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Transactions of the American Society of Civil Engineers (Volume 81) online

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360 subway tunxel wokk

Trimming at Portal and Widening Out for Station Platforms.

Generally, only a few feet of rock cover was fo\ind at the portals,
and, as this rock was seamy and disintegrated, the excavation was
started about 5 ft. below the line of the finished roof and gradually
brought up to grade in about 100 ft. At the 95th Street portal, where
the work was in the station, no attempt was made at first to excavate
for the station platforms, the contractor intending to come back
later, after the lower-level structure had been completed, and do this
part of the work.

Before the portals were trimmed and the excavation was widened
out for the station platforms, the plans were changed so as to sub-
stitute steel columns with longitudinal beams or girders on top for
the reinforced concrete center wall originally called for. This change
of plan greatly simplified the work, and lessened the risk of excavating
for the station platforms and trimming at the portals.

As has been noted previously, the rock at the portals was very
poor (Fig. 14), and particular care had to be taken not to expose
too much of it at a time. The structure for the lower level was first
completed (Fig. 16), and also for the upper level inside the portal,
where the excavation had already been made to the full section.
The work at the center was trimmed carefully to the neat line for
about 20 ft., commencing at the point where the upper level had
already been completed, and working toward the portal (Fig. 15).
While the center was being trimmed, the rock on the sides was made
secure by posting or cribbing from the roof of the structure of the
lower level. The center line steel and concrete wall was then built
for about 15 ft., and carried up solid to the rock above. After the
rock was thus caught up at the center, the roof on one side was
trimmed and the arch placed (Fig. 17), after which the other side was
completed. In this way, by working from the finished structure toward
the portal, trimming small stretches at a time, and keeping the
exposed rock in the roof well supported, the trimming at the portals
and the widening out for the station platforms were accomplished

Excavation, 99th to 102d Street.

Between 99th and 102d Streets, the transition is made from a
double-deck tunnel structure to one with four tracks on the same



level. The span of the tunnel at 99th Street is 32 ft. (Fig. 19), and
this gradually increases until, at 100th Street, the span is 60 ft.
(Plate IV). At this point, the local tracks have been offset sufficiently
to clear the two center tracks in the lower level, and continue north-
ward in two separate one-track tunnels, the rock core between them
(over the center tracks) not being removed. (Plate TV.)




,, 'i^^®»r.„

Fig. 16.
In making the excavation for the widening north of 99th Street,
a section approximating that of the typical double-deck tunnel was
first taken out, and the structure for the lower level completed. The
roof was then trimmed at the center to permit the erection of the
center steel, and, after the rock was solidly blocked up from the tops
of the columns, the excavation was increased to its full width without
requiring any additional timbering, except for occasional posting
under unsound rock.


The most difficult part of the tunnel work on Lexington Avenue
was the excavation for the transition between 100th and 102d Streets.
The tunnel for this stretch had a span of 60 ft., and the rock was
cut up and disintegrated, and would hardly stand without support
for the span of one track (15 ft.)- The situation was complicated
further by the fact that the plans did not contemplate the excavation
of the rock core over the center tracks (lower level) and between the
local tracks on the sides.

The general scheme of prosecuting the work was to complete first
the excavation for the center traeks, build this part of the structure,
and, after the rock over the roof was properly caught" up, to make
the excavation for the local tracks on the sides. The excavation
for the two center tracks was continued northward to about 100th
Street without encountering any special difficulties. Going north
from 100th Street, the rock began to get bad, and it became evident
that it would not be safe to make the excavation for the full width
of the two-track structure without the use of timbering. As the con-
tractor desired to continue the use of his air shovel for mucking,
and as the use of the ordinary methods of timbering requiring posting
would interfere with the operation of the shovel, it was decided to
narrow the excavation to a width of about 18 ft., this being sufficient
to permit the use of the air shovel. The excavation was confined
to one side, so that, when completed, the structure for one track
could be built. It was hoped that the rock would arch for this small
span, and that by this procedure there would be no necessity for
timbering. This scheme was successful for the greater part of the
work, but occasionally there were places where, even with such a
small spaa, it was necessary to support the roof. In these cases, in
order to permit the use of the air shovel for mucking, the timbering
had to be placed so that it would not interfere with the shovel or
with the construction that was to follow later.

The general manner of putting in roof supports in these cases
(Fig. 21) was about as follows: When unsoimd rock was encountered,
the excavation was advanced with a small heading (8 by 8 ft.), the
rock in the heading being secured temi)orarily by posting. At a
point where the excavation to the neat line had been completed pre-
viously, recesses were cut in the side rock above the line of the
roof of the finished structure, and 24 or 26-in. I-beams were placed

Fig. 17. — Half of Roof in 96th Street Station Concreted.

Fig. 18. — Rock Conditions at 102d Street Portal.





2-26"rs, 150 lb. 1«-47t5^


crosswise, with the ends of the beams concreted into these recesses.
A temporary horsehead was then set up in the heading, and longi-
tudinal beams were placed, supported on the horsehead and the cross-
beams. The rock was then blocked up from the longitudinal beams,
and the section was increased to its full width, after which another
set of cross-beams was put in just below the horsehead, and the
longitudinal beams were brought to bear on this new set. The small
heading was then advanced another 50 ft., and the operation repeated.

These systems of timbering were used for about 200 ft. of the
tunnel, and though they were efficient for the purpose of supporting
the rock and permitting the use of the shovel, they interfered seriously
with the progress of the work, as it took about a week to put in about
50 ft. of the timbering, diiring which period the work of excavation
bad to be discontinued. For this reason, toward the close of the
job, the use of the air shovel was abandoned, the excavation was
confined to only one track at a time, and all loose rock was carefully
removed. In some cases it became necessary to remove the rock
as high as 12 ft. above the roof line, and though the contractor did
not receive any payment for the excavation outside of the neat lines,
he preferred to remove all loose and dangerous rock rather than
attempt to hold it in place with timber. A powerful electric search-
light was kept on the job at all times, and examinations of the roof
were made several times a week, all loose rock being removed.

The rock throughout this stretch was very poor, and, as very
little timbering was used, it was necessary that the excavation be
followed by the construction as soon as possible, for, though the roof
was carefully scaled, the constant blasting loosened up the rock, so that
it was inadvisable to leave it exposed and unsupported for any
considerable length of time. Besides, the contractor was not permitted
to widen the center excavation for the two tracks until the structure
for the one track had been completed and the rock over it had been
caught up, or to make the excavation for either local track on the
side until the roof of the structure for the adjacent express track
had been completed and the rock over it had been safely caught up.

At first, the space over the roof was filled with hand-packed rock,
but this proved unsatisfactory, for, when the excavation was made
for the local tracks on the sides, the hand-packing was not sufficient
to hold the rock core over the express tracks in place. Horizontal



VOL. LXXXI, No, 1388.



West Local Track

Till* part of ^^

East Local Track




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seams started to develop in the core, and the voids in the hand-
packing as well as the cracks in the rock core were then grouted with
Portland cement grout to prevent bringing concentrated loads on the
roof. After this, where the excess space was not too large, or where
the rock was very poor, the roof concrete was carried solid to the rock
above; where the rock broke very high, continuous longitudinal con-
crete walls, from 2 to 4 ft. thick, were built over each of the partition
walls of the structure and carried solid to the rock above, and the
space between the walls was filled with hand-packing (Plate VII).

No attempt was made to excavate for the local tracks on the sides
luitil the adjacent express track structure had been completed and
the overlying rock had been caught up. The plans called for an
emergency exit to the surface at 100th Street, with a cross-drift over
the express tracks connecting the two outside tracks. The contractor
used this shaft and drift as working points from which to make the
excavation for the local tracks.

While the excavation for the local tracks was being made north
and south from 100th Street, work was also started at the 102d Street
portal. At this point, the structure consists of four tracks on the
same level, the tunnel having a cross-section of 60 by 17 ft. The
rock as exposed at the portal was faulted and broken up, and it was
clear that it would not be safe to excavate for more than one track
at a time. (Fig. 18.) The excavation was first made for the west,
outside (local) track, and carried south about 75 ft. from the portal.
A cross-drift, about 20 ft. wide, was then carried to the east neat line,
and the excavation for the east, outside (local) track was extended
north to the portal. After the structure for this part of the excavation
had been completed and the roof had been concreted solid to the
rock above, the excavation for the two center tracks was made, but
prior to this, and as an additional precaution against a movement
of the rock over the portal, concrete buttress walls (about 3 ft. thick)
were built up against the face of the portal, and rested on the roof
of the finished structure in the open cut beyond the portal. Three
buttress walls were built, one over each of the partition walls of the
subway (Fig. 20).

No special difficulties were encomitered in making the excavation
for the local tracks on the sides. Precautions, however, had to be
taken to protect the adjacent finished structure (Fig. 22).



Fig. 23. — Excavation for Local Tracks in Four-Track Tunnel.

Fig. 24. — Subway Stkucture Damaged by Blasting.

Fig. 25. — Damaged Columns Removed and Beams Supported by 12 h\ 12-In Posts.

Fig. 26. — Beam Placed Between Roof Beams to Stiffen Them and Distribute
THE Load on the Side-Wall.


At first, the excavation for each local track was made as a separate
tunnel, leaving a core-wall, from 3 to 4 ft. thick, between the excava-
tion and the finished structure. The core-wall was kept about 25 ft.
behind the heading, and was shattered so much by the adjacent blasting
that it could be easily removed with little drilling and blasting. This
method was soon abandoned, as considerable damage was done to
the finished structure, by pieces of rock being blown against the
columns during the blasting, and also by the rock of the core-
wall being jammed against the columns. The columns were protected
by timber planks, and, in some cases, by encasing them in the concrete
partition walls called for by the plans. Though in some instances
the concrete was injured by the blasting, the damage done to the
structure was less serious than in the cases where concrete was not
put in.

Yery good results, as far as protecting the steel was concerned,
were obtained by drilling the holes laterally and firing the rock away
from the finished structure. Practically, this consisted of taking
out a center heading and later removing the top of the section with
breaking-down holes. When the bench was removed, a 4-ft. core-wall
was left temporarily between the excavation and the finished structure.
This method was soon abandoned, as its use generally required plat-
forms or scaffolding on which to set up the drills.

The final and most successfvil method used was to place a continu-
ous bulkhead of 3-in. planks between the steel and the rock to be
excavated, and to brace the columns and partition wall over to the
center wall with two 6 by 12-in. braces. The excavation was made
with a small top heading and three benches, a 6-ft. core-wall being
left temporarily between the bench and the columns. The core was
really a part of the bench that had not been drilled, but it was
shattered so much by the other blasting that it could be removed later
with very little drilling and blasting (Fig. 23).

Considerable damage was done to the structure adjacent to which
blasting was done (Fig. 24). The contractor was required to cut out
and replace in a satisfactory manner about 200 ft. of 16-in. reinforced
concrete wall and columns. Prior to removing the columns, the roof
beams were posted up with 12 by 12-in. timbers to prevent any settle-
ment (Fig. 25). In some cases the ends of the center track roof -beams
were badly damaged as well as the columns, and it was not con-



sidered safe to attempt to remove them. In these cases a 12-in.
I-beam was placed between the roof-beams to stiffen them and
to distribute the load over the concrete wall instead of directly
on the columns when the side-walls for the local track were
placed (Fig. 2G). In some cases, also, where jack-arches were used
in the roof, they were badly damaged. As it was not considered safe
to remove these arches and replace them, 6-in. cross-beams were
introduced in the bottom of the arch and grouted, as shown in Fig. 27.




Proposed Longitudinal
6 Beamb

Recesses in arcli hauncli
(for 6 beams 18 "apart.

Fig. 27.

Some repair work was also necessary to the local track structures
at 56th and 74th Streets, where they had settled on account of the
excavation for the express track tunnel. North of 74th Street, con-
siderable voids were found under the track floor. The ground at
this point was a soft alluvial soil, and it did not seem likely that any
satisfactory results could be obtained by grouting. Accordingly, the


contractor was ordered to re-build the footings under tlie columns
and carry them down to the soil. The track floors were also re-built.
South of 74th Street the void space was found under the floor for
about 100 ft. of the structure, the voids in some cases being as great
as 1 ft. The work in the express tunnel had drained the soil at
this point so that it was compact and dry when repairs were to be
made. Holes were placed in the local track floor about 10 ft. apart,
and the voids were filled with grout. After this was done, investi-
gating holes were again made through the floor and grout, and
failed to disclose any void space. At 56th Street, when settlement
began to take place, the contractor immediately grouted the space
under the local track floor, and this did much toward checking the settle-
ment. Later, when test holes were made through the local track
fl.oor, the grout, in some cases, was found to be 20 in. thick, and,
as this rested on good soil, it was not necessary to make any material
repairs, as it was possible to work up a new grade with the structure
in its final location.

Handling of Muck.

In the work on Sections 8 and 9, the mucking was done by hand;
on Sections 10 and 11, air shovels were used. The excavated material
was loaded into large iron buckets, commonly known on the work as
"battleships", and was not handled again until dumped into the
scows for disposal. The flat-top trucks used were fitted with cradles
to receive the bottom of the "battleships".


The contractor's plant was operated by compressed air and elec-
tricity. The power-plant for the air was at 96th Street and East
River. Electric current was furnished by the New York Edison Com-

Compressed- Air Plant. — The compressed-air plant consisted of five
Tngersoll-Rand compressors, each with a capacity of 2 100 cu. ft. of
free air per min., and five General Electric synchronous motors, each of
350 h.p., 6 600 volts, and 24.7 amperes. Eive receivers were used,
two 6 by 18 ft., and three 5 by 15 ft. The air was brought to Lexington
Avenue through 96th Street in a 10-in. pipe line. The pipe line was
extended north and south of 96th Street to 53d and 106th Streets, and
connections were made at the shafts as required. The air was com-


pressed to a pressure of 100 lb., and was delivered in the headings at
about 90 lb.

Shovel. — Four 38-ton Marion shovels, Model No. 40, with 1-yd.
buckets, were used on Sections 10 and 11. The shovels were provided
with 18-ft. booms when working in the double-deck tunnels, but these
were cut down to 15 ft. when the shovel was used in the single-deck

Hoists. — The electric hoists used at the surface at the shafts were
generally Lambert, direct-current, /jO-h.p. 230 volts, and 220 amperes.
The hoisting engines used below for hauling the mucking cars were
Lambert 7 by 10-in. double-drum, and were operated by compressed air.

Electric Searchlight. — The electric searchlight, used in examining
the roof of the tunnel before the lining had been placed, was made
by the Rushmore Dynamo Works, being described as Type A, 110
volts, and 20 amperes.

Pumps. — In the tunnel, 6-in. Cameron suction pumps, operated by
compressed air, were used to discharge the water into sumps, and
from there the water was discharged into the sewers by electrically-
operated centrifugal pumps.

"Battleships." — The "battleships", or buckets, were made of ^-in.
wrought iron, and were 4 ft. 8 in. by 7 ft. by 3 ft. 10 in. Their
capacity was 4.6 cu. yd., water measure.

Drills and Columns. — Ingersoll-Rand 6-in. columns were used to
drill the headings. The tripod drills used were generally Ingersoll-
Eand, Type E-44 (with 3-1-in. cylinder), F-94 (Sf-in. cylinder), and
E-33 (3^-in. cylinder). A depth of about 2 ft. was drilled with each
sharpening of the steel.

The extensive use of the tripod drills was probably due to the
fact that, when this job started, the hammer type then on the market
was not very efficient. The maximum length of steel that could be
used with such drills at that time was 6 ft. Toward the close of
the work, several new kinds of rotary hand-drills were put on the
market, and these proved so satisfactory that they practically sup-
planted the heavier drills formerly used in this work. The first hand-
drills used were the McKiernan-Terry non-rotating hand-drill, Style
B. These were replaced later by the Ingersoll-Eand rotating hand
drills, Type BCR No. 33 and BCR No. 430. The superiority of these
small machines over the heavy tripod drills is shown by the fact


that they will drill, on an average, about 30 ft. per hour, and are now
supplied with steels up to 12 ft. in length. The saving in labor
and power has contributed to the success of these small drills. An
ordinary tripod drill with a 3g-in. cylinder requires, at 90 lb. pressure,
159 ft. of air, and must have a drill runner and a driller's helper to
run it. The BCR No. 33 hand-drill, at the same pressure, requires
90 ft. of air, and can be run by a driller without a helper. The tripod
drills require the steel to be changed every 2 ft.; but, with the BCR
drill, from 6 to 8 ft. can be drilled without a change.

Drill Steel. — For the large drills, 1^-in. octagonal steel was used;
and for the small drills, |-in. hollow hexagonal steel. A set of steels
for the large drills was made up as follows:

Length of steel.

Diameter of steel.

2 ft.





4 "


6 "


8 "


10 "


12 "


14 "


Cost Data.

The following figures may be considered fairly accurate, as repre-
senting the cost of the various classes of work indicated:

Cost of excavation per cubic yard in double-deck tunnels,
Sections 10 and 11; sound rock not requiring timber-
ing; mucking done by air shovel $5.00

Cost of tunnel excavation per cubic yard in sound rock
tunnel, no timbering being used (two-track tunnel.
Sections 8 and 9) $7.00

Cost of tunnel excavation per cubic yard in luisound rock
tunnels, requiring segmental timbering (two-track tun-
nels, Sections 8 and 9) $10.00

Cost of tunnel excavation in compressed air work (10 to 16
lb.). Only top of heading excavated. Segmental tim-
bering used (two-track tunnels, Sections 8 and 9) . . . . $15.00



In computing the foregoing figures, the following scale of wages
and general charges were assumed, the scale of wages being based
on an 8-hour day:

Superintendent $300.00 per month.

Tunnel foreman 200.00 " "

Heading foreman .... 5.00 per day.
Mucking foreman . . . 4.00

Driller 3.68

Driller's helper 2.00



Shovel runner



Blacksmith's helper .


Electrician's helper .

Drill repairer 3.00

Timekeeper 3.00

Hoist runner 4.75

Signalman 2.00

Three-horse team 9.00

Master mechanic 5.00

Team checker 3.00

Powder $0.14 per lb.

Dump 0.30 per cu. yd.

Plant running and de-
preciation 1.42 per cu. yd.*

Administration charges. 10% of cost of labor and materials.

Concrete Lining.

The plans for the subway structure in the tunnel did not contem-
plate the placing of the concrete solid to rock in all cases. Where
the structure had an arched roof, the side- walls were in all cases to
be concreted solid to rock up to 2 ft. above the springing line of the
arch. Where the rock was good and did not require any timbering
during the progress of the excavation, the regular construction ^hown

* The figures for the Manhattan tunnels of the Pennsylvania Railroad are given
in Transactions, Am. Sec. C. E., Vol. LXVIII, p. 192.

Fig. 28. — Longitudinal Concrete Walls Over Roof of Tunnel.

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