upon 240 Concrete tunnel lining 244 With asphalt 243 With linseed oil 243 Atlantic Avenue subway.. . 169 Subway, Buda-Pest 163 Water-hoisting vs. pumping in mines, cost data 195 Water-hoist, electric 196 Wet gravel, shaft-sinking in... 57 Wires, connecting. 25 Appendix Glossary of some of the more unusual terms used in tunneling 103 INDEX TO ILLUSTRATIONS PAGE AIR-LOCK, Hughes 224 Hyde Park tunnel 224 Kiel dry-dock for workmen 231 Kiel dry-dock for materials 233 Morison 229 O'Rourke 219 Victoria Bridge 230 Zschokke-Terrier 221 Air-valve, pressure regulating. 232 Blasting nomenclature, diagram 56 BLASTING Square center-cut. . 37 V-shaped center-cut 38 Methods N. Y. subway.... 41 Brick, crates for handling 184 Caisson, O'Rourke wooden.... 217 Caissons used at Meudon tun- nel 90 Cast-iron lining rings, East River gas tunnel 123 Cement mortar car, Mullan tunnel 179 Concrete invert, form of in CONCRETE LINING, Boston sub- way ". 119 Peekskill tunnel 194 Concrete mixers, New Orleans drainage works 182 Crown-bars made of old rails. . 86 Dump-car, New Orleans drain- age 182 Dumping wagon, the Shadbolt. 178 Dynamite thawer 29 Dynamite-thawing house 31 Hoisting cage and head house. 51 Hoist-hook, detaching 181 McBean sub-aqueous tunnel... 129 Mold for side-walls, N. Y. sub- way 109 Pilot-tunnel system 92 Plant, arrangement of, on New Orleans drainage works. 183 Plummet lamp 248 Quicksand, sewer tunnel in 93 Sand, sewer tunnel in 97 PAGE Sand-chamber and caisson sys- tem 88 Scraper-loading device in Kel- logg tunnel 175 SHAFT-FRAMING, longitudinal section 60 Connection with rock at bottom 61 Top and bottom sets 59 Shaft-lining, Aspen tunnel 64 Shaft-dump, automatic 177 Sheet-piling shaft, N. Y. sub- way 62 SHEET-PILING, Harlem River tunnel 127 Device for cushioning blow on 63 SHIELD, Blackwell tunnel 115 Boston subway. ...... .121, 158 East River gas tunnel 123 Mass. Pipe Line Gas Co. . . 143 Metropolitan Railway, Paris 15! Orleans Railway, Paris 147 St. Clair tunnel 117 Screw-jack type 139 Shankland's 140 Spree tunnel, Berlin 118 SIMPLON TUNNEL Map of routes 251 Profile 252 Air circulation in 259 Brandt rotary drill 271 Brandt rotary, mounted... 272 Extra heavy lining 279 Cross-galleries 268 I-beam and timber frames. 281 Lining construction 278 Progressive stages in tim- bering 277 Refuge chambers 269 Sequence of excavation 270 Sequence of timbering in soft rock 282, 283 Standard sections 267 Standard timbering 276 Suggested arch construc- tion 284 313 INDEX TO ILLUSTRATIONS PAGE SIMPLON TUNNEL Ventilating plant, Italian end 258 Ventilating plant, Swiss end 257 Skips and cages 56, 57 STEEL SHAFTHOUSE, elevation.. 55 Plan 54 SUBWAY Boston, in concrete and brickwork, 157 Boston, general plan in steel 155 Boston, Atlantic Avenue station 159 Detail of building side- walls 160 Detail of building arch. 161 Buda-Pest, section 162 New York, in steel ai.d concrete 164 New York, earth and reck sections 165 New York, methcd of ex- cavating, east of Fifth Avenue 166 New York, method of ex- cavating between Fifth and Sixth Avenues 167 Atlantic Avenue, Brooklyn 169 Tunnel alignment, Dunham method I TUNNEL, Cascade, map of 8 Excavating and lining plant of 172 Cincinnati Water Works section 286 East end shaft 289 Cross-sectioning device... 247 Tunnel driving, various sys- tems of 66 Harlem River, twin sec- tion 124 Working platform, guide frames, etc 126 Harlem River, plan for connecting two systems.. 133 PAGE: TUNNEL P. C. & W. R. R. standard section IQ 1 Pennsylvania R. R., Hud- son River cross-section.. 135 Details of bore-seg- ments 136 Screw-pile shaft fit- tings 137 Expansion joint for lining .' I3& TUNNEL CENTERS Boulder tunnel 103. Cincinnati Southern R. R. standard plan ioo> Musconetcong tunnel 105 New York subway 108 Norfolk & Western R. R. . 101 Set-screw and rollers under 102 Steel, East Boston tunnel. . 109- TIMBERING American system, Little Tom tunnel 77 Austrian system 75 Belgian system 71 Brooklyn sand tunnel 82 Crow's Nest Pass tunnel. . 78 Crutch system 81 Hoosac tunnel 60^ Iron crown-bar system.... 84 Musconetcong tunnel 68 Meem system 83; Needles used in Meem sys- tem 85 N. Y. subway 106 Ozernitz tunnel 73 Revere Beach tunnel 94, 95 St. Cloud tunnel 70 Triebitz tunnel 72 VENTILATING SYSTEM, Balti- more and Potomac R. R. tunnel, Baltimore 20& Boston subway 156, 205 Mersey tunnel 209 Pennsylvania Avenue sub- way, Philadelphia 210 Saccardo system of 204 Vernier scale for transferring line down shaft 12 12 IS DUE ON THE STAMPED BELOW DATE VD 02 UNIVERSITY OF CALIFORNIA LIBRARY