AMERICAN SOCIETY OF CIVIL ENGINEERS
INSTITUTED 1852
TRANSACTIONS
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in its publications.
Paper No. 1359
THE ASTORIA TUNNEL UNDER THE EAST RIVER
WITH DISCUSSION BY MESSRS. F. LAVIS, MILTON H. FREEMAN, W. 11. BRADLEY, JAMES F. SANBORN, EDWARD WEGMANN, 11. C. KELLOGG, W. W. BRUSH, THOMAS H. WIGGIN, VVILLIAM CULLEN MORRIS, AND JOHN VIPOND DAVIES.
The object of this paper is to describe in general the design and construction of a tunnel of large magnitude, but generally simple in character, and to treat more particularly certain difficulties due to physical conditions encountered and methods used in overcoming them.
The work described consisted of sinking two shafts, 242 and 277 ft. deep, respectively, and driving a tunnel, 18 ft. on the vertical and 19 ft. on the horizontal axis' between these shafts, a distance of 4662 ft., through rock under a river with a depth of water of 100 ft. The main problem was to drive through a zone of decomposed rock extending on the line of the tunnel for a distance of 450 ft.
The paper is divided into fifteen parts, as follows:
l.-History of project and economic reasons for removal of gas plants from Borough of Manhattan to remote districts, by providing transmission of gas through a tunnel under the East River.
2.-General description of the construction.
3.-Description of the plant.
4.--Sinking of the shafts, 30 and 42 ft. external diameter, respectively.
5.-Tunnel driving through various rocks under normal conditions. Geology of line of tunnel. Details of work accomplished, and rates of progress.
6.-Tunneling through decomposed rocks under heavy water pressure, together with a geological description of the sheared contacts and conditions as actually found. In this part is described the method of thorough exploration of the rock formation by test drilling in advance and the consolidation of decomposed material by cement grouting to produce a rock formation through which the tunnel could be safely advanced by ordinary blasting. It also describes the methods of drilling, both with percussion and diamond drills, in preparation for grouting; the practical application and extent of the grouting operations; the use of buttresses to face rotten rock to permit of grouting; and the use of emergency bulkheads to see-Lire the safety of the work and the employees.
7.-Flooding of entire work by breaking out of seam before it was securely grouted and controlled.
8.-Unwatering the tunnel and finally plugging and securing the source of water inlet and solidifying the rock; the methods considered and those adopted; the use of the air lift; the condition of the Portland cement after grouting; and the -final completion of the tunnel excavation.
9.-Cast-steel lining used through the bad rock section. Assumptions as to the design of the lining, the details, and the erection.
10.-Drainage of the tunnel.
11.-Ventilation of the tunnel.
12.-Lighting of the tunnel.
13.-Triangulation and alignment; methods used and results obtained.
14.---Qualitities of items making up the work; and details of costs of all work executed under normal conditions.
15.-The laying of the gas mains in the tunnel, Two lines of 72-in. cast-iron pipe, each pipe length weighing 26 000 11.). Heaviest cast-iron pipe ever manufactured. Special machinery designed and used for laying pipe. Special machine designed and made for testing joints of pipes as laid. Jointing and caulking of pipe mains.
The writer has endeavored to give a comprehensive description of the work as a whole, and to emphasize the portion of the paper covering the operation of passing through the zone of bad rock. It is hoped that the photographs and drawings which accompany the paper will assist in making clear the actual conditions encountered in the field.
About 35 years ago, before the general introduction of electricity, the production of gas for illuminating and heating purposes within the City of New York had reached such a point, with reference to the occupation of lands for manufacturing plants and local interference with city development, as to have made it desirable to consider the removal of these industries from the densely populated sections of the city.
Consequently, on June 21st, 1886, at the request of Mr. James W. Smith, then President of the Consolidated Gas Company, a report outlining the future policy of the Company was presented by Air. William H. Bradley, then Engineer of the 44th Street Station of the Company, now Chief Engineer, in which the removal of the gas plants from Manhattan Island was strongly advocated. Following this report, the question was thoroughly ventilated in the public press, with strong advocacy of the suggestion that all companies then manufacturing gas on the Island of Manhattan should remove to sites outside the city, and that a great central manufacturing plant should be created on the Flushing Meadows, from which gas should be piped to a convenient point whence it might be conveyed by tunnel under the East River to Manhattan For several years, however, nothing was done with this proposition. At that time the Ravenswood Gas Company, having a small manufacturing plant at the foot of Webster Avenue, East River, supplied gas locally in Long Island City. About 1891, this company was reorganized by Air. Emerson McMillin, its corporate title was changed to East River Gas Company, and it obtained from the Legislature of the State of New York the necessary franchise rights to supply gas to New York City by a tunnel to be constructed under the East River.
In 1892 and 1893 the writer's firm constructed, for this new corporation, a small tunnel (internal diameter 10 ft. 2 in. in the por THE ASTORIA TUNNEL 597
tions which were iron lined and a rectangular section 10 by 8 ft. in the portions in solid rock) under the East River, crossing the two channels and Blackwell's Island. This tunnel (shown on Plate XXIV) extends from the foot of East 71st Street, Manhattan, to the Ravenswood works of the Company at the foot of Webster Avenue, Long Island City. Borings and soundings were made at close intervals across the channels, and as far as information could be obtained (with the extremely rapid current running in the East and West Channels of the East River), there was every reason to believe that the construction of a tunnel on that line would be through a practically continuous bed of rock, although the geological information indicated clearly the intrusion of a seam of dolomitic limestone under each channel.
The work on this tunnel was let out by contract, and proceeded very slowly for a considerable time, when, having sunk both shafts and having turned the tunnel on the Manhattan side of the river, decomposed rock was encountered at the contact between the gneiss and dolomite under the West Channel. The contractors immediately abandoned the work, and it was then carried on by the writer's firm, as Constructing Engineers, for account, and on behalf, of the Gas Company.
This tunnel was at a depth of nearly 100 ft. below mean low water. The depth of the water in the West Channel was 65 ft., but that in the East Channel was only about 30 ft. Under the West Channel two comparatively narrow sheared contacts in the dolomite rock were badly decomposed; under the East Channel the contacts between the Fordham gneiss, the mica schist, and the dolomitic formation were also extensively distorted, and, to some extent, decomposed, but the whole of this tunnel was completed successfully with the use of air pressure, the depth not being too great to prohibit this method of construction.
After the completion of this tunnel the East River Gas Company passed into the ownership of the Consolidated Gas Company, and thereafter, the Astoria Light, Heat and Power Company was organized to construct a great central gas manufacturing plant to supply gas to all the constituent companies. This plant was established on a large tract of property at Lawrence Point, Long Island, at the northerly end of the channel known as Hell Gate.
For several years gas from both the Astoria and Ravenswood Plants, for the supply of Manhattan and The Bronx, had been carried through a large pipe line to Ravenswood and thence to Manhattan through the 71st Street tunnel in two 36-in. mains The supply for The Bronx had been conducted in pipes laid in open cofferdam construction across the Harlem River, involving a devious detour.
About 1903 it became necessary to consider an independent means of conducting to Manhattan the gas manufactured at the Astoria Plant, as at that time the center of gravity of the gas consumption of the Boroughs of Manhattan and The Bronx combined was at a point south of the Harlem River.
Long legal proceedings, to obtain an easement for a right of way for a tunnel or other means of communication, delayed procedure with this undertaking for several years.
The line of this tunnel was definitely fixed by the necessities of the commercial situation, regardless of geological considerations, as the New York terminus had to be at 111th Street and Pleasant Avenue, where the Gas Company had a distributing station, and the Long Island terminus bad to be on the property of the Company at Astoria, just north of Winthrop 'Avenue. The line, therefore, was laid out between these two points, the Astoria end being kept as close as possible to Winthrop Avenue, in order to conform to the final layout planned for the gas holders of the Company. This line passes under Ward's Island, where it was intended to sink an intermediate shaft for construction purposes, and from this shaft it was contemplated to drive a branch tunnel to a point in The Bronx. Borings were made at the sites of the entrance, outlet and intermediate shafts, and the geological features were studied carefully.
As the depth of the water in the channels on this line was somewhat in excess of 100 ft., and was so great that it was impossible to use air pressure, and as the known geological conditions made it certain that the contacts between the gneiss and dolomite formations would give more or less trouble, it was considered desirable to place the tunnel deep in the rock, in order to minimize trouble from open seams. On the other hand, the necessity (in event of a deeper location) for lengthening vertically the pipes for carrying the gas made it undesirable that these shafts should be deeper than was reasonably THE ASTORIA TUNNEL 599
necessary to assure that the tunnel would pass below any serious difficulties of geological contact. Ultimately, the depth for the tunnel was decided on as 1861 ft. below mean sea level at the Manhattan Shaft descending to 218 ft. below that level at the Long Island Shaft. Within a prism on this line and grade, easements for right of way were acquired, and all legal proceedings were completed.
As before stated, these legal proceedings consumed considerable time, and in the interim the center of gravity of gas consumption had moved north of the Harlem River, with every indication that it would extend still farther north; and, by the time the Gas Company was ready to proceed with the work, it bad become desirable to discontinue, for the time being, the plan for constructing the tunnel on the original line to 111th Street, and, instead, to proceed with that of delivering gas directly from the Astoria Plant to the Borough of The Bronx. At the same time, the Company did not desire, by any means, to abandon its rights to construct at a later date the tunnel from Astoria to East 111th Street, as originally laid out. This rearrangement necessitated the retention of the Shaft near Winthrop Avenue, Astoria, and the purchase of land at Port Morris, at the foot of 132d Street, fronting on the East River, on which to construct a shaft as the northerly outlet of the tunnel, near to, and suitable for a connection with, the distribution system of the Central Union Gas Works, at the foot of 138th Street and Locust Avenue, The Bronx.
The location of the underground prism for the easement for construction of the proposed future tunnel to 111th Street determined the depth of the Astoria Shaft for the tunnel to 132d Street, and an allowance for the necessary drainage gradient toward Astoria determined the limitations of depth at the Bronx Shaft. At the same time, the grade of the tunnel was lowered to the utmost limit permissible within the prism forming the subterranean easement, as it was recognized that on this line the axis of the tunnel would be nearly parallel to the line of strike of the rock, and consequently to the planes of contact between the different geological formations to be penetrated, and therefore, in all probability, would involve more difficulties than the previously projected tunnel to 111th Street, which passed almost at right angles across these contacts. However, the
Gas Company considered that, notwithstanding this, it would be simpler and wiser to face the constructive difficulties than to be under the necessity of adopting a new location which would involve a revival of the entire legal proceedings; and, on this basis, the work hereinafter described was designed and carried out. Plate XXV is a profile of the tunnel and the river bottom.
On account of the uncertainties which might arise in construction, as well as for various other reasons, the Company decided not to invite bids from contractors on this undertaking, but to carry out the work departmentally by its own forces, and the writer's firm was retained as Constructing Engineers in respect to the design and construction.
The following description records for the most part a work of tunnel construction of large magnitude, but comparatively simple in character, excepting only that the general location was at a deep level, with access only at vertical terminal shafts nearly a mile apart, and practically entirely below navigable waterways.
The intention, therefore, in the following presentation, is to describe, in outline only, the work of normal character involved in this construction, and to emphasize more particularly the difficulties encountered, and the methods by which they were overcome.
The construction involved in this undertaking consisted of a vertical shaft, 277 ft. deep, on the property of the Astoria Light, Heat and Power Company, at Astoria, a vertical shaft, 242 ft. deep, on private property in The Bronx, and a tunnel connecting these shafts.
Anticipating the future construction of the previously planned tunnel direct to 111th Street, Manhattan, the shaft at Astoria was made larger than the one at The Bronx, in order to accommodate the future shaft installation necessary for the two tunnels; and a short portion of the tunnel on the line to 111th Street, Borough of Manhattan, was constructed, so that, as future necessities arose, this tunnel could be extended without disturbing the Astoria-Bronx service.
The necessities for the gas distribution involved the provision of two 72-in. castiron mains from Astoria to The Bronx, with space in the upper portion of the tunnel for future developments and utilities.
This caused the adoption of a tunnel cross-section 18 ft. on the vertical axis and 19 ft. on the horizontal axis. The vertical pipe risers, elevator frames, etc., made it necessary that the shaft should be 26 ft. in internal diameter at the Bronx terminal, and, though the original plan for an Astoria-Manhattan tunnel required a shaft at Astoria of only this same size, the modification, to provide for both a Bronx and a Manhattan tunnel, made it necessary to increase the internal diameter of the Astoria Shaft to 34 1/2 ft.
Borings at the shaft sites showed that on the Astoria side there was a solid rock floor approximately 50 ft. below the surface of the ground, or about 40 ft. below mean sea level, the overlying material being a natural deposit of sand, gravel, and boulders, which, so near the East River, practically assured considerable water inflow in excavation. At the Bronx Shaft the rock floor was only some 13 ft. below the surface of the ground, and was overlaid with boulders, beach sand, and gravel. Soundings along the line of the tunnel indicated two river channels, each having a water depth of approximately 100 ft., with a high reef lying between them. The geologic survey maps indicated certain changes in the geological formation, with Stockbridge dolomite lying between the Fordham gneiss, which exists at the locations of the two shafts and extends for a considerable distance from each. The two deep-water channels clearly define the contacts at each end between the gneiss and dolomite.
The properties for plant use, which were fenced in for the exclusive use of the Tunnel Department, consisted of a plot 255 by 230 ft., aggregating 1.35 acres, at the Astoria Shaft, and a plot 394 by 100 ft.,
-.regating 0.96 acre, at the Bronx Shaft. For the transportation of men and materials between the two plants, a strong, gasoline, motordriven boat, commonly called an "oyster boat", was purchased. The hull was of wood, 51 ft. long and 141 ft. beam. The boat was equipped with an excellent, 25-h.p., direct-driven engine, with screw propeller,
In laying out the plant, careful consideration was given the question of water transportation for excavated material, involving the use of scows and the utilization of the excavated material to fill other lands owned by the Company. A dock existed at the Astoria plant, but there was only a broken rock shore with extremely steep slopes THE ASTORIA TUNNEL 603
at the Bronx plant, at which site a crib dock had to be built. At the Astoria dock, 230 ft. frontage was allotted to the Tunnel Department, and this provided berths for two scows; at the Bronx dock only one scow could be docked on the frontage of 108 ft.
As the tunnel was to be entirely in rock, it was desirable to use a car of as large a capacity as possible, with its body so low that a man could readily load.it. For handling rock excavation the writer has found that a car having a wooden body is more convenient and economical in operation and maintenance than a steel car. Figs. 1 and 3 illustrate the car designed for this purpose; it consisted of .9 substantial steel underframe with an oak box body. Dumping arrangements were avoided, as they would have introduced additional height and an increase in mechanism subject to damage.
The dumps, which were placed directly over the scows at the docks, consisted of a revolving tipple, Fig. 2, such as used in coal-mining practice, operated with a 3cylinder air engine, and the cars were turned completely over in discharging into the chutes.
In order to discharge excavated material into the scows, an elevated deck was built at each shaft, extending from the shaft to the dock. Having ample space at the Astoria Shaft, a trestle loop was built entirely around the shaft location, so that the cars could be operated around the loop, with an extension to the dock, as well as a connection to the rock crusher which was used during part of the tunnel construction. Electric locomotives were used for operating the cars on these trestles between the shafts and the docks. Although there were two such locomotives at each shaft, only one was in service at any given time. These were 3-ton mine locomotives, manufactured by the Westinghouse Electric Company, equipped with two 8-h.p. 250-volt, direct-current motors, with a drawbar pull of 900 lb. at 6.6 miles per hour. Power for the locomotives was supplied by third-rail contact from the tunnel lighting circuit.
The mechanical plant at each shaft was planned with the expectation that considerable water (and consequent pumping) would be encountered in the tunnel driving, and that a full complement of rock drills and labor-saving devices would be necessary, and with the intention of constructing half the length of the tunnel from each shaft. The following plant was used. . THE ASTORIA TUNNEL 605
Four 302-h.p. Heine water-tube boilers,
Six 20-in. Typhoon turbine blowers-L. J. Wing Manufacturing Company.
Two 100-lb. pressure, Ingersoll-Rand air compressors; total capacity, 3 200 cu. ft. per min.
Two 42-in. Ingersoll-Rand after-coolers.
Two 54 by 120-in. Ingersoll-Rand air receivers.
One hot-well tank, 48 in. diameter, 96 in. high-G.- Stuebner.
Two 50-kw., 200-ampere, 250-volt, General Electric generators.
Two 75-h.p. Harrisburg Foundry and Machine Company, horizontal engines.
One Walker Electric Company switch-board for 250-kw. generators.
Two 1 200-boiler h.p. Worthington boiler feed pumps.
One 250-gal. per min. Worthington duplex pump.
One surface condenser and feed-water heater combined-12 600 lb. of steam per hour-Wheeler Condenser and Engineering Company.
One vacuum oil separator and simplex pump-12 000 lb. steam per hourWarren Webster Company and Warren Steam Pump Company.
Two closed water-tube feed-water heaters-800 h.p. to raise 24000 lb. of water per hour from 60 to 200' Fahr.-F. L. Patterson and Company.
One 30-gal. oil filter-Hall Manufacturing Company. Surface
One 45-ft. derrick.
Two 50-ft. derricks.
Three Lidgerwood Manufacturing Company hoisting engines for derricks.
One 1-cu. yd. Smith concrete mixer and engine.
One No. 4 gyratory stone crusher-Allis-Chalrners Company.
One 8 by 12-in. Buckeye vertical engine. 606 THE ASTORIA TUNNEL
Two 100-lb. pressure, Ingersoll-Rand air compressors; total capacity, 3 200 cu. ft. per min.
Two 42-in. Ingersoll-Rand after-coolers.
Two 54 by 120-in. Ingersoll-Rand air receivers.
One hot-well tank, 48-in. diameter, 96 in. high-G. Stuebner.
Two 50-kw., 200-ampere, 250-volt, General Electric generators.
Two 75-h.p. Harrisburg Foundry and Machine Company, horizontal engines.
One Walker Electric Company switch-board for 250-kw. generators.
Two I 200-boiler h.p. Worthington boiler feed pumps.
One 250-gal. per min. Worthington duplex pump.
One surface condenser and feed-water heater combined-12 600 lb. of steam per hour-Wheeler Condenser and Engineering Company.
One vacuum oil separator and simplex pump-12 000 lb. steam per hourWarren Webster Company and Warren Steam Pump Company.
One 30-gal. oil filter.
Two 50-ft. derricks.
Two 8 1/4 by 10-in. non-reversible engines for derrick-Lidgerwood Manufacturing Company.
One 1-cu. yd. Smith concrete mixer and engine.
One 42-in. Ingersoll-Rand air reheater.
One 60-h.p. vertical boiler-Wickes Brothers.
Two 3-ton electric mine locomotives-Westinghouse and Baldwin Companies.
One 10 by 12-in., reversible, compound-geared, elevator engineLidgerwood Manufacturing Company.
One 12 1/4 by 15-in., reversible, link-motion, single-geared elevator engine-Lidgerwood Manufacturing Company.
One 66 by 72-in. passenger elevator cage.
Two 66 by 96-in. material elevator cages.
Four 1 1/2-yd. shaft buckets-G. Stuebner.
Three 3/4-yd. tip buckets-G. Stuebner. 608
THE ASTORIA TUNNEL
TUNNEL EQUIPMENT.
"
"
"
per
"
"
" "
"
min.
C.,
I ~
4 "
9 "
44
Two 12-in. Sirocco fans with motors-American Blower Company.
One 30-in. ventilating fan and engine-B. F. Sturtevant.
One 42-in. centrifugal blower and engine--B. F. Sturtevant.
Astoria Shaft.-The sinking of the Astoria Shaft began on September 12th, 1910. Steel sheet-piling of United States Steel Company section was used for the exterior sheeting through the earth section, for a depth of 52 ft., and was braced with 16sided timber frames, 4 ft. apart, strapped at the joints with steel plates, to which were attached turnbuckle tie-rods extending across the shaft for use in maintaining the circular form. (Fig. 4.) The dump trestle having been constructed to circular form at a height of 15 ft. above the ground, and the excavation being removed to 8 ft. below the ground, a frame was prepared to the correct circular form, plumbed accurately below the trestle form, and served as a guide for driving the sheet-piling. The piling was cut in two lengths for the total depth, with joints staggered, and was driven with an Arnott 2 000-lb. steam pile-hammer suspended from a derrick.
Excavation was removed as the sheet-piling was driven, in order to avoid any distortion by over-driving against boulders or rock.
Having sunk the shaft to rock level, excavation was carried down into the rock about 4 ft. below the point of the piling, and concrete was placed to half the ultimate thickness for the full depth of the excavation, in order to secure the sheet-piling and timber frames from injury during the further extension of the shaft construction.
Bronx Shaft.-At the Bronx Shaft, the shallow depth of the overlying soil and material, as well as its character, made it unnecessary to use steel sheet-piling. Wooden sheeting of 4-in. tongued and grooved stuff, supported by 12-sided timber frames, 4 ft. apart, was used through the 13 ft. of earth to rock level; the permanent lining inside this sheeting was concreted on reaching the rock floor.
Shaft sinking in rock was carried out by the ordinary methods, the usual practice being to line up with concrete every 30 ft., as the 610 THE ASTORIA TUNNEL
rock was of treacherous character, and the introduction of the lining insured the employees against accidents.
For hoisting and removing the rock excavated from the shafts, and to avoid. the danger of using a swinging bucket operated from the boom of a derrick, the permanent head-frame, Fig. 5, to be equipped later for the use of elevator cages, was erected, with overhead hoisting sheaves and the regular elevator hoisting engines. One of these elevator wells was then fitted with guide-framing below the landing, and at the level of the landing a broad-gauge track crossed the elevator opening, with trap-doors fitted to insure safety. The spoil buckets were hoisted through this trap and landed on a flatcar run through the elevator opening before the hoisting rope was detached.
Water entered from numerous rock joints at various points in sinking the shafts, but not in such volume as to retard the progress of the work, except by the time lost in the removal by the derrick of the pumps and hose when blasting. This shaft water was readily handled in each shaft by one 350-gal. per min. steamdriven pump.
Two water rings were placed in each shaft as the sinking proceeded, in order to intercept the water seepage and prevent it from pouring on the men working below. Each ring was simply a 6-in. wooden shelf with gutter board sheathed with zinc, and a 3-in. pipe extending to the shaft bottom for drainage. Later, these leaks were stopped by grouting, while the driving of the tunnel was in progress.
Astoria Shaft.-At the bottom of the Astoria Shaft the design provided for an enlargement, about 41 ft. high, 34 1/2 ft. wide, and extending some 19 ft. beyond the neat shaft lines. This was to be used ultimately as an operating chamber for the distribution of gas, but it, as well as the short length of 100 ft. of tunnel in the direction of the future Manhattan Shaft at 111th Street, was utilized, during the construction of the tunnel, as a pump chamber and store-room. This enlargement extended 16 ft. below the tunnel invert, and, in addition, contained a 5-ft. circular sump 8 ft. deep, so that ample provision was afforded for the accumulation of the expected water flows and for settling any solid matter carried with the water.
Bronx Shaft Sump.-As the tunnel drained southward toward Astoria, a similar sump was not required in the Bronx Shaft, but ample precautions were taken by the construction of a rectangular sump, 21 ft. long, 12 ft. wide, and 81 ft. deep.
TABLE 2.-DIMENSIONS OF SHAFTS.
Bronx Heading.-The Bronx Shaft reached a sufficient depth for turning the beading on February 12th, 1911, and the latter was driven for a short length before completing the shaft and sump, so that tunnel driving really began on March 8th, 1911, and continued under normal conditions through sound, close-grained gneiss until August 29th, 1911. At that time the first appreciable delay occurred when the beading entered the expected contact seam of decomposed, waterbearing dolomite, '971 ft. from the shaft center, at which point the water depth in the river is 80 ft. below mean sea level, and the deep river channel corresponds in location to this dolomitic intrusion.
Astoria Heading.-At the Astoria end, work on the main tunnel did Dot begin until April 8th, 1911, when the headings of both the Bronx and Manhattan Tunnels were already turned. As in The Bronx, the headings were turned when the shaft reached the level of the floor of the top beading, and prior to completing the shaft sinking; the advance toward The Bronx continued until April 23d, 1911, during which time about 80 ft. of the Manhattan Branch Tunnel were driven. Owing to the large chamber arrangements necessary at the bottom of the Astoria Shaft, work on the main tunnel was not resumed from this end until June 23d, 1911, and it continued without incident until November 7th, 1912, a distance of 3 536 ft. from the shaft center.
Geology.-For the first 1200 ft. from Astoria the tunnel was driven through a bard, compact, and tough granitic gneiss, requiring heavy drilling and large consumption of powder. For the next 2 336 ft. the tunnel passed through the dolomite, and the passage through the easterly contact between the gneiss and the dolomite was made without any apparent disturbance or shear of the geological structure, a condition quite different from the contact encountered in the Bronx heading, where the geological change was featured by violent shear, accompanied by innumerable water fissures and excessive disintegration. At a point 3 536 ft. from the Astoria Shaft, this heading met the first indications of the water-bearing disintegration of the westerly contact between the gneiss and the dolomite. (Fig. 6.) The final results developed the fact that the entire width of this decomposed contact normal to the strike was some 150 ft., whereas the angle of crossing made THE ASTORIA TUNNEL
by the tunnel involved a total distance of 350 ft., measured on the axis of the tunnel, or 450 ft. between points of contact on the two side lines.
Excavation.-For the tunnel excavation, the top-heading-and-bench method was adopted, maintaining the bench some 50 ft. behind the heading. During the early part of the work the arch lining was not placed as the excavation advanced, these exposed sections being concreted later by using steel forms, and work was performed simultaneously with, and without hindrance to, the driving of the heading and bench. On deciding to place the arch lining along with the tunnel advance, a system of alternate excavating and concreting was adopted, with excellent results as to progress attained. This method consisted of excavating both the heading and bench from 8 A. M. Monday to 8 P. Al. the following Friday, the remainder of the 6-day week (Until 8 A. M. Sunday) being occupied in placing the concrete arch. By this method the maximum monthly progress was made, being 269 ft. of full tunnel section excavated and arch lined. The average progress maintained by this method was 53 ft. of heading, bench, and concrete arch per 6-day week, which, in volumetric measure, equalled 675 cu. yd. of neat-line excavation and 81 cu. yd. of neat-line concrete arch.
The average unit drilling and blasting quantities incidental to driving the tunnel 4 274 lin. ft., or 92% of the total length, under normal conditions, are presented in Table 4.
Overbreakcage.-Notwithstanding numerous experiments in the placing of drill holes for face of heading and bench, it was found that neither the gneiss nor the dolomite rock could be blasted without great 618 THE ASTORIA TUNNEL
irregularity in cross-section. The large quantities of blasting gelatine needed to pull the rock caused considerable overbreakage. Careful and repeated cross-section measurements, checked by the volume of concrete used to complete the lining, indicated that, notwithstanding the particular care taken, overbreakage outside of the neat line of minimum lining section in the sound sections of good rock amounted to 18% in the gneiss and 12 1/2% in the dolomite.
Drilling and Firing.-The typical arrangement and length of drill holes for blasting, for both heading and bench, are given in the diagram, Fig. 7, as applicable to both the gneiss and dolomite, under normal conditions. In all cases holes were started with 3-in. drills, which were reduced 1/4-in. in diameter with each 2-ft. advance, to a final diameter of 1 3/4-in. for the 12-ft. holes.
Fig. 7 also indicates graphically the arrangement of wiring, and the order of shooting, the holes.
Two double-strength "Victor" fuses were always used in regular course to insure the proper explosion of charges.
All firing was done by magneto batteries maintained about 500 ft. back of the heading, the wire connections to the heading always being strung on the side of the tunnel opposite that on which electric light wires were placed.
Both for heading and bench excavation #-in. steel shoveling plates were used on the floors for facilitating the mucking operations.
In the varied classes of rock throughout the tunnel headings the speed of drilling was 9.9 lin. ft. per hour per percussion machine. The bench drilling was easily maintained at the equivalent rate of progress.
Practically all the best known brands of drill steel furnished in the New York market were tried out on the work, resulting in the adoption of "ABC nontempering" steel, which, in these rocks and under the conditions, was found more durable and showed less breakage in dressing and drilling than the others.
The average progress of excavation attained during the tunnel driving under normal conditions, consisting of 4 274 lin. ft., or 92% of the ultimate length, and, based on the advance of one heading only, is given in Table 5. In this tabulation only the total accumulative time chargeable to excavation is considered, with a 24-hour actual working day as the unit. THE ASTORIA TUNNEL
In Driving through Dolomitic Formation, the Heading Holes were all lengthened I ft.
FIG. 7.
TABLE 5.-PROGRESS OF ROCK EXCAVATION IN TUNNEL UNDER NORMAL CONDITIONS.
Linear feet AVERAGE DAILY PROGRESS.
Based on the results in Table 5, the average monthly (30-day) advance of completed tunnel, excavation only, was 284 lin. ft., or 4054 actual cu. yd., in one heading.
Although the rate of progress was not as great as in other tunnels, of which reports have been published, the results obtained are thought to be very satisfactory, considering the general conditions of hoisting from a deep level, particularly as at no time was it considered by the management desirable to enter into the system of bonusing men to obtain record results. The entire work was carried out on a normal wage basis, without any attempt to offer other or special inducements to the labor to accomplish records. The progress of the work was perfectly regular and remarkably uniform, both at the Bronx and Astoria Shafts, up to the time of meeting the contact of decomposed rock at each end.
Concrete Arch.-The portion of sound rock tunnel driven from both the Bronx and Astoria Shafts was a bard, solid structure, but the rock indicated extensive jointing, with a tendency to scale away and for blocks of rock to fall without warning, a condition due to the character of the rock and also to the heavy blasting operations. Therefore what bad been anticipated to be an untimbered tunnel, necessitated early the consideration either of timbering or of carrying the lining along with the tunnel operations, in order to insure the safety of the workmen. After careful consideration of the advantages and disadvantages of these two methods, it was decided to construct the arch lining, and, on account of the original cross-section adopted, to THE ASTORIA TUNNEL 621
finish this arch lining to a skewback intended for the bottom concrete in which the permanent cast-iron gas mains were to be solidly embedded; this arch lining, hanging to the arch, was supported only on the irregularly jointed section of the rock walls.
Change of Design.-From the commencement of this work it had been contemplated to embed the cast-iron gas pipes solidly and permanently in concrete, and to make a floor above them, but, after 2 867 ft. had been lined in this way, the design was reconsidered and 6. revision made, whereby the pipes would be left exposed and a deck would be inserted above them. The tunnel has been left completed according to this plan (Fig. 8). This obviously necessitated, subsequent to the completion of other parts of the tunnel lining, cutting out portions of the arch lining and skewback which had previously been constructed. In the remaining length of the tunnel, the arch concrete was supported by timber sills on posts, the side-walls and invert not being placed until the complete excavation of the tunnel from end to end, when the sills and posts were removed as the wall lining proceeded.
This method of procedure was peculiar, in that, for the entire job, the arch lining was first executed. Then, when the tunnel was holed through, and the steel lining, hereinafter described, was being erected in the decomposed section, the invert was put in place by trimming the rock floor, in lengths ahead of concreting and laying the invert, to accurately placed side-forms. The forward end of each length of invert was laid out with a curved cross-form which gave accurately the section of the concrete to be laid; this was swept with straight-edges, using the last completed length of invert for the rear sweep and a wooden form for the forward end. The joints at the side-forms, as well as the cross-joints, were designed so as to lock thoroughly with the abutting concrete to be placed later. On the completed invert, after it had come to strength, was laid a track of 60-in. gauge, on which were operated two complete collapsible steel forms, each 50 ft. long; and these were used for the construction of the intervening side-walls, the two side-walls being concreted simultaneously. These forms, Fig. 9, were set up 100 ft. apart, and were advanced 100 ft. at each move, so that each form was used for alternate lengths of side-wall lining, thus permitting the setting up of one form while the concreting was proceeding in the other; this enabled continuous working operations.
THE ASTORIA TUNNEL
Although these forms ran on the 60-in. track laid on the tunnel invert, they had on the bottom frame a standard tunnel-gauge track, with a short incline at each end, so that other operations in the tunnel could proceed by running the tunnel cars through the lower portion of the steel frame. There was an elevator at each end of each form to raise the concrete cars to the upper level, so that they could be run to any point for dumping. The collapsible feature of the steel forms was obtained by using jacks and turnbuckles, and the upper platform of the forms, which was the dumping platform, was practically at the springing line of the arch where the joint was made between the side-walls and the arch already in place.
Before placing the forms the surfaces were well oiled. The moving was done by a small air-driven engine on the dumping platform. This engine was also used to operate the elevator. These forms worked admirably after they had been reconstructed, to some extent, to meet the conditions. The progress obtained with their use was one 50-ft. section each working day, and this rate was maintained with almost perfect regularity for a length of 3 310 ft. of tunnel.
The proper keying of the side-wall concrete to the arch skewback was accomplished, after a number of experimental methods were tested, by forming a wooden chute at the base of the joint and to a level of about 1 ft. above it, through which wet concrete was filled in and rammed into the joint with rods, in order to work the concrete into close contact with the arch skewback and enable the air bubbles to escape. This left a projecting lump of concrete at the joint, but, just prior to moving the forms forward, these chutes were removed and the projecting concrete was chipped off to the neat lines while* the concrete was still green. The results of this method were quite satisfactory.
Throughout the work of placing the concrete lining in the arch, side-walls, and inverts, it was considered, owing to the heavy pressures which would come on the lining by any seepage of water, that all voids between the arch section and the solid rock should be entirely filled with concrete. Plums of broken stone, however, were used freely where the concrete exceeded in thickness the neat section. Consequently, no loose packing of rock. behind the arch or walls was done in any portion. of the work, and, throughout the tunnel, on the com
pletion of the entire lining from end to end, grouting was carried out by the use of grout pipes which bad previously been left projecting from the lining so as to insure absolute solidity of the lining.
6.-TUNNELING UNDER ADVERSE CONDITIONS THROUGH DECOMPOSED
WATER-13EARING DOLOMITE.
As stated previously, no evidence of any shear or disintegration was disclosed at the eastern contact between the gneiss and the dolomite; but the western contact, as encountered from the Astoria end, was featured by some 354 ft. (along the tunnel center line) of highly decomposed dolomite with a heavy flow of water. It is interesting to note that, of this 354-ft. belt, the eastern side was advanced to a farther state of decomposition than the western, the rock mass containing countless seams of decomposed material and pockets of residual clay, all so disintegrated and distorted that the cleavage planes were not distinguishable, and though the strike maintained regularity, the dip was most irregular; in fact, at numerous points it was indeterminable.
The seams were so extremely decomposed that the material consisted only of a micaceous greensand, so porous that, on exposure, water quickly formed a free passage. Usually, these seams were little better than loose sand, although at times they choked the rock seam to such an extent as to yield practically no flow of water.
The first contact with the decomposed rock (which was met in driving the Bronx heading) seemed to indicate the likelihood of getting through the contact without serious difficulties, as the tunnel, after careful grouting, was advanced a considerable distance in rock, which, though excessively distorted and water-bearing, bad sufficient strength to carry the pressures without danger. At the same time, it was desirable to protect this heading as it advanced, and the arch was carried on heavy timbering in order to guard against falling rock. Having extended this length on timbering, it was thought that the insertion of cast-iron lining for this section might enable the work to advance successfully, particularly as the rock appeared to be getting stronger and harder beyond the first point of contact. As immediate delivery could be obtained of cast-iron segments made from the patterns from which the Pennsylvania North River Tunnel segments were constructed, a short length of 50 lin. ft. was cast, delivered, and promptly THE ASTORIA TUNNEL 627
erected in this wet, water-bearing, rock section. Then, inside the iron lining, concrete was inserted to the neat finished section adopted for the tunnel. This lined section remained in place in the finished work as an intermediate portion between two sections of cast-steel internal lining subsequently erected, which the following record describes.
The seams of greensand developed a maximum width of about 6 ft. at 3 750 ft. from the Astoria Shaft (Fig. 10). In this vicinity also, various pockets in the greensand seams were disclosed; one in particular being 4 ft. square and 20 ft. long, from which the previous water flows had evidently washed the sandy material.
On Plate XXIV, taken from the published Geological Survey, which presents the historical geology surrounding the Astoria Tunnel, it will be observed that there is a non-conformity in the plan defining the positions of the lines of contact as between the north and south sides of the Bronx Kills. This has been accounted for by assuming the existence of a cross-fault between Randall's Island and The Bronx, marking the course of the Bronx Kills.' Although no conclusive evidence of the existence of such a cross-fault was observed during the driving of the tunnel, indications of its possible existence and proximity were observed. The material encountered in the vicinity of the assumed cross-fault was so disintegrated and decomposed, and the conditions for observations were so unfavorable, that it is doubtful if such a fault would be readily recognized in passing through it.
It has been assumed, however, that the tunnel passed through this hypothetical cross-fault, as shown on Plate XXVI, this assumption being based on two important facts:
(1) It is quite natural that a cross-fault should have a limit of length, so that, in the case of this particular one, though it may extend through the Bronx Kills, as assumed, it may not necessarily extend to the path of the Astoria Tunnel. Such being the case, it seems possible that the actual fault at its eastern end terminates very close to the tunnel path, and that this end, instead of consisting of an abrupt fracture, is a gradual bend or distortion of the rock mass. That such a distortion was passed through is clearly shown on Plate XXVI. 'This. distortion of the. actual line, of contact between the 628 THE ASTORIA TUNNEL
hard micaceous gneiss on the west and the badly decomposed dolomite on the east, was encountered by an abrupt bend, 858 ft. from the center of the Bronx Shaft, and extended along the tunnel line some 70 ft. The maximum distortion was 10 ft., at a point midway along its length, at 'which point the hypothetical crossfault has been assumed.
(2) The rock structure encountered at this point (893 ft. from the center of the Bronx Shaft), in addition to being extremely porous, was greatly shattered, more so than at any other point in the tunnel. The dolomite, especially, appeared like a mosaic of inlaid tile slabs, quite small (3 to 4 sq. in.), and readily removed by hand, although the individual pieces were moderately bard. It was at this place (Fig. 11) that three large water-flows burst forth at various times. One was an average single flow of 1000 gal. per min., and in addition to this water, it carried in sediment large quantities of greensand and countless bard rock fragments. Here, too, it was necessary to terminate two beading drifts from the Bronx end. To the north of the assumed cross-fault, the actual -contact between the gneiss and dolomite consisted of a continuous small seam, I in. wide, of soft brown mud, and to the south of this point the contact plane was featured by a 3 to 4-ft. seam of hard, firm, bluish-green clay.
In this section of New York City, observation has established the existence of cross-faults, one at 138th Street and St. Nicholas Avenue, and one parallel to it, south of Hell Gate, and crossing the East River north of Blackwell's Island.
Water Flows.-The water-bearing fissures in the 354 ft. of decomposed dolomite were quite numerous, sixteen appreciable streams, each averaging from 300 to 10 000 gal. per min., under a full pressure head of 95 lb., having been encountered. These flows were usually quite sudden, and were accompanied by an inrush of greensand, the maximum flow of 10 000 gal. alone washing in 400 cu. yd. of sand, coal, etc.' and, during a period of 6 weeks, some 1700 cu. yd. of sand were washed into the Astoria heading. The establishment of a direct connection to the river bed was proved by the appearance of air bubbles on the river surface during grouting operations in the headings, as well as by the quantities of coal, wood, shells, bricks, etc., washed in at various times.
Method of Attack.-On account of the great depth of the tunnel and the resultant pressure head (95 lb. per sq. in.), any compressed-air methods of attack were out of the question, and, on account of the THE ASTORIA TUNNEL 631
necessities of the gas supply, it was not desired to go to any lower level in an attempt to pass under the disintegrated bed of dolomite. It was consequently necessary to drive the tunnel at the original depth and alignment, so that the proposition presented was a difficult one.
The theory on which tunneling operations were executed through the decomposed rock formation was the thorough exploration of the formations ahead by test holes and the consolidation of the rock by grouting. It was very obvious, in working in a narrow top heading, even by drilling numerous holes in the form of a fan, that a very limited area could be reached for consolidation, and as the percussion drill, working on more or less horizontal or dry holes, is only capable of extending to a depth of about 20 ft., the tunnel section which it is possible to consolidate is very short, particularly in view of the fact that there is a definite limit to the number of grout holes which can be drilled into the face of such a small heading (Fig. 12), and that considerable time must be allowed for cement grout to attain strength to permit of blasting safely. It was obvious, therefore, that a greater area of attack must be provided, and this was done on the theory of diverting the beading from the straight line to lines external to the final side lines of the tunnel, following the line of the strike of the sound rock as far as possible to permit of cross access to the decomposed strata. By doing this a long face could be exposed from which the drilling could proceed. Further, whenever the rock was sound and reasonably hard, a full and adequate anchorage for the grout pipes was naturally provided, but, if the rock was decomposed, seamy, and water-bearing, it was usually found to be so soft that proper anchorage could not be obtained for the grout pipes. In such cases it became necessary to construct buttress faces to the soft rock after exposure, before grout pipe holes could be drilled and pipes inserted. The work was carried out on the further theory that grouting above the extrados of the arch and outside the sidewalls, within the limit of the top heading, would in all reasonable probability cut off the direct access of heavy water flow and consequent danger of breaks occurring in the bottom. This was carried out to the end of the work and proved successful, as was illustrated by the fact that it was found unnecessary to do any grouting of considerable extent in order to take out the later bench excavation, the water-bearing seams having evidently been 632
THE ASTORIA TUNNEL
plugged at the higher level and the resistance of the decomposed material in the seams being adequate to resist any indirect access or flow.
Reference has been made to the necessity for buttressing the face of soft rock to provide anchorage for grout pipes, in the event of the rock being unsound and not giving adequate security for the insertion of such pipes. In such cases, owing to the high pressures involved, these concrete buttresses were allowed to set for practically two weeks on each occasion before they could be utilized.
When such buttresses were set and thoroughly hard, or when sound rock existed, the process of preparing the grout pipes for use, as indicated by Fig. 13, was generally as follows:
The drilling was commenced with 6-in. percussion drills, and entered from 3 to 4 ft. deep into the concrete buttress or hard rock. A piece
B
T-eleseop 1100 aggluo _ap~ed wit
DIAGRAM ILLUSTRATING INSERTION OF
GROUT PIPES IN ROCK FOR HIGH-PRESSURE GROUTING.
FIG. 13.
of 4-in. pipe, about 1 ft. longer that the depth of the bole, was then
wrapped tightly with bagging and wound around with marline to secure
it tightly to the pipe, the quantity of bagging being put on up to
practically the dimensions of the 6-in. hole. The wrapped pipe was
then inserted in the bole, and driven to its extreme end, no thread,
flange, or other protector being put on the inner end of this first
length of pipe. When thus inserted the wrapping was caulked back
into the bole, and steel wedges were inserted and driven tightly between
the 6-in. hole in the rock and the body of the 4-in. pipe. These wedges
were driven so hard as to indent the 4-in. pipe and secure it rigidly.
A screwed flange was then put on the outer end of this 4-in. nipple
and an open gate-valve was attached to the flange, in order to provide
a clear opening equal to the diameter of the pipe. Drilling then proceeded through the gate-valve, commencing with 3-in. percussion drills and telescoping if necessary, as the drilling advanced. The length of the test holes rarely exceeded 20 ft. Of course, it will be understood that where the drilling was carried out from narrow cross-headings, and the holes were drilled at an angle with the strike, the effective length was reduced on account of the lack of clearance to insert long drills.
Reference is made in the following pages to the use of the diamond drill. On first meeting the decomposed rock at the Bronx end, a
7/8-in. diamond drill was set up in the heading and holes were driven, one at the elevation of the heading, horizontally at right angles to the strike of the rock, in order to intercept the seams at right angles to the general strike; and two holes straight ahead on the axis of the tunnel, one horizontally and one pointing downward. The bole at right angles to the strike of the rock was extended in only some 50 ft., but the long holes ahead were extended for about 200 ft., and these drill holes gave an excellent idea regarding the conditions to be met, as far as drilling could be accomplished with the small machine used. At a later date, a heavier diamond drill, capable of drilling 3-in. holes, was used, and gave much more satisfactory results. The use of the diamond drill for long holes was extended considerably, previous to and after the flooding of the tunnel, giving long penetration and providing a means for grouting at considerable distances. The later diamond drill outfit was of the Sullivan type, of heavy construction, and proved to be admirably adapted to work of this character. In the entire construction through this decomposed rock section, some 3 300 test holes were drilled, aggregating a length of about 43 300 ft. by percussion drills, in addition to seventeen diamond drill borings aggregating a length of 1500 ft.
Grouting in the Astoria Tunnel has probably exceeded very greatly that in any other work executed, in consolidating soft fissured rock, and in stopping extensive and large leaks at high pressure. Grouting at a higher pressure was done on the Catskill Aqueduct, though the volume of inflow was probably very much less. In the case of the Astoria Tunnel, the grouting was a continuous operation for consolidating and cementing decomposed rock throughout the entire length of the sheared contact between the gneiss and dolomite, and as such 634 THE ASTORIA TUNNEL I
served the purpose, a. result which has not, it is thought, been approached or attempted in other work. The work involved was the conversion of a rotted and decomposed rock filled with fissures into a solid and substantial substance through which the tunnel could be driven and, incidentally, at the same time, stop the influx of water. In the grouting operations it was found to be almost impossible to grout into a seam of decomposed dolomite sand. This would apply equally to any other sand or material filling seams, which is likely to be scoured out by a flow of water. On meeting a seam filled with decomposed rock sand, the indications on this work were, that the sand was practically impervious, but, after a short exposure to water flow, the soft rock abutting on the seam became water-loaded and softened; then the passage of small quantities of water loosened and demoralized the sand filling the seams, following which the sand was scoured out, thus forming an open water channel. Therefore, it was found particularly desirable, after drilling grout holes into a seam filled with sand, to rake the sand out with rods, as far as was feasible, and then to allow these test holes to flow freely, by blowing with highpressure air or in any other way, the idea being to get the sand to flow with the water and thus empty the seam, after which the grouting operation was much more thorough, successful, and permanent. When these seams were emptied of the sand and grouted at high pressure the result was practically a solid rock formation, and the tunnel could be built by blasting operations with security; whereas a seam not so clear of sand would resist the flow of grout and be a menace to the future advance of the tunneling operations.
Glass Tunnel Model.-In order to present clearly the actual geological information, disclosed both by direct observations and test-bole exploration, so as to determine the most advantageous direction of drift attack, an unusual method was designed by the field engineers and applied to this work. This consisted of a glass plate tunnel model. As the general strike of the rock containing the numerous seams of disintegration was nearly parallel to the tunnel line, and the dip was decidedly irregular, it was impracticable to plot the geological data on drawings and still have them clear and of working value, as they could not conveniently be superimposed. This condition was admirably simplified by this glass plate model, constructed at the tunnel works. This method of geological plotting proved quite successful, as
the conditions of the explored rock Structure were clearly presented at a glance, proving an important factor in the determination of the various methods of attack adopted.
This model consisted of a series of glass plates, 16 in. square, placed upright in a skeleton frame, 12 ft. long, and arranged to scale corresponding to the 5-ft. tunnel stationing. As the tunnel driving proceeded, the actual lines, drifts, bulkheads, timbers, iron rings, etc., together with the exposed disintegrated seams and the testhole information, were all painted with oil colors on the plates, this work being always maintained up to date, so that the conditions actually existing were always visible.
Blasting was naturally performed with very light charges, necessitated by the unsound strata, as water flows were easily started, not only by the shattering of the rock in their immediate vicinity, but by the concussions from blasting in sound rock at a considerable distance from the dangerous strata. In one instance, at the Astoria end, a 50-ft. length of drift was temporarily lost by this latter condition. The caution and care with which the rock was thoroughly sounded and scaled immediately following blasting is shown by the fact that no serious injuries or fatalities occurred, which is regarded as unusual, in view of the extremely unsound condition of the rock.
Grouting.-During the early stages of adverse tunneling, the grouting of the waterbearing fissures was performed with ordinary grout machines, using a neat Portland cement mortar at a pressure varying from 100 to 200 lb. per sq. in. This made it necessary, in September, 1911, to put in a steam-driven, straight-line booster at each plant. Grouting continued with this pressure for some months, but it became apparent as the work proceeded that an air pressure of even 200 lb. was insufficient to insure success.
For successful grouting into narrow seams it is essential to obtain a high initial velocity of grout flow, in order to overcome the frictional resistance; consequently, to grout against a water head of approximately 100 lb. per sq. in., more than 100 lb. additional pressure was found to be necessary. The increase of the starting pressure insured the initial flow, and the expansion of the air, even down to 200 lb. or less, was adequate to maintain the continuity of the flow. The use of the high pressure also insured that the seam would be packed 636 THE ASTORIA TUNNEL
more tightly and that the grout would be more dense when it had taken its ultimate set and attained strength.
Consequently, an additional steam-driven straight-line booster was erected at the Astoria end in November, 1912, this machine being capable of developing an air pressure of 500 lb. per sq. in., for which special grout machines were constructed. The injection of cement into the water-bearing fissures at this pressure (500 lb.) was exceptionally effective, and was undoubtedly a valuable factor in the ultimate success in driving through the unsound water-bearing rock.
The disintegrated rock structure (Fig. 14) frequently necessitated the construction of concrete wall buttresses, in order to withstand the high grouting pressures -used, and considerable difficulty was experienced during the early stages of the work in preventing the injected cement from washing out of the water-bearing crevices. Unsuccessful efforts were made to prevent this by mixing oats and bran with the cement mortar, as used in other subaqueous tunnels.
Another method introduced, which proved of great benefit and aided in securing the injected cement, consisted of the addition of a handful of fine-cut cotton waste to each batch of grout, which by fibrous reinforcement of the cement held it in place while it was setting. During lengthy grouting periods, two machines were used alternately in series, thereby maintaining a continuous injected flow.
The special machines for grouting with 500 lb. air pressure 'were designed and assembled at the tunnel works. The general arrangement and capacity were identical with the riveted pans for 200 lb. pressure, with the exception of some details designed to resist the higher pressure. The entire pan and the cover were made of cast steel, carefully annealed and tested, and having no joints other than that of the cover. The heads were made in convex form; one end was cast in one piece with the body, and the other was a cast-steel removable cover with male and female bolted flanged joints. In operation these pans were very reliable, and, when required, one pan was operated 25 hours without a stop, and discharged 4 500 bags of cement at pressures varying from 350 to 500 lb. Extra heavy 2-in. screwed pipe was used for the transmission of the high-pressure air from the engineroom to the heading, with the exception of the first 600 ft., where extra heavy 4-in. pipe was used to give greater storage capacity. Special 1-in. hose was used to make the connection between the air line
pitch. Knox standard couplings were fitted to each end. A special 2-in. grout hose was used, this also being of 6-ply rubber and canvas, wound with 3 -in., half-round wire, '-in. pitch.
Bulkheads.-Prior to entering the belt of disintegration at each end, adequate precaution was taken to guard against flooding, by the construction of full tunnel section emergency bulkheads, well back from the point of attack. As the headings proceeded, additional emergency bulkheads were built as close to the heading as the work permitted. These were to the heading size only, as the bench was not removed through this soft-ground section until after the meeting of the headings.
The first emergency bulkhead of full tunnel section, built at the Bronx end, was of a concrete buttress type, fitted with two guillotine doors and not reinforced. A guillotine type of door was considered in the first design to be the most certain in action. The clear openings of these doors were about 5 ft. square, of such size as to permit a tunnel car to pass through. These doors were never actually closed or used, but in constructing later doors it was considered preferable to adopt a simpler form of top-hinged flap, so that, in case of necessity, by cutting away the wire rope supports, they would drop readily into position, this type being not only cheaper to build but simpler in operation, and throughout the remainder of the work such doors were used. Some of the full tunnel section bulkheads, as well as the emergency bulkheads, were reinforced and some were not, the design being modified for each individual case. These doors were used only occasionally, and, as hereinafter stated, gave excellent results in operation. Owing to the necessity for knowing that these doors were always in working order, and for trying them out from time to time, they were equipped on the outer side with tripping devices and rams operated by compressed air from the tunnel line for raising them when they were desired to be opened. Valve arrangements were provided so that the door could be operated from inside or outside; thus, in the event of any one being accidentally left on the wrong side, it was possible for him to open the door and release himself.
Numerous solid beading and wall buttresses were constructed from time to time, for the reasons previously stated. This concreting, of 640 THE ASTORIA TUNNEL
course, necessitated frequent and unusual delays, the accumulated lost time incurred by this work accounting for at least 50% of the time required to tunnel the 354 ft. of unsound rock, as generally from 10 to 14 days were allowed for the concrete to set sufficiently for 500 lb. grouting pressure.
During the bench removal, after holing through the headings, full section tunnel emergency bulkheads were necessary, these being generally about 14 ft. thick. As the bench excavation proceeded, these bulkheads were kept fairly close to the point of work, in order to facilitate transportation. The continual construction of heavy timber runways was necessitated by the fact that it was desirable to place the emergency bulkhead doors well above the invert, in order to prevent them from becoming clogged by the sandy sediment in the inflowing water. Drainage through the bulkheads was provided by 6 and 8-in. pipes, passing below the doorways, but at a sufficient height from the bottom to prevent them from being clogged by the sand. These drains were equipped on the shaft side with standard gate-valves to permit of their being closed.
Bench Excavation.-After the meeting of the headings, on July 17th, 1913, efforts were concentrated on the removal of the remaining bench, which, at that time, amounted to 474 lin. ft. This length of excavation was attacked simultaneously from the Astoria and Bronx sides. In the first 237 ft. on the Astoria side only good sound dolomite was encountered, no trouble was experienced, and the immediate lining of this excavation was not necessary. On the Bronx side the lower west portion of the bench face consisted of hard soun