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AMERICAN SOCIETY OF CIVIL ENGINEERS

INSTITUTED 1852


TRANSACTIONS

Paper No. 1156


THE NEW YORK TUNNEL EXTENSION OF THE
PENNSYLVANIA 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 Terminal
Station-West is bounded as follows: By the east line of Ninth Avenue; by
the south side of 31st Street to a point about 200 ft. west of Ninth
Avenue; by a line running parallel to Ninth Avenue and about 200 ft.
therefrom, from the south side of 31st Street to the boundary line between
the 31st and 32d Street properties; by this line to the east line of Tenth
Avenue; by the east line of Tenth Avenue to the boundary line between the
32d and 33d Street properties; by this line to the east line of Ninth
Avenue. The area is approximately 6.3 acres.

_House-Wrecking._--The property between Ninth and Tenth Avenues was covered
with buildings, 94 in number, used as dwelling and apartment houses and
church properties, and it was necessary to remove these before starting the
construction. Most of the property was bought outright by the Railroad
Company, but in some cases condemnation proceedings had to be instituted in
order to acquire possession. In the case of the property of the Church of
St. Michael, fronting on Ninth Avenue, 31st and 32d Streets, the Railroad
Company 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, and
school, to the satisfaction of the Church of St. Michael, to hand over
these buildings in a completed condition, and to pay the cost of moving
from the old to the new buildings, before the old properties would be
turned over to the Railroad Company.

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

The bricks were cleaned and sold directly from the site, as were
practically all the fixtures in the buildings. The stone fronts were broken
up 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 and
smaller timber was sold for firewood, but most of it was given away or
burned on the premises.

_Contracts and Agreements._--The main contract, awarded to the New York
Contracting Company-Pennsylvania Terminal on April 28th, 1906, included
about 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., of
framed 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 for
the various classes of work in each of these divisions. The prices quoted
for excavation included placing the material on scows supplied by the
Railroad Company at the pier at the foot of West 32d Street, on the North
River; there was a clause in the contract, however, by which the contractor
could be required to make complete disposal of all excavated material at an
additional 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 easterly
portion of the Terminal, the New York Contracting Company-Pennsylvania
Terminal had excavated under Ninth Avenue a cut which came to the grade of
32d Street about midway between Ninth and Tenth Avenues, and a trestle was
constructed from this point over Tenth Avenue and thence to the disposal
pier at the foot of West 32d Street.

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

_Geology._--The rock encountered may be classed as "gneiss"; its character
varied from granite to mica schist. It was made up of quartz, feldspar, and
mica, and there were also some isolated specimens of pyrites, hornblend,
tourmaline, and serpentine. On the south side of the work, just west of
Ninth Avenue, there were excellent examples of "contortions" of veins of
quartz in the darker rock. On the east side of Ninth Avenue, near the north
end of the work, glacial marks were found on the rock surface. The general
direction of the stratification was north 5° west, and the general incline
about 60° with the horizontal. As a rule, the rock broke sharply along the
line of stratification. On the south side it broke better than on the north
side, where it was usually softer and more likely to slide; and this,
together with the fact that in winter it was subject to alternate freezing
and thawing and in summer to the direct rays of the sun, made it rather
difficult 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., and
the construction over this area of a steel viaduct, the deck of which was
about 24 ft. below the surface, for the ultimate support of the Ninth
Avenue structures.

The following estimated quantities appear in the contract: Excavation of
rock, 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, 504,000
ft., B.M.; structural steel, 1,320,000 lb., etc.

While this excavation was being done it was necessary to support and
maintain the three-track elevated railway structure of the Interborough
Rapid 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 City
Railway Company, and various pipes, sewers, and conduits, and to maintain
all surface vehicular and pedestrian traffic. All structures were left in
place with the exception of the pipes, most of which were temporarily cut
out. The 48-in. brick sewer in the center of Ninth Avenue was broken, and
the sewage was pumped across the excavation through a smaller pipe.

The general method adopted was as follows: The east and west sides of the
avenue were closed, vehicular traffic was turned into the center, and a
trestle for pedestrians was constructed west of the westerly elevated
railway columns. All structures were then supported on transverse girders,
running across the avenue, below the surface, and these rested on concrete
piers on the central rock core. The sides of the avenue were then excavated
to sub-grade, and the permanent steel viaduct was erected on both sides of
the avenue as close as possible to the central rock core. The weight of all
structures was then transferred to the permanent steel viaduct, erected on
the sides of the avenue, by timber bents under the transverse girders
resting on the permanent steel viaduct, and all weight was thus taken off
the central rock core. This core was then excavated to sub-grade, the
permanent viaduct was completed, and all structures were placed on its
deck, using concrete piers and timber bents.

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

_Elevated Railway Structure of the Interborough Rapid Transit
Company._--The Ninth Avenue Elevated Railway was built between 1877 and
1880 as a two-track structure, the design being such as to permit a third
or central track to be added later, and this was built in 1894. It is
supported on columns under the outside tracks, about 43 ft. from center to
center 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 points
of bearing near the extremities at the top; each of the outside tracks is
supported on two longitudinal latticed girders and the central track on
two plate girders; between the columns, transverse girders are spliced to
the outside track cross-frames, and carry the central track system. It was
not thought desirable to put brackets on the columns near the street level
to support the structure temporarily, and, as there is an expansion joint
at each column, and as the transverse girders carrying the central track
system are not rigidly attached to the longitudinal girders carrying the
outside tracks, the central track could not be supported by supporting the
outside tracks; therefore, independent supports for each track, in the form
of 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 side
are wide in order to allow a 24-in. water main to pass directly beneath the
columns. The foundations are usually on rock.

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

[Illustration: PLATE XLVII, FIG. 2.--TW 17, P.N.Y. & L.I.R.R. Terminal
Station West. View of East side of 9th Ave. looking North from a point 100
feet 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. Terminal
Station 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. Terminal
Station 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 street
surface prior to the commencement of the work.

The east track is used for north-bound local trains, the west track for
south-bound local trains, and the central track for south-bound express
trains between 7 and 9.30 A.M. and for north-bound express trains between
2.30 and 7 P.M. It is said that an average of 90,000 passengers are carried
over this structure every 24 hours.

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

_Forty-eight-Inch Brick Sewer._--This sewer was in the center of Ninth
Avenue, with the invert about 12 ft. below the surface, and manholes about
100 ft. apart, and had to be abandoned in this position to allow the
transverse girders to be put in place to carry all structures while the
excavation was being done.

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

_Street Surface._--It was the original intention to close and excavate the
east side of the avenue and to erect there a street-traffic trestle before
closing the west side, but, at the contractor's request, both sides were
closed, and all vehicular traffic was turned into the center. A light
trestle 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 of
these were cut out temporarily, at the contractor's request, to be replaced
subsequently.

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

The overhead girders, known as girders "B", were therefore designed as
shown on Fig. 1, and put in place as shown on Figs. 2 and 3. The outside
tracks were blocked directly on these girders, and the central track was
supported by blocking up the transverse girders on I-beams placed between
the girders "B"; and no blocking was placed between the girders "B" and the
longitudinal girders carrying the central track. The weight on each column
was 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. per
lin. ft. of single track, with the weight of a car at 39,000 lb., was
assumed. Several feet of earth, between the structure and the rock, were
mined out, and the structure was supported on I-beams and posts, and
ultimately on the transverse girders by using timber bents under the
I-beams, as shown on Fig. 3.

_Water Mains and Sewer._--Cradles were designed for the support of the
48-in. and 24-in. water mains, resting on the transverse girders, and the
48-in. cast-iron sewer on the east side of the avenue was carried on
I-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, referred
to above, were known as girders "C," and they were put in place at first
resting on concrete piers on the central core; the weight of all structures
was placed on them while the sides of the avenue were being excavated, and
the sides of the viaduct were being built. The ends of these girders were
then picked up on the sides of the viaduct, and, spanning the central rock
core, carried all structures while the core was being excavated and the
viaduct completed. New foundations were then placed on the deck of the
viaduct 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 viaduct
are shown on Fig. 2. They were of long-leaf yellow pine. These girders were
located so that a cradle could be laid on them east of the elevated railway
structure to carry a proposed 48-in. cast-iron water main.

_Girders "B."_--Eighteen of these girders were required, each weighing
about 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 railway
structure, pipes, etc., supported during the work, amounted to about 5,000
tons.

_Details of the Work._--The method in general is shown on Figs. 4 and 5. At
first the east side of the avenue was closed and excavated down to rock,
the earth was mined out under alternate yokes of the surface railway
structure, and temporary posts were placed under the yokes to support the
structure while the remainder of the earth was being removed. Then
needle-beams and posts were placed under each yoke. The concrete forming
the track structure was then enclosed with planking to prevent it from
cracking and falling. I-beams were then placed under the needle-beams
carrying the structures, and these were carried on posts; they were changed
alternately until the excavation had been taken out to a depth of about 16
ft. below the surface. In placing these I-beams, heavier blocking was used
in the center of the span than at the ends where the bents would come, to
prevent the subsidence of the track owing to the sag in the I-beams. As
much excavation, to a depth of about 20 ft., was taken out adjoining the
elevated railway foundations as could be done with safety. Fig. 2, Plate
XLVII, 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 by
Fig. 3, Plate XLVII, were placed parallel to the elevated railway, with
blocking between them and the girders "B." Double bents, independent
of each other, were placed under the ends of these temporary shoring
girders, and these were braced securely to prevent possible dislodgment
during the removal of the rock. The weight of the structure was then taken
by jacking up the girders near the bents until the column was lifted off
the old foundation; blocking was put in between the girders and the bents
during the jacking, so that when the jacks were released the base of the
column was still clear of the old foundation. One 80-ton jack was used for
this 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 STAGES
OF 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 Posts
placed under Surface Railway Tracks. Girders _B_ and Temporary Shoring
Girders _C_ for supporting Elevated Ry. in place.

No. 3

I's in place under Surface Ry. Tracks. Elevated Ry. carried on Temporary
Shoring Girders, and Girders _C_ in place. 24" Water Main carried on Timber
Cradle 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 Girders
removed and Permanent Bents resting on Girders _C_ in place. Bents in place
on Girders _C_ carrying Surface Railway. East and West sides of Avenue
excavated down to Sub-Grade and Five rows of Permanent Steel in place on
each side. Bents erected on Permanent Steel to catch ends of Girders _C_
while 2 outside Concrete Piers are removed and 6th row of Permanent Steel
on 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 Permanent
Steel. 48" C.l. Sewer carried on Brackets on Girders _C_.

No. 6

Excavation Completed. ]

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

The columns being thus supported on temporary shoring girders, the old
foundations were removed and the excavation was taken down to a level about
16 ft. below the surface.

Two sets of three of the girders "C" were then put in place under the
avenue 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 the
outside pier would be 18 ft. from the center of the avenue and 32 ft. from
the house line. This is shown on Fig. 5 and on Fig. 3, Plate XLVII. Four
small piers were used, as they could be more easily removed than one
continuous pier. The girders "C" were set to line and grade, and the piers
were built under them, great care being taken to get the concrete well
under the girders so as to give a firm bearing.

After these girders "C" were in place it was necessary to remove the
temporary shoring girders before the bents could be erected on girders "C"
to support girders "B," being in the same plane; and provision had to be
made to support the structure while this was being done. Therefore, double
bents 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 sills
resting on the girders "C," and blocking was put in between the sills and
the rock to carry the full weight of the structure. Later, when the weight
of the structure was carried on the permanent bents, this blocking was
knocked out, but the bents were left in to carry the weight of the column
itself, which was swinging more or less from the structure above. The
weight of the structure was placed on these bents directly beneath the
columns by jacking up the temporary girders again, putting blocking between
the bents and the base of the columns, and taking out the blocking which
had been put in previously under the temporary shoring girders. The 24-in.
water main was carried over the excavation on cables from the temporary
shoring girders, except when they were being jacked up, at which time posts
were placed beneath it.

Anchor-bolts were put in place between the column bases and the bents
directly beneath, in order to increase the lateral stiffness, and raker
braces were also used. This having been done, the temporary shoring girders
were moved south to the next column, where the process was repeated. The
timber bents, shown in detail by Fig. 2, were then put in place as shown by
Figs. 4 and 5, and by Fig. 3, Plate XLVII. These bents were framed as
tightly as possible, using generally a 20-ton jack, and they were erected
simultaneously at each pair of columns. The weight was taken on these
columns by jacking up directly beneath the column base and taking out the
blocking between this base and the bent directly beneath the column. On
releasing the jack the weight was transferred to the permanent timber
bents, and the east and west columns of each pair were transferred on the
same day. One 80-ton jack was used on the easterly columns and two were
necessary on the westerly columns, one on each side of the 24-in. water
main. The raker braces of these permanent bents were not framed as tightly
as the main posts, in order that the main post should carry the entire
weight and the raker braces merely steady the structure.

Timber bents were erected on girders "C" to carry the I-beams under the
surface railway structure, as shown on Fig. 3, and all temporary posts
under these I-beams were removed. The bents were framed with a jack, as
tightly 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 of
the avenue, it will be seen that all structures were thus carried on
girders "C."

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

A very careful record of levels, taken on the elevated railway columns, was
kept, observations being made during each jacking up and at least twice a
week during the progress of the work. The columns were usually kept about
1/2 in. high so as to allow for compression in the timber bents.

As a rule, no jacking of the elevated railway structure was done while
trains were passing over, and trains were flagged during the operation.
There was generally very little delay, as all jacking was done between
10.30 A.M. and 2.30 P.M., when the traffic was lightest, and frequently the
jacking was done between trains, causing no delay whatever. Steel clamps
were placed, three on the top and three on the bottom of each set of the
girders "C," to bind them together and cause them to act as a unit.

All structures then being supported on girders "C," which were carried on
four concrete piers resting on the central rock core, the excavation on the
sides of the avenue was continued down to sub-grade and the east and west
portions of the concrete north abutment were constructed. The central rock
core was about 36 ft. wide on the top and 45 ft. wide on the bottom, and at
the center of 32d Street it was about 42 ft. high.

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

[Illustration: PLATE XLVIII, FIG. 1.--TW 33, P.T. & T.R.R. Co. Terminal
Station West. East side of 9th Ave. looking North from 31st St., showing
rock excavation and supports of 9th Ave. structures. Dec. 28, 07.]

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

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

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

Fig. 4, Plate XLVII, and Fig. 1, Plate XLVIII, show the structures
supported on the central rock core and the excavation on the east side to
permit of the erection of the permanent viaduct girders. Fig. 1, Plate
XLVIII, shows also the easterly portion of the concrete north abutment.
Fig. 2, Plate XLVIII, shows five rows of the permanent viaduct girders
erected on the east side of the work.

The excavation of the sides of the avenue having been completed, and six
rows of permanent viaduct girders erected on both sides, timber bents, as
shown on Figs. 2, 4, 5, and 6, were erected on this steel to support the
ends of the girders "C" and carry the structure while the rock core was
being excavated. Fig. 3, Plate XLVIII, shows the method of taking the
weight on these bents. Four 80-ton jacks were used, and oak blocks were
placed on the top of each jack to transmit pressure to a temporary oak cap
under the girders "C" independent of the bents; all four of these jacks
were operated simultaneously, and the girders "C" were lifted off the bents
and clear of the concrete piers. Oak filling pieces were then inserted
between the bents and the girders "C," so that when the jacks were released
the girders "C" were clear of the concrete piers. Fig. 3, Plate XLVIII,
shows that the girders have been lifted off the piers. Elevations were
taken on each set of girders during each operation, and careful
observations were made on the elevated railway columns. Where the rock was
very close to these bents, the open space between the posts was filled with
blocking so that there would be less danger of the bent shifting if struck
by blasted materials. Fig. 3, Plate XLVIII, shows one of these bents filled
with blocking.

All structures being carried on girders "C," which, in turn, were carried
on 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 views
of the work at this stage.

The central portion of the viaduct was then erected, and, using concrete
piers and timber bents, all structures were placed on its deck. Fig. 3,
Plate XLIX, shows the piers under the elevated railway columns prior to the
removal 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 by
the city on a cradle built by the Railroad Company on girders "C" on the
east side of the avenue. This is part of the high-pressure system, and the
location and elevation of this water main were taken into consideration
when the underpinning was designed. This main, and the 48-in. cast-iron
sewer bracketed to girders "C," are shown on Fig. 4, Plate XLVIII.

Elevations had been taken on marks on the elevated railway columns
between 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 structure
during the progress of the excavation.

At the extreme south end of the work the procedure was changed. The east
side was excavated down to sub-grade, the east portion of the south
abutment was constructed, and six rows of the permanent steel viaduct were
erected. Very little excavation had been done on the west side of the
avenue at the south end of the work, and it would have delayed the
completion of the work to have waited for the excavation for and the
construction of the west portion of the south abutment and the erection of
the steel; therefore, instead of supporting the girders "C" on the central
rock 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. The
central portion of the avenue was excavated in advance of the west portion.
The permanent viaduct girders were put in place from east to west across
the avenue, and the girders "C" were supported on the deck of the permanent
viaduct approximately under the west elevated railway columns before the
west portion of the avenue was excavated, the central portion of the south
abutment having been constructed before the west portion. This procedure
was 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 of
the south abutment. Figs. 2 and 4, Plate XLIX, and Fig. 2, Plate LII, show
various stages of the work at the south end.

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

[Illustration: PLATE XLIX, FIG. 2.--TW 84, P.T. & T.R.R. Co. Terminal
Station 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 piers
under 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 100
feet South of center line, showing underpinning of Ninth Avenue structure
taken at sub-grade. May 25, 09.]

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

No blasting was done near the supports of the elevated railway structure
while trains were passing over it, and occasionally trains were stopped
during a heavy or uncertain blast. A watchman on the surface, day and
night, and at first one and later two flagmen on the elevated railway
structure, were on duty at all times, reporting to the Interborough Rapid
Transit Company, by whom they were employed. Log mats and timber protection
for the girders and the columns of the permanent viaduct were used, as
shown 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 of
the concrete abutments.

In excavating the sides of the avenue, the rock broke better on the east
than on the west side, where large seams developed and some slides
occurred.

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

No attempt was made to water-proof these abutments, but, in the rear of the
wall, open spaces were left, about 6 ft. from center to center, which were
connected 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 the
rock open and the joints in the boxes and against the rock plastered with
mortar in advance of the wall. A hose was used to run water through these
drains during the placing of the concrete, for the purpose of washing out
any grout which might run into them. Each box was washed out at frequent
intervals, and there was no clogging of the drains whatever. This method
of keeping the drains open was adopted and used successfully for the entire
work. The abutments were built of concrete, and the mixture was 1 part of
cement, 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 spaded
away from the face of the wall as the concrete was laid. Chutes were used
inside the form, if the concrete had to drop some distance. Work was
continued day and night, without any intermission, from the time of
commencement to the time of completion of each section.

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

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


WORK BETWEEN NINTH AND TENTH AVENUES.

_General Description._--The work involved the excavation of about 5.4
acres, between the west house line of Ninth Avenue and the east house line
of Tenth Avenue, to an average depth of about 50 ft., the construction of a
stone masonry portal at Tenth Avenue leading to the River Tunnels, and the
construction around the site of the concrete retaining and face walls.

The following estimated quantities appear in the contract: Excavation of
rock 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, 4,100
cu. 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 all
excavated material on scows at Pier 62, North River. Prior to this contract
this pier had been used by the New York Contracting Company-Pennsylvania
Terminal, for the disposal of excavated material from east of Ninth
Avenue. In order to get the material to the pier, the contractor had
excavated a cut under Ninth Avenue which came to the grade of 32d Street
about midway between Ninth and Tenth Avenues, and a trestle was constructed
from this point over Tenth Avenue and thence to the pier. Fig. 2, Plate
XLVII, shows the east end of this cut, and Fig. 1, Plate L, shows the
trestle, looking east from Tenth Avenue.

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

At three points south of 32d Street and at one point north of 32d Street
near Tenth Avenue, cuts were made in the rock to sub-grade, and from these
cuts, together with the cuts on the west side of Ninth Avenue, all widening
out was done and the excavation was completed. Fig. 1, Plate L, shows the
excavation of the three cuts on the south side of 32d Street, the steam
shovel operating on the north side of that street, and the
material-disposal tracks and trestle. Fig. 3, Plate LII, shows the cuts
joined up and the excavation along the south side practically completed.

On the north side of the work, between Stations 182 + 90 and 183 + 65, the
rock was low, and provision had to be made for maintaining the yards to the
north 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 wall
which was to be put in later. On the same side of the work, between
Stations 188 + 24 and 188 + 46, the rock was exceedingly poor, and as a
small frame house on the adjoining lot was considered to be in an unsafe
condition, a rubble masonry retaining wall was built. As the building
adjoining the south side of the work at Tenth Avenue was on an earth
foundation, it was necessary to underpin it before the excavation could be
done. The building was supported on needles, and rubble masonry was put in
from the bottom of the old foundation to the rock. The foundation of 413
West 31st Street, immediately west of the Express Building site, was of
very poor masonry, and it was necessary to rebuild it prior to taking out
the adjoining excavation.

[Illustration: PLATE L, FIG. 1.--TW 23, P.N.Y. & L.I.R.R. Terminal Station
West. 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 Station
West. 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 Elevated
Railway, showing condition of work. May 26, 09.]

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

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

The excavated material was loaded by derricks on cars at the top of the
excavation, these cars being on tracks having a direct connection with the
disposal 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 laid
out there, and the excavated material was loaded on cars at the bottom and
hoisted by derricks to cars on the disposal trestle. A locomotive was
lowered to the bottom of the excavation on August 25th, 1907, and a derrick
started operating at the bottom on August 27th, 1907. The commencement of
this work by derricks at the bottom is shown by Fig. 3, Plate LII. In
general, the disposal tracks were maintained about on the center line of
31st Street until the excavation had been carried as close to them as
possible, and on October 16th, 1907, they were shifted to the extreme north
side of the work, as shown by Fig. 2, Plate L. A portion of the old trestle
was left in place near Tenth Avenue, a derrick was erected thereon, and the
tracks were used for cars to receive the excavated material hoisted from
sub-grade. The disposal trestle was maintained in this position until such
time as it would interfere with the excavation, and then the tracks were
abandoned. This was done on November 11th, 1908. Fig. 3, Plate L, shows the
finishing 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 then
be run from Seventh to Tenth Avenue at sub-grade. On October 24th, 1908,
the connection with the disposal trestle east of Ninth Avenue was
abandoned, and all excavated material was hoisted from sub-grade at Tenth
Avenue by derricks.

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

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

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

The drill holes were laid out by the blaster, and the general method of
drilling 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 at
the bottom they would be considerably less than 8 ft. apart. They were
drilled about 10 ft. deep, and blasting logs were used, as it was necessary
to 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 sufficiently
to start another cut.

After a side cut about 20 ft. deep had been made, the side holes were
drilled 20 ft. deep, and the holes were loaded and tamped for the full
20-ft. cut. Under the terms of the specifications, the contractor was
required to complete the excavation on the sides by drilling broaching
holes.

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

In the steam-shovel work on the east side of Ninth Avenue, spring holes
were used. They were formed by drilling a 20-ft. hole and exploding at the
bottom of it, without tamping, two or three sticks of dynamite, and
repeating this process with heavier charges until there had been formed at
the 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 was
possible 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 the
east side of Ninth Avenue where the heavy cutting was sometimes extended
beyond the east house line.

From the best records obtainable, the average progress in drilling was
about 33 lin. ft. per 8-hour shift. The average number of cubic yards of
excavation per drill shift was 13.9, and the average amount of drilling per
cubic yard of excavation was 2.4 ft.; this covered more than 27,000 drill
shifts.

The dynamite was practically all 60%, and the average excavation per pound
of dynamite was 2.2 cu. yd. The contractor employed an inspector of
batteries and fuses, who, using an instrument for that purpose, tested the
wiring of each blast prior to firing, in order to discover any short
circuits, and thus prevent the danger of leaving unexploded dynamite in the
holes.

The average quantity of excavation per derrick shift of 10 hours, covering
7,400 shifts, 87% of the excavation being rock, was 50 cu. yd., and the
average 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 would
handle about 40 cu. yd. per shift, whereas, if operating at the bottom of
the cut, it would handle about 60 cu. yd. per shift. The elevator derricks
at Tenth Avenue were very efficient, and each could take care of the
material from four derricks at the bottom, hoisting 250 cu. yd. per shift a
height of 60 ft.

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

The excavation, therefore, was laid out so that the back of the retaining
wall would not encroach on the adjoining property, but would practically
coincide 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 seat
3-1/2 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 maximum
height 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 base
of 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 design
is shown on Fig. 8.

In considering the design of the face wall it was felt that, the wall being
so thin, ample provision should be made to prevent any accumulation of
water and consequent pressure back of the wall; therefore, no attempt was
made to water-proof it, but provision was made to carry off any water which
might appear in the rock. Box drains, 2 ft. wide and 6 ft. from center to
center, 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., any
water 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 than
through 2 ft. of concrete. These drains were connected with pipes leading
through 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 the
wall so materially, that it was thought desirable to tie the wall to the
rock. This was done by drilling into the rock holes from 6 to 15 ft. in
depth, and grouting into each hole a 1-1/2-in. rod having a split end and a
steel wedge. The outer end of each rod was fitted with a 12 by 12 by
1/2-in. plate and a nut, and extended into the wall, thus tying the
concrete securely to the rock. The drains being 6 ft. from center to
center, the tie-rods were placed midway between them, and 6 ft., from
center to center, vertically and horizontally. Fig. 8 shows the arrangement
of these rods and drains. Around the Express Building site, just west of
Ninth 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 batter
on the 31st Street wall was made variable, the top and bottom being
constant distances from the center line and on different grades.

The retaining walls were water-proofed with three layers of felt and
coal-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 joints
open on the lower half, and this was covered with 1 ft. of broken stone and
sand before any back-fill was placed on it.

The arrangement of the drains was as follows: The 6-in. drain back of the
retaining wall was connected with one of the box drains in the rear of the
face wall by a cast-iron pipe or wooden box every 24 ft., and this ran
through the base of the retaining wall. Midway between these pipes, a
connection was made at the bridge seat between the drain in the rear of the
face wall and the gutter formed at the rear of the bridge seat to carry off
rain-water coming down the face of the wall above. All the box drains,
except those connected with the drains back of the retaining wall, were
sealed at the elevation of the base of the retaining wall, as noted
previously.

The specifications required vitrified pipe to be laid through the retaining
wall, but, owing to the difficulty of holding the short lengths of pipe in
place during the laying of wet concrete, they were dispensed with, and
either iron pipes or wooden boxes were used.

_Tie-Rods._--When the excavation on the sides had been completed, movable
drilling platforms were erected, as shown by Fig. 4, Plate L. The holes
were drilled on a pitch of 2 in. per ft. with the horizontal. The depths of
the holes were decided by the engineer, and were on the basis of a minimum
depth of 5 ft. in perfect rock; the character of the rock, therefore, and
the presence of seams, determined the depths of the holes. Each hole was
partly filled with grout, and the rod, with the steel wedge in the split
end, was inserted and driven with a sledge so that the wedge, striking the
bottom 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 form
which could be withdrawn, but it was finally decided to build boxes in
which the side toward the rock was open and the joints in the boxes and
against the rock were plastered with cement mortar. These boxes were left
in place. Fig. 1, Plate LI, shows the tie-rods and box drains in place, and
holes being cut near the bottom of the drains for the pipes leading through
the wall.

_Forms._--Fig. 1, Plate LI, shows the form used on the south side of the
work. The materials were of good quality, and the form, which was about 50
ft. long, was used to build twelve sections, or about 600 ft. of wall. The
form was tied in at the top and bottom by cables attached to rods drilled
into the rock, and it was thought that, with the trusses to stiffen the
middle section of the form, it would not be necessary to use raker braces
against it. This would have been desirable, as the placing of the raker
braces took considerable time. It was found, however, that the form was not
sufficiently rigid, as it bulged at the middle section and could not be
held 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 the
form and fastened to the tie-rods, and thus the form was held in place
successfully. On the forms built later, the trusses were omitted, and raker
braces, about every 6 ft., were used. The rods which screwed into the
turnbuckles were removed before the form was moved. The photograph, Fig. 4,
Plate LII, was taken inside the concrete form for the lower face wall on
the north side, and shows the drains leading through the wall, the
turnbuckles attached to the tie-rods, the cables attached to rods in the
rock, and the braces to keep the form from coming in; these braces, of
course, were removed as the concrete came up. The form was built low and
wedged 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 its
new 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 face
wall, was left out, so that the bottom of the form for the upper face wall
could be braced against it. The top of this form was tied by cables
attached to rods in the rock and by rods with turnbuckles running from back
to front of the form; braces were also put in from the back of the
retaining 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 rods
with turnbuckles which passed through the form and were fastened to each of
the tie-rods drilled into the rock, as was also done in the case of the
lower face wall. It was generally possible to hold the form to true
position in this manner, but occasionally it had a tendency to bulge; when
this occurred, the rods leading through the form and fastened to the
tie-rods were tightened up, the placing of the concrete was slowed up, and
no serious bulging occurred.

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

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

[Illustration: PLATE LI, FIG. 1.--TW 66, P.N.Y. & L.I.R.R. Terminal Station
West. 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 showing
chutes. 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 New
York to New Jersey. Feb. 9, 07.]

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

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

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

_Upper Face and Retaining Wall._--In cases where the top of the retaining
wall was at a higher elevation than the mixer, it was necessary to raise
the concrete in a bucket with a derrick, and dump it into cars on the
trestle 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 to
the top of the retaining wall. At the commencement of each section of the
retaining wall a layer of mortar was put on the rock. A 1:2:3 mixture of
concrete was used in the face wall, and a 1:3:6 mixture in the retaining
wall.

As the face walls were so thin, the number of batches of concrete per hour
was reduced, for the form filled so rapidly that the concrete, before it
set, exerted an excessive pressure against the form, and this tended to
make it bulge. The proper rate at which to place the concrete behind a form
50 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 concrete
walls were started, the contractor suggested using forms 100 ft. long and
building the walls in sections of that length; it was decided, however, to
limit 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 the
forms were removed, irregular cracks appeared in the walls between the
joints in practically every section. It was thought that these cracks might
be due to the wall being very thin and being held at the back by the
tie-rods; there was also quite a material change in the section of the wall
at each drainage box. Although it was admitted that these cracks would have
no effect on the stability of the wall, it was thought that, for appearance
sake, it would be desirable to prevent or control them, if possible. The
first method suggested was to shorten the sections to 25 ft., which would
give an expansion and contraction joint every 25 ft., it being thought that
sections of this length would not crack between the joints. This, however,
was not considered desirable. An effort was then made to prevent cracks in
a section of wall, about 46 ft. long, on the south side, by using
longitudinal reinforcement. In the lower and upper face walls, 3/4-in.
square twisted steel rods were placed longitudinally about 4 in. in from
the face and about 1 ft. 4 in. apart vertically. The sections of these
walls were finished on April 10th, and May 5th, 1909, respectively. At
present there are no indications of cracks in these sections, and they are
practically the only ones in the south walls which do not show irregular
cracks.

It was decided, however, that, inasmuch as the cracks did not affect the
stability of the walls, the increased cost of thus reinforcing the
remaining walls was not warranted. An effort to control the cracks was made
by placing corrugated-iron diaphragms in the form, dividing each 50-ft.
section into three parts. The diaphragms were 1 ft. wide, and were placed
with the outer edge 1 in. in from the face of the wall, but in the copings
they were omitted. The purpose of these diaphragms was to provide weak
sections in the walls, so that if there was any tendency to crack it would
occur along the line of the diaphragms. Corrugated iron was used for the
diaphragms instead of sheet iron as it was more easily maintained in a
vertical position. The general arrangement of the diaphragms is shown on
Fig. 4, Plate LII. The results obtained by using diaphragms have been quite
satisfactory, and cracks approximately straight and vertical have usually
appeared opposite the diaphragms soon after the forms were removed.
Diaphragms were used on all the remaining walls, with the exception of
those between Stations 187 + 07 and 188 + 83 on the north side, where the
rock was of poor character and bad slides had occurred. Between these
points, 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 ELEVATED
RAILROAD.]

[Illustration: PLATE LII, FIG. 2.--TW 100. P.T. & T.R.R. Co. Terminal
Station 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. Terminal
Station West. View showing excavation 9th and 10th Avenues South of 32nd
St. looking West from Sta. 184. Aug. 17, 07.]

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

_Tenth Avenue Portal._--The design of the Tenth Avenue Portal is shown on
Fig. 9. The stone selected came from the Millstone Granite Company's
Quarries, 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 certain
stones in each course were sent long and were cut on the ground, in order
to make proper closures. Drains were left behind the portal around the back
of each arch, leading down to the bottom, and through the concrete base at
each side of the portal and in the central core-wall; all these drains have
been discharging water.

_Power-House._--The old church at No. 236 West 34th Street, between Seventh
and Eighth Avenues, was turned over to the New York Contracting
Company-Pennsylvania Terminal for a power-house to supply compressed air
for use on the Terminal Station work between Seventh and Ninth Avenues and
the work below sub-grade as well as that on the Terminal Station-West. Four
straight-line compressors and one cross-compound Corliss compressor were
installed, the steam being supplied by three Stirling boilers. Three
electrically-driven air compressors, using current at 6,600 volts, were
also installed, and the total capacity of the power-house was about 19,000
cu. 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 the
foot of West 32d Street, North River, was leased by the Pennsylvania
Railroad Company. The entire pier, with the exception of the piles, was
taken down, and the piles which would be in the path of the proposed tunnel
were withdrawn prior to the building of the tunnels and the construction of
the pier for disposal purposes. Subsequent to the driving of the tunnels
there was a considerable settlement in the pier, especially noticeable at
the 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 the
decks 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 were
used, not only for loading heavy stones and skips, but also with a
clam-shell bucket for bringing in broken stone and sand for use in the
work. Large quantities of pipe, conduits, brick, etc., were also brought to
this 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 by
the diagram, Fig. 10.

The position of Assistant Engineer, in responsible charge of Construction
and 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 Night
Inspector, respectively, in charge of outside work during the entire
carrying out of the contract.

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

Prior to the commencement of the work, elevations were taken on the surface
at 10-ft. intervals, and elevations of the rock surface were taken on these
points as the rock was uncovered. Cross-sections were made and used in
computing the progress and final estimates.

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

A daily report was sent to the Chief Office showing the quantities of
excavation removed and concrete built, the force in the field, the plant at
work, etc., during the previous day. At the end of each month a description
of 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 progress
of the concrete walls, were also sent.


COST ACCOUNT.

From the records of labor and material obtained in the field, and from
estimated charges for administration and power, an estimate was made of the
cost to the contractor for doing various classes of work. It was necessary
to estimate the administration and power charges, as the contractor's
organization and power-house were also controlling and supplying power to
the Terminal Station work east of Ninth Avenue and also the work below
sub-grade. The labor and material charges in the field were placed directly
against the class of work on which they were used and the administration
and general charges (which included superintendence, lighting, etc.) were
apportioned to the various classes of work in proportion to the value of
the labor done.


STATISTICS.

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

The total weight supported during the work under Ninth Avenue was about
5,000 tons.

\U$1\EThe average daily traffic over the Ninth Avenue Elevated Railway was
90,000 passengers, and, during the progress of the excavation and
underpinning, about 100,000,000 passengers were carried over that
structure.

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 was
about 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 the
excavation 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 of
equipping and maintaining the field office amounted to 2.8% of the cost of
the work executed, 2.7% being for engineering salaries alone.

FOOTNOTES:

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