End pipe connections may be changed to suit connections of rodding
outfit, care being taken to use a connection which will not split and
expand the mandrel if it should be driven back into it, in attempting
to ram the mandrel back when stuck in a duct.
Connection at Head End may be dispensed with, if the mandrel is
threaded through ducts by rods attached to the trailing end.]
Wooden rods were used at first, but proved entirely too light, as the
mandrels used were a close fit, and it required considerable effort to
push them through 400 ft. of conduit. Iron pipe with ordinary couplings
was next tried, but the couplings broke quite often, as the threads
became worn in uncoupling the sections to move the rods from one line to
another, and the break was generally inside a duct line. The long
couplings were finally adopted, and a set of rods was put in each line,
that is, six sets in all, so that when coupled up they remained in the
line until it was finished. The expense of the extra quantity of pipe
thus required was more than offset by the decreased labor cost.
It was thought necessary at first to run a cutter, Fig. 15, _E_, through
the conduits ahead of the final rodding mandrel, but this was soon found
to be unnecessary except in a very few instances, and, after a short
experience, the cutter was only used at places where an obstruction was
encountered by the mandrel.
At such times as the pipe became uncoupled inside the duct line, the
part remaining inside was recovered by the use of the tool shown at _D_,
Fig. 15, called a "weasel." In two instances, the mandrel became stuck
in such a manner that the duct line had to be cut into in order to take
it out.
The best day's work of the rodding gang (1 foreman and 4 men) was 20,400
duct ft. of the 4-way conduit in the telegraph and telephone line, and
19,200 duct ft. of single conduit on the low-tension line, an average
day's work under ordinary conditions being about 10,000 duct ft. The
cost, including labor, material, and all tools, for rodding for the
whole work was slightly less than 0.2 cent per duct ft. The average cost
of the single conduit was about 0.25 cents per ft., and of the 4-way,
0.15 cents per ft. About 10% of the conduit lines were rodded twice,
owing to partial sections having been rodded once before completion. The
best continuous work on rodding was done between October 22d and 29th,
1908, when in 7 working days, 105,600 duct ft. were rodded, an average
of a little more than 15,000 ft. per day.
_Bench-walls._--The original design for the tunnels provided for the
construction of a brick arch above a point 22° above the springing line,
that is, the part above the side-walls (Fig. 10). It was thought
desirable, therefore, in designing the bench-wall forms, to provide for
placing the concrete in the side-walls and bench-walls at one operation.
These forms, as first designed, are shown by Fig. 2, Plate XXV, and the
details in Fig. 16, _A_ and _A'_; they were built of steel, the facing
plates being 5/16 in. thick, in pieces 4 ft. 6 in. wide, and in length
about 6 in. more than the height of the bench-wall.
[Illustration: Fig. 16. [Full Page]
DETAILS OF TRAVELING FORMS USED IN THE CONSTRUCTION OF THE BENCH WALLS
A'. CROSS-SECTION OF STEEL FORM
A. LONGITUDINAL SECTION AND ELEVATION OF STEEL FORM USED AT
WEEHAWKEN END
B. DETAILS OF SCREW-JACKS FOR ADJUSTING FORM TO LINE
C. SECTION _C_-_D_ SHOWING CONNECTION OF FACE PLATES TO I-BEAM
UPRIGHTS
D. DETAILS OF WOODEN FORMS USED AT WESTERN END: CROSS-SECTION,
PART LONGITUDINAL SECTION
No chutes were used with these forms, the wheel-barrows being dumped
from the runways on the sides.]
The design was controlled very largely by the necessity of providing the
requisite clearance for the locomotives and muck cars, and the principal
feature was the support of the forms on two trusses, one at either side,
the front ends of which were supported from the foundation on a long
leg, as shown in Fig. 3, Plate XXV, and the rear ends directly on the
journal-boxes of wheels traveling on a rail on the top of the finished
bench, as shown in Fig. 2, Plate XXV.
Although it had been decided to substitute concrete for brick in the
arch before any of the lining was actually placed, two sets of forms for
the Weehawken end had already been ordered and delivered, so it was
decided to use them as designed, and place the side-wall with the bench.
The forms were designed so that 30-ft. lengths could be built, and this
was done at the start, but owing to the occurrence of the refuge niches,
ladders, etc., at 25-ft. intervals, it was soon seen that it would be
advisable to build the bench-wall in sections of that length (25 ft.),
or multiples of it, and as the clearance conditions seemed to preclude
the possibility of making the forms 50 ft. long, 25 ft. was adopted.
This permitted the removal of one of the panels, 4 ft. 6 in. wide, and
at the same time it was decided to remove the side-wall forms. This
decreased the load on the trusses considerably, but being still a trifle
weak, they were strengthened by the substitution of 1¼-in. truss rods
instead of the ¾-in. rods used originally. The top platform and the
cross-bracing were also stiffened a little and tightened up to prevent
racking.
The construction of the side-walls in conjunction with the bench-wall
was abandoned for three reasons: First, it was found that there would be
a much more even distribution of the work by including the side-wall
with the arch rather than with the bench; second, there was difficulty
in getting a good finish for the top of the bench-wall, as of course a
top form for the latter had to be placed to prevent the concrete from
squeezing up when the side-wall was built above it, which prevented
troweling; the third reason was the weakness of the whole form as
designed, and the increasing difficulty of adjusting it to line as the
work progressed, the principal difficulty being with the curved
side-wall forms.
The bench-wall forms were set in position, after they had been moved
ahead, by first blocking the bottom against the face of the foundation,
as shown by Fig. 13. As previously noted, this foundation face had been
built very carefully to line. The back end of the form, of course, was
blocked tightly against the end of the previously finished section, and
the top was made plumb by the adjusting screwjacks shown in Fig. 16,
_B_. At first these screws were ¾-in., but they were afterward changed
to 1¼-in. The only points which it was necessary for the alignment corps
to give in setting these forms was a grade at each of the front ends for
the top of the finished bench.
The steel face forms in both tunnels gave excellent results, as far as
smoothness of finish was concerned, but, owing to the imperviousness of
the steel, small air holes were formed in the surface, though not in
sufficient numbers or size to cause trouble or disfigure the work in any
way.
The design of the bench-wall forms used at the western end, where this
differs from the steel form, is shown by Fig. 16, _D_. The principal
features in which they differed from those used at the Weehawken end was
in the substitution of 2½-in. tongued and grooved hard pine for the
face. This timber was of the very best quality obtainable, each piece
being especially selected and as nearly clear and free from knots or
other defects as it was possible to get it. The edges of each piece were
planed at the back so as to insure a tight joint on the face, and all
joints were shellacked. These forms were used, without renewal of the
face timber and with only two planings, for a length of 2,500 ft., or
100 separate sections, and gave good satisfaction.
In order to obtain a surface to which the face lagging could be
fastened, wooden uprights were used and were reinforced on either side
by light channels bolted together through the timber, in place of the
=I=-beams used on the steel forms. The lagging was nailed to these
uprights by 6-in. wire nails driven through the top edges of each piece
as it was placed in position, thus leaving the surface entirely clear
and free from any marks or nail holes, and in condition for planing when
this became necessary. Runways for wheeling the concrete were built one
either side over the bench-walls instead of having a center platform
with chutes, as was used at Weehawken.
When the original lagging had become too much worn for further use, it
was resurfaced with strips of 7/8 by 2½-in., clear, tongued and grooved,
hard pine, placed vertically, which did fairly well and lasted to the
end (about 1,000 ft.), although it was not altogether satisfactory, and
the last eight or ten sections built had to be rubbed down with a wooden
float in order to obtain a suitable finish.
In designing the forms for all exposed surfaces in the tunnels, it was
the desire of the contractors to obtain directly from them a surface
which would be satisfactory to the engineers without further finishing
than the patching of minor defects. In this they were generally quite
successful, and excellent results were obtained, as shown in the view of
the finished tunnel, Fig. 2, Plate XXVII. The surface of the bench-walls
was obtained solely by spading the face with a flat spade as the work
progressed. No after treatment was resorted to, except for the few
sections where the forms became worn. The top of the bench-wall was
finished with a float about 2 or 3 hours after the concrete was placed.
When the work was well organized, a bench-wall was built at each end
each day, one day in the North Tunnel, and the following day in the
South. During the time sand-walls were being built, a sand-wall and
bench-wall were built on alternate days in each tunnel, care being taken
that when a bench-wall was being built in one tunnel, the sand-wall was
being built in the other, this being necessary in order to equalize the
work of the night gang and the conduit layers as well as the
transportation.
The conduit layers on the day shift, two or three men and a foreman,
required about 2 hours in the forenoon and 1 hour in the afternoon to
lay their portion of the conduits, and usually finished this work by 3
P.M. At other times during the shift they were utilized at those points
where rock packing was heaviest, and when the packing was brought in in
the large cars, as shown in Fig. 1, Plate XXVI, these men helped unload
it so that the track could be cleared as soon as possible. When
water-proofing was to be done, the number of men in this gang was
increased, so as to enable them to do that work also.
[Illustration: Plate XXVI.
Fig. 1: K 167. P.R.R. Tunnels, N. R. Div. Sect. K. (Bergen Hill
Tunnels.) View of form for circuit breaker chamber at Sta. 286, and
travelling gantry for placing concrete in arches, looking Easterly
from near Sta. 280+85, South Tunnel. Oct. 3, 08.
Fig. 2: K 166. P.R.R. Tunnels, N. R. Div. Sect. K. (Bergen Hill
Tunnels.) View of forms for storage chamber at Sta. 294+24, looking
Southward. Sept. 17, 08.
Fig. 3: K 163. P.R.R. Tunnels, N. R. Div. Sect. K. (Bergen Hill
Tunnels.) Tunnel lining. Rock packing over arches, South tunnel Sta.
???+?? end of completed section. May 19, 08.
Fig. 4: K 168. P.R.R. Tunnels, N. R. Div. Sect. K. (Bergen Hill
Tunnels.) Showing method of waterproofing in timbered tunnel section
at Weehawken end. Oct. 21, 08.]
A gang of four rough carpenters and a foreman was employed on the day
shift; they moved and set the bench-wall forms or sand-wall forms, as
the case might be, and moved the traveling gantry into position. This
was done in the afternoon, and required about 3 hours. They also took
out, cleaned, repaired, and set all ditch forms, all passenger forms,
circuit-breaker forms, and did all other repair work. The ladder forms,
the refuge-niche forms, and overhead conductor pocket forms were
attended to by one man, who set, removed, cleaned, and repaired them.
The carpenters on the night shift set the arch centers and gantries,
also the manhole forms when needed. The conduit layers on the night
shift laid up half the 4-way conduits (3-high) and one-third of the
single ducts (4-high). This one gang laid the conduits in two sections
of bench-wall each night, that is, one section at Weehawken and the
other at the western end.
In concreting the bench-walls, the concrete was first placed on the side
containing the single conduit until it reached the top of the four tiers
laid, then the concrete gang was turned over to the side with the 4-way
conduits while four more tiers of single conduits were laid, the work
thus progressing, the conduits being laid on one side while concrete was
placed on the other. On the side of the 4-way conduits the concrete was
built in two layers while that on the side of the single ducts was built
in three; the interval between the different layers was not sufficiently
long to prevent a complete bond being obtained, and there were only one
or two instances where there was any mark on the face to indicate a
break.
After the work had been in progress some time, it was found to be quite
feasible to build all the 4-way conduits at night and half the single
conduits, that is, 6 ducts high, as the mandrels proved amply sufficient
to hold them in place; in fact, had it been necessary, the writer has no
doubt that all the ducts might have been laid and held in place with
very little extra precaution, by the use of the expanding mandrels,
as described under the head of conduit laying. A =V=-shaped joint about
½ in. deep was made between each section of bench-wall so that the
expansion cracks would follow this joint rather than show irregularly on
the face. These joints divided the face into the even 25-ft. panels, and
were very effectual in concealing what few cracks there were.
After the construction of the sand-walls was discontinued, the space
behind the bench-walls, between the neat line and the rock, was filled
with rock packing, which was generally built, part way up at least, as a
dry wall ahead of the construction of the bench-wall, or it was put in
place simultaneously with the concrete, care being taken to keep it as
free as possible for the drainage of any water there might be. Toward
the latter part of the work, owing to the difficulty of getting
sufficient rock packing during the day, a rough back form for the
bench-wall was built at the neat line, in places where the section was
at all large, and the space was filled with rock afterward, generally at
night or on Sundays.
In the sections where water-proofing was required, where no sand-wall
was built, the rock was taken out for 2 ft. outside the neat line,
if the excavation was not already that far out (at the expense of the
contractors, who preferred to do this rather than build the sand-walls
for the short sections required), so that there would be sufficient room
for placing the water-proofing on the back of the bench-walls, as shown
by Fig. 18, _E_. The water-proofing of these sections was left until
just before the arch was to be built, and after being placed it was
protected by a single row of brick laid on edge before the rock packing
was filled in.
_Arches._--The centering used for the arches is shown very clearly in
Fig. 4, Plate XXV, which is a view of the back end of the first section
built at Weehawken. In this part of the tunnel, the lower part of the
arch, about 5 ft. above the bench-wall, was built first, as previously
referred to, but the centers, as will be seen, were built so that they
could be used for the whole of the arch. The forward bulkhead, and the
shoveling platform on a section being built, are shown in Fig. 3, Plate
XXVI.
The front bulkheads used were made in nine sections, bolted to a 2½ by
2½-in. angle bent to the radius of the arch, as shown in Fig. 3, Plate
XXVI, and fitting on the end of the lagging; when set they were braced
partly against the rock of the roof and partly against the gantry. After
the ribs and part of the lagging had been set by the night gang for a
fresh section of arch, the braces holding the bulkheads were knocked
out, the concrete placed during the day having set sufficiently by this
time; the whole of the bulkhead was then easily moved ahead, sliding
along the lagging to the forward end, and made ready for the next day's
work. The middle section at the top was taken out temporarily, to
facilitate working at the sides, until it was needed.
The traveling gantry used in handling the concrete for the arch is shown
in Fig. 1, Plate XXVI, which also shows the form for the circuit-breaker
chamber, and a car of rock packing on the track beneath.
The arches were built in 10-ft. sections, the ribs being spaced 5 ft.
apart, the end ribs of each section supporting the end of the lagging on
two adjoining sections. Five sets of lagging and ten ribs were used at
each place where the arch was being built, thus giving each section
practically 4 days' set before removing the centers. Probably in the
greater part of the work the centers could have been removed in from 40
to 48 hours after the concrete had been placed, but 3 days was
considered the least time which would certainly be safe at all times,
and the contractors thought that the very slight additional expense
involved in leaving the centers up 4 days was more than warranted by the
additional feeling of security.
The lagging was made from 3 by 6-in. clear, hard pine, 10 ft. long,
dressed to about 2½ in. in thickness, about 5½ in. in width, and the
sides to radial lines. As it was placed, every third or fourth piece was
lightly nailed to the ribs; when the latter were released and taken
down, the nails pulled out, and the lagging was left in place until one
piece was pried out, allowing the others to fall. A light =A=-frame,
about 8 ft. long, spanning the bench-walls, was placed below, in order
to break the fall and allow the lagging to slide to the top of the
bench-walls rather than fall to the track beneath.
Cross-passages between the two tunnels were built every 300 ft., their
form being shown on Plate VIII of the paper by Mr. Jacobs. There were
two circuit-breaker chambers, one at Station 286 and the other at
Station 310. Steel doors are provided so that all the openings between
the two tunnels can be closed. At Station 294+24, the core-wall broke
through for a length of about 40 ft., and instead of filling this in,
a storage chamber 34 ft. long and 11 ft. wide, inside, was built there,
the form for which is shown in Fig. 2, Plate XXVI. This photograph, as
well as Fig. 1, Plate XXVI, a form for a circuit-breaker chamber, shows
the method of setting the steel doors in the forms, so that they were
built into the concrete instead of being fastened in with expansion
bolts afterward, thus showing a perfect fit and a much neater job.
During construction the arches in each tunnel were kept even with each
other, so that when the cross-passages were reached, they, and the
sections of arch which they joined, could be completed at one operation.
By the methods used on this work, one section of arch was easily built
in a shift, so that the monolithic construction of each section was
easily secured, and concrete, as wet as it was possible to handle with
shovels, could be used for all except the last 5 ft. or so at the top,
thus getting a structure which was as nearly impervious as possible
under the circumstances.
The gangs placing the arches were paid over-time when they were required
to work after 6 o'clock to finish their section, which was generally
only necessary when the quantity of rock packing to be placed was very
large. If they finished their section before 6 o'clock, however, they
were allowed to quit when this was done, and were given a full day's
pay. The difference in time, when there was any, was usually due to the
greater or less quantity of rock packing, as the excavation varied from
the standard section line.
In building the arches, the night gang set the two ribs (one at the
center and one at the forward end of the section to be built), placed
the lagging on the sides, 4 or 5 ft. high, built the shoveling platform
on the horizontal cross-braces of the ribs, and placed the traveling
gantry in position for use. The forward end of the gantry (that is, the
end farthest from the arch being built), as shown in Fig. 1, Plate XXVI,
was loaded with rock packing to be used as required. As the concrete was
brought into the tunnel it was hoisted and dumped on the end of the
gantry next the arch, and shoveled from there to the platform on the
ribs and from there into place. The rock packing brought in during the
day was dumped on the front or back end of the gantry, as was most
convenient, and handled into the work in the intervals between batches
of concrete. The concrete and rock packing, with the back-lagging and
water-proofing, where these were used, were placed simultaneously, or
nearly so, and brought up the sides together until the key was reached;
the latter was then worked from the back toward the front. The key was
usually made about 5 ft. wide, the lagging for this width was made 5 ft.
long and put up in two sections. It was found to be more convenient to
have the key of this width than narrower.
The method used in making the closures where two sections of the arch
came together is shown by Fig. 17.
[Illustration: Fig. 17. [Full Page]
SKETCH SHOWING METHOD OF MAKING ARCH CLOSURE
CROSS-SECTION OF TUNNEL SHOWING JACK PARTLY EXTENDED
LONGITUDINAL SECTION OF TUNNEL SHOWING JACK PARTLY EXTENDED
PLAN OF BOX; END VIEW
PLAN OF PLUNGER, BOTTOM OF BOX; END VIEW OF PLUNGER,
JACK FULLY EXTENDED]
_Water-proofing._--As already pointed out, the original design for the
lining of these tunnels provided for a brick arch. It was intended to
cover this arch with water-proofing, this latter extending over the
whole of the roof and down the sides as far as the bottom of the conduit
lines. The water-proofing was to be placed against the sand-walls on the
sides, up to the top of the side walls, Figs. 10 and 14. Over the arch,
after being placed, it was to be protected by an armor course of brick,
laid flat, the space between the brick and the excavation, which was
required to be not less than 4 in. (and, as a matter of fact, was
actually a great deal more), being filled with rock packing. Besides
filling the space, this latter was designed to allow any water from the
roof of the tunnel to find its way easily to the top of the sand-wall,
from there being carried through the 4-in. cast-iron pipes, shown on
Plate VIII[4] to the side ditches in the floor of the tunnel.
[Footnote 4: Of the paper by Mr. Jacobs.]
All the water-proofing placed in these tunnels was of felt and pitch,
six-ply felt and seven layers of pitch. The felt was required to be
Hydrex, or of equal quality, and the pitch, "Straight run coal-tar pitch
which will soften at 60° Fahr., of a grade in which the distillate oils
will have a specific gravity of 1.05."
In addition to tests as to the above qualities, the pitch was analyzed
to determine the amount of free carbon it contained, and was not
accepted if this fell below 20 per cent.
It was considered quite important that there should be absolutely free
drainage on the outer side of the lining, so that there would be no
chance for any water to acquire a head. More than three-quarters of the
length of these tunnels is below the level of mean high water, and while
it was hardly expected that there would be any direct connection between
the water in the Hudson River and the groundwater of the section
penetrated, it was thought wise to provide ample drainage.
Before the lining was started, however, the excavation had progressed
sufficiently to show that the tunnels, while very wet in places, and
varying from that to quite damp, would be, on the whole, much dryer than
had been anticipated. It was then decided to substitute concrete for the
brick in the arch and omit the water-proofing over the top, except at
places where water came into the tunnels in sufficiently large
quantities to form practically a continuous stream. Three general types
of construction for the arch were decided on, as shown in Fig. 18. The
first, as shown at _A_, was to be used where the tunnel was quite dry.
In this type, the sand-wall was omitted entirely, and the concrete and
rock packing were built up together, the rock packing impinging to a
certain extent on the concrete, and the concrete squeezing somewhat into
the rock packing, as shown by Fig. 4, Plate XXV. The section shown at
_B_ was used where the tunnels were damp, or where there were slight
droppers not forming a continuous stream. The back lagging, of 1-in.
boards, which was left in place, provided a practically smooth outer
surface on the concrete arch, and allowing the concrete and rock packing
to be built almost simultaneously. It was considered that the free
drainage through the rock packing, the surface of the boards, and the
smooth outer surface of the concrete in the arch would allow the
comparatively small quantity of water in these parts of the tunnel to
find its way to the sides, and thence to the ditches at the bottom,
rather than to percolate through the concrete, and this proved to be
very generally the case, as is shown by the dry condition of the tunnel
as built. The back lagging was used over the arch, both where the
sand-wall was built and where it was omitted, as well as being placed
over the water-proofing of the arch as an armor course where
water-proofing was required. Where the sand-walls were built and
water-proofed, and where the water-proofing was not carried over the
arch, the water-proofing was turned in at the top, as shown at _C_, Fig.
18.
[Illustration: Fig. 18. [Full Page]
VARIOUS TYPES OF ARCHES, AND WATER-PROOFING USED
Method of Lapping Mats over Arch
Method of making joint when work on section was not continuous. Part
of joint on radial line, part sloping slightly toward outside of
arch.
DETAILS OF WATER-PROOFING
One layer of felt with 4" overlap to be nailed to lagging of inch
boards, using tin washers on nails over the whole of the intrados
of the arch before starting any concrete or placing any of the
permanent felt and pitch water-proofing. The water-proofing over
the arch can be laid in mats of three thicknesses of felt properly
joined together with pitch made as shown diagrammatically at "_x_"
Each of these mats of three-ply felt will be overlapped half the
width of the mat, as shown diagrammatically at "_y_"]
The third method provided for water-proofing the whole of the arch, and
was the same as _B_ except for the addition of the water-proofing inside
the back lagging. In placing this water-proofing, the felt was cut in
strips about 11 ft. long (about 1 ft. longer than the length of a
section of arch), and six thicknesses were cemented together with hot
pitch. These mats were then laid shingle-fashion, as shown at _D_, Fig.
18, up the sides of the arch until a space about 5 ft. wide remained at
the crown; shorter mats were then brought out over this, laying them
perpendicular to the axis of the tunnel. Care was taken in making all
laps, irrespective of the direction in which the arch was built, so that
they would lay with the grade, that is, so that the water would tend to
flow over the edges of the laps rather than against them.
Most of the wet sections of the tunnel were at the ends, where
sand-walls had been built for the purpose of providing a smooth surface
against which the water-proofing was to be placed; there were several
wet places at isolated points in the tunnels, however, and, in order to
avoid building sand-walls at these points, the method shown at _E_, Fig.
18, was adopted. This involved a slightly larger excavation, 2 ft.
outside of the neat line, up to the height of the top of the bench,
where there was not already that much room. The bench-wall was built
with a back form on the neat line, the water-proofing was placed as
shown, protected by an armor course of brick, and then continued over
the arch when this latter was built. The excavation and refilling with
rock packing were done at the contractor's expense, which he was willing
to assume rather than build these short sections of sand-wall.
[Illustration: Plate XXVII.
Fig. 1: K 181. P.R.R. Tunnels, N. R. Div. Sect. K. (Bergen Hill
Tunnels.) Timbered section near Weehawken Shaft, showing method of
placing waterproofing and keying arch. Dec. 8, 08.
Fig. 2: K 184. P.R.R. Tunnels, N. R. Div. Sect. K. (Bergen Hill
Tunnels). View of completed tunnel looking Eastward from Sta.
323+60. South Tunnel. Feb. 8, 09.
Fig. 3: K 149. P.R.R. Tunnels, N. R. Div. Sect. K. (Bergen Hill
Tunnels) Hackensack Portal, general view of completed Portal, and
arches through cut and cover section looking East. Oct. 15, 07.
Fig. 4: K 190. P.R.R. Tunnels, N. R. Div. Sect. K. (Bergen Hill
Tunnels.) Hackensack Approach. General view, looking East. March 16,
09.]
The method of water-proofing that part of the timbered section which was
very wet, is shown at _F_, Fig. 18, and in Fig. 4, Plate XXVI, and
Fig. 1, Plate XXVII. A lagging of 1-in. boards was nailed up the sides
and to the soffit of the segmental timbering, all the spaces outside of
this lagging being carefully filled with rock packing. Before starting
any concrete work, a single thickness of water-proofing felt was nailed
to the inner side of the lagging, which not only served to protect the
finished surfaces of the concrete from the water which fell copiously
from the roof, but also provided a comparatively dry surface to which
the regular six-ply water-proofing could be cemented with pitch and held
in position, while the concrete was placed against it.
In placing the water-proofing in this section on the sides, the strips
of felt were placed vertically, nailed at the top to the wall-plate, to
support their weight, and lapped and cemented with pitch to the sides as
on the sand-walls, except that there was no trouble from the overhang.
After the bench-wall had been built, the felt was cut just below the
nails and about 2 ft. above the top of the bench, so that the mats which
were placed over the arch could be inserted behind it. The roof was
covered with three-ply mats and lapped over a little more than half, as
shown diagrammatically on the drawing.
When the upper part of the arch was reached, where the cementing
strength of the pitch was not sufficient to hold the felt in place, the
mats were braced temporarily from the centering, as shown by Fig. 1,
Plate XXVII, until the concrete could be packed against it.
Where the water-proofing was placed against the sand-wall, the method of
securing the sheets at the top is shown in the small sketch on Fig. 14
and by Figs. 3 and 4, Plate XXIV. Fig. 3, Plate XXV, shows the laps of
the sheets and the method of hanging. At the start an attempt was made
to stick the water-proofing to the sand-wall, but this could not be done
on account of its dampness and the overhang at the top.
The sand-wall water-proofing was kept about 35 ft. ahead of the finished
bench-wall, as shown by Fig. 3, Plate XXV. As the bench-wall form was
moved ahead and set, the mat was braced back against the sand-wall from
the forms at a point just above the top of the finished bench, care
being taken to avoid wrinkles, as, if these were once formed, it was
practically impossible to straighten them out.
The completion of the bench-wall left the upper part of this
water-proofing stretched taut across the curved top of the sand-wall,
forming a chord of the arc. As the arch was built up, the top was
gradually slackened so as to allow the concrete to press the mat back
into place until the top of the sand-wall was reached, when the end was
turned in, as shown at _C_, Fig. 18, or the water-proofing was continued
over the arch, if that was necessary.
The desire to obtain a dry tunnel, and the methods adopted to secure it,
were responsible in a great measure for the decision to build the arch
in short lengths, as well as the reasons given under the head of arches.
Had the tunnels been dry throughout, the method shown at _A_, Fig. 18,
could have been used exclusively, and, except for the fact that
monolithic concrete might not have been obtained, there would have been
no objection to building longer lengths.
The quantity of water reaching the tunnel drains and flowing out of
their lower ends after the completion of the lining was about 100,000
gal. per day, or 75 gal. per min.; of this it is estimated that
considerably less than 1% comes through the lining in the form of leaks.
The very general distribution of this water over the roof is indicated
by the fact that, during the excavation of the first 1,000 ft. of both
tunnels from the Weehawken end, oilskins had to be provided for the
laborers to induce them to work at all. The success, therefore, of the
rock packing as a means of diverting this water to the side drains, is
shown, especially in view of the fact that, excluding the cut-and-cover
section, only 10% of the length of the arch, 1,189 ft., was
water-proofed.
Considerable care was taken to make all joints in the concrete which
were in such a position that water might follow through them to the
inside of the tunnel lining, in such a manner that they would slope
outward toward the rock. The top of the sand-wall is shown by Figs. 14
and 18. The slope of the back of the foundation may be noted in Fig. 18,
and the method of making the joint in the arch, in the few instances
where a section was not completed at one operation, is shown at _A_,
Fig. 18. These joints in the arch were not allowed to be made above a
point 60° above the springing line.