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

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assuming a value of 0.83 for the coefficient of friction for both stone
on stone and stone on wood, the ultimate resistance in this case
should be about 2 500 lb. Under the maximum pressure developed in
this test (2 400 lb.), no indication of failure was evident. The excess-
ive deflection of the embankment made it impracticable to carry this
test further. The friction along the face in contact with the board
would evidently be more effective the lower the point of application
of the pressure. These results should be of value in the design of
bulkhead walls.

The theoretical active pressure for the embankment in Test 1
would be about 280 lb., and that in Test 2, about 170 lb. If the curve
for Test 1, Fig. 13, is extended, it will indicate a zero deflection at
800 lb., and for Test 2, a zero deflection at about 600 lb. In Test 4,
the board rested against a wale near the top before the pressure was
applied, a thin slab of wood having been placed between the board and
this wale. Any movement of the embankment would release the slab
of wood, and this occurred when the springs indicated a pressure of
850 lb., checking the results obtained from the deflection curve as
closely as could be expected. These results seem to indicate a maxi-
mum resistance, without deflection, of about three times the active

pressure.

Construction.

Pile-Driving. — The driving of the sheet-pile pockets in the designed
shape was accomplished by driving four timber piles in the location
for each pocket, and these served to support a plank templet slightly
smaller than the size of the pocket, around which the steel piles were
set. The piles of the first five pockets were set in such order that
the closure occurred in the inshore panel, the remaining pockets being
set so that the closure came in the diaphragm common to adjoining
pockets, it being easier to get a good fit for the closure pile in the
straight diaphragm than in the curved inner panel.

In setting the piles, their own weight caused them to settle in the
mud to a depth of about 20 ft., so that they were required to be driven
only about 10 ft. The driving was done with a "!N"ew Monarch" type
of steam hammer, weighing about 4 000 lb., bolted to a frame which
fitted over the piles and held the hammer in a vertical position, the



518 COFFER-DAM FOE 1 000-FOOT PIEK

hammer plate being wide enough to drive three piles at once. After
being driven in sets of three, the individual piles were driven with a
follower, in order to insure contact of each with the rock. As the
first five pockets were in the area formerly occupied by the inner end
of the West 47th Street pier, a considerable quantity of timber was
encountered, which made the setting and driving of the piles difficult.
In the case of Pockets 3, 4, and 5, timber was encountered near the
surface of the mud, which caused some of the piles to project so high
when they were set that it was necessary to drive them with a steam
hammer down to grade, which would allow the adjoining piles to be
entered. This resulted in throwing Pockets 4 and 5 so far out of
plumb that the piles adjoining the closure pile in each pocket were
farther apart at the bottom than at the top. The hard driving neces-
sary to draw these adjoining piles together caused the rupture of one
jaw of the closure pile in Pocket 5, leaving a gap in the inner panel
of about 25 ft. from the rock bottom. A similar condition was pro-
duced in placing the closure pile in the diaphragm between Pockets
8 and 9, it being impossible to detect the fact that the closure pile
had passed out of the adjoining jaws.

There was no difficulty in driving the piles to rock between
Pockets 8 and 35, the bottom having been dredged to 30 ft. below low
water, removing practically all the timber usually found embedded in
the upper surface of the mud.

At the beginning of the return at West 44th Street, however, a
great deal of trouble was caused by the proximity of the two large
cylindrical pockets to the inner end of the 44th Street pier. Before
dredging was done at this point, a timber crib occupied a large part
of the area covered by Pockets 35 and 36, extending under the inshore
end of the pier shed. In dredging with a dipper-dredge it was impos-
sible to clear out the bottom of the crib close to the shed on account
of the danger of damaging the structure, consequently some of the
piles in Pockets 36 and 35J encountered the projecting ends of the
round crib timbers. Very hard driving was required to put down the
piles which were close to the crib, four piles in Pocket 35^ requiring
24 hours of driving with a 2-ton steam hammer. Apparently, these
four piles passed through three courses of crib logs, as the very bad
driving occurred in three stages, yet there were no indications that they
were parting from each other or curling up, and they finally brought



COFFEE-DAM FOR 1000-FOOT PIER '519

up solidly on the rock. Evidently, however, there was a rupture, as
practically all the leakage of the entire dam took place through the
outshore side of Pocket 35^.

The setting of pockets, which was begun with No. 1, on April
]Oth, 1914, was continued until No. 27 was reached, on June 19th,
1914. Owing to a change in plan, setting was then suspended until
October 5th, when it was resumed in No. 35, the cylindrical pocket,
and carried thence to Pocket 44. Pockets 28 to 30 were then set,
Nos. 31 to 33 being omitted until the lighter had completed the
removal, from the rear of the dam, of all the mud which it could not
reach from a position outside the dam. The lighter was then placed
outside the dam and the remaining pockets were set, the closure being
made in Pocket 31 in the middle of the inshore and outshore panels.

Dredging and Filling PocJcets. — The weakness at these two points
was soon developed when the filling of the pockets was begun. In the
case of Pocket 5, the mud had been dredged from the inshore side to
a depth of about 30 ft. below low water, the material being placed in
the pocket to a grade of about 7 ft. above low water. There was thus
a head of about 37 ft. of mud on the inner panel, which, after the
lapse of a few hours, completed the opening of the gap at the
closure pile.

In order to repair the damage it was necessary to remove some of
the filling which had been placed in Pockets 6 and 7, and thus allow
the corner pile between Pockets 5 and 6 to be pulled back into a
vertical position. The distorted piles of the ruptured panel were
removed and new piles were placed, two being added to the original
number to fill the space caused by the spreading of the corners when
the filling was suddenly released.

The failure of the diaphragm between Pockets 8 and 9 occurred
when the filling in No. 8 had reached — 12, and in No. 9 when it had
reached — 20, and the mud inshore from the two pockets had been
dredged to about — 40 ft. The original plan, in constructing the
dam, was to dredge the material in the rear overlying the rock, place
it in the pockets, and then proceed to deposit rip-rap at the rear; and,
when the rip-rap had reached the level of the mud, outshore from
the dam, to deposit filling outshore in sufficient quantity to counteract
the pressure of the rip-rap.



530 COFFER-DAM FOR 1 000-FOOT PIER

The failure of Pockets 5 and 8 made it evident that this procedure
would have to be modified, unless there was assurance that the closure
piles were not under considerable initial stress. A number of the
closure piles had required considerable driving, and it was decided to
avoid unduly stressing them by proceeding as follows : The mud in the
rear of the dam was excavated for the length of two pockets and taken
to sea; rip-rap was then deposited until it reached the grade of the
original bottom in the pockets; filling was then placed in the pockets,
and a head of mud and earth of about 10 ft. over the grade of the
rip-rap was maintained as the placing of rip-rap was continued. Suf-
ficient tension was thus maintained in the walls of the pocket to make
them water-tight without subjecting them to severe loads. The filling
comprised a mixture of mud and cellar earth, the latter being dumped
from trucks which were driven along a platform built on top of the
dam. As the earth was dumped in the middle of the pockets, its
greater weight forced the mud up along the walls, providing a seal
which proved to be absolutely water-tight.

During the time required for the foregoing operation of dredging
and filling, which averaged about 10 days for each pocket, the xinbal-
anced pressure of the mud in the pockets and also that outshore from
the latter caused them to lean inshore. The mud in which the piles were
set is of a stiff, clay-like consistency which will stand at a steep slope
for a considerable time if undisturbed. The impact of the 2-yd.
buckets of mud on the original filling in the pockets apparently was
sufficient to destroy the cohesion in the mass, causing it to exert pres-
sure tending to tip the pocket inshore. The maximum movement of
a pocket (No. 16) immediately after the completion of the dredging
v/as i ft. in 24 hours, and there was a maximum total movement of
about 2J ft. in the 10 days required to restore the balance of pressure
on the sides of the pocket. The average movement during the time
of placing the filling was about IJ ft. The balance of pressure, once
restored, was easily maintained by placing the earth embankment out-
shore to counteract the pressure of the rip-rap.

In dredging and filling the cylindrical pockets (ISTos. 35 and 36) a
different procedure was necessary, on account of the change in the
type of construction. "Whereas, in the small pockets, the pressure of
the mud inside tended to hold them in the same shape as when they
were set, in these cylinders, as it was necessary to clear the inside




Fig. 14. — Laying Out Templates for Driving Sheet-Piling.



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Fig. 15. — Sheet-Piling i.-or Pockets Deiven.




Fig. 16. — Driving Steel Sheet-Piling for Coffer-Dam.





Fig. 17. — Large Pocket, and Rip-Rap Embankment, West 44th Street.



COFFEE-DAM FOE 1 000-FOOT PIEE 525

of mud in order to bring the rip-rap in contact with the rock bottom,
there was some danger that the pressure of the mud around the out-
side might distort or collapse the cylinders. This danger was avoided
by dredging around the outside of the cylinders at the same time
that deepening was going on within, except on the sides which were
adjacent to the crib. Here the proximity of the crib precluded any
dredging, and it was necessary, in order to hold the pockets in shape,
to leave a fillet of stiff mud around that portion of the circumference
which received pressure from the outside. In each cylinder the rock
was cleared of mud for about three-quarters of the area of the bottom.
Immediately after the completion of dredging the rip-rap was deposited
uniformly around the circumference, maintaining practically the cir-
cular shape throughout the operation.

Pumping. — The unwatering of the coiler-dam was begun on March
29th, 1915, with a Morris 10-in. centrifugal steam pump, set on skids
resting on the rip-rap embankment. Steam for this pump was fur-
nished by a 50-h.p. locomotive boiler placed on the top of the dam.
With this pump the level of the water was lowered from to — 13 ft.
in 19 days, the pump being operated only 16 hours per day, in order
to allow the rip-rap embankment to consolidate itself. Meanwhile
(April 13th), a leak began developing in the single line of piling
along the face of the crib at 47th Street, about 100 ft. from the river,
and, by April 18th, this had reached the capacity of the pump. The
single line of piling which forms the dam along 47th Street was
driven on a line parallel to, and from 4 to 5 ft. from, a rock-filled
timber crib which extends along 47th Street. Along the face of this
crib, at the point where the leakage took place, there was none of the
stiif mud which acted as a seal elsewhere along the dam. Further-
more, the rock fill in the cells of the crib was so porous that the river
water had free access to the piling, and, although earth filling was
deposited between the face of the crib and the sheet-piling, its thick-
ness (about 4 ft.) was not sufficient to prevent a considerable flow
between the piles and the rock. In order to place against the foot of
the piling material which would not be drawn through by the flow of
water, wooden piles were driven at intervals of from 4 to 5 ft. between
the steel piling and the face of the crib. These were then withdrawn,
and the holes filled with a mixture of sand and horse manure by ram-
ming down charges of this material with the pile until the stiffness



536



COFFEB-DAM FOE 1 OOO-FOOT PIER



Unbalanced Pressure, in Thousands of Pounds

00 55 o; M

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Movement of Dam, in Feet



























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Online LibraryAmerican Society of Civil EngineersTransactions of the American Society of Civil Engineers (Volume 81) → online text (page 43 of 167)