====================+=====+===============+====================
Part. | No. | Material. | Weight, in pounds.
--------------------+-----+---------------+--------------------
Middle top casting | 1 | Cast steel | 880
End top castings | 2 | " " | 1,718
Lining castings | 3 | " " | 18,232
Sump segment | 1 | Cast iron | 3,560
--------------------+-----+---------------+--------------------
Total weight per sump, exclusive of bolts | 24,390
==========================================+====================
_Turnbuckle Reinforcement for Cast-Iron Segments._--During the period of
construction, a certain number of cast-iron segments, mostly in the
roof, but in some cases at Manhattan in the invert, behind the river
lines, became cracked owing to uneven pressures of the ground. Before
the concrete lining was put in, considerable discussion occurred as to
the wisest course to pursue with regard to these broken plates. It was
finally thought best not to take the plates out, as more harm than good
might be done, but to reinforce them with turnbuckles, as shown in Fig.
15. The number of broken segments was distributed as follows:
North Manhattan Tunnel 87, chiefly in silt (not under the river),
South Manhattan Tunnel 7, chiefly in silt ( " " " " ),
North Weehawken Tunnel 24, chiefly in sand ( " " " " ),
South Weehawken Tunnel 48, chiefly in silt, under the Fowler
Warehouse.
The chief features of the tunnel lining have now been described, and,
before giving any account of the methods of work, it will be well to
mention briefly the salient features of the concrete lining which is
placed within the actual lining.
Design of Concrete Lining.
This concrete lining will be considered and described in the following
order:
The New York Shield Chambers,
Standard Cross-Section of Concrete Lining of Shield-Driven
Tunnels,
Final Lines and Grades, and How Obtained,
Steel Rod Reinforcement of Concrete,
Cross-Passage Lining,
Special Provision for Surveys and Observations.
[Illustration: SUBAQUEOUS TUNNELS TURNBUCKLES AND RODS REINFORCING
TUNNEL SEGMENTS FIG. 15.]
_The New York Shield Chambers._--The cross-section of the concrete
lining of these chambers is shown by Plate XXXII, referred to in the
Land Tunnel Section. They are of the twin-tunnel double-bench type. The
deep space beneath the floor is used as a sump for drainage, and
manholes for access to the cable conduits are placed in the benches.
[Illustration: TYPES OF CONCRETE LINING OF SHIELD-DRIVEN TUNNELS. FIG.
16.]
_Standard Cross-Section of Concrete Lining of Shield-Driven
Tunnels._--The cross-section of the concrete lining of the tube tunnel
is shown in Fig. 16. There are two main types, one extending from the
shield chambers to the first bore segment, that is, to where the tunnel
leaves solid ground and passes into silt, and the other which extends
the rest of the way. The first type has a drain in the invert, the
second has not.
The height from the top of the rail to the soffit of the arch being less
than 16 ft. 11 in., overhead pockets for the suspension of electrical
conductors were set in the concrete arch on the vertical axis line at
10-ft. centers. These pockets are shown in Fig. 16. The benches are
utilized for the cable conduits in the usual way. Ladders are provided
on one side at 25-ft. and on the other side at 50-ft. intervals, to
give access from the track level to the top of the benches. Refuge
niches for trackmen are placed at 25-ft. intervals on the single-way
conduits side only, as there is not enough room in front of the 4-way
ducts. Manholes for giving access to the cable conduits, both power, and
telephone and telegraph, are at 400-ft. intervals.
_Final Lines and Grades, and How Obtained._--It may be well to explain
here how the final lines and grades for the track, and therefore for the
concrete lining, were obtained and determined. It is first to be
premised that the standard cross-section of the tunnel (that is, of the
concrete and iron lining combined) is not maintained throughout the
tunnel. In other words, the metal lining is of course uniform, or
practically so, throughout; the interior surface of the concrete lining
is also uniform from end to end, but the metal lining, owing to the
difficulty of keeping the shields, and hence the tunnels built within
them, exactly on the true line and grade, is not on such lines and
grades; the concrete lining is built exactly on the pre-arranged lines
and grades, consequently, the relative positions of the concrete and
metal linings vary continually along the length of the structure,
according to whether the metal lining is higher or lower than it should
be, further to the north or to the south, or any combination of these.
As before stated, it was strongly desired to encroach as little as
possible on the standard 2-ft. concrete arch, and after some discussion
it was decided that a thickness of 1 ft. 6 in. was the thinnest it was
advisable to allow. This made it possible to permit the metal lining of
the tunnel to be 6 in. lower, in respect to the level of the track at
any point, than the standard section shows, and also allowed the center
line of the track to have an eccentricity of 6 in. either north or south
of the center line of the tunnel. This only left to be settled the
extent to which the metal lining might be higher in respect to the track
than that shown on the standard section.
This amount was governed by the desirability of keeping sufficient
clearance between the top of the rail and the iron lining in the invert
to admit of the attachment of pile foundations and all the accompanying
girder-track system which would necessarily be caused by the use of
piles, should it ever become apparent after operation was begun, that,
after all, it was essential to have the tunnels supported in this way.
Careful studies were made of the clearance necessary, and it was
decided that 4 ft. 9 in. was the minimum allowable depth from the top of
the rail to the outside of the iron at the bottom. This meant that the
iron lining could be 3 in. higher, with respect to the track level, than
that shown on the standard section.
All the determining factors for fixing the best possible lines and
grades for the track within the completed metal lining were now at hand.
In March, 1908, careful surveys of plan and elevation were made of the
tunnels at intervals of 25 ft. throughout. The following operations were
then performed to fix on the best lines and grades:
First, for Line: It has been explained that the permissible deviation of
the center line of the track on either side of the center line of the
tunnel was 6 in. Had the metal lining been invariably of the true
diameter, it would have been necessary to survey only one side of the
tunnel; this would have given a line parallel to the center line, and
might have been plotted as such; then, by setting off 6 in. on either
side of this line, there would have been obtained a pair of parallel
lines within which the center line of the track must lie. Owing to
variations in the diameter of the tunnel, however, such a method was not
permissible, and therefore the following process was used:
When running the survey lines through the tunnel (which were the center
lines used in driving the shields), offsets were taken to the inner
edges of the flanges of the metal lining, both on the north and south
sides, at axis level at each 25-ft. interval. On the plat on which the
survey lines were laid down, and at each point surveyed, a distance was
laid off to north and south equal to the following distances:
Offset, as measured in the tunnel to north (or south), minus 10.08 ft.
This 10.08 ft. (or 10 ft, 1 in.) represents 10 ft. 7 in., the true
radius to inside of iron, minus 6 in., the permissible lateral deviation
of the track from the axis of the tunnel.
The result of this process was two lines, one on either side of the
survey lines, not parallel to it or to each other, but approaching each
other when the horizontal diameter was less than the true diameter,
receding from each other when the diameter was more, and exactly 12 in.
apart when the diameter was correct. As long as the center line of the
track lay entirely within these two limiting lines, the condition that
the concrete arch should not be 6 in. less in thickness than the
standard 2 ft. was satisfied, and in order to arrive at the final line,
the longest possible tangents that would be within these limits were
adopted as the final lines; and, as the survey lines were those used in
driving the tunnel shields (that is, the lines to which it was intended
that the track should be built), the amount by which the new lines thus
obtained deviated from the survey lines was a measure of the deviation
of the finally adopted track and concrete line from the original
contract lines.
Next, for Grades: The considerations for grade were very similar to
those for line. If the vertical diameter of the tunnel had been true at
each 25-ft. interval surveyed, it would have been correct to plot the
elevations of the crown (or invert) as a longitudinal section of the
tunnel, and to have set up over those points others 6 in. above (as the
metal lining could have been 6 in. lower than the standard section,
which is equivalent to the track being an equal amount higher), and
below these crown or invert elevations others 3 in. lower (as the metal
lining could be 3 in. higher).
Then, by joining the points 6 in. above in one line and those 3 in.
below in another, there would have been obtained lines of limitation
between which the track grades must lie. However, as the tunnel diameter
was not uniformly correct, a modification of this method had to be made,
as in the case of the line determination, the principle, however,
remaining the same.
The elevations were taken on the inner edges of the circumferential
flanges of the metal lining, not only in the bottom, but also in the
top, of the tunnel, at each 25-ft. interval; then, for the upper limit
of the track at each such interval the following was plotted:
Elevation of inner edge of flange at top, minus 16.58 ft.
This 16.58 ft. (or 16 ft. 7 in.) was obtained thus: The standard height
from the top of the rail to the inner edge of the iron flange is 17 ft.
1 in., but, as the track may be 6 in. above the standard or normal, the
minimum height permissible is 16 ft. 7 in. For the lower limit of track
at each 25-ft. interval the following was plotted:
Elevation of inner edge of flange at bottom, plus 3.83 ft.
This 3.83 ft. (or 3 ft. 10 in.) was obtained thus: The standard height
from the top of the rail to the inner edge of the iron flange is 4 ft. 1
in. (5 ft. to outside of iron, less 11 in. for depth of flange), but,
as the track may be 3 in. below the standard, the minimum height
permissible is 4 ft, 1 in. less 3 in., or 3 ft. 10 in.
By plotting the elevations thus obtained, two lines were obtained which
were not parallel but were closer together or further apart according as
the actual vertical diameter was less or greater than the standard, and
the track grade had to lie within these two lines in order to comply
with the requirements indicated above. The results of these operations
for the North Tunnel are shown on Plate XXXVI.
The greatest deviations between the lines and grades in the subaqueous
tunnels as determined by these means and those as originally laid out in
the contract drawings are on the Weehawken side, and were caused by the
unexpected behavior of the tunnel when the shields were driven "blind"
into the silt, causing a rise which could not be overcome, and the
thrusting aside of one tunnel by the passage of the neighboring one. Had
this unfortunate incident not occurred, it is clear that it would have
been possible to adhere very closely indeed to the contract lines and
grades, although the deviation is small, considering all things.
The internal outline of the concrete cross-section is uniform
throughout, and is built on the lines and grades thus described.
_Steel Rod Reinforcement of Concrete._--The original intention had been
to line the metal lining of the tube tunnels with plain concrete, but,
as the discussion on the foundation question continued, it was felt
advisable, while still it was intended to put in the foundations, to
guard against any stresses which were likely to come on the structure,
by using a system of steel rods embedded circumferentially within the
concrete. Designs were made on this basis, and even the necessary
material prepared, before the decision to omit the piles altogether was
reached. However, in order to provide a safeguard for the structure
where it is partly or wholly beyond the solid rock, it was decided to
use reinforcement, even with the piles omitted.
For this purpose the tunnel was considered as a girder, and longitudinal
reinforcement was provided at the top and bottom. The top reinforcement
extends from a point 25 ft. behind the point where the crown of the
tunnel passes out of rock on the New York side to where the crown passes
into rock on the New Jersey side. The bottom reinforcement extends from
where the invert of the tunnel passes out of rock on the New York side
to where it passes into rock on the New Jersey side.
The reinforcement both at top and bottom consists of twenty 1-in. square
twisted rods, ten placed symmetrically on either side of the vertical
axis, 9 in. apart from center to center and set 4 in. (to their centers)
back from the face of the concrete.
As a further precaution, circumferentially-placed rods were used on the
landward side of the river lines, mainly to assist in preventing the
distortion of shape which might occur here, either under present
conditions, such as under the Fowler Warehouse at Weehawken, or under
any possible different future conditions, such as might be brought about
by building some new structure in the vicinity of the tunnels.
For purposes of classification of the circumferential reinforcement, the
tunnel was divided into two types, "_B_" and "_C_"; (Type "_A_" covering
the portion which, being wholly in solid rock, was not reinforced at
all).
Type "_B_" covers the part of the tunnels on both sides of the river
lying between the point where the top of the tunnel passes out of rock
and the point where the invert passes out of rock on the Manhattan side,
or out of gravel on the Weehawken side. The reinforcement consists of
twenty 1-in. square longitudinal rods in the crown of the tunnel, as
described for the general longitudinal reinforcement, together with
1-in. square circumferential rods at 10-in. centers, and extending over
the arch to 2 ft. 3 in. below the horizontal axis.
Type "_C_" extends from the latter limit of Type "_B_" to the river line
on each side, and consists of longitudinal reinforcement in both top and
bottom, as described before, together with circumferential reinforcement
entirely around the tunnel, and formed of 1-in. square twisted rods at
15-in. centers.
Type "_D_" consists of longitudinal reinforcement only, and extends from
river line to river line, thus occupying 72.5% of the length in which
concrete is used. The reinforcement consists of twenty 1-in. twisted
rods at 9-in. centers in the crown, and twenty 1-in. rods at 9-in.
centers in the invert. In addition to the three standard types, "_B_,"
"_C_," and "_D_," there were two sub-types which were used in Type
"_D_," and in conjunction with it wherever the thickness of the center
of the concrete arch became less than 1 ft. 6 in., measuring to the
outside of the metal lining. This thickness was one of the limits used
in laying out the lines and grades, and in general the arch was not less
than this. There were one or two short lengths, however, where it was
less, for, if the arch thickness requirement had been adhered to, it
would have resulted in a break of line or grade for the sake of perhaps
only a few feet of thin arch, and it was here that the sub-types came
into play.
Sub-type 1 was used where the arch was less than 1 ft. 6 in. thick at
the top. The extra reinforcement here consisted of 1-in. square twisted
rods, 16 ft. long, laid circumferentially in the crown at 10-in.
centers.
Sub-type 2 was used where the arch was less than 1 ft. 6 in. thick at
the side. The extra reinforcement here consisted of 1-in. square twisted
rods, 16 ft. long, laid circumferentially, at the side on which the
concrete was thin, at 10-in. centers. Very little of either of these two
sub-types was used. The entire scheme is shown graphically and clearly
on Plate XXXVII.
_Cross-Passage Lining._--There are two main types of cross-passages:
Lined with steel plates, and unlined.
There is only one example of lining with steel plates, namely, the most
western one at Weehawken. This is built in rock which carried so much
water that, in order to keep the tunnels and the passage dry, it was
decided to build a concrete-lined passage, without attempting to stop
the flow of water, and within this to place a riveted steel lining, not
in contact with the concrete, but with a space between the two. This
space was drained and the water led back to the shield chamber and
thence to the Weehawken Shaft sump. The interior of the steel lining is
covered with concrete.
In the passages not lined with steel plates the square concrete lining
is rendered on the inside with a water-proof plaster. Each of the
passages is provided with a steel door.
_Provisions in Concrete Lining for Surveys and Observations._--The long
protracted discussion as to the provision for foundations in these
tunnels led to many surveys, tests, and observations, which were carried
out during the constructive period, and, as it was desired to continue
as many of these observations as possible up to and after the time when
traffic started, certain provisions were made in the concrete lining
whereby these requirements might be fulfilled. The chief points on which
information was desired were as follows:
The change in elevation of the tunnel,
The change in lateral position of the tunnel,
The change in shape of the tunnel,
The tidal oscillation of the tunnel.
A detailed account of these observations will be found in another paper
on this work, but it may be said now that it was very desirable to be
able to get this information independently of the traffic as far as
possible, and therefore provision was made for carrying on the
observations from the side benches.
For studying the changes in level of the tunnel, a permanent bench-mark
is established in each tunnel where it is in the solid rock and
therefore not subject to changes of elevation; throughout the tunnel,
brass studs are set in the bench at intervals of about 300 ft. A series
of levels is run every month from the stable bench-mark on each of these
brass plugs, thus obtaining an indication of the change of elevation
that the tunnels have undergone during the month.
These results are checked on permanent bench-marks in the subaqueous
portion of the tunnels. These consist of rods, encased in pipes of
larger diameter, which extend down through the tunnel invert into the
bed-rock below the tunnel. Leakage is kept out by a stuffing-box in the
invert. By measuring between a point on these rods where they pass
through the invert and the tunnel itself a direct reading of the change
of elevation of the tunnel is obtained. These measurements are taken at
weekly intervals, and, as the tunnels are subject to tidal influences,
being lower at high tide than at low tide, are always taken under the
same conditions as to height of water in the river. These permanent
bench-marks are at Stations 209 + 05 and 256 + 02 (about 100 ft. on the
shoreward side of the river line in each case) in the South Tunnel, at
Stations 220 + 00 and 243 + 86, also in the South Tunnel, and at Station
231 + 78 in the North Tunnel. In order to study the lateral change of
position, a base line was established on the side bench at each end of
each tunnel in the portion built through the solid rock.
At intervals of about 300 ft. throughout each tunnel, alignment pockets
are formed in the concrete arch, also above the bench, on the south
bench of the North Tunnel and the north bench of the South Tunnel. In
each pocket is placed a graduated and verniered brass bar, so that, when
the base line is projected on these bars, the lateral movement of the
tunnel can be read directly. As it was desirable to have as much
cross-connection as possible between the tunnels at the points where the
instruments were to be set up, five of the main survey stations were set
opposite each of the five cross-passages. Then, for the purpose of
increasing the cross-connection still further, pipes 6 in. in diameter
were put through from one tunnel to the other at axis level at Stations
220 + 60, 231 + 78, 234 + 64, 241 + 99, and 251 + 13, and a survey
station was put in opposite each one.
Points were established at Station 220 + 00, which is the point of
intersection for the curve on the original center line of the tunnel,
and also at Station 220 + 23, where the intersection of the track center
line comes in the North Tunnel. As it was desirable to have the survey
stations not much more than 300 ft. apart, so as to obtain clear sights,
other stations were established so that the distances between survey
stations were at about that interval.
For studying changes of shape in the tunnel, brass "diameter markers"
were inserted at each survey station in the concrete lining at the
extremities of the vertical and horizontal axes. These were pieces of
brass bar, 3/8 in. in diameter and 6 in. long, set in the concrete and
projecting 5/8 in. into the tunnel, so that a tape could be easily held
against the marker and read.
For obtaining the tidal oscillation of elevation of the tunnel,
recording gauges are attached to the invert of the tunnel at each of the
five permanent bench-marks referred to above in such a way that the
recording pencil of the gauge is actuated by the rod of the permanent
bench-mark. A roll of graduated paper is driven by clock-work below the
recording pencil which thus marks automatically the relative movement
between the moving tunnel and the stable rods. These have shown that in
the subaqueous part of the tunnel there is a regular tidal fluctuation
of elevation, the tunnel moving down as the tide rises, and rising again
when the tide falls. For an average tide of about 5 ft. the tunnel
oscillation would be about 1/8 in. Before the concrete lining was
placed, there was a tidal change in the shape of the tunnel, which
flattened about 1/64 in. at high tide. After the concrete lining was
placed, this distortion seemed to cease.
The general design and plan of the work have been described, and before
giving any account of the contractor's methods in carrying it out, Table
22, showing the chief quantities of work in the river tunnels, is
presented.
Methods of Construction.
The following is an account of the methods used by the contractor in
carrying out the plans which have already been described. First, it may
be well to point out the sequence of events as they developed in this
work. These events may be divided into six periods.
_1._--Excavation and Iron Lining: June, 1903, to
November, 1906;
_2._--Caulking and grummeting the iron lining:
November, 1906, to June, 1907;
_3._--Surveys, tests and observations: April, 1907, to
April, 1908;
_4._--Building cross-passages and capping pile bores:
April, 1908, to November, 1908;
_5._--Placing the concrete lining: November, 1908, to
June, 1909;
_6._--Cleaning up and various small works: June, 1909,
to November, 1909.
The tunnels were under an average air pressure of 25 lb. per sq. in.
above normal for all except Periods 5 and 6, during which times there
was no air pressure in the tunnels.
All the work will be described in this paper except that under Period 3
which will be found in another paper.
_Period 1.--Excavation and Iron Lining, June, 1903, to November,
1906._--Table 23 gives the chief dates in connection with this period.
_Manhattan Shield Chambers._--The Manhattan shield chamber construction
will be first described. The Weehawken shield chambers have been
described under the Land Tunnel Section, as they are of the regular
masonry-lined Land Tunnels type, whereas the Manhattan chambers are of
segmental iron lining with a concrete inner lining.
During the progress of excavation, the location of the New York shield
chambers was moved back 133 ft., as previously described in the "Land
Tunnel" Section, and when the location had been finally decided, there
was a middle top heading driven all through the length now occupied by
the shield chamber. Narrow cross-drifts were taken out at right angles
to the top heading, and from the ends of these the wall-plate headings
were taken out. Heavy timbering was used, as the rock cover was only
about 6 ft., and the whole span to be covered was 60 ft. The process
adopted was to excavate and timber the north side first, place the iron
lining, and then excavate the south side, using the iron of the north
side as the supports for the north ends of the segmental timbering of
the south. The only incident of note was that at 2:00 A.M., on October
20th, 1904, the rock at the west end of the south wall-plate heading was
pierced. Water soon flooded the workings, and considerable disturbance
was caused in the New York Central Railroad yard above. The cavity on
the surface was soon filled in, but to stop the flow of mud and water
was quite a troublesome job.