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+The Project Gutenberg EBook of Transactions of the American Society of
+Civil Engineers, Vol. LXVIII, Sept. 1910, by James H. Brace and Francis Mason
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Transactions of the American Society of Civil Engineers, Vol. LXVIII, Sept. 1910
+       The New York Tunnel Extension of the Pennsylvania Railroad.
+       The Cross-Town Tunnels. Paper No. 1158
+
+Author: James H. Brace and Francis Mason
+
+Release Date: August 13, 2006 [EBook #19037]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK TRANSACTIONS OF THE AMERICAN ***
+
+
+
+
+Produced by Juliet Sutherland, Jacqueline Jeremy and the
+Online Distributed Proofreading Team at http://www.pgdp.net
+
+
+
+
+
+
+
+
+
+AMERICAN SOCIETY OF CIVIL ENGINEERS
+
+INSTITUTED 1852
+
+
+TRANSACTIONS
+
+Paper No. 1158
+
+
+THE NEW YORK TUNNEL EXTENSION OF THE
+PENNSYLVANIA RAILROAD.
+THE CROSS-TOWN TUNNELS.[A]
+
+BY JAMES H. BRACE AND FRANCIS MASON, MEMBERS, AM. SOC. C. E.
+
+
+
+
+In this paper, it is proposed to describe the construction of the
+tunnels extending eastward from the easterly extension of the Terminal
+Station to the permanent shafts east of First Avenue.
+
+They were located under 32d and 33d Streets from the station to Second
+Avenue, and thence, curving to the left, passed under private property
+and First Avenue to the shafts, as described in a preceding paper.
+Typical cross-sections of the tunnels are shown on Plate XII.[B]
+
+On May 29th, 1905, a contract was entered into with the United
+Engineering and Contracting Company for the performance of this work.
+This contract provided that work on each pair of tunnels should be
+carried on from two shafts. The first, here referred to as the First
+Avenue Shafts, were located just east of that avenue and directly over
+the line of the tunnels; the other two, called the Intermediate Shafts,
+were located on private property to the north of each pair of tunnels in
+the blocks between Fourth and Madison Avenues. It was originally
+intended to do all the work of construction from these four shafts.
+Workings were started both east and west from the Intermediate Shafts,
+and those to the west were to be continued to the Terminal Station.
+After the change of plans, described in a previous paper, it was decided
+to sink a third shaft on each line. These were known as the West Shafts,
+and were located between Sixth and Seventh Avenues. Finally, it was
+found necessary to build a portion of the tunnels on each line west of
+Sixth Avenue in open cut. The locations of the shafts are shown on Plate
+XIV.[C]
+
+The First Avenue shafts were built by S. Pearson and Son, Inc., for the
+joint use of the two contractors, as described in the paper on the
+tunnels under the East River. While the shafts were being sunk, the
+full-sized tunnels were excavated westward by the contractor for the
+river tunnels for a distance of 50 ft., and top headings for 50 ft.
+farther. By this means, injury to the caissons and to the contractor's
+plant in the shafts by the subsequent work in the Cross-Town Tunnels was
+avoided. The west half of the shaft was for the exclusive use of the
+contractor for the Cross-Town Tunnels.
+
+
+CONTRACTOR'S PLANT.
+
+The method of handling the work adopted by the contractor was, broadly
+speaking, as follows: Excavation was usually carried on by modifications
+of the top-heading and bench method, the bench being carried as close to
+the face as possible in order to allow the muck from the heading to be
+blasted over the bench into the full section. The spoil was loaded into
+3-yd. buckets (designed by the contractor and hereinafter described), by
+steam shovels operated by compressed air, and hauled to the shafts by
+electric locomotives. Electrically-operated telphers, suspended from a
+timber trestle, hoisted the buckets, and, traveling on a mono-rail
+track, deposited them on wagons for transportation to the dock. Arriving
+at the dock, the buckets were lifted by electrically-operated stiff-leg
+derricks and their contents deposited on scows for final disposal. The
+spoil was thus transported from the heading to the scow without breaking
+bulk.
+
+When concreting was in progress, the spoil buckets were returned to the
+shafts loaded with sand and stone. The concrete materials were deposited
+in storage bins placed in the shafts, from which they were fed to the
+mixers located at the foot of the shaft about on a level with the crown
+of the tunnels. The concrete was transported to the forms in side-dump,
+steel, concrete cars, hauled by the electric locomotives.
+
+Electrical power was adopted largely on account of the restricted area
+at the shaft sites, where a steam plant would have occupied considerable
+space of great value for other purposes. The installation of a steam
+plant at the Intermediate Shafts, which were located in a high-class
+residential district, would have been highly objectionable to the
+neighboring property owners, on account of the attendant noise, smoke,
+and dirt, and, in addition, the cost of the transportation of fuel would
+have been a serious burden. Except for the forges and, toward the last,
+the steam locomotives, not a pound of coal was burned on the work. The
+use of the bucket and telpher also eliminated most of the objectionable
+noise incident to the transfer of spoil from tunnel cars to ordinary
+wagons at the shaft sites. Power plants were installed at the North
+Shaft near First Avenue and at the rear of the 33d Street Intermediate
+Shaft.
+
+_First Avenue Plant._--Fig. 1, Plate LVIII, is a general view of the
+First Avenue plant. The power-house at the corner of 34th Street and
+First Avenue supplied compressed air for operating drills, shovels,
+pumps, and hoists in the tunnels driven from the river shafts, and in it
+three Laidlaw-Dunn-Gordon compressors were installed. The largest was a
+32 by 20 by 30-in., two-stage, cross-compound, direct-connected to a
+Fort Wayne 480 h.p., 230-volt, direct-current, constant-speed motor run
+at 100 rev. per min. This compressor was rated at 2,870 cu. ft. of free
+air per minute at a pressure of 100 lb. It was governed by throttling
+the suction, the governor being controlled by the pressure in the air
+receiver and the motor running continuously at a constant speed. The two
+others were of similar type, one was 22-1/2 by 14 by 18-in., rated at
+1,250 cu. ft. of free air at a pressure of 100 lb., the other was 16 by
+10 by 18-in., rated at 630 cu. ft. They were fitted with 9-ft.
+fly-wheels, and were driven at 150 rev. per min. by 105-h.p., General
+Electric, 220-volt, compound-wound, direct-current motors running at 655
+rev. per min. The larger of these two compressors was driven by two of
+the motors belted in tandem, and the smaller was belt-connected to a
+third motor. The compressors were water-jacketed and had small
+inter-coolers, the water supply for which was itself cooled in a Wheeler
+Condenser and Engineering Company's water-cooling tower. The pump and
+the blower operating it were electrically driven.
+
+The telphers, used for hoisting muck from the tunnels and for lowering
+supplies, were each hung from single rails on a timber trestle, about
+40 ft. high, spanning and connecting the two shafts. One machine was
+provided for each shaft, and where their tracks crossed 33d Street they
+were separated sufficiently to permit the machines to pass each other.
+At this point, and covering the street, a large platform was provided,
+on which the trucks were loaded and unloaded (Fig. 2, Plate LVIII), and
+from which they descended by an incline on First Avenue leading south to
+32d Street. The platform also covered practically all the yard at the
+South Shaft and materially increased the available working area. The
+telphers were built by the Dodge Cold Storage Company, and were operated
+by a 75-h.p. General Electric motor for hoisting and a 15-h.p. Northern
+Electric Company motor for propulsion. Their rated lifting capacity was
+10,000 lb. at a speed of 200 ft. per min.
+
+The carpenter shop and machine-shop, both of which served the entire
+work, were conveniently located in small buildings on the loading
+platform. In the former the saws were each run independently by small
+electric motors suspended under the platform. The heavy forms and form
+carriages used in lining the tunnels with concrete were fabricated and
+stored on the platform outside. The machine-shop lathes, etc., were all
+belted to one shaft driven by an 8-h.p. General Electric motor. Above
+the machine-shop was a locker-room and below it on the street level was
+the main blacksmith shop for the work. Subsidiary blacksmith shops were
+located at each of the other shafts. The storeroom and additional
+locker-rooms were located above the power-plant in the North Shaft yard,
+and isolated from the other structures was a small oil-house. Additional
+storage space was provided by the contractor on 32d Street just west of
+First Avenue by renting three old buildings and the yards in the rear of
+them and of the Railroad Company's cement warehouse adjacent. Here
+electric conduits, pipe, castings, and other heavy and bulky supplies
+were stored.
+
+During excavation the headings were supplied with forced ventilation
+through 12-in. and 14-in. No. 16, spiral-riveted, asphalted pressure
+pipes, canvas extensions being used beyond the ends of the pipes. A No.
+4 American Blower, located at the top of each shaft and driven by a
+15-h.p. General Electric motor, supplied the air.
+
+[Illustration: PLATE LVIII, FIG. 1.--VIEW OF FIRST AVENUE PLANT.]
+
+[Illustration: PLATE LVIII, FIG. 2.--TELPHER STRUCTURE AND LOADING
+PLATFORM, FIRST AVENUE SHAFT.]
+
+[Illustration: PLATE LVIII, FIG. 3.--HEADWORKS AT 33D STREET:
+INTERMEDIATE SHAFT.]
+
+[Illustration: PLATE LVIII, FIG. 4.--LOADING SPOIL ON BARGES, 35TH
+STREET PIER.]
+
+A concrete-mixing plant was placed in each shaft, the mixer being
+located high enough to discharge into cars at about the level of the
+springing line of the arch. Above the mixers were the measuring
+hoppers set in the floor of a platform which was large enough to carry
+half a day's supply of cement. At the South Shaft the cement was
+delivered to this floor from the loading platform through a spiral steel
+chute; at the North Shaft it was lowered in buckets by the telpher. The
+sand and stone were drawn into the hoppers through short chutes from the
+base of the storage bins which occupied the remaining height of the
+shaft--about 50 ft. At the South Shaft the bins were of concrete and
+steel, about 6 by 12 ft. in section, and attached to the central wall of
+the caisson. Sand and stone were delivered into them from dump-wagons on
+the loading platform. At the North Shaft steel-plate bins were used, and
+were supplied with material by the buckets handled by the telpher. The
+mixers were No. 5 Smith, belt-connected to 25-h.p. motors, and about 0.8
+cu. yd. of concrete was mixed at a batch. The concrete cars were steel
+side-dumpers of the Wiener or Koppel type.
+
+In order to be able to continue concreting during the winter, when
+neither sand nor stone could be obtained by water, practically all the
+space under the loading platforms in the South Shaft yards not occupied
+by the blacksmith shop was filled with these materials, which were
+placed in storage in the late fall.
+
+_Intermediate-Shaft Plant._--The air-compressing plant was located at
+the rear of the 33d Street Intermediate Shaft, and supplied air for
+driving the tunnels east and west from the Intermediate Shafts on both
+32d and 33d Streets. Two compressors, the same as the large
+Laidlaw-Dunn-Gordon machine at First Avenue, were installed here, with a
+similar water-cooling tower.
+
+Both shafts were on private property, owned by the Railroad Company, on
+the north side of the streets, and each was equipped with two telphers
+supported on timber trestles, similar to those at First Avenue. Here,
+however, the buckets were placed on wagons standing at the curb, as
+shown by Fig. 3, Plate LVIII.
+
+Blowers for ventilation were installed at each shaft, as at First
+Avenue, and, after the excavation had proceeded some distance, small
+blacksmith shops, for sharpening drill steel and making minor repairs,
+were located in the tunnels near the shafts.
+
+The concrete plant in each shaft was similar in arrangement to those at
+First Avenue, but the storage bins had wooden walls made of 2 by 4-in.
+and 2 by 6-in. scantling nailed flat on each other.
+
+The contractor's office on 33d Street backed up against the 32d Street
+shaft site, and the basement was used as a storeroom for supplies for
+both shafts.
+
+After the decision to do part of the work between Sixth and Seventh
+Avenues in open cut, an 8-in. air main was laid in 33d Street to the
+West Shafts, and air was supplied from the Intermediate Shaft for work
+on both streets in that neighborhood.
+
+_West-Shaft Plant._--West of Sixth Avenue, between 32d and 33d Streets
+and adjacent to the open-cut sections, the Railroad Company obtained
+from the Hudson and Manhattan Railroad Company the use of a large area
+from which the buildings had recently been removed, and gave the use of
+it to the contractor. This was of great value in prosecuting the west
+end of the work. The two West Shafts were located in the streets and
+were supplied with short timber trestles similar to those at the
+Intermediate Shafts. One telpher was taken from each of the Intermediate
+Shafts to operate at each of the West Shafts. In addition, a number of
+stiff-leg derricks were set up along the open-cut section, and were
+operated by Lidgerwood or Lambert air hoisting engines, or by electric
+motors, as circumstances dictated. A 15-ton Bay City locomotive crane
+was also used along part of the open-cut work on 32d Street.
+
+Several concrete plants were installed at points along the open-cut
+section, and were moved from place to place, the same general
+arrangement being adopted as at the plants already described. No. 3 and
+No. 4 Ransome mixers were used, and were generally set up at about the
+level of the top of the arch. The sand and stone storage bins were made
+of scantlings spiked together, and were necessarily rather shallow on
+account of the proximity of the tunnels to the street surface.
+
+_Thirty-fifth Street Pier._--For the receipt and disposal of materials
+at the 35th Street pier, four stiff-leg derricks, operated by electric
+hoisting engines, were installed. Two were used in lifting the muck
+buckets from the wagons and dumping their contents on the scows for
+final disposal (Fig. 4, Plate LVIII); and the other two were fitted with
+clam-shell buckets for unloading sand and broken stone from barges and
+depositing the materials in large hoppers, from which they were drawn
+into wagons for transportation to the various concrete plants. A large
+part of the cement (all of which was supplied by the Railroad Company)
+was also unloaded at the 35th Street pier and hauled directly to the
+work, the surplus being stored temporarily in the Company's cement
+warehouses on 32d, 33d and 35th Streets, near First Avenue, from which
+it was drawn as required. On the dock was located the main powder
+magazine, a small concrete structure. Considerable use was also made of
+neighboring piers for unloading electric conduits, lumber, steel, etc.
+
+[Illustration: FIG. 1. SPECIAL STEEL BUCKET
+    PLAN OF BUCKET
+    END VIEW
+    SIDE VIEW OF BUCKET
+    SECTION AT A-A]
+
+_Tunnel Plant._--The spoil buckets, designed by D. L. Hough and George
+Perrine, Members, Am. Soc. C. E., were a novel feature of the work.
+These buckets are shown in detail in Fig. 1 and various photographs.
+They were of 3 cu. yd. capacity and were split longitudinally, the two
+halves being pinned at the apices of the ends. For lifting, they were
+suspended from eyes at that point, and, when dumping, trip ropes were
+hooked into eyes at the bottom of each side; lifting the trip ropes or
+lowering the hoisting rope split the bucket, as shown in Fig. 4, Plate
+LVIII, and dumped the contents. They were transported in the tunnel on
+flat cars, and in the street on wagons, both cars and wagons being
+provided with cradles shaped to receive the bottom of the bucket.
+
+In the tunnels the loading was done with air-operated steam shovels,
+four (Model 20) Marion shovels being used at various points of the work.
+In Fig. 1, Plate LIX, one of these is shown loading the bucket. The cars
+were hauled by General Electric, standard, 10-ton, mine locomotives, the
+current for which was taken at 220 volts from a pair of No. 00 copper
+trolley wires suspended from the roof of the tunnel. The collector was a
+small four-wheeled buggy riding on the wires and connected to the
+locomotive by several hundred feet of cable wound on a reel for use
+beyond the end of the trolley wire. Two 8-1/2-ton, Davenport, steam
+locomotives were also used in 32d Street, toward the end of the work,
+after the headings had been holed through and the tunnels would quickly
+clear themselves of gas and smoke. The steam shovels were supplemented
+by two Browning, 15-ton, locomotive cranes, which handled the spoil in
+places where timbering interfered with the operation of the shovels. All
+tracks were of 3-ft. gauge throughout and laid with 40-lb. rails.
+
+Practically all the heavy drilling was done with Ingersoll drills (Model
+E 52), the trimming being largely done with jap and baby drills. A large
+number of pumps were used at various points on the work, and practically
+all were of Cameron make, the largest ones at the shaft being 10 by 5 by
+13-in. The grout machines were of the vertical-cylinder, air-stirring
+type.
+
+
+SHAFT SINKING.
+
+The sinking of the Intermediate Shafts was the first work undertaken by
+the contractor.
+
+The 33d Street Shaft was 34.5 ft. long, 21 ft. wide, and 83 ft. deep.
+The rock surface averaged 5 ft. below the ground surface. Sinking was
+started on July 10th, 1905, and was completed on October 3d, 1905, the
+rock being hard and dry. The average daily rate was 0.73 ft. and an
+average of 17.1 cu. yd. were excavated per day, with two shifts of 8 hr.
+each. The first shift started at 6 A. M. and the second at 2.30 P. M.,
+ending at 11 P. M. These hours were adopted in order to avoid undue
+disturbance during the night.
+
+[Illustration: PLATE LIX, FIG. 1.--AIR-OPERATED STEAM SHOVEL USED IN
+TUNNEL.]
+
+[Illustration: PLATE LIX, FIG. 2.--TIMBERING IN TOP HEADINGS ABOVE
+I-BEAMS.]
+
+[Illustration: PLATE LIX, FIG. 3.--FIRST SECTION OF CONCRETE LINING AT
+FIFTH AVENUE.]
+
+[Illustration: PLATE LIX, FIG. 4.--TIMBERING AND RUBBLE MASONRY OVER
+I-BEAMS.]
+
+Before blasting the first lift of rock, channel cuts 5 or 6 ft. deep
+were made along the sides of the shaft, in order to avoid damage to the
+walls of neighboring buildings. Timbering was required for a depth of
+only 10 ft. below the surface of the ground.
+
+A drift, 30.6 ft. long, 17 ft. wide, and 27 ft. high, connected the
+south end of the shaft with the tunnels. The drift was excavated in
+three stages, a top heading and a bench in two lifts. While blasting the
+cut in the top heading, there was enough concussion to break glass in
+the neighboring buildings. The use of a radialax machine reduced the
+concussion somewhat, but it was very quickly abandoned on account of the
+length of time required for the drilling.
+
+The construction of the 32d Street Shaft was quite similar to the one on
+33d Street. It was 31.5 ft. long, 20.5 ft. wide, and 71 ft. deep. The
+depth of earth excavation averaged 19.5 ft. The rock in this shaft was
+seamy and not quite as hard or dry as that in 33d Street, and timbering
+was required for practically the full depth to the crown of the drift.
+Sinking was started on May 15th, 1905, and was completed on October
+26th, 1905. The daily average rate was 0.30 ft. in earth and 0.52 ft. in
+rock. The drift was excavated in much the same manner as the one in 33d
+Street, but the rock being softer the radialax machine was not used.
+
+
+TUNNEL EXCAVATION.
+
+During the early part of the work, the contractor devoted his entire
+attention to the work of excavation. Nearly all the excavation east of
+Fifth Avenue was done before any of the lining was placed. At a number
+of points west of Fifth Avenue and at a few points to the east the
+nature of the rock was such that the two operations had to be done
+simultaneously.
+
+_Single-Tunnel Method._--For an average distance of 350 ft. west from
+the First Avenue Shafts there were four single tunnels. The rock was
+sound and comparatively dry. A top heading of the full size of the
+tunnel and about 8 ft. high was first driven. It was drilled by four
+drills mounted on two columns, and was blasted in the ordinary way. The
+bench was about 13 ft. high. Tripod drills, standing on the bench,
+drilled the usual holes, but, owing to the lack of head-room, steels
+long enough to reach the bottom of the bench could not be used. Tripod
+drills were set as low as possible at the foot of the bench and drilled
+lifting holes. These holes were inclined downward from 10° to 15° to the
+horizontal, and were spaced to converge at the location of the drainage
+ditches. The heading was usually driven from 10 to 20 ft. in advance of
+the bench. At this distance a large part of the muck from the heading
+was shot backward over the bench. In the single tunnels the muck was
+loaded by hand.
+
+_Twin-Tunnel Methods._--From the end of the single-track tunnel westward
+to Fifth Avenue on 33d Street, and to Madison Avenue on 32d Street, with
+some exceptions, each pair of tunnels was excavated for the entire width
+at one operation. Three different methods of work were extensively used.
+They were the double-heading method, the center-heading method, and the
+full-sized-heading method, and these differed only in the manner of
+drilling and blasting. The bench was usually within 10 or 15 ft. of the
+face of the heading, and was drilled and fired in the same way as in the
+single tunnels. After the installation of the permanent plant, most of
+the muck was handled by steam shovels.
+
+In the double-heading method, shown on Plate LVII, the top headings for
+each tunnel of the pair were driven separately, leaving a short rock
+core-wall between them. The headings were drilled from columns in the
+manner described for the single tunnels. The temporary rock dividing
+wall between the headings was drilled by a tripod drill on the bench of
+one of the headings, and was fired with the bench.
+
+In the center-heading method, also shown on Plate LVII, only one heading
+was driven. It was rectangular in shape, about 8 ft. high and 14 ft.
+wide. It was located on the center line between the tunnels. In general,
+the face was from 6 to 12 ft., or the length of one or two rounds, in
+advance of the remainder of the face at the top. The center heading was
+drilled by four drills mounted on two columns. By turning these drills
+to the side, they were used for holes at right angles to the line of the
+tunnels, by which the remainder of the face of the heading was blasted.
+By turning the drills downward, the bench holes under the center heading
+were also drilled. The center heading explored the rock in advance of
+the full-width heading, and gave a good idea as to the care needed in
+firing.
+
+For the full-width-heading method, Fig. 2, ten drills were mounted on
+five columns set abreast across the face. Holes were drilled to form a
+cut near the center line between the tunnels. The remainder of the holes
+were located so that they would draw into the cut. The bench was
+frequently drilled from the same set-up of columns by turning the
+drills downward. In sound rock this method proved to be the most rapid
+of any.
+
+Practically all trimming was left until immediately before the
+concreting. It was then taken up as a separate operation, but proved to
+be costly and tedious, and a hindrance to the placing of the lining.
+
+_Materials Encountered._--All the rock encountered was the familiar
+Hudson schist, but it varied widely in its mineral constituents and in
+its physical characteristics. In many places where the rock surface was
+penetrated, a fine sand was found that was probably quicksand. The
+material above the rock in the open-cut sections was mostly sand.
+
+[Illustration: FIG. 2. METHOD OF EXCAVATING WITH FULL-WIDTH HEADING
+CROSS-TOWN TUNNELS, MANHATTAN
+    SIDE ELEVATION
+    FRONT ELEVATION
+    PLAN SHOWING POSITION OF COLUMNS FOR DRILLING FACE]
+
+The concurrence of the watercourse, shown on General Viele's map of
+Manhattan Island (Plate IX[D]), with the points where difficulties in
+the construction of the tunnels were encountered has been noted in a
+previous paper.
+
+In all cases where the course of this ancient stream was crossed (except
+at its final intersection of 33d Street), the rock was found to be very
+soft and disintegrated, a large quantity of water was encountered, and
+heavy timbering was required. The construction at these localities will
+be taken up later. In addition, disintegrated rock, but of a less
+troublesome character, was invariably met under the depressions in the
+rock surface developed by the borings from the streets and test holes
+from the tunnels. Many of these places required timbering, and no
+timbering was elsewhere necessary except at the portals. These
+coincident conditions were especially marked in 32d Street, which for a
+long distance closely adjoins the course of the former creek.
+
+_Disposal of Spoil._--The materials excavated from the tunnels were
+dumped at the 35th Street pier on barges furnished by the Railroad
+Company under another contract, and were towed to points near the
+Bayonne peninsula where the spoil was used principally in the
+construction of the Greenville Freight Yards and the line across the
+Hackensack Meadows to the tunnels. Details of this work will be given in
+a subsequent paper. After December, 1907, when the excavation was about
+85% completed, the contractor furnished the barges and effected the
+complete disposal of the spoil.
+
+_Difficulties of Excavation._--As stated in a previous paper, the
+excavation of the Twin Tunnel in 33d Street was continued westward to
+the west line of Fifth Avenue on the original grade. At that point the
+contractor started three drifts in the three-track section. The relation
+of the drifts to each other and to the cross-section are shown by Fig. 3.
+The center heading was driven a little in advance of those on the
+sides. At a distance of 65 ft. west of Fifth Avenue the rock surface was
+broken through in the top of the heading, and a very fine sand was
+encountered. For some distance east of this point the rock was badly
+disintegrated, and the heading required timbering. Through the soft
+material, tight lagging was placed on the sides and roof of the heading,
+and the face was protected by breast boards. There was a moderate flow
+of water through the cracks, and, in spite of every effort, some of the
+fine sand was constantly carried into the heading.
+
+In one or two instances considerable ground was lost at the face. On the
+evening of December 14th, 1906, as a heavy coal wagon was passing along
+33d Street above the heading, the rear wheels dropped through the
+asphalt pavement. An examination disclosed a cavity under the pavement
+about 14 ft. long, 12 ft. wide and 14 ft. deep. Evidently, the fine sand
+had gradually settled into the voids caused by the loss of material at
+the face, and the settlement broke the brick sewer over the heading. The
+sewer was temporarily repaired, and the hole in the street was filled
+before morning. A tight bulkhead was built across the heading, and work
+was abandoned at that point. The north drift was advanced to a point
+108 ft. west of Fifth Avenue where sand was also encountered and a
+considerable run occurred. After that time all work on the three-track
+section was discontinued.
+
+The Company then took up the consideration of changes in plan. To
+determine the difficulties of driving a Twin Tunnel at a lower
+elevation, an exploration drift, 8 ft. high and 12 ft. wide, was driven
+on the center line of the street as a top heading on the proposed new
+grade. Test holes were drilled above this heading and to the sides. The
+results indicated that there was sufficient rock cover of fair quality
+to enable the Twin Tunnel to be driven without great risk. The new plan
+(continuing the Twin Tunnel westward at a lower grade) was adopted in
+March, 1907, and work was immediately resumed at Fifth Avenue.
+
+The relation between the cross-sections under the old and new plans at
+that point is shown by Fig. 3. Before the new section was excavated it
+was necessary to support the timber work in the old headings. The plan
+adopted is also shown by Fig. 3. The rock was excavated under the center
+heading, as shown in cross-section, for a length of about 3 ft. A girder
+composed of two 18-in. I-beams was then put in position over each line
+and supported on the sides by posts. The ends at the center lines
+between the tunnels were supported on short posts bearing on the rock
+bench. The support of the timbering in the headings was then transferred
+to the girders by additional posts. Blocking was also inserted between
+the tops of the beams and the rock walls between the headings. Fig. 2,
+Plate LIX, gives a good idea of the timber work in the top headings
+above the I-beams. When the roof had been made secure, the removal of
+the bench was begun. As the work advanced it was necessary to replace
+the short posts at the center of the tunnel by others of full height,
+and there was considerable settlement in the I-beams during this
+operation. When the bench had been removed to a point 61 ft. west of
+Fifth Avenue, settlement was detected in the street surface above. Bench
+excavation was suspended and a section of the permanent lining, 35 ft.
+long, was placed. The space between the lining and the beams and between
+the beams and the roof was filled with rubble masonry. Grout pipes were
+built into the masonry and later all voids were filled with grout. Fig.
+3, Plate LIX, shows the first section of the concrete lining completed
+and part of the rubble in place; and Fig. 4, Plate LIX, shows details of
+the work above the tunnels. A second section of bench was next removed
+and more lining was placed. Work was continued in this way until all the
+roof at the old three-track headings had been secured. In this portion
+of the work the posts were embedded in the concrete.
+
+Between Fifth and Sixth Avenues there were two more sections of bad rock
+where it was necessary to support the roof with steel beams. At these
+latter points there were no complications with the excavation for the
+Three-Track Tunnel, and the work was much simpler. To avoid leaving the
+center posts in the permanent work, two rows of temporary posts were
+placed, as shown by Fig. 1, Plate LX, the center wall and skewback were
+built, and the posts were removed, as shown by Fig. 2, Plate LX, before
+placing the remainder of the lining.
+
+In 32d Street the normal progress of the excavation was frequently
+interrupted by encountering soft and unsound rock. In the excavation
+between the East River and the Intermediate Shafts it was possible to
+overcome these conditions by temporarily narrowing the excavation on one
+side and supporting the roof on 16 by 16-in. transverse timbers caught
+in niches in the rock at the sides, leaving sufficient room for the
+steam shovel to work through. In order to save time, the height of the
+excavation was not increased before placing these timbers, so that,
+previous to the concreting, they all required to be raised to clear the
+masonry lining and were then supported on posts on the center line
+between the tunnels. This permitted the remainder of the excavation to
+be made, and such additional timbering as was required was placed. At
+most of these sections a brick arch and water-proofing were used, on
+account of the presence of water. In certain places the center line
+posts were buried in the core-wall, and, in order to permit the placing
+of the water-proofing, were then cut off one by one flush with its top
+as the load was transferred to the completed masonry. In other cases the
+load was transferred to posts clear of the masonry and the center line
+posts were entirely removed. Under such conditions the normal concrete
+methods, to be described later, could not be used, and special forms
+were substituted.
+
+[Illustration: FIG. 3. CONSTRUCTION OF TWIN TUNNELS, THROUGH EXCAVATION
+STARTED FOR THREE-TRACK TUNNEL IN 33D STREET NEAR 5TH AVENUE]
+
+In this section of the work the most serious difficulties were
+encountered near Fourth Avenue a short distance east of the Intermediate
+Shaft, and beneath the site of the old pond shown on General Viele's
+map. The rock cover was known from the boring to be very thin, and the
+presence of the subway overhead caused some anxiety. The excavation was
+at first taken out to practically full width and timbered, but the rock
+became so treacherous that the heading was narrowed to a width
+sufficient for one tunnel only. With this span the rock in the roof held
+without timbering. As the masonry lining approached, sufficient trimming
+was done to permit the placing of the core-wall and one arch. Above the
+completed core-wall and brick arch the voids were filled solid with
+rubble masonry to give an unyielding support to the roof. The excavation
+of the remaining width of tunnel was then undertaken. Near the west side
+of Fourth Avenue, the excavation broke out of rock at the top, and fine
+sand and gravel with a large quantity of water were encountered. The
+work of excavation was arduous, and proceeded very slowly, on account of
+the care with which it was executed. Only a small amount of sand entered
+the tunnel, but the lining was placed as soon as the excavation was
+completed. Rubble masonry packing and grout ejected through pipes built
+into the arch were used to fill the voids above the roof. As a further
+precaution against the settlement of the subway, 2-in. pipes were washed
+down from the street above the point where soft ground was exposed in
+the roof of the tunnel, and through them grout was forced into the
+ground at various depths. Careful levels show that no settlement of the
+subway has taken place.
+
+West of the Intermediate Shaft the tunnel was excavated for full width
+until bad rock was encountered about 60 ft. west of Madison Avenue. (See
+General Viele's map, Plate IX.) Timbering was used for a short distance,
+and then the heading and bench were narrowed to 18 ft., and steam-shovel
+excavation was abandoned. As the heading advanced the rock grew steadily
+softer, the difficult conditions in this locality culminating when a
+slushy disintegrated feldspar was met, requiring poling and breasting.
+Thereafter the rock improved markedly, but near the east side of Fifth
+Avenue its thickness above the roof was found to be only 1-1/2 ft.,
+and the advance was stopped, pending a decision as to a change of plan.
+
+[Illustration: PLATE LX, FIG. 1.--DOUBLE ROW OF POSTS UNDER I-BEAMS,
+SUPPORTING ROOF IN BAD ROCK SECTION.]
+
+[Illustration: PLATE LX, FIG. 2.--CENTER WALL AND SKEWBACK UNDER I-BEAMS,
+AFTER REMOVAL OF DOUBLE ROW OF POSTS.]
+
+[Illustration: PLATE LX, FIG. 3.--TIMBERING IN FULL-WIDTH HEADING OF
+THREE-TRACK TUNNEL.]
+
+[Illustration: PLATE LX, FIG. 4.--UNDERPINNING WALLS IN OPEN-CUT
+SECTION.]
+
+After some delay, an exploration drift, similar to the one already
+described, was driven through to Sixth Avenue, and a change in plan was
+made, substantially the same as for the 33d Street tunnels. Enlargement
+to full size was at once started, but, for 400 ft. the rock was very
+soft and poor, and required extremely careful handling. The exploration
+drift was widened out to the full Twin-Tunnel width, and I-beams were
+placed and supported, in much the same manner as in 33d Street. The rock
+was so soft that it was frequently necessary to drive poling boards
+ahead as the face was mined out with picks and shovels. The load was
+very heavy, and the work the most difficult encountered in the tunnels.
+
+After this stage of the enlargement was reached, the excavation of the
+bench and the placing of the lining proceeded alternately, with the
+I-beams temporarily supported on long posts while the concrete core-wall
+was being built. Considerable settlement took place while shifting the
+posts, and eventually showed on the street surface and in the adjacent
+sidewalk vaults, but no damage was done to the structural portions of
+the buildings.
+
+While the above work had been going on westward from Fifth Avenue, the
+excavation of the Twin Tunnel eastward from the end of the open-cut
+section at Sixth Avenue had been proceeding rapidly, and, toward the end
+of the difficult Fifth Avenue work, it was being attacked from both
+directions.
+
+
+PROGRESS OF EXCAVATION.
+
+Owing to the numerous sections of poor rock, interspersed throughout the
+work with stretches of sound rock, the progress of the excavation was
+very irregular, especially in 32d Street. The rate of excavation in good
+ground is shown in Table 1. In the sections of bad ground, the
+operations of excavation, timbering, and lining were often carried on
+alternately, and it is impracticable to include them in the table.
+
+TABLE 1.--PROGRESS AND METHODS OF EXCAVATION IN GOOD GROUND.
+
+THIRTY-THIRD STREET.
+
+============================================================
+           1                 |   2    |          3         |
+-----------------------------+--------+--------------------+
+                             |        |                    |
+                             |        |                    |
+   Type of excavation.       |Tunnels.|    Worked from:    |
+                             |        |                    |
+                             |        |                    |
+-----------------------------+--------+--------------------+
+Full-sized single tunnel     |   B    |  1st Ave. shaft.   |
+                             |        |                    |
+Full-sized single tunnel     |   A    |  1st Ave. shaft.   |
+                             |        |                    |
+Full-sized twin tunnel       |A and B |  1st Ave. shaft.   |
+                             |        |                    |
+                             |        |                    |
+                             |        |                    |
+Full-sized twin tunnel       |A and B |Intermediate shaft. |
+                             |        |  (West of shaft.)  |
+                             |        |                    |
+                             |        |                    |
+Full-sized twin tunnel       |A and B |Intermediate shaft. |
+                             |        |  (East of shaft.)  |
+                             |        |                    |
+                             |        |                    |
+Full-sized twin tunnel       |A and B |Intermediate shaft. |
+                             |        |  (East of shaft.)  |
+                             |        |                    |
+                             |        |                    |
+Exploration drift            |A and B |Intermediate shaft. |
+                             |        |  (West of shaft.)  |
+                             |        |                    |
+Twin tunnel. Enlargement     |A and B |     West shaft.    |
+  of exploration drift       |        |  (East of shaft.)  |
+=============================+========+=====================
+
+======================================================================
+           4                      |    5   |      6     |      7     |
+----------------------------------+--------+------------+------------+
+                                  |        |   Length   |   Average  |
+             DATES.               |  Time  |   tunnel   |   advance  |
+----------------------------------|elapsed,| excavated, |   per day, |
+               |                  |   in   |     in     |     in     |
+     From      |        To        |  days. |linear feet.|linear feet.|
+----------------------------------+--------+------------+------------+
+Feb. 28, 1906. |May  12, 1906.    |    74  |     346    |     4.7    |
+               |                  |        |            |            |
+Feb. 28, 1906. |Apr. 30, 1906.    |    62  |     255    |     4.1    |
+               |                  |        |            |            |
+Aug. 23, 1906. |Jan.  5, 1907.    |   136  |     789    |     5.8    |
+               |                  |        |            |            |
+               |                  |        |            |            |
+               |                  |        |            |            |
+Apr.  4, 1906. |Oct. 31, 1906.    |   210  |     730    |     3.5    |
+               |                  |        |            |            |
+               |                  |        |            |            |
+               |                  |        |            |            |
+Apr.  4, 1906. |Oct. 31, 1906.    |   210  |     783    |     3.7    |
+               |                  |        |            |            |
+               |                  |        |            |            |
+               |                  |        |            |            |
+Nov.  1, 1906. |Dec. 26, 1906.    |    56  |     311    |     5.5    |
+               |                  |        |            |            |
+               |                  |        |            |            |
+               |                  |        |            |            |
+Mar.  1, 1907. |July 23, 1907.    |   145  |     947    |     6.5    |
+               |                  |        |            |            |
+               |                  |        |            |            |
+Sept. 6, 1907. |Dec.  4, 1907.    |    89  |     603    |     6.8    |
+               |                  |        |            |            |
+===============+==================+========+============+=============
+
+=====================================================
+                        8
+-----------------------------------------------------
+
+
+            Methods and conditions.
+
+
+-----------------------------------------------------
+Top heading and bench. Muck loaded by hand.
+
+ "     "     "    "      "    "    "    "
+
+Top full-width heading and bench. Muck loaded
+  by steam shovel. Working exclusively on this
+  heading.
+
+Top center heading and bench. Muck loaded by
+  steam shovel. Working alternately in headings
+  east and west of the shaft.
+
+Top center heading and bench. Muck loaded by
+  steam shovel. Working alternately in headings
+  east and west of the shaft.
+
+Top full-width heading and bench. Muck loaded
+  by steam shovel working exclusively on this
+  heading.
+
+Exploration drift about 9 ft. by 12 ft. Mucking
+  by hand. Fourteen timber bents were placed in
+  March, and seven in April, 1907.
+
+Drift excavated to full width and bench. Muck
+  loaded by steam shovel.
+=====================================================
+
+
+THIRTY-SECOND STREET.
+
+============================================================
+           1                 |   2    |          3         |
+-----------------------------+--------+--------------------+
+                             |        |                    |
+                             |        |                    |
+   Type of excavation.       |Tunnels.|    Worked from:    |
+                             |        |                    |
+                             |        |                    |
+-----------------------------+--------+--------------------+
+Full-sized single tunnel     |   C    |  1st Ave. shaft.   |
+                             |        |                    |
+Full-sized single tunnel     |   D    |  1st Ave. shaft.   |
+                             |        |                    |
+Full-sized twin tunnel       |C and D |  1st Ave. shaft.   |
+                             |        |                    |
+                             |        |                    |
+                             |        |                    |
+Narrowed twin tunnel         |   C    |Intermediate shaft. |
+                             |        |  (East of shaft.)  |
+                             |        |                    |
+                             |        |                    |
+Narrowed twin tunnel         |   C    |Intermediate shaft. |
+                             |        |  (East of shaft.)  |
+                             |        |                    |
+                             |        |                    |
+                             |        |                    |
+                             |        |                    |
+Full-sized twin tunnel       |C and D |Intermediate shaft. |
+                             |        |  (West of shaft.)  |
+                             |        |                    |
+Exploration drift            |C and D |Intermediate shaft. |
+                             |        |  (West of shaft.)  |
+                             |        |                    |
+Twin tunnel. Enlargement    }|C and D |{  Eastward from    |
+  of exploration drift      }|        |{     open cut.     |
+                             |        |                    |
+Twin tunnel. Enlargement    }|C and D |{  Eastward from    |
+  of exploration drift      }|        |{     open cut.     |
+                             |        |                    |
+=============================+========+=====================
+
+
+
+==================================+========+============+=============
+           4                      |    5   |      6     |      7     |
+----------------------------------+--------+------------+------------+
+                                  |        |   Length   |   Average  |
+            DATES.                |  Time  |   tunnel   |   advance  |
+----------------------------------|elapsed,| excavated, |   per day, |
+               |                  |   in   |     in     |     in     |
+     From      |        To        |  days. |linear feet.|linear feet.|
+----------------------------------+--------+------------+------------+
+ Jan. 25, 1906.|Apr. 30, 1906.    |   95   |     367    |     3.9    |
+               |                  |        |            |            |
+ Jan. 27, 1906.|Apr. 30, 1906.    |   93   |     354    |     3.8    |
+               |                  |        |            |            |
+{May. 22, 1906.|July 24, 1906.[E]}|  173   |     810    |     4.7    |
+{Aug. 11, 1906.|Nov. 29, 1906.   }|        |            |            |
+               |                  |        |            |            |
+               |                  |        |            |            |
+ Mar. 19, 1906.|May  28, 1906.    |   70   |      58    |     0.8    |
+               |                  |        |            |            |
+               |                  |        |            |            |
+               |                  |        |            |            |
+{May  29, 1906.|July  3, 1906.[E]}|  208   |   1,206    |     5.8    |
+{July 18, 1906.|July 31, 1906.   }|        |            |            |
+{Aug. 12, 1906.|Nov. 23, 1906.   }|        |            |            |
+{Jan. 15, 1907.|Feb.  5, 1907.   }|        |            |            |
+{Feb. 17, 1907.|Mar. 21, 1907.   }|        |            |            |
+               |                  |        |            |            |
+ Dec.  1, 1905.|May. 10, 1906.    |  161   |     225    |     1.4    |
+               |                  |        |            |            |
+               |                  |        |            |            |
+ Feb.  1, 1907.|Sept.13, 1907.    |  225   |   1,033    |     4.6    |
+               |                  |        |            |            |
+               |                  |        |            |            |
+}Feb.  1, 1908.|Feb. 14, 1908.    |   14   |      65    |     4.6    |
+}              |                  |        |            |            |
+               |                  |        |            |            |
+}Feb. 15, 1908.|Apr. 14, 1908.    |   59   |     524    |     8.9    |
+}              |                  |        |            |            |
+               |                  |        |            |            |
+======================================================================
+
+[Footnote E: Time and distance omitted while working
+through timbered stretches.]
+
+=======================================================
+                        8
+-------------------------------------------------------
+            Methods and conditions.
+-------------------------------------------------------
+Top heading and bench. Muck loaded by hand.
+
+ "     "     "    "      "    "    "    "
+
+Double heading and bench. Muck loaded by steam
+  shovel. Stretches aggregating 200 ft. narrowed
+  to about 25 ft. and later enlarged are included.
+
+Excavation about 30 ft. wide. Top full-width heading
+  and bench. Muck loaded by hand. Steam shovel
+  not installed.
+
+Excavation about 30 to 35 ft. wide. Top full-width
+  by hand and part by steam shovel.
+
+
+
+
+Double heading and bench. Part of the muck handled
+  by hand and part by steam shovel.
+
+Exploration drift about 10 ft. by 13 in. Muck loaded by
+  hand. 14 ft. timbered.
+
+At portal of twin tunnels. Drift excavated to full
+  width and bench. Muck loaded by hand. 12 ft.
+  timbered.
+
+Drift excavated to full width and bench. Muck loaded
+  by steam shovel. Full-width tunnel timbered for 26
+  ft. independently of the main excavation.
+=======================================================
+
+
+THREE-TRACK TUNNEL EXCAVATION.
+
+When it became evident that the work through the Fifth Avenue section
+would be extremely slow, shafts were sunk in each street between Sixth
+and Seventh Avenues. The shafts, as shown on Plate XIV, were located in
+the streets, but in such a way as to block only half of the roadway. At
+the same time it was decided to construct in open cut about 200 ft. of
+the Three-Track Tunnel at the west end of the contract in 32d Street,
+where the rock surface was below the top of the tunnel. It was hoped
+that the remainder of the work could be built without opening the
+street, but further investigation showed that this was impracticable,
+and eventually all the Three-Track Tunnel in 32d Street, except 120 ft.
+east of the shaft, was built in open cut.
+
+_Thirty-second Street Work in Tunnel._--Following the sinking of the
+shaft, a drift was driven across the street at the crown of the tunnel,
+and a top heading on the south side was excavated in both directions.
+Frequent cross-drifts to the north side showed that the rock was nowhere
+very sound and that, except for a short distance east of the shaft, it
+was distinctly unfavorable for the wide Three-Track excavation. In this
+stretch the north ends of these cross-cuts were connected by a second
+heading, and wall-plates and sets of three-segment arch timbering were
+set up to support the roof of the drifts. The cross-cuttings were
+gradually widened and timbered until the entire excavation had been made
+down to the level of the wall-plates, as shown in Fig. 3, Plate LX. The
+bench was then excavated in two lifts, leaving the wall-plates supported
+on narrow longitudinal berms, which were removed in short sections to
+permit the placing of posts under the wall-plates.
+
+_Thirty-second Street Open-Cut Work._--Before actual open-cut excavation
+was started, all buildings facing it were underpinned to rock. For this
+purpose, a trench was dug along the face of the buildings and of the
+same depth as their cellars. Holes were cut in the front foundation
+walls through which long needle-beams (Fig. 4, Plate LX) were inserted
+and jacked up on blocking placed on the cellar floor and in the trench,
+until the weight of the building had been taken off its foundations. A
+close-sheeted trench was then sunk to rock under the front building
+walls, and a light rubble masonry retaining wall was built in it to
+support the building permanently. Frequently, the excavation for the
+underpinning wall, which was taken out in sections from 30 to 40 ft.
+long, and in places was carried to a depth of 40 ft., was very
+troublesome on account of the large quantity of water encountered and
+the fineness of the sand, which exhibited a tendency to flow when
+saturated.
+
+The Elevated Railroad columns in Sixth Avenue, near the north and south
+lines of 32d Street, were underpinned in a manner similar to the
+building foundations, while those on the center line of the street were
+supported by girders riveted to them close under the track level. The
+girders in turn were supported on posts footed on the new underpinning
+of the adjacent columns. On the completion of the tunnels, concrete
+piers were built up from the roof of the tunnel to form a permanent
+foundation for the center-line columns. The area to be excavated under
+Sixth Avenue was enclosed by a rubble masonry retaining wall constructed
+in a trench.
+
+Open-cut excavation was started by planking over the street on stringers
+resting on transverse 12 by 12-in. caps. The caps were gradually
+undermined and supported on temporary posts which were then replaced by
+short posts resting on 12 by 12-in. sills about 7 ft. below the cap. The
+operation was then repeated and the sill was supported on another set of
+short posts resting on a second sill. When the excavation had been
+carried down in this manner to the level of the top of the tunnel,
+diagonal 3 by 10-in. timbers were cut in between the posts and sills to
+form a species of double A-frame, the legs of which rested in niches cut
+in the rock and on posts carried up the face of the underpinning wall,
+and the whole was stiffened with vertical tie-rods. This construction is
+shown by Fig. 3, Plate LXII. The brick sewer was replaced temporarily by
+one of riveted steel pipe. This pipe and the water and gas pipes and
+electric conduits were suspended from the timbers as the pipes were
+uncovered.
+
+Excavation in rock was made by sinking a pit to sub-grade for the full
+width of the tunnel and advancing the face of the pit in several lifts,
+the muck being blown over the slope and loaded into buckets at its foot.
+
+The work was attacked at several places simultaneously, and the spoil
+was hoisted by derricks located at convenient points along the side of
+the cut.
+
+_Thirty-third Street Work in Tunnel and Open Cut._--The West 33d Street
+Shaft was similar to the one in 32d Street, and was sunk during
+February, March, and April, 1907, through 10 ft. of earth, 21 ft. of
+soft rock, and 29 ft. of fairly hard rock. It was necessary to timber
+heavily the upper 30 ft. of the shaft. The timber later showed evidences
+of severe strain, and had to be reinforced.
+
+[Illustration: Plate LXI.--EXCAVATION AND TIMBERING IN HEAVY GROUND
+OF THREE-TRACK TUNNEL OF 33D ST.]
+
+As soon as the shaft excavation was deep enough, a drift was driven
+part way across the tunnels, and top headings were started both east and
+west to explore the rock. The heading to the west was divided into two
+drifts, as shown on Plate LXI. These two drifts were continued to the
+west end of the contract, and were then enlarged to a full-sized heading
+and timbered, as shown on Plate LXI and Fig. 3, Plate LX. The rock near
+the shaft contained many wet rusty seams, and settlement was detected in
+the segmental tunnel timbering soon after the widening of the heading
+was completed. Short props were placed under the timbers, and the street
+surface was opened with a view of stripping the earth down to the rock
+and thus lightening the load on the timbering. Street traffic was
+maintained on a timber structure with posts eventually carried down to
+the rock surface, and the walls of the buildings on the north side of
+the street were underpinned to rock. The settlement of the tunnel
+timbering was checked for a time, and the bench was excavated as shown
+on Plate LXI. In this work the cut in the center was first made, and the
+short props were replaced by struts, as shown; after this the berms were
+removed and the side posts were placed. While building the brick arches,
+holes were left in the masonry around the struts. After the masonry had
+hardened, piers were built on the arches to support the segmental
+timbers. The struts were then removed and the openings filled with
+masonry. The voids above the arch were packed with rock and afterward
+thoroughly grouted.
+
+The timbers near the shaft continued to settle, and, although they had
+been placed from 9 to 12 in. above the level of the top of the masonry,
+by October 1st, they encroached 9 in. within the line of masonry. It was
+then decided to remove the rock for a distance of 48 ft. west of the
+shaft, and build this portion of the tunnel in open cut. The posts
+supporting the deck forming the street surface were replaced by an
+A-frame structure similar to that developed for the 32d Street open cut,
+without interruption of the street traffic.
+
+After making the open cut to the westward of the shaft, there was a slip
+in the rock north of and adjoining the shaft. Fortunately, the timbers
+did not give way entirely, and no damage was done. The open cut was
+extended eastward for a distance of 46 ft., making the total length of
+tunnel built in open cut on this street 94 ft.
+
+East of the shaft, for a distance of about 125 ft., the rock was broken
+and could not be excavated to full size without timbering the roof, but
+between this section of poor rock and those already mentioned in
+connection with the work at Fifth Avenue, there was a stretch of 600 ft.
+of good rock where all the spoil was handled with a steam shovel.
+
+
+TWIN-TUNNEL LINING.
+
+The masonry lining for the tunnels was not started until the late fall
+of 1906, after excavation had been in progress for a year and a half. At
+that time concreting was started in the single tunnels westward from the
+First Avenue Shafts, and by spring was in full swing in the Twin
+Tunnels.
+
+The plans contemplated the use of a complete concrete lining except
+where large quantities of water were encountered; in which case the
+arches, beginning at a point 15° above the springing line, were to be
+built of vitrified paving brick. By reference to Plate XII it will be
+seen that the water-proofing, which in the concrete-roof tunnels
+extended the full height of the sides to the 15° line, was carried in
+the brick-roof tunnels completely around the extrados of the arch. The
+cross-sections also show the location of the electric conduits which
+were buried in the mass of the side and core-walls and which limited the
+height to which the concrete could be carried in one operation.
+
+The same general scheme of operations was used wherever possible
+throughout the Twin-Tunnel work, but was subject to minor modifications
+as circumstances dictated. Concrete was first deposited in the bottom,
+to the grade of the flow line of the drains; after it had set,
+collapsible box forms, of 2-in. plank with 3-in. plank tops, were laid
+on it to form the ditch and the shoulders for the flagstone covers. The
+track, which had previously been blocked up on the rock between the
+ditches, was raised and supported on the ditch boxes above the finished
+floor level. At the same time, light forms were braced from the ditch
+boxes to the grade of the base of the low-tension and telephone-duct
+bank. After depositing the concrete to this level, the telephone ducts
+were laid.
+
+The forms for the water-proofing or sand-wall up to the 15° line and for
+the main side-walls and core-walls were built in 30-ft. panels and were
+supported on carriages, which, traveling on a broad-gauge track above
+the ditches, moved along the tunnel, section by section, as the work
+advanced. The panels were hung loosely from joists carrying a platform
+on the top chord of the carriage trusses, and were adjusted
+transversely by bracing and wedging them out from the carriage. The
+small forms for the refuge niches, ladders, etc., were collapsible, and
+were spiked to the main panel forms just previous to the deposition of
+the concrete. The concrete was deposited from the platform on top of the
+carriage, to which the cars were elevated in various ways. Plate LXI
+shows the details of the carriages, and is self-explanatory.
+
+The concrete for the sand-walls and the core-wall, to the level of the
+sidewalk, was deposited at the same time; two carriages in each tunnel,
+placed opposite each other, forming a 60-ft. length, were used at each
+setting. The floor section of the 4-in. tile drains had been laid with
+the floor concrete, and, as the sand-wall concrete was deposited, the
+drains were brought up simultaneously, broken stone being deposited
+between the tile and the rock to form a blind drain and afford access to
+the open joints of the tile for the water entering the tunnel through
+seams in the rock. The drains were spaced at intervals not exceeding 25
+ft., depending on the wetness of the rock, and were placed at similar
+intervals in the core-wall under the lowest projecting points of the
+rock on the center line between the tunnels. A small ditch lined with
+loose 6-in. vitrified half pipe was provided in the top of the sand-wall
+to collect the water from the extrados of the arch and lead it to the
+top of the drains. Great difficulty was experienced in maintaining these
+drains clear, and, on completion of the work, a large amount of labor
+was expended in removing obstructions from the floor sections, the only
+portion then accessible.
+
+After water-proofing the sand-walls and laying the low-tension ducts, a
+second pair of carriages, with panels on one side only, for 60 ft. of
+side-wall and skewback to the 15° line, were set and braced against the
+core-wall. These forms are shown in connection with the carriage on
+Plate LXI. They were concreted to the base of the high-tension duct
+bank, and, after the concrete had hardened and the bank of ducts had
+been laid, the concreting was completed in a second operation.
+
+In places where the roof was supported temporarily by posts and heavy
+timbering, such as at Fifth Avenue, the form carriages could not be
+used, and special methods were devised to suit the local conditions.
+Usually, the panels were stripped from the carriages and moved from
+section to section by hand, and, when in position, were braced to the
+timbering.
+
+The arch centers were built up of two 5 by 3 by 3/8-in. steel angles,
+and, when set, were blocked up on the sidewalks opposite each other in
+the two tunnels. A temporary platform was laid on the bottom chord
+angles of the ribs, on which the concrete was dumped, the same as on the
+form carriages. The lagging used was 3 by 3-in. dressed pine or spruce
+16 ft. long, and was placed as the concreting of the arch proceeded
+above the 15° line on the side-wall and above the sidewalk on the
+core-wall. After the arch had reached such a height that the concrete
+could not be passed over the lagging directly from the main platform, it
+was cast on a small platform on the upper horizontal bracing of the
+centers, shown in Fig. 3, Plate LIX, and was thence shoveled into the
+work. In the upper part of the arch the face of the concrete was kept on
+a radial plane, and, when only 3 ft. remained to be placed, it was keyed
+in from one end, the key lagging being set in about 5-ft. lengths. The
+arches were concreted usually in 60-ft. lengths.
+
+Where brick arches were used, the core-wall skewback was concreted
+behind special forms set up on the sidewalks, or the arch ribs and
+lagging were used for forms, and the brick arch was not started until
+after the concrete had set. In laying the brick in the arch, the five
+courses of the ring were carried up as high as the void between the
+extrados and the rock would permit and still leave a working space in
+which to place the water-proofing. This was usually not more than 3 ft.,
+except on the core-wall side. The felt and pitch water-proofing was then
+laid for that height, joined to the previous water-proofing on the
+side-walls, and was followed by the brick armor course over the
+water-proofing and by the rock packing, after which another lift of
+brick was laid and the operations were repeated. The large void (Fig. 1,
+Plate LXII) above the core-wall gave convenient access for working on
+top of the adjacent sides of the roof, and the keying of the arches and
+the water-proofing and rock packing above the core-wall were usually
+carried on from that point, the work progressing from one end.
+
+The concrete for all work above the floor was dumped on the platform of
+the carriages, to which it was transported in the early part of the work
+in cars running on a high-level track laid on long ties, resting on the
+finished sidewalks. This arrangement, although requiring a large amount
+of timber for the track, permitted the muck to be carried out on the
+low-level track without interference. Later, when the advance of the
+heading had ceased and the heavy mucking was over, all concrete was
+transported on the floor level, and the cars were lifted to the carriage
+platforms by elevators and were hauled by hoisting engines up a movable
+incline. The latter method is shown by Fig. 3, Plate LIX.
+
+_Water-Proofing._--The water-proofing referred to above was in all cases
+felt and pitch laid with six thicknesses of felt and seven of pitch. The
+sub-contractor for the work was the Sicilian Asphalt Paving Company. All
+joints were lapped at least 1 ft., and, where work was suspended for a
+time and a bevel lap could not be made, the edges of the felt were left
+unpitched for 1 ft. and the newer work was interlaced with the old. This
+method was not always successful, however, on account of the softening
+of the unpitched felt on long-continued exposure to the water. The felt
+used was mainly "Tunaloid," together with some "Hydrex." It weighed
+about 12 lb. per 100 sq. ft. when saturated and coated on one side only,
+and contained about 25% of wool. The coal-tar pitch used had a melting
+point of 100° Fahr.
+
+After the completion of the tunnel, the concrete arch showed some
+leakage and in places unsightly lime deposits. It was determined to
+attempt to stop these leaks by the application of a water-proof cement
+coating on the intrados of the arch. Extended experimental application
+of two varieties of materials used for this purpose--"Hydrolithic"
+cement and the U. S. Water-proofing Company's compound--have been made
+with apparent success up to the present time, and the results after the
+lapse of a considerable period are awaited with interest.
+
+_Duct Laying._--The position of the electric conduits, buried in the
+heart of the concrete walls, interfered greatly with the economical and
+speedy placing of the lining, and their laying proved to be one of the
+most troublesome features of the work. The power conduits were
+single-way, with the bank for high-tension cables separated in the
+side-walls from the low-tension bank, as shown on Plate XII. The
+conduits for telephone and telegraph service were four-way, and were
+located in the core-wall. All ducts had 3/4-in. walls and a minimum
+clear opening of 3-3/8 in. square, with corners rounded. They were laid
+with joints broken in all directions, and in about 1/4-in. beds of
+1:2-1/2 mortar. Flat steel bond-irons, 2 by 1/8 in., with split and bent
+ends, were placed in the joints at intervals of 3 ft. and projected into
+the concrete 3 in. on each side, tying together the concrete on opposite
+sides of the ducts. The joints were wrapped with a 6-in. strip of
+10-oz. duck saturated with neat-cement grout, and, in addition, the
+power conduits were completely covered with a 1/2-in. coat of mortar to
+prevent the intrusion of cement and sand from the fluid concrete. The
+four-way conduits were plastered only over the wraps. Splicing chambers
+were provided at intervals of 400 ft.
+
+[Illustration: PLATE LXII, FIG. 1.--WATER-PROOFING OVER BRICK
+ARCHES.]
+
+[Illustration: PLATE LXII, FIG. 2.--TRESTLE USED IN CONCRETING IN
+THREE-TRACK TUNNEL.]
+
+[Illustration: PLATE LXII, FIG. 3.--METHOD OF STREET SUPPORT OVER
+OPEN-CUT EXCAVATION.]
+
+[Illustration: PLATE LXII, FIG. 4.--JUNCTION OF TWIN AND THREE-TRACK
+TUNNELS.]
+
+
+THREE-TRACK TUNNEL LINING.
+
+In the Three-Track Tunnels, a heavy brick arch was used for those
+portions constructed in tunnel, while, in the open-cut sections, the
+roof was of concrete. Both were completely water-proofed on the roof and
+sides, and in the tunnel sections the space above the brick roof was
+filled with rock packing. On account of the unstable nature of the rock
+encountered throughout, the voids in the packing were afterward filled
+with grout.
+
+By reference to the cross-sections, Plate XII, it will be seen that the
+haunches of the arch were tied together by steel I-beams anchored in the
+concrete, with the object of making the structure self-supporting in the
+event of the removal of the adjacent rock for deep cellar excavations.
+This construction materially influenced the contractor's method of
+placing the masonry lining.
+
+After depositing the floor concrete, by the same method that was used in
+the Twin Tunnels, a timber trestle (Fig. 2, Plate LXII) was erected to
+the height of the underside of the I-beam ties, the posts being footed
+in holes, about 3 in. deep, left in the concrete floor to prevent
+slipping. In the open-cut sections the sand-wall forms were of undressed
+plank tacked to the studding and braced from the trestle; in the tunnel
+section they were spiked to the face of the posts supporting the
+timbering.
+
+The side-wall forms were made up in panels about 3 by 10 ft., and were
+clamped to studs by U-shaped irons passing around the stud and bolted to
+the cleats on the back of the panels, the studs being braced from the
+trestle. The side-wall concrete was deposited in three sections. The
+first was brought up just above the sidewalk and formed the bench for
+the high-tension ducts; the second carried the wall up to the springing
+line. Before placing the third section the I-beam ties were set in
+position (Fig. 3, Plate LXII) on top of the trestle, and the reinforcing
+rods in the haunch of the arch were hung from them. The concrete was
+carried up to a skewback for the arch, as shown in the brick-roof
+cross-section (Plate XII) and embedded the ends of the ties.
+
+The centers for the arches stood on the I-beam ties, and the tops of the
+hangers, for the permanent support of the ties near their center, were
+inserted through the lagging. The brick arch, water-proofing, and rock
+packing were laid up in lifts, in the same manner as in the Twin Tunnel,
+with grout pipes built in at intervals of about 8 ft. The concrete arch
+was placed in sections, from 25 to 50 ft. in length, with a rather wet
+mixture and a back form on the steep slope of the extrados.
+
+The concrete for the sand-walls and lower part of side-walls was handled
+on tracks and platforms laid on cantilever beams at mid-height of the
+trestle, as shown by Fig. 3, Plate LXII. For the walls above the
+springing line, the tracks were laid on top of the I-beam ties, and some
+of the arch concrete, also, was delivered from the mixer at that level
+and hauled up an incline to the level of the top of the arch. By far the
+greater part, however, was turned out from mixers set on the completed
+arch, and was transported on tracks hung in part from the street
+timbering.
+
+_Completion._--Except in the heavily-timbered portions, such as at Fifth
+Avenue, where the load had to be transferred from posts to the completed
+masonry section by section, the lining of the tunnels presented no
+special difficulty. The large number of small forms to be set, and the
+mutual interference of the concreting and duct-laying operations proved
+to be the most troublesome features of the work.
+
+The restoration of the streets, public utilities, etc., at the open-cut
+sections was a slow and tedious operation, but the tunnels themselves
+were completed in March, 1909, 3 years and 10 months after the inception
+of the work. The finished tunnels are shown by the photograph, Fig. 4,
+Plate LXII, taken at the junction of the twin and three-track types.
+
+FOOTNOTES:
+
+[Footnote A: Presented at the meeting of December 1st, 1909.]
+
+[Footnote B: Of the paper by Mr. Noble.]
+
+[Footnote C: Of the paper by Mr. Noble.]
+
+[Footnote D: Of the paper by Mr. Noble.]
+
+
+
+
+
+
+End of the Project Gutenberg EBook of Transactions of the American Society
+of Civil Engineers, Vol. LXVIII, Sept. 1910, by James H. Brace and Francis Mason
+
+*** END OF THIS PROJECT GUTENBERG EBOOK TRANSACTIONS OF THE AMERICAN ***
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+
+The Project Gutenberg EBook of Transactions of the American Society of
+Civil Engineers, Vol. LXVIII, Sept. 1910, by James H. Brace and Francis Mason
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Transactions of the American Society of Civil Engineers, Vol. LXVIII, Sept. 1910
+       The New York Tunnel Extension of the Pennsylvania Railroad.
+              The Cross-Town Tunnels. Paper No. 1158
+
+Author: James H. Brace and Francis Mason
+
+Release Date: August 13, 2006 [EBook #19037]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK TRANSACTIONS OF THE AMERICAN ***
+
+
+
+
+Produced by Juliet Sutherland, Jacqueline Jeremy and the
+Online Distributed Proofreading Team at http://www.pgdp.net
+
+
+
+
+
+
+</pre>
+
+<h2>AMERICAN SOCIETY OF CIVIL ENGINEERS<br /><br /></h2>
+
+<h3>INSTITUTED 1852</h3>
+
+<hr style="width: 45%;" />
+
+<h1>TRANSACTIONS</h1>
+
+<hr style="width: 35%;" />
+
+<h3>Paper No.&nbsp;1158</h3>
+
+<hr style="width: 45%;" />
+
+<h1>THE NEW YORK TUNNEL EXTENSION OF THE<br />
+PENNSYLVANIA RAILROAD.<br />
+THE CROSS-TOWN TUNNELS.<a name="FNanchor_A_1" id="FNanchor_A_1"></a><a href="#Footnote_A_1" class="fnanchor">[A]</a></h1>
+
+
+<h2><span class="smcap">BY JAMES H.&nbsp;BRACE AND FRANCIS MASON, MEMBERS, AM.&nbsp;SOC.&nbsp;C.&nbsp;E.</span></h2>
+
+<hr style="width: 45%;" />
+
+<p>In this paper, it is proposed to describe the construction of the
+tunnels extending eastward from the easterly extension of the Terminal
+Station to the permanent shafts east of First Avenue.</p>
+
+<p>They were located under 32d and 33d Streets from the station to Second
+Avenue, and thence, curving to the left, passed under private property
+and First Avenue to the shafts, as described in a preceding paper.
+Typical cross-sections of the tunnels are shown on Plate XII.<a name="FNanchor_B_2" id="FNanchor_B_2"></a><a href="#Footnote_B_2" class="fnanchor">[B]</a></p>
+
+
+
+<p>On May 29th, 1905, a contract was entered into with the United
+Engineering and Contracting Company for the performance of this work.
+This contract provided that work on each pair of tunnels should be
+carried on from two shafts. The first, here referred to as the First
+Avenue Shafts, were located just east of that avenue and directly over
+the line of the tunnels; the other two, called the Intermediate Shafts,
+were located on private property to the north of each pair of tunnels in
+the blocks between Fourth and Madison Avenues. It was originally
+intended to do all the work of construction from these four shafts.
+Workings were started both east and west <span class="pagenum"><a name="Page_392" id="Page_392">[Page 392]</a></span>from the Intermediate Shafts,
+and those to the west were to be continued to the Terminal Station.
+After the change of plans, described in a previous paper, it was decided
+to sink a third shaft on each line. These were known as the West Shafts,
+and were located between Sixth and Seventh Avenues. Finally, it was
+found necessary to build a portion of the tunnels on each line west of
+Sixth Avenue in open cut. The locations of the shafts are shown on Plate&nbsp;XIV.<a name="FNanchor_C_3" id="FNanchor_C_3"></a><a href="#Footnote_C_3" class="fnanchor">[C]</a></p>
+
+
+<p>The First Avenue shafts were built by S.&nbsp;Pearson and Son, Inc., for the
+joint use of the two contractors, as described in the paper on the
+tunnels under the East River. While the shafts were being sunk, the
+full-sized tunnels were excavated westward by the contractor for the
+river tunnels for a distance of 50 ft., and top headings for 50 ft.
+farther. By this means, injury to the caissons and to the contractor's
+plant in the shafts by the subsequent work in the Cross-Town Tunnels was
+avoided. The west half of the shaft was for the exclusive use of the
+contractor for the Cross-Town Tunnels.</p>
+
+
+<p class="sectionh">Contractor's Plant</p>
+
+<p>The method of handling the work adopted by the contractor was, broadly
+speaking, as follows: Excavation was usually carried on by modifications
+of the top-heading and bench method, the bench being carried as close to
+the face as possible in order to allow the muck from the heading to be
+blasted over the bench into the full section. The spoil was loaded into
+3-yd. buckets (designed by the contractor and hereinafter described), by
+steam shovels operated by compressed air, and hauled to the shafts by
+electric locomotives. Electrically-operated telphers, suspended from a
+timber trestle, hoisted the buckets, and, traveling on a mono-rail
+track, deposited them on wagons for transportation to the dock. Arriving
+at the dock, the buckets were lifted by electrically-operated stiff-leg
+derricks and their contents deposited on scows for final disposal. The
+spoil was thus transported from the heading to the scow without breaking
+bulk.</p>
+
+<p>When concreting was in progress, the spoil buckets were returned to the
+shafts loaded with sand and stone. The concrete materials were deposited
+in storage bins placed in the shafts, from which they were fed to the
+mixers located at the foot of the shaft about on a level with the crown
+of the tunnels. The concrete was transported to the forms in side-dump,
+steel, concrete cars, hauled by the electric locomotives.</p>
+
+<p><span class="pagenum"><a name="Page_393" id="Page_393">[Page 393]</a></span>Electrical power was adopted largely on account of the restricted area
+at the shaft sites, where a steam plant would have occupied considerable
+space of great value for other purposes. The installation of a steam
+plant at the Intermediate Shafts, which were located in a high-class
+residential district, would have been highly objectionable to the
+neighboring property owners, on account of the attendant noise, smoke,
+and dirt, and, in addition, the cost of the transportation of fuel would
+have been a serious burden. Except for the forges and, toward the last,
+the steam locomotives, not a pound of coal was burned on the work. The
+use of the bucket and telpher also eliminated most of the objectionable
+noise incident to the transfer of spoil from tunnel cars to ordinary
+wagons at the shaft sites. Power plants were installed at the North
+Shaft near First Avenue and at the rear of the 33d Street Intermediate
+Shaft.</p>
+
+<p><i>First Avenue Plant.</i>&mdash;<a href="#plate_lviii_1">Fig.&nbsp;1, Plate&nbsp;LVIII</a>, is a general view of the
+First Avenue plant. The power-house at the corner of 34th Street and
+First Avenue supplied compressed air for operating drills, shovels,
+pumps, and hoists in the tunnels driven from the river shafts, and in it
+three Laidlaw-Dunn-Gordon compressors were installed. The largest was a
+32 by 20 by 30-in., two-stage, cross-compound, direct-connected to a
+Fort Wayne 480 h.p., 230-volt, direct-current, constant-speed motor run
+at 100 rev.&nbsp;per min. This compressor was rated at 2,870&nbsp;cu.&nbsp;ft.&nbsp;of free
+air per minute at a pressure of 100&nbsp;lb. It was governed by throttling
+the suction, the governor being controlled by the pressure in the air
+receiver and the motor running continuously at a constant speed. The two
+others were of similar type, one was 22-1/2 by 14 by 18-in., rated at
+1,250&nbsp;cu.&nbsp;ft. of free air at a pressure of 100 lb., the other was 16 by
+10 by 18-in., rated at 630&nbsp;cu.&nbsp;ft. They were fitted with 9-ft.
+fly-wheels, and were driven at 150 rev.&nbsp;per min. by 105-h.p., General
+Electric, 220-volt, compound-wound, direct-current motors running at 655&nbsp;rev. per min. The larger of these two compressors was driven by two of
+the motors belted in tandem, and the smaller was belt-connected to a
+third motor. The compressors were water-jacketed and had small
+inter-coolers, the water supply for which was itself cooled in a Wheeler
+Condenser and Engineering Company's water-cooling tower. The pump and
+the blower operating it were electrically driven.</p>
+
+<p>The telphers, used for hoisting muck from the tunnels and for lowering
+supplies, were each hung from single rails on a timber trestle,<span class="pagenum"><a name="Page_394" id="Page_394">[Page 394]</a></span> about
+40&nbsp;ft. high, spanning and connecting the two shafts. One machine was
+provided for each shaft, and where their tracks crossed 33d Street they
+were separated sufficiently to permit the machines to pass each other.
+At this point, and covering the street, a large platform was provided,
+on which the trucks were loaded and unloaded (<a href="#plate_lviii_2">Fig.&nbsp;2, Plate&nbsp;LVIII</a>), and
+from which they descended by an incline on First Avenue leading south to
+32d Street. The platform also covered practically all the yard at the
+South Shaft and materially increased the available working area. The
+telphers were built by the Dodge Cold Storage Company, and were operated
+by a 75-h.p. General Electric motor for hoisting and a 15-h.p. Northern
+Electric Company motor for propulsion. Their rated lifting capacity was
+10,000&nbsp;lb. at a speed of 200&nbsp;ft. per min.</p>
+
+<p>The carpenter shop and machine-shop, both of which served the entire
+work, were conveniently located in small buildings on the loading
+platform. In the former the saws were each run independently by small
+electric motors suspended under the platform. The heavy forms and form
+carriages used in lining the tunnels with concrete were fabricated and
+stored on the platform outside. The machine-shop lathes, etc., were all
+belted to one shaft driven by an 8-h.p. General Electric motor. Above
+the machine-shop was a locker-room and below it on the street level was
+the main blacksmith shop for the work. Subsidiary blacksmith shops were
+located at each of the other shafts. The storeroom and additional
+locker-rooms were located above the power-plant in the North Shaft yard,
+and isolated from the other structures was a small oil-house. Additional
+storage space was provided by the contractor on 32d Street just west of
+First Avenue by renting three old buildings and the yards in the rear of
+them and of the Railroad Company's cement warehouse adjacent. Here
+electric conduits, pipe, castings, and other heavy and bulky supplies
+were stored.</p>
+
+<p>During excavation the headings were supplied with forced ventilation
+through 12-in. and 14-in. No.&nbsp;16, spiral-riveted, asphalted pressure
+pipes, canvas extensions being used beyond the ends of the pipes. A No.
+4 American Blower, located at the top of each shaft and driven by a
+15-h.p. General Electric motor, supplied the air.</p>
+
+
+<p class="figcenter"><a name="plate_lviii_1" id="plate_lviii_1"></a>
+<img src="images/395a.jpg" title="View of First Avenue Plant" height="286" width="400" alt="View of First Avenue Plant" /></p>
+
+<p class="caption"><span class="smcap">Plate LVIII, Fig. 1.&mdash;View of First Avenue Plant</span>.</p>
+
+
+<p class="figcenter"><a name="plate_lviii_2" id="plate_lviii_2"></a>
+<img src="images/395b.jpg" title="Telpher Structure and Loading Platform, First Avenue Shaft" height="289" width="400" alt="Telpher Structure and Loading Platform, First Avenue Shaft" /></p>
+
+<p class="caption"><span class="smcap">Plate LVIII, Fig. 2.&mdash;Telpher Structure and Loading Platform, First Avenue Shaft</span>.</p>
+
+
+<p class="figcenter"><a name="plate_lviii_3" id="plate_lviii_3"></a>
+<img src="images/395c.jpg" title="Headworks at 33D Street: Intermediate Shaft" height="289" width="400" alt="Headworks at 33D Street: Intermediate Shaft" /></p>
+
+<p class="caption"><span class="smcap">Plate LVIII, Fig. 3.&mdash;Headworks at 33D Street: Intermediate Shaft</span>.</p>
+
+
+<p class="figcenter"><a name="plate_lviii_4" id="plate_lviii_4"></a>
+<img src="images/395d.jpg" title="Loading Spoil on Barges, 35th Street Pier" height="289" width="400" alt="Loading Spoil on Barges, 35th Street Pier" /></p>
+
+<p class="caption"><span class="smcap">Plate LVIII, Fig. 4.&mdash;Loading Spoil on Barges, 35th Street Pier</span>.</p>
+
+<p>A concrete-mixing plant was placed in each shaft, the mixer being
+located high enough to discharge into cars at about the level of the
+springing line of the arch. Above the mixers were the measuring<span class="pagenum"><a name="Page_395" id="Page_395">[Page 395]</a></span>
+hoppers set in the floor of a platform which was large enough to carry
+half a day's supply of cement. At the South Shaft the cement was
+delivered to this floor from the loading platform through a spiral steel
+chute; at the North Shaft it was lowered in buckets by the telpher. The
+sand and stone were drawn into the hoppers through short chutes from the
+base of the storage bins which occupied the remaining height of the
+shaft&mdash;about 50&nbsp;ft. At the South Shaft the bins were of concrete and
+steel, about 6 by 12&nbsp;ft. in section, and attached to the central wall of
+the caisson. Sand and stone were delivered into them from dump-wagons on
+the loading platform. At the North Shaft steel-plate bins were used, and
+were supplied with material by the buckets handled by the telpher. The
+mixers were No.&nbsp;5 Smith, belt-connected to 25-h.p. motors, and about 0.8&nbsp;cu.&nbsp;yd. of concrete was mixed at a batch. The concrete cars were steel
+side-dumpers of the Wiener or Koppel type.</p>
+
+<p>In order to be able to continue concreting during the winter, when
+neither sand nor stone could be obtained by water, practically all the
+space under the loading platforms in the South Shaft yards not occupied
+by the blacksmith shop was filled with these materials, which were
+placed in storage in the late fall.</p>
+
+<p><i>Intermediate-Shaft Plant.</i>&mdash;The air-compressing plant was located at
+the rear of the 33d Street Intermediate Shaft, and supplied air for
+driving the tunnels east and west from the Intermediate Shafts on both
+32d and 33d Streets. Two compressors, the same as the large
+Laidlaw-Dunn-Gordon machine at First Avenue, were installed here, with a
+similar water-cooling tower.</p>
+
+<p>Both shafts were on private property, owned by the Railroad Company, on
+the north side of the streets, and each was equipped with two telphers
+supported on timber trestles, similar to those at First Avenue. Here,
+however, the buckets were placed on wagons standing at the curb, as
+shown by <a href="#plate_lviii_3">Fig.&nbsp;3, Plate&nbsp;LVIII</a>.</p>
+
+<p>Blowers for ventilation were installed at each shaft, as at First
+Avenue, and, after the excavation had proceeded some distance, small
+blacksmith shops, for sharpening drill steel and making minor repairs,
+were located in the tunnels near the shafts.</p>
+
+<p>The concrete plant in each shaft was similar in arrangement to those at
+First Avenue, but the storage bins had wooden walls made of 2 by 4-in.
+and 2 by 6-in. scantling nailed flat on each other.</p>
+
+<p><span class="pagenum"><a name="Page_396" id="Page_396">[Page 396]</a></span>The contractor's office on 33d Street backed up against the 32d Street
+shaft site, and the basement was used as a storeroom for supplies for
+both shafts.</p>
+
+<p>After the decision to do part of the work between Sixth and Seventh
+Avenues in open cut, an 8-in. air main was laid in 33d Street to the
+West Shafts, and air was supplied from the Intermediate Shaft for work
+on both streets in that neighborhood.</p>
+
+<p><i>West-Shaft Plant.</i>&mdash;West of Sixth Avenue, between 32d and 33d Streets
+and adjacent to the open-cut sections, the Railroad Company obtained
+from the Hudson and Manhattan Railroad Company the use of a large area
+from which the buildings had recently been removed, and gave the use of
+it to the contractor. This was of great value in prosecuting the west
+end of the work. The two West Shafts were located in the streets and
+were supplied with short timber trestles similar to those at the
+Intermediate Shafts. One telpher was taken from each of the Intermediate
+Shafts to operate at each of the West Shafts. In addition, a number of
+stiff-leg derricks were set up along the open-cut section, and were
+operated by Lidgerwood or Lambert air hoisting engines, or by electric
+motors, as circumstances dictated. A 15-ton Bay City locomotive crane
+was also used along part of the open-cut work on 32d Street.</p>
+
+<p>Several concrete plants were installed at points along the open-cut
+section, and were moved from place to place, the same general
+arrangement being adopted as at the plants already described. No.&nbsp;3 and
+No.&nbsp;4 Ransome mixers were used, and were generally set up at about the
+level of the top of the arch. The sand and stone storage bins were made
+of scantlings spiked together, and were necessarily rather shallow on
+account of the proximity of the tunnels to the street surface.</p>
+
+<p><i>Thirty-fifth Street Pier.</i>&mdash;For the receipt and disposal of materials
+at the 35th Street pier, four stiff-leg derricks, operated by electric
+hoisting engines, were installed. Two were used in lifting the muck
+buckets from the wagons and dumping their contents on the scows for
+final disposal (<a href="#plate_lviii_4">Fig.&nbsp;4, Plate&nbsp;LVIII</a>); and the other two were fitted with
+clam-shell buckets for unloading sand and broken stone from barges and
+depositing the materials in large hoppers, from which they were drawn
+into wagons for transportation to the various concrete plants. A large
+part of the cement (all of which was supplied by the Railroad Company)
+was also unloaded at the 35th Street<span class="pagenum"><a name="Page_397" id="Page_397">[Page 397]</a></span> pier and hauled directly to the
+work, the surplus being stored temporarily in the Company's cement
+warehouses on 32d, 33d and 35th Streets, near First Avenue, from which
+it was drawn as required. On the dock was located the main powder
+magazine, a small concrete structure. Considerable use was also made of
+neighboring piers for unloading electric conduits, lumber, steel, etc.</p>
+
+<p class="figcenter"><a name="fig._1" id="fig._1"></a><a href="images/397x.png" title="Special Steel Bucket">
+<img src="images/397.png" title="Special Steel Bucket" height="500" width="600" alt="Special Steel Bucket" /></a></p>
+
+<p class="caption"><span class="smcap">Fig.&nbsp;1</span>. SPECIAL STEEL BUCKET</p>
+
+<p><i>Tunnel Plant.</i>&mdash;The spoil buckets, designed by D.&nbsp;L. Hough and George
+Perrine, Members, Am.&nbsp;Soc.&nbsp;C.&nbsp;E., were a novel feature of the work.
+These buckets are shown in detail in <a href="#fig._1">Fig.&nbsp;1</a> and various photographs.
+They were of 3&nbsp;cu.&nbsp;yd. capacity and were split longitudinally, the two
+halves being pinned at the apices of the ends. For lifting, they were
+suspended from eyes at that point, and, when dumping, trip ropes were
+hooked into eyes at the bottom of each side; lifting the trip ropes or
+lowering the hoisting rope split the bucket, as shown in <a href="#plate_lviii_4">Fig.&nbsp;4, Plate&nbsp;LVIII</a>, and dumped the contents. They were transported in the tunnel on
+flat cars, and in the street on wagons, both cars and<span class="pagenum"><a name="Page_398" id="Page_398">[Page 398]</a></span> wagons being
+provided with cradles shaped to receive the bottom of the bucket.</p>
+
+<p>In the tunnels the loading was done with air-operated steam shovels,
+four (Model 20) Marion shovels being used at various points of the work.
+In <a href="#plate_lix_1">Fig.&nbsp;1, Plate&nbsp;LIX</a>, one of these is shown loading the bucket. The cars
+were hauled by General Electric, standard, 10-ton, mine locomotives, the
+current for which was taken at 220 volts from a pair of No.&nbsp;00 copper
+trolley wires suspended from the roof of the tunnel. The collector was a
+small four-wheeled buggy riding on the wires and connected to the
+locomotive by several hundred feet of cable wound on a reel for use
+beyond the end of the trolley wire. Two 8-1/2-ton, Davenport, steam
+locomotives were also used in 32d Street, toward the end of the work,
+after the headings had been holed through and the tunnels would quickly
+clear themselves of gas and smoke. The steam shovels were supplemented
+by two Browning, 15-ton, locomotive cranes, which handled the spoil in
+places where timbering interfered with the operation of the shovels. All
+tracks were of 3-ft. gauge throughout and laid with 40-lb. rails.</p>
+
+<p>Practically all the heavy drilling was done with Ingersoll drills (Model
+E 52), the trimming being largely done with jap and baby drills. A large
+number of pumps were used at various points on the work, and practically
+all were of Cameron make, the largest ones at the shaft being 10 by 5 by
+13-in. The grout machines were of the vertical-cylinder, air-stirring
+type.</p>
+
+
+<p class="sectionh">Shaft Sinking.</p>
+
+<p>The sinking of the Intermediate Shafts was the first work undertaken by
+the contractor.</p>
+
+<p>The 33d Street Shaft was 34.5&nbsp;ft. long, 21&nbsp;ft. wide, and 83&nbsp;ft. deep.
+The rock surface averaged 5&nbsp;ft. below the ground surface. Sinking was
+started on July 10th, 1905, and was completed on October 3d, 1905, the
+rock being hard and dry. The average daily rate was 0.73&nbsp;ft. and an
+average of 17.1&nbsp;cu.&nbsp;yd. were excavated per day, with two shifts of 8&nbsp;hr.
+each. The first shift started at 6&nbsp;A.&nbsp;M. and the second at 2.30&nbsp;P.&nbsp;M.,
+ending at 11&nbsp;P.&nbsp;M. These hours were adopted in order to avoid undue
+disturbance during the night.</p>
+
+<p class="figcenter"><a name="plate_lix_1" id="plate_lix_1"></a>
+<img src="images/399a.jpg" title="Air-Operated Steam Shovel Used in Tunnel" height="290" width="400" alt="Air-Operated Steam Shovel Used in Tunnel" /></p>
+
+<p class="caption"><span class="smcap">Plate LIX, Fig. 1.&mdash;Air-Operated Steam Shovel Used in Tunnel</span>.</p>
+
+
+<p class="figcenter"><a name="plate_lix_2" id="plate_lix_2"></a>
+<img src="images/399b.jpg" title="Timbering in Top Headings Above I-Beams" height="290" width="400" alt="Timbering in Top Headings Above I-Beams" /></p>
+
+<p class="caption"><span class="smcap">Plate LIX, Fig. 2.&mdash;Timbering in Top Headings Above I-Beams</span>.</p>
+
+
+<p class="figcenter"><a name="plate_lix_3" id="plate_lix_3"></a>
+<img src="images/399c.jpg" title="First Section of Concrete Lining at Fifth Avenue" height="288" width="400" alt="First Section of Concrete Lining at Fifth Avenue" /></p>
+
+<p class="caption"><span class="smcap">Plate LIX, Fig. 3.&mdash;First Section of Concrete Lining at Fifth Avenue</span>.</p>
+
+
+<p class="figcenter"><a name="plate_lix_4" id="plate_lix_4"></a>
+<img src="images/399d.jpg" title="Timbering and Rubble Masonry Over I-Beams" height="288" width="400" alt="Timbering and Rubble Masonry Over I-Beams" /></p>
+
+<p class="caption"><span class="smcap">Plate LIX, Fig. 4.&mdash;Timbering and Rubble Masonry Over I-Beams</span>.</p>
+
+<p>Before blasting the first lift of rock, channel cuts 5 or 6&nbsp;ft. deep
+were made along the sides of the shaft, in order to avoid damage to the<span class="pagenum"><a name="Page_399" id="Page_399">[Page 399]</a></span>
+walls of neighboring buildings. Timbering was required for a depth of
+only 10&nbsp;ft. below the surface of the ground.</p>
+
+<p>A drift, 30.6&nbsp;ft. long, 17&nbsp;ft. wide, and 27&nbsp;ft. high, connected the
+south end of the shaft with the tunnels. The drift was excavated in
+three stages, a top heading and a bench in two lifts. While blasting the
+cut in the top heading, there was enough concussion to break glass in
+the neighboring buildings. The use of a radialax machine reduced the
+concussion somewhat, but it was very quickly abandoned on account of the
+length of time required for the drilling.</p>
+
+<p>The construction of the 32d Street Shaft was quite similar to the one on
+33d&nbsp;Street. It was 31.5&nbsp;ft. long, 20.5&nbsp;ft. wide, and 71&nbsp;ft. deep. The
+depth of earth excavation averaged 19.5&nbsp;ft. The rock in this shaft was
+seamy and not quite as hard or dry as that in 33d Street, and timbering
+was required for practically the full depth to the crown of the drift.
+Sinking was started on May 15th, 1905, and was completed on October
+26th, 1905. The daily average rate was 0.30&nbsp;ft. in earth and 0.52&nbsp;ft. in
+rock. The drift was excavated in much the same manner as the one in 33d
+Street, but the rock being softer the radialax machine was not used.</p>
+
+
+<p class="sectionh">Tunnel Excavation.</p>
+
+<p>During the early part of the work, the contractor devoted his entire
+attention to the work of excavation. Nearly all the excavation east of
+Fifth Avenue was done before any of the lining was placed. At a number
+of points west of Fifth Avenue and at a few points to the east the
+nature of the rock was such that the two operations had to be done
+simultaneously.</p>
+
+<p><i>Single-Tunnel Method.</i>&mdash;For an average distance of 350&nbsp;ft. west from
+the First Avenue Shafts there were four single tunnels. The rock was
+sound and comparatively dry. A top heading of the full size of the
+tunnel and about 8&nbsp;ft. high was first driven. It was drilled by four
+drills mounted on two columns, and was blasted in the ordinary way. The
+bench was about 13&nbsp;ft. high. Tripod drills, standing on the bench,
+drilled the usual holes, but, owing to the lack of head-room, steels
+long enough to reach the bottom of the bench could not be used. Tripod
+drills were set as low as possible at the foot of the bench and drilled
+lifting holes. These holes were inclined downward from 10&deg; to 15&deg; to the
+horizontal, and were spaced to converge at the location of the<span class="pagenum"><a name="Page_400" id="Page_400">[Page 400]</a></span> drainage
+ditches. The heading was usually driven from 10 to 20&nbsp;ft. in advance of
+the bench. At this distance a large part of the muck from the heading
+was shot backward over the bench. In the single tunnels the muck was
+loaded by hand.</p>
+
+<p><i>Twin-Tunnel Methods.</i>&mdash;From the end of the single-track tunnel westward
+to Fifth Avenue on 33d Street, and to Madison Avenue on 32d Street, with
+some exceptions, each pair of tunnels was excavated for the entire width
+at one operation. Three different methods of work were extensively used.
+They were the double-heading method, the center-heading method, and the
+full-sized-heading method, and these differed only in the manner of
+drilling and blasting. The bench was usually within 10 or 15&nbsp;ft. of the
+face of the heading, and was drilled and fired in the same way as in the
+single tunnels. After the installation of the permanent plant, most of
+the muck was handled by steam shovels.</p>
+
+<p>In the double-heading method, shown on Plate&nbsp;LVII, the top headings for
+each tunnel of the pair were driven separately, leaving a short rock
+core-wall between them. The headings were drilled from columns in the
+manner described for the single tunnels. The temporary rock dividing
+wall between the headings was drilled by a tripod drill on the bench of
+one of the headings, and was fired with the bench.</p>
+
+<p>In the center-heading method, also shown on Plate&nbsp;LVII, only one heading
+was driven. It was rectangular in shape, about 8&nbsp;ft. high and 14 ft.
+wide. It was located on the center line between the tunnels. In general,
+the face was from 6 to 12 ft., or the length of one or two rounds, in
+advance of the remainder of the face at the top. The center heading was
+drilled by four drills mounted on two columns. By turning these drills
+to the side, they were used for holes at right angles to the line of the
+tunnels, by which the remainder of the face of the heading was blasted.
+By turning the drills downward, the bench holes under the center heading
+were also drilled. The center heading explored the rock in advance of
+the full-width heading, and gave a good idea as to the care needed in
+firing.</p>
+
+<p>For the full-width-heading method, <a href="#fig._2">Fig.&nbsp;2</a>, ten drills were mounted on
+five columns set abreast across the face. Holes were drilled to form a
+cut near the center line between the tunnels. The remainder of the holes
+were located so that they would draw into the cut. The bench was
+frequently drilled from the same set-up of columns by turning the<span class="pagenum"><a name="Page_401" id="Page_401">[Page 401]</a></span>
+drills downward. In sound rock this method proved to be the most rapid
+of any.</p>
+
+<p>Practically all trimming was left until immediately before the
+concreting. It was then taken up as a separate operation, but proved to
+be costly and tedious, and a hindrance to the placing of the lining.</p>
+
+<p><i>Materials Encountered.</i>&mdash;All the rock encountered was the familiar
+Hudson schist, but it varied widely in its mineral constituents and in
+its physical characteristics. In many places where the rock surface was
+penetrated, a fine sand was found that was probably quicksand. The
+material above the rock in the open-cut sections was mostly sand.</p>
+
+<p class="figcenter"><a name="fig._2" id="fig._2"></a><a href="images/401x.png" title="Method of Excavating with Full-Width Heading Cross-Town Tunnels, Manhattan">
+<img src="images/401.png" title="Method of Excavating with Full-Width Heading Cross-Town Tunnels, Manhattan" height="507" width="600" alt="Method of Excavating with Full-Width Heading Cross-Town Tunnels, Manhattan" /></a></p>
+
+<p class="caption"><span class="smcap">Fig.&nbsp;2.&mdash;Method of Excavating with Full-Width Heading Cross-Town Tunnels, Manhattan</span>.</p>
+
+<p>The concurrence of the watercourse, shown on General Viele's map of
+Manhattan Island (Plate&nbsp;IX<a name="FNanchor_D_4" id="FNanchor_D_4"></a><a href="#Footnote_D_4" class="fnanchor">[D]</a>), with the points where difficulties in
+the construction of the tunnels were encountered has been noted in a
+previous paper.</p>
+
+<p><span class="pagenum"><a name="Page_402" id="Page_402">[Page 402]</a></span>In all cases where the course of this ancient stream was crossed (except
+at its final intersection of 33d Street), the rock was found to be very
+soft and disintegrated, a large quantity of water was encountered, and
+heavy timbering was required. The construction at these localities will
+be taken up later. In addition, disintegrated rock, but of a less
+troublesome character, was invariably met under the depressions in the
+rock surface developed by the borings from the streets and test holes
+from the tunnels. Many of these places required timbering, and no
+timbering was elsewhere necessary except at the portals. These
+coincident conditions were especially marked in 32d Street, which for a
+long distance closely adjoins the course of the former creek.</p>
+
+<p><i>Disposal of Spoil.</i>&mdash;The materials excavated from the tunnels were
+dumped at the 35th Street pier on barges furnished by the Railroad
+Company under another contract, and were towed to points near the
+Bayonne peninsula where the spoil was used principally in the
+construction of the Greenville Freight Yards and the line across the
+Hackensack Meadows to the tunnels. Details of this work will be given in
+a subsequent paper. After December, 1907, when the excavation was about
+85% completed, the contractor furnished the barges and effected the
+complete disposal of the spoil.</p>
+
+<p><i>Difficulties of Excavation.</i>&mdash;As stated in a previous paper, the
+excavation of the Twin Tunnel in 33d Street was continued westward to
+the west line of Fifth Avenue on the original grade. At that point the
+contractor started three drifts in the three-track section. The relation
+of the drifts to each other and to the cross-section are shown by <a href="#fig._3">Fig.&nbsp;3</a>.
+The center heading was driven a little in advance of those on the
+sides. At a distance of 65&nbsp;ft. west of Fifth Avenue the rock surface was
+broken through in the top of the heading, and a very fine sand was
+encountered. For some distance east of this point the rock was badly
+disintegrated, and the heading required timbering. Through the soft
+material, tight lagging was placed on the sides and roof of the heading,
+and the face was protected by breast boards. There was a moderate flow
+of water through the cracks, and, in spite of every effort, some of the
+fine sand was constantly carried into the heading.</p>
+
+<p>In one or two instances considerable ground was lost at the face. On the
+evening of December 14th, 1906, as a heavy coal wagon was passing along
+33d Street above the heading, the rear wheels dropped through the
+asphalt pavement. An examination disclosed a cavity<span class="pagenum"><a name="Page_403" id="Page_403">[Page 403]</a></span> under the pavement
+about 14&nbsp;ft. long, 12&nbsp;ft. wide and 14&nbsp;ft. deep. Evidently, the fine sand
+had gradually settled into the voids caused by the loss of material at
+the face, and the settlement broke the brick sewer over the heading. The
+sewer was temporarily repaired, and the hole in the street was filled
+before morning. A tight bulkhead was built across the heading, and work
+was abandoned at that point. The north drift was advanced to a point
+108&nbsp;ft. west of Fifth Avenue where sand was also encountered and a
+considerable run occurred. After that time all work on the three-track
+section was discontinued.</p>
+
+<p>The Company then took up the consideration of changes in plan. To
+determine the difficulties of driving a Twin Tunnel at a lower
+elevation, an exploration drift, 8&nbsp;ft. high and 12&nbsp;ft. wide, was driven
+on the center line of the street as a top heading on the proposed new
+grade. Test holes were drilled above this heading and to the sides. The
+results indicated that there was sufficient rock cover of fair quality
+to enable the Twin Tunnel to be driven without great risk. The new plan
+(continuing the Twin Tunnel westward at a lower grade) was adopted in
+March, 1907, and work was immediately resumed at Fifth Avenue.</p>
+
+<p>The relation between the cross-sections under the old and new plans at
+that point is shown by <a href="#fig._3">Fig.&nbsp;3</a>. Before the new section was excavated it
+was necessary to support the timber work in the old headings. The plan
+adopted is also shown by <a href="#fig._3">Fig.&nbsp;3</a>. The rock was excavated under the center
+heading, as shown in cross-section, for a length of about 3&nbsp;ft. A girder
+composed of two 18-in. I-beams was then put in position over each line
+and supported on the sides by posts. The ends at the center lines
+between the tunnels were supported on short posts bearing on the rock
+bench. The support of the timbering in the headings was then transferred
+to the girders by additional posts. Blocking was also inserted between
+the tops of the beams and the rock walls between the headings. <a href="#plate_lix_2">Fig.&nbsp;2, Plate&nbsp;LIX</a>, gives a good idea of the timber work in the top headings
+above the I-beams. When the roof had been made secure, the removal of
+the bench was begun. As the work advanced it was necessary to replace
+the short posts at the center of the tunnel by others of full height,
+and there was considerable settlement in the I-beams during this
+operation. When the bench had been removed to a point 61&nbsp;ft. west of
+Fifth Avenue, settlement was detected in the street surface above. Bench
+excavation was<span class="pagenum"><a name="Page_404" id="Page_404">[Page 404]</a></span> suspended and a section of the permanent lining, 35 ft.
+long, was placed. The space between the lining and the beams and between
+the beams and the roof was filled with rubble masonry. Grout pipes were
+built into the masonry and later all voids were filled with grout. <a href="#plate_lix_3">Fig.&nbsp;3, Plate&nbsp;LIX</a>, shows the first section of the concrete lining completed
+and part of the rubble in place; and <a href="#plate_lix_4">Fig.&nbsp;4, Plate&nbsp;LIX</a>, shows details of
+the work above the tunnels. A second section of bench was next removed
+and more lining was placed. Work was continued in this way until all the
+roof at the old three-track headings had been secured. In this portion
+of the work the posts were embedded in the concrete.</p>
+
+<p>Between Fifth and Sixth Avenues there were two more sections of bad rock
+where it was necessary to support the roof with steel beams. At these
+latter points there were no complications with the excavation for the
+Three-Track Tunnel, and the work was much simpler. To avoid leaving the
+center posts in the permanent work, two rows of temporary posts were
+placed, as shown by <a href="#plate_lx_1">Fig.&nbsp;1, Plate&nbsp;LX</a>, the center wall and skewback were
+built, and the posts were removed, as shown by <a href="#plate_lx_2">Fig.&nbsp;2, Plate&nbsp;LX</a>, before
+placing the remainder of the lining.</p>
+
+<p>In 32d Street the normal progress of the excavation was frequently
+interrupted by encountering soft and unsound rock. In the excavation
+between the East River and the Intermediate Shafts it was possible to
+overcome these conditions by temporarily narrowing the excavation on one
+side and supporting the roof on 16 by 16-in. transverse timbers caught
+in niches in the rock at the sides, leaving sufficient room for the
+steam shovel to work through. In order to save time, the height of the
+excavation was not increased before placing these timbers, so that,
+previous to the concreting, they all required to be raised to clear the
+masonry lining and were then supported on posts on the center line
+between the tunnels. This permitted the remainder of the excavation to
+be made, and such additional timbering as was required was placed. At
+most of these sections a brick arch and water-proofing were used, on
+account of the presence of water. In certain places the center line
+posts were buried in the core-wall, and, in order to permit the placing
+of the water-proofing, were then cut off one by one flush with its top
+as the load was transferred to the completed masonry. In other cases the
+load was transferred to posts clear of the masonry and the center line
+posts were entirely removed. Under such conditions the normal concrete
+methods, to be described later, could not be used, and special forms
+were substituted.<span class="pagenum"><a name="Page_405" id="Page_405">[Page 405]</a></span></p>
+
+<p class="figcenter"><a name="fig._3" id="fig._3"></a><a href="images/405x.png" title="Method of Excavating with Full-Width Heading Cross-Town Tunnels, Manhattan">
+<img src="images/405.png" title="Construction of Twin Tunnels, Through Excavation Started for Three-Track Tunnel in 33d Street near 5th Avenue" height="433" width="300" alt="Construction of Twin Tunnels, Through Excavation Started for Three-Track Tunnel in 33d Street near 5th Avenue" /></a></p>
+
+<p class="caption"><span class="smcap">Fig.&nbsp;3</span>.&mdash;CONSTRUCTION OF TWIN TUNNELS, THROUGH EXCAVATION STARTED FOR THREE-TRACK TUNNEL IN 33D STREET NEAR 5TH AVENUE</p>
+
+<p><span class="pagenum"><a name="Page_406" id="Page_406">[Page 406]</a></span>In this section of the work the most serious difficulties were
+encountered near Fourth Avenue a short distance east of the Intermediate
+Shaft, and beneath the site of the old pond shown on General Viele's
+map. The rock cover was known from the boring to be very thin, and the
+presence of the subway overhead caused some anxiety. The excavation was
+at first taken out to practically full width and timbered, but the rock
+became so treacherous that the heading was narrowed to a width
+sufficient for one tunnel only. With this span the rock in the roof held
+without timbering. As the masonry lining approached, sufficient trimming
+was done to permit the placing of the core-wall and one arch. Above the
+completed core-wall and brick arch the voids were filled solid with
+rubble masonry to give an unyielding support to the roof. The excavation
+of the remaining width of tunnel was then undertaken. Near the west side
+of Fourth Avenue, the excavation broke out of rock at the top, and fine
+sand and gravel with a large quantity of water were encountered. The
+work of excavation was arduous, and proceeded very slowly, on account of
+the care with which it was executed. Only a small amount of sand entered
+the tunnel, but the lining was placed as soon as the excavation was
+completed. Rubble masonry packing and grout ejected through pipes built
+into the arch were used to fill the voids above the roof. As a further
+precaution against the settlement of the subway, 2-in. pipes were washed
+down from the street above the point where soft ground was exposed in
+the roof of the tunnel, and through them grout was forced into the
+ground at various depths. Careful levels show that no settlement of the
+subway has taken place.</p>
+
+<p>West of the Intermediate Shaft the tunnel was excavated for full width
+until bad rock was encountered about 60&nbsp;ft. west of Madison Avenue. (See
+General Viele's map, Plate&nbsp;IX.) Timbering was used for a short distance,
+and then the heading and bench were narrowed to 18 ft., and steam-shovel
+excavation was abandoned. As the heading advanced the rock grew steadily
+softer, the difficult conditions in this locality culminating when a
+slushy disintegrated feldspar was met, requiring poling and breasting.
+Thereafter the rock improved markedly, but near the east side of Fifth
+Avenue its thickness above<span class="pagenum"><a name="Page_407" id="Page_407">[Page 407]</a></span> the roof was found to be only 1-1/2 ft.,
+and the advance was stopped, pending a decision as to a change of plan.</p>
+
+
+<p class="figcenter"><a name="plate_lx_1" id="plate_lx_1"></a>
+<img src="images/407a.jpg" title="Double Row of Posts Under I-Beams, Supporting Roof in Bad Rock Section" height="289" width="400" alt="Double Row of Posts Under I-Beams, Supporting Roof in Bad Rock Section" /></p>
+
+<p class="caption"><span class="smcap">Plate LX, Fig. 1.&mdash;Double Row of Posts Under I-Beams, Supporting Roof in Bad Rock Section</span>.</p>
+
+
+<p class="figcenter"><a name="plate_lx_2" id="plate_lx_2"></a>
+<img src="images/407b.jpg" title="Center Wall and Skewback Under I-Beams, After Removal of Double Row of Posts" height="289" width="400" alt="Center Wall and Skewback Under I-Beams, After Removal of Double Row of Posts" /></p>
+
+<p class="caption"><span class="smcap">Plate LX, Fig. 2.&mdash;Center Wall and Skewback Under I-Beams, After Removal of Double Row of Posts</span>.</p>
+
+
+<p class="figcenter"><a name="plate_lx_3" id="plate_lx_3"></a>
+<img src="images/407c.jpg" title="Timbering in Full-Width Heading of Three-Track Tunnel" height="285" width="400" alt="Timbering in Full-Width Heading of Three-Track Tunnel" /></p>
+
+<p class="caption"><span class="smcap">Plate LX, Fig. 3.&mdash;Timbering in Full-Width Heading of Three-Track Tunnel</span>.</p>
+
+
+<p class="figcenter"><a name="plate_lx_4" id="plate_lx_4"></a>
+<img src="images/407d.jpg" title="Underpinning Walls in Open-Cut Section" height="290" width="400" alt="Underpinning Walls in Open-Cut Section" /></p>
+
+<p class="caption"><span class="smcap">Plate LX, Fig. 4.&mdash;Underpinning Walls in Open-Cut Section</span>.</p>
+
+<p>After some delay, an exploration drift, similar to the one already
+described, was driven through to Sixth Avenue, and a change in plan was
+made, substantially the same as for the 33d Street tunnels. Enlargement
+to full size was at once started, but, for 400&nbsp;ft. the rock was very
+soft and poor, and required extremely careful handling. The exploration
+drift was widened out to the full Twin-Tunnel width, and I-beams were
+placed and supported, in much the same manner as in 33d Street. The rock
+was so soft that it was frequently necessary to drive poling boards
+ahead as the face was mined out with picks and shovels. The load was
+very heavy, and the work the most difficult encountered in the tunnels.</p>
+
+<p>After this stage of the enlargement was reached, the excavation of the
+bench and the placing of the lining proceeded alternately, with the
+I-beams temporarily supported on long posts while the concrete core-wall
+was being built. Considerable settlement took place while shifting the
+posts, and eventually showed on the street surface and in the adjacent
+sidewalk vaults, but no damage was done to the structural portions of
+the buildings.</p>
+
+<p>While the above work had been going on westward from Fifth Avenue, the
+excavation of the Twin Tunnel eastward from the end of the open-cut
+section at Sixth Avenue had been proceeding rapidly, and, toward the end
+of the difficult Fifth Avenue work, it was being attacked from both
+directions.</p>
+
+
+<h3><span class="smcap">Progress of Excavation</span>.</h3>
+
+<p>Owing to the numerous sections of poor rock, interspersed throughout the
+work with stretches of sound rock, the progress of the excavation was
+very irregular, especially in 32d Street. The rate of excavation in good
+ground is shown in Table&nbsp;1. In the sections of bad ground, the
+operations of excavation, timbering, and lining were often carried on
+alternately, and it is impracticable to include them in the table.</p>
+
+<p><span class="pagenum"><a name="Page_408" id="Page_408">[Page 408]</a></span></p>
+<p><span class="pagenum"><a name="Page_409" id="Page_409">[Page 409]</a></span></p>
+
+<h3>TABLE 1.&mdash;<span class="smcap">Progress and Methods of Excavation in Good Ground</span>.</h3>
+
+<h3 class="left"><span class="smcap">Thirty-Third Street</span>.</h3>
+
+<table summary="progress and methods of excavation in good ground thirty-third street">
+<colgroup span="9">
+<col width="auto"></col>
+<col width="auto"></col>
+<col width="auto"></col>
+<col width="auto"></col>
+<col width="auto"></col>
+<col width="auto"></col>
+<col width="auto"></col>
+<col width="auto"></col>
+<col width="auto"></col>
+</colgroup>
+<tr>
+<td class="tda" rowspan="2">Type of excavation.</td>
+<td class="tdb" rowspan="2">Tunnels.</td>
+<td class="tdb" rowspan="2">Worked from:</td>
+<td class="tdb" colspan="2"><span class="smcap">Dates</span>.</td>
+<td class="tdb" rowspan="2">Time<br />elapsed,<br />in<br />days.</td>
+<td class="tdb" rowspan="2">Length of<br />tunnel<br />excavated,<br />in<br />linear feet.</td>
+<td class="tdb" rowspan="2">Average<br />advance<br />per day,<br />in<br />linear feet.</td>
+<td class="tdc" rowspan="2">Methods and conditions.</td>
+</tr>
+<tr>
+<td class="tdb">From</td>
+<td class="tdb">To</td>
+</tr>
+
+<tr>
+<td class="tdd">Full-sized single tunnel</td>
+<td class="tde">B</td>
+<td class="tde">1st Ave. shaft.</td>
+<td class="tdf">Feb. 28, 1906.</td>
+<td class="tdf">May 12, 1906.</td>
+<td class="tdg">74</td>
+<td class="tdg">346</td>
+<td class="tdg">4.7</td>
+<td class="tdh">Top heading and bench. Muck loaded by hand.</td>
+</tr>
+<tr>
+<td class="tdi">Full-sized single tunnel</td>
+<td class="tdj">A</td>
+<td class="tdj">1st Ave. shaft.</td>
+<td class="tdk">Feb. 28, 1906.</td>
+<td class="tdk">Apr. 30, 1906.&nbsp;&nbsp;&nbsp;</td>
+<td class="tdl">62</td>
+<td class="tdl">255</td>
+<td class="tdl">4.1</td>
+<td class="tdm">&nbsp; &nbsp;"&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;" &nbsp; &nbsp; &nbsp;  &nbsp;" &nbsp; &nbsp; &nbsp; " &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; " &nbsp; &nbsp; &nbsp; &nbsp;"&nbsp; &nbsp; &nbsp;&nbsp;"&nbsp; &nbsp;&nbsp; "</td>
+</tr>
+<tr>
+<td class="tdi">Full-sized twin tunnel</td>
+<td class="tdj">A and B</td>
+<td class="tdj">1st Ave. shaft.</td>
+<td class="tdk">Aug. 23, 1906.</td>
+<td class="tdk">Jan. 5, 1907.</td>
+<td class="tdl">136</td>
+<td class="tdl">789</td>
+<td class="tdl">5.8</td>
+<td class="tdm">Top full-width heading and bench. Muck loaded<br />
+by steam shovel. Working exclusively on this<br />
+heading.</td>
+</tr>
+<tr>
+<td class="tdi">Full-sized twin tunnel</td>
+<td class="tdj">A and B</td>
+<td class="tdj">Intermediate shaft.<br />(West of shaft.)</td>
+<td class="tdk">Apr. 4, 1906.</td>
+<td class="tdk">Oct. 31, 1906.</td>
+<td class="tdl">210</td>
+<td class="tdl">730</td>
+<td class="tdl">3.5</td>
+<td class="tdm">Top center heading and bench. Muck loaded by<br />
+steam shovel. Working alternately in headings<br />
+east and west of the shaft.</td>
+</tr>
+<tr>
+<td class="tdi">Full-sized twin tunnel</td>
+<td class="tdj">A and B</td>
+<td class="tdj">Intermediate shaft.<br />(East of shaft.)</td>
+<td class="tdk">Apr. 4, 1906.</td>
+<td class="tdk">Oct. 31, 1906.</td>
+<td class="tdl">210</td>
+<td class="tdl">783</td>
+<td class="tdl">3.7</td>
+<td class="tdm">Top center heading and bench. Muck loaded by<br />
+steam shovel. Working alternately in headings<br />
+east and west of the shaft.</td>
+</tr>
+
+<tr>
+<td class="tdi">Full-sized twin tunnel</td>
+<td class="tdj">A and B</td>
+<td class="tdj">Intermediate shaft.<br />(East of shaft.)</td>
+<td class="tdk">Nov. 1, 1906.</td>
+<td class="tdk">Dec. 26, 1906.</td>
+<td class="tdl">56</td>
+<td class="tdl">311</td>
+<td class="tdl">5.5</td>
+<td class="tdm">Top full-width heading and bench. Muck loaded<br />
+by steam shovel working exclusively on this<br />
+heading.</td>
+</tr>
+
+<tr>
+<td class="tdi">Exploration drift</td>
+<td class="tdj">A and B</td>
+<td class="tdj">Intermediate shaft.<br />(West of shaft.)</td>
+<td class="tdk">Mar. 1, 1907.</td>
+<td class="tdk">July 23, 1907.</td>
+<td class="tdl">145</td>
+<td class="tdl">947</td>
+<td class="tdl">6.5</td>
+<td class="tdm">Exploration drift about 9 ft. by 12 ft. Mucking<br />
+by hand. Fourteen timber bents were placed in<br />
+March, and seven in April, 1907.</td>
+</tr>
+
+<tr>
+<td class="tdn">Twin tunnel. Enlargement<br />of exploration drift</td>
+<td class="tdo">A and B</td>
+<td class="tdo">West shaft.<br />
+(East of shaft.)</td>
+<td class="tdp">Sept. 6, 1907.</td>
+<td class="tdp">Dec. 4, 1907.</td>
+<td class="tdq">89</td>
+<td class="tdq">603</td>
+<td class="tdq">6.8</td>
+<td class="tdr">Drift excavated to full width and bench. Muck<br />
+loaded by steam shovel.</td>
+</tr>
+</table>
+
+<h3 class="left"><span class="smcap">Thirty-Second Street</span>.</h3>
+
+<table summary="progress and methods of excavation in good ground thirty-second street">
+<colgroup span="9">
+<col width="auto"></col>
+<col width="auto"></col>
+<col width="auto"></col>
+<col width="auto"></col>
+<col width="auto"></col>
+<col width="auto"></col>
+<col width="auto"></col>
+<col width="auto"></col>
+<col width="auto"></col>
+</colgroup>
+<tr>
+<td class="tda" rowspan="2">Type of excavation.</td>
+<td class="tdb" rowspan="2">Tunnels.</td>
+<td class="tdb" rowspan="2">Worked from:</td>
+<td class="tdb" colspan="2"><span class="smcap">Dates</span>.</td>
+<td class="tdb" rowspan="2">Time<br />elapsed,<br />in<br />days.</td>
+<td class="tdb" rowspan="2">Length of<br />tunnel<br />excavated,<br />in<br />linear feet.</td>
+<td class="tdb" rowspan="2">Average<br />advance<br />per day,<br />in<br />linear feet.</td>
+<td class="tdc" rowspan="2">Methods and conditions.</td>
+</tr>
+<tr>
+<td class="tdb">From</td>
+<td class="tdb">To</td>
+</tr>
+
+<tr>
+<td class="tdd">Full-sized single tunnel</td>
+<td class="tde">C</td>
+<td class="tde">1st Ave. shaft.</td>
+<td class="tdf">Jan. 25, 1906.</td>
+<td class="tdf">Apr. 30, 1906.</td>
+<td class="tdg">95</td>
+<td class="tdg">367</td>
+<td class="tdg">3.9</td>
+<td class="tdh">Top heading and bench. Muck loaded by hand.</td>
+</tr>
+<tr>
+<td class="tdi">Full-sized single tunnel</td>
+<td class="tdj">D</td>
+<td class="tdj">1st Ave. shaft.</td>
+<td class="tdk">Jan. 27, 1906.</td>
+<td class="tdk">Apr. 30, 1906.</td>
+<td class="tdl">93</td>
+<td class="tdl">354</td>
+<td class="tdl">3.8</td>
+<td class="tdm">&nbsp; &nbsp;"&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;" &nbsp; &nbsp; &nbsp;  &nbsp;" &nbsp; &nbsp; &nbsp; " &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; " &nbsp; &nbsp; &nbsp; &nbsp;"&nbsp; &nbsp; &nbsp;&nbsp;"&nbsp; &nbsp;&nbsp; "</td>
+</tr>
+<tr>
+<td class="tdi">Full-sized twin tunnel</td>
+<td class="tdj">C and D</td>
+<td class="tdj">1st Ave. shaft.</td>
+<td class="tdk">May 22, 1906.<br />
+Aug. 11, 1906.</td>
+<td class="tdk">July 24, 1906.<a href="#Footnote_E_5" class="fnanchor">[E]</a><br />
+Nov. 29, 1906. </td>
+<td class="tdl">173</td>
+<td class="tdl">810</td>
+<td class="tdl">4.7</td>
+<td class="tdm">Double heading and bench. Muck loaded by steam<br />
+shovel. Stretches aggregating 200 ft. narrowed<br />
+to about 25 ft. and later enlarged are included. </td>
+</tr>
+<tr>
+<td class="tdi">Narrowed twin tunnel</td>
+<td class="tdj">C</td>
+<td class="tdj">Intermediate shaft.</td>
+<td class="tdk">Mar. 19, 1906.</td>
+<td class="tdk">May 28, 1906.</td>
+<td class="tdl">70</td>
+<td class="tdl">58</td>
+<td class="tdl">0.8</td>
+<td class="tdm">Excavation about 30 ft. wide. Top full-width heading<br />
+and bench. Muck loaded by hand. Steam shovel<br />
+not installed. </td>
+</tr>
+<tr>
+<td class="tdi">Full-sized twin tunnel</td>
+<td class="tdj">C</td>
+<td class="tdj">Intermediate shaft.<br />(East of shaft.)</td>
+<td class="tdk">May 29, 1906.<br />
+July 18, 1906.<br />
+Aug. 12, 1906.<br />
+Jan. 15, 1907.<br />
+Feb. 17, 1907.<br /></td>
+<td class="tdk">July 3, 1906<a href="#Footnote_E_5" class="fnanchor">[E]</a><br />
+July 31, 1906. <br />
+Nov. 23, 1906. <br />
+Feb. 5, 1907. <br />
+Mar. 21, 1907. </td>
+<td class="tdl">208</td>
+<td class="tdl">1,206</td>
+<td class="tdl">5.8</td>
+<td class="tdm">Excavation about 30 to 35 ft. wide. Top full-width<br />
+heading and bench. Muck loaded by steam shovel. </td>
+</tr>
+
+<tr>
+<td class="tdi">Full-sized twin tunnel</td>
+<td class="tdj">C and D</td>
+<td class="tdj">Intermediate shaft.<br />(West of shaft.)</td>
+<td class="tdk">Dec. 1, 1905.</td>
+<td class="tdk">May 10, 1906.</td>
+<td class="tdl">161</td>
+<td class="tdl">225</td>
+<td class="tdl">1.4</td>
+<td class="tdm">Double heading and bench. Part of the muck handled<br />
+by hand and part by steam shovel.<br /></td>
+</tr>
+
+<tr>
+<td class="tdi">Exploration drift</td>
+<td class="tdj">C and D</td>
+<td class="tdj">Intermediate shaft.<br />(West of shaft.)</td>
+<td class="tdk">Feb. 1, 1907.</td>
+<td class="tdk">Sept. 13, 1907.</td>
+<td class="tdl">225</td>
+<td class="tdl">1,033</td>
+<td class="tdl">4.6</td>
+<td class="tdm">Exploration drift about 10 ft. by 13 in. Muck loaded<br />
+by hand. 14 ft. timbered.</td>
+</tr>
+
+<tr>
+<td class="tdi">Twin tunnel. Enlargement<br />of exploration drift</td>
+<td class="tdj">C and D</td>
+<td class="tdj">Eastward from<br />
+open cut.</td>
+<td class="tdk">Feb. 1, 1908.<br /></td>
+<td class="tdk">Feb. 14, 1908.</td>
+<td class="tdl">14</td>
+<td class="tdl">65</td>
+<td class="tdl">4.6</td>
+<td class="tdm">At portal of twin tunnels. Drift excavated to full<br />
+width and bench. Muck loaded by hand. 12 ft.<br />
+timbered. </td>
+</tr>
+
+<tr>
+<td class="tdn">Twin tunnel. Enlargement<br />of exploration drift</td>
+<td class="tdo">C and D</td>
+<td class="tdo">Eastward from<br />
+open cut.</td>
+<td class="tdp">Feb. 15, 1908.<br /></td>
+<td class="tdp">Apr. 14, 1908.</td>
+<td class="tdq">59</td>
+<td class="tdq">524</td>
+<td class="tdq">8.9</td>
+<td class="tdr">Drift excavated to full width and bench. Muck loaded<br />
+by steam shovel. Full-width tunnel timbered for 26<br />
+ft. independently of the main excavation. </td>
+</tr>
+</table>
+
+
+
+<div class="footnote"><p><a name="Footnote_E_5" id="Footnote_E_5"></a><span class="label">[E]</span>Time and distance omitted while working through timbered stretches.</p></div>
+
+
+
+<p><span class="pagenum"><a name="Page_410" id="Page_410">[Page 410]</a></span></p>
+
+<p class="sectionh">Three-Track Tunnel Excavation.</p>
+
+<p>When it became evident that the work through the Fifth Avenue section
+would be extremely slow, shafts were sunk in each street between Sixth
+and Seventh Avenues. The shafts, as shown on Plate&nbsp;XIV, were located in
+the streets, but in such a way as to block only half of the roadway. At
+the same time it was decided to construct in open cut about 200 ft. of
+the Three-Track Tunnel at the west end of the contract in 32d Street,
+where the rock surface was below the top of the tunnel. It was hoped
+that the remainder of the work could be built without opening the
+street, but further investigation showed that this was impracticable,
+and eventually all the Three-Track Tunnel in 32d Street, except 120 ft.
+east of the shaft, was built in open cut.</p>
+
+<p><i>Thirty-second Street Work in Tunnel.</i>&mdash;Following the sinking of the
+shaft, a drift was driven across the street at the crown of the tunnel,
+and a top heading on the south side was excavated in both directions.
+Frequent cross-drifts to the north side showed that the rock was nowhere
+very sound and that, except for a short distance east of the shaft, it
+was distinctly unfavorable for the wide Three-Track excavation. In this
+stretch the north ends of these cross-cuts were connected by a second
+heading, and wall-plates and sets of three-segment arch timbering were
+set up to support the roof of the drifts. The cross-cuttings were
+gradually widened and timbered until the entire excavation had been made
+down to the level of the wall-plates, as shown in <a href="#plate_lx_3">Fig.&nbsp;3, Plate&nbsp;LX</a>. The
+bench was then excavated in two lifts, leaving the wall-plates supported
+on narrow longitudinal berms, which were removed in short sections to
+permit the placing of posts under the wall-plates.</p>
+
+<p><i>Thirty-second Street Open-Cut Work.</i>&mdash;Before actual open-cut excavation
+was started, all buildings facing it were underpinned to rock. For this
+purpose, a trench was dug along the face of the buildings and of the
+same depth as their cellars. Holes were cut in the front foundation
+walls through which long needle-beams (<a href="#plate_lx_4">Fig.&nbsp;4, Plate&nbsp;LX</a>) were inserted
+and jacked up on blocking placed on the cellar floor and in the trench,
+until the weight of the building had been taken off its foundations. A
+close-sheeted trench was then sunk to rock under the front building
+walls, and a light rubble masonry retaining wall was built in it to
+support the building permanently. Frequently, the excavation for the
+underpinning wall, which was taken out in sections from 30 to 40 ft.
+long, and in places was carried to a depth of 40 ft., was very
+troublesome on account of the large quantity of water encountered and
+the fineness of the sand, which exhibited a tendency to flow when
+saturated.</p>
+
+<p><span class="pagenum"><a name="Page_411" id="Page_411">[Page 411]</a></span>The Elevated Railroad columns in Sixth Avenue, near the north and south
+lines of 32d Street, were underpinned in a manner similar to the
+building foundations, while those on the center line of the street were
+supported by girders riveted to them close under the track level. The
+girders in turn were supported on posts footed on the new underpinning
+of the adjacent columns. On the completion of the tunnels, concrete
+piers were built up from the roof of the tunnel to form a permanent
+foundation for the center-line columns. The area to be excavated under
+Sixth Avenue was enclosed by a rubble masonry retaining wall constructed
+in a trench.</p>
+
+<p>Open-cut excavation was started by planking over the street on stringers
+resting on transverse 12 by 12-in. caps. The caps were gradually
+undermined and supported on temporary posts which were then replaced by
+short posts resting on 12 by 12-in. sills about 7&nbsp;ft. below the cap. The
+operation was then repeated and the sill was supported on another set of
+short posts resting on a second sill. When the excavation had been
+carried down in this manner to the level of the top of the tunnel,
+diagonal 3 by 10-in. timbers were cut in between the posts and sills to
+form a species of double A-frame, the legs of which rested in niches cut
+in the rock and on posts carried up the face of the underpinning wall,
+and the whole was stiffened with vertical tie-rods. This construction is
+shown by <a href="#plate_lx_3">Fig.&nbsp;3, Plate&nbsp;LXII</a>. The brick sewer was replaced temporarily by
+one of riveted steel pipe. This pipe and the water and gas pipes and
+electric conduits were suspended from the timbers as the pipes were
+uncovered.</p>
+
+<p>Excavation in rock was made by sinking a pit to sub-grade for the full
+width of the tunnel and advancing the face of the pit in several lifts,
+the muck being blown over the slope and loaded into buckets at its foot.</p>
+
+<p>The work was attacked at several places simultaneously, and the spoil
+was hoisted by derricks located at convenient points along the side of
+the cut.</p>
+
+<p><i>Thirty-third Street Work in Tunnel and Open Cut.</i>&mdash;The West 33d Street
+Shaft was similar to the one in 32d Street, and was sunk during
+February, March, and April, 1907, through 10&nbsp;ft. of earth, 21&nbsp;ft. of
+soft rock, and 29&nbsp;ft. of fairly hard rock. It was necessary to timber
+heavily the upper 30&nbsp;ft. of the shaft. The timber later showed evidences
+of severe strain, and had to be reinforced.</p>
+
+<p class="figcenter"><a name="plate_lxi" id="plate_lxi"></a><a href="images/412x.png" title="EXCAVATION AND TIMBERING IN HEAVY GROUND OF THREE-TRACK TUNNEL OF 33D ST.">
+<img src="images/412.png" title="EXCAVATION AND TIMBERING IN HEAVY GROUND OF THREE-TRACK TUNNEL OF 33D ST." height="404" width="600" alt="EXCAVATION AND TIMBERING IN HEAVY GROUND OF THREE-TRACK TUNNEL OF 33D ST." /></a></p>
+
+
+<p class="caption">Plate&nbsp;LXI.&mdash;EXCAVATION AND TIMBERING IN HEAVY GROUND OF THREE-TRACK TUNNEL OF 33D ST.</p>
+
+
+<p>As soon as the shaft excavation was deep enough, a drift was<span class="pagenum"><a name="Page_412" id="Page_412">[Page 412]</a></span> driven
+part way across the tunnels, and top headings were started both east and
+west to explore the rock. The heading to the west was divided into two
+drifts, as shown on <a href="#plate_lxi">Plate&nbsp;LXI</a>. These two drifts were continued to the
+west end of the contract, and were then enlarged to a full-sized heading
+and timbered, as shown on <a href="#plate_lxi">Plate&nbsp;LXI</a> and <a href="#plate_lx_3">Fig.&nbsp;3, Plate&nbsp;LX</a>. The rock near
+the shaft contained many wet rusty seams, and settlement was detected in
+the segmental tunnel timbering soon after the widening of the heading
+was completed. Short props were placed under the timbers, and the street
+surface was opened with a view of stripping the earth down to the rock
+and thus lightening the load on the timbering. Street traffic was
+maintained on a timber structure with posts eventually carried down to
+the rock surface, and the walls of the buildings on the north side of
+the street were underpinned to rock. The settlement of the tunnel
+timbering was checked for a time, and the bench was excavated as shown
+on <a href="#plate_lxi">Plate&nbsp;LXI</a>. In this work the cut in the center was first made, and the
+short props were replaced by struts, as shown; after this the berms were
+removed and the side posts were placed. While building the brick arches,
+holes were left in the masonry around the struts. After the masonry had
+hardened, piers were built on the arches to support the segmental
+timbers. The struts were then removed and the openings filled with
+masonry. The voids above the arch were packed with rock and afterward
+thoroughly grouted.</p>
+
+<p>The timbers near the shaft continued to settle, and, although they had
+been placed from 9 to 12&nbsp;in. above the level of the top of the masonry,
+by October 1st, they encroached 9&nbsp;in. within the line of masonry. It was
+then decided to remove the rock for a distance of 48&nbsp;ft. west of the
+shaft, and build this portion of the tunnel in open cut. The posts
+supporting the deck forming the street surface were replaced by an
+A-frame structure similar to that developed for the 32d Street open cut,
+without interruption of the street traffic.</p>
+
+<p>After making the open cut to the westward of the shaft, there was a slip
+in the rock north of and adjoining the shaft. Fortunately, the timbers
+did not give way entirely, and no damage was done. The open cut was
+extended eastward for a distance of 46 ft., making the total length of
+tunnel built in open cut on this street 94 ft.</p>
+
+<p>East of the shaft, for a distance of about 125 ft., the rock was broken
+and could not be excavated to full size without timbering the roof, but
+between this section of poor rock and those already men<span class="pagenum"><a name="Page_413" id="Page_413">[Page 413]</a></span>tioned in
+connection with the work at Fifth Avenue, there was a stretch of 600 ft.
+of good rock where all the spoil was handled with a steam shovel.</p>
+
+
+<p class="sectionh">Twin-Tunnel Lining.</p>
+
+<p>The masonry lining for the tunnels was not started until the late fall
+of 1906, after excavation had been in progress for a year and a half. At
+that time concreting was started in the single tunnels westward from the
+First Avenue Shafts, and by spring was in full swing in the Twin
+Tunnels.</p>
+
+<p>The plans contemplated the use of a complete concrete lining except
+where large quantities of water were encountered; in which case the
+arches, beginning at a point 15&deg; above the springing line, were to be
+built of vitrified paving brick. By reference to Plate&nbsp;XII it will be
+seen that the water-proofing, which in the concrete-roof tunnels
+extended the full height of the sides to the 15&deg; line, was carried in
+the brick-roof tunnels completely around the extrados of the arch. The
+cross-sections also show the location of the electric conduits which
+were buried in the mass of the side and core-walls and which limited the
+height to which the concrete could be carried in one operation.</p>
+
+<p>The same general scheme of operations was used wherever possible
+throughout the Twin-Tunnel work, but was subject to minor modifications
+as circumstances dictated. Concrete was first deposited in the bottom,
+to the grade of the flow line of the drains; after it had set,
+collapsible box forms, of 2-in. plank with 3-in. plank tops, were laid
+on it to form the ditch and the shoulders for the flagstone covers. The
+track, which had previously been blocked up on the rock between the
+ditches, was raised and supported on the ditch boxes above the finished
+floor level. At the same time, light forms were braced from the ditch
+boxes to the grade of the base of the low-tension and telephone-duct
+bank. After depositing the concrete to this level, the telephone ducts
+were laid.</p>
+
+<p>The forms for the water-proofing or sand-wall up to the 15&deg; line and for
+the main side-walls and core-walls were built in 30-ft. panels and were
+supported on carriages, which, traveling on a broad-gauge track above
+the ditches, moved along the tunnel, section by section, as the work
+advanced. The panels were hung loosely from joists carrying a platform
+on the top chord of the carriage trusses, and were<span class="pagenum"><a name="Page_414" id="Page_414">[Page 414]</a></span> adjusted
+transversely by bracing and wedging them out from the carriage. The
+small forms for the refuge niches, ladders, etc., were collapsible, and
+were spiked to the main panel forms just previous to the deposition of
+the concrete. The concrete was deposited from the platform on top of the
+carriage, to which the cars were elevated in various ways. <a href="#plate_lxi">Plate&nbsp;LXI</a>
+shows the details of the carriages, and is self-explanatory.</p>
+
+<p>The concrete for the sand-walls and the core-wall, to the level of the
+sidewalk, was deposited at the same time; two carriages in each tunnel,
+placed opposite each other, forming a 60-ft. length, were used at each
+setting. The floor section of the 4-in. tile drains had been laid with
+the floor concrete, and, as the sand-wall concrete was deposited, the
+drains were brought up simultaneously, broken stone being deposited
+between the tile and the rock to form a blind drain and afford access to
+the open joints of the tile for the water entering the tunnel through
+seams in the rock. The drains were spaced at intervals not exceeding 25
+ft., depending on the wetness of the rock, and were placed at similar
+intervals in the core-wall under the lowest projecting points of the
+rock on the center line between the tunnels. A small ditch lined with
+loose 6-in. vitrified half pipe was provided in the top of the sand-wall
+to collect the water from the extrados of the arch and lead it to the
+top of the drains. Great difficulty was experienced in maintaining these
+drains clear, and, on completion of the work, a large amount of labor
+was expended in removing obstructions from the floor sections, the only
+portion then accessible.</p>
+
+<p>After water-proofing the sand-walls and laying the low-tension ducts, a
+second pair of carriages, with panels on one side only, for 60 ft. of
+side-wall and skewback to the 15&deg; line, were set and braced against the
+core-wall. These forms are shown in connection with the carriage on
+<a href="#plate_lxi">Plate&nbsp;LXI</a>. They were concreted to the base of the high-tension duct
+bank, and, after the concrete had hardened and the bank of ducts had
+been laid, the concreting was completed in a second operation.</p>
+
+<p>In places where the roof was supported temporarily by posts and heavy
+timbering, such as at Fifth Avenue, the form carriages could not be
+used, and special methods were devised to suit the local conditions.
+Usually, the panels were stripped from the carriages and moved from
+section to section by hand, and, when in position, were braced to the
+timbering.</p>
+
+<p><span class="pagenum"><a name="Page_415" id="Page_415">[Page 415]</a></span>The arch centers were built up of two 5 by 3 by 3/8-in. steel angles,
+and, when set, were blocked up on the sidewalks opposite each other in
+the two tunnels. A temporary platform was laid on the bottom chord
+angles of the ribs, on which the concrete was dumped, the same as on the
+form carriages. The lagging used was 3 by 3-in. dressed pine or spruce
+16 ft. long, and was placed as the concreting of the arch proceeded
+above the 15&deg; line on the side-wall and above the sidewalk on the
+core-wall. After the arch had reached such a height that the concrete
+could not be passed over the lagging directly from the main platform, it
+was cast on a small platform on the upper horizontal bracing of the
+centers, shown in <a href="#plate_lix_3">Fig.&nbsp;3, Plate&nbsp;LIX</a>, and was thence shoveled into the
+work. In the upper part of the arch the face of the concrete was kept on
+a radial plane, and, when only 3&nbsp;ft. remained to be placed, it was keyed
+in from one end, the key lagging being set in about 5-ft. lengths. The
+arches were concreted usually in 60-ft. lengths.</p>
+
+<p>Where brick arches were used, the core-wall skewback was concreted
+behind special forms set up on the sidewalks, or the arch ribs and
+lagging were used for forms, and the brick arch was not started until
+after the concrete had set. In laying the brick in the arch, the five
+courses of the ring were carried up as high as the void between the
+extrados and the rock would permit and still leave a working space in
+which to place the water-proofing. This was usually not more than 3 ft.,
+except on the core-wall side. The felt and pitch water-proofing was then
+laid for that height, joined to the previous water-proofing on the
+side-walls, and was followed by the brick armor course over the
+water-proofing and by the rock packing, after which another lift of
+brick was laid and the operations were repeated. The large void (<a href="#plate_lxii_1">Fig.&nbsp;1, Plate&nbsp;LXII</a>) above the core-wall gave convenient access for working on
+top of the adjacent sides of the roof, and the keying of the arches and
+the water-proofing and rock packing above the core-wall were usually
+carried on from that point, the work progressing from one end.</p>
+
+<p>The concrete for all work above the floor was dumped on the platform of
+the carriages, to which it was transported in the early part of the work
+in cars running on a high-level track laid on long ties, resting on the
+finished sidewalks. This arrangement, although requiring a large amount
+of timber for the track, permitted the muck to be carried out on the
+low-level track without interference. Later, when the<span class="pagenum"><a name="Page_416" id="Page_416">[Page 416]</a></span> advance of the
+heading had ceased and the heavy mucking was over, all concrete was
+transported on the floor level, and the cars were lifted to the carriage
+platforms by elevators and were hauled by hoisting engines up a movable
+incline. The latter method is shown by <a href="#plate_lix_3">Fig.&nbsp;3, Plate&nbsp;LIX</a>.</p>
+
+<p><i>Water-Proofing.</i>&mdash;The water-proofing referred to above was in all cases
+felt and pitch laid with six thicknesses of felt and seven of pitch. The
+sub-contractor for the work was the Sicilian Asphalt Paving Company. All
+joints were lapped at least 1 ft., and, where work was suspended for a
+time and a bevel lap could not be made, the edges of the felt were left
+unpitched for 1&nbsp;ft. and the newer work was interlaced with the old. This
+method was not always successful, however, on account of the softening
+of the unpitched felt on long-continued exposure to the water. The felt
+used was mainly "Tunaloid," together with some "Hydrex." It weighed
+about 12&nbsp;lb. per 100&nbsp;sq.&nbsp;ft. when saturated and coated on one side only,
+and contained about 25% of wool. The coal-tar pitch used had a melting
+point of 100&deg; Fahr.</p>
+
+<p>After the completion of the tunnel, the concrete arch showed some
+leakage and in places unsightly lime deposits. It was determined to
+attempt to stop these leaks by the application of a water-proof cement
+coating on the intrados of the arch. Extended experimental application
+of two varieties of materials used for this purpose&mdash;"Hydrolithic"
+cement and the U.&nbsp;S. Water-proofing Company's compound&mdash;have been made
+with apparent success up to the present time, and the results after the
+lapse of a considerable period are awaited with interest.</p>
+
+<p><i>Duct Laying.</i>&mdash;The position of the electric conduits, buried in the
+heart of the concrete walls, interfered greatly with the economical and
+speedy placing of the lining, and their laying proved to be one of the
+most troublesome features of the work. The power conduits were
+single-way, with the bank for high-tension cables separated in the
+side-walls from the low-tension bank, as shown on Plate&nbsp;XII. The
+conduits for telephone and telegraph service were four-way, and were
+located in the core-wall. All ducts had 3/4-in. walls and a minimum
+clear opening of 3-3/8 in. square, with corners rounded. They were laid
+with joints broken in all directions, and in about 1/4-in. beds of
+1:2-1/2 mortar. Flat steel bond-irons, 2 by 1/8 in., with split and bent
+ends, were placed in the joints at intervals of 3 ft. and projected into
+the concrete 3 in. on each side, tying together the concrete on opposite
+sides of the ducts. The joints were wrapped with a 6-in. strip of
+10-oz.duck saturated with neat-cement grout, and, in addition, the
+power conduits were completely covered with a 1/2-in. coat of mortar to
+prevent the intrusion of cement and sand from the fluid concrete. The
+four-way conduits were plastered only over the wraps. Splicing chambers
+were provided at intervals of 400 ft.</p>
+
+<p class="figcenter">
+<a name="plate_lxii_1" id="plate_lxii_1"></a>
+<img src="images/417a.jpg" title="Water-Proofing Over Brick Arches" height="288" width="400" alt="Water-Proofing Over Brick Arches" /></p>
+
+<p class="caption"><span class="smcap">Plate LXII, Fig. 1.&mdash;Water-Proofing Over Brick Arches</span>.</p>
+
+
+<p class="figcenter"><a name="plate_lxii_2" id="plate_lxii_2"></a>
+<img src="images/417b.jpg" title="Trestle Used in Concreting in Three-Track Tunnel" height="290" width="400" alt="Trestle Used in Concreting in Three-Track Tunnel" /></p>
+
+<p class="caption"><span class="smcap">Plate LXII, Fig. 2.&mdash;Trestle Used in Concreting in Three-Track Tunnel</span>.</p>
+
+
+<p class="figcenter"><a name="plate_lxii_3" id="plate_lxii_3"></a>
+<img src="images/417c.jpg" title="Method of Street Support Over Open-Cut Excavation" height="288" width="400" alt="Method of Street Support Over Open-Cut Excavation" /></p>
+
+<p class="caption"><span class="smcap">Plate LXII, Fig. 3.&mdash;Method of Street Support Over Open-Cut Excavation</span>.</p>
+
+
+<p class="figcenter"><a name="plate_lxii_4" id="plate_lxii_4"></a>
+<img src="images/417d.jpg" title="Junction of Twin and Three-Track Tunnels" height="289" width="400" alt="Junction of Twin and Three-Track Tunnels" /></p>
+
+<p class="caption"><span class="smcap">Plate LXII, Fig. 4.&mdash;Junction of Twin and Three-Track Tunnels</span>.</p>
+
+<p><span class="pagenum"><a name="Page_417" id="Page_417">[Page 417]</a></span></p>
+
+<p class="sectionh">Three-Track Tunnel Lining</p>
+
+<p>In the Three-Track Tunnels, a heavy brick arch was used for those
+portions constructed in tunnel, while, in the open-cut sections, the
+roof was of concrete. Both were completely water-proofed on the roof and
+sides, and in the tunnel sections the space above the brick roof was
+filled with rock packing. On account of the unstable nature of the rock
+encountered throughout, the voids in the packing were afterward filled
+with grout.</p>
+
+<p>By reference to the cross-sections, Plate&nbsp;XII, it will be seen that the
+haunches of the arch were tied together by steel I-beams anchored in the
+concrete, with the object of making the structure self-supporting in the
+event of the removal of the adjacent rock for deep cellar excavations.
+This construction materially influenced the contractor's method of
+placing the masonry lining.</p>
+
+<p>After depositing the floor concrete, by the same method that was used in
+the Twin Tunnels, a timber trestle (<a href="#plate_lxii_2">Fig.&nbsp;2, Plate&nbsp;LXII</a>) was erected to
+the height of the underside of the I-beam ties, the posts being footed
+in holes, about 3 in. deep, left in the concrete floor to prevent
+slipping. In the open-cut sections the sand-wall forms were of undressed
+plank tacked to the studding and braced from the trestle; in the tunnel
+section they were spiked to the face of the posts supporting the
+timbering.</p>
+
+<p>The side-wall forms were made up in panels about 3 by 10 ft., and were
+clamped to studs by U-shaped irons passing around the stud and bolted to
+the cleats on the back of the panels, the studs being braced from the
+trestle. The side-wall concrete was deposited in three sections. The
+first was brought up just above the sidewalk and formed the bench for
+the high-tension ducts; the second carried the wall up to the springing
+line. Before placing the third section the I-beam ties were set in
+position (<a href="#plate_lxii_3">Fig.&nbsp;3, Plate&nbsp;LXII</a>) on top of the trestle, and the reinforcing
+rods in the haunch of the arch were hung from them. The concrete was
+carried up to a skewback for the arch, as shown in the<span class="pagenum"><a name="Page_418" id="Page_418">[Page 418]</a></span> brick-roof
+cross-section (Plate&nbsp;XII) and embedded the ends of the ties.</p>
+
+<p>The centers for the arches stood on the I-beam ties, and the tops of the
+hangers, for the permanent support of the ties near their center, were
+inserted through the lagging. The brick arch, water-proofing, and rock
+packing were laid up in lifts, in the same manner as in the Twin Tunnel,
+with grout pipes built in at intervals of about 8&nbsp;ft. The concrete arch
+was placed in sections, from 25 to 50&nbsp;ft. in length, with a rather wet
+mixture and a back form on the steep slope of the extrados.</p>
+
+<p>The concrete for the sand-walls and lower part of side-walls was handled
+on tracks and platforms laid on cantilever beams at mid-height of the
+trestle, as shown by <a href="#plate_lxii_3">Fig.&nbsp;3, Plate&nbsp;LXII</a>. For the walls above the
+springing line, the tracks were laid on top of the I-beam ties, and some
+of the arch concrete, also, was delivered from the mixer at that level
+and hauled up an incline to the level of the top of the arch. By far the
+greater part, however, was turned out from mixers set on the completed
+arch, and was transported on tracks hung in part from the street
+timbering.</p>
+
+<p><i>Completion.</i>&mdash;Except in the heavily-timbered portions, such as at Fifth
+Avenue, where the load had to be transferred from posts to the completed
+masonry section by section, the lining of the tunnels presented no
+special difficulty. The large number of small forms to be set, and the
+mutual interference of the concreting and duct-laying operations proved
+to be the most troublesome features of the work.</p>
+
+<p>The restoration of the streets, public utilities, etc., at the open-cut
+sections was a slow and tedious operation, but the tunnels themselves
+were completed in March, 1909, 3 years and 10 months after the inception
+of the work. The finished tunnels are shown by the photograph, <a href="#plate_lxii_4">Fig.&nbsp;4, Plate&nbsp;LXII</a>, taken at the junction of the twin and three-track types.</p>
+
+<div class="footnotes"><h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_A_1" id="Footnote_A_1"></a><a href="#FNanchor_A_1"><span class="label">[A]</span></a> Presented at the meeting of December 1st, 1909.</p></div>
+
+<div class="footnote"><p><a name="Footnote_B_2" id="Footnote_B_2"></a><a href="#FNanchor_B_2"><span class="label">[B]</span></a> Of the paper by Mr.&nbsp;Noble.</p></div>
+
+<div class="footnote"><p><a name="Footnote_C_3" id="Footnote_C_3"></a><a href="#FNanchor_C_3"><span class="label">[C]</span></a> Of the paper by Mr.&nbsp;Noble.</p></div>
+
+<div class="footnote"><p><a name="Footnote_D_4" id="Footnote_D_4"></a><a href="#FNanchor_D_4"><span class="label">[D]</span></a> Of the paper by Mr.&nbsp;Noble.</p></div>
+
+</div>
+
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
+End of the Project Gutenberg EBook of Transactions of the American Society
+of Civil Engineers, Vol. LXVIII, Sept. 1910, by James H. Brace and Francis Mason
+
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+The Project Gutenberg EBook of Transactions of the American Society of
+Civil Engineers, Vol. LXVIII, Sept. 1910, by James H. Brace and Francis Mason
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Transactions of the American Society of Civil Engineers, Vol. LXVIII, Sept. 1910
+       The New York Tunnel Extension of the Pennsylvania Railroad.
+       The Cross-Town Tunnels. Paper No. 1158
+
+Author: James H. Brace and Francis Mason
+
+Release Date: August 13, 2006 [EBook #19037]
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK TRANSACTIONS OF THE AMERICAN ***
+
+
+
+
+Produced by Juliet Sutherland, Jacqueline Jeremy and the
+Online Distributed Proofreading Team at http://www.pgdp.net
+
+
+
+
+
+
+
+
+
+AMERICAN SOCIETY OF CIVIL ENGINEERS
+
+INSTITUTED 1852
+
+
+TRANSACTIONS
+
+Paper No. 1158
+
+
+THE NEW YORK TUNNEL EXTENSION OF THE
+PENNSYLVANIA RAILROAD.
+THE CROSS-TOWN TUNNELS.[A]
+
+BY JAMES H. BRACE AND FRANCIS MASON, MEMBERS, AM. SOC. C. E.
+
+
+
+
+In this paper, it is proposed to describe the construction of the
+tunnels extending eastward from the easterly extension of the Terminal
+Station to the permanent shafts east of First Avenue.
+
+They were located under 32d and 33d Streets from the station to Second
+Avenue, and thence, curving to the left, passed under private property
+and First Avenue to the shafts, as described in a preceding paper.
+Typical cross-sections of the tunnels are shown on Plate XII.[B]
+
+On May 29th, 1905, a contract was entered into with the United
+Engineering and Contracting Company for the performance of this work.
+This contract provided that work on each pair of tunnels should be
+carried on from two shafts. The first, here referred to as the First
+Avenue Shafts, were located just east of that avenue and directly over
+the line of the tunnels; the other two, called the Intermediate Shafts,
+were located on private property to the north of each pair of tunnels in
+the blocks between Fourth and Madison Avenues. It was originally
+intended to do all the work of construction from these four shafts.
+Workings were started both east and west from the Intermediate Shafts,
+and those to the west were to be continued to the Terminal Station.
+After the change of plans, described in a previous paper, it was decided
+to sink a third shaft on each line. These were known as the West Shafts,
+and were located between Sixth and Seventh Avenues. Finally, it was
+found necessary to build a portion of the tunnels on each line west of
+Sixth Avenue in open cut. The locations of the shafts are shown on Plate
+XIV.[C]
+
+The First Avenue shafts were built by S. Pearson and Son, Inc., for the
+joint use of the two contractors, as described in the paper on the
+tunnels under the East River. While the shafts were being sunk, the
+full-sized tunnels were excavated westward by the contractor for the
+river tunnels for a distance of 50 ft., and top headings for 50 ft.
+farther. By this means, injury to the caissons and to the contractor's
+plant in the shafts by the subsequent work in the Cross-Town Tunnels was
+avoided. The west half of the shaft was for the exclusive use of the
+contractor for the Cross-Town Tunnels.
+
+
+CONTRACTOR'S PLANT.
+
+The method of handling the work adopted by the contractor was, broadly
+speaking, as follows: Excavation was usually carried on by modifications
+of the top-heading and bench method, the bench being carried as close to
+the face as possible in order to allow the muck from the heading to be
+blasted over the bench into the full section. The spoil was loaded into
+3-yd. buckets (designed by the contractor and hereinafter described), by
+steam shovels operated by compressed air, and hauled to the shafts by
+electric locomotives. Electrically-operated telphers, suspended from a
+timber trestle, hoisted the buckets, and, traveling on a mono-rail
+track, deposited them on wagons for transportation to the dock. Arriving
+at the dock, the buckets were lifted by electrically-operated stiff-leg
+derricks and their contents deposited on scows for final disposal. The
+spoil was thus transported from the heading to the scow without breaking
+bulk.
+
+When concreting was in progress, the spoil buckets were returned to the
+shafts loaded with sand and stone. The concrete materials were deposited
+in storage bins placed in the shafts, from which they were fed to the
+mixers located at the foot of the shaft about on a level with the crown
+of the tunnels. The concrete was transported to the forms in side-dump,
+steel, concrete cars, hauled by the electric locomotives.
+
+Electrical power was adopted largely on account of the restricted area
+at the shaft sites, where a steam plant would have occupied considerable
+space of great value for other purposes. The installation of a steam
+plant at the Intermediate Shafts, which were located in a high-class
+residential district, would have been highly objectionable to the
+neighboring property owners, on account of the attendant noise, smoke,
+and dirt, and, in addition, the cost of the transportation of fuel would
+have been a serious burden. Except for the forges and, toward the last,
+the steam locomotives, not a pound of coal was burned on the work. The
+use of the bucket and telpher also eliminated most of the objectionable
+noise incident to the transfer of spoil from tunnel cars to ordinary
+wagons at the shaft sites. Power plants were installed at the North
+Shaft near First Avenue and at the rear of the 33d Street Intermediate
+Shaft.
+
+_First Avenue Plant._--Fig. 1, Plate LVIII, is a general view of the
+First Avenue plant. The power-house at the corner of 34th Street and
+First Avenue supplied compressed air for operating drills, shovels,
+pumps, and hoists in the tunnels driven from the river shafts, and in it
+three Laidlaw-Dunn-Gordon compressors were installed. The largest was a
+32 by 20 by 30-in., two-stage, cross-compound, direct-connected to a
+Fort Wayne 480 h.p., 230-volt, direct-current, constant-speed motor run
+at 100 rev. per min. This compressor was rated at 2,870 cu. ft. of free
+air per minute at a pressure of 100 lb. It was governed by throttling
+the suction, the governor being controlled by the pressure in the air
+receiver and the motor running continuously at a constant speed. The two
+others were of similar type, one was 22-1/2 by 14 by 18-in., rated at
+1,250 cu. ft. of free air at a pressure of 100 lb., the other was 16 by
+10 by 18-in., rated at 630 cu. ft. They were fitted with 9-ft.
+fly-wheels, and were driven at 150 rev. per min. by 105-h.p., General
+Electric, 220-volt, compound-wound, direct-current motors running at 655
+rev. per min. The larger of these two compressors was driven by two of
+the motors belted in tandem, and the smaller was belt-connected to a
+third motor. The compressors were water-jacketed and had small
+inter-coolers, the water supply for which was itself cooled in a Wheeler
+Condenser and Engineering Company's water-cooling tower. The pump and
+the blower operating it were electrically driven.
+
+The telphers, used for hoisting muck from the tunnels and for lowering
+supplies, were each hung from single rails on a timber trestle, about
+40 ft. high, spanning and connecting the two shafts. One machine was
+provided for each shaft, and where their tracks crossed 33d Street they
+were separated sufficiently to permit the machines to pass each other.
+At this point, and covering the street, a large platform was provided,
+on which the trucks were loaded and unloaded (Fig. 2, Plate LVIII), and
+from which they descended by an incline on First Avenue leading south to
+32d Street. The platform also covered practically all the yard at the
+South Shaft and materially increased the available working area. The
+telphers were built by the Dodge Cold Storage Company, and were operated
+by a 75-h.p. General Electric motor for hoisting and a 15-h.p. Northern
+Electric Company motor for propulsion. Their rated lifting capacity was
+10,000 lb. at a speed of 200 ft. per min.
+
+The carpenter shop and machine-shop, both of which served the entire
+work, were conveniently located in small buildings on the loading
+platform. In the former the saws were each run independently by small
+electric motors suspended under the platform. The heavy forms and form
+carriages used in lining the tunnels with concrete were fabricated and
+stored on the platform outside. The machine-shop lathes, etc., were all
+belted to one shaft driven by an 8-h.p. General Electric motor. Above
+the machine-shop was a locker-room and below it on the street level was
+the main blacksmith shop for the work. Subsidiary blacksmith shops were
+located at each of the other shafts. The storeroom and additional
+locker-rooms were located above the power-plant in the North Shaft yard,
+and isolated from the other structures was a small oil-house. Additional
+storage space was provided by the contractor on 32d Street just west of
+First Avenue by renting three old buildings and the yards in the rear of
+them and of the Railroad Company's cement warehouse adjacent. Here
+electric conduits, pipe, castings, and other heavy and bulky supplies
+were stored.
+
+During excavation the headings were supplied with forced ventilation
+through 12-in. and 14-in. No. 16, spiral-riveted, asphalted pressure
+pipes, canvas extensions being used beyond the ends of the pipes. A No.
+4 American Blower, located at the top of each shaft and driven by a
+15-h.p. General Electric motor, supplied the air.
+
+[Illustration: PLATE LVIII, FIG. 1.--VIEW OF FIRST AVENUE PLANT.]
+
+[Illustration: PLATE LVIII, FIG. 2.--TELPHER STRUCTURE AND LOADING
+PLATFORM, FIRST AVENUE SHAFT.]
+
+[Illustration: PLATE LVIII, FIG. 3.--HEADWORKS AT 33D STREET:
+INTERMEDIATE SHAFT.]
+
+[Illustration: PLATE LVIII, FIG. 4.--LOADING SPOIL ON BARGES, 35TH
+STREET PIER.]
+
+A concrete-mixing plant was placed in each shaft, the mixer being
+located high enough to discharge into cars at about the level of the
+springing line of the arch. Above the mixers were the measuring
+hoppers set in the floor of a platform which was large enough to carry
+half a day's supply of cement. At the South Shaft the cement was
+delivered to this floor from the loading platform through a spiral steel
+chute; at the North Shaft it was lowered in buckets by the telpher. The
+sand and stone were drawn into the hoppers through short chutes from the
+base of the storage bins which occupied the remaining height of the
+shaft--about 50 ft. At the South Shaft the bins were of concrete and
+steel, about 6 by 12 ft. in section, and attached to the central wall of
+the caisson. Sand and stone were delivered into them from dump-wagons on
+the loading platform. At the North Shaft steel-plate bins were used, and
+were supplied with material by the buckets handled by the telpher. The
+mixers were No. 5 Smith, belt-connected to 25-h.p. motors, and about 0.8
+cu. yd. of concrete was mixed at a batch. The concrete cars were steel
+side-dumpers of the Wiener or Koppel type.
+
+In order to be able to continue concreting during the winter, when
+neither sand nor stone could be obtained by water, practically all the
+space under the loading platforms in the South Shaft yards not occupied
+by the blacksmith shop was filled with these materials, which were
+placed in storage in the late fall.
+
+_Intermediate-Shaft Plant._--The air-compressing plant was located at
+the rear of the 33d Street Intermediate Shaft, and supplied air for
+driving the tunnels east and west from the Intermediate Shafts on both
+32d and 33d Streets. Two compressors, the same as the large
+Laidlaw-Dunn-Gordon machine at First Avenue, were installed here, with a
+similar water-cooling tower.
+
+Both shafts were on private property, owned by the Railroad Company, on
+the north side of the streets, and each was equipped with two telphers
+supported on timber trestles, similar to those at First Avenue. Here,
+however, the buckets were placed on wagons standing at the curb, as
+shown by Fig. 3, Plate LVIII.
+
+Blowers for ventilation were installed at each shaft, as at First
+Avenue, and, after the excavation had proceeded some distance, small
+blacksmith shops, for sharpening drill steel and making minor repairs,
+were located in the tunnels near the shafts.
+
+The concrete plant in each shaft was similar in arrangement to those at
+First Avenue, but the storage bins had wooden walls made of 2 by 4-in.
+and 2 by 6-in. scantling nailed flat on each other.
+
+The contractor's office on 33d Street backed up against the 32d Street
+shaft site, and the basement was used as a storeroom for supplies for
+both shafts.
+
+After the decision to do part of the work between Sixth and Seventh
+Avenues in open cut, an 8-in. air main was laid in 33d Street to the
+West Shafts, and air was supplied from the Intermediate Shaft for work
+on both streets in that neighborhood.
+
+_West-Shaft Plant._--West of Sixth Avenue, between 32d and 33d Streets
+and adjacent to the open-cut sections, the Railroad Company obtained
+from the Hudson and Manhattan Railroad Company the use of a large area
+from which the buildings had recently been removed, and gave the use of
+it to the contractor. This was of great value in prosecuting the west
+end of the work. The two West Shafts were located in the streets and
+were supplied with short timber trestles similar to those at the
+Intermediate Shafts. One telpher was taken from each of the Intermediate
+Shafts to operate at each of the West Shafts. In addition, a number of
+stiff-leg derricks were set up along the open-cut section, and were
+operated by Lidgerwood or Lambert air hoisting engines, or by electric
+motors, as circumstances dictated. A 15-ton Bay City locomotive crane
+was also used along part of the open-cut work on 32d Street.
+
+Several concrete plants were installed at points along the open-cut
+section, and were moved from place to place, the same general
+arrangement being adopted as at the plants already described. No. 3 and
+No. 4 Ransome mixers were used, and were generally set up at about the
+level of the top of the arch. The sand and stone storage bins were made
+of scantlings spiked together, and were necessarily rather shallow on
+account of the proximity of the tunnels to the street surface.
+
+_Thirty-fifth Street Pier._--For the receipt and disposal of materials
+at the 35th Street pier, four stiff-leg derricks, operated by electric
+hoisting engines, were installed. Two were used in lifting the muck
+buckets from the wagons and dumping their contents on the scows for
+final disposal (Fig. 4, Plate LVIII); and the other two were fitted with
+clam-shell buckets for unloading sand and broken stone from barges and
+depositing the materials in large hoppers, from which they were drawn
+into wagons for transportation to the various concrete plants. A large
+part of the cement (all of which was supplied by the Railroad Company)
+was also unloaded at the 35th Street pier and hauled directly to the
+work, the surplus being stored temporarily in the Company's cement
+warehouses on 32d, 33d and 35th Streets, near First Avenue, from which
+it was drawn as required. On the dock was located the main powder
+magazine, a small concrete structure. Considerable use was also made of
+neighboring piers for unloading electric conduits, lumber, steel, etc.
+
+[Illustration: FIG. 1. SPECIAL STEEL BUCKET
+    PLAN OF BUCKET
+    END VIEW
+    SIDE VIEW OF BUCKET
+    SECTION AT A-A]
+
+_Tunnel Plant._--The spoil buckets, designed by D. L. Hough and George
+Perrine, Members, Am. Soc. C. E., were a novel feature of the work.
+These buckets are shown in detail in Fig. 1 and various photographs.
+They were of 3 cu. yd. capacity and were split longitudinally, the two
+halves being pinned at the apices of the ends. For lifting, they were
+suspended from eyes at that point, and, when dumping, trip ropes were
+hooked into eyes at the bottom of each side; lifting the trip ropes or
+lowering the hoisting rope split the bucket, as shown in Fig. 4, Plate
+LVIII, and dumped the contents. They were transported in the tunnel on
+flat cars, and in the street on wagons, both cars and wagons being
+provided with cradles shaped to receive the bottom of the bucket.
+
+In the tunnels the loading was done with air-operated steam shovels,
+four (Model 20) Marion shovels being used at various points of the work.
+In Fig. 1, Plate LIX, one of these is shown loading the bucket. The cars
+were hauled by General Electric, standard, 10-ton, mine locomotives, the
+current for which was taken at 220 volts from a pair of No. 00 copper
+trolley wires suspended from the roof of the tunnel. The collector was a
+small four-wheeled buggy riding on the wires and connected to the
+locomotive by several hundred feet of cable wound on a reel for use
+beyond the end of the trolley wire. Two 8-1/2-ton, Davenport, steam
+locomotives were also used in 32d Street, toward the end of the work,
+after the headings had been holed through and the tunnels would quickly
+clear themselves of gas and smoke. The steam shovels were supplemented
+by two Browning, 15-ton, locomotive cranes, which handled the spoil in
+places where timbering interfered with the operation of the shovels. All
+tracks were of 3-ft. gauge throughout and laid with 40-lb. rails.
+
+Practically all the heavy drilling was done with Ingersoll drills (Model
+E 52), the trimming being largely done with jap and baby drills. A large
+number of pumps were used at various points on the work, and practically
+all were of Cameron make, the largest ones at the shaft being 10 by 5 by
+13-in. The grout machines were of the vertical-cylinder, air-stirring
+type.
+
+
+SHAFT SINKING.
+
+The sinking of the Intermediate Shafts was the first work undertaken by
+the contractor.
+
+The 33d Street Shaft was 34.5 ft. long, 21 ft. wide, and 83 ft. deep.
+The rock surface averaged 5 ft. below the ground surface. Sinking was
+started on July 10th, 1905, and was completed on October 3d, 1905, the
+rock being hard and dry. The average daily rate was 0.73 ft. and an
+average of 17.1 cu. yd. were excavated per day, with two shifts of 8 hr.
+each. The first shift started at 6 A. M. and the second at 2.30 P. M.,
+ending at 11 P. M. These hours were adopted in order to avoid undue
+disturbance during the night.
+
+[Illustration: PLATE LIX, FIG. 1.--AIR-OPERATED STEAM SHOVEL USED IN
+TUNNEL.]
+
+[Illustration: PLATE LIX, FIG. 2.--TIMBERING IN TOP HEADINGS ABOVE
+I-BEAMS.]
+
+[Illustration: PLATE LIX, FIG. 3.--FIRST SECTION OF CONCRETE LINING AT
+FIFTH AVENUE.]
+
+[Illustration: PLATE LIX, FIG. 4.--TIMBERING AND RUBBLE MASONRY OVER
+I-BEAMS.]
+
+Before blasting the first lift of rock, channel cuts 5 or 6 ft. deep
+were made along the sides of the shaft, in order to avoid damage to the
+walls of neighboring buildings. Timbering was required for a depth of
+only 10 ft. below the surface of the ground.
+
+A drift, 30.6 ft. long, 17 ft. wide, and 27 ft. high, connected the
+south end of the shaft with the tunnels. The drift was excavated in
+three stages, a top heading and a bench in two lifts. While blasting the
+cut in the top heading, there was enough concussion to break glass in
+the neighboring buildings. The use of a radialax machine reduced the
+concussion somewhat, but it was very quickly abandoned on account of the
+length of time required for the drilling.
+
+The construction of the 32d Street Shaft was quite similar to the one on
+33d Street. It was 31.5 ft. long, 20.5 ft. wide, and 71 ft. deep. The
+depth of earth excavation averaged 19.5 ft. The rock in this shaft was
+seamy and not quite as hard or dry as that in 33d Street, and timbering
+was required for practically the full depth to the crown of the drift.
+Sinking was started on May 15th, 1905, and was completed on October
+26th, 1905. The daily average rate was 0.30 ft. in earth and 0.52 ft. in
+rock. The drift was excavated in much the same manner as the one in 33d
+Street, but the rock being softer the radialax machine was not used.
+
+
+TUNNEL EXCAVATION.
+
+During the early part of the work, the contractor devoted his entire
+attention to the work of excavation. Nearly all the excavation east of
+Fifth Avenue was done before any of the lining was placed. At a number
+of points west of Fifth Avenue and at a few points to the east the
+nature of the rock was such that the two operations had to be done
+simultaneously.
+
+_Single-Tunnel Method._--For an average distance of 350 ft. west from
+the First Avenue Shafts there were four single tunnels. The rock was
+sound and comparatively dry. A top heading of the full size of the
+tunnel and about 8 ft. high was first driven. It was drilled by four
+drills mounted on two columns, and was blasted in the ordinary way. The
+bench was about 13 ft. high. Tripod drills, standing on the bench,
+drilled the usual holes, but, owing to the lack of head-room, steels
+long enough to reach the bottom of the bench could not be used. Tripod
+drills were set as low as possible at the foot of the bench and drilled
+lifting holes. These holes were inclined downward from 10 deg. to 15 deg. to the
+horizontal, and were spaced to converge at the location of the drainage
+ditches. The heading was usually driven from 10 to 20 ft. in advance of
+the bench. At this distance a large part of the muck from the heading
+was shot backward over the bench. In the single tunnels the muck was
+loaded by hand.
+
+_Twin-Tunnel Methods._--From the end of the single-track tunnel westward
+to Fifth Avenue on 33d Street, and to Madison Avenue on 32d Street, with
+some exceptions, each pair of tunnels was excavated for the entire width
+at one operation. Three different methods of work were extensively used.
+They were the double-heading method, the center-heading method, and the
+full-sized-heading method, and these differed only in the manner of
+drilling and blasting. The bench was usually within 10 or 15 ft. of the
+face of the heading, and was drilled and fired in the same way as in the
+single tunnels. After the installation of the permanent plant, most of
+the muck was handled by steam shovels.
+
+In the double-heading method, shown on Plate LVII, the top headings for
+each tunnel of the pair were driven separately, leaving a short rock
+core-wall between them. The headings were drilled from columns in the
+manner described for the single tunnels. The temporary rock dividing
+wall between the headings was drilled by a tripod drill on the bench of
+one of the headings, and was fired with the bench.
+
+In the center-heading method, also shown on Plate LVII, only one heading
+was driven. It was rectangular in shape, about 8 ft. high and 14 ft.
+wide. It was located on the center line between the tunnels. In general,
+the face was from 6 to 12 ft., or the length of one or two rounds, in
+advance of the remainder of the face at the top. The center heading was
+drilled by four drills mounted on two columns. By turning these drills
+to the side, they were used for holes at right angles to the line of the
+tunnels, by which the remainder of the face of the heading was blasted.
+By turning the drills downward, the bench holes under the center heading
+were also drilled. The center heading explored the rock in advance of
+the full-width heading, and gave a good idea as to the care needed in
+firing.
+
+For the full-width-heading method, Fig. 2, ten drills were mounted on
+five columns set abreast across the face. Holes were drilled to form a
+cut near the center line between the tunnels. The remainder of the holes
+were located so that they would draw into the cut. The bench was
+frequently drilled from the same set-up of columns by turning the
+drills downward. In sound rock this method proved to be the most rapid
+of any.
+
+Practically all trimming was left until immediately before the
+concreting. It was then taken up as a separate operation, but proved to
+be costly and tedious, and a hindrance to the placing of the lining.
+
+_Materials Encountered._--All the rock encountered was the familiar
+Hudson schist, but it varied widely in its mineral constituents and in
+its physical characteristics. In many places where the rock surface was
+penetrated, a fine sand was found that was probably quicksand. The
+material above the rock in the open-cut sections was mostly sand.
+
+[Illustration: FIG. 2. METHOD OF EXCAVATING WITH FULL-WIDTH HEADING
+CROSS-TOWN TUNNELS, MANHATTAN
+    SIDE ELEVATION
+    FRONT ELEVATION
+    PLAN SHOWING POSITION OF COLUMNS FOR DRILLING FACE]
+
+The concurrence of the watercourse, shown on General Viele's map of
+Manhattan Island (Plate IX[D]), with the points where difficulties in
+the construction of the tunnels were encountered has been noted in a
+previous paper.
+
+In all cases where the course of this ancient stream was crossed (except
+at its final intersection of 33d Street), the rock was found to be very
+soft and disintegrated, a large quantity of water was encountered, and
+heavy timbering was required. The construction at these localities will
+be taken up later. In addition, disintegrated rock, but of a less
+troublesome character, was invariably met under the depressions in the
+rock surface developed by the borings from the streets and test holes
+from the tunnels. Many of these places required timbering, and no
+timbering was elsewhere necessary except at the portals. These
+coincident conditions were especially marked in 32d Street, which for a
+long distance closely adjoins the course of the former creek.
+
+_Disposal of Spoil._--The materials excavated from the tunnels were
+dumped at the 35th Street pier on barges furnished by the Railroad
+Company under another contract, and were towed to points near the
+Bayonne peninsula where the spoil was used principally in the
+construction of the Greenville Freight Yards and the line across the
+Hackensack Meadows to the tunnels. Details of this work will be given in
+a subsequent paper. After December, 1907, when the excavation was about
+85% completed, the contractor furnished the barges and effected the
+complete disposal of the spoil.
+
+_Difficulties of Excavation._--As stated in a previous paper, the
+excavation of the Twin Tunnel in 33d Street was continued westward to
+the west line of Fifth Avenue on the original grade. At that point the
+contractor started three drifts in the three-track section. The relation
+of the drifts to each other and to the cross-section are shown by Fig. 3.
+The center heading was driven a little in advance of those on the
+sides. At a distance of 65 ft. west of Fifth Avenue the rock surface was
+broken through in the top of the heading, and a very fine sand was
+encountered. For some distance east of this point the rock was badly
+disintegrated, and the heading required timbering. Through the soft
+material, tight lagging was placed on the sides and roof of the heading,
+and the face was protected by breast boards. There was a moderate flow
+of water through the cracks, and, in spite of every effort, some of the
+fine sand was constantly carried into the heading.
+
+In one or two instances considerable ground was lost at the face. On the
+evening of December 14th, 1906, as a heavy coal wagon was passing along
+33d Street above the heading, the rear wheels dropped through the
+asphalt pavement. An examination disclosed a cavity under the pavement
+about 14 ft. long, 12 ft. wide and 14 ft. deep. Evidently, the fine sand
+had gradually settled into the voids caused by the loss of material at
+the face, and the settlement broke the brick sewer over the heading. The
+sewer was temporarily repaired, and the hole in the street was filled
+before morning. A tight bulkhead was built across the heading, and work
+was abandoned at that point. The north drift was advanced to a point
+108 ft. west of Fifth Avenue where sand was also encountered and a
+considerable run occurred. After that time all work on the three-track
+section was discontinued.
+
+The Company then took up the consideration of changes in plan. To
+determine the difficulties of driving a Twin Tunnel at a lower
+elevation, an exploration drift, 8 ft. high and 12 ft. wide, was driven
+on the center line of the street as a top heading on the proposed new
+grade. Test holes were drilled above this heading and to the sides. The
+results indicated that there was sufficient rock cover of fair quality
+to enable the Twin Tunnel to be driven without great risk. The new plan
+(continuing the Twin Tunnel westward at a lower grade) was adopted in
+March, 1907, and work was immediately resumed at Fifth Avenue.
+
+The relation between the cross-sections under the old and new plans at
+that point is shown by Fig. 3. Before the new section was excavated it
+was necessary to support the timber work in the old headings. The plan
+adopted is also shown by Fig. 3. The rock was excavated under the center
+heading, as shown in cross-section, for a length of about 3 ft. A girder
+composed of two 18-in. I-beams was then put in position over each line
+and supported on the sides by posts. The ends at the center lines
+between the tunnels were supported on short posts bearing on the rock
+bench. The support of the timbering in the headings was then transferred
+to the girders by additional posts. Blocking was also inserted between
+the tops of the beams and the rock walls between the headings. Fig. 2,
+Plate LIX, gives a good idea of the timber work in the top headings
+above the I-beams. When the roof had been made secure, the removal of
+the bench was begun. As the work advanced it was necessary to replace
+the short posts at the center of the tunnel by others of full height,
+and there was considerable settlement in the I-beams during this
+operation. When the bench had been removed to a point 61 ft. west of
+Fifth Avenue, settlement was detected in the street surface above. Bench
+excavation was suspended and a section of the permanent lining, 35 ft.
+long, was placed. The space between the lining and the beams and between
+the beams and the roof was filled with rubble masonry. Grout pipes were
+built into the masonry and later all voids were filled with grout. Fig.
+3, Plate LIX, shows the first section of the concrete lining completed
+and part of the rubble in place; and Fig. 4, Plate LIX, shows details of
+the work above the tunnels. A second section of bench was next removed
+and more lining was placed. Work was continued in this way until all the
+roof at the old three-track headings had been secured. In this portion
+of the work the posts were embedded in the concrete.
+
+Between Fifth and Sixth Avenues there were two more sections of bad rock
+where it was necessary to support the roof with steel beams. At these
+latter points there were no complications with the excavation for the
+Three-Track Tunnel, and the work was much simpler. To avoid leaving the
+center posts in the permanent work, two rows of temporary posts were
+placed, as shown by Fig. 1, Plate LX, the center wall and skewback were
+built, and the posts were removed, as shown by Fig. 2, Plate LX, before
+placing the remainder of the lining.
+
+In 32d Street the normal progress of the excavation was frequently
+interrupted by encountering soft and unsound rock. In the excavation
+between the East River and the Intermediate Shafts it was possible to
+overcome these conditions by temporarily narrowing the excavation on one
+side and supporting the roof on 16 by 16-in. transverse timbers caught
+in niches in the rock at the sides, leaving sufficient room for the
+steam shovel to work through. In order to save time, the height of the
+excavation was not increased before placing these timbers, so that,
+previous to the concreting, they all required to be raised to clear the
+masonry lining and were then supported on posts on the center line
+between the tunnels. This permitted the remainder of the excavation to
+be made, and such additional timbering as was required was placed. At
+most of these sections a brick arch and water-proofing were used, on
+account of the presence of water. In certain places the center line
+posts were buried in the core-wall, and, in order to permit the placing
+of the water-proofing, were then cut off one by one flush with its top
+as the load was transferred to the completed masonry. In other cases the
+load was transferred to posts clear of the masonry and the center line
+posts were entirely removed. Under such conditions the normal concrete
+methods, to be described later, could not be used, and special forms
+were substituted.
+
+[Illustration: FIG. 3. CONSTRUCTION OF TWIN TUNNELS, THROUGH EXCAVATION
+STARTED FOR THREE-TRACK TUNNEL IN 33D STREET NEAR 5TH AVENUE]
+
+In this section of the work the most serious difficulties were
+encountered near Fourth Avenue a short distance east of the Intermediate
+Shaft, and beneath the site of the old pond shown on General Viele's
+map. The rock cover was known from the boring to be very thin, and the
+presence of the subway overhead caused some anxiety. The excavation was
+at first taken out to practically full width and timbered, but the rock
+became so treacherous that the heading was narrowed to a width
+sufficient for one tunnel only. With this span the rock in the roof held
+without timbering. As the masonry lining approached, sufficient trimming
+was done to permit the placing of the core-wall and one arch. Above the
+completed core-wall and brick arch the voids were filled solid with
+rubble masonry to give an unyielding support to the roof. The excavation
+of the remaining width of tunnel was then undertaken. Near the west side
+of Fourth Avenue, the excavation broke out of rock at the top, and fine
+sand and gravel with a large quantity of water were encountered. The
+work of excavation was arduous, and proceeded very slowly, on account of
+the care with which it was executed. Only a small amount of sand entered
+the tunnel, but the lining was placed as soon as the excavation was
+completed. Rubble masonry packing and grout ejected through pipes built
+into the arch were used to fill the voids above the roof. As a further
+precaution against the settlement of the subway, 2-in. pipes were washed
+down from the street above the point where soft ground was exposed in
+the roof of the tunnel, and through them grout was forced into the
+ground at various depths. Careful levels show that no settlement of the
+subway has taken place.
+
+West of the Intermediate Shaft the tunnel was excavated for full width
+until bad rock was encountered about 60 ft. west of Madison Avenue. (See
+General Viele's map, Plate IX.) Timbering was used for a short distance,
+and then the heading and bench were narrowed to 18 ft., and steam-shovel
+excavation was abandoned. As the heading advanced the rock grew steadily
+softer, the difficult conditions in this locality culminating when a
+slushy disintegrated feldspar was met, requiring poling and breasting.
+Thereafter the rock improved markedly, but near the east side of Fifth
+Avenue its thickness above the roof was found to be only 1-1/2 ft.,
+and the advance was stopped, pending a decision as to a change of plan.
+
+[Illustration: PLATE LX, FIG. 1.--DOUBLE ROW OF POSTS UNDER I-BEAMS,
+SUPPORTING ROOF IN BAD ROCK SECTION.]
+
+[Illustration: PLATE LX, FIG. 2.--CENTER WALL AND SKEWBACK UNDER I-BEAMS,
+AFTER REMOVAL OF DOUBLE ROW OF POSTS.]
+
+[Illustration: PLATE LX, FIG. 3.--TIMBERING IN FULL-WIDTH HEADING OF
+THREE-TRACK TUNNEL.]
+
+[Illustration: PLATE LX, FIG. 4.--UNDERPINNING WALLS IN OPEN-CUT
+SECTION.]
+
+After some delay, an exploration drift, similar to the one already
+described, was driven through to Sixth Avenue, and a change in plan was
+made, substantially the same as for the 33d Street tunnels. Enlargement
+to full size was at once started, but, for 400 ft. the rock was very
+soft and poor, and required extremely careful handling. The exploration
+drift was widened out to the full Twin-Tunnel width, and I-beams were
+placed and supported, in much the same manner as in 33d Street. The rock
+was so soft that it was frequently necessary to drive poling boards
+ahead as the face was mined out with picks and shovels. The load was
+very heavy, and the work the most difficult encountered in the tunnels.
+
+After this stage of the enlargement was reached, the excavation of the
+bench and the placing of the lining proceeded alternately, with the
+I-beams temporarily supported on long posts while the concrete core-wall
+was being built. Considerable settlement took place while shifting the
+posts, and eventually showed on the street surface and in the adjacent
+sidewalk vaults, but no damage was done to the structural portions of
+the buildings.
+
+While the above work had been going on westward from Fifth Avenue, the
+excavation of the Twin Tunnel eastward from the end of the open-cut
+section at Sixth Avenue had been proceeding rapidly, and, toward the end
+of the difficult Fifth Avenue work, it was being attacked from both
+directions.
+
+
+PROGRESS OF EXCAVATION.
+
+Owing to the numerous sections of poor rock, interspersed throughout the
+work with stretches of sound rock, the progress of the excavation was
+very irregular, especially in 32d Street. The rate of excavation in good
+ground is shown in Table 1. In the sections of bad ground, the
+operations of excavation, timbering, and lining were often carried on
+alternately, and it is impracticable to include them in the table.
+
+TABLE 1.--PROGRESS AND METHODS OF EXCAVATION IN GOOD GROUND.
+
+THIRTY-THIRD STREET.
+
+============================================================
+           1                 |   2    |          3         |
+-----------------------------+--------+--------------------+
+                             |        |                    |
+                             |        |                    |
+   Type of excavation.       |Tunnels.|    Worked from:    |
+                             |        |                    |
+                             |        |                    |
+-----------------------------+--------+--------------------+
+Full-sized single tunnel     |   B    |  1st Ave. shaft.   |
+                             |        |                    |
+Full-sized single tunnel     |   A    |  1st Ave. shaft.   |
+                             |        |                    |
+Full-sized twin tunnel       |A and B |  1st Ave. shaft.   |
+                             |        |                    |
+                             |        |                    |
+                             |        |                    |
+Full-sized twin tunnel       |A and B |Intermediate shaft. |
+                             |        |  (West of shaft.)  |
+                             |        |                    |
+                             |        |                    |
+Full-sized twin tunnel       |A and B |Intermediate shaft. |
+                             |        |  (East of shaft.)  |
+                             |        |                    |
+                             |        |                    |
+Full-sized twin tunnel       |A and B |Intermediate shaft. |
+                             |        |  (East of shaft.)  |
+                             |        |                    |
+                             |        |                    |
+Exploration drift            |A and B |Intermediate shaft. |
+                             |        |  (West of shaft.)  |
+                             |        |                    |
+Twin tunnel. Enlargement     |A and B |     West shaft.    |
+  of exploration drift       |        |  (East of shaft.)  |
+=============================+========+=====================
+
+======================================================================
+           4                      |    5   |      6     |      7     |
+----------------------------------+--------+------------+------------+
+                                  |        |   Length   |   Average  |
+             DATES.               |  Time  |   tunnel   |   advance  |
+----------------------------------|elapsed,| excavated, |   per day, |
+               |                  |   in   |     in     |     in     |
+     From      |        To        |  days. |linear feet.|linear feet.|
+----------------------------------+--------+------------+------------+
+Feb. 28, 1906. |May  12, 1906.    |    74  |     346    |     4.7    |
+               |                  |        |            |            |
+Feb. 28, 1906. |Apr. 30, 1906.    |    62  |     255    |     4.1    |
+               |                  |        |            |            |
+Aug. 23, 1906. |Jan.  5, 1907.    |   136  |     789    |     5.8    |
+               |                  |        |            |            |
+               |                  |        |            |            |
+               |                  |        |            |            |
+Apr.  4, 1906. |Oct. 31, 1906.    |   210  |     730    |     3.5    |
+               |                  |        |            |            |
+               |                  |        |            |            |
+               |                  |        |            |            |
+Apr.  4, 1906. |Oct. 31, 1906.    |   210  |     783    |     3.7    |
+               |                  |        |            |            |
+               |                  |        |            |            |
+               |                  |        |            |            |
+Nov.  1, 1906. |Dec. 26, 1906.    |    56  |     311    |     5.5    |
+               |                  |        |            |            |
+               |                  |        |            |            |
+               |                  |        |            |            |
+Mar.  1, 1907. |July 23, 1907.    |   145  |     947    |     6.5    |
+               |                  |        |            |            |
+               |                  |        |            |            |
+Sept. 6, 1907. |Dec.  4, 1907.    |    89  |     603    |     6.8    |
+               |                  |        |            |            |
+===============+==================+========+============+=============
+
+=====================================================
+                        8
+-----------------------------------------------------
+
+
+            Methods and conditions.
+
+
+-----------------------------------------------------
+Top heading and bench. Muck loaded by hand.
+
+ "     "     "    "      "    "    "    "
+
+Top full-width heading and bench. Muck loaded
+  by steam shovel. Working exclusively on this
+  heading.
+
+Top center heading and bench. Muck loaded by
+  steam shovel. Working alternately in headings
+  east and west of the shaft.
+
+Top center heading and bench. Muck loaded by
+  steam shovel. Working alternately in headings
+  east and west of the shaft.
+
+Top full-width heading and bench. Muck loaded
+  by steam shovel working exclusively on this
+  heading.
+
+Exploration drift about 9 ft. by 12 ft. Mucking
+  by hand. Fourteen timber bents were placed in
+  March, and seven in April, 1907.
+
+Drift excavated to full width and bench. Muck
+  loaded by steam shovel.
+=====================================================
+
+
+THIRTY-SECOND STREET.
+
+============================================================
+           1                 |   2    |          3         |
+-----------------------------+--------+--------------------+
+                             |        |                    |
+                             |        |                    |
+   Type of excavation.       |Tunnels.|    Worked from:    |
+                             |        |                    |
+                             |        |                    |
+-----------------------------+--------+--------------------+
+Full-sized single tunnel     |   C    |  1st Ave. shaft.   |
+                             |        |                    |
+Full-sized single tunnel     |   D    |  1st Ave. shaft.   |
+                             |        |                    |
+Full-sized twin tunnel       |C and D |  1st Ave. shaft.   |
+                             |        |                    |
+                             |        |                    |
+                             |        |                    |
+Narrowed twin tunnel         |   C    |Intermediate shaft. |
+                             |        |  (East of shaft.)  |
+                             |        |                    |
+                             |        |                    |
+Narrowed twin tunnel         |   C    |Intermediate shaft. |
+                             |        |  (East of shaft.)  |
+                             |        |                    |
+                             |        |                    |
+                             |        |                    |
+                             |        |                    |
+Full-sized twin tunnel       |C and D |Intermediate shaft. |
+                             |        |  (West of shaft.)  |
+                             |        |                    |
+Exploration drift            |C and D |Intermediate shaft. |
+                             |        |  (West of shaft.)  |
+                             |        |                    |
+Twin tunnel. Enlargement    }|C and D |{  Eastward from    |
+  of exploration drift      }|        |{     open cut.     |
+                             |        |                    |
+Twin tunnel. Enlargement    }|C and D |{  Eastward from    |
+  of exploration drift      }|        |{     open cut.     |
+                             |        |                    |
+=============================+========+=====================
+
+
+
+==================================+========+============+=============
+           4                      |    5   |      6     |      7     |
+----------------------------------+--------+------------+------------+
+                                  |        |   Length   |   Average  |
+            DATES.                |  Time  |   tunnel   |   advance  |
+----------------------------------|elapsed,| excavated, |   per day, |
+               |                  |   in   |     in     |     in     |
+     From      |        To        |  days. |linear feet.|linear feet.|
+----------------------------------+--------+------------+------------+
+ Jan. 25, 1906.|Apr. 30, 1906.    |   95   |     367    |     3.9    |
+               |                  |        |            |            |
+ Jan. 27, 1906.|Apr. 30, 1906.    |   93   |     354    |     3.8    |
+               |                  |        |            |            |
+{May. 22, 1906.|July 24, 1906.[E]}|  173   |     810    |     4.7    |
+{Aug. 11, 1906.|Nov. 29, 1906.   }|        |            |            |
+               |                  |        |            |            |
+               |                  |        |            |            |
+ Mar. 19, 1906.|May  28, 1906.    |   70   |      58    |     0.8    |
+               |                  |        |            |            |
+               |                  |        |            |            |
+               |                  |        |            |            |
+{May  29, 1906.|July  3, 1906.[E]}|  208   |   1,206    |     5.8    |
+{July 18, 1906.|July 31, 1906.   }|        |            |            |
+{Aug. 12, 1906.|Nov. 23, 1906.   }|        |            |            |
+{Jan. 15, 1907.|Feb.  5, 1907.   }|        |            |            |
+{Feb. 17, 1907.|Mar. 21, 1907.   }|        |            |            |
+               |                  |        |            |            |
+ Dec.  1, 1905.|May. 10, 1906.    |  161   |     225    |     1.4    |
+               |                  |        |            |            |
+               |                  |        |            |            |
+ Feb.  1, 1907.|Sept.13, 1907.    |  225   |   1,033    |     4.6    |
+               |                  |        |            |            |
+               |                  |        |            |            |
+}Feb.  1, 1908.|Feb. 14, 1908.    |   14   |      65    |     4.6    |
+}              |                  |        |            |            |
+               |                  |        |            |            |
+}Feb. 15, 1908.|Apr. 14, 1908.    |   59   |     524    |     8.9    |
+}              |                  |        |            |            |
+               |                  |        |            |            |
+======================================================================
+
+[Footnote E: Time and distance omitted while working
+through timbered stretches.]
+
+=======================================================
+                        8
+-------------------------------------------------------
+            Methods and conditions.
+-------------------------------------------------------
+Top heading and bench. Muck loaded by hand.
+
+ "     "     "    "      "    "    "    "
+
+Double heading and bench. Muck loaded by steam
+  shovel. Stretches aggregating 200 ft. narrowed
+  to about 25 ft. and later enlarged are included.
+
+Excavation about 30 ft. wide. Top full-width heading
+  and bench. Muck loaded by hand. Steam shovel
+  not installed.
+
+Excavation about 30 to 35 ft. wide. Top full-width
+  by hand and part by steam shovel.
+
+
+
+
+Double heading and bench. Part of the muck handled
+  by hand and part by steam shovel.
+
+Exploration drift about 10 ft. by 13 in. Muck loaded by
+  hand. 14 ft. timbered.
+
+At portal of twin tunnels. Drift excavated to full
+  width and bench. Muck loaded by hand. 12 ft.
+  timbered.
+
+Drift excavated to full width and bench. Muck loaded
+  by steam shovel. Full-width tunnel timbered for 26
+  ft. independently of the main excavation.
+=======================================================
+
+
+THREE-TRACK TUNNEL EXCAVATION.
+
+When it became evident that the work through the Fifth Avenue section
+would be extremely slow, shafts were sunk in each street between Sixth
+and Seventh Avenues. The shafts, as shown on Plate XIV, were located in
+the streets, but in such a way as to block only half of the roadway. At
+the same time it was decided to construct in open cut about 200 ft. of
+the Three-Track Tunnel at the west end of the contract in 32d Street,
+where the rock surface was below the top of the tunnel. It was hoped
+that the remainder of the work could be built without opening the
+street, but further investigation showed that this was impracticable,
+and eventually all the Three-Track Tunnel in 32d Street, except 120 ft.
+east of the shaft, was built in open cut.
+
+_Thirty-second Street Work in Tunnel._--Following the sinking of the
+shaft, a drift was driven across the street at the crown of the tunnel,
+and a top heading on the south side was excavated in both directions.
+Frequent cross-drifts to the north side showed that the rock was nowhere
+very sound and that, except for a short distance east of the shaft, it
+was distinctly unfavorable for the wide Three-Track excavation. In this
+stretch the north ends of these cross-cuts were connected by a second
+heading, and wall-plates and sets of three-segment arch timbering were
+set up to support the roof of the drifts. The cross-cuttings were
+gradually widened and timbered until the entire excavation had been made
+down to the level of the wall-plates, as shown in Fig. 3, Plate LX. The
+bench was then excavated in two lifts, leaving the wall-plates supported
+on narrow longitudinal berms, which were removed in short sections to
+permit the placing of posts under the wall-plates.
+
+_Thirty-second Street Open-Cut Work._--Before actual open-cut excavation
+was started, all buildings facing it were underpinned to rock. For this
+purpose, a trench was dug along the face of the buildings and of the
+same depth as their cellars. Holes were cut in the front foundation
+walls through which long needle-beams (Fig. 4, Plate LX) were inserted
+and jacked up on blocking placed on the cellar floor and in the trench,
+until the weight of the building had been taken off its foundations. A
+close-sheeted trench was then sunk to rock under the front building
+walls, and a light rubble masonry retaining wall was built in it to
+support the building permanently. Frequently, the excavation for the
+underpinning wall, which was taken out in sections from 30 to 40 ft.
+long, and in places was carried to a depth of 40 ft., was very
+troublesome on account of the large quantity of water encountered and
+the fineness of the sand, which exhibited a tendency to flow when
+saturated.
+
+The Elevated Railroad columns in Sixth Avenue, near the north and south
+lines of 32d Street, were underpinned in a manner similar to the
+building foundations, while those on the center line of the street were
+supported by girders riveted to them close under the track level. The
+girders in turn were supported on posts footed on the new underpinning
+of the adjacent columns. On the completion of the tunnels, concrete
+piers were built up from the roof of the tunnel to form a permanent
+foundation for the center-line columns. The area to be excavated under
+Sixth Avenue was enclosed by a rubble masonry retaining wall constructed
+in a trench.
+
+Open-cut excavation was started by planking over the street on stringers
+resting on transverse 12 by 12-in. caps. The caps were gradually
+undermined and supported on temporary posts which were then replaced by
+short posts resting on 12 by 12-in. sills about 7 ft. below the cap. The
+operation was then repeated and the sill was supported on another set of
+short posts resting on a second sill. When the excavation had been
+carried down in this manner to the level of the top of the tunnel,
+diagonal 3 by 10-in. timbers were cut in between the posts and sills to
+form a species of double A-frame, the legs of which rested in niches cut
+in the rock and on posts carried up the face of the underpinning wall,
+and the whole was stiffened with vertical tie-rods. This construction is
+shown by Fig. 3, Plate LXII. The brick sewer was replaced temporarily by
+one of riveted steel pipe. This pipe and the water and gas pipes and
+electric conduits were suspended from the timbers as the pipes were
+uncovered.
+
+Excavation in rock was made by sinking a pit to sub-grade for the full
+width of the tunnel and advancing the face of the pit in several lifts,
+the muck being blown over the slope and loaded into buckets at its foot.
+
+The work was attacked at several places simultaneously, and the spoil
+was hoisted by derricks located at convenient points along the side of
+the cut.
+
+_Thirty-third Street Work in Tunnel and Open Cut._--The West 33d Street
+Shaft was similar to the one in 32d Street, and was sunk during
+February, March, and April, 1907, through 10 ft. of earth, 21 ft. of
+soft rock, and 29 ft. of fairly hard rock. It was necessary to timber
+heavily the upper 30 ft. of the shaft. The timber later showed evidences
+of severe strain, and had to be reinforced.
+
+[Illustration: Plate LXI.--EXCAVATION AND TIMBERING IN HEAVY GROUND
+OF THREE-TRACK TUNNEL OF 33D ST.]
+
+As soon as the shaft excavation was deep enough, a drift was driven
+part way across the tunnels, and top headings were started both east and
+west to explore the rock. The heading to the west was divided into two
+drifts, as shown on Plate LXI. These two drifts were continued to the
+west end of the contract, and were then enlarged to a full-sized heading
+and timbered, as shown on Plate LXI and Fig. 3, Plate LX. The rock near
+the shaft contained many wet rusty seams, and settlement was detected in
+the segmental tunnel timbering soon after the widening of the heading
+was completed. Short props were placed under the timbers, and the street
+surface was opened with a view of stripping the earth down to the rock
+and thus lightening the load on the timbering. Street traffic was
+maintained on a timber structure with posts eventually carried down to
+the rock surface, and the walls of the buildings on the north side of
+the street were underpinned to rock. The settlement of the tunnel
+timbering was checked for a time, and the bench was excavated as shown
+on Plate LXI. In this work the cut in the center was first made, and the
+short props were replaced by struts, as shown; after this the berms were
+removed and the side posts were placed. While building the brick arches,
+holes were left in the masonry around the struts. After the masonry had
+hardened, piers were built on the arches to support the segmental
+timbers. The struts were then removed and the openings filled with
+masonry. The voids above the arch were packed with rock and afterward
+thoroughly grouted.
+
+The timbers near the shaft continued to settle, and, although they had
+been placed from 9 to 12 in. above the level of the top of the masonry,
+by October 1st, they encroached 9 in. within the line of masonry. It was
+then decided to remove the rock for a distance of 48 ft. west of the
+shaft, and build this portion of the tunnel in open cut. The posts
+supporting the deck forming the street surface were replaced by an
+A-frame structure similar to that developed for the 32d Street open cut,
+without interruption of the street traffic.
+
+After making the open cut to the westward of the shaft, there was a slip
+in the rock north of and adjoining the shaft. Fortunately, the timbers
+did not give way entirely, and no damage was done. The open cut was
+extended eastward for a distance of 46 ft., making the total length of
+tunnel built in open cut on this street 94 ft.
+
+East of the shaft, for a distance of about 125 ft., the rock was broken
+and could not be excavated to full size without timbering the roof, but
+between this section of poor rock and those already mentioned in
+connection with the work at Fifth Avenue, there was a stretch of 600 ft.
+of good rock where all the spoil was handled with a steam shovel.
+
+
+TWIN-TUNNEL LINING.
+
+The masonry lining for the tunnels was not started until the late fall
+of 1906, after excavation had been in progress for a year and a half. At
+that time concreting was started in the single tunnels westward from the
+First Avenue Shafts, and by spring was in full swing in the Twin
+Tunnels.
+
+The plans contemplated the use of a complete concrete lining except
+where large quantities of water were encountered; in which case the
+arches, beginning at a point 15 deg. above the springing line, were to be
+built of vitrified paving brick. By reference to Plate XII it will be
+seen that the water-proofing, which in the concrete-roof tunnels
+extended the full height of the sides to the 15 deg. line, was carried in
+the brick-roof tunnels completely around the extrados of the arch. The
+cross-sections also show the location of the electric conduits which
+were buried in the mass of the side and core-walls and which limited the
+height to which the concrete could be carried in one operation.
+
+The same general scheme of operations was used wherever possible
+throughout the Twin-Tunnel work, but was subject to minor modifications
+as circumstances dictated. Concrete was first deposited in the bottom,
+to the grade of the flow line of the drains; after it had set,
+collapsible box forms, of 2-in. plank with 3-in. plank tops, were laid
+on it to form the ditch and the shoulders for the flagstone covers. The
+track, which had previously been blocked up on the rock between the
+ditches, was raised and supported on the ditch boxes above the finished
+floor level. At the same time, light forms were braced from the ditch
+boxes to the grade of the base of the low-tension and telephone-duct
+bank. After depositing the concrete to this level, the telephone ducts
+were laid.
+
+The forms for the water-proofing or sand-wall up to the 15 deg. line and for
+the main side-walls and core-walls were built in 30-ft. panels and were
+supported on carriages, which, traveling on a broad-gauge track above
+the ditches, moved along the tunnel, section by section, as the work
+advanced. The panels were hung loosely from joists carrying a platform
+on the top chord of the carriage trusses, and were adjusted
+transversely by bracing and wedging them out from the carriage. The
+small forms for the refuge niches, ladders, etc., were collapsible, and
+were spiked to the main panel forms just previous to the deposition of
+the concrete. The concrete was deposited from the platform on top of the
+carriage, to which the cars were elevated in various ways. Plate LXI
+shows the details of the carriages, and is self-explanatory.
+
+The concrete for the sand-walls and the core-wall, to the level of the
+sidewalk, was deposited at the same time; two carriages in each tunnel,
+placed opposite each other, forming a 60-ft. length, were used at each
+setting. The floor section of the 4-in. tile drains had been laid with
+the floor concrete, and, as the sand-wall concrete was deposited, the
+drains were brought up simultaneously, broken stone being deposited
+between the tile and the rock to form a blind drain and afford access to
+the open joints of the tile for the water entering the tunnel through
+seams in the rock. The drains were spaced at intervals not exceeding 25
+ft., depending on the wetness of the rock, and were placed at similar
+intervals in the core-wall under the lowest projecting points of the
+rock on the center line between the tunnels. A small ditch lined with
+loose 6-in. vitrified half pipe was provided in the top of the sand-wall
+to collect the water from the extrados of the arch and lead it to the
+top of the drains. Great difficulty was experienced in maintaining these
+drains clear, and, on completion of the work, a large amount of labor
+was expended in removing obstructions from the floor sections, the only
+portion then accessible.
+
+After water-proofing the sand-walls and laying the low-tension ducts, a
+second pair of carriages, with panels on one side only, for 60 ft. of
+side-wall and skewback to the 15 deg. line, were set and braced against the
+core-wall. These forms are shown in connection with the carriage on
+Plate LXI. They were concreted to the base of the high-tension duct
+bank, and, after the concrete had hardened and the bank of ducts had
+been laid, the concreting was completed in a second operation.
+
+In places where the roof was supported temporarily by posts and heavy
+timbering, such as at Fifth Avenue, the form carriages could not be
+used, and special methods were devised to suit the local conditions.
+Usually, the panels were stripped from the carriages and moved from
+section to section by hand, and, when in position, were braced to the
+timbering.
+
+The arch centers were built up of two 5 by 3 by 3/8-in. steel angles,
+and, when set, were blocked up on the sidewalks opposite each other in
+the two tunnels. A temporary platform was laid on the bottom chord
+angles of the ribs, on which the concrete was dumped, the same as on the
+form carriages. The lagging used was 3 by 3-in. dressed pine or spruce
+16 ft. long, and was placed as the concreting of the arch proceeded
+above the 15 deg. line on the side-wall and above the sidewalk on the
+core-wall. After the arch had reached such a height that the concrete
+could not be passed over the lagging directly from the main platform, it
+was cast on a small platform on the upper horizontal bracing of the
+centers, shown in Fig. 3, Plate LIX, and was thence shoveled into the
+work. In the upper part of the arch the face of the concrete was kept on
+a radial plane, and, when only 3 ft. remained to be placed, it was keyed
+in from one end, the key lagging being set in about 5-ft. lengths. The
+arches were concreted usually in 60-ft. lengths.
+
+Where brick arches were used, the core-wall skewback was concreted
+behind special forms set up on the sidewalks, or the arch ribs and
+lagging were used for forms, and the brick arch was not started until
+after the concrete had set. In laying the brick in the arch, the five
+courses of the ring were carried up as high as the void between the
+extrados and the rock would permit and still leave a working space in
+which to place the water-proofing. This was usually not more than 3 ft.,
+except on the core-wall side. The felt and pitch water-proofing was then
+laid for that height, joined to the previous water-proofing on the
+side-walls, and was followed by the brick armor course over the
+water-proofing and by the rock packing, after which another lift of
+brick was laid and the operations were repeated. The large void (Fig. 1,
+Plate LXII) above the core-wall gave convenient access for working on
+top of the adjacent sides of the roof, and the keying of the arches and
+the water-proofing and rock packing above the core-wall were usually
+carried on from that point, the work progressing from one end.
+
+The concrete for all work above the floor was dumped on the platform of
+the carriages, to which it was transported in the early part of the work
+in cars running on a high-level track laid on long ties, resting on the
+finished sidewalks. This arrangement, although requiring a large amount
+of timber for the track, permitted the muck to be carried out on the
+low-level track without interference. Later, when the advance of the
+heading had ceased and the heavy mucking was over, all concrete was
+transported on the floor level, and the cars were lifted to the carriage
+platforms by elevators and were hauled by hoisting engines up a movable
+incline. The latter method is shown by Fig. 3, Plate LIX.
+
+_Water-Proofing._--The water-proofing referred to above was in all cases
+felt and pitch laid with six thicknesses of felt and seven of pitch. The
+sub-contractor for the work was the Sicilian Asphalt Paving Company. All
+joints were lapped at least 1 ft., and, where work was suspended for a
+time and a bevel lap could not be made, the edges of the felt were left
+unpitched for 1 ft. and the newer work was interlaced with the old. This
+method was not always successful, however, on account of the softening
+of the unpitched felt on long-continued exposure to the water. The felt
+used was mainly "Tunaloid," together with some "Hydrex." It weighed
+about 12 lb. per 100 sq. ft. when saturated and coated on one side only,
+and contained about 25% of wool. The coal-tar pitch used had a melting
+point of 100 deg. Fahr.
+
+After the completion of the tunnel, the concrete arch showed some
+leakage and in places unsightly lime deposits. It was determined to
+attempt to stop these leaks by the application of a water-proof cement
+coating on the intrados of the arch. Extended experimental application
+of two varieties of materials used for this purpose--"Hydrolithic"
+cement and the U. S. Water-proofing Company's compound--have been made
+with apparent success up to the present time, and the results after the
+lapse of a considerable period are awaited with interest.
+
+_Duct Laying._--The position of the electric conduits, buried in the
+heart of the concrete walls, interfered greatly with the economical and
+speedy placing of the lining, and their laying proved to be one of the
+most troublesome features of the work. The power conduits were
+single-way, with the bank for high-tension cables separated in the
+side-walls from the low-tension bank, as shown on Plate XII. The
+conduits for telephone and telegraph service were four-way, and were
+located in the core-wall. All ducts had 3/4-in. walls and a minimum
+clear opening of 3-3/8 in. square, with corners rounded. They were laid
+with joints broken in all directions, and in about 1/4-in. beds of
+1:2-1/2 mortar. Flat steel bond-irons, 2 by 1/8 in., with split and bent
+ends, were placed in the joints at intervals of 3 ft. and projected into
+the concrete 3 in. on each side, tying together the concrete on opposite
+sides of the ducts. The joints were wrapped with a 6-in. strip of
+10-oz. duck saturated with neat-cement grout, and, in addition, the
+power conduits were completely covered with a 1/2-in. coat of mortar to
+prevent the intrusion of cement and sand from the fluid concrete. The
+four-way conduits were plastered only over the wraps. Splicing chambers
+were provided at intervals of 400 ft.
+
+[Illustration: PLATE LXII, FIG. 1.--WATER-PROOFING OVER BRICK
+ARCHES.]
+
+[Illustration: PLATE LXII, FIG. 2.--TRESTLE USED IN CONCRETING IN
+THREE-TRACK TUNNEL.]
+
+[Illustration: PLATE LXII, FIG. 3.--METHOD OF STREET SUPPORT OVER
+OPEN-CUT EXCAVATION.]
+
+[Illustration: PLATE LXII, FIG. 4.--JUNCTION OF TWIN AND THREE-TRACK
+TUNNELS.]
+
+
+THREE-TRACK TUNNEL LINING.
+
+In the Three-Track Tunnels, a heavy brick arch was used for those
+portions constructed in tunnel, while, in the open-cut sections, the
+roof was of concrete. Both were completely water-proofed on the roof and
+sides, and in the tunnel sections the space above the brick roof was
+filled with rock packing. On account of the unstable nature of the rock
+encountered throughout, the voids in the packing were afterward filled
+with grout.
+
+By reference to the cross-sections, Plate XII, it will be seen that the
+haunches of the arch were tied together by steel I-beams anchored in the
+concrete, with the object of making the structure self-supporting in the
+event of the removal of the adjacent rock for deep cellar excavations.
+This construction materially influenced the contractor's method of
+placing the masonry lining.
+
+After depositing the floor concrete, by the same method that was used in
+the Twin Tunnels, a timber trestle (Fig. 2, Plate LXII) was erected to
+the height of the underside of the I-beam ties, the posts being footed
+in holes, about 3 in. deep, left in the concrete floor to prevent
+slipping. In the open-cut sections the sand-wall forms were of undressed
+plank tacked to the studding and braced from the trestle; in the tunnel
+section they were spiked to the face of the posts supporting the
+timbering.
+
+The side-wall forms were made up in panels about 3 by 10 ft., and were
+clamped to studs by U-shaped irons passing around the stud and bolted to
+the cleats on the back of the panels, the studs being braced from the
+trestle. The side-wall concrete was deposited in three sections. The
+first was brought up just above the sidewalk and formed the bench for
+the high-tension ducts; the second carried the wall up to the springing
+line. Before placing the third section the I-beam ties were set in
+position (Fig. 3, Plate LXII) on top of the trestle, and the reinforcing
+rods in the haunch of the arch were hung from them. The concrete was
+carried up to a skewback for the arch, as shown in the brick-roof
+cross-section (Plate XII) and embedded the ends of the ties.
+
+The centers for the arches stood on the I-beam ties, and the tops of the
+hangers, for the permanent support of the ties near their center, were
+inserted through the lagging. The brick arch, water-proofing, and rock
+packing were laid up in lifts, in the same manner as in the Twin Tunnel,
+with grout pipes built in at intervals of about 8 ft. The concrete arch
+was placed in sections, from 25 to 50 ft. in length, with a rather wet
+mixture and a back form on the steep slope of the extrados.
+
+The concrete for the sand-walls and lower part of side-walls was handled
+on tracks and platforms laid on cantilever beams at mid-height of the
+trestle, as shown by Fig. 3, Plate LXII. For the walls above the
+springing line, the tracks were laid on top of the I-beam ties, and some
+of the arch concrete, also, was delivered from the mixer at that level
+and hauled up an incline to the level of the top of the arch. By far the
+greater part, however, was turned out from mixers set on the completed
+arch, and was transported on tracks hung in part from the street
+timbering.
+
+_Completion._--Except in the heavily-timbered portions, such as at Fifth
+Avenue, where the load had to be transferred from posts to the completed
+masonry section by section, the lining of the tunnels presented no
+special difficulty. The large number of small forms to be set, and the
+mutual interference of the concreting and duct-laying operations proved
+to be the most troublesome features of the work.
+
+The restoration of the streets, public utilities, etc., at the open-cut
+sections was a slow and tedious operation, but the tunnels themselves
+were completed in March, 1909, 3 years and 10 months after the inception
+of the work. The finished tunnels are shown by the photograph, Fig. 4,
+Plate LXII, taken at the junction of the twin and three-track types.
+
+FOOTNOTES:
+
+[Footnote A: Presented at the meeting of December 1st, 1909.]
+
+[Footnote B: Of the paper by Mr. Noble.]
+
+[Footnote C: Of the paper by Mr. Noble.]
+
+[Footnote D: Of the paper by Mr. Noble.]
+
+
+
+
+
+
+End of the Project Gutenberg EBook of Transactions of the American Society
+of Civil Engineers, Vol. LXVIII, Sept. 1910, by James H. Brace and Francis Mason
+
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