=====+=============================+=============================+
| North Manhattan. | South Manhattan. |
+-----------------------------+----------------------+------+
| Number of | Station |Lin. | Number of | Station |Lin. |
| rings | of |ft. | rings | of |ft. |
| erected. | leading |for | erected. | leading |for |
+-----------+ ring. |month.+-----------+ ring. |month.|
|For | To | | |For |To | | |
Month|month|date | | |month|date | | |
-----+-----+-----+----------+------+-----+-----+----------+------+
1905 | | | | | | | | |
May | 26 | 26|200 + 83.7| 63.7 | | | | |
June | 26 | 52|201 + 49.0| 65.3 | | | | |
July | 28 | 80|202 + 19.2| 70.2 | | | | |
Aug | 26 | 106|202 + 84.3| 65.1 | | | | |
Sept | 21 | 127|203 + 36.8| 52.5 | 31 | 31|200 + 96.4| 76.4 |
Oct | 25 | 152|203 + 99.4| 63.6 | 45 | 76|202 + 09.2|112.8 |
Nov | 31 | 183|204 + 76.9| 77.5 | 31 | 107|202 + 86.5| 77.3 |
Dec | 59 | 242|206 + 24.6|147.7 | 34 | 141|208 + 71.8| 85.3 |
1906 | | | | | | | | |
Jan | 94 | 336|208 + 59.8|235.2 | 27 | 168|304 + 39.4| 67.6 |
Feb | 78 | 414|210 + 54.9|195.1 | 64 | 232|205 + 99.6|160.2 |
Mar | 56 | 470|211 + 95.2|140.3 | 96 | 328|208 + 39.9|240.3 |
April| 119 | 589|214 + 93.0|297.8 | 84 | 412|210 + 59.1|210.2 |
May | 129 | 718|218 + 15.7|322.7 | 70 | 482|212 + 25.3|165.2 |
June | 218 | 936|232 + 60.9|545.2 | 140 | 622|215 + 75.5|350.2 |
July | 155 |1,091|227 + 48.5|387.6 | 82 | 704|217 + 80.7|205.2 |
Aug | 145 |1,236|231 + 11.2|362.7 | 134 | 838|221 + 15.8|335.1 |
Sept | 89 |1,325|233 + 34.1|222.9 | 168 |1,006|225 + 35.8|420.0 |
Oct | | | | | 105 |1,111|227 + 98.6|262.8 |
Nov | | | | | 7 |1,118|228 + 16.8| 18.2 |
=====+=====+=====+==========+======+=====+=====+==========+======+
=====+=============================+============================+========
| North Weehawken. | South Weehawken. |
+-----------------------------+----------------------------+Average
| Number of | Station |Lin. | Number of | Station |Lin. |progress
| rings | of |ft. | rings | of |ft. |per
| erected. | leading |for | erected. | leading |for |shield
+-----------+ ring. |month.+-----------+ ring. |month|lin. ft.
|For | To | | |For |To | | |per
Month|month|date | | |month|date | | |month.
-----+-----+-----+----------+------+-----+-----+----------+-----+--------
1905 | | | | | | | | |
May | | | | | | | | | 15.9
June | 24 | 24|260 + 76.6| 59.3 | 12 | 12|260 + 70.0| 30.0| 38.6
July | 12 | 36|260 + 46.6| 30.0 | 15 | 27|260 + 32.4| 37.6| 34.4
Aug | 15 | 51|260 + 09.1| 37.5 | 16 | 43|260 + 07.4| 25.0| 31.9
Sept | 1 | 52|260 + 06.6| 2.5 | 18 | 61|259 + 47.2| 60.2| 47.9
Oct | 10 | 62|259 + 81.5| 25.1 | 20 | 81|258 + 97.2| 50.0| 62.9
Nov | 29 | 91|259 + 09.0| 72.5 | 39 | 120|257 + 99.7| 97.5| 81.2
Dec | 46 | 137|257 + 94.0|115.0 | 77 | 197|256 + 07.1|192.6| 135.1
1906 | | | | | | | | |
Jan | 77 | 214|256 + 01.4|192.6 | 73 | 270|254 + 24.6|182.5| 169.4
Feb | 133 | 347|252 + 68.6|332.8 | 165 | 435|250 + 11.7|412.9| 275.2
Mar | 142 | 489|249 + 13.3|355.3 | 111 | 546|247 + 34.0|277.7| 253.4
April| 32 | 521|248 + 33.3| 80.0 | 78 | 624|245 + 38.9|195.1| 195.7
May | 121 | 642|245 + 30.6|302.7 | 2 | 626|245 + 33.9| 5.0| 198.9
June | 162 | 804|241 + 25.3|405.3 | 157 | 788|241 + 41.1|392.8| 423.4
July | 113 | 917|238 + 42.4|282.9 | 118 | 901|238 + 45.9|295.2| 292.7
Aug | 138 |1,055|234 + 97.1|345.3 | 140 |1,041|234 + 95.8|850.1| 348.3
Sept | 55 |1,110|233 + 59.5|137.6 | 177 |1,218|230 + 52.8|443.0| 305.9
Oct | 1 |1,111|233 + 57.0| 2.5 | 94 |1,312|228 + 16.8|236.0| 125.3
Nov | 9 |1,120|233 + 34.1| 22.9 | | | | | 10.3
-----+-----+-----+----------+------+-----+-----+----------+-----+--------
A ½-in. air line was taken direct from the working chamber to the
recording gauges in the engine-room, which enabled the engine-room force
to keep a constant watch on the air conditions below. To avoid undue
rise of pressure, a safety valve was set on the air line at each lock,
set to blow off if the air pressure rose above that desired. The
compressor plant was ample, except, as before described, when passing
the gravel section at Weehawken.
Records were kept of the air supply, and it may be said here that the
quantity of free air per man per hour was in general between 1,500 and
5,000 cu. ft., though in the open gravel where the escape was great it
was for a time as much as 10,000 cu. ft. For more than half the silt
period it was kept between 3,000 and 4,000 cu. ft., but when it seemed
proved beyond doubt that any quantity more than 2,000 cu. ft. had no
beneficial effect on health, no attempt was made to deliver more, and on
two separate occasions for two consecutive weeks it ran as low as 1,000
cu. ft. without any increase in the number of cases of bends.
The amount of CO_{2} in the air was also measured daily, as the
specifications called for not more than 1 part of CO_{2} per 1,000 parts
of air. The average ranged between 0.8 and 1.5 parts per 1,000, though
in exceptional cases it fell as low as 0.3 and rose to 4.0. The air
temperature in the tunnels usually ranged from 55° to 60° Fahr., which
was the temperature also of the surrounding silt, though at times, in
the earlier parts of the work when grouting extensively in long sections
of the tunnel in rock, it varied from 85° to 110° Fahr.
_Grouting._--Grout of one part of Portland cement to one part of sand by
volume was forced outside the tunnel lining by air pressure through
1½-in. tapped and plugged grout holes formed in each segment for this
purpose, wherever the ground was not likely to squeeze in upon the metal
lining as soon as this was erected. That is to say, it was used
everywhere up to the river line; between river lines it was not used
except at the New York bulkhead wall in order to fill voids in the
rip-rap, and at the point of junction of the shields where the space
between the metal lining and the shield skins outside it was grouted.
Cow Bay sand was used, and it had to be screened to remove particles
greater than 1/10 in. in diameter, which would choke the valves. For
later grouting work, namely, in the top of the concrete lining inside
the metal lining, Rockaway Beach sand was used. This is very fine, and
did not need screening; it cost more, but the saving of screening and
the non-blocking of valves, etc., resulted in a saving.
The grout was mixed in a machine shown in Fig. 2, Plate XLI, which is a
view of the grouting operation.
The grout pipes were not screwed directly into the tapped hole in the
segments, but a pipe containing a nipple and valve was screwed into the
grout hole and the grout pipe screwed to the pipe. This prevented the
waste of grout, enabled the valve to be closed and the grout pipe
disconnected, and the pipe to be left in position until the grout had
set. In the full rock section, 20 or 30 rings were put in without
grouting; then the shield was stopped, the last two or three rings were
detached and pulled ahead by the shield, a masonry stop-wall was built
around the outside of the last ring left in, and the whole 20 or 30
rings were grouted at one time. In the landward silt and gravel each
ring had to be grouted as soon as the shield had left it, in order to
avoid the flattening caused by the weight coming on the crown while the
sides were as yet unsupported. The grout was prevented from reaching the
tail of the shield by plugging up the space with empty cement bags,
assisted by segmental boards held against the face of the leading ring
by U-shaped clamps, fitting over the front circumferential flange of the
ring and the boards, and tightened by wedges. The air pressure varied
between 70 and 100 lb. per sq. in. above normal.
The force consisted of one pipe-fitter and one or two laborers employed
part of their time. When a considerable length was being grouted at a
time, as in the full rock section, many laborers were employed for a
short period.
Transportation and Disposal.
The transportation and disposal will be described under the following
headings:
Receipt and Unloading of Materials,
Surface Transportation,
Tunnel Transportation,
Disposal.
_Receipt and Unloading of Materials._--At the Manhattan Shaft the
contractor laid a spur siding into the yard from the freight tracks of
the New York Central Railroad, which immediately adjoins the yard on the
west. There was also wharfage on the river front about 1,500 ft. away.
At the Weehawken Shaft there were four sidings from the Erie Railroad
and one from the West Shore Railroad. Access to the river was gained by
a trestle direct from the yard, and Baldwin Avenue adjoined the yard.
All the iron lining arrived by railroad. It was unloaded by derricks,
and stacked so that it was convenient for use in the tunnel. The
Manhattan derricks were a pair of steel ones with 39-ft. booms, worked
by a 30-h.p., 250-volt, electric motor. There was also a stiff-leg
derrick with 50-ft. boom, on a platform near the shaft, which was worked
by a 40-h.p., 250-volt motor. At Weehawken there were two 45-ft. boom,
stiff-leg derricks of 2 tons capacity, one worked by a 42-h.p.
Lidgerwood boiler and engine, and the other by a 25-h.p., 250-volt,
electric motor. These derricks were set on elevated trestles near the
Erie Railroad sidings. There was a 50-ft. stiff-leg derrick with a
70-h.p. Lidgerwood boiler and engine near the cement warehouse on the
West Shore Railroad.
The storage area for iron lining was 1,800 sq. ft. at Manhattan and
63,000 sq. ft. at Weehawken; the maximum quantity of lining in storage
at any one time was 150 rings at Manhattan and 1,200 rings at Weehawken.
The cement, which was issued and sold by the Company to the contractor,
was kept in cement warehouses; that at the New York side was at Eleventh
Avenue and 38th Street, or some 1,200 ft. from the shaft, to which it
was brought by team; that at Weehawken was adjacent to the shaft, with a
2-ft. gauge track throughout it and directly connected with the shaft
elevator.
_Surface Transportation._--In the early days the excavation was handled
in scale-boxes of 1 cu. yd. capacity which were hoisted up the shafts by
a derrick, but, when the iron period began, two-cage elevators were put
in at each shaft. They were worked by a single, friction-drum,
Lidgerwood, steam hoisting engine of 40 h.p.
All materials of construction were loaded on cars on the surface at the
point where they were stored, and hauled on these to the elevators,
sent down the shaft, and taken along the tunnels to the desired point
without unloading.
The narrow-gauge railway on the surface and in the tunnel was of 2-ft.
gauge with 20-lb. rails. About 70 flat cars and 50 mining cars were used
at each shaft. On the surface at Manhattan these were moved by hand, but
at Weehawken, where distances were greater, two electric locomotives on
the overhead trolley system were used.
_Tunnel Transportation._--The mining cars shown in Fig. 19 were of 1¼
cu. yd. capacity. The short wheel base and unbalanced loading caused a
good many upsets, but they were compact, easily handled, and could be
dumped from either side or end.
[Illustration: MUCK CAR (AS USED IN RIVER TUNNELS) CAPACITY 5,000 LBS.
OR 1¼ CU. YD. FIG. 19.]
The flat cars shown in Fig. 20 were of 3 tons capacity, and could hold
two tunnel segments. As the working face was down grade from the shafts,
the in-bound cars were run by gravity. For out-bound cars a cable
haulage system was used, consisting of double-cylinder, Lidgerwood,
single friction-drum, hoisting engines (No. 32) of 6 h.p., with
cylinders 5 in. in diameter and 6 in. stroke and drums 10 in. in
diameter. These were handily moved from point to point, but, as there
was no tail rope, several men had to be used to pull the cable back to
the face. After the second air-lock bulkhead walls had been built, a
continuous-cable system, worked electrically, was put in each tunnel
between the first and second air-locks.
The engine consisted of an electric motor driving a 3-ft. 6-in. drum
hoist around which a ¾-in. steel wire cable passed three times. The
cable was led around a sheave, down the tunnel on the right side of the
in-bound track, and returned on the left side of the out-bound track. It
was then carried around a set of sheaves, where a tension of 1,000 lb.
was supplied by a suspended weight which acted on a sheave with a
sliding axle on the tension carriage. The cable was supported throughout
its length on 8-in. pulleys set in the floor at 50-ft. intervals. All
the guide sheaves were 36 in. in diameter.
[Illustration: FLAT CAR FOR TUNNEL SEGMENTS CAPACITY 6,000 LBS. FIG.
20.]
Each car was attached to the cable by a grip at its side. This was
fastened and unfastened by hand, but was automatically released just
before reaching the turn in the cable near each lock. This system could
haul without difficulty an unbalanced load of 10 muck cars, spaced 100
ft. apart, up a 2% grade. The cable operated over about 1,000 ft. of
tunnel, the motor being placed at the top of the grade. The driving
motor was of the semi-armored, 8-pole, series-wound type, rated at 25
h.p., 635 rev. per min., and using direct current at 220 volts. The
speed of handling the cars was limited by their having to pass through
the air-locks on a single track. As many as 106 cars have been hauled
each way in one 8-hour shift.
_Disposal._--At Manhattan the tunnel muck was carried from the elevator
over the upper level of the yard trestle and dumped into bins on the 33d
Street side, whence it was teamed to the public dump at 30th Street and
North River. At Weehawken the rock excavation was removed by the Erie
Railroad on flat cars on which it was dumped by the tunnel contractor,
but all the silt muck was teamed away to some marshy ground where
dumping privileges were obtained.
The typical forces employed on transportation were as follows:
_Receipt and Unloading of Material: Surface Transportation and
Disposal._
At Manhattan Shaft, on 10-hour shifts:
2 Engineers on derricks. @ $3.00 per day.
2 Foremen. " 3.25 " "
15 Laborers loading and unloading iron. " 1.75 " "
7 Laborers on disposal. " 1.75 " "
6 Teams. " 7.50 " "
At Weehawken Shaft, on 10-hour shifts:
3 Engineers on derricks and locomotives. @ $3.00 per day.
16 Laborers loading and unloading iron. " 1.75 " "
3 Foremen. " 3.50 " "
11 Laborers on disposal. " 1.75 " "
6 Teams on disposal. " 6.50 " "
Tunnel Transportation (Including Shaft Elevator):
Shaft elevators and to and from the first air-lock on 10-hour shift:
2 Engineers. @ $3.00 per day.
2 Signalmen. " 2.00 " "
1 Foreman. " 3.00 " "
12 Laborers. " 1.75 " "
Between first lock and working face, on 8-hour shifts, the force varied:
From 1 to 3 (average 2) Hoist engineers @ $3.00 per day.
From 0 to 2 (average 1) Lockman " 2.75 " "
From 1 to 2 (average 2) Trackmen " 3.00 " "
From 2 to 7 (average 4) Cablemen
(pulling back cable) " 3.00 " "
_Pumping._--The water was taken out of the invert by a 4-in. blow-pipe
which was always kept up to a point near the shield and discharged into
the sump near the shaft.
When the air pressure was removed and the blow-pipe device,
consequently, was unavailable, small Cameron pumps, driven by compressed
air, and having a capacity of about 140 gal. per hour, were used, one
being set up wherever it was necessary to keep the invert dry; for
example, at points where caulking was in progress.
_Lighting._--The tunnels were lighted by electricity, the current being
supplied, at a pressure of 250 volts, from the dynamos in the
contractor's power-house.
Two 0000 wire cables were used as far as the second air-locks, about
1,650 ft. from the power-house, on each side; and beyond that point, to
the junction of the shields (about 1,750 ft.), 00 and 0 wires were used.
These cables also carried the current for the cable haulage system. Two
rows of 16-c.p. lamps, provided with reflectors, were used in each
tunnel; one row was along the side just above the axis, with the lights
at about 30-ft. intervals; the other along the crown, with the lamps
halfway between the side lamps, also at 30-ft. intervals. At points
where work was in progress three groups of 5 lights each were used. The
tunnels as a whole were well lighted, and in consequence work of all
kinds was much helped.
_Period No. 2._--_Caulking and Grummeting._--_November, 1906, to June,
1907._--After the metal lining had been built completely across the
river in both tunnels, the work of making it water-tight was taken up.
This consisted in caulking into the joints between the plates a mixture
of sal-ammoniac and iron borings which set up into a hard rusty mass,
and in taking out each bolt and placing around the shank under the
washer at each end a grummet made of yarn soaked in red lead. These
grummets were made by the contractor on the works, and consisted of
three or four strands of twisted hemp yarn, known as "lath yarn," making
up a rope-like cross-section about ¼ in. in diameter. Usually, one of
these under each washer was enough, but in wet gravel, or where bolts
were obliquely in the bolt-holes, two were used at each end. After
pulling the grummets in, all the nuts were pulled up tight by wrenches
about 3 ft. long, with two men on one wrench. Bolts were not passed as
tight unless the nut resisted the weight of an average man on a
2½-ft. wrench.
Before putting in the caulking mixture, the joints were carefully
scraped out with a special tool, cleaned with cotton waste, and washed
with a stream of water. The usual mixture for sides and invert was about
2 lb. of sal-ammoniac and 1 lb. of sulphur to 250 lb. of iron filings or
borings. In the arch, 4 lb. of sal-ammoniac and 3 lb. of sulphur to 125
lb. of filings was the mixture. A small hand-hammer was used to drive
the caulking tool, but, in the sides and invert, air hammers were used
with some advantage. The success of work of this kind depends entirely
on the thoroughness with which the mixture is hammered in; and the
inspection, which was of an exceedingly monotonous nature, called for
the greatest care and watchfulness on the part of the Company's forces,
especially in the pocket iron, where each bolt had to be removed, the
caulking done at the bottom of the pockets put in, the bolts replaced;
and the rest of the pockets filled. The results have been satisfactory,
as the leakage under normal air and prior to placing the concrete
averaged about 0.14 gal. per lin. ft. of tunnel per 24 hours, which is
about 0.0035 gal. per lin. ft. of joint per 24 hours. With each linear
foot of joint is included the leakage from 1.27 bolts. Afterward, when
the concrete lining was in, the leakage was found to be about 0.05 to
0.06 gal. per lin. ft. of tunnel per 24 hours, which compares favorably
with the records of other lined tunnels. The typical gang employed on
this work was as follows:
_In Pocket Iron:_
1 General foreman @ $5.00 per day.
1 Mixer " 3.00 " "
1 Nipper " 3.00 " "
5 Caulkers " 3.00 " "
10 Grummeters " 3.00 " "
_In Pocketless Iron:_
1 General foreman @ $5.00 per day.
1 Mixer " 3.00 " "
1 Nipper " 3.00 " "
3 Caulkers " 3.00 " "
12 Grummeters " 3.00 " "
The average amount of caulking and grummeting done per shift with such a
gang was (with pocketless grooves), 348 lin. ft. of joint and 445 bolts
grummeted; and in pocket iron: 126 lin. ft. of joint and 160 bolts
grummeted.
The caulking and grummeting work was finished in June, 1907, this
completing the second period.
_Period No. 3._--_Experiments, Tests, and Observations._--_April, 1907,
to April, 1908._--The third period, that of tests and observations in
connection with the question of foundations, is dealt with in another
paper. It occupied from April, 1907, to November, 1908. The results of
the information then gathered was that it was not thought advisable to
go on with the foundations.
_Period No. 4._--_Capping Pile Bores, Sinking Sumps, and Building
Cross-Passages._--_April, 1908, to November, 1908._--In order to reduce
the leakage from the bore segments to the least possible amount before
placing the concrete lining, it was decided to remove the plugs and
replace them with flat cover-plates; these have been described before,
together with the filling of Bore Segments No. 2 with mortar to reduce
the leakage around the distance piece.
During this period the turnbuckles to reinforce the broken plates were
put in, and the sump sunk at the lowest point of the tunnel. These sumps
have been described in a previous part of this paper; they were put down
without trouble. As much as possible of the concrete lining was put in
before the lining castings were taken into the tunnel, as the space
inside was very restricted. The first lining casting was bolted to the
flat flanges of the sump segment, the bolts holding the latter to the
adjacent segments were removed, and the whole was forced down with two
of the old shield jacks, taking a bearing on the tunnel. The two
together exerted a pressure of about 150 tons. The plugs in the bottom
of the sump segment were taken out, and pipes were put in, through which
the silt squeezed up into the tunnel and relieved the pressure on the
sump segment.
If the silt did not flow freely, a water-jet was used. The sump was kept
plumb by regulating the jacks. In this way the sump was sunk, adding
lining sections one by one, and finally putting on the top segment,
which was composed of three pieces.
The time taken to sink one sump was about 4 days, working one 8-hour
shift per day, and not counting the time taken to set up the jacks and
bracing. The sinking of each section took from 4 to 6 hours. The air
pressure was 25 lb. and the hydrostatic head 41 lb. per sq. in. The
force was 1 assistant superintendent at $6.00 per day, 1 foreman at
$4.50, and 6 laborers at $3.00 per day.
_Cross-Passages._--It was during this period that the five
cross-passages previously mentioned were built. In the case of those in
the rock, careful excavation was needed so as to avoid breaking the iron
lining. Drilling was done from both ends, the holes were closely spaced,
and about 2 ft. 6 in. deep, and light charges of powder were used. The
heading, 5 by 7 ft. in cross-section, was thus excavated in five
lengths, with 24 holes to a length, and about 23 lin. ft. of hole per
yard. About 5.3 lb. of powder per cu. yd. was used. The sides, top, and
bottom were then drilled at a very sharp angle to the face and the
excavation was trimmed to the right size. This widening out took about
7½ ft. of hole per cu. yd., and 0.9 lb. of powder.
In the passages in silt the excavation had to be 12 ft. wide and 13 ft.
8 in. high to give enough room inside the timbers. The plates at one end
of the passage were first removed. An air pressure of 17 lb. was
carried, which was enough to keep the silt from squeezing in and yet
left it soft enough to be chopped with a spade.
A top heading, of full width and 6 ft. 8 in. high, was first taken out,
and the roof was sheathed with 2-in. boards held by 10 by 10-in. head
trees at 3-ft. centers, with 10 by 10-in. side trees. The lower 7 ft. of
bench was then taken out, a tight floor of 6 by 6-in. cross-timber was
put in, and also longer side trees, the head trees being temporarily
held by two longitudinal 10 by 10-in. stringers blocked in place. The
bulk of the space between the side trees was filled with 10 by 10-in.
posts and blocking. The plates at the other end of the passage were then
taken out from the other tunnel.
After the excavation was out, the outer reinforced concrete lining was
built. Rough forms were used, as the interior surfaces of the passages
were to be rendered with a water-proofing cement. A few grout pipes
were built in, and all voids outside the concrete were grouted. Grouting
was also done through the regular grout holes of the metal lining around
the openings.
In the case of the most westerly of the cross-passages at Weehawken,
which was in badly seamed rock carrying much water, a steel
inter-lining, rather smaller than the concrete, was put in. The space
between the concrete and the steel was left open, so that water coming
through the concrete lining was stopped by the steel plate. This water
was led back to the shield chamber in a special drain laid in the bench
of the river tunnel and behind the ducts. From the shield chamber the
water ran with the rest of the drainage from the Weehawken Land Tunnels
to the Weehawken Shaft sump.
[Illustration: TYPICAL CROSS-SECTIONS SHOWING SUCCESSIVE STAGES IN
PLACING CONCRETE IN RIVER TUNNELS FIG. 21.]
_Period No. 5._--_Placing the Concrete Lining._--_November, 1908, to
June, 1909._--During the fifth period the concrete lining was put in.
This lining was placed in stages, as follows: First, the invert; second,
the duct bench; third, the arch; fourth, the ducts; and fifth, the face
of the bench. This division can be seen by reference to Fig. 21.
All the work was started on the landward ends and carried toward the
middle of the river from both sides. Except where the Weehawken force
passed the lowest point of the tunnel, which is at Station 241 or nearly
900 ft. to the west of the middle of the river, all the work was down
grade.
Before any concrete was placed, the surface of the iron was cleaned with
scrapers and wire brushes, and washed with water. Any leaks in the
caulking and grummeting (finished by June, 1907, and therefore all more
than 12 months old) were repaired. All the grout hole plugs were
examined, and the plugs in any leaking ones were taken out, smeared
with red lead, and replaced. The leakage in the caulking was due to the
fact that the tunnel had been settling slightly during the whole 12
months of pile tests, and, therefore, had opened some of the joints.
After the caulking had been repaired and the surface thoroughly cleaned,
the flanges were covered with neat cement (put on dry or poured on in
the form of thick grout) just before the concrete was placed.
_Invert Concrete._--The form used for the landward type of concrete,
that is, the one with a middle drain, consisted of a frame made of a
pair of trussed steel rails on each side of the tunnel and connected at
intervals with 6 by 6-in. cross-timbers; two "wing forms" were hung from
this frame by adjustable arms. These wings formed the curved sides of
the invert, the lip, and the form for the middle drain. The whole form
was supported on three wheels, two on the rear end running on a rail
laid on the finished concrete, and the third in front attached to the
frame by a carriage and running on a rail temporarily laid on the iron
lining. The form was braced from the iron lining by 6 by 6-in. blocks.
For the soft-ground type of invert, namely, the one without the middle
drain, a form of the same general type was used, except that the form
for the middle drain was removed. After the form had been in use for
some time, "key pieces" (made of strips of wood about 1 ft. 3 in. in
length and 3 by 3 in. in cross-section) were nailed circumferentially on
the under side of the wings at 2-ft. intervals. This was done because,
at the time, it was not known whether ballasted tracks or some form of
rigid concrete track construction would be adopted, and, if the latter,
it was desirable not to have the surface smooth.
The concrete was received in cars at the rear end of the form and dumped
on a temporary platform. It was then loaded into wheel-barrows on the
runways, as shown in Fig. 22. The concrete was thrown from the barrows
into the invert, where it was spaded and tamped.
In cases where there was steel-rod reinforcement, the concrete was first
brought up to the level of the underside of these rods, which came
between the wings; the rods were laid in place, and then more concrete
was placed over the rods and brought up to the level of the bottom of
the wings. Where there was no reinforcement, the concrete was brought up
in one lift.
[Illustration: CONCRETE FORM STANDARD IN RIVER TUNNELS FIG. 22.]
After this was finished, the concrete behind the wings was placed,
thoroughly spaded and tamped, and, where there were longitudinal
reinforcing rods, these were put in at their proper level. Where there
were circumferential rods, the 16-ft. rods had already been put in when
the lower part of the concrete was placed. As the invert was being
finished off, the 8-ft. rods were embedded and tied in position.
The longitudinal rods were held in place at the leading end of each
length of arch by the wooden bulkhead, through which holes were drilled
in the proper position. At the rear end they were tied to the rods
projecting from the previous length. The quantity of water used in
mixing the invert concrete needed very nice adjustment; if too wet, the
middle would bulge and rise when the weight of the sides came on it;
and, if too dry, it would not pack properly between the flanges of the
iron lining. The difficulties as to this were often increased by the
flow of accumulated leakage water from the tunnel behind on the concrete
while it was being put in. To prevent this, a temporary dam of sand bags
was always built across the last length of finished invert concrete
before beginning a new length. A sump hole, about 4 by 1 ft. and 1 ft.
deep, was left every 800 ft. along the tunnel, and a small Cameron pump
was put there to pump out the water.
The invert forms were left in place about 12 hours after the pour was
finished. The average time taken to fill a length of 30 feet was 7
hours, the form was then left 12 hours, and it took 2 hours to set it up
anew. The total time for one length, therefore, was 21 hours, equal to
34 ft. per 24 hours. At one place, a 45-ft. form was used, and this gave
an average speed of 45 ft. per 24 hours.
An attempt was made to build the invert concrete without forms (seeing
that a rough finish was desired, as previously explained, to form a key
for possible sub-track concrete), but it proved a failure.
The typical working force (excluding transport) was as follows:
1 Foreman @ $3.25 per shift.
2 Spaders " 2.00 " "
9 Laborers " 1.75 " "
The average time taken to lay a 30-ft. length of invert was 7 hours; the
two spaders remained one hour extra, smoothing off the surface.
For setting the form, the force was:
1 Foreman @ $4.50 per shift.
5 Carpenters " 3.25 " "
6 Carpenters' helpers " 2.25 " "
The average time taken to erect a form was 2 hours, 1 carpenter and 1
helper remaining until the concrete was finished.
_Duct Bench Concrete._--The duct bench (as described previously) is the
portion of the concrete on which the ducts are laid. The exact height of
the steps was found by trial, so as to bring the top of the ducts into
the proper position with regard to the top and the face of the bench.
Both kinds of duct bench forms were of the same general type. A drawing
of one of them is shown on Plate XLII. The form consisted of a skeleton
framework running on wheels on a track at the level of the temporary
transportation tracks. The vertical faces of the steps were formed by
boards supported from the uprights by adjustable arms. The horizontal
surfaces were formed by leveling off the concrete with a shovel at the
top of the vertical boards. Where the sheets of expanded metal used for
bonding came at a step, the lower edge of the boards forming the back of
the step was placed 1 in. above the one forming the front of it; but,
when the expanded metal came in the middle of a step, a slot 1 in. wide
was left at that point to accommodate it.
A platform was formed on the top of the framework for the form, and on
this a car forming a sort of traveling stage was run. There was ample
room to maintain traffic on a single track through the form. A
photograph of the form is shown in Fig. 1, Plate XLIII.
The concrete, for the most part, was received at the form in ¾-cu. yd.
dumping buckets. The buckets were lifted by the rope from a small
hoisting engine. This rope passed over a pulley attached to the crown of
the tunnel and dumped into the traveling stage on the top of the form.
In this the concrete was moved along to the point where it was to be
deposited, and there it was thrown out by shovels into the form below.
For a portion of the period, while the duct bench concrete was being
laid, it was not necessary to maintain a track for traffic through the
form and, during that period, the concrete for the lower step was placed
from below the form, the concrete being first dumped on a temporary
stage at the lower track level.
Owing to the horizontal faces of the steps being uncovered, there was a
tendency for the concrete there to rise when concrete was placed in the
steps above. For this part of the work, also, it was necessary to see
that the concrete was not mixed too wet, for, when that was the case,
the concrete in the upper steps was very apt to flow out at the top of
the lower one. At the same time, there was the standing objection to the
mixture being too dry, namely, the responsibility of getting a
sufficient amount of spading and tamping done. Particulars of the exact
quantity of water used are given later in describing "Mixing." Fig. 2,
Plate XLIII, illustrates the process of laying.
In the section of the tunnel in which there were circumferential
reinforcement rods in the duct bench, the rods were in place before the
laying commenced, as they had been placed with the invert concrete. The
circumferential reinforcing rods in the arch came down into the upper
part of the duct bench concrete; these rods were put in position and
tied to the iron lining in the crown at the same time as the duct bench
concrete was being finished off. Openings for the manholes were left in
the duct bench at the regular stationing.
The average time taken to fill a length of 35 ft. was about 6 hours; the
form was then left in position for about 8 hours--usually enough to let
the concrete set properly--and then moved ahead; it then took about 3
hours to set it up again ready to continue work. The total time for a
length, therefore, was about 17 hours, equal to an average progress of
about 49 ft. per day. The average force engaged in duct bench concrete
(not including transport) was:
1 Foreman @ $3.25 per day.
2 Spaders " 2.00 " "
9 Laborers " 1.75 " "
_Arch Concrete._--By far the greater part of the arch work was put in
with traveling centers before the face of the bench was built, in which
case the whole of the arch was built at once. A short length of arch at
each end of the tunnel was built after the face of the bench, in which
case the haunches or lower 5 ft. were laid first and the upper part of
the arch later.
The first traveling centers were used on the New York side, and were 50
ft. long. The laggings were of 4-in. yellow pine, built up in panels 10
ft. long and 16 in. wide for the sides, and solely longitudinal lagging
5 ft. long for the key.
It was pretty certain that the results to be obtained from forms of such
a length would not be satisfactory, and this was pointed out to the
contractor, who, however, obtained permission to use them on trial.
Grout pipes were built in, as it was not likely that the concrete could
be packed tightly into the upper part of the lining.
[Illustration: PLATE XLIII. TRANS. AM. SOC. CIV. ENGRS. VOL. LXVIII, No.
1155. HEWETT AND BROWN ON PENNSYLVANIA R. R. TUNNELS: NORTH RIVER
TUNNELS. FIG. 1.]
[Illustration: PLATE XLIII. TRANS. AM. SOC. CIV. ENGRS. VOL. LXVIII, No.
1155. HEWETT AND BROWN ON PENNSYLVANIA R. R. TUNNELS: NORTH RIVER
TUNNELS. FIG. 2.]
After about 300 lin. ft. of arch had been built with these forms, a test
hole was cut out and large voids were found, and, to confirm this,
another hole was cut, and similar conditions observed.
The results were so unsatisfactory that orders were given that the use
of longitudinal key lagging should be discontinued, and cross or block
lagging used instead. These block laggings were 6 in. in length (in the
direction of the tunnel) and 2 ft. in width; at the same time, the
system of grout pipes was changed. This will be described later under
"Grouting." It was soon found that with block lagging a better job could
be made of packing the concrete up into the keys, but the time taken to
"key up" a 50-ft. length was so great that the rest of the arch had set
by the time the key was finished. Despite a lot of practice, this was
the case, even in the unreinforced type. When the reinforcing rods were
met, the time for keying up became still greater, and therefore the
contractor was directed to shorten the forms to 20-ft. lengths. A
typical working force for a 50-ft. length was:
1 Foreman @ $3.25 per day.
4 Spaders " 2.00 " "
12 Laborers " 1.75 " "
Details of the 20-ft. forms are shown on Plate XLIV. The lower 4 ft. of
lagging was built on swinging arms, which could be loosened to allow the
centers to be dropped and moved ahead. The rest of the lagging was built
up in panels 10 ft. long and 1 ft. 4 in. high. The ribs rested on a
longitudinal timber on each side; these were blocked up from the top
step of the duct bench concrete. When the form was set, or when it was
released, it was moved ahead on rollers placed under it.
The concrete was received at the form in ¾-cu. yd. dumping buckets;
from the flat cars on which they were run, these were hoisted to the
level of the lower platform of the arch form. At this level the concrete
was dumped on a traveling car or stage, and moved in that to the point
on the form where it was to be placed. For the lower part of the arch,
the concrete was thrown directly into the form from this traveling
stage, but, for the upper part, it was first thrown on the upper
platform of the arch. The hoisting was done by a small Lidgerwood
compressed-air hoister, and set up on an overhead platform across the
tunnel. The pulley over which the cable from the hoister passed was
attached to the iron lining near one end of the form, and the traveling
stage ran back from the arch form on a trailer, shown on Plate XLIV.
When it was impossible to hang a pulley--owing to the concrete arch
having been built at the point where the trailer stood--an =A=-frame was
built on the trailer, and the pulley was attached to that.
In laying the lower part of the arch, about 1 ft. of lagging (including
the swinging arms) was first set, the other panels being pulled up
toward the top of the arch. When that was filled, the next panel above
was lowered into place, and the work continued. As the concrete rose
toward the key, it was packed up to a radial surface, so that the arch
would not be unduly weakened if the sides set before the key was placed.
All the time, great care was taken to see that the concrete was
carefully packed into the segments of the metal lining. The quantity of
water used in the concrete was carefully regulated, more being used in
the lower than in the upper parts of the arch.
In places where there were no reinforcing rods, the width of the
concrete key was the length of the block lagging, namely, 2 ft. Where
there was circumferential reinforcement, the key had to be more than 5
ft. wide, in order to take the 5-ft. closure rods used in the key. This
naturally increased the time of keying very much. On the places where
the 5-ft. longitudinal laggings were used, it was impossible to fill the
flanges of the metal lining much higher than their undersides.
As the concrete used in the key had to be much drier than that used
elsewhere, it was not easy to get a good surface. This trouble was
overcome by putting a thin layer of mortar on the laggings just before
the concrete was put in.
The overhead conductor pockets were a great hindrance to the placing of
the key concrete, especially where the iron was below true grade.
Whenever an especially troublesome one was met, a special grout pipe was
put in to fill up unavoidable holes by grouting after the concrete had
set. All the circumferential reinforcing rods were bent in the tunnel by
bending them around a curved form of less diameter than the required
bend. This generally left them all right in the middle of their length,
but with their end portions too straight; in such cases the ends were
bent again. All rods were compared with a template before being passed
for use.
The arch forms were left up for 48 hours after keying was finished.
Levels taken after striking the forms showed that no appreciable
settlement occurred. An average gang for a 20-ft. length of arch was:
1 Foreman @ $3.25 per shift.
2 Spaders " 2.00 " "
10 Laborers " 1.75 " "
Table 30 shows the progress attained under various conditions.
Whenever the face of the bench concrete was constructed before the arch,
the latter was built in two separate portions, that is, the bottom 5
ft., or "haunches" of the arch, as they were termed, were built on each
side and the rest of the arch later. This involved the use of two
separate sets of forms, namely, for the haunch and for the arch. Not
very much arch was built in this way, and, as the methods were in
principle precisely the same as those used when all the arch was built
in one operation, no detailed description is needed.
No provision was made in the contract for grouting the concrete arch,
but it soon became evident that by ordinary methods the top part of the
concrete could not be packed solid against the iron segments, especially
in the keys. As it was imperative to have the arch perfectly solid, it
was determined to fill these unavoidable gaps with a 1:1 Portland cement
grout, at the same time making every effort to reduce the spaces to a
minimum. This made it necessary to build grout pipes into the concrete
as it was put in.
The first type of grout pipe arrangement is shown as Type _A_, in Fig.
23. This was used with the longitudinal key laggings; when this method
was found to be no good, and cross-laggings were used, the system shown
as Type _B_, in Fig. 23, was adopted, in which vents were provided to
let out the air during grouting. The expense of these pipes was high,
and the contractor obtained permission to use sheet-iron tubes, which,
however, were found to be unsuitable, so that the screwed pipes were
used again. The contractor next obtained permission to try dispensing
altogether with the vent pipes, and so Type _C_, in Fig. 23 was evolved.
This, of course, was found to be worse than any of the other systems, as
the imprisoned air made it impossible to force grout in. Several other
modifications were made, and are shown in Fig. 23.
It was then decided to devise as perfect a system as possible, without
allowing the question of cost to be the ruling factor, and to use that
system throughout. In this system, shown as Type _S_, in Fig. 23, most
of the vent pipes were contained in the concrete, and their size was
independent of the thickness of the arch, so that they were easily
fixed in position and not subject to disturbance while placing the
concrete. This system was used for about 80% of the total length of the
tunnel, and proved entirely satisfactory. The machine used for grouting
was the same as that used for grouting outside the metal lining.
TABLE 30.--AVERAGE TIME TAKEN FOR VARIOUS OPERATIONS CONNECTED WITH
BUILDING CONCRETE ARCHES IN SUBAQUEOUS TUNNELS.
==========+=============+========+================+=========+=========+
Average |Type of |Length |Time, in hours, |Time, |Time, |
time |reinforcement|of |moving and |in hours,|in hours,|
in hours, | |section,|erecting forms. |placing |placing |
form stood| |in | |concrete |concrete |
after | |feet. | |in arch. |in key. |
filing. | | | | | |
| | | | | |
----------+-------------+--------+----------------+---------+---------+
70 | { A | } 50 | 20 | 15 | 15.40 |
| {day work | } | ______/\______ | | |
| | |/ \| | |
| { A | } |Moving Erecting| | |
| {day work | } 20 | 2 3 | 8.30 | 2.40 |
| | | | | |
53 | { B | } | | | |
| {day work | } 20 | 2 3 | 10.40 | 11.20 |
| | | | | |
58 | { C | } | | | |
| {day work | } 20 | 2 3 | 11.00 | 7.20 |
| | | | | |
58 | { D | } | | | |
| {day work | } 20 | 2 3 | 9.30 | 4.35 |
| | | | | |
53 | { D | } | | | |
| {day work | } 20 | 2 3 | 6.15 | 2.05 |
| | | | | |
53 | {Sub-Type | } 20 | 2 3 | 6.00 | 3.00 |
| No. 1 | } | | | |
| piece work | } | | | |
==========+=============+========+================+=========+=========+
==========+=========+===========+===========+============
Average |Time, |Total Time |Total time |Remarks.
time |in hours,|in hours, |in hours, |
in hours, |placing |for moving,|per linear |
form stood|concrete |erecting, |foot, |
after |in key |and filling|for moving,|
filing. |and arch | |erecting, |
| | |and filling|
----------+---------+-----------+-----------+------------
70 | 30.40 | 50.40 | 1.01 |
| | | |
| | | |
| | | |
| 11.10 | 16.10 | 0.50 |
| | | |
53 | | | |Includes
| 22.10 | 27.00 | 1.35 |placing rods
| | | |
58 | | | |
| 18.20 | 23.20 | 1.16 | do.
| | | |
58 | | | |
| 14.25 | 19.25 | 0.91 | do.
| | | |
53 | | | |
| 8.20 | 13.20 | 0.05 | do.
| | | |
53 | 9.00 | 14.00 | 0.70 | do.
| | | |
| | | |
==========+=========+===========+===========+============
[Illustration: FIG. 23.]
The only compressed air available was the high-pressure supply, at about
90 lb.; a reducing valve, to lower this pressure to 30 lb. was used
between the air line and the grouting machine. This was thought to be
about as high a pressure as the green concrete arch would stand, and,
even as it was, at one point a section about 2 ft. by 1 ft. was blown
out.
A rough traveling stage resting on the bottom step of the duct bench
concrete was used as a working platform. In the earlier stages of the
work the grouting was carried on in a rather haphazard manner, but, when
the last system of grout and vent pipes was adopted; the work was
undertaken systematically, and was carried out as follows:
Two 20-ft. lengths of arch were grouted at one time, and, in order to
prevent the grout from flowing along the arch and blocking the pipes in
the next lengths, a bulkhead of plaster was made at the end of every
second length to confine the grout.
After a section had been grouted, test holes were drilled every 50 ft.
along the crown to see that all the voids were filled; if not, holes
were drilled in the arch, both for grouting and for vents, and the
faulty section was re-grouted. An average of ¾ bbl. of cement and an
equal quantity of sand was used per linear foot of tunnel. The average
amount put in by one machine per shift was 15 bbl., and therefore the
average length of tunnel grouted per machine per shift was 20 ft. The
typical working force was:
1 Foreman @ $3.75 per shift
1 Laborer running grout machine " 2.00 " "
2 Laborers handling cement and sand. " 1.75 " "
1 Laborer tending valve and grout pipes " 1.75 " "
After the grouting was finished, the arches were rubbed over with wire
brushes to take off discoloration, and rough places at the junctions of
adjoining lengths or left by the block laggings were bush-hammered.
_Face of Bench Concrete._--The form used for this portion of the work is
shown on Plate XLV. It consisted of a central framework traveling on
wheels, and, from the framework, two vertical forms were suspended, one
on each side, and equal in height to the whole height of the bench.
Adjusting screws were fitted at intervals both at top and bottom, and
thus the position of the face forms could be adjusted accurately. The
face forms were built very carefully of 3-in. tongued and grooved yellow
pine, and one 50-ft. form was used for 3,000 ft. of tunnel without
having the face renewed. Great care was taken to set these forms true to
line and grade, as the appearance of the tunnel would have been ruined
by any irregularity. Joints between successive lengths were finished
with a =V=-groove.
The concrete was received at the form in dumping buckets; these were
hoisted to the top of the form by a Lidgerwood hoister fixed to a
trailer. The concrete was placed in the form by shoveling it from the
traveling stage down chutes fitted to its side. The quantity of water to
be used in the mixture needed careful regulation. The first few batches
in the bottom had to be very wet, and were made with less stone than the
upper portion, in order that the concrete would pack solidly around the
niche box forms and other awkward corners.
The forms for the ladders and refuge niches were fastened to the face of
the bench forms by bolts which could be loosened before the main form
was moved ahead, and in this way the ladder and niche forms were left in
position for some time after the main form was removed.
At first the forms were kept in place for 36 hours after finishing a
length, but, after a little experience, 24 hours was found to be enough.
In the summer, when the rise of temperature quickened the set, the time
was brought down to 18 hours. The average time taken for a 50-ft. length
was:
Laying concrete 4½ hours.
Interval for setting 18 "
Moving forms ahead and resetting 5 "
-------
Total 27½ hours.
The typical working gang was:
_Laying Concrete._
1 Foreman @ $3.25 per shift.
2 Spaders " 2.00 " "
8 Laborers " 1.75 " "
_Moving and Setting Forms._
1 Foreman @ $4.00 per shift.
10 Laborers " 1.75 " "
After the forms were removed, any rough places at the lower edge, where
the concrete joins the "lip," were bush-hammered; no other cleaning work
was done.
_Duct Laying and Rodding._--The design and location of the ducts have
already been described. It will have been seen that the duct-bench
concrete was laid in steps, on which the ducts were laid, hence the
maintenance of the grade and line in the ducts was an easy matter. The
only complication was the expanded metal bonds, which were bent up out
of the way of the arch forms and straightened out again after the arch
forms had passed. The materials, such as ducts, sand, and cement, were
brought into the tunnel by the regular transportation gang. The mortar
was mixed in a wooden trough about 10 ft. long, 2 ft. 6 in. wide and 8
in. deep.
After the single-way ducts had been laid, all the joints were plastered
with mortar, in order to prevent any foreign substance from entering the
ducts. This was not necessary with the multiple duct, as the joints were
wrapped with cotton duck. The ducts were laid on a laying mandrel, and,
as soon as possible after the concrete was laid around a set of ducts,
they were "rodded" with a rodding mandrel. Not many obstructions were
met, and these were usually some stray laying mandrel which had been
left in by mistake, or collections of mortar where the plastering of the
single-way joints had been defective.
In the 657,000 duct ft. of conduit in the river tunnels only eight
serious obstructions were met. That the work was of exceptionally high
quality is shown by the fact that a heavy 3-in. lead cable has been
passed through from manhole to manhole (450 ft.) in 6 min., and the
company, engaged to lay the cables in these ducts, broke all its
previous records for laying, not only for tunnel work, but also in the
open.
Fig. 1, Plate XXXV, shows a collection of the tools and arrangements
used in laying and rodding ducts. The typical working force was:
_Laying Multiple Ducts._
1 Foreman @ $3.50 per shift.
9 Laborers " 1.75 " "
_Laying Single-Way Ducts._
1 Foreman @ $3.50 per shift.
8 Laborers " 1.75 " "
_Rodding Multiple Ducts._
1 Foreman @ $3.50 per shift.
5 Laborers " 1.75 " "
_Rodding Single-Way Ducts._
1 Foreman @ $3.50 per shift.
5 Laborers " 1.75 " "
The average progress per 10-hour shift with such gangs was:
Laying multiple ducts 4,000 duct ft.
Laying single-way ducts 1,745 " "
Rodding multiple ducts 4,040 " "
Rodding single-way ducts 2,532 " "
No detailed description need be given of the concreting of the
cross-passages, pump chambers, sumps, and other small details, the
design of which has been previously shown. The concrete was finished on
June 1st, 1909.
_Period No. 6._--_Final Cleaning Up._--_June, 1909, to November,
1909._--As soon as all the concrete was finished, the work of cleaning
up the invert was begun. A large quantity of débris littered the
tunnels, and it was economical to remove it as quickly as possible. The
remaining forms were first removed, and hoisting engines, supported on
cross-timber laid across the benches, were set up in the middle of the
tunnel at about 500-ft. intervals.
Work was carried on day and night, and about 169 ft. of single tunnel
was cleared per 10-hour shift. Work was begun on May 28th, and finished
on July 15th, 1909. For part of the time it was carried on at two points
in each tunnel, working toward the two shafts, but when the work in the
Weehawken Shaft, which was being done at the same time, blocked egress
from that point, all material was sent out by the Manhattan Shaft.
The total quantity of material removed was 5,350 cu. yd., or about 0.44
cu. yd. per lin. ft. of tunnel. The average force per shift was:
_In Tunnel._
3 Foremen @ $3.25 per shift
1 Hoist engineer " 3.00 " "
1 Signalman " 2.00 " "
38 Laborers " 1.75 " "
_On the Surface._
1 Foreman @ $3.25 per shift
1 Hoist engineer " 3.00 " "
1 Signalman " 2.00 " "
12 Laborers " 1.75 " "
After the cleaning out had been done, the contractor's main work was
finished. However, quite a considerable force was employed, up to
November, 1909, in doing various incidental jobs, such as the
installation of permanent ventilation conduits and nozzles at the
intercepting arch near the Manhattan Shaft, the erection of a head-house
over the Manhattan Shaft, and collecting and putting in order all the
miscellaneous portable plant, which was either sold or returned to
store, sorting all waste materials, such as lumber, piping, and scraps
of all kinds, and, in general, restoring the sites of the working yards
to their original condition.
Concrete Mixing.
The plant used in mixing the concrete for the land tunnels was pulled
down and re-erected before the concrete work in the river tunnels was
begun. At the New York shaft two new bins for sand and stone were built,
bringing the total capacity up to 950 cu. yd. Two No. 6 Ransome mixers,
driven electrically by 30-h.p. General Electric motors, using current
from the contractor's generators, were set up on a special platform in
the intercepting arch.
At Manhattan the sand and stone were received from the bins in chutes at
a small hopper built on the permanent upper platform of the intercepting
arch. Bottom-dumping cars, divided by a partition into two portions,
arranged to hold the proper quantities of sand and stone for a 4-bag
batch of concrete, were run on a track on this upper platform, filled
with the proper quantities of sand and stone, and then run back and
dumped into the hoppers of the mixer. After mixing, the batch was run
down chutes into the tunnel cars standing on the track below. The water
was brought in pipes from the public supply. It was measured in barrels
by a graduated scale within the barrels. The water was not put into the
mixer until the sand and stone had all run out of the mixer hopper. The
mixture was revolved for about 1½ min., or about 20 complete
revolutions.
At Weehawken Shaft the mixing plant was entirely rebuilt. Four large
bins, two for sand and two for stone, were built in the shaft. Together,
they held 430 cu. yd. of stone and 400 cu. yd. of sand. The sand and
stone were dumped directly into the bins from the cars on the trestle
which ran from the wharf to the shaft. The materials were run through
chutes directly from the bins to the hoppers of the mixers, where they
were measured. Two No. 6 Ransome mixers, electrically driven, were used
here, as at New York, and, as there, the water was led into measuring
tanks before being let into the mixer.
The quantity of water used in the various parts of the concrete
cross-section, for a 4-bag batch consisting of 1 bbl. (380 lb.) of
cement, 8.75 cu. ft. of sand, and 17.5 cu. ft. of stone, is given in
Table 31.
TABLE 31.--QUANTITY OF WATER PER 4-BAG BATCH OF CONCRETE, IN U.S.
GALLONS.
==========================+==========+==========+==========
Portion of cross-section. | Maximum. | Minimum. | Average.
--------------------------+----------+----------+----------
Invert | 40 | 20 | 26
Duct bench | 36 | 21 | 27
Arch (excluding key) | 37 | 19 | 25
Key of arch | 27 | 15 | 20
Face of bench | 31 | 22 | 27
==========================+==========+==========+==========
The maximum quantities were used when the stone was dry and contained
more than the usual proportion of fine material, the minimum quantity
when the sand was wet after rain.
The resulting volumes of one batch, for various kinds of stone, are
given in Table 32.