Transactions of the American Society of Civil Engineers, vol. LXVIII, Sept. 1910
J >> James H. Brace, Francis Mason and S. H. Woodard >> Transactions of the American Society of Civil Engineers, vol. LXVIII, Sept. 1910AMERICAN SOCIETY OF CIVIL ENGINEERS
INSTITUTED 1852
TRANSACTIONS
Paper No. 1159
THE NEW YORK TUNNEL EXTENSION OF THE PENNSYLVANIA RAILROAD.
THE EAST RIVER TUNNELS.[A]
BY JAMES H. BRACE, FRANCIS MASON, AND S. H. WOODARD, MEMBERS, AM. SOC.
C. E.
This paper will be limited to a consideration of the construction of the
tunnels, the broader questions of design, etc., having already been
considered in papers by Brig.-Gen. Charles W. Raymond, M. Am. Soc. C.
E., and Alfred Noble, Past-President, Am. Soc. C. E.
The location of the section of the work to be considered here is shown
on Plate XIII of Mr. Noble's paper. There are two permanent shafts on
each side of the East River and four single cast-iron tube tunnels, each
about 6,000 ft. long, and consisting of 3,900 ft. between shafts under
the river, and 2,000 ft. in Long Island City, mostly under the depot and
passenger yard of the Long Island Railroad. This tube-tunnel work was
naturally a single job. The contract for its construction was let to S.
Pearson and Son, Incorporated, ground being broken on May 17th, 1904.
Five years later, to a day, the work was finished and received its final
inspection for acceptance by the Railroad Company.
The contract was of the profit-sharing type, and required an audit, by
the Railroad Company, of the contractor's books, and a careful system of
cost-keeping by the Company's engineers, so that it is possible to
include in the following some of the unit costs of the work. These are
given in two parts: The first is called the unit labor cost, and is the
cost of the labor in the tunnel directly chargeable to the thing
considered. It does not include the labor of operating the plant, nor
watchmen, yardmen, pipemen, and electricians. The second is called "top
charges," a common term, but meaning different things to different
contractors and engineers. Here, it is made to include the cost of the
contractor's staff and roving laborers, such as pipemen, electricians,
and yardmen, the cost of the plant and its operation, and all
miscellaneous expenses, but does not include any contractor's profit,
nor cost of materials entering permanent work.
The contractor's plant is to be described in a paper by Henry Japp,[B]
M. Am. Soc. C. E., and will not be dealt with here.
The contractors carried on their work from three different sites. From
permanent shafts, located near the river in Manhattan, four shields were
driven eastward to about the middle of the river; and, from two similar
shafts at the river front in Long Island City, four shields were driven
westward to meet those from Manhattan. From a temporary shaft, near East
Avenue, Long Island City, the land section of about 2,000 ft. was driven
to the river shafts.
[Footnote A: Presented at the meeting of December 15th, 1909.]
[Footnote B: _Transactions_, Am. Soc. C. E., Vol. LXIX. p. 1.]
TUNNELS FROM EAST AVENUE TO THE RIVER SHAFTS.
The sinking of the temporary shaft at East Avenue was a fairly simple
matter. Rough 6 by 12-in. sheet-piling, forming a rectangle, 127 by 34
ft., braced across by heavy timbering, was driven about 28 ft. to rock
as the excavation progressed. Below this, the shaft was sunk into rock,
about 27 ft., without timbering. As soon as the shaft was down, on
September 30th, 1904, bottom headings were started westward in Tunnels
_A_, _B_, and _D_. When these had been driven about half the distance to
the river shafts, soft ground was encountered. (See Station 59, Plate
XIII.) As the ground carried considerable water, it was decided to use
compressed air. Bulkheads were built in the heading, and, with an air
pressure of about 15 lb. per sq. in., the heading was driven through the
soft ground and into rock by ordinary mining methods. The use of
compressed air was then discontinued. West of this soft ground, a top
heading, followed by a bench, was driven to the soft ground at about
Station 66. Tunnel _C_, being higher, was more in soft ground, and at
first it was the intention to delay its excavation until it had been
well drained by the bottom headings in the tunnels on each side. A
little later it was decided to use a shield without compressed air. This
shield had been used in excavating the stations of the Great Northern
and City Tunnel in London. It was rebuilt, its diameter being changed
from 24 ft. 8-1/2 in. to 23 ft. 5-1/4 in. It proved too weak, and after
it had flattened about 4 in. and had been jacked up three times, the
scheme was abandoned, the shield was removed, and work was continued by
the methods which were being used in the other tunnels. The shield was
rather light, but probably it would have been strong enough had it been
used with compressed air, or had the material passed through been all
earth. Here, there was a narrow concrete cradle in the bottom, with rock
up to about the middle of the tunnel, which was excavated to clear the
shield, and gave no support on its sides. The shield was a cylinder
crushed between forces applied along the top and bottom.
With the exception of this trial of a shield in Tunnel _C_, and a novel
method in Tunnel _B_, where compressed air, but no shield, was used, the
description of the work in one tunnel will do for all.
From the bottom headings break-ups were started at several places in
each tunnel where there was ample cover of rock above. Where the roof
was in soft ground, top headings were driven from the points of break-up
and timbered. As soon as the full-sized excavation was completed, the
iron lining was built, usually in short lengths.
It will be noticed on Plate XIII that there is a depression in the rock
between Station 65 and the river shafts, leaving all the tunnels in soft
ground. As this was directly under the Long Island Railroad passenger
station, it was thought best to use a shield and compressed air. This
was done in Tunnels _A_, _C_, and _D_, one shield being used
successively for all three. It was first erected in Tunnel _D_ at
Station 64 + 47. From there it was driven westward to the river shaft.
It was then taken apart and re-erected in Tunnel _C_ at Station 63 + 63
and driven westward to the shaft. It was then found that there would not
be time for one shield to do all four lines. The experience in Tunnels
_C_ and _D_ had proven the ground to be much better than had been
expected. There was considerable clay in the sand, and, with the water
blown out by compressed air, it was very stable. A special timbering
method was devised, and Tunnel _B_ was driven from Station 66 + 10 to
the shaft with compressed air, but without a shield. In the meantime the
shield was re-erected in Tunnel _A_ and was shoved through the soft
ground from Station 65 + 48 nearly to the river shaft, where it was
dismantled.
There was nothing unusual about the shield work; it was about the same
as that under the river, which is fully described elsewhere. In spite of
great care in excavating in front of the shield, and prompt grouting
behind it, there was a small settlement of the building above, amounting
to about 1-1/2 in. in the walls and about 5 in. in the ground floors
which were of concrete laid like a sidewalk directly upon the ground.
Whether this settlement was due to ground lost in the shield work or to
a compacting of the ground on account of its being dried out by
compressed air, it is impossible to say.
The interesting features of this work from East Avenue to the river
shafts are the mining methods and the building of the iron tube without
a shield.
EXCAVATION IN ALL ROCK.
Where the tunnel was all in good rock two distinct methods were used.
The first was the bottom-heading-and-break-up, and the second, the
top-heading-and-bench method. The first is illustrated by Figs. 1 and 2,
Plate LXIII. The bottom heading, 13 ft. wide and 9 ft. high, having
first been driven, a break-up was started by blasting down the rock,
forming a chamber the full height of the tunnel. The timber platform,
shown in the drawing, was erected in the bottom heading, and extended
through the break-up chamber. The plan was then to drill the entire face
above the bottom heading and blast it down upon the timber staging, thus
maintaining a passage below for the traffic from the heading and
break-ups farther down the line. Starting with the condition indicated
by Plate XIII, the face was drilled, the columns were then taken down
and the muck pile was shoveled through holes in the staging into muck
cars below. The face was then blasted down upon the staging, the drill
columns were set up on the muck pile, and the operation was repeated.
This method has the advantage that the bottom heading can be pushed
through rapidly, and from it the tunnel may be attacked at a number of
points at one time. It was found to be more expensive than the
top-heading-and-bench method, and as soon as the depression in the rock
at about Station 59 was passed, a top heading about 7 ft. high, and
roughly the segment of a 23-ft. circle, was driven to the next soft
ground in each of the four tunnels. The remainder of the section was
taken out in two benches, the first, about 4 ft. high, was kept about
15 ft. ahead of the lower bench, which was about the remaining 11 ft.
high.
EXCAVATION IN EARTH AND ROCK.
About 2,500 ft. of tunnel, the roof of which was in soft ground, was
excavated in normal air by the mining-and-timbering method. In the
greater part of this the rock surface was well above the middle of the
tunnel. The method of timbering and mining, while well enough known, has
not been generally used in the United States.
[Illustration: PLATE LXIII]
Starting from the break-up in all rock, as described above, and
illustrated on Plate XIII, when soft ground was approached, a top
heading was driven from the rock into and through the earth. This
heading was about 7 ft. high and about 6 ft. wide. This was done by the
usual post, cap, and poling-board method. The ground was a running sand
with little or no clay, and, at first, considerable water, in places.
All headings required side polings. The roof poling boards were about
2-1/2 or 3 ft. above the outside limit of the tunnel lining, as
illustrated by Figs. 3, 4, and 5, Plate LXIII. The next step was to
place two crown-bars, _AA_, usually about 20 ft. long, under the caps.
Posts were then placed under the bars, and poling boards at right angles
to the axis of the tunnel were then driven out over the bars. As these
polings were being driven, the side polings of the original heading were
removed, and the earth was mined out to the end of these new transverse
polings. Breast boards were set on end under the ends of the transverse
polings when they had been driven out to their limit. Side bars, _BB_,
were then placed as far out as possible and supported on raking posts.
These posts were carried down to rock, if it was near, if not, a sill
was placed.
A new set of transverse polings was driven over these side bars and the
process was repeated until the sides had been carried down to rock or
down to the elevation of the sills supporting the posts, which were
usually about 4 ft. above the axis of the tunnel.
The plan then was to excavate the remainder of the section and build the
iron lining in short lengths, gradually transferring the weight of the
roof bars of the iron lining as the posts were taken out. This meant
that not more than four rings, and often only one ring, could be built
before excavation and a short length of cradle became necessary. Before
the posts under the roof bars could be built and the weight transferred
to the iron lining, a grout dam was placed at the leading end of the
iron lining, and grout was brought up to at least 45 deg. from the top. Such
workings were in progress at as many as eight places in one tunnel at
the same time. Where there was only the ordinary ground-water to contend
with, the driving of the top heading drained the ground very thoroughly,
and the enlarging was done easily and without a serious loss of ground.
Under these conditions the surface settlement was from 6 in. to 2 ft.
Under Borden Avenue, there was more water, which probably came from a
leaky sewer; it was not enough to form a stream, but just kept the
ground thoroughly saturated. There was a continued though hardly
perceptible flow of earth through every crevice in the timbering during
the six or eight weeks between the driving of the top heading and the
placing of the iron lining; and here there was a settlement of from 4 to
8 ft. at the surface.
TUNNELING IN COMPRESSED AIR WITHOUT A SHIELD.
When it became evident that there would not be time for one shield to do
the soft ground portions of all four tunnels under the Long Island
Railroad station, a plan was adopted and used in Tunnel B which, while
not as rapid, turned out to be as cheap as the work done by the shields.
Figs. 6 and 7, Plate LXIII, and Fig. 1, Plate LXIV, illustrate this work
fairly well. The operation of this scheme was about as follows: Having
the iron built up to the face of the full-sized excavation, a hole or
top heading, about 3 ft. wide and 4 or 5 ft. high, was excavated to
about 10 ft. in advance. This was done in a few hours without timbering
of any kind; but, as soon as the hole or heading was 10 ft. out, 6 by
12-in. laggings or polings were put up in the roof, with the rear ends
resting on the iron lining and the leading ends resting on vertical
breast boards. The heading was then widened out rapidly and the lagging
was placed, down to about 45 deg. from the crown. The forward ends of the
laggings were then supported by a timber rib and sill. Protected by this
roof, the full section was excavated, and three rings of the iron lining
were built and grouted, and then the whole process was repeated.
[Illustration: PLATE LXIV, FIG. 1.--TUNNELING IN COMPRESSED AIR WITHOUT
SHIELD.]
[Illustration: PLATE LXIV, FIG. 2.--T-HEAD AIR-LOCK.]
[Illustration: PLATE LXIV, FIG. 3.--CUTTING EDGE OF CAISSON ASSEMBLED.]
[Illustration: PLATE LXIV, FIG. 4.--CAISSON SUPPORTED ON JACKS AND
BLOCKS.]
CONCRETE CRADLES, HAND-PACKED STONE AND GROUTING.
Had the East Avenue Tunnel been built by shields, as was contemplated at
the time of its design, the space between the limits of excavation
and the iron lining would have been somewhat less than by the method
actually used, especially in the earth portions. This space would have
been filled with grout ejected through the iron lining. The change in
the method of doing the work permitted the use of cheaper material, in
place of part of the grout, and, at the same time, facilitated the work.
The tube of cast-iron rings is adapted to be built in the tail of the
shield. Where no shield was used, after the excavation was completed and
all loose rock was removed, timbers were fixed across the tunnel from
which semicircular ribs were hung, below which lagging was placed. The
space between this and the rough rock surface was filled with concrete.
This formed a cradle in which the iron tube could be erected, and, at
the same time, occupied space which would have been filled by grout, at
greater cost, had a shield been used.
As soon as each ring of iron was erected, the space between it and the
roof of the excavation was filled with hand-packed stone. At about every
sixth ring a wall of stone laid in mortar was built between the lining
and the rock to serve as a dam to retain grout. The interstices between
the hand-packed stones were then filled with 1 to 1 grout of cement and
sand, ejected through the iron lining. The concrete cradles averaged
1.05 cu. yd. per ft. of tunnel, and cost, exclusive of materials, $6.70
per cu. yd., of which $2.25 was for labor and $4.45 was for top charges.
The hand-packed stone averaged 1-1/2 cu. yd. per ft. of tunnel, and cost
$2.42 per cu. yd., of which $0.98 was for labor and $1.44 was for top
charges.
ERECTION OF IRON LINING.
The contractors planned to erect the iron lining with erectors of the
same pattern as that used on the shield under the river, mounted on a
traveling stage. These will be described in detail in Mr. Japp's paper.
Two of these stages and erectors worked in each tunnel at different
points. The tunnel was attacked from so many points that these erectors
could not be moved from working to working. The result was that about
58% of the lining was built by hand. At first thought, this seems to be
a crude and extravagant method, as the plates weighed about 1 ton each
and about 20,000 were erected by hand. As it turned out, the cost was
not greater than for those erected by machinery, taking into account the
cost of erectors and power. This, however, was largely because the hand
erection reduced the amount of work to be done by the machines so much
that the machines had an undue plant charge.
The hand erection was very simple. A portable hand-winch, with a 3/8-in.
wire rope, was set in any convenient place. The wire rope was carried to
a snatch-block fastened to the top of the iron previously built; or,
where the roof was in soft ground, the timbering furnished points of
attachment. The end of the wire rope was then hooked to a bolt hole in a
new plate, two men at the winch lifted the plate, and three or four
others swung it into approximate place, and, with the aid of bars and
drift-pins, coaxed it into position and bolted it. Where there was no
timbering above the iron, sometimes the key and adjoining plates were
set on blocking on a timber staging and then jacked up to place.
LONG ISLAND SHAFTS.
The river shafts were designed to serve both as working shafts and as
permanent openings to the tunnels, and were larger and more substantial
than would have been required for construction purposes. Plate X of Mr.
Noble's paper shows their design. They consist of two steel caissons,
each 40 by 74 ft. in plan, with walls 5 ft. thick filled with concrete.
A wall 6 ft. thick separated each shaft into two wells 29 by 30 ft.,
each directly over a tunnel. Circular openings for the tunnel, 25 ft. in
diameter, were provided in the sides of the caissons. During the sinking
these were closed by bulkheads of steel plates backed by horizontal
steel girders. The shafts were sunk as pneumatic caissons to a depth of
78 ft. below mean high water. There have been a few caissons which were
larger and were sunk deeper than these, but most large caissons have
been for foundations, such as bridge piers, and have been stopped at or
a little below the surface of the rock. The unusual feature of the
caissons for the Long Island shaft is that they were sunk 54 ft. through
rock.
It had been hoped that the rock would prove sound enough to permit
stopping the caissons at or a little below the surface and continuing
the excavation without sinking them further; for this reason only the
steel for the lower 40 ft. of the caissons was ordered at first.
The roof of the working chamber was placed 7 ft. above the cutting edge.
It was a steel floor, designed by the contractors, and consisted of
five steel girders, 6 ft. deep, 29 ft. long, and spaced at 5-ft.
centers. Between were plates curved upward to a radius of 4 ft. Each
working chamber had two shafts, 3 ft. by 5 ft. in cross-section, with a
diaphragm dividing it into two passages, the smaller for men and the
larger for muck buckets. On top of these shafts were Moran locks.
Mounted on top of the caisson was a 5-ton Wilson crane, which would
reach each shaft and also the muck cars standing on tracks on the ground
level beside the caissons. Circular steel buckets, 2 ft. 6 in. in
diameter and 3 ft. high, were used for handling all muck. These were
taken from the bottom of the working chamber, dumped in cars, and
returned to the bottom without unhooking. Work was carried on by three
8-hour shifts per day. The earth excavation was done at the rate of
about 67 cu. yd. per day from one caisson. The rock excavation,
amounting to about 6,200 cu. yd. in each caisson, was done at the rate
of about 44.5 cu. yd. per day. The average rate of lowering, when the
cutting edge of the south caisson was passing through earth, was 0.7 ft.
per day. In rock, the rate was 0.48 ft. per day in the south caisson,
and 0.39 ft. per day in the north caisson.
At the beginning all lowering was done with sixteen hydraulic jacks.
Temporary brackets were fastened to the outside of the caisson. A
100-ton hydraulic jack was placed under each alternate bracket and under
each of the others there was blocking. The jacks were connected to a
high-pressure pump in the power-house. As the jacks lifted the caisson,
the blocking was set for a lower position, to which the caisson settled
as the jacks were exhausted. After the caisson had penetrated the earth
about 10 ft., the outside brackets were removed and the lowering was
regulated by blocking placed under brackets in the working chamber. The
caisson usually rested on three sets of blockings on each side and two
on each end. The blocking was about 4 ft. inside the cutting edge. In
the rock, as the cutting edge was cleared for a lowering of about 2 ft.,
6 by 8-in. oak posts were placed under the cutting-edge angle. When a
sufficient number of posts had been placed, the blocking on which the
caisson had rested was knocked or blasted out, and the rock underneath
was excavated. The blocking was then re-set at a lower elevation. The
posts under the cutting edge were then chopped part way through and the
air pressure was lowered about 10 lb., which increased the net weight to
more than 4,000,000 lb. The posts then gradually crushed and the
caissons settled to the new blocking. The tilt or level of the caisson
was controlled by chopping the posts more on the side which was desired
to move first.
The caisson nearly always carried a very large net weight, usually about
870 tons. The concrete in the walls, which was added as the caisson was
being sunk, was kept at about the elevation of the ground. There was
generally a depth of from 5 to 20 ft. of water ballast on top of the
roof of the working chamber. The air pressure in the working chamber was
usually much less than the hydrostatic head outside the caisson. For
example, the average air pressure in the south caisson during January,
1906, was 16-1/2 lb., while the average head was 62.5 ft., equivalent to
27 lb. per sq. in. Under these conditions, there was a continued but
small leakage into the caisson of from 15,000 to 20,000 gal. per day.
In the rock the excavation was always carried from 2 to 5 in. outside
the cutting edge. As soon as the cutting edge was cleared, bags of clay
were placed under it in a well-tiered, solid pile, so that when the
caisson was lowered the bags were cut through and most of the clay, bags
and all, was squeezed back of the cutting edge between the rock and the
caisson.
Table 1 shows the relation of the final position of the caissons to that
designed.
The cost of rock excavation in the caisson was $4.48 per cu. yd. for
labor and $10.54 for top charges.
The bottom of the shaft is an inverted concrete arch, 4 ft. thick,
water-proofed with 6-ply felt and pitch. As soon as the caisson was down
to its final position and the excavation was completed, concrete was
deposited on the uneven rock surfaces, brought up to the line of the
water-proofing, and given a smooth 1-in. mortar coat. The felt was stuck
together in 3-ply mats on the surface with hot coal-tar pitch. These
were rolled and sent down into the working chamber, where they were put
down with cold pitch liquid at 60 deg. Fahr. Each sheet of felt overlapped
the one below 6 in. The water-proofing was covered by a 1-in. mortar
plaster coat, after which the concrete of the 4-ft. inverted arch was
placed. While the water-proofing and concreting were being done, the air
pressure was kept at from 30 to 33 lb. per sq. in., the full hydrostatic
head at the cutting edge. After standing for ten days, the air pressure
was taken off, and the removal of the roof of the working chamber was
begun. The water-proofing was done by the Union Construction and
Waterproofing Company.
TABLE 1.--RELATION OF THE FINAL POSITION OF THE CAISSONS TO THAT
DESIGNED.
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LOCATION.| LONG ISLAND CITY. |
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Shaft. | North. | South. |
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Corner. | High. | East. | North. | High. | East. | North. |
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Northeast|0.21 ft.|0.08 ft.|0.05 ft.|0.32 ft.|0.15 ft.|0.28 ft.|
Northwest|0.22 " |0.08 " |0.02 " |0.00 " |0.15 " |0.12 " |
Southwest|0.27 " |0.14 " |0.02 " |0.18 " |0.45 " |0.12 " |
Southeast|0.23 " |0.14 " |0.05 " |0.39 " |0.45 " |0.28 " |
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LOCATION.| MANHATTAN. |
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Shaft. | North. | South. |
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Corner. | High. | East. | South. | High. | East or West.|North or South.|
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Northeast|0.23 ft.|0.74 ft.|0.38 ft.|0.00 ft.|0.06 ft. east.|0.04 ft. south.|
Northwest|0.00 " |0.74 " |0.22 " |0.08 " |0.06 " " |0.13 " north.|
Southwest|0.11 " |0.31 " |0.22 " |0.21 " |0.45 " west.|0.13 " " |
Southeast|0.46 " |0.31 " |0.38 " |0.04 " |0.45 " " |0.04 " south.|
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