AMERICAN SOCIETY OF CIVIL ENGINEERS

INSTITUTED 1852

TRANSACTIONS

Paper No. 1156

THE NEW YORK TUNNEL EXTENSION OF THEPENNSYLVANIA RAILROAD. 

THE TERMINAL STATION-WEST. [A]

BY B. F. CRESSON, JR. , M. AM. SOC. C. E. 

_Location of Work. _--The area covered by the work of the TerminalStation-West is bounded as follows: By the east line of Ninth Avenue; bythe south side of 31st Street to a point about 200 ft. West of NinthAvenue; by a line running parallel to Ninth Avenue and about 200 ft. Therefrom, from the south side of 31st Street to the boundary line betweenthe 31st and 32d Street properties; by this line to the east line of TenthAvenue; by the east line of Tenth Avenue to the boundary line between the32d and 33d Street properties; by this line to the east line of NinthAvenue. The area is approximately 6. 3 acres. 

_House-Wrecking. _--The property between Ninth and Tenth Avenues was coveredwith buildings, 94 in number, used as dwelling and apartment houses andchurch properties, and it was necessary to remove these before starting theconstruction. Most of the property was bought outright by the RailroadCompany, but in some cases condemnation proceedings had to be instituted inorder to acquire possession. In the case of the property of the Church ofSt. Michael, fronting on Ninth Avenue, 31st and 32d Streets, the RailroadCompany agreed to purchase a plot of land on the south side of 34th Street, west of Ninth Avenue, and to erect thereon a church, rectory, convent, andschool, to the satisfaction of the Church of St. Michael, to hand overthese buildings in a completed condition, and to pay the cost of movingfrom the old to the new buildings, before the old properties would beturned over to the Railroad Company. 

The house-wrecking was done by well-known companies under contract with theRailroad Company. These companies took down the buildings and removed allthe materials as far as to the level of the adjacent sidewalks. Thebuilding materials became the property of the contractors, who usually paidthe Railroad Company for the privilege of doing the house-wrecking. Thework was done between April and August, 1906, but the buildings of theChurch of St. Michael were torn down between June and August, 1907. 

The bricks were cleaned and sold directly from the site, as werepractically all the fixtures in the buildings. The stone fronts were brokenup and left on the premises. Some of the beams were sold on the premises, but most of them were sent to the storage yards. Some of the lath andsmaller timber was sold for firewood, but most of it was given away orburned on the premises. 

_Contracts and Agreements. _--The main contract, awarded to the New YorkContracting Company-Pennsylvania Terminal on April 28th, 1906, includedabout 502, 000 cu. Yd. Of excavation (about 90% being rock), 17, 820 cu. Yd. Of concrete walls, 1, 320, 000 lb. Of structural steel, 638, 000 ft. , B. M. , offramed timber, etc. , etc. 

This contract was divided into two parts: "Work In and Under Ninth Avenue"and "Work Between Ninth and Tenth Avenues, " and unit prices were quoted forthe various classes of work in each of these divisions. The prices quotedfor excavation included placing the material on scows supplied by theRailroad Company at the pier at the foot of West 32d Street, on the NorthRiver; there was a clause in the contract, however, by which the contractorcould be required to make complete disposal of all excavated material at anadditional unit price, and this clause was enforced on January 1st, 1909, when about 94% of the excavation had been done. 

For the purpose of disposing of the excavated material in the easterlyportion of the Terminal, the New York Contracting Company-PennsylvaniaTerminal had excavated under Ninth Avenue a cut which came to the grade of32d Street about midway between Ninth and Tenth Avenues, and a trestle wasconstructed from this point over Tenth Avenue and thence to the disposalpier at the foot of West 32d Street. 

On May 11th, 1906, the work of excavation was commenced on the east side ofNinth Avenue, and on July 9th, 1906, on the south side of 31st Street, between Ninth and Tenth Avenues. From the beginning, the excavation wascarried on by day and night shifts, except on Sundays and holidays, untilJanuary, 1909, except that during the period from November, 1907, toOctober, 1908, the night shift was discontinued. 

_Geology. _--The rock encountered may be classed as "gneiss"; its charactervaried from granite to mica schist. It was made up of quartz, feldspar, andmica, and there were also some isolated specimens of pyrites, hornblend, tourmaline, and serpentine. On the south side of the work, just west ofNinth Avenue, there were excellent examples of "contortions" of veins ofquartz in the darker rock. On the east side of Ninth Avenue, near the northend of the work, glacial marks were found on the rock surface. The generaldirection of the stratification was north 5° west, and the general inclineabout 60° with the horizontal. As a rule, the rock broke sharply along theline of stratification. On the south side it broke better than on the northside, where it was usually softer and more likely to slide; and this, together with the fact that in winter it was subject to alternate freezingand thawing and in summer to the direct rays of the sun, made it ratherdifficult to get a good foundation for the retaining walls. 

WORK IN AND UNDER NINTH AVENUE. 

_General Description. _--The work involved the excavation of about 375 ft. Of the full width of Ninth Avenue to an average depth of about 58 ft. , andthe construction over this area of a steel viaduct, the deck of which wasabout 24 ft. Below the surface, for the ultimate support of the NinthAvenue structures. 

The following estimated quantities appear in the contract: Excavation ofrock, 72, 600 cu. Yd. ; excavation of all materials except rock, 9, 300 cu. Yd. ; concrete (1:3:6) in abutments, etc. , 1, 680 cu. Yd. ; timber, 504, 000ft. , B. M. ; structural steel, 1, 320, 000 lb. , etc. 

While this excavation was being done it was necessary to support andmaintain the three-track elevated railway structure of the InterboroughRapid Transit Company, of which 18 columns, or a length of about 340 ft. , were affected, the two-track surface railway structure of the New York CityRailway Company, and various pipes, sewers, and conduits, and to maintainall surface vehicular and pedestrian traffic. All structures were left inplace with the exception of the pipes, most of which were temporarily cutout. The 48-in. Brick sewer in the center of Ninth Avenue was broken, andthe sewage was pumped across the excavation through a smaller pipe. 

The general method adopted was as follows: The east and west sides of theavenue were closed, vehicular traffic was turned into the center, and atrestle for pedestrians was constructed west of the westerly elevatedrailway columns. All structures were then supported on transverse girders, running across the avenue, below the surface, and these rested on concretepiers on the central rock core. The sides of the avenue were then excavatedto sub-grade, and the permanent steel viaduct was erected on both sides ofthe avenue as close as possible to the central rock core. The weight of allstructures was then transferred to the permanent steel viaduct, erected onthe sides of the avenue, by timber bents under the transverse girdersresting on the permanent steel viaduct, and all weight was thus taken offthe central rock core. This core was then excavated to sub-grade, thepermanent viaduct was completed, and all structures were placed on itsdeck, using concrete piers and timber bents. 

The design and erection of the permanent steel viaduct and the permanentfoundations on its deck were done under another contract, apart from theNorth River Division work, and are not described in this paper. 

_Elevated Railway Structure of the Interborough Rapid TransitCompany. _--The Ninth Avenue Elevated Railway was built between 1877 and1880 as a two-track structure, the design being such as to permit a thirdor central track to be added later, and this was built in 1894. It issupported on columns under the outside tracks, about 43 ft. From center tocenter longitudinally and 22 ft. 3 in. From center to center transversely, the central track being carried by transverse girders between the columns. 

The columns carrying the structure are of fan top design, with the pointsof bearing near the extremities at the top; each of the outside tracks issupported on two longitudinal latticed girders and the central track ontwo plate girders; between the columns, transverse girders are spliced tothe outside track cross-frames, and carry the central track system. It wasnot thought desirable to put brackets on the columns near the street levelto support the structure temporarily, and, as there is an expansion jointat each column, and as the transverse girders carrying the central tracksystem are not rigidly attached to the longitudinal girders carrying theoutside tracks, the central track could not be supported by supporting theoutside tracks; therefore, independent supports for each track, in the formof overhead girders, had to be provided. The columns rest on brick piers, each having four 2-in. Anchor-bolts. The brick foundations on the west sideare wide in order to allow a 24-in. Water main to pass directly beneath thecolumns. The foundations are usually on rock. 

[Illustration: PLATE XLVII, FIG. 1. --TW 4, P. N. Y. & L. I. R. R. TerminalStation West. View of 9th Ave. Looking Northwest from 32nd Street, prior tocommencement of work. April 23, 06. ]

[Illustration: PLATE XLVII, FIG. 2. --TW 17, P. N. Y. & L. I. R. R. TerminalStation West. View of East side of 9th Ave. Looking North from a point 100feet south of 33rd St. Showing condition of work. July 23, 06. ]

[Illustration: PLATE XLVII, FIG. 3. --TW 25, P. N. Y. & L. I. R. R. TerminalStation West. View showing permanent and temporary supports of 9th Ave. Structures, looking Northwest from 31st. St. April 24, 07. ]

[Illustration: PLATE XLVII, FIG. 4. --TW 28, P. T. & T. R. R. Co. TerminalStation West. East side of 9th Avenue, North of 32nd St. Looking West, showing rock excavation and supports of 9th Avenue structures. Aug. 17, 07. ]

Fig. 1, Plate XLVII, shows the elevated railway structure and the streetsurface prior to the commencement of the work. 

The east track is used for north-bound local trains, the west track forsouth-bound local trains, and the central track for south-bound expresstrains between 7 and 9. 30 A. M. And for north-bound express trains between2. 30 and 7 P. M. It is said that an average of 90, 000 passengers are carriedover this structure every 24 hours. 

_Surface Railway Structure of the New York City Railway Company. _--This isan electric surface railway of the ordinary type, the rail and slot beingbedded in concrete, with cast-iron yokes every 5 ft. There are manholesevery 100 ft. , and cleaning-out holes every 15 ft. Power conduits arebedded in the concrete on the east side of the east track. 

_Forty-eight-Inch Brick Sewer. _--This sewer was in the center of NinthAvenue, with the invert about 12 ft. Below the surface, and manholes about100 ft. Apart, and had to be abandoned in this position to allow thetransverse girders to be put in place to carry all structures while theexcavation was being done. 

_Twenty-four-Inch Cast-Iron Water Main. _--This water main was laid underthe west elevated railway columns, with its top about 3 ft. Below thesurface, a space being left for it in the brick foundations, and a largecolumn base casting being used to span it. Valves were installed, one northof 33d Street and one south of 31st Street, prior to excavating near thepipe, so that if it was broken the water could be shut off promptly. 

_Street Surface. _--It was the original intention to close and excavate theeast side of the avenue and to erect there a street-traffic trestle beforeclosing the west side, but, at the contractor's request, both sides wereclosed, and all vehicular traffic was turned into the center. A lighttrestle on the west side of the avenue provided for pedestrian traffic. 

_Other Sub-surface Structures. _--There were various gas mains, water mains, electric conduits, manholes, hydrants, etc. , in the avenue, and most ofthese were cut out temporarily, at the contractor's request, to be replacedsubsequently. 

_Supports for Elevated Railway Structure. _--As stated previously, thecentral track had to be supported independently. 

The overhead girders, known as girders "B", were therefore designed asshown on Fig. 1, and put in place as shown on Figs. 2 and 3. The outsidetracks were blocked directly on these girders, and the central track wassupported by blocking up the transverse girders on I-beams placed betweenthe girders "B"; and no blocking was placed between the girders "B" and thelongitudinal girders carrying the central track. The weight on each columnwas assumed to be 172, 000 lb. 

[Illustration: FIG. 1. (Full page image)

DETAILS OF STEEL GIRDERS, ETC. SUPPORTING NINTH AVENUE STRUCTURES]

_Supports for Surface Railway Structure. _--A uniform load of 3, 000 lb. Perlin. Ft. Of single track, with the weight of a car at 39, 000 lb. , wasassumed. Several feet of earth, between the structure and the rock, weremined out, and the structure was supported on I-beams and posts, andultimately on the transverse girders by using timber bents under theI-beams, as shown on Fig. 3. 

_Water Mains and Sewer. _--Cradles were designed for the support of the48-in. And 24-in. Water mains, resting on the transverse girders, and the48-in. Cast-iron sewer on the east side of the avenue was carried onI-beams bracketed to the ends of the transverse girders, as shown on Figs. 1 and 2. 

[Illustration: FIG. 2. (Full page image)

METHOD OF SUPPORTING ELEVATED RAILWAY STRUCTURE]

[Illustration: FIG. 3. (Full page image)

METHOD OF SUPPORTING TRACKS OF NEW YORK CITY RAILWAY CO. ]

_Girders "C. "_--The transverse girders below the street surface, referredto above, were known as girders "C, " and they were put in place at firstresting on concrete piers on the central core; the weight of all structureswas placed on them while the sides of the avenue were being excavated, andthe sides of the viaduct were being built. The ends of these girders werethen picked up on the sides of the viaduct, and, spanning the central rockcore, carried all structures while the core was being excavated and theviaduct completed. New foundations were then placed on the deck of theviaduct to carry all structures. 

Fifty-four of these girders were required, each weighing about 19, 000 lb. The bents carrying the ends of these girders on the sides of the viaductare shown on Fig. 2. They were of long-leaf yellow pine. These girders werelocated so that a cradle could be laid on them east of the elevated railwaystructure to carry a proposed 48-in. Cast-iron water main. 

_Girders "B. "_--Eighteen of these girders were required, each weighingabout 6, 000 lb. The timber bents supporting these girders, shown on Fig. 2, were of long-leaf yellow pine. 

The total weight, including the elevated railway structure, surface railwaystructure, pipes, etc. , supported during the work, amounted to about 5, 000tons. 

_Details of the Work. _--The method in general is shown on Figs. 4 and 5. Atfirst the east side of the avenue was closed and excavated down to rock, the earth was mined out under alternate yokes of the surface railwaystructure, and temporary posts were placed under the yokes to support thestructure while the remainder of the earth was being removed. Thenneedle-beams and posts were placed under each yoke. The concrete formingthe track structure was then enclosed with planking to prevent it fromcracking and falling. I-beams were then placed under the needle-beamscarrying the structures, and these were carried on posts; they were changedalternately until the excavation had been taken out to a depth of about 16ft. Below the surface. In placing these I-beams, heavier blocking was usedin the center of the span than at the ends where the bents would come, toprevent the subsidence of the track owing to the sag in the I-beams. Asmuch excavation, to a depth of about 20 ft. , was taken out adjoining theelevated railway foundations as could be done with safety. Fig. 2, PlateXLVII, shows this condition of the work. The 48-in. Brick sewer was broken, and the sewage was pumped across the excavation. 

The overhead girders "B" were then put in place, and two of the girders "C"were used as temporary shoring girders at each column. These, as shown byFig. 3, Plate XLVII, were placed parallel to the elevated railway, withblocking between them and the girders "B. " Double bents, independentof each other, were placed under the ends of these temporary shoringgirders, and these were braced securely to prevent possible dislodgmentduring the removal of the rock. The weight of the structure was then takenby jacking up the girders near the bents until the column was lifted offthe old foundation; blocking was put in between the girders and the bentsduring the jacking, so that when the jacks were released the base of thecolumn was still clear of the old foundation. One 80-ton jack was used forthis purpose, and the general method is shown by Fig. 1, Plate LII. 

[Illustration: FIG. 4. (Full page image)

METHOD OF EXCAVATING NINTH AVENUE PLAN AND ELEVATION SHOWING VARIOUS STAGESOF THE WORK]

[Illustration: FIG. 5. (Full page image)

METHOD OF EXCAVATING NINTH AVENUE SECTIONS SHOWING VARIOUS STAGES OF WORK

No. 1

Condition Prior to Commencement of Work

No. 2

East side of Avenue cut down about 20 ft. Beams with Supporting Postsplaced under Surface Railway Tracks. Girders _B_ and Temporary ShoringGirders _C_ for supporting Elevated Ry. In place. 

No. 3

I's in place under Surface Ry. Tracks. Elevated Ry. Carried on TemporaryShoring Girders, and Girders _C_ in place. 24" Water Main carried on TimberCradle and sewage carried through Pipe _R_. Foot Walk carried on Girders_C_ in place on West Side of Avenue. 

No. 4

Elevated Railway carried on Bents under Columns. Temporary Shoring Girdersremoved and Permanent Bents resting on Girders _C_ in place. Bents in placeon Girders _C_ carrying Surface Railway. East and West sides of Avenueexcavated down to Sub-Grade and Five rows of Permanent Steel in place oneach side. Bents erected on Permanent Steel to catch ends of Girders _C_while 2 outside Concrete Piers are removed and 6th row of Permanent Steelon each side is put in place. 

No. 5

Two outside Concrete Piers removed and 6th row of Permanent Steel in place. Girders _C_ carrying all structures now resting on Bents on PermanentSteel. 48" C. L. Sewer carried on Brackets on Girders _C_. 

No. 6

Excavation Completed. ]

Temporary raker braces were placed against the structure to prevent lateralmovement. Four sets of these temporary shoring girders were used in thismanner, two sets starting at the north end and two sets at about the middleof the work, and these sets were moved south as they were released. 

The columns being thus supported on temporary shoring girders, the oldfoundations were removed and the excavation was taken down to a level about16 ft. Below the surface. 

Two sets of three of the girders "C" were then put in place under theavenue at each column, each set being placed on four concrete piers 6 ft. Square with spaces of 4 ft. Between them, so that the outside of theoutside pier would be 18 ft. From the center of the avenue and 32 ft. Fromthe house line. This is shown on Fig. 5 and on Fig. 3, Plate XLVII. Foursmall piers were used, as they could be more easily removed than onecontinuous pier. The girders "C" were set to line and grade, and the pierswere built under them, great care being taken to get the concrete wellunder the girders so as to give a firm bearing. 

After these girders "C" were in place it was necessary to remove thetemporary shoring girders before the bents could be erected on girders "C"to support girders "B, " being in the same plane; and provision had to bemade to support the structure while this was being done. Therefore, doublebents were erected directly beneath the columns, as shown by Figs. 2, 4, and 5, and by Fig. 3, Plate XLVII. These were built with their sillsresting on the girders "C, " and blocking was put in between the sills andthe rock to carry the full weight of the structure. Later, when the weightof the structure was carried on the permanent bents, this blocking wasknocked out, but the bents were left in to carry the weight of the columnitself, which was swinging more or less from the structure above. Theweight of the structure was placed on these bents directly beneath thecolumns by jacking up the temporary girders again, putting blocking betweenthe bents and the base of the columns, and taking out the blocking whichhad been put in previously under the temporary shoring girders. The 24-in. Water main was carried over the excavation on cables from the temporaryshoring girders, except when they were being jacked up, at which time postswere placed beneath it. 

Anchor-bolts were put in place between the column bases and the bentsdirectly beneath, in order to increase the lateral stiffness, and rakerbraces were also used. This having been done, the temporary shoring girderswere moved south to the next column, where the process was repeated. Thetimber bents, shown in detail by Fig. 2, were then put in place as shown byFigs. 4 and 5, and by Fig. 3, Plate XLVII. These bents were framed astightly as possible, using generally a 20-ton jack, and they were erectedsimultaneously at each pair of columns. The weight was taken on thesecolumns by jacking up directly beneath the column base and taking out theblocking between this base and the bent directly beneath the column. Onreleasing the jack the weight was transferred to the permanent timberbents, and the east and west columns of each pair were transferred on thesame day. One 80-ton jack was used on the easterly columns and two werenecessary on the westerly columns, one on each side of the 24-in. Watermain. The raker braces of these permanent bents were not framed as tightlyas the main posts, in order that the main post should carry the entireweight and the raker braces merely steady the structure. 

Timber bents were erected on girders "C" to carry the I-beams under thesurface railway structure, as shown on Fig. 3, and all temporary postsunder these I-beams were removed. The bents were framed with a jack, astightly as possible, and very little settlement of the track occurred. 

A cradle was then built under the 24-in. Water main and placed on girders"C, " and, as a temporary footwalk had been constructed on the west side ofthe avenue, it will be seen that all structures were thus carried ongirders "C. "

All structures were put on the girders "C" before continuing the excavationon the sides of the avenue because, in case of a slide of rock, there wouldbe less danger than to individual structures. The outside piers, onwhich the girders "C" rested, might even be lost, without affecting thestability of the structure, and posting could readily be done beneath thesegirders in case of necessity. 

A very careful record of levels, taken on the elevated railway columns, waskept, observations being made during each jacking up and at least twice aweek during the progress of the work. The columns were usually kept about1/2 in. High so as to allow for compression in the timber bents. 

As a rule, no jacking of the elevated railway structure was done whiletrains were passing over, and trains were flagged during the operation. There was generally very little delay, as all jacking was done between10. 30 A. M. And 2. 30 P. M. , when the traffic was lightest, and frequently thejacking was done between trains, causing no delay whatever. Steel clampswere placed, three on the top and three on the bottom of each set of thegirders "C, " to bind them together and cause them to act as a unit. 

All structures then being supported on girders "C, " which were carried onfour concrete piers resting on the central rock core, the excavation on thesides of the avenue was continued down to sub-grade and the east and westportions of the concrete north abutment were constructed. The central rockcore was about 36 ft. Wide on the top and 45 ft. Wide on the bottom, and atthe center of 32d Street it was about 42 ft. High. 

It was the original intention to excavate a sufficient width of the sidesof the avenue to erect six rows of the permanent steel viaduct, 5 ft. Fromcenter to center, and this was done on the south portion of the work. Onthe north portion, however, the rock was of poor quality, and it wasthought best to excavate for only five rows at first, to erect the fiverows of permanent steel and put the timber bents in place under the ends ofthe girders "C, " in order to give them some support while the outsideconcrete piers were being removed and the excavation was being widened outto permit the erection of the sixth row. Additional raker braces were putin these bents temporarily, and were removed when the sixth row of steelhad been erected. This is shown on Figs. 4 and 5. 

[Illustration: PLATE XLVIII, FIG. 1. --TW 33, P. T. & T. R. R. Co. TerminalStation West. East side of 9th Ave. Looking North from 31st St. , showingrock excavation and supports of 9th Ave. Structures. Dec. 28, 07. ]

[Illustration: PLATE XLVIII, FIG. 2. --TW 39, P. T. & T. R. R. Co. TerminalStation West. East side of 9th Ave. Looking North from 31st Street, showingrock excavation and permanent steel work. March 24, 08. ]

[Illustration: PLATE XLVIII, FIG. 3. --TW 73, P. T. & T. R. R. Co. TerminalStation West. West side of Ninth Ave. Jacking up girders "C" at ElevatedRailroad Column 491, showing method of taking weight on permanent viaductgirders. Nov. 14, 08. ]

[Illustration: PLATE XLVIII, FIG. 4. --TW 58, P. T. & T. R. R. Co. TerminalStation West. East side of Ninth Ave. Looking North from 31st St. , showingunderpinning of Ninth Ave. Structures. Aug. 10, 08. ]

Fig. 4, Plate XLVII, and Fig. 1, Plate XLVIII, show the structuressupported on the central rock core and the excavation on the east side topermit of the erection of the permanent viaduct girders. Fig. 1, PlateXLVIII, shows also the easterly portion of the concrete north abutment. Fig. 2, Plate XLVIII, shows five rows of the permanent viaduct girderserected on the east side of the work. 

The excavation of the sides of the avenue having been completed, and sixrows of permanent viaduct girders erected on both sides, timber bents, asshown on Figs. 2, 4, 5, and 6, were erected on this steel to support theends of the girders "C" and carry the structure while the rock core wasbeing excavated. Fig. 3, Plate XLVIII, shows the method of taking theweight on these bents. Four 80-ton jacks were used, and oak blocks wereplaced on the top of each jack to transmit pressure to a temporary oak capunder the girders "C" independent of the bents; all four of these jackswere operated simultaneously, and the girders "C" were lifted off the bentsand clear of the concrete piers. Oak filling pieces were then insertedbetween the bents and the girders "C, " so that when the jacks were releasedthe girders "C" were clear of the concrete piers. Fig. 3, Plate XLVIII, shows that the girders have been lifted off the piers. Elevations weretaken on each set of girders during each operation, and carefulobservations were made on the elevated railway columns. Where the rock wasvery close to these bents, the open space between the posts was filled withblocking so that there would be less danger of the bent shifting if struckby blasted materials. Fig. 3, Plate XLVIII, shows one of these bents filledwith blocking. 

All structures being carried on girders "C, " which, in turn, were carriedon the sides of the permanent viaduct, the central core was excavated. Fig. 4, Plate XLVIII, and Figs. 1, 2, 3, and 4, Plate XLIX, show various viewsof the work at this stage. 

The central portion of the viaduct was then erected, and, using concretepiers and timber bents, all structures were placed on its deck. Fig. 3, Plate XLIX, shows the piers under the elevated railway columns prior to theremoval of girders "C. "

[Illustration: FIG. 6. (Full page image)

GENERAL ARRANGEMENT OF TEMPORARY AND PERMANENT STRUCTURES]

During the latter part of 1908 a 48-in. Cast-iron water main was laid bythe city on a cradle built by the Railroad Company on girders "C" on theeast side of the avenue. This is part of the high-pressure system, and thelocation and elevation of this water main were taken into considerationwhen the underpinning was designed. This main, and the 48-in. Cast-ironsewer bracketed to girders "C, " are shown on Fig. 4, Plate XLVIII. 

Elevations had been taken on marks on the elevated railway columnsbetween 30th and 34th Streets at the time the original surveys were made, in 1902, and these marks were used to test the level of the structureduring the progress of the excavation. 

At the extreme south end of the work the procedure was changed. The eastside was excavated down to sub-grade, the east portion of the southabutment was constructed, and six rows of the permanent steel viaduct wereerected. Very little excavation had been done on the west side of theavenue at the south end of the work, and it would have delayed thecompletion of the work to have waited for the excavation for and theconstruction of the west portion of the south abutment and the erection ofthe steel; therefore, instead of supporting the girders "C" on the centralrock core, the east ends were taken up on the permanent viaduct girders, and the west ends were supported on a concrete pier on the rock. Thecentral portion of the avenue was excavated in advance of the west portion. The permanent viaduct girders were put in place from east to west acrossthe avenue, and the girders "C" were supported on the deck of the permanentviaduct approximately under the west elevated railway columns before thewest portion of the avenue was excavated, the central portion of the southabutment having been constructed before the west portion. This procedurewas adopted only at the north girders "C" at elevated railway column No. 488, the south set of girders "C" being on the rock immediately south ofthe south abutment. Figs. 2 and 4, Plate XLIX, and Fig. 2, Plate LII, showvarious stages of the work at the south end. 

[Illustration: PLATE XLIX, FIG. 1. --TW 60, P. T. & T. R. R. Co. TerminalStation West. Under Ninth Ave. , looking South from North abutment, showingunderpinning and excavation of rock core. Aug. 13, 08. ]

[Illustration: PLATE XLIX, FIG. 2. --TW 84, P. T. & T. R. R. Co. TerminalStation West. View looking toward Ninth Ave. From South side of 31st St. , 200 feet West of Ninth Ave. Jan. 28, 09. ]

[Illustration: PLATE XLIX, FIG. 3. --TW 88, P. T. & T. R. R. Co. N. R. Div. Terminal Station West. Center line of 32nd St. , looking East from Sta. 183+50, showing excavation under Ninth Avenue, permanent concrete piersunder Elevated Railway Columns and removal of temporary shoring girders"C". April 8, 09. ]

[Illustration: PLATE XLIX, FIG. 4. --TW 95, P. T. & T. R. R. Co. N. R. Div. Terminal Station West. View under Ninth Avenue looking Southward from 100feet South of center line, showing underpinning of Ninth Avenue structuretaken at sub-grade. May 25, 09. ]

It was made a practice all through the work to transfer the weight of thestructures very positively from one support to another by lifting thembodily by jacks, and putting in filler pieces before releasing the jacks, not trusting to wedging to transfer the loads. In fact, apart from theboxing-in of the surface railway concrete, no wedges whatever were used. This appears to have been a decided advantage, for, with the constantpounding of trains on the elevated railway and the jarring due to heavytrucks on the pavement blocks, it is very likely that wedging would havebecome loosened and displaced, whereas, with blocking, there was little orno tendency toward displacement due to vibration. Although the vibration ofthe structure, when a long length was supported on girders "C" resting onthe permanent viaduct girders on the sides of the avenue, appeared to beconsiderable, not only vertically but transversely, very carefulobservation showed that the sag in the girder "C" due a live load of threeelevated railway trains, one surface railway car, and one heavy truck, amounted to 1/8 in. The sideway vibration did not amount to more than 1/32in. On either side of the normal position. More vibration was caused byheavy trucks and wagons going over the stone pavement than by the elevatedrailway trains or surface cars. 

No blasting was done near the supports of the elevated railway structurewhile trains were passing over it, and occasionally trains were stoppedduring a heavy or uncertain blast. A watchman on the surface, day andnight, and at first one and later two flagmen on the elevated railwaystructure, were on duty at all times, reporting to the Interborough RapidTransit Company, by whom they were employed. Log mats and timber protectionfor the girders and the columns of the permanent viaduct were used, asshown by Figs. 1 and 4, Plate XLIX, during the excavation of the rock core, and timber was also used to protect the face of the completed portions ofthe concrete abutments. 

In excavating the sides of the avenue, the rock broke better on the eastthan on the west side, where large seams developed and some slidesoccurred. 

_Abutments. _--As shown on Fig. 7, the face of the north abutment has abatter of 2 in. To the foot, and the face of the south abutment has avariable batter, the base being on a grade and the bridge seat being level, and both maintaining a uniform distance from the center of the TerminalYard. The back walls of the abutments were not built until the steel hadbeen put in place. 

No attempt was made to water-proof these abutments, but, in the rear of thewall, open spaces were left, about 6 ft. From center to center, which wereconnected with drain pipes at the base of and extending through the wall, for the purpose of carrying off any water that might develop in the rock. These drains were formed by building wooden boxes with the side toward therock open and the joints in the boxes and against the rock plastered withmortar in advance of the wall. A hose was used to run water through thesedrains during the placing of the concrete, for the purpose of washing outany grout which might run into them. Each box was washed out at frequentintervals, and there was no clogging of the drains whatever. This methodof keeping the drains open was adopted and used successfully for the entirework. The abutments were built of concrete, and the mixture was 1 part ofcement, 3 parts of sand, and 6 parts of broken stone. 

The concrete was mixed in a No. 3 Ransome mixer, and was placed very wet. No facing mixture or facing diaphragms were used, but the stone was spadedaway from the face of the wall as the concrete was laid. Chutes were usedinside the form, if the concrete had to drop some distance. Work wascontinued day and night, without any intermission, from the time ofcommencement to the time of completion of each section. 

The face of the concrete wall was rubbed and finished in a manner similarto that used on the walls between Ninth and Tenth Avenues, as describedlater. 

Fig. 2, Plate LII, shows the east and central portions of the southabutment, completed and carrying the permanent viaduct, and the excavationcompleted for the west portion. 

WORK BETWEEN NINTH AND TENTH AVENUES. 

_General Description. _--The work involved the excavation of about 5. 4acres, between the west house line of Ninth Avenue and the east house lineof Tenth Avenue, to an average depth of about 50 ft. , the construction of astone masonry portal at Tenth Avenue leading to the River Tunnels, and theconstruction around the site of the concrete retaining and face walls. 

The following estimated quantities appear in the contract: Excavation ofrock in trenches, 3, 400 cu. Yd. ; excavation of rock in pit, 377, 000 cu. Yd. ; excavation of all materials except rock in trenches, 6, 500 cu. Yd. ;excavation of all materials except rock in pit, 34, 000 cu. Yd. ; concrete, 1:3:6, in retaining walls, 4, 580 cu. Yd. ; concrete, 1:3:6, in face walls, 7, 460 cu. Yd. ; concrete, 1:2:3, with 3/4-in. Stone, in face walls, 4, 100cu. Yd. ; stone masonry in portal, 247 cu. Yd. , etc. , etc. 

[Illustration: Fig. 7. (Full page image)

NINTH AVE. ABUTMENTS & KEY PLAN]

As previously stated, the contract price included the placing of allexcavated material on scows at Pier 62, North River. Prior to this contractthis pier had been used by the New York Contracting Company-PennsylvaniaTerminal, for the disposal of excavated material from east of NinthAvenue. In order to get the material to the pier, the contractor hadexcavated a cut under Ninth Avenue which came to the grade of 32d Streetabout midway between Ninth and Tenth Avenues, and a trestle was constructedfrom this point over Tenth Avenue and thence to the pier. Fig. 2, PlateXLVII, shows the east end of this cut, and Fig. 1, Plate L, shows thetrestle, looking east from Tenth Avenue. 

A 30-ton steam shovel was brought to the south side of the work, andcommenced operating on July 9th, 1906. After working there about a month, the earth had been practically stripped off the rock, and the shovel wasmoved over to the north side where it excavated both earth and rock untilAugust 10th, 1907. 

At three points south of 32d Street and at one point north of 32d Streetnear Tenth Avenue, cuts were made in the rock to sub-grade, and from thesecuts, together with the cuts on the west side of Ninth Avenue, all wideningout was done and the excavation was completed. Fig. 1, Plate L, shows theexcavation of the three cuts on the south side of 32d Street, the steamshovel operating on the north side of that street, and thematerial-disposal tracks and trestle. Fig. 3, Plate LII, shows the cutsjoined up and the excavation along the south side practically completed. 

On the north side of the work, between Stations 182 + 90 and 183 + 65, therock was low, and provision had to be made for maintaining the yards to thenorth of the site. Therefore a rubble-masonry retaining wall was built, with the face about 2 ft. North of the face of the proposed concrete wallwhich was to be put in later. On the same side of the work, betweenStations 188 + 24 and 188 + 46, the rock was exceedingly poor, and as asmall frame house on the adjoining lot was considered to be in an unsafecondition, a rubble masonry retaining wall was built. As the buildingadjoining the south side of the work at Tenth Avenue was on an earthfoundation, it was necessary to underpin it before the excavation could bedone. The building was supported on needles, and rubble masonry was put infrom the bottom of the old foundation to the rock. The foundation of 413West 31st Street, immediately west of the Express Building site, was ofvery poor masonry, and it was necessary to rebuild it prior to taking outthe adjoining excavation. 

[Illustration: PLATE L, FIG. 1. --TW 23, P. N. Y. & L. I. R. R. Terminal StationWest. View looking Eastward from Tenth Ave. , showing work between Ninth &Tenth Avenues. Dec. 26, 06. ]

[Illustration: PLATE L, FIG. 2. --TW 35, P. T. & T. R. R. Co. Terminal StationWest. View looking Northwest from Sta. 184, 120 feet South of center line. Dec. 31, 07. ]

[Illustration: PLATE L, FIG. 3. --TW 96, P. T. & T. R. R. Co. N. R. Div. Terminal Station West. View looking West from Ninth Avenue ElevatedRailway, showing condition of work. May 26, 09. ]

[Illustration: PLATE L, FIG. 4. --TW 104, P. N. Y. & L. I. R. R. Terminal StationWest. View from Tenth Avenue looking East, showing progress of concretewalls. Aug. 7, 09. ]

Along the north side, between Stations 186 + 50 and 187 + 50, the wallssupporting the adjoining back yards were of poor quality and had to berenewed by the contractor before excavation could be done. 

The excavated material was loaded by derricks on cars at the top of theexcavation, these cars being on tracks having a direct connection with thedisposal trestle, as shown by Fig. 1, Plate L. As soon as it could be done, derricks were placed at the bottom of the excavation; tracks were then laidout there, and the excavated material was loaded on cars at the bottom andhoisted by derricks to cars on the disposal trestle. A locomotive waslowered to the bottom of the excavation on August 25th, 1907, and a derrickstarted operating at the bottom on August 27th, 1907. The commencement ofthis work by derricks at the bottom is shown by Fig. 3, Plate LII. Ingeneral, the disposal tracks were maintained about on the center line of31st Street until the excavation had been carried as close to them aspossible, and on October 16th, 1907, they were shifted to the extreme northside of the work, as shown by Fig. 2, Plate L. A portion of the old trestlewas left in place near Tenth Avenue, a derrick was erected thereon, and thetracks were used for cars to receive the excavated material hoisted fromsub-grade. The disposal trestle was maintained in this position until suchtime as it would interfere with the excavation, and then the tracks wereabandoned. This was done on November 11th, 1908. Fig. 3, Plate L, shows thefinishing of the excavation on the north side of the work. On August 30th, 1908, a cut was made under Ninth Avenue at sub-grade, and cars could thenbe run from Seventh to Tenth Avenue at sub-grade. On October 24th, 1908, the connection with the disposal trestle east of Ninth Avenue wasabandoned, and all excavated material was hoisted from sub-grade at TenthAvenue by derricks. 

As previously stated, the contractor was required to make complete disposalof all excavated material after January 1st, 1909, but was allowed the useof the pier until January 20th, 1909, after which date the materials werehoisted by derricks at Tenth Avenue, loaded on 2-horse trucks, andtransported to the 30th Street pier, North River, where it was loaded onscows by two electric derricks. A considerable amount of the rockexcavation was broken up and used for back-fill. 

_Earth Excavation. _--Practically all the earth excavation, amounting toabout 57, 000 cu, yd. , was done with steam shovels. The average quantity ofearth excavated by a steam shovel per 10-hour shift was 180 cu. Yd. Thismaterial was loaded on side-dump cars and taken to the disposal pier whereit was dumped through chutes to the decks of scows. Inasmuch as thequantity of earth excavation was small, as compared with the rock, theearth was used principally for the first layer on the scows for padding, sothat small stones might be dumped through the chutes without injuring thedecks. 

_Rock Excavation. _--As previously stated, the rock broke better on thesouth than on the north side, where there were several slides, andconsiderable excavation had to be taken out beyond the neat line requiredin the specifications. The worst slide occurred at midnight on July 3d, 1909, at about Station 188 + 50. The last blast, to complete the excavationto sub-grade at this point, had been fired in the afternoon of the sameday, and the mucking was practically completed. Great care had been takenin excavating near this point, as it was evident that the rock was not of avery stable character, but, when the excavation had been completed, it wasthought that the rock remaining in place would stand. The volume ofmaterial brought down by this slide amounted to about 200 cu. Yd. The rockon the south side broke very well, and there were no slides of anyconsequence. 

The drill holes were laid out by the blaster, and the general method ofdrilling for different classes of work was as follows: In breaking down, the holes were started about 8 ft. Apart, on a slight batter, so that atthe bottom they would be considerably less than 8 ft. Apart. They weredrilled about 10 ft. Deep, and blasting logs were used, as it was necessaryto load quite heavily in order to lift the material and start the cut. After the cut had been made, side holes were shot to widen out sufficientlyto start another cut. 

After a side cut about 20 ft. Deep had been made, the side holes weredrilled 20 ft. Deep, and the holes were loaded and tamped for the full20-ft. Cut. Under the terms of the specifications, the contractor wasrequired to complete the excavation on the sides by drilling broachingholes. 

The maximum length of drill steel was about 20 ft. , and, where theexcavation plane of broaching was more than 20 ft. In depth, the contractorwas permitted to start the holes back of the broaching line, in order toallow for setting up the drills on the second lift. A distance of about 8in. Was usually allowed for setting up a drill. The broaching line waspainted on the surface of the rock in advance of the drilling, and thebatter of the drill was tested with a specially designed hand-level inwhich the bubble came to a central position when the face of the level wason the required batter. Holes were also drilled in front of this broachingline, and, when the excavation had been taken out to within about 6 ft. Infront of it, the holes immediately in front were loaded, and also aboutevery third one of the broaching holes, and, unless the rock was very bad, it usually broke sharply at the broaching line. Occasionally, the broachingholes which were not loaded were filled with sand, which gave rather betterresults than leaving them open. 

In the steam-shovel work on the east side of Ninth Avenue, spring holeswere used. They were formed by drilling a 20-ft. Hole and exploding at thebottom of it, without tamping, two or three sticks of dynamite, andrepeating this process with heavier charges until there had been formed atthe bottom of the hole a large cavity which would hold from 100 to 200 lb. Of dynamite. Face holes and breast holes were also drilled, and it waspossible by this method to drill and break up a cut 20 ft. Deep and 15 ft. Thick. The only place where spring holes were used on this work was on theeast side of Ninth Avenue where the heavy cutting was sometimes extendedbeyond the east house line. 

From the best records obtainable, the average progress in drilling wasabout 33 lin. Ft. Per 8-hour shift. The average number of cubic yards ofexcavation per drill shift was 13. 9, and the average amount of drilling percubic yard of excavation was 2. 4 ft. ; this covered more than 27, 000 drillshifts. 

The dynamite was practically all 60%, and the average excavation per poundof dynamite was 2. 2 cu. Yd. The contractor employed an inspector ofbatteries and fuses, who, using an instrument for that purpose, tested thewiring of each blast prior to firing, in order to discover any shortcircuits, and thus prevent the danger of leaving unexploded dynamite in theholes. 

The average quantity of excavation per derrick shift of 10 hours, covering7, 400 shifts, 87% of the excavation being rock, was 50 cu. Yd. , and theaverage force per shift, including only foreman and laborers, was 13 men. It was found that a derrick operating at the top of a 20-ft. Cut wouldhandle about 40 cu. Yd. Per shift, whereas, if operating at the bottom ofthe cut, it would handle about 60 cu. Yd. Per shift. The elevator derricksat Tenth Avenue were very efficient, and each could take care of thematerial from four derricks at the bottom, hoisting 250 cu. Yd. Per shift aheight of 60 ft. 

_Concrete Retaining and Face Walls. _--It was essential to have the greatestspace possible at the bottom of the excavation, and, inasmuch as the yardwas to be left open, it was necessary to provide some facing for the rockon the sides in order to prevent disintegration, due to exposure, and givea finished appearance to the work. Above the rock surface a retaining wallof gravity section was designed, the top being slightly higher than theyards of the adjoining properties. The face wall was designed to be as thinas possible, in order to allow the maximum space for tracks. 

The excavation, therefore, was laid out so that the back of the retainingwall would not encroach on the adjoining property, but would practicallycoincide with the property line at positions of maximum depth. 

The batter on the face of the wall was 2 in. Per ft. , and a bridge seat3-1/2 ft. Wide was formed at an elevation of 22 ft. , minimum clearance, above the top of the rail. This bridge seat was made level. The maximumheight of the south wall is 49 ft. , and of the north wall 65 ft. 

The face walls were classed as "Upper Face Walls, " extending from the baseof the retaining wall to the bridge seat, and as "Lower Face Walls, "extending from the bridge seat to the base of the wall. The general designis shown on Fig. 8. 

In considering the design of the face wall it was felt that, the wall beingso thin, ample provision should be made to prevent any accumulation ofwater and consequent pressure back of the wall; therefore, no attempt wasmade to water-proof it, but provision was made to carry off any water whichmight appear in the rock. Box drains, 2 ft. Wide and 6 ft. From center tocenter, were placed against the rock, so that, there being but 4 ft. Between the drains, and the wall having a minimum thickness of 2 ft. , anywater in the rock would not have to go more than 2 ft. To reach a drain, and would probably pass along the face of the rock to a drain rather thanthrough 2 ft. Of concrete. These drains were connected with pipes leadingthrough the wall at its base. 

[Illustration: FIG. 8. (Full page image)

RETAINING AND FACE WALLS NORTH SIDE]

These box drains occurred so frequently, and decreased the section of thewall so materially, that it was thought desirable to tie the wall to therock. This was done by drilling into the rock holes from 6 to 15 ft. Indepth, and grouting into each hole a 1-1/2-in. Rod having a split end and asteel wedge. The outer end of each rod was fitted with a 12 by 12 by1/2-in. Plate and a nut, and extended into the wall, thus tying theconcrete securely to the rock. The drains being 6 ft. From center tocenter, the tie-rods were placed midway between them, and 6 ft. , fromcenter to center, vertically and horizontally. Fig. 8 shows the arrangementof these rods and drains. Around the Express Building site, just west ofNinth Avenue, on the south side of the work, the bridge seat was omitted, and the face wall was designed 2 ft. Thick from top to bottom. The batteron the 31st Street wall was made variable, the top and bottom beingconstant distances from the center line and on different grades. 

The retaining walls were water-proofed with three layers of felt andcoal-tar pitch, which was protected by 4 in. Of brick masonry. A 6-in. Vitrified drain pipe was laid along the back of the wall, with the jointsopen on the lower half, and this was covered with 1 ft. Of broken stone andsand before any back-fill was placed on it. 

The arrangement of the drains was as follows: The 6-in. Drain back of theretaining wall was connected with one of the box drains in the rear of theface wall by a cast-iron pipe or wooden box every 24 ft. , and this ranthrough the base of the retaining wall. Midway between these pipes, aconnection was made at the bridge seat between the drain in the rear of theface wall and the gutter formed at the rear of the bridge seat to carry offrain-water coming down the face of the wall above. All the box drains, except those connected with the drains back of the retaining wall, weresealed at the elevation of the base of the retaining wall, as notedpreviously. 

The specifications required vitrified pipe to be laid through the retainingwall, but, owing to the difficulty of holding the short lengths of pipe inplace during the laying of wet concrete, they were dispensed with, andeither iron pipes or wooden boxes were used. 

_Tie-Rods. _--When the excavation on the sides had been completed, movabledrilling platforms were erected, as shown by Fig. 4, Plate L. The holeswere drilled on a pitch of 2 in. Per ft. With the horizontal. The depths ofthe holes were decided by the engineer, and were on the basis of a minimumdepth of 5 ft. In perfect rock; the character of the rock, therefore, andthe presence of seams, determined the depths of the holes. Each hole waspartly filled with grout, and the rod, with the steel wedge in the splitend, was inserted and driven with a sledge so that the wedge, striking thebottom of the hole first, would cause the split end of the rod to open. Each hole was then entirely filled with neat cement grout. 

_Box Drains. _--Various methods of forming the box drains were considered, such as using half-tile drains, or a metal form, or a collapsible formwhich could be withdrawn, but it was finally decided to build boxes inwhich the side toward the rock was open and the joints in the boxes andagainst the rock were plastered with cement mortar. These boxes were leftin place. Fig. 1, Plate LI, shows the tie-rods and box drains in place, andholes being cut near the bottom of the drains for the pipes leading throughthe wall. 

_Forms. _--Fig. 1, Plate LI, shows the form used on the south side of thework. The materials were of good quality, and the form, which was about 50ft. Long, was used to build twelve sections, or about 600 ft. Of wall. Theform was tied in at the top and bottom by cables attached to rods drilledinto the rock, and it was thought that, with the trusses to stiffen themiddle section of the form, it would not be necessary to use raker bracesagainst it. This would have been desirable, as the placing of the rakerbraces took considerable time. It was found, however, that the form was notsufficiently rigid, as it bulged at the middle section and could not beheld by the trusses. Two or three sets of raker braces, about 12 ft. Apart, were used, and in addition, rods with turnbuckles were placed through theform and fastened to the tie-rods, and thus the form was held in placesuccessfully. On the forms built later, the trusses were omitted, and rakerbraces, about every 6 ft. , were used. The rods which screwed into theturnbuckles were removed before the form was moved. The photograph, Fig. 4, Plate LII, was taken inside the concrete form for the lower face wall onthe north side, and shows the drains leading through the wall, theturnbuckles attached to the tie-rods, the cables attached to rods in therock, and the braces to keep the form from coming in; these braces, ofcourse, were removed as the concrete came up. The form was built low andwedged up into position. After a section of concrete had set sufficiently, the wedges were knocked out, the form was lowered and moved from the wall, and was then moved along the lowest waling piece by block and tackle to itsnew position. 

Fig. 4, Plate L, shows the forms used on the north side of the work. 

A section, 1 ft. Square, at the top of the bridge seat of the lower facewall, was left out, so that the bottom of the form for the upper face wallcould be braced against it. The top of this form was tied by cablesattached to rods in the rock and by rods with turnbuckles running from backto front of the form; braces were also put in from the back of theretaining wall form to the walls of buildings along the property lines, when this could be done. The middle section of the form was held by rodswith turnbuckles which passed through the form and were fastened to each ofthe tie-rods drilled into the rock, as was also done in the case of thelower face wall. It was generally possible to hold the form to trueposition in this manner, but occasionally it had a tendency to bulge; whenthis occurred, the rods leading through the form and fastened to thetie-rods were tightened up, the placing of the concrete was slowed up, andno serious bulging occurred. 

Bulkheads at the ends of the sections were built of rough planking securelybraced to the rock, except that a planed board was laid up against the faceof the form to make a straight joint. At the end of each section a V wasformed, as shown by Fig. 1, Plate LI. At all corners, a "return, " orportion of the wall running at right angles, was built, and no section ofwall was stopped at a corner. 

_Filling Forms of Lower Face Walls. _--A temporary trestle was erected abovethe elevation of the bridge seat, and a track, leading from the mixer tothe form to be filled, was laid on it. At the commencement of each sectiona layer of mortar (1 part of cement to 2-1/2 parts of sand) was depositedon the bottom. A 1:3:6 mixture of concrete was used; it was run from themixer into dump-cars and deposited in the form through chutes, three ofwhich were provided for each 50-ft. Section, the average length. Theconcrete was mixed wet, and was not rammed; the stone was spaded back fromthe face, and no facing mixture or facing diaphragms were used. Work oneach section was continued day and night without any intermission from thetime of commencement to the time of completion. At frequent intervals thebox drains were washed out thoroughly with a hose, in order to prevent themfrom clogging up with grout. 

[Illustration: PLATE LI, FIG. 1. --TW 66, P. N. Y. & L. I. R. R. Terminal StationWest. Box drains and tie rods, South side, Sta. 184+80 to 185+14. Sept. 17, 08. ]

[Illustration: PLATE LI, FIG. 2. ]

[Illustration: PLATE LI, FIG. 3. --P 46. P. R. R. Tunnels, N. R. Div. Sect. Gy. West. Disposal trestle just before demolition. View of South side showingchutes. Jan. 21, 09. ]

[Illustration: PLATE LI, FIG. 4. --A 54. P. R. R. Tunnels, N. R. Div. Sect. Gy. West & Oj. View across North River on line of Tunnels, looking from NewYork to New Jersey. Feb. 9, 07. ]

In the first few sections of wall, the form was filled to within 1 in. Ofthe top of the bridge seat and allowed to set for about 2 hours; it wasthen finished to the proper elevation with a plaster of 1 part of cement to1 part of sand. This did not prove satisfactory, as there were indicationsof checking and cracking, and, later, the form was filled to the requiredelevation and the surface floated. The form was allowed to remain in placefor from 18 to 24 hours, depending on the weather. In most cases, immediately after the form had been moved, a scaffold was erected againstthe face of the wall, and the face was wet and thoroughly rubbed, firstwith a wooden float and then with a cement brick, until the surface wassmooth and uniform. 

The section 1 ft. Square at the top of the bridge seat, which was left outin order to brace the bottom of the form for the upper face wall, wasfilled in after the walls had been completed. The old concrete was verythoroughly cleaned before the new concrete was placed on it, and a gutterwas formed at the rear connecting with the box drains back of the wall tocarry off rain-water coming down the face of the upper walls. 

In hot weather the walls were thoroughly wetted down several times a dayfor several days after the form had been removed. 

_Upper Face and Retaining Wall. _--In cases where the top of the retainingwall was at a higher elevation than the mixer, it was necessary to raisethe concrete in a bucket with a derrick, and dump it into cars on thetrestle above the top of the coping. Concrete was deposited through chutes, as in the lower face wall, continuously from the bottom of the face wall tothe top of the retaining wall. At the commencement of each section of theretaining wall a layer of mortar was put on the rock. A 1:2:3 mixture ofconcrete was used in the face wall, and a 1:3:6 mixture in the retainingwall. 

As the face walls were so thin, the number of batches of concrete per hourwas reduced, for the form filled so rapidly that the concrete, before itset, exerted an excessive pressure against the form, and this tended tomake it bulge. The proper rate at which to place the concrete behind a form50 ft. Long, with a wall 2 ft. Thick, was found to be about fifteen 1/2-yd. Batches per hour. 

_Cracks in Walls and Longitudinal Reinforcement. _--Before the concretewalls were started, the contractor suggested using forms 100 ft. Long andbuilding the walls in sections of that length; it was decided, however, tolimit the length to 50 ft. 

The south walls, in sections approximately 50 ft. Long, were built first, starting at Tenth Avenue and extending for about 500 ft. Soon after theforms were removed, irregular cracks appeared in the walls between thejoints in practically every section. It was thought that these cracks mightbe due to the wall being very thin and being held at the back by thetie-rods; there was also quite a material change in the section of the wallat each drainage box. Although it was admitted that these cracks would haveno effect on the stability of the wall, it was thought that, for appearancesake, it would be desirable to prevent or control them, if possible. Thefirst method suggested was to shorten the sections to 25 ft. , which wouldgive an expansion and contraction joint every 25 ft. , it being thought thatsections of this length would not crack between the joints. This, however, was not considered desirable. An effort was then made to prevent cracks ina section of wall, about 46 ft. Long, on the south side, by usinglongitudinal reinforcement. In the lower and upper face walls, 3/4-in. Square twisted steel rods were placed longitudinally about 4 in. In fromthe face and about 1 ft. 4 in. Apart vertically. The sections of thesewalls were finished on April 10th, and May 5th, 1909, respectively. Atpresent there are no indications of cracks in these sections, and they arepractically the only ones in the south walls which do not show irregularcracks. 

It was decided, however, that, inasmuch as the cracks did not affect thestability of the walls, the increased cost of thus reinforcing theremaining walls was not warranted. An effort to control the cracks was madeby placing corrugated-iron diaphragms in the form, dividing each 50-ft. Section into three parts. The diaphragms were 1 ft. Wide, and were placedwith the outer edge 1 in. In from the face of the wall, but in the copingsthey were omitted. The purpose of these diaphragms was to provide weaksections in the walls, so that if there was any tendency to crack it wouldoccur along the line of the diaphragms. Corrugated iron was used for thediaphragms instead of sheet iron as it was more easily maintained in avertical position. The general arrangement of the diaphragms is shown onFig. 4, Plate LII. The results obtained by using diaphragms have been quitesatisfactory, and cracks approximately straight and vertical have usuallyappeared opposite the diaphragms soon after the forms were removed. Diaphragms were used on all the remaining walls, with the exception ofthose between Stations 187 + 07 and 188 + 83 on the north side, where therock was of poor character and bad slides had occurred. Between thesepoints, in order to strengthen the wall, twisted steel rods, 1 in. Square, were placed longitudinally, 6 in. In from the face of the wall and 2 ft. Apart vertically, between Elevations 295 and 335. 

[Illustration: PLATE LII, FIG. 1. --GIRDERS UNDER 9TH AVENUE ELEVATEDRAILROAD. ]

[Illustration: PLATE LII, FIG. 2. --TW 100. P. T. & T. R. R. Co. TerminalStation West. Showing excavation of completion of South abutment 9th Ave. And method of Supporting Elevated Railway Column 488. July 21, 09. ]

[Illustration: PLATE LII, FIG. 3. --TW 31. P. T. & T. R. R. Co. TerminalStation West. View showing excavation 9th and 10th Avenues South of 32ndSt. Looking West from Sta. 184. Aug. 17, 07. ]

[Illustration: PLATE LII, FIG. 4. --TW 101. P. T. & T. R. R. Co. TerminalStation West. Inside of concrete form for lower-face wall, showing drains, tie rods, diaphragms and methods employed for tying in the form in additionto braces outside. July 21, 09. ]

_Tenth Avenue Portal. _--The design of the Tenth Avenue Portal is shown onFig. 9. The stone selected came from the Millstone Granite Company'sQuarries, Millstone Point, Conn. , and is a close-grained granite. Fig. 2, Plate LI, shows the completed portal. 

Practically all the stone cutting was done at the quarry, but certainstones in each course were sent long and were cut on the ground, in orderto make proper closures. Drains were left behind the portal around the backof each arch, leading down to the bottom, and through the concrete base ateach side of the portal and in the central core-wall; all these drains havebeen discharging water. 

_Power-House. _--The old church at No. 236 West 34th Street, between Seventhand Eighth Avenues, was turned over to the New York ContractingCompany-Pennsylvania Terminal for a power-house to supply compressed airfor use on the Terminal Station work between Seventh and Ninth Avenues andthe work below sub-grade as well as that on the Terminal Station-West. Fourstraight-line compressors and one cross-compound Corliss compressor wereinstalled, the steam being supplied by three Stirling boilers. Threeelectrically-driven air compressors, using current at 6, 600 volts, werealso installed, and the total capacity of the power-house was about 19, 000cu. Ft. Of free air per minute compressed to 90 lb. Per sq. In. 

_Disposal Pier. _--The disposal pier (old No. 62 and new No. 72), at thefoot of West 32d Street, North River, was leased by the PennsylvaniaRailroad Company. The entire pier, with the exception of the piles, wastaken down, and the piles which would be in the path of the proposed tunnelwere withdrawn prior to the building of the tunnels and the construction ofthe pier for disposal purposes. Subsequent to the driving of the tunnelsthere was a considerable settlement in the pier, especially noticeable atthe telphers, and finally these had to be abandoned on this account. Fig. 3, Plate LI, shows the chutes through which the earth was dumped on thedecks of the scows to form a padding on which to dump the heavier rock. Fig. 4, Plate LI, shows the derricks at the end of the pier. These wereused, not only for loading heavy stones and skips, but also with aclam-shell bucket for bringing in broken stone and sand for use in thework. Large quantities of pipe, conduits, brick, etc. , were also brought tothis pier for use on the work. 

[Illustration: FIG. 9. (Full page image)

PORTAL, RETAINING AND FACE WALLS, TENTH AVENUE]

ORGANIZATION OF ENGINEERING FORCE IN FIELD. 

The design and execution of the work were under the direction of Charles M. Jacobs, M. Am. Soc. C. E. , Chief Engineer, and James Forgie, M. Am. Soc. C. E. , Chief Assistant Engineer. The writer acted as Resident Engineer. 

[Illustration: Fig. 10. ]

The general organization of the engineering force in the field is shown bythe diagram, Fig. 10. 

The position of Assistant Engineer, in responsible charge of Constructionand Records, has been filled in turn by Messrs. A. W. Gill, N. C. McNeil, Jun. Am. Soc. C. E. , and W. S. Greene, Assoc. M. Am. Soc. C. E. 

Messrs. A. P. Combes and T. B. Brogan have acted as Chief Inspector and NightInspector, respectively, in charge of outside work during the entirecarrying out of the contract. 

Base lines had been established on Ninth and Tenth Avenues for the Terminalwork east of Ninth Avenue and for the Tunnel work west of Tenth Avenue, and these lines, together with bench-marks similarly established, were usedin laying out the Terminal Station-West work. 

Prior to the commencement of the work, elevations were taken on the surfaceat 10-ft. Intervals, and elevations of the rock surface were taken on thesepoints as the rock was uncovered. Cross-sections were made and used incomputing the progress and final estimates. 

Very careful records were kept of labor, materials, derrick performances, steam-shovel performances, quantity of dynamite used, etc. , and, inaddition, a diary was kept giving a description of the work and materialsused each day; various tables and diagrams were also prepared. 

A daily report was sent to the Chief Office showing the quantities ofexcavation removed and concrete built, the force in the field, the plant atwork, etc. , during the previous day. At the end of each month a descriptionof the work done during that month, with quantities, force of men employed, percentages of work done, etc. , was sent to the Chief Office. Two diagrams, showing cross-sections and contours of the excavation done and the progressof the concrete walls, were also sent. 

COST ACCOUNT. 

From the records of labor and material obtained in the field, and fromestimated charges for administration and power, an estimate was made of thecost to the contractor for doing various classes of work. It was necessaryto estimate the administration and power charges, as the contractor'sorganization and power-house were also controlling and supplying power tothe Terminal Station work east of Ninth Avenue and also the work belowsub-grade. The labor and material charges in the field were placed directlyagainst the class of work on which they were used and the administrationand general charges (which included superintendence, lighting, etc. ) wereapportioned to the various classes of work in proportion to the value ofthe labor done. 

STATISTICS. 

The total weight of the structural steel used during the underpinning ofNinth Avenue was 1, 475, 000 lb. 

The total weight supported during the work under Ninth Avenue was about5, 000 tons. 

\U$1\EThe average daily traffic over the Ninth Avenue Elevated Railway was90, 000 passengers, and, during the progress of the excavation andunderpinning, about 100, 000, 000 passengers were carried over thatstructure. 

The total excavation was 521, 000 cu. Yd. , of which 87% was solid rock. 

The average drill performance was about 33 lin. Ft. Per 8-hour shift. 

The average number of cubic yards of excavation per drill shift was 13. 9. 

The average number of feet of drilling per cubic yard of excavation wasabout 2. 4. 

The average excavation per pound of dynamite was 2. 2 cu. Yd. 

The average amount of excavation per derrick shift of ten hours, 87% of theexcavation being rock, was 50 cu. Yd. 

The average derrick force per shift, including only foreman and laborers, was 13 men. 

The salaries of the engineering staff in the field and the expenses ofequipping and maintaining the field office amounted to 2. 8% of the cost ofthe work executed, 2. 7% being for engineering salaries alone. 

FOOTNOTES:

[Footnote A: Presented at the meeting of April 6th, 1910. ]