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Title: Transactions of the American Society of Civil Engineers, vol. LXVIII, Sept. 1910 - The New York Tunnel Extension of the Pennsylvania Railroad. - The East River Tunnels. Paper No. 1159
Author: Brace, James H., Mason, Francis, Woodard, S. H.
Language: English
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*** Start of this LibraryBlog Digital Book "Transactions of the American Society of Civil Engineers, vol. LXVIII, Sept. 1910 - The New York Tunnel Extension of the Pennsylvania Railroad. - The East River Tunnels. Paper No. 1159" ***
AMERICAN 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° 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° 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° 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.
================================================================
LOCATION.| LONG ISLAND CITY. |
----------------------------------------------------------------
Shaft. | North. | South. |
----------------------------------------------------------------
Corner. | High. | East. | North. | High. | East. | North. |
----------------------------------------------------------------
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 " |
================================================================
=============================================================================
LOCATION.| MANHATTAN. |
-----------------------------------------------------------------------------
Shaft. | North. | South. |
-----------------------------------------------------------------------------
Corner. | High. | East. | South. | High. | East or West.|North or South.|
-----------------------------------------------------------------------------
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.|
=============================================================================
The cost of labor in compressed air chargeable to concreting was $3.40
per cu. yd.
After the roof of each working chamber had been removed, the shield was
erected on a timber cradle in the bottom of the shaft, in position to be
shoved out of the opening in the west side of the caisson. Temporary
rings of iron lining were erected across the shaft in order to furnish
something for the shield jacks to shove against.
The roof of the working chamber was then re-erected about 35 ft. above
its original position and about 8 ft. above the tunnel openings. This
time, instead of the two small shafts which were in use during the
sinking of the caisson, a large steel shaft with a T-head lock was
built. This is illustrated in Fig. 2, Plate LXIV. The shaft was 8 ft. in
diameter. Inside there was a ladder and an elevator cage for lowering
and hoisting men and the standard 1-yd. tunnel cars. At the top, forming
the head of the T, there were two standard tunnel locks.
MANHATTAN SHAFTS.
A permanent shaft, similar to the river shafts in Long Island City, was
constructed at Manhattan over each pair of tunnels. Each shaft was
located across two lines, with its longer axis transverse to the
tunnels. Plate XIII shows their relative positions. They were divided
equally by a reinforced concrete partition wall transverse to the line
of the tunnels. On completion, the western portions were turned over to
the contractor for the cross-town tunnels for his exclusive use.
_South Shaft._--Work on the south shaft was started on June 9th, 1904,
with the sinking of a 16 by 16-ft. test pit in the center of the south
half of the south shaft, which reached disintegrated rock at a depth of
about 20 ft.
Starting in August, the full shaft area, 74 by 40 ft., was taken out in
an open untimbered cut to the rock, and a 20 by 50-ft. shaft was sunk
through the rock to tunnel grade, leaving a 10 or 12-ft. berm around it.
(Fig. 1, Plate LXX.)
The erection of the caisson was started, about the middle of January, on
the rock berm surrounding the 20 by 50-ft. shaft and about 15 ft. below
the surface. Fig. 3, Plate LXIV, shows the cutting edge of the caisson
assembled. The excavation of the small shaft had shown that hard rock
and only a very small quantity of water would be encountered, and that
the caisson need be sunk only a short distance below the rock surface.
Therefore, no working-chamber roof was provided, the caisson was built
to a height of only 40 ft., and the circular openings were permanently
closed.
The assembling of the caisson took 2-1/2 months, and on April 2d
lowering was started. Inverted brackets were bolted temporarily to the
cutting-edge stiffening brackets, and the sinking was carried on by
methods similar to those used at Long Island. The jacks and blocking
supporting the caisson are shown in Fig. 4, Plate LXIV. As soon as the
cutting edge entered the rock, which was drilled about 6 in. outside of
the neat lines, the space surrounding the caisson was back-filled with
clay and muck to steady it and provide skin friction. As the friction
increased, the walls were filled with concrete, and as the caisson
slowly settled, it was checked and guided by blocking. The cutting edge
finally came to rest 31 ft. below mean high water, the sinking having
been accomplished in about seven weeks, at an average rate of 0.50 ft.
per day.
The final position of the cutting edge in relation to its designed
position is shown in Table 1.
A berm about 4 ft. wide was left at the foot of the caisson below which
the rock was somewhat fissured and required timbering. The cutting edge
of the caisson was sealed to the rock with grout on the outside and a
concrete base to the caisson walls on the inside, the latter resting on
the 4-ft. berm. Following the completion of the shaft, the permanent
sump was excavated to grade for use during construction.
_North Shaft._--The north shaft had to be sunk in a very restricted
area. The east side of the caisson cleared an adjoining building at one
point by only 1 ft., while the northwest corner was within the same
distance of the east line of First Avenue. As in the case of the Long
Island shafts, the steelwork for only the lower 40 ft. was ordered at
the start. This height was completely assembled before sinking was
begun. The caisson was lowered in about the same manner as those
previously described. The bearing brackets for the hydraulic jacks were
attached, as at the south shaft, to the inside of the cutting-edge
brackets. The east side of the caisson was in contact with the
foundations of the neighboring building, while the west side was in much
softer material. As a consequence, the west side tended to settle more
rapidly and thus throw the caisson out of level and position. To
counteract that tendency, it was necessary to load the east wall heavily
with cast-iron tunnel sections, in addition to the concrete filling in
the walls.
Soon after sinking was begun, a small test shaft was sunk to a point
below the elevation of the top of the tunnels. The rock was found to be
sound, hard, and nearly dry. It was then decided to stop the caisson as
soon as a foundation could be secured on sound rock. The latter was
found at a depth of 38 ft. below mean high water. With the cutting edge
seated at that depth, the top of the caisson was only 2 ft. above mean
high water, and as this was insufficient protection against high tides,
a 10-ft. extension was ordered for the top. Work, however, went on
without delay on the remainder of the excavation. The junction between
the cutting edge and the rock was sealed with concrete and grout. The
caisson was lowered at an average rate of 0.53 ft. per day. The size of
the shaft below the cutting edge was 62 ft. 7 in. by 32 ft. The average
rate of excavation during the sinking in soft material was 84 cu. yd.
per day. The average rate of rock excavation below the final position of
the cutting edge was 125 cu. yd. per day. There were night and day
shifts, each working 10 hours. Excavation in earth cost $3.96 per cu.
yd., of which $1.45 was for labor and $2.51 for top charges, etc. The
excavation of rock cost $8.93 per cu. yd., $2.83 being for labor and
$6.10 for top charges.
The final elevations of the four corners of the cutting edge, together
with their displacement from the desired positions, are shown in Table
1.
RIVER TUNNELS.
The four river tunnels, between the Manhattan and Long Island City
shafts, a distance of about 3,900 ft., were constructed by the shield
method. Eight shields were erected, one on each line in each shaft, the
four from Manhattan working eastward to a junction near the middle of
the river with the four working westward from Long Island City. Toward
the end of the work it was evident that the shields in Tunnels _B_, _C_,
and _D_ would meet in the soft material a short distance east of the
Blackwell's Island Reef if work were continued in all headings. In order
that the junction might be made in firm material, work from Manhattan in
those three tunnels was suspended when the shields reached the edge
of the ledge. The shields in Tunnel _A_ met at a corresponding point
without the suspension of work in either. An average of 1,760 ft. of
tunnel was driven from Manhattan and 2,142 ft. from Long Island City.
[Illustration: PLATE LXV, FIG. 1.--SHIELD FITTED WITH SECTIONAL SLIDING
HOODS AND SLIDING EXTENSIONS TO THE FLOORS.]
[Illustration: PLATE LXV, FIG. 2.--SHIELD FITTED WITH FIXED HOODS AND
FIXED EXTENSIONS TO THE FLOORS.]
TUNNELS DRIVEN EASTWARD FROM MANHATTAN.
_Materials and Inception of Work._--The materials encountered are shown
in the profile on Plate XIII, and were similar in all the tunnels. In
general, they were found to be about as indicated in the preliminary
borings. The materials met in Tunnel _A_ may be taken as typical of all.
From the Manhattan shaft eastward, in succession, there were 123 ft. of
all-rock section, 87 ft. of part earth and part rock, 723 ft. of all
earth, 515 ft. of part rock and part earth, 291 ft. of all rock, and 56
ft. of part rock and part earth.
The rock on the Manhattan side was Hudson schist, while that in the reef
was Fordham gneiss. Here, as elsewhere, they resembled each other
closely; the gneiss was slightly the harder, but both were badly seamed
and fissured. Wherever it was encountered in this work, the rock surface
was covered by a deposit of boulders, gravel, and sand, varying in
thickness from 4 to 10 ft. and averaging about 6 ft.
The slope of the surface of the ledge on the Manhattan side averaged
about 1 vertical to 4 horizontal. The rock near the surface was full of
disintegrated seams, and was badly broken up. It was irregularly
stratified, and dipped toward the west at an angle of about 60 degrees.
Large pieces frequently broke from the face and slid into the shield,
often exposing the sand. The rock surface was very irregular, and was
covered with boulders and detached masses of rock embedded in coarse
sand and gravel. The sand and gravel allowed the air to escape freely.
By the time the shields had entirely cleared the rock, the material in
the face had changed to a fine sand, stratified every few inches by very
thin layers of chocolate-colored clayey material. This is the material
elsewhere referred to as quicksand. As the shield advanced eastward, the
number and thickness of the layers of clay increased until the clay
formed at least 20% of the entire mass, and many of the layers were 2
in. thick.
At a distance of about 440 ft. beyond the Manhattan ledge, the material
at the bottom of the face changed suddenly to one in which the layers
of clay composed probably 98% of the whole. The sand layers were not
more than 1/16 in. thick and averaged about 2 in. apart. The surface of
the clay rose gradually for a distance of 40 ft. in Tunnels _A_ and _B_,
and 100 ft. in Tunnels _C_ and _D_, when gravel and boulders appeared at
the bottom of the shield. At that time the clay composed about one-half
of the face.
The surfaces of both the clay and gravel were irregular, but they rose
gradually. After rock was encountered, the formations of gravel and clay
were roughly parallel to the rock surface.
As the surface of the rock rose they disappeared in order and were again
encountered when the shields broke out of rock on the east side of the
Blackwell's Island Reef. East of the reef a large quantity of coarse
open sand was present in the gravel formations before the clay appeared
below the top of the cutting edge. In Tunnels _C_ and _D_ this was
especially difficult to handle. It appears to be a reasonable assumption
that the layer of clay was continuous across the reef. Wherever the clay
extended above the top of the shield it reduced the escape of air
materially. It is doubtless largely due to this circumstance that the
part-rock sections in the reef were not the most difficult portions of
the work.
While sinking the lower portions of the shafts the tunnels were
excavated eastward in the solid rock for a distance of about 60 ft.,
where the rock at the top was found to be somewhat disintegrated. This
was as far as it was considered prudent to go with the full-sized
section without air pressure. At about the same time top headings were
excavated westward from the shafts for a distance of 100 ft., and the
headings were enlarged to full size for 50 ft. The object was to avoid
damage to the shaft and interference with the river tunnel when work was
started by the contractor for the cross-town tunnel.
[Illustration: PLATE LXVI, FIG. 1.--REAR OF SHIELD SHOWING COMPLETE
FITTINGS.]
[Illustration: PLATE LXVI, FIG. 2.--SHIELD WITH LOWER PORTION OF
BULKHEAD REMOVED.]
The shields were erected on timber cradles in the shaft, and were shoved
forward to the face of the excavation. Concrete bulkheads, with the
necessary air-locks, were then built across the tunnels behind the
shields. The shields were erected before the dividing walls between the
two contracts were placed. Rings of iron tunnel lining, backed by
timbers spanning the openings on the west side, were erected temporarily
across the shafts in order to afford a bearing for the shield jacks
while shoving into the portals. The movement of the shield eastward was
continued in each tunnel for a distance of about 60 ft., and the
permanent cast-iron tunnel lining was erected as the shield advanced.
Before breaking out of rock, it was necessary to have air pressure in
the tunnels. This required the building of bulkheads with air-locks
inside the cast-iron linings just east of the portals. Before erecting
the bulkheads it was necessary to close the annular space between the
iron tunnel lining and the rock. The space at the portal was filled with
a concrete wall. After about twenty permanent rings had been erected in
each tunnel, two rings were pulled apart at the tail of the shield and a
second masonry wall or dam was built. The space between the two dams was
then filled with grout. To avoid the possibility of pushing the iron
backward after the air pressure was on, rings of segmental plates, 5/8
in. thick and 13-7/8 in. wide, were inserted in eighteen circumferential
joints in each tunnel between the rings as they were erected. The plates
contained slotted holes to match those in the segments. After the rings
left the shield, the plates were driven outward, and projected about 5
in. When the tunnel was grouted, the plates were embedded.
The bulkheads were completed, and the tunnels were put under air
pressure on the following dates:
Line _D_, on October 5th, 1905;
Line _C_, on November 6th, 1905;
Line _B_, on November 25th, 1905;
Line _A_, on December 1st, 1905.
This marked the end of the preparatory period.
In the deepest part of the river, near the pier-head line on the
Manhattan side, there was only 8 ft. of natural cover over the tops of
the tunnels. This cover consisted of the fine sand previously described,
and it was certain that the air would escape freely from the tunnels
through it. To give a greater depth of cover and to check the loss of
air, the contractor prepared to cover the lines of the tunnels with
blankets of clay, which, however, had been provided for in the
specifications. Permits, as described later, were obtained at different
times from the Secretary of War, for dumping clay in varying thicknesses
over the line of work. The dumping for the blanket allowed under the
first permit was completed in February, 1906. The thickness of this
blanket varied considerably, but averaged 10 or 12 ft. on the Manhattan
side. The original blanket was of material advantage, but the depth of
clay was insufficient to stop the loss of air.
The essential parts of the shields in the four tunnels were exactly
alike. Those in Tunnels _B_ and _D_, however, were originally fitted
with sectional sliding hoods and sliding extensions to the floors of the
working chambers, as shown by Fig. 1, Plate LXV. The shields in Tunnels
_A_ and _C_ were originally fitted with fixed hoods and fixed extensions
to the floors, as shown in Fig. 2, Plate LXV. A full description of the
shields will be found in Mr. Japp's paper.
The shields in each pair of tunnels were advanced through the solid rock
section about abreast of each other, until test holes from the faces
indicated soft ground within a few feet. As the distance between the
sides of the two tunnels was only 14 ft., it was thought best to let
Tunnels _B_ and _D_ gain a lead of about 100 ft. before Tunnels _A_ and
_C_ opened out into soft ground, in order that a blow from one tunnel
might not extend to the other. Work in Tunnel _C_ was shut down on
December 23d, 1905, after exposing sand to a depth of 3 ft. at the top,
and it remained closed for seven weeks. Work in Tunnel _A_ was suspended
on September 29th, 1905. By the time Tunnel _B_ had made the required
advance, it, together with Tunnels _C_ and _D_, was overtaxing the
capacities of the compressor plant. Only a little work was done in
Tunnel _C_ until July, 1906, and work in Tunnel _A_ was not resumed
until October 22d, 1906.
TUNNELS DRIVEN WESTWARD FROM LONG ISLAND CITY.
_Materials and Inception of the Work._--The materials met in Tunnel A
are typical of all four tunnels. From the Long Island shafts westward,
in succession, there were 124 ft. of all-rock section, 125 ft. of part
rock and part earth section, 22 ft. of all-rock section, 56 ft. of part
rock and part earth section, 387 ft. of all-rock section, 70 ft. of part
earth and part rock section, and 1,333 ft. of all-earth section.
[Illustration: PLATE LXVII]
The materials passed through are indicated on Plate XIII. The rock was
similar to that of the Blackwell's Island Reef, and was likewise covered
by a layer of sand and boulders. The remainder of the soft ground was
divided into three classes. The first was a very fine red sand, which
occurred in a layer varying in thickness from 6 ft. to at least 15 ft.
It may have been much deeper above the tunnel. It is the quicksand
usually encountered in all deep foundations in New York City. The
following is the result of the sifting test of this sand:
Held on No. 30 sieve 0.6%
Passed No. 30, " " No. 40 " 0.4%
" No. 40, " " No. 50 " 0.7%
" No. 50, " " No. 60 " 2.4%
" No. 60, " " No. 80 " 14.9%
" No. 80, " " No. 100 " 54.0%
" No. 100, " " No. 200 " 8.0%
" No. 200 " 19.0%
------
100.0%
This means that grains of all but 4% of it were less than 0.0071 in. in
diameter. The 19% which passed the No. 200 sieve, the grains of which
were 0.0026 in. or less in diameter, when observed with a microscope
appeared to be perfectly clean grains of quartz; to the eye it looked
like ordinary building sand, sharp, and well graded from large to small
grains. This sand, with a surplus of water, was quick. With the water
blown out of it by air pressure, it is stable, stands up well, and is
very easy to work. It appears to be the same as the reddish quicksand
found in most deep excavations around New York City.
The second material was pronounced "bull's liver" by the miners as soon
as it was uncovered. "Bull's liver" seems to be a common term among
English-speaking miners the world over. It is doubtful, however, if it
is always applied to the same thing. In this case it consisted of layers
of blue clay and very fine red sand. The clay seemed to be perfectly
pure and entirely free from sand. It would break easily with a clean,
almost crystalline, fracture, and yet it was soft and would work up
easily. The layers of clay varied in thickness from 1/16 in. to 1 in.,
while the thickness of the sand layer varied from 1/4 in. to several
inches. The sand was the same as the quicksand already described.
The "bull's liver" was ideal material in which to work a shield. It
stood up as well and held the air about as well as clay, and was much
easier to handle.
The third material was a layer of fine gray sand which was encountered
in the top of all the tunnels for about 400 ft. just east of Blackwell's
Island Reef. It was very open, and had grains of rather uniform size.
During the starting out of the tunnels from the shafts, and for more
than a year afterward, the roof of the working chamber in the caissons
and the locks previously described under the Long Island shafts took the
place of the bulkhead across the tunnels for confining the air pressure.
The first work in air pressure was to remove the shield plug closing the
opening in the side of the shaft. This being done, the shield was shoved
through the opening, and excavation begun.
At the start the shields were fitted with movable platforms, but no
hoods of any kind were placed until after the rock excavation was
completed.
METHODS OF EXCAVATION.
The distribution of materials to be excavated, as previously outlined,
divided the excavation into three distinct classes, for which different
methods had to be developed.
These three classes were:
_First._--All-rock section.
_Second._--Rock in the bottom, earth in the top.
_Third._--All-earth section.
The extent of the second and third classes was much greater than that of
the first, and they, of course, determined the use of the shield.
Shields had not previously been used extensively in rock work, either
where the face was wholly or partly in rock, and it was necessary to
develop the methods by experience. The specifications required that
where rock was present in the bottom, a bed of concrete should be laid
in the form of a cradle on which to advance the shield.
_All Rock._--At different times, three general methods were used for
excavating in all-rock sections. They may be called: The bottom-heading
method; the full-face method; and the center-heading method.
The bottom-heading method was first tried. A heading, about 8 ft. high
and 12 ft. wide, was driven on the center line, with its bottom as
nearly as possible on the grade line of the bottom of the tunnel. It was
drilled in the ordinary manner by four drills mounted on two columns.
The face of the headings varied from 10 to 30 ft. in advance of the
cutting edge. After driving the heading for about 10 ft., the bottom was
cleared out and a concrete cradle was set. The width of the cradles
varied, but was generally from 8 to 10 ft.
The excavation was enlarged to full size as the shield advanced, the
drills being mounted in the forward compartments of the shield, as
shown by Fig. 1, Plate LXVII, which represents the conditions after the
opening had been cut in the bulkhead, but before the new methods,
mentioned later, had been developed.
[Illustration: PLATE LXVIII]
The sides and top were shot downward into the heading. The area of the
face remaining behind the heading was large, and a great number of holes
and several rounds were required to fire the face to advantage. As soon
as firing was started at the face, the heading was completely blocked,
and operations there had to be suspended until the mucking was nearly
completed. The bottom-heading method was probably as good as any that
could be devised for use with the shields as originally installed. All
the muck had to be taken from the face by hand and handled through the
chutes or doors. By drilling from the shield, some muck was blasted on
to the extensions of the floors and could be handled from the upper
compartments. At best, however, the shield with the closed transverse
bulkhead was a serious obstacle to rapid work in rock sections.
The full-face method was only used where the rock was not considered
safe for a heading. A cut was fired at the bottom, together with side
holes, in a manner quite similar to that adopted in the first set of
holes for a bottom heading. The cradle was then placed, in lengths of
either 2.5 or 5 ft., after which the remainder of the face was fired in
the same manner as for the bottom-heading method. The closed transverse
bulkhead with air-locks, as shown in Fig. 1, Plate LXVI, was placed in
the shield in the hope that it would only be necessary to maintain the
full air pressure in the working compartments in front of the bulkhead.
It was also thought that some form of bulkhead which could be closed
quickly and tightly would be necessary to prevent flooding the tunnel in
case of blows. While no attempt was ever made to reduce the pressure
behind the shield bulkhead, it was obvious from the experience with
Tunnels _B_ and _D,_ while working in the sand between Manhattan and the
reef, that the plan was not practicable, and that the closed bulkhead in
the bottom was a hindrance instead of a safeguard. As soon as rock was
encountered in those tunnels at the west edge of the reef, the
contractor cut through the bulkheads and altered them, as shown in Fig.
2, Plate LXVI.
Taking advantage of the experience gained, openings were cut through the
bulkheads in Shields _A_ and _C_, while they were shut down near the
edge of the Manhattan ledge. In erecting the shields at Long Island
City in May and June, 1906, openings were also provided. These shields
had to pass through about 700 ft. of rock at the start, the greater
portion of which was all-rock section. It was at that point that
openings were first used extensively and methods were developed, which
would not have been possible except where ears could be passed through
the shield. The bottom-heading method was first tried, but the working
space in front of the shield was cramped, and but few men could be
employed in loading the cars. To give more room, the heading was
gradually widened. The enlargement at the top, when made from the
shield, blocked all work at the face of the heading while the former
operation was in progress. To reduce the delays, the heading was raised,
thus reducing the quantity of rock left in the top, and the bottom was
taken out as a bench. To avoid blocking the tracks when firing the top,
a heavy timber platform was built out from the floors of the middle
working compartments. Most of the muck from the top was caught on the
platform and dropped into cars below. This method of working is shown by
Fig. 2, Plate LXVII. The platforms were not entirely satisfactory, and,
later, the drills in the heading were turned upward and a top bench was
also drilled and fired, as shown by Fig. 3, Plate LXVII. There was then
so little excavation left in the top that the muck was allowed to fall
on the tracks and was quickly cleared away. The method just outlined is
called the center-heading method, and was the most satisfactory plan
devised for full-rock sections.
_Excavation in Part Rock and Part Earth._--This was probably the most
difficult work encountered, particularly when the rock was covered with
boulders and coarse sharp sand which permitted a free escape of air. It
was necessary, before removing the rock immediately under the soft
ground, to excavate the earth in advance of the shield to a point beyond
where the rock was to be disturbed, and to support, in some way, the
roof, sides, and face of the opening thus made. The hoods were designed
mainly for the purpose of supporting the roof and the sides. With the
fixed hood it was necessary either to excavate for the distance of the
desired shove in front of it or else to force the hood into the
undisturbed material. To avoid this difficulty, the sliding hoods were
tried as an experiment.
In using the sliding hood, which will be described in detail in Mr.
Japp's paper, the segments commencing at the top were forced forward by
the screw rod, one at a time, as far as possible into the undisturbed
material. Just enough material was then removed from underneath and in
front of the section to free it, and it was again forced forward. These
operations were repeated until the section had been extended far enough
for a shove. As soon as two or three sections had been pushed forward in
this way, the face near the advance end of the sliding hood was
protected by a breast board set on edge and braced from the face.
Gradually, all the segments were worked forward, and, at the same time,
the whole soft ground face was sheeted with timber. At times polings
were placed over the extended segments in order to make room for a
second shove, as shown on Plate LXVIII. When the shield was advanced the
nuts on the screw rods were loosened and the sections of the hoods were
telescoped on to the shield. The idea was ingenious, but proved
impracticable, because of the unequal relative movements of the top and
bottom of the shield in shoving, bringing transverse strains on the hood
sections.
[Illustration: PLATE LXIX]
With the fixed hood, poling boards were used to support the roof and
sides, and the face was supported in the manner described for the
sliding hoods. The polings were usually maple or oak planks, 2 in.
thick, about 8 in. wide, and 6-1/2 ft. long. In advancing the face, the
top board of the old breast was first removed, then the material was
carefully worked out for the length of the poling. The latter was then
placed, with the rear end resting over the hood and the forward end
forced as far as possible into the undisturbed material. When two or
three polings had been placed, a breast board was set. After several
polings were in position, their forward ends were supported by some form
a cantilever attached to the hood. Plate LXIX shows one kind of
supports. In this way all the soft material was excavated down to the
rock surface, and the roof, sides, and face were sheeted with timber. In
shoving, the polings in the roof and sides were lost. It was found that
the breast could usually be advanced 5 ft. with safety. The fixed hood
made it possible to set the face about 7 or 8 ft. in front of the
cutting edge without increasing the length of the polings. This distance
was ample for two shoves, and was generally adopted, although a great
many faces were set for one shove only.
Fixed hoods were substituted for those of the sliding type, originally
placed on Shields _B_ and _D_ at Manhattan, at about the time the latter
encountered the rock at the reef.
In placing the polings and breasting, all voids behind them were filled
as far as possible with marsh hay or bags of sawdust or clay. To prevent
loss of air in open material, the joints between the boards were
plastered with clay especially prepared for the purpose in a pug mill.
The sliding extensions to the floors of the working compartments were
often used, in the early part of the work, to support the timber face or
loose rock, as shown in Fig. 1, Plate LXVIII. At such times the front of
the extensions was held tightly against the planking by the pressure of
the floor jacks. While shoving, the pressure on the floor jacks was
gradually released, allowing the floors to slide back into the shield
and still afford support to the face. The extensions also afforded
convenient working platforms. They were subject to severe bending
strains while the shield was being shoved, however, and the cast-iron
rams were frequently broken or jammed. The extensions did not last
beyond the edge of the ledge at Manhattan, nor more than about half
through the rock work at Long Island City. The fixed extensions
originally placed on Shields _A_ and _C_ at Manhattan were not
substantial enough, and lasted only a few days.
Wherever the rock face was sufficiently sound and high, a bottom heading
was driven some 20 or 30 ft. in advance of the shield. The heading was
driven and the cradle placed independently of the face of the soft
ground above, and in the manner described for all-rock sections. The
remainder of the rock face was removed by firing top and side rounds
into the bottom heading after the soft ground had been excavated. Great
care had to be taken in firing in order not to disturb the timber work
or break the rock away from under the breast boards. If either occurred,
a serious run was likely to follow. The bottom-heading method is shown
by Figs. 1, 2, and 3, Plate LXVIII, and the breasting and poling by Fig.
2, Plate LXX.
In the early part of the work, where a bottom heading was impracticable,
the soft ground was first excavated as described above, and the rock was
drilled by machines mounted on tripods, and fired as a bench. By this
plan no drilling could be done until the soft ground was removed. This
is called the rock-bench method.
Later the rock-cut method was devised. Drills were set up on columns in
the bottom compartments of the shield, and the face was drilled while
work was in progress on the soft ground above. The drilling was done
either for a horizontal or vertical cut and side and top rounds. The
drillers were protected while at work by platforms of timber built out
from the floors of the compartments above. This plan, while probably not
quite as economical of explosives, saved nearly all the delay due to
drilling the bench.
[Illustration: PLATE LXX, FIG. 1.--SMALL SHAFT SUNK TO ROCK.]
[Illustration: PLATE LXX, FIG. 2.--BREASTING AND POLING IN FRONT OF
SHIELD.]
[Illustration: PLATE LXX, FIG. 3.--SHUTTERS ON FRONT OF SHIELD.]
[Illustration: PLATE LXX, FIG. 4.--HYDRAULIC ERECTOR PLACING SEGMENT.]
_All-Earth Section._--As described by Messrs. Hay and Fitzmaurice, in a
paper on the Blackwall Tunnel,[C] the contractor had used, with marked
success, shutters in the face of the shield for excavating in loose open
material. He naturally adopted the method for the East River work. When
the shields in Tunnels _B_ and _D_, at Manhattan, the first to be driven
through soft ground, reached a point under the actual bulkhead line,
work was partly suspended and shutters were put in place in the face of
the top and center compartments. The shutters in the center compartments
in Shield _D_ are shown in Fig. 3, Plate LXX, while the method of work
with the shutters is shown by Figs. 4, 5, 6, and 7, Plate LXVIII. Fig. 4
on that plate shows the shield ready for a shove. As the pressure was
applied to the shield jacks, men loosened the nuts on the screws holding
the ends of the shutters, and allowed the latter to slide back into the
working compartments. At the end of the shove, the shutters were in the
position shown in Fig. 5, Plate LXVIII. In preparing for a new shove,
the slides in the shutters were opened, and the material in front was
raked into the shield. At the same time, the shutters were gradually
worked forward. The two upper shutters in a compartment were generally
advanced from 12 to 15 in., after which the muck could be shoveled out
over the bottom shutters, as shown on Fig. 6, Plate LXVIII, and Fig. 3,
Plate LXX. No shutters were placed in the bottom compartments, and as
the air pressure was not generally high enough to keep the face dry at
the bottom, these compartments were pretty well filled with the soft,
wet quicksand. Just before shoving, this material was excavated to a
point where it ran in faster than it could be taken out. Much of the
excavation in the bottom compartment was done by the blow-pipe. During
the shove the material from the bottom compartment often ran back
through the open door in the transverse bulkhead, as shown by Fig. 5,
Plate LXVIII.
In the Blackwall Tunnel the material was reported to have been loose
enough to keep in close contact with the shutters at all times. In the
East River Tunnels this was not the case. The sand at the top was dry
and would often stand with a vertical face for some hours. In advancing
the shutters, it was difficult to bring them into close contact with the
face at the end of the operation. The soft material at the bottom was
constantly running into the lower compartment and undermining the stiff
dry material at the top. The latter gradually broke away, and, at times,
the actual face was some feet in advance of the shutters. Under those
circumstances, the air escaped freely through the unprotected sand face.
The joints of the shutters were plastered with clay, but this did not
keep the air from passing out through the lower compartments. This
condition facilitated the formation of blows, which were of constant
occurrence where shutters were used in the sand. In Tunnels _B_ and _D_,
at Manhattan, the shutters were used in the above manner clear across to
the reef. In Tunnel _C_, which was considerably behind Tunnels _B_ and
_D_, the shutters, although placed, were never used against the face,
and the excavation was carried on by poling the top and breasting the
face. The change resulted in much better progress and fewer blows. The
excavation through the soft material in Tunnel _C_ had just been
completed when Tunnel _A_ was started, and the gangs of workmen were
exchanged.
The work in soft ground in Tunnel _A_ thus gained the benefit of the
experience in Tunnel _C_. Shutters were placed only in the top
compartments in this tunnel, and, as in Tunnel _C_, were never used in
contact with the face. The method of work is shown by Figs. 1, 2, and 3,
Plate LXXI. The result was still more rapid progress in Tunnel _A_, and
although the loss of air was fully as great in this tunnel as in the
other three, there was only one blow which caused any considerable loss
of pressure. In Tunnels _A_ and _C_ the diaphragms in the rear of the
center compartments of the lower tiers of working chambers were removed
before the shields entered the soft ground. The change was not of as
much advantage in soft ground as in rock, but it facilitated the removal
of the soft wet sand in the bottom. In Tunnel _A_, after encountering
gravel, a belt conveyor was suspended from the traveling stage with one
end projecting through the opening into the working compartment. The use
of the conveyor made it possible to continue mucking at the face while
the bottom plates of the iron lining were being put in place, and
resulted in a material increase in the rate of progress.
[Illustration: PLATE LXXI]
The shutters were not placed on the Long Island shields at all. Just
before the shields passed into all soft ground, a fixed hood was
attached to each.
The method of working in soft ground from Long Island City is
illustrated by Plate LXXII. The full lines at the face of the shield
show the position of the earth before a shove of the shield, and the
dotted lines show the same after the shove. The face was mined out to
the front of the hood and breasted down to a little below the floor of
the top pockets of the shield. In the middle pocket the earth was
allowed to take its natural slope back on the floor. Toward the rear of
the bottom pockets it was held by stop-planks. The air pressure was
always about equal to the hydrostatic head at the middle of the shield,
so that the face in the upper and middle pockets was dry. In the lower
pockets it was wet, and flowed under the pressure of shoving the shield.
By this method 4,195 lin. ft. of tunnel was excavated by the four Long
Island shields in 120 days, from November 1st, 1907, to March 1st, 1908.
This was an average of 8.74 ft. per day per shield.
The rate of progress, the nature of the materials, and the methods
adopted are shown in Table 2.
_Preparations for Junction of Shields._--As previously mentioned, the
Manhattan shields were stopped at the edge of the reef. Before making
the final shove of those shields, special polings were placed with
unusual care. The excavation was bell-shaped to receive the Long Island
shields. The arrangement of the polings is shown by Figs. 4 and 5, Plate
LXXI. After the shields were shoved into final position, as shown at the
right in Fig. 5, the rear end of the polings rested over the cutting
edge and allowed room for the removal of the hood. After the latter had
been accomplished, the temporary bulkheads of concrete and clay bags
were built as a precaution against blows when the shields were close
together. An 8-in. pipe was then driven forward through the bulkhead for
distances varying from 30 to 100 ft., in order to check the alignment
and grade between the two workings before the shields were actually
shoved together. The errors in the surveys were negligible, but here, as
elsewhere, the shields were not exactly in the desired position, and it
took careful handling to bring the cutting edges together. The Long
Island shields were driven to meet those from Manhattan.
TABLE 2.--RATE OF PROGRESS, NATURE OF MATERIALS, AND METHODS ADOPTED IN
CONSTRUCTION OF EAST RIVER TUNNELS.
LINE A, LONG ISLAND.
--------------+-----------------+-------------------+-------------------------+
| | Station: | Date: |
| |---------+---------+------------+------------+
| | | | | |
Material. | Method. | From | To | From | To |
--------------+-----------------+---------+---------+------------+------------+
All rock |Bottom heading | 69+39.9 | 69+79 |Aug. 2, '06|Sept 25, '06|
| | | | | |
All rock |Center heading | 69+79 | 70+64 |Sept 25, '06|Nov. 21, '06|
| | | | | |
Earth and rock|Center heading | 70+64 | 71+34 |Nov. 21, '06|Dec. 30, '06|
| | | | | |
Earth and rock|Bottom heading | 71+34 | 71+89 |Dec. 30, '06|Feb. 13, '07|
| | | | | |
All rock |Bottom heading | 71+89 | 72+11 |Feb. 13, '07|Feb. 21, '07|
| | | | | |
Earth and rock|Center heading | 72+11 | 72+67 |Feb. 21, '07|Mar. 19, '07|
| | | | | |
All rock |Center heading | 72+67 | 76+54 |Mar. 19, '07|Sept 6, '07|
| | | | | |
Earth and rock|Going out of rock| 76+54 | 77+24 |Sept 6, '07|Oct. 4, '07|
| | | | | |
All earth |Soft ground | 77+24 | 90+57.3 |Oct. 4, '07|Mar. 26, '08|
--------------+-----------------+---------+---------+------------+------------+
--------------+------+--------+--------+--------------------------------------+
| | |Rate of | |
|Number| |progress| |
| of | Linear |in feet | |
Material. | days.| feet. |per day.| Remarks |
--------------+------+--------+--------+--------------------------------------+
All rock | 54 | 39.1 | 0.724 | |
| | | | |
All rock | 57 | 85 | 1.49 | |
| | | | |
Earth and rock| 39 | 70 | 1.79 | |
| | | | |
Earth and rock| 45 | 55 | 1.22 | |
| | | | |
All rock | 8 | 22 | 2.75 | |
| | | | |
Earth and rock| 26 | 56 | 2.15 | |
| | | | |
All rock | 171 | 387 | 2.26 | |
| | | | |
Earth and rock| 28 | 70 | 2.50 | |
| | | | |
All earth | 174 |1,333.3 | 7.66 | |
--------------+------+--------+--------+--------------------------------------+
LINE B, LONG ISLAND.
--------------+-----------------+-------------------+-------------------------+
| | Station: | Date: |
| |---------+---------+------------+------------+
| | | | | |
Material. | Method. | From | To | From | To |
--------------+-----------------+---------+---------+------------+------------+
All rock |Bottom heading | 69+29.6 | 70+46 |Oct. 16, '06|Nov. 20, '06|
| | | | | |
Earth and rock|Bottom heading | 70+46 | 71+95 |Nov. 20, '06|Feb. 23, '07|
| | | | | |
All rock |Bottom heading | 71+95 | 72+25 |Feb. 23, '07|Mar. 6, '07|
| | | | | |
Earth and rock|Center heading | 72+25 | 72+60 |Mar. 6, '07|Mar. 24, '07|
| | | | | |
All rock |Going out of rock| 72+60 | 76+57 |Mar. 24, '07|Aug. 7, '07|
| | | | | |
Earth and rock|Soft ground | 76+57 | 77+30 |Aug. 7, '07|Sept 5, '07|
| | | | | |
All earth |Soft ground | 77+30 | 90+49.6 |Sept 5, '07|Mar. 19, '08|
--------------+-----------------+---------+---------+------------+------------+
--------------+------+--------+--------+--------------------------------------+
| | |Rate of | |
|Number| |progress| |
| of | Linear |in feet | |
Material. | days.| feet. |per day.| Remarks |
--------------+------+--------+--------+--------------------------------------+
All rock | 35 | 116.4 | 3.33 | |
| | | | |
Earth and rock| 95 | 149 | 1.57 | |
| | | | |
All rock | 11 | 30 | 2.73 | |
| | | | |
Earth and rock| 18 | 35 | 1.94 | |
| | | | |
All rock | 136 | 397 | 2.92 | |
| | | | |
Earth and rock| 29 | 73 | 2.52 | |
| | | | |
All earth | 196 |1,319.6 | 6.73 | |
--------------+------+--------+--------+--------------------------------------+
LINE C, LONG ISLAND.
--------------+-----------------+-------------------+-------------------------+
| | Station: | Date: |
| |---------+---------+------------+------------+
| | | | | |
Material. | Method. | From | To | From | To |
--------------+-----------------+---------+---------+------------+------------+
All rock |Bottom heading | 68+61.9 | 69+93 |June 11, '06|Oct. 16, '06|
| | | | | |
Earth and rock|Bottom heading | 69+93 | 71+65 |Oct. 16, '06|Feb. 7, '07|
| | | | | |
All rock |Bottom heading | 71+65 | 71+91 |Feb. 7, '07|Feb. 13, '07|
| | | | | |
All rock |Center heading | 71+91 | 75+81 |Feb. 13, '07|July 20, '07|
| | | | | |
Earth and rock|Going out of rock| 75+81 | 76+56 |July 20, '07|Aug. 25, '07|
| | | | | |
All earth |Soft ground | 76+56 | 90+44.4 |Aug. 25, '07|Mar. 17, '08|
--------------+-----------------+---------+---------+------------+------------+
--------------+------+--------+--------+--------------------------------------+
| | |Rate of | |
|Number| |progress| |
| of | Linear |in feet | |
Material. | days.| feet. |per day.| Remarks |
--------------+------+--------+--------+--------------------------------------+
All rock | 127 | 131.1 | 1.03 | |
| | | | |
Earth and rock| 114 | 172 | 1.51 | |
| | | | |
All rock | 6 | 26 | 4.33 | |
| | | | |
All rock | 157 | 390 | 2.48 | |
| | | | |
Earth and rock| 36 | 75 | 2.08 | |
| | | | |
All earth | 205 |1,388.4 | 6.77 | |
--------------+------+--------+--------+--------------------------------------+
LINE D, LONG ISLAND.
--------------+-----------------+-------------------+-------------------------+
| | Station: | Date: |
| |---------+---------+------------+------------+
| | | | | |
Material. | Method. | From | To | From | To |
--------------+-----------------+---------+---------+------------+------------+
Rock |Bottom heading | 68+50.6 | 69+77 |June 2, '06|Oct. 24, '06|
| | | | | |
Earth and rock|Bottom heading | 69+77 | 71+22 |Oct. 24, '06|Jan. 13, '06|
| | | | | |
All rock |Bottom heading | 71+23 | 72+00 |Jan. 13, '07|Mar. 3, '07|
| | | | | |
All rock |Center heading | 72+00 | 75+73 |Mar. 3, '07|July 10, '07|
| | | | | |
Earth and rock|Going out of rock| 75+73 | 77+63 |July 10, '07|Sept 25, '07|
| | | | | |
All earth |Soft ground | 77+63 | 90+38.6 |Sept 25, '07|Mar. 7. '08|
--------------+-----------------+---------+---------+------------+------------+
--------------+------+--------+--------+--------------------------------------+
| | |Rate of | |
|Number| |progress| |
| of | Linear |in feet | |
Material. | days.| feet. |per day.| Remarks |
--------------+------+--------+--------+--------------------------------------+
Rock |144 | 126.4 | 0.87 | |
| | | | |
Earth and rock| 81 | 145 | 1.79 | |
| | | | |
All rock | 49 | 78 | 1.59 | |
| | | | |
All rock |129 | 373 | 2.89 | |
| | | | |
Earth and rock| 77 | 190 | 2.47 | |
| | | | |
All earth |164 |1,275.6 | 7.78 | |
--------------+------+--------+--------+--------------------------------------+
LINE A, MANHATTAN.
--------------+-----------------+-------------------+-------------------------+
| | Station: | Date: |
| |---------+---------+------------+------------+
| | | | | |
Material. | Method. | From | To | From | To |
--------------+-----------------+---------+---------+------------+------------+
{|Top heading |108+43 |107+74 |July 20, '05|Aug. 3, '05|
Rock {|Top lift of bench|108+43 |107+74 |Aug. 8, '05|Aug. 23, '05|
{|Bottom lift of |108+43 |107+74 |Aug. 30, '05|Sept 27, '05|
{| bench | | | | |
| | | | | |
Rock {|Bottom heading |107+74 |107+21 |Sept 27, '05|Oct. 23, '05|
{|Bottom heading |107+74 |107+21 |Nov. 30, '05|Dec. 29, '05|
| | | | | |
Mixed |Bottom heading |107+21 |106+99 |Oct. 26, '06|Nov. 20, '06|
| | | | | |
Mixed |Rock bench |106+99 |106+34 |Nov. 20, '06|Jan. 13, '07|
| | | | | |
Earth |Poling and |106+34 | 99+11 |Jan. 13, '07|Apr. 17, '07|
| breasting | | | | |
| | | | | |
Mixed |Rock cut | 99+11 | 93+96 |Apr. 17, '07|Oct. 24, '07|
| | | | | |
Rock |Bottom heading | 93+96 | 93+58 |Oct. 24, '07|Nov. 14, '07|
| | | | | |
Rock |Center heading | 93+58 | 92+42 |Nov. 14, '07|Dec. 27, '07|
| | | | | |
Rock |Bottom heading | 92+42 | 91+05 |Dec. 27, '07|Feb. 24, '08|
| | | | | |
Mixed |Rock cut | 91+05 | 90+57 |Feb. 24, '08|Mar. 20, '08|
--------------+-----------------+---------+---------+------------+------------+
--------------+------+--------+--------+--------------------------------------+
| | |Rate of | |
|Number| |progress| |
| of | Linear |in feet | |
Material. | days.| feet. |per day.| Remarks |
--------------+------+--------+--------+--------------------------------------+
{| 14} | | {|Excavation in normal air, and before |
Rock {| 15}57| 69 | 1.21 {|advance of shield. |
{| 28} | | {| |
{| | | {| |
| | | | |
Rock {| 26}55| 53 | 0.96 {|Bottom heading timbered to avoid the |
{| 29} | | {|possibility of a break. |
| | | | |
Mixed | 25 | 22 | 0.88 |Bottom heading timbered. |
| | | | |
Mixed | 54 | 65 | 1.20 | |
| | | | |
Earth | 94 | 723 | 7.69 | |
| | | | |
| | | | |
Mixed |190 | 515 | 2.71 | |
| | | | |
Rock | 21 | 38 | 1.81 | |
| | | | |
Rock | 46 | 116 | 2.52 | |
| | | | |
Rock | 59 | 137 | 2.32 | |
| | | | |
Mixed | 25 | 48 | 1.92 | |
--------------+------+--------+--------+--------------------------------------+
LINE B, MANHATTAN.
--------------+-----------------+-------------------+-------------------------+
| | Station: | Date: |
| |---------+---------+------------+------------+
| | | | | |
Material. | Method. | From | To | From | To |
--------------+-----------------+---------+---------+------------+------------+
{|Top heading |108+35 |107+87 |July 6, '05|July 27, '05|
{|Top lift of bench|108+35 |107+87 |Aug. 3, '05|Aug. 14, '05|
Rock {|Bottom lift of | | | | |
{| bench |108+35 |108+15 |Aug. 26, '05|Aug. 30, '05|
{|Bottom lift of | | | | |
{| bench |108+15 |107+87 |Sept 11, '05|Sept 26, '05|
| | | | | |
Rock |Bottom heading |107+87 |107+00 |Oct. 23, '05|Jan. 17, '06|
| | | | | |
Mixed |Bottom heading |107+00 |106+64 |Jan. 17, '06|Feb. 12, '06|
| | | | | |
Mixed |Rock bench |106+64 |106+31 |Feb. 12, '06|Mar. 1, '06|
| | | | | |
Earth |Poling and |106+31 |105+58 |Mar. 1, '06|Apr. 3, '06|
| breasting | | | | |
| | | | | |
|Shutters in | | | | |
Earth | contact with |105+58 | 99+19 |Apr. 9, '06|Nov. 1, '06|
| face | | | | |
| | | | | |
Mixed |Rock bench | 99+19 | 98+44 |Nov. 1. '06|Dec. 29, '06|
| | | | | |
Mixed |Bottom heading | 98+44 | 97+76 |Dec, 29, '06|Feb. 12, '07|
| | | | | |
Mixed |Rock cut | 97+66 | 93+84 |Feb. 12, '07|Aug. 6, '07|
| | | | | |
Rock |Full face | 93+84 | 93+21 |Aug. 6, '07|Sept 2, '07|
| | | | | |
Rock |Center Heading | 93+21 | 92+30 |Sept 2, '07|Oct. 12, '07|
| | | | | |
Rock |Bottom heading | 92+30 | 90+99 |Oct. 12, '07|Dec. 6, '07|
| | | | | |
Mixed |Rock cut | 90+99 | 90+49.6 |Dec. 6, '07|Jan. 3, '08|
--------------+-----------------+---------+---------+------------+------------+
--------------+------+--------+--------+--------------------------------------+
| | |Rate of | |
|Number| |progress| |
| of | Linear |in feet | |
Material. | days.| feet. |per day.| Remarks |
--------------+------+--------+--------+--------------------------------------+
{| 21} | | {| |
{| 11} | | {| |
Rock {| }51| 48 | 0.94 {|Excavation done in normal air and |
{| 4} | | {|before advance of shield. |
{| } | | {| |
{| 15} | | {| |
| | | | |
Rock | 86 | 87 | 1.01 | |
| | | | |
Mixed | 26 | 36 | 1.38 | |
| | | | |
Mixed | 17 | 33 | 1.94 | |
| | | | |
Earth | | | | |
| 33 | 73 | 2.21 | |
| | | | |
| | | | |
Earth |206 | 639 | 3.10 | |
| | | | |
| | | | |
Mixed | 58 | 75 | 1.30 | |
| | | | |
Mixed | 45 | 68 | 1.51 | |
| | | | |
Mixed |175 | 392 | 2.24 | |
| | | | |
Rock | 27 | 63 | 2.33 | |
| | | | |
Rock | 40 | 91 | 2.28 | |
| | | | |
Rock | 55 | 131 | 2.38 | |
| | | | |
Mixed | 28 | 49.4 | 1.76 | |
--------------+------+--------+--------+--------------------------------------+
LINE C, MANHATTAN.
--------------+-----------------+-------------------+-------------------------+
| | Station: | Date: |
| |---------+---------+------------+------------+
| | | | | |
Material. | Method. | From | To | From | To |
--------------+-----------------+---------+---------+------------+------------+
{|Top heading |107+79.03|107+69 |Dec. 20, '04|Dec. 27, '04|
{|Top heading |107+69 |107+23 |Jan. 1, '05|Jan. 15, '05|
Rock {|Excavating bench |107+79 |107+23 |Jan. 21, '05|Feb. 28, '05|
{|Bottom heading |107+23 |106+72 |Mar. 1, '05|Mar. 11, '05|
{|Bottom heading |107+23 |107+15 |Oct. 12, '05|Oct. 27, '05|
{| | | | | |
| | | | | |
Rock |Bottom heading |107+15 |106+62 |Nov. 6, '05|Dec. 2, '05|
| | | | | |
| | | | | |
Mixed |Bottom heading |106+62 |106+55 |Dec. 2, '05|Dec. 23, '05|
| | | | | |
| | | | | |
Mixed |Bottom heading |106+55 |106+17 |Feb. 12, '06|Mar. 22, '06|
| | | | | |
Mixed |Rock cut |106+17 |105+85 |Apr. 2, '06|Apr. 20, '06|
| | | | | |
Mixed |Rock cut |105+85 |105+55 |July 27, '06|Aug. 26, '06|
| | | | | |
| | | | | |
Earth |Breasting and |105+55 | 99+40 |Aug. 26, '06|Jan. 2, '07|
| poling | | | | |
| | | | | |
Mixed |Rock cut | 99+40 | 98+70 |Jan. 2, '07|Feb. 6, '07|
| | | | | |
Rock |Full face | 98+70 | 98+60 |Feb. 6, '07|Feb. 12, '07|
| | | | | |
Mixed |Bottom heading | 98+60 | 98+39 |Feb. 12, '07|Mar. 6, '07|
| | | | | |
Rock |Bottom heading | 98+39 | 98+17 |Mar. 6, '07|Mar. 15, '07|
| | | | | |
Mixed |Rock cut | 98+17 | 95+68 |Mar. 15, '07|July 30, '07|
| | | | | |
Rock |Middle heading | 95+68 | 94+61 |July 30, '07|Aug. 21, '07|
| | | | | |
Mixed |Rock cut | 94+61 | 93+56 |Aug. 21, '07|Oct. 3, '07|
| | | | | |
Rock |Middle heading | 93+56 | 92+73 |Oct. 3, '07|Nov. 11, '07|
| | | | | |
Mixed |Rock cut | 92+73 | 90+55 |Nov. 11, '07|Feb. 13, '08|
| | | | | |
Mixed |Rock cut | 90+55 | 90+44.4 |Feb. 25, '08|Mar. 3, '08|
--------------+-----------------+---------+---------+------------+------------+
--------------+------+--------+--------+--------------------------------------+
| | |Rate of | |
|Number| |progress| |
| of | Linear |in feet | |
Material. | days.| feet. |per day.| Remarks |
--------------+------+--------+--------+--------------------------------------+
{| 7} | | {|Stopped to brace portal. No work done |
{| 14} | | {|from March 12th to October 11th, 1905,|
Rock {| 38} | 54 | 0.77 {|except a little trimming in September.|
{| 10} | | {|All work up to this date done in |
{| 15} | | {|normal air. Heading advanced to 106+70|
{| } | | {|and bulkheaded. |
| | | | |
Rock | 26 | 53 | 2.04 | |
| | | | |
| | | {|Heading advanced to 106 + 40. Shut |
Mixed | 21 | 7 | 0.33 {|down in order that Line D might have a|
| | | {|lead. |
| | | | |
Mixed | 38 | 38 | 1.00 {|Shut down on account of air shortage. |
| | | | |
Mixed | 18 | 32 | 1.78 |Shut down on account of air shortage. |
| | | | |
Mixed | 30 | 30 | 1.00 |Shut down April 20th to July 27th, |
| | | |1906. |
| | | | |
Earth |127 | 615 | 4.84 | |
| | | | |
| | | | |
Mixed | 35 | 70 | 2.00 | |
| | | | |
Rock | 6 | 10 | 1.66 | |
| | | | |
Mixed | 22 | 21 | 0.95 | |
| | | | |
Rock | 9 | 22 | 2.44 | |
| | | | |
Mixed |110 | 249 | 2.26 |Heading advanced to 97+82. |
| | | | |
Rock | 49 | 107 | 2.18 | " " " 94+35. |
| | | | |
Mixed | 43 | 106 | 2.46 | |
| | | | |
Rock | 39 | 83 | 2.13 | |
| | | | |
Mixed | 94 | 218 | 2.32 |Shut down until Line D shields met. |
| | | | |
Mixed | 6 | 11 | 1.83 | |
--------------+------+--------+--------+--------------------------------------+
LINE D, MANHATTAN.
--------------+-----------------+---------+---------+------------+------------+
{|Top heading |107+70.49|107+16 |Dec. 9, '04|Jan. 31, '05|}
{|Removing bench |107+70.49|107+35 |Jan. 1, '05|Jan. 27, '05|}
Rock {|Bottom heading |107+35 |106+80 |Jan. 30, '05|Feb. 10, '05|}
{|Trimming |107+70 |106+80 |Mar. 29, '05|Apr. 12, '05|}
{|Trimming |107+70 |106+80 |Aug. 31, '05|Sept 19, '05|}
| | | | | |
Rock |Bottom heading |106+80 |106+67 |Oct. 5, '05|Nov. 8, '05|
| | | | | |
Mixed |Bottom heading |106+67 |106+39 |Nov. 8, '05|Dec. 23, '05|
| | | | | |
|Sliding hood and | | | | |
Mixed |breasting. Rock |106+29 |105+70 |Dec. 23, '05|Jan. 24, '06|
|bench | | | | |
| | | | | |
Earth |Poling and |105+70 |104+61 |Jan. 24, '06|Feb. 27, '06|
|breasting | | | | |
| | | | | |
| | | | | |
Earth |Poling, breasting|104+61 |103+90 |Mar. 2, '06|Mar. 31, '06|
| and shutters | | | | |
| | | | | |
| | | | | |
Earth |Shutters |103+90 | 99+41 |Apr. 20, '06|Sept 3, '06|
| | | | | |
| | | | | |
Mixed |Bottom bench | 99+41 | 99+17 |Sept 3, '06|Sept 23, '06|
| | | | | |
Mixed |Bottom heading | 99+17 | 98+50 |Oct. 2, '06|Nov. 24, '06|
| | | | | |
| | | | | |
Rock |Bottom heading | 98+50 | 97+72 |Nov. 24, '06|Jan. 16, '07|
| | | | | |
Mixed |Bottom heading | 97+72 | 97+27 |Jan. 16, '07|Feb. 10, '07|
| | | | | |
Mixed |Rock cut | 97+27 | 95+72 |Feb. 10, '07|Apr. 23, '07|
| | | | | |
Rock |Middle heading | 95+72 | 95+57 |Apr. 23, '07|May 11, '07|
| | | | | |
Rock |Middle heading | 95+57 | 94+65 |May 23, '07|June 17, '07|
| | | | | |
| | | | | |
Mixed |Middle heading | 94+65 | 94+41 |June 17, '07|June 25, '07|
| | | | | |
Mixed |Rock cut | 94+41 | 94+03 |June 25, '07|July 13, '07|
| | | | | |
Rock |Middle heading | 94+03 | 92+64 |July 13, '07|Sept 12, '07|
| | | | | |
Mixed |Middle heading | 92+64 | 92+54 |Sept 12, '07|Sept 20, '07|
| | | | | |
Rock |Middle heading | 92+54 | 92+50 |Sept 20, '07|Sept 21, '07|
| | | | | |
Mixed |Rock cut | 92+50 | 90+38.66|Sept 21, '07|Jan. 8, '08|
--------------+-----------------+---------+---------+------------+------------+
--------------+------+--------+--------+--------------------------------------+
| | |Rate of | |
|Number| |progress| |
| of | Linear |in feet | |
Material. | days.| feet. |per day.| Remarks |
--------------+------+--------+--------+--------------------------------------+
{| | | | |
{| | | | |
Rock {|123 | 90 | 0.73 |In normal air. |
{| | | | |
{| | | | |
| | | | |
Rock | 34 | 13 | 0.40 |Bottom heading timbered. |
| | | | |
Mixed | 45 | 38 | 0.84 | |
| | | | |
| | | | |
Mixed | 32 | 59 | 1.84 | |
| | | | |
| | | | |
Earth | 31 | 109 | 3.41 | |
| | | | |
| | | | |
| | | |Three days' delay to set shutters in |
Earth | 29 | 71 | 2.45 |top. Shut down 20 days to permit |
| | | |consolidation of the river bed and to |
| | | |repair broken plates. |
| | | | |
Earth |136 | 449 | 3.40 |Four days of 136, delay account of |
| | | |flood. |
| | | | |
Mixed | 20 | 24 | 1.20 | |
| | | | |
Mixed | 53 | 67 | 1.27 |Thirteen days' shut-down to put on |
| | | |hood. |
| | | | |
Rock | 53 | 78 | 1.47 | |
| | | | |
Mixed | 25 | 45 | 1.40 | |
| | | | |
Mixed | 72 | 155 | 2.15 | |
| | | | |
Rock | 18 | 15 | 0.83 | |
| | | | |
Rock | 25 | 92 | 3.68 |Twelve days' delay to repair cutting |
| | | |edge. |
| | | | |
Mixed | 8 | 24 | 3.00 | |
| | | | |
Mixed | 18 | 38 | 2.11 | |
| | | | |
Rock | 61 | 139 | 2.28 | |
| | | | |
Mixed | 8 | 10 | 1.25 | |
| | | | |
Rock | 1 | 4 | 4.00 | |
| | | | |
Mixed |109 | 211.34| 1.94 | |
--------------+------+--------+--------+--------------------------------------+
Openings were made between the headings as follows:
Tunnel _D_, February 20th, 1908;
Tunnel _B_, March 3d, 1908;
Tunnel _C_, March 5th, 1908;
Tunnel _A_, March 18th, 1908.
It was necessary to cut away the projecting floors of the working
compartments before the cutting edges could be shoved together.
_Contractor's Organization._--Tunnel operations were carried on
continuously for thirteen days out of fourteen, regular work being shut
down for repairs on alternate Sundays. When the required pressure was
more than 32 lb., four gangs of laborers were employed, each gang
working two shifts of 3 hours each, with an intermission of 3 hours
between the shifts. When the pressure was less than 32 lb., three gangs
were employed, each gang covering 8 hours, but with an intermission of
about 1/2 hour in low pressure for lunch.
_Air Pressures Required._--During the greater portion of the work in
soft ground, pressure was maintained which would about balance the
hydrostatic head at the axis of the tunnel. This required a pressure
varying from 30 to 34 lb. per sq. in. above that of the atmosphere. In
Tunnels _B_ and _D_, at Manhattan, during the work in soft ground,
pressures as high as 37 lb. were maintained for considerable periods of
time; in the firm material near the reef 28 lb. was often sufficient.
While removing the broken plates, the pressure was raised for a short
time to 42 lb., and was maintained between 37-1/2 and 40 lb. for a
little more than one month.
_Air Supply._--For regular operation the contractor furnished four
compressors on each side of the river, each having a rated capacity of
5,000 cu. ft. of free air per minute delivered at 50 lb. above normal,
when running at the rate of 100 rev. per min. An additional compressor
of the same capacity was supplied on each side of the river, in
compliance with the requirement for 25% excess capacity; the additional
compressors had also high-pressure air cylinders which could be
connected at will, and in which the pressure could be increased to 150
lb., and the air used to supply rock drills, grouting machines, etc. The
entire combination on each side of the river, therefore, was rated at
25,000 cu. ft. of free air per minute, or a mean of 6,250 cu. ft. per
heading. Its safe working capacity was not far from 20,000 cu. ft. per
min.
The shields broke through rock surface in Tunnels _B_, _C_, and _D_, at
Manhattan, in November and December, 1905. The consumption of air in the
four tunnels soon exceeded 15,000 cu. ft. for 24 hours, and in Tunnel
_D_, on several occasions, it exceeded 7,000 cu. ft. for a like period.
Blows had become frequent, and it was evident that the air plant was
inadequate for driving four tunnels at once in the open material east of
the Manhattan rock. Work in Tunnel _A_, therefore, was not resumed,
after the suspension on December 29th, for about ten months, and Tunnel
_C_ was also closed down for more than four months of the time between
December, 1905, and July, 1906. During this period the capacity of the
plant was increased from the rated 25,000 cu. ft. of free air per
minute, to 35,000. In Tunnel _D_ the material had gradually become
firmer, with more clay and less escape of air, as the Blackwell's Island
Reef was approached, and, at the end of the period, the rock surface was
within 3 ft. of the top of the shield; in Tunnel _B_, the rock of the
reef was still a little below the shield, but the overlying material
contained a large proportion of clay and held air very well. Tunnel _C_
was still in open material, but, with two lines safe and with the
increased air plant, it was deemed best to resume work in Tunnel _A_,
which was done on October 23d, 1906. Thenceforward work was continuous
in all headings until the meeting points with the Long Island shields
were reached.
This period, January to October, 1906, inclusive, was the most strenuous
of the entire work, particularly the first six months. With one and, at
times, two tunnels closed down, the consumption of air in the headings
from Manhattan was an average of more than 20,000 cu. ft. per min. for
periods of from 30 to 60 days; it was often more than 25,000 cu. ft. for
24 hours, with a maximum of nearly 29,000 cu. ft., and doubtless this
was exceeded considerably for shorter periods. On several occasions the
quantity supplied to a single tunnel averaged more than 15,000 cu. ft.
per min. for 24 hours. The greatest averages for 24 hours were obtained
later in Tunnel _A_, after the resumption of work there, and exceeded
19,000 cu. ft., but the conditions in the headings of the other lines
were then so favorable that the work was carried on continuously in all.
The deficiency in the original plant at Manhattan was so marked, and the
need of driving all headings from Long Island simultaneously so clear,
that it was decided to increase the rated capacity of the Long Island
compressor plant to 45,400 cu. ft. of free air per minute, which was
10,400 cu. ft. greater than the capacity of the Manhattan plant after
the latter had been augmented.
[Illustration: PLATE LXXII]
The earth encountered on emerging from rock, when driving westward from
Long Island, was far more compact and less permeable to air than on the
Manhattan side, but for a distance of from 400 to 600 ft. immediately
east of the reef, it was a clean open sand, and, while the shields were
passing through this, the quantity of air supplied to the four headings
seldom fell below 20,000 cu. ft. per min.; it was usually more than
25,000 cu. ft., with a recorded maximum of 33,400 cu. ft. Although this
was greater than ever used on the Manhattan side, it was more uniformly
distributed among the several headings, and in none equalled the maximum
observed on the Manhattan side, the largest having been 12,700 cu. ft.
per min. for 24 hours; it must be remembered, however, that at one time
only two tunnels were in progress in the bad material in the tunnels
from Manhattan.
From the foregoing experience, it would seem that the plant finally
furnished at Long Island, having a rated capacity of 45,400 cu. ft. of
free air per minute, would have been a reasonable compliance with the
original actual needs on the Manhattan side and _vice versa_; the plant
finally developed on the Manhattan side, having a rated capacity of
35,000 cu. ft. of free air per minute, would have sufficed for the Long
Island side.
The total quantity of free air compressed for the supply of the working
chambers of the tunnels and the Long Island caissons was 34,109,000,000
cu. ft., and, in addition, 10,615,000,000 cu. ft. were compressed to
between 80 and 125 lb. for power purposes, of which at least 80% was
exhausted in the compressed-air working chambers. The total supply of
free air to each heading while under pressure, therefore, averaged about
3,550 cu. ft. per min.
The quantity of air escaping during a sudden blow-out is apparently much
smaller than might be supposed. Investigation of a number of cases,
showing large pressure losses combined with a long stretch of tunnel
supplying a relatively large reservoir of air, disclosed that a maximum
loss of about 220,000 cu. ft. of free air occurred in 10 min. This
averages only a little more than 19,000 cu. ft. per min., the maximum
recorded supply to one tunnel for a period of 24 hours. Of this
quantity, however, probably from 30 to 40% escaped in the first 45
seconds, while the remainder was a more or less steady loss up to the
time when the supply could be increased sufficiently to maintain the
lowered pressure. Very few blows showed losses approaching this in
quantity, but the inherent inaccuracy of the observations make the
foregoing figures only roughly approximate.
[Footnote C: _Minutes of Proceedings_, Inst. C. E., Vol. CXXX, p. 50.]
SPECIAL DIFFICULTIES.
The most serious difficulties of the work came near the start. In Tunnel
_D_ blows and falls of sand from the face were frequent after soft
ground was met in the top. About six weeks after entering the full sand
face, and before the shutters had been installed, the shield showed a
decided tendency to settle, carrying the tunnel lining down with it and
resulting in a number of badly broken plates in the bottom of the rings.
Notwithstanding the use of extremely high vertical leads,[D] the sand
was so soft that the settlement of the shield continued for about
fifteen rings, the maximum being nearly 9 in. below grade. The
hydrostatic head at mid-height of the tunnel was 32-1/2 lb., and the
raising of the air pressure to 37 lb., as was done at this time, was
attended with grave danger of serious blows, on account of the recent
disturbance of the natural cover by the pulling and re-driving of piles
in the reconstruction of the Long Island ferry slips directly above. It
dried the face materially, however, and the shield began to rise again,
and had practically regained the grade when the anticipated blow-outs
occurred, culminating with the entrance of rip-rap from the river bed
into the shield and the flooding of the tunnel with 4 ft. of sand and
water at the forward end. The escape of air was very great, and, as a
pressure of more than 28 lb. could not be maintained, the face was
bulkheaded and the tunnel was shut down for three weeks in order to
permit the river bed to consolidate.
This was the most serious difficulty encountered on any part of the
work, and, coming at the very start, was exceedingly discouraging.
During the shut-down the broken plates were reinforced temporarily with
steel ribs and reinforced concrete (Fig. 1, Plate LXXIII) which, on
completion of the work, were replaced by cast-steel segments, as
described elsewhere. Practically, no further movement of iron took
place, and the loss of grade caused by the settlement of the shield,
which was by far the largest that ever occurred in this work, was not
sufficient to require a change in the designed grade or alignment of the
track. Work was resumed with the shutters in use at the face as an aid
to excavation. The features of extreme seriousness did not recur, but
for two months the escape of air continued to be extremely large, an
average of 15,000 cu. ft. per min. being required on many days during
this period.
[Illustration: PLATE LXXIII, FIG. 1.--TEMPORARY REINFORCEMENT OF BROKEN
PLATES AND REMOVAL OF A PLATE IN SECTIONS.]
[Illustration: PLATE LXXIII, FIG. 2.--HEAVY CAST-STEEL PATCH ATTACHED TO
BENT SEGMENT OF CUTTING EDGE.]
[Illustration: PLATE LXXIII, FIG. 3.--INFLOW OF SOFT CLAY THROUGH
SHIELD.]
[Illustration: PLATE LXXIII, FIG. 4.--REINFORCEMENT OF BROKEN PLATE WITH
LONG POLT AND TWISTED STEEL RODS.]
In Tunnel _B_, after passing out from under the bulkhead line, in April,
1906, the loss of air became very great, and blow-outs were of almost
daily occurrence until the end of June. At the time of the blows the
pressure in the tunnel would drop from 2 to 8 lb., and it generally took
some hours to raise the pressure to what it was before the blow. During
that time regular operations were interrupted. In the latter part of
June a permit was obtained allowing the clay blanket to be increased in
thickness up to a depth of water of 27 ft. at mean low tide. The
additional blanket was deposited during the latter part of June and
early in July, and almost entirely stopped the blows.
By the end of the month the natural clay, previously described, formed
the greater portion of the face, and, from that time forward, played an
important part in reducing the quantity of air required. During April
and the early part of May the work was under the ferry racks of the Long
Island Railroad. The blanket had to be placed by dumping the clay from
wheel-barrows through holes in the decking.
In Tunnel _A_ a bottom heading had been driven 23 ft. in advance of the
face at the time work was stopped at the end of 1905. During the ten
months of inactivity the seams in the rock above opened. The rock
surface was only from 2 to 4 ft. below the top of the cutting edge for a
distance of about 60 ft. Over the rock there were large boulders
embedded in sharp sand. It was an exceedingly difficult operation to
remove the boulders and place the polings without starting a run. The
open seams over the bottom heading also frequently caused trouble, as
there were numerous slides of rock from the face which broke up the
breasting and allowed the soft material from above to run into the
shield. There were two runs of from 50 to 75 cu. yd. and many smaller
ones.
[Footnote D: The lead of the shield is the angular divergence of its
axis from the axis of the tunnel and, in this tunnel, was measured as
the offset in 23 ft. It was called + when the shield was pointed upward
from grade, and - when pointed downward.]
GUIDING THE SHIELDS.
Little difficulty was experienced at any time in driving the shield
close to the desired line, but it was much harder to keep it on grade.
In rock section, where the cradle could be set far enough in advance to
become hard before the shield was shoved over it, there was no trouble
whatever. Where the cradle could be placed only a very short time before
it had to take the weight of the shield, the case was quite different.
The shield had a tendency to settle at the cutting edge, and when once
pointed downward it was extremely difficult to change its direction. It
was generally accomplished by embedding railroad rails or heavy oak
plank in the cradle on solid foundation. This often had to be repeated
several times before it was successful. In soft ground it was much
easier to change the direction of the shield, but, owing to the varying
nature of the material, it was sometimes impossible to determine in
advance how the shield should be pointed. It was found by experience at
Manhattan that the iron lining remained in the best position in relation
to grade when the underside of the bottom of the shield at the rear end
was driven on grade of the bottom of the iron, but if the rate of
progress was slow, it was better to drive the shield a little higher.
In the headings from Long Island, which, as a rule, were in soft ground,
the cutting edges of the shields were kept from 4 to 8 in. higher, with
respect to the grade line, than the rails. The shields would then
usually move parallel to the grade line, though this was modified
considerably by the way the mucking was done and by the stiffness of the
ground at the bottom of the shield.
On the average, the shields were shoved by from ten to twelve of the
bottom jacks, with a pressure of about 4,000 lb. per sq. in. The jacks
had 9-in. plungers, which made the average total force required to shove
the shield 2,800,000 lb. In the soft ground, where shutters were used,
all of the twenty-seven jacks were frequently used, and on several
occasions the pressure exceeded 6,000 lb. per sq. in. With a unit
pressure of 6,000 lb. per sq. in., the total pressure on the shield with
all twenty-seven jacks in operation was 5,154 tons.
INJURIES TO SHIELDS.
There were only two instances of damage to the essential structural
features of the shields. The most serious was in Tunnel _D_ where the
cutting edge at the bottom of the shield was forced up a slightly
sloping ledge of rock. A bow was formed in the steel casting which was
markedly increased with the next few shoves. Work was suspended, and a
heavy cast-steel patch, filling out the bow, was attached to the bent
segments, as shown in Fig. 2, Plate LXXIII. No further trouble was
experienced with the deformed portion. The other instance was in Tunnel
_B_, from Long Island, where a somewhat similar but less serious
accident occurred and was treated in a like manner.
_Bulkheads._--At Manhattan, bulkheads had to be built near the shafts
before the tunnels could be put under pressure. After 500 ft. of tunnel
had been built on each line, the second bulkheads were constructed. The
air pressure between the first and second bulkheads was then reduced to
between 15 and 20 lb. When the shields had been advanced for 1,500 ft.,
the third set of bulkheads was built. Nearly all the broken plates which
were removed were located between the first and third bulkheads at
Manhattan. Before undertaking this operation, the doors of the locks in
the No. 3 bulkheads were reversed to take pressure from the west. By
this means it was possible to carry on the work of dismantling the
shields under comparatively low pressure simultaneously with the removal
of the broken plates.
At Long Island City the roofs of the caissons served the purpose of the
No. 1 bulkheads. Two other sets of bulkheads were erected, the first
about 500 ft. and the second about 1,500 ft. from the shafts.
SETTLEMENT AT SURFACE OF GROUND.
The driving of such portions of the river tunnels, with earth top, as
were under the land section, caused a settlement at the surface varying
usually from 3 to 6 in. The three-story brick building at No. 412 East
34th Street required extensive repairs. This building stood over the
section of part earth and part rock excavation where the tunnels broke
out from the Manhattan ledge and where there were a number of runs of
sand into the shield. In fact, the voids made by those runs eventually
worked up to the surface and caused the pavement of the alley between
the buildings to drop 4 or 5 ft. over a considerable area. The tunnels
also passed directly under the ferry bridges and racks of the Long
Island Railroad at East 34th Street. Tunnels _B_ and _D_ were constantly
blowing at the time, and, where progress was slow, caused so much
settlement that one of the racks had to be rebuilt. Tunnel _A_, on the
other hand, where progress was rapid, caused practically no settlement
in the racks.
CLAY BLANKET.
As previously mentioned, clay was dumped over the tunnels in varying
depths at different times. A material was required which would pack
into a compact mass and would not readily erode under the influence of
the tidal currents of the river and the escape of the great volumes of
air which often kept the water in the vicinity of the shields in violent
motion. Suitable clay could not be found in the immediate vicinity of
the work. Materials from Shooter's Island and from Haverstraw were tried
for the purpose. The Government authorities did not approve of the
former, and the greater portion of that used came from the latter point.
Although a number of different permits governing the work were granted,
there were three important ones. The first permit allowed a blanket
which roughly followed the profile of the tunnels, with an average
thickness of 10 ft. on the Manhattan side and somewhat less on the Long
Island City side. The second general permit allowed the blanket to be
built up to a plane 27 ft. below low water. This proved effective in
checking the tendency to blow, but allowed considerable loss of air.
Finally, dumping was allowed over limited and marked areas up to a plane
of 20 ft. below low water. Wherever advantage was taken of this last
authority, the excessive loss of air was almost entirely stopped. After
all the shields had been well advanced out into the river, the blanket
behind them was dredged up, and the clay used over again in advance of
the shield.
Soundings were taken daily over the shields, and, if marked erosion was
found, clay was dumped into the hole. Whenever a serious blow occurred,
a scowload of clay was dumped over it as soon as possible and without
waiting to make soundings. For the latter purposes a considerable
quantity of clay was placed in storage in the Pidgeon Street slip at
Long Island City, and one or two bottom-dump scows were kept filled
ready for emergencies. Mr. Robert Chalmers, who had charge of the
soundings for the contractor, states that "the depressions in the
blanket caused by erosion due to the escape of air were, as a rule,
roughly circular in plan and of a curved section somewhat flat in the
center." Satisfactory soundings were never obtained in the center of a
violent blow, but the following instance illustrates in a measure what
occurred. Over Tunnel _B_, at Station 102+80, there was normally 36 ft.
of water, 7 ft. of clay blanket, and 20 ft. of natural cover. Air was
escaping at the rate of about 10,000 cu. ft. per min., and small blows
were occurring once or twice daily. On June 22d, soundings showed 54 ft.
of water. A depth of 18 ft. of the river bottom had been eroded in about
two days. On the next day there were taken out of the shield boulders
which had almost certainly been deposited on the natural river bed. Clay
from the blanket also came into the shields on a number of occasions
during or after blows. The most notable occasion was in September, 1907,
when the top of the shield in Tunnel _D_ was emerging from the east side
of Blackwell's Island Reef. The sand in the top was very coarse and
loose, and allowed the air to escape very freely. The fall of a piece of
loose rock from under the breast precipitated a run of sand which was
followed by clay from the blanket, which, in this locality, was largely
the softer redredged material. Mucking out the shield was in progress
when the soft clay started flowing again and forced its way back into
the tunnel for a distance of 20 ft., as shown in Fig. 3, Plate LXXIII.
Ten days of careful and arduous work were required to regain control of
the face and complete the shove, on account of the heavy pressure of the
plastic clay.
The clay blanket was of the utmost importance to the work throughout,
and it is difficult to see how the tunnels could have been driven
through the soft material on the Manhattan side without it.
The new material used in the blanket amounted to 283,412 cu. yd., of
which 117,846 cu. yd. were removed from over the completed tunnels and
redeposited in the blanket in advance of the shields. A total of 88,059
cu. yd. of clay was dumped over blows. The total cost of placing and
removing the blanket was $304,056.
IRON LINING.
The standard cast-iron tunnel lining was of the usual tube type, 23 ft.
in outside diameter. The rings were 30 in. wide, and were composed of
eleven segments and a key. The webs of the segments were 1-1/2 in. thick
in the central portion, increasing to 2-3/8 in. at the roots of the
flanges, which were 11 in. deep, 2-1/4 in. thick at the root, and 1-1/2
in. at the edge, and were machined on all contact faces. Recesses were
cast in the edge of the flanges, forming a groove, when the lining was
in place, 1-1/2 in. deep and about 3/8 in. wide, to receive the
caulking. The bolt holes were cored in the flanges, and the bosses
facing the holes were not machined. The customary grout hole was tapped
in the center of each plate for a standard 1-1/4-in. pipe. In this work,
experience indicated that the standard pipe thread was too fine, and
that the taper was objectionable. Each segment weighed, approximately,
2,020 lb., and the key weighed 520 lb., the total weight being 9,102 lb.
per lin. ft. of tunnel. Fig. 1 shows the details of the standard heavy
lining.
In addition to the standard cast-iron lining, cast-steel rings of the
same dimensions were provided for use in a short stretch of the tunnel,
when passing from a rock to a soft ground foundation, where it was
anticipated that unequal settlement and consequent distortion and
increase in stress might occur, but, aside from the small regular drop
of the lining as it passed out of the tail of the shield, no such
settlement was observed.
Two classes of lighter iron, one with 1-in. web and 8-in. flanges and
the other with 1-1/4-in. web and 9-in. flanges--the former weighing
5,166 lb. per lin. ft. of tunnel and the latter, 6,776 lb.--were
provided for use in the land sections between East Avenue and the Long
Island City shafts. Two weights of extra heavy segments for use at the
bottom of the rings were also furnished. The so-called _XX_ plates had
webs and flanges 1/4 in. thicker than the standard segment and the _YY_
plates were similarly 1/2 in. heavier. The conditions under which they
were used will be referred to later. All the castings were of the same
general type as shown by Fig. 1.
Rings tapering 3/4 in. and 1-1/2 in. in width were used for changes in
alignment and grade, the former being used approximately at every fourth
ring on the 1° 30' curves. The 1-1/2-in. tapers were largely used for
changes in grade where it was desired to free the iron from binding on
the tail of the shield. Still wider tapers would have been advantageous
for quick results in this respect.
No lug was cast on the segments for attachment to the erector, but in
its place the gadget shown on Fig. 4, Plate LXX, was inserted in one of
the pairs of bolt holes near the center of the plate, and was held in
position by the running nut at one end.
In the beginning it was expected that the natural shape of the rings
would not show more than 1 in. of shortening of the vertical diameter;
this was slightly exceeded, however, the average distortion throughout
the tunnels being 1-7/16 in. The erectors were attached to the shield
and in such a position that they were in the plane of the center of the
ring to be erected when the shove was made without lead and just far
enough to permit placing the segments. If the shield were shoved too
far, a rare occurrence, the erection was inconvenienced. In driving with
high vertical leads, which occurred more frequently, the disadvantage
of placing the erector on the shield was more apparent. Under such
conditions the plane of the erector's motion was acutely inclined to the
plane of the ring, and, after placing the lower portion of the ring, it
was usually necessary to shove the shield a few inches farther in order
to place the upper plates. The practical effect of this action is
referred to later.
[Illustration: FIG. 1.]
At first the erection of the iron in the river tunnels interfered
somewhat with the mucking operations, but the length of time required to
complete the latter was ample for the completion of the former; and the
starting of a shove was seldom postponed by reason of the non-completion
of a ring. After the removal of the bottom of the diaphragms, permitting
the muck cars to be run into the shield and beyond, the two operations
were carried on simultaneously without serious interference. The
installation of the belt conveyor for handling the soft ground spoil in
Tunnel _A_ was of special benefit in this respect.
Preparatory to the final bolt tightening of each ring as erected, a
15-ton draw-jack, consisting of a small pulling-jack inserted in a light
eye-bar chain, was placed on the horizontal diameter, and frequently the
erectors were also used to boost the crown of the iron, the object being
to erect the ring truly circular. Before shoving, a 1-1/4-in.
turn-buckle was also placed on the horizontal diameter in order to
prevent the spreading of the iron, previous to filling the void outside
with grout. The approach of the supports for the upper floor of the
trailing platform necessitated the removal of these turnbuckles from all
but the three leading rings, but if the iron showed a tendency to
continue distortion, they were re-inserted after the passage of the
trailing platform and remained until the arch of the concrete lining was
placed.
The cost of handling and erecting the iron varied greatly at different
times, averaging, for the river tunnels, $3.32 per ton for the directly
chargeable labor of handling and erecting, to which must be added $7.54
for "top charges." The cost of repairing broken plates is included in
this figure.
_Broken Plates._--During the construction of the river section of the
tunnels, a number of segments were found to have been broken while
shoving the shield. The breaks, which with few exceptions were confined
to the three or four bottom plates, almost invariably occurred on the
advanced face of the ring, and rarely extended beyond the bottom of the
flange. A careful study of the breaks and of the shoving records
disclosed several distinct types of fracture and three principal known
causes of breakage by the shield.
In the first case, the accidental intrusion of foreign material between
the jack head and the iron caused the jack to take its bearings on the
flange above its normal position opposite the web of the ring, and
resulted usually in the breaking out of a piece of the flange or in
several radiating cracks with or without a depression of the flange.
These breaks were very characteristic, and the cause was readily
recognizable, even though the intruding substance was not actually
observed.
In the second case, the working of a hard piece of metal, such as a
small tool, into the annular space between the iron and the tail of the
shield, where it was caught on the bead and dragged along as the shield
advanced, was the known cause of a number of broken segments. Such
breaks had no particular characteristic, but were usually close above
the line of travel of the lost tool or metal. Their cause was determined
by the finding of a heavy score on the underside of the segment or the
discovery of the tool wedged in the tail of the shield or lying under
the broken plate when it was removed. It is probable that a number of
breaks ascribed to unknown causes should be placed in this class.
The third cause includes the largest number of breaks, and, while
difficult to define closely, is the most interesting. Broadly speaking,
the breaks resulted from the movements of the shield in relation to the
position of the tunnel lining. While shoving through soft ground, it was
frequently difficult to apply sufficient power to the lower jacks to
complete the full shove of 30 in. on the desired alignment. The shield,
therefore, was driven upward at the beginning of the shove, and, as the
sand packed in front of the shield and more power was required, it was
furnished by applying the upper jacks. The top of the shield was slowly
pushed over, and, at the close of the shove, the desired position had
been obtained; but the shield had been given a rocking motion with a
decided lifting of the tail toward the close of the shove. A similar
lifting of the tail occurred when, with high vertical leads, the top of
the shield was pushed over in order to place the upper plates of the
ring. Again, when the shield was driven above grade and it was desired
to descend, the passage of the shield over the summit produced a like
effect. In all these movements, with the space between the tail of the
shield and the iron packed tight with pugging, the upward thrust of the
shield tended to flatten the iron in the bottom and occasional broken
plates were the result. The free use of the taper rings, placed so as to
relieve the binding of the lining on the tail of the shield, forces the
tunnel to follow the variations in the grade of the shield, but reduces
greatly the injuries to the rings from this action.
In Tunnel _D_, where very high vertical leads were required through the
soft sand, combined with a marked tendency of the shield to settle, the
shield was badly cramped on the iron and dragged along it at the top.
The bearing of the iron on its soft foundation tended to thrust up the
bottom in this case also, as shown by the opening of the bottom
cross-joints when the bolts were slackened to relieve the strain during
a shove. The anticipated cracks in the crown plates, which have been
more frequently observed in other tunnels, did not occur here, and were
not found elsewhere except in one place in Tunnel _B_ where they were
traced to a similar action of the shield. The cracks resulting from the
movements of the shield, as briefly described above, in this third case
were not confined to any particular type, but occurred more frequently
at the extreme end of the circumferential flange than at any other
point.
The number of broken plates occurring in the river tunnels was 319, or
0.42% of the total number erected. Of these, 52 were found and removed,
either before or immediately after a shove, by far the greater number
being broken in handling before or during erection. The remaining 267
are considered below.
_Repair of Broken Plates._--On the completion of a shove, the tail of
the shield lacked about 5 in. of covering the full width of the last
ring, and the removal of a plate broken during the shove, therefore,
would have exposed the ground at the tail of the shield. With a firm
material in the bottom, this introduced no particular difficulties, and,
under such conditions, a broken plate was usually removed at once. In
the sand, however, and especially on the Manhattan side where it was
quick and flowing, the removal of a plate was attended with some danger,
and such plates were usually left to be removed on the completion of the
tunnel. Many of these had been reinforced by the use of _XX_, _YY_, and
steel segments placed adjacent to the break in the following rings.
After the meeting of the shields, the postponed replacement of the
broken segments was taken up. The pressure was raised sufficiently to
dry thoroughly the sand outside the segments, which were drilled and
broken out usually in quarters as shown on Fig. 1, Plate LXXIII. A steel
segment was then inserted in the ring and drawn into place by
turnbuckles. The application of the draw-jack, with a pull of about 30
tons to each end successively, brought the plate to a firm bearing on
the radial joints at the ends.
Where the broken plate was isolated and was reinforced by steel or extra
heavy segments in the adjacent ring, the crack, if slight, was simply
caulked to insure water-tightness. If, however, the crack was opened or
extended to the web of the plate, the cross-flanges were tied together
by a 1-1/2-in. by 7-ft. bolt, inserted through the bolt holes nearest
the broken flange. The long bolt acted in the nature of a bow string,
and was provided at its ends with two nuts set on opposite sides of the
cross-joints to replace the standard bolts removed for its insertion.
Fig. 4, Plate LXXIII shows one of these bolts in place. In addition, all
broken plates remaining in the tunnel were reinforced with 1-in.
twisted-steel rods in the concrete lining, also shown in Fig. 4, Plate
LXXIII.
_Special Construction at River Shield Junctions._--Dismantling the
shields was started as soon as they came to rest in their final position
with the cutting edges together. The plans contemplated their entire
removal, with the exception of the cylindrical skins and cast-steel
cutting edges. Inside the former the standard tunnel lining was erected
to within 4 ft. of the heels of the cutting edges. Spanning the latter,
and forming the continuous metal tunnel lining, the special construction
shown by Fig. 2 was built. This consisted of a 1-1/4 in. rolled-steel
ring, 7 ft. long, erected inside the cutting edges, with an annular
clearance of 1 in., and two special cast-iron rings shaped to connect
the rolled-steel ring with the normal lining. One flange of the special
cast-iron rings was of the standard type, the other was returned 9 in.
in the form of a ring, the inside diameter of which was the same as the
outside diameter of the rolled-steel ring to which it was bolted.
The space between the standard and special construction was of varying
width at the various shields, and was filled with a closure ring cast to
the lengths determined in the field. Fig. 2 shows the completed
construction.
Hook-bolts, screwed through threaded holes and buried in 1 to 1 Portland
cement grout ejected through similar holes, reinforced the rolled-steel
ring against external water pressure. In two of the tunnels the concrete
lining was carried completely through the junction, and covered the
whole construction, while in the remaining two tunnels it was omitted at
the rolled-steel ring, leaving the latter exposed and set back about 3
in. from the face of the concrete.
[Illustration: FIG. 2.]
GROUTING.
Except as previously noted, the voids outside of the tunnel lining were
filled with grout ejected through the grout holes in each segment. The
possibility was always present that Portland cement, if used for grout
in the shield-driven tunnels, would flow forward around the shield and
set hard, "freezing" the shield to the rock or the iron lining, or at
least forming excrescences upon it, which would render its control
difficult. With this in mind, the contractors proposed to substitute an
English Blue Lias lime as a grouting material. Grout of fresh English
lime containing a moderate quantity of water set very rapidly in air to
the consistency of chalk. Its hydraulic properties, however, were
feeble, and in the presence of an excess of water it remained at the
consistency of soft mud. It was not suitable, therefore, as a supporting
material for the tunnel.
An American lime, made in imitation of the Lias lime, but having greater
hydraulic properties, was tried, but proved unsatisfactory. Two brands
of natural cement were also tried and rejected, but a modified
quick-setting natural cement, manufactured especially for this work, was
eventually made satisfactory, and by far the largest part of the
river-tunnel grouting was done with this material mixed 1 to 1 by
volume. East of the Long Island shafts the work which was built without
shields was grouted principally with Portland cement and sand mixed 1 to
1 by volume.
In the river tunnels large quantities of the English lime were used neat
as grout over the top of the tunnel in attempts to stop losses of air
through the soft ground. It was not of great efficiency, however, in
this respect until the voids outside of the lining had been filled above
the crown. Its properties of swelling and quick setting in the dry sand
at that point then became of value. The use of dry lime in the face,
where the escaping air would carry it into the voids of the sand and
choke them, was much more promptly efficacious in checking the loss.
With the exception of the English lime, all grout was mixed 1 to 1 with
sand in a Cockburn continuous-stirring machine operated by a 3-cylinder
air engine. The grout machine was placed on the lower floor of the
trailing platform shown on Plate LXXII, while the materials were placed
on the upper platform, and, together with the water, were fed into the
machine through a hole in the upper floor. The sand was bagged in the
yard, and the cars on which the materials were sent into the tunnels
were lifted by an elevator to the level of the upper floor of the
trailing platform before unloading.
Great difficulty was experienced in preventing the waste of the fluid
grout ahead of the shield and into the tail through the space between it
and the iron lining. In a full soft ground section, the first condition
did not usually arise. In the full-rock sections the most efficient
method of checking the waste was found to be the construction of dams or
bulkheads outside the lining between it and the rock surface. For this
purpose, at intervals of about 30 ft., the leading ring and the upper
half of the preceding one were disconnected and pulled forward
sufficiently to give access to the exterior. A rough dam of rubble, or
bags of mortar or clay, was then constructed outside the iron, and the
rings were shoved back and connected up. In sections containing both
rock and soft ground, grout dams were built at the cutting edge at
intervals, and were carried up as high as circumstances permitted.
The annular space at the tail of the shield was at all times supposed to
be packed tight with clay and empty bags, but the pugging was difficult
to maintain against the pressure of the grout. For a time, 1/2-in.
segmental steel plates, slipped down between the jackets and the iron,
were used to retain the pugging, but their displacement resulted in a
number of broken flanges, and their use was abandoned. In their place,
2-in. segmental plates attached to the jack heads were substituted with
more satisfactory results. Notwithstanding these devices, the waste of
grout at the tail was very great.
The soft ground material on various portions of the work acted very
differently. The clay and "bull's liver" did not cave in upon the iron
lining for several hours after the shield had passed, sometimes not for
a day or more, which permitted the space between it and the iron to be
grouted. The fine gray or beach sand and the quicksand closed in almost
at once. The quicksand has a tendency to fill in under the iron from the
sides and in places to leave a cavity at about the horizontal diameter
which was not filled from above, as the sand, being dried out by the
air, stood up fairly well and did not cave against the iron, except
where nearly horizontal at the top.
The total quantity of grout used on the work was equivalent in set
volume to 249,647 bbl. of 1 to 1 Portland cement grout, of which 233,647
bbl. were ejected through the iron lining, an average of 14.93 bbl. per
lin. ft. The cost of grout ejected outside of the river tunnels was 93
cents per bbl. for labor and $2.77 for "top charges." East of the Long
Island shaft the corresponding costs were $0.68 and $1.63, the
difference being partly due to the large percentages of work done in the
normal air at the latter place.
CAULKING AND LEAKAGE.
Up to August, 1907, the joints between the segments of the cast-iron
lining were caulked with iron filings and sal ammoniac, mixed in the
proportion of 400 to 1 by weight. With the air pressure balancing the
hydrostatic head near the tunnel axis, it was difficult to make the
rust-joint caulking tight below the axis against the opposing water
pressure; this form of caulking was also injured in many places by
water dripping from service pipes attached to the tunnel lining. A few
trials of lead wire caulked cold gave such satisfactory results that it
was adopted as a substitute. Pneumatic hammers were used successfully on
the lead caulking, but were only used to a small extent on the rust
borings, which were mostly hand caulked. Immediately before placing the
concrete lining, all leaks, whether in the rust borings or lead, were
repaired with lead, and the remainder of the groove was filled with 1 to
1 Portland cement mortar, leaving the joints absolutely water-tight at
that time. The subsequent development of small seepages through the
concrete would seem to indicate that the repair work should have been
carried on far enough in advance of the concreting to permit the
detection of secondary leaks which might develop slowly. The average
labor cost chargeable against the caulking was 12 cents per lin. ft., to
which should be added 21.8 cents for "top charges."
Unfortunately, it was necessary to place the greater part of the
concrete lining in the river tunnels during the summer months when the
temperature at the point of work frequently exceeded 85°; and the
temperature of the concrete while setting was much higher. This abnormal
heat, due to chemical action in the cement, soon passed away, and, with
the approach of winter, the contraction of the concrete resulted in
transverse cracks. By the middle of the winter these had developed quite
uniformly at the ends of each 30-ft. section of concrete arch as placed,
and frequently finer cracks showed at about the center of each 30-ft.
section.
While the temperature of the concrete was falling, a like change was
taking place in the cast-iron lining, with resulting contraction. The
lining had been erected in compressed air, the temperature of which
averaged about 70° in winter and higher in summer. Compressed air having
been taken off in the summer of 1908, the tunnels then acquired the
lower temperature of the surrounding earth, slowly falling until
mid-winter. The contraction of the concrete, firmly bedded around the
flanges of the iron, and showing cracks at fairly uniform intervals,
probably localized the small corresponding movements of the iron near
the concrete cracks, and resulted in a loosening of the caulking at
these points. With the advent of cold weather, damp spots appeared in
numerous places on the concrete, and small seepages showed through quite
regularly at the temperature cracks, in some cases developing
sufficiently to be called leaks. Only a few, however, were measurable in
amount.
Early in January small brass plugs were firmly set on opposite sides of
a large number of cracks, and caliper readings and air temperature
observations were taken regularly throughout the winter and spring. The
widths of the cracks and the amount of leakage at them increased with
each drop in temperature and decreased as the temperature rose again,
but until spring the width of the cracks did not return to the same
point with each return of temperature.
The leakage was similar in all four tunnels, but was largest in amount
in Tunnel _D_, where, at the beginning of February, the ordinary flow
was about 0.0097 cu. ft. per sec., equivalent to 0.00000347 cu. ft. per
sec. per lin. ft. of tunnel. Of this amount 0.0065 cu. ft. per sec.
could be accounted for at eight of the cracks showing measurable
leakage, leaving 0.0032 cu. ft. per sec. or 0.00000081 cu. ft. per sec.
per lin. ft. of tunnel to be accounted for as general seepage
distributed over the whole length.
It was not feasible to stop every leak in the tunnel, most of which were
indicated simply by damp spots on the concrete; a rather simple method
was devised, however, for stopping the leaks at the eight or ten places
in each tunnel where water dripped from the arch or flowed down the face
of the concrete. The worst leak in any tunnel flowed about 0.0023 cu.
ft. per sec. To stop these leaks, rows of 1-in. holes, at about 4-in.
centers, were drilled with jap drills through the concrete to the flange
of the iron. These rows were from 3 to 18 ft. long, extending 1 ft. or
more beyond the limits of the leak. The bottoms of the holes were
directly on the caulking groove and the pounding of the drill usually
drove the caulking back, so that the leak became dry or nearly so after
the holes were drilled. If left alone the leaks would gradually break
out again in a few hours or a few days and flow more water than before.
They were allowed to do this, however, in only a few cases as
experiments. After the holes were drilled, the bottom 4 in. next the
flange was filled with soft neat cement mortar. Immediately on top of
this was placed two plugs of neat cement about 2-1/2 in. long, which
were 5 or 6 hours old and rather hard. Each was tamped in with a round
caulking tool of the size of the hole driven with a sledge hammer. On
top of this were driven in the same way two more plugs of neat cement of
the same size, which were hard set. These broke up under the blows of
the hammer, and caulked the hole tight. When finished, the tamping tool
would ring as though it was in solid rock. Great pressure was exerted on
the plastic mortar in the bottom of the hole, which resulted in the
re-caulking of the joint of the iron. No further measurable leakage
developed in the repaired cracks, during a period of four months, and
the total leakage has been reduced to about 0.002 cu. ft. per sec. in
each tunnel, an average of 0.00000051 cu. ft. per sec. per lin. ft.
SUMP AND PUMP CHAMBERS.
To take care of the drainage of the tunnels, a sump with a pump chamber
above it was provided for each pair of tunnels. The sumps were really
short tunnels underneath the main ones and extending approximately
between the center lines of the latter. They were 10 ft. 9-1/2 in. in
outside diameter and 44 ft. long. The water drops directly from the
drains in the center lines of the tunnels into the sumps. Above the
sumps and between the tunnels, a pump chamber 19 ft. 5 in. long was
built. Above the end of the latter, opposite the sump, a cross-passage
was constructed between the bench walls of the two tunnels. This passage
gives access from either tunnel through an opening in the floor to the
pump chamber and through the latter to the sump.
From the preliminary borings it was thought that the sumps were located
so that the entire construction would be in rock. This proved to be the
case on Tunnels _C_ and _D_, but not on Tunnels _A_ and _B_. The
position of the rock surface in the latter is shown by Fig. 3. After the
excavation was completed in Tunnel _B_, January 1st, 1908, the plates
were removed from the side of the tunnel at the cross-passage, and a
drift was driven through the earth above the rock surface across to the
lining of Tunnel _A_. The heading was timbered as shown by Fig. 3. There
was practically no loss of air from the drift, but the clay blanket had
been removed from over this locality and the situation caused some
anxiety. In order to make the heading as secure as possible, the 24-in.
I-beams, shown on Fig. 3, were attached to the lining of the two
tunnels. The beams formed a support for the permanent concrete roof arch
of the passage, which was placed at once. At the same time plates were
removed from the bottom in Tunnel _B_ over the site of the sump, and a
heading was started on the line of the sump toward Tunnel _A_. As soon
as the heading had been driven beyond the center line of the pump
chamber, a bottom heading was driven from a break-up westward in the
pump chamber and a connection was made with the cross-passage. The iron
lining of the pump chamber was next placed, from the cross-passage
eastward. The soft ground was excavated directly in advance of the
lining, and the ground was supported by polings in much the same manner
as described for shield work. On account of bad ground and seams of sand
encountered in the rock below the level of the cross-beams, the entire
west wall of the pump chamber was placed before enlarging the sump to
full size. This was also judicious, in order to support as far as
possible the iron lining of the tunnels. The sump was then excavated to
full size. The iron lining of the sump and the east wall of the pump
chamber were placed as soon as possible. The voids outside the iron
lining of the sump and the pump chamber were filled as completely as
possible with concrete, and then thoroughly grouted. Finally, the
concrete lining was put in place inside of the iron.
As shown by Fig. 3, the excavation of these chambers left a considerable
portion of the iron lining of the tunnels temporarily unsupported on the
lower inner quarter. To guard against distortion, a system of diagonals
and struts was placed as shown.
The floor of the pump chamber was water-proofed with felt and pitch in a
manner similar to that described for the caissons at Long Island City.
It was not possible to make the felt stick to the vertical walls with
soft pitch, which was the only kind that could be used in compressed
air, and, therefore, the surfaces were water-proofed by a wall of
asphalt brick laid in pitch melting at 60° Fahr. Forms were erected on
the neat line, and the space to the rock was filled with concrete making
a so-called sand-wall similar to that commonly used for water-proofing
with felt and pitch. The bricks were then laid to a height of four or
five courses. The joints were filled with pitch instead of mortar.
Sheets of tin were then placed against the face of the wall and braced
from the concrete forms. As much pitch as possible was then slushed
between the brick and the sand-wall, after which the concrete in the
main wall was filled up to the top of the water-proofing course. The tin
was then withdrawn and the operation repeated. This method was slow and
expensive, but gave good results. Ordinary pitch could not be used on
account of the fumes, which are particularly objectionable in
compressed air. The 60° pitch was slightly heated in the open air before
using.
[Illustration: FIG. 3.]
The sump and pump chamber on Tunnels _C_ and _D_ differed from the one
described only in minor details; but, being wholly constructed in rock,
presented fewer difficulties and permitted a complete envelope of
water-proofing to be placed in the top.
CONCRETE LINING.
The placing of concrete inside the iron tube was done by an organization
entirely separate from the tunneling force. A mixing plant was placed in
each of the five shafts. The stone and sand bins discharged directly
into mixers below, which, in turn, discharged into steel side-dump
concrete cars. All concrete was placed in normal air.
The first step, after the iron lining was scraped clean and washed down
and all leaks were stopped, was the placing of biats, marked _B_ on
Plate LXXIV. These were made up of a 6 by 12-in. yellow pine timber, 17
ft. long, with two short lengths of the same size spliced to its ends by
pieces of 12-in. channels, 3 ft. 9 in. long, clamped upon the sides.
These biats were placed every 5 ft. along the tunnel in rings having
side keys. Next, a floor, 13 ft. wide, was laid on the biats and two
tracks, of 30-in. gauge and 6-1/2-ft. centers, were laid upon the floor.
There were three stages in the concreting. Fig. 2, Plate LXXIV, shows
the concrete in place at the end of the first, and Fig. 3, Plate LXXIV,
at the end of the second stage. The complete arch above the bench walls
was done in the last operation.
Two 3 by 10-in. soldiers (_SS_ in Figs. 1 and 2, Plate LXXIV) were
fastened to each biat and braced across by two horizontal and two
diagonal braces. To each pair of soldiers a floor template, _T_, was
then nailed. The form for the center drain was then suspended as shown
in Fig. 1, Plate LXXIV. Three pieces of shuttering, _FFF_, 20 ft. long,
were then nailed to the bottom of the soldiers. One is all that would
have been needed for the first concrete placed, but it was easier to
place them at this stage than later, when there was less room. Three
rough shutters were also nailed to the curved portion for the floor
template. Opposite each biat, a bracket, _bb_, was then nailed, which
carries a set of rough boards which formed the risers for the duct
steps. Everything was then ready for concreting except that, where
refuge niches occurred, a form for the portion of the niche below the
seat was nailed to the shuttering. This form is shown at _R_ in Fig. 1,
Plate LXXIV.
[Illustration: PLATE LXXIV]
The concrete was dumped down on each side from side-dump cars standing
on the track, and, falling between the risers for the duct steps, ran or
was shoveled under the forms and down into the bottom. The horizontal
surface on each side the center drain was smoothed off with a shovel.
The workmen became very skillful at this, and got a fairly smooth
surface. This concrete was usually placed in lengths of 45 or 60 ft.
After setting for about 24 hours, the brackets, _bb_, were removed,
together with the shuttering on the steps. The triangular pieces, _t_ in
Fig. 1, Plate LXXIV, were not removed until later. Instead, a board was
laid upon this lower step on which the duct layers could work. This and
the triangular piece were not removed until just before the bench
concrete was placed. This was important, as otherwise the bond between
the old and new concrete would be much impaired by dirt ground into the
surface of the old concrete. The ducts were then laid, as shown in Fig.
2, Plate LXXIV.
The remaining shutters for the face of the bench walls were then placed.
The remainder of the forms for the refuge niches, _RR_, in Fig. 1, Plate
LXXIV, were nailed to the shutters, the steel beam over the niche was
laid in place, the forms for the ladders, _L_ in Fig. 2, Plate LXXIV,
which occur every 25 ft., were tacked to the shutters, the shutters and
forms were given a coat of creosote oil, and then all was ready for
placing the bench concrete.
The specifications required a 2-in. mortar face to be placed on all
exposed surfaces and the remainder to be smoothed with a trowel and
straight-edge. After about 48 hours, the biats were blocked up on the
bench, and all forms between the bench walls below the working floor
were removed.
The centering for the arch concrete consisted of simple 5 by 3-1/2 by
5/16-in. steel-angle arch ribs, curved to the proper radius, spaced at
5-ft. intervals. Each rib was made up of two pieces spliced together at
the top. Two men easily handled one of these pieces. After splicing, the
rib was supported by four hanger-bolts fastened to the iron lining as
shown in Fig. 3, Plate LXXIV.
In the early part of the work, two additional bolts were used about half
way up on the side between the upper and lower hanger-bolts. It was soon
found that by placing the strut between the tunnel lining and the crown
of the rib, these hanger-bolts could be dispensed with. The lagging was
of 3-in. dressed yellow pine, 12 in. wide, and in 15-ft. lengths. Each
piece had three saw cuts on the back, from end to end, allowing it to be
bent to the curve of the arch; it was kept curved by an iron strap
screwed to the back. The arches were put in, either in 15, 30 or 45-ft.
lengths, depending on what was ready for concrete and what could be done
in one continuous working. The rule was that when an arch was begun, the
work must not stop until it was finished. An arch length always ended in
the middle of a ring. The lagging was placed to a height of about 6 ft.
above the bench before any concreting was done. When the concrete had
been brought up to that point, lagging was added, one piece at a time,
just ahead of the concrete, up to the crown, where a space of about 18
in. was left. When the lagging had reached the upper hanger-bolts, they
were removed, which left only the two bottom bolts fixed in the
concrete. Most of these were unscrewed from the eye and saved, as tin
sleeves were placed around them before concreting. Two cast-iron eyes
were lost for every 5 ft. of tunnel. To place the key concrete, a stage
was set up in the middle of the floor, and, beginning at one end, about
2 ft. of block lagging was placed. Over this, concrete was packed,
filling the key as completely as possible. This was done partly by
shoveling and using a short rammer, and partly by packing with the hands
by the workmen, who wore rubber gloves for the purpose. Another 2 ft. of
lagging was then placed, and the operation was repeated, and thus
working backward, foot by foot, the key was completed. This is the usual
way of keying a concrete arch, but in this case the difficulty was
increased by the flanges of the iron lining. It was practically
impossible to fill all parts of the pockets formed by these flanges. To
meet this difficulty, provision was made for grouting any unfilled
space. As the concrete was being put in, tin pipes were placed with
their tops nearly touching the iron lining, and their bottoms resting on
the lagging. Each pocket was intended to have two of these pipes, one to
grout through and the other to act as a vent for the escape of air. Each
center key ring had six pipes, and each side key had eight. The bottoms
of the pipes were held by a single nail driven half way into the
lagging. This served to keep the pipes in position and to locate them
after the lagging was taken down.
The cost of labor in the tunnels directly chargeable to concrete was
$1.80 per cu. yd. The top charges, exclusive of the cost of materials
(cement, sand, and stone), amounted to $3.92.
ELECTRIC CONDUITS.
In one bench wall of each tunnel there were fifteen openings for power
cables and in the other, between the river shafts, there were forty
openings for telephone, telegraph, and signal cables. East of the Long
Island shaft, the number of the latter was reduced to twenty-four. The
telephone ducts were all of the four-way type. The specifications
required that the power ducts should have an opening of not less than
3-1/2 in., nor more than 3-7/8 in., and that after laying they should
pass a 4-ft. mandrel, 3-3/8 in. at the leading end and 2-5/8 in. at the
other. The outside dimension was limited between 5 and 5-3/8 in. The
openings of the four-way ducts were required to be not less than 3-3/8
in., nor more than 3-5/8 in., and after laying to pass a 5-ft. mandrel,
3-1/4 in. at the leading end and 2-1/2 in. at the other. The outside
dimensions were limited between 9 and 9-1/2 in. All were to be laid in
1/4-in. beds of mortar. The specifications were not definite as to the
shape of the opening, but those used were square with corners rounded to
a radius of 3/8 in. The four-ways were 3 ft. long, and the singles, 18
in.
A study of the foregoing dimensions will show that the working limits
were narrow. Such narrow limits would not pay for the ordinary conduit
line in a street, where there is more room. In the tunnel greater
liberality meant either reducing the number of conduits or encroaching
on the strength of the concrete tunnel lining. The small difference of
only 1/8 in. in the size of the mandrel, or a clearance of only 1/16 in.
on each side, no doubt did increase the cost of laying somewhat, though
not as much as might at first be supposed. All bottom courses were laid
to a string, in practically perfect line and grade, and all joints were
tested with mandrels which were in all openings, and pulled forward as
each piece of conduit was laid. As the workmen became skillful, the
progress was excellent.
All costs of labor in the tunnel chargeable to duct laying amounted to
$0.039 per ft. of duct; top charges brought this up to $0.083.
The serious problem was to guard against grout and mortar running into
the duct opening through the joints from the concrete, which was a
rather wet mixture. Each joint was wrapped, when laid, with canvas,
weighing 10 oz. per sq. yd., dipped in cement grout immediately before
using. These wraps were 6 in. wide, and were cut long enough to go
around the lap about the middle of the duct. As soon as all the ducts
were laid, the entire bank was plastered over with fairly stiff mortar,
which, when properly done, closed all openings. The plastering was not
required by the specifications, but was found by the contractor to
result in a saving in ultimate cost.
The concrete on the two sides of the bank of ducts was bonded together
by 2 by 1/8-in. steel bonds between the ducts, laid across in horizontal
joints. Both ends were split into two pieces, 1 in. long, one of which
was turned up and the other down. These bonds projected 1-1/2 in. into
the concrete on either side. Where the bond came opposite the risers of
the duct step, against which the ducts were laid, recesses were provided
for the projecting bond. This was done by nailing to the rough shutters
for the steps a form which when removed left a dove-tailed vertical
groove. This form was made in two pieces, one tapering inward and the
other with more taper outward. As the bonds were placed, these grooves
were filled with mortar.
The ducts usually received their final rodding with the specification
mandrel a month or more after they were laid, after which all openings
into splicing chambers were stopped by wooden plugs, 8 in. long tapering
from 3-3/4 in. at one end to 2-3/4 in. at the other end, and shaped to
fit the opening tightly. At first the plugs were paraffined, to keep
them from swelling and breaking the ducts, but were not successful, as
the paraffin lubricated them so that they would not stay in place. They
were expensive, and there was some swelling in the best that were
obtained. A better plug was made by using no paraffin, but by making six
saw cuts, three horizontal and three vertical, in the larger end,
cutting to within about 2 in. of the smaller end. The swelling of the
wood was then taken up by the saw cuts and the spring of the wood.
The splicing chambers are at 400-ft. intervals. They are 6 ft. long, 4
ft. 9 in. high, with a width varying from 3 ft. 2 in. at the top to 1
ft. 2 in. at the bottom.
*** End of this LibraryBlog Digital Book "Transactions of the American Society of Civil Engineers, vol. LXVIII, Sept. 1910 - The New York Tunnel Extension of the Pennsylvania Railroad. - The East River Tunnels. Paper No. 1159" ***
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