_Preliminary Considerations._--For the placing of the concrete lining, a
sub-contract was given to Messrs. King, Rice and Ganey, by Mr. Bradley,
which provided substantially that all materials should be supplied by
him, and delivered to the sub-contractors at track level, at or near the
point in the tunnel at which they were to be placed, and that he would
supply light and power; the sub-contractors were to supply the plant,
forms, and labor necessary for placing the concrete and water-proofing,
building the conduit lines, manholes, etc., etc., to complete the
lining, the general form of which is shown on Plate VIII of the paper by
Mr. Jacobs, and in Fig. 10. The latter also shows the different sections
into which the lining was divided for purposes of construction, and the
nomenclature adopted for each. It may be noted, incidentally, that the
cubic contents of the lining per linear foot of tunnel is almost exactly
half the quantity excavated, out to the standard section lines, and as
there was some excavation outside of these lines, all of which had to be
replaced, the actual quantity of material which had to be brought back
into the tunnel was quite a little more than half the quantity taken
out. It will be evident, therefore, that the question of transportation
was an important one.
[Illustration: Fig. 10.
SKETCH SHOWING DIVISION OF LINING FOR PURPOSES OF CONSTRUCTION,
AND NAMES OF SECTIONS]
An essential part of the agreement with the sub-contractors provided
that the operations incident to the placing of the lining should be
carried on so as to provide at all times space for a single track of
3-ft. gauge, running through the work, and the necessary clearance for
the locomotives and cars used in hauling out the muck. A clearance
diagram of one of the "dinkys" used in the tunnels, and its relation to
the forms used, is shown by Fig. 12 and also by Fig. 16, the 4-yd.
Allison cars, used for handling the muck, taking practically the same
width, although they were not quite as high. This requirement and the
limited space available must be kept in mind in considering the design
finally adopted for the forms and plant required in placing the lining.
It should also be kept in mind that, with the rolling stock used, there
was only room for a single track through that part of the tunnel where
any concrete had been built. As the concrete progressed, therefore, the
length of single track was necessarily lengthened, and the problem of
transportation was made increasingly difficult.
In working out a design for the bench-wall forms, another highly
important and controlling factor, which had to be considered, was the
arrangement of the conduit lines, as shown in the general
cross-section.[2]
[Footnote 2: Plate VIII of the paper by Mr. Jacobs.]
The quantities of the various materials in the lining, per linear foot
of tunnel, were as follows:
Concrete 7.64 cu. yd.
Rock packing: Paid for 1.48 cu. yd.
Outside standard section line 1.74 " "
------------ 3.22 " "
Iron and steel 44.2 lb.
Vitrified conduits 84.0 duct ft.
Water-proofing 13.0 sq. ft.
Flags 3.3 " "
_General Methods._--The lining was started at both ends of the tunnels
before the headings were finally holed through, so that there was
practically a separate organization at each end, each in charge of one
of the members of the firm. The work at the Weehawken end was started
first, and the plant and scheme of working adopted there was thoroughly
tried out before the plant for the western end was built, consequently,
the latter was somewhat more efficient, being designed in the light of
the experience gained at the Weehawken end.
The general sequence of the plan first adopted in placing the concrete
is shown by Fig. 10. The concrete was first placed in the foundations up
to the elevation of the bottom of the conduit bines, this work, of
course, being kept well in advance; next followed, in the order named,
the sand-walls, water-proofing, conduits, bench-walls, and finally the
arch. The foundation was built in any convenient lengths, multiples of
16 ft., the length of one section of form, the sand-walls in lengths of
from 25 to 35 ft., the bench-walls in 25-ft. lengths, and the arch in
10-ft. lengths. Concrete was placed during the day shift only, the forms
being moved partly at night, and partly on the alternate days when
concrete was not being placed in them.
Five gangs were organized at each end, the first placed concrete in the
foundations in both tunnels, as the excavation was ready. In each tunnel
there was a gang which built sand-wall one day and bench-wall the next,
the two tunnels alternating so that only one bench-wall was built each
day, and finally a gang in each tunnel building arches, a 10-ft. section
being completed each day. During the night shift, the arch forms and
travelers were moved, and all other forms, etc., were made ready for the
concrete to be placed the following day. Some of the conduit laying was
done by the night shift, but part of it was necessarily done during the
day, as the concrete was built up. A small gang was kept busy in both
tunnels, during the day shift, laying conduits and water-proofing. The
latter two operations were generally performed by the same gang.
This organization, of course, required considerable regularity in the
work, and this was finally attained, but at the beginning many sections
were often not finished on time, thus creating considerable confusion.
The progress possible with this organization (finally maintained with
great regularity) was 75 ft. of bench-wall and 60 ft. of arch per week
at each of the two working faces in each tunnel. This allowed the
bench-wall to gain considerably on the arch, and therefore at a suitable
point, as shown on the progress diagram, Fig. 9, a third pair of arches
was started, one in each tunnel, increasing the progress on the arches
to 180 ft. per week in each tunnel.
_Mixing and Transportation._--All the concrete used on this section was
mixed in Hains mixers, one being at each end. At the Weehawken shaft the
mixer was installed in the framework supporting the head-house and
elevators; and storage bins were arranged above, as shown by Fig. 11,
_A_, the whole structure being somewhat strengthened to allow this to be
done. At the western end the mixer was placed immediately under the bins
of the stone crusher, as shown by Fig. 11, _B_, the track below being
connected directly with the tunnels. The stone bin under the screen of
the crusher plant at the Hackensack end was divided into three parts,
the center being filled with sand by a derrick having a clam-shell
bucket, the other two with stone directly from the screen above.
This type of mixer proved very efficient on this work. The largest
number of full batches (0.8 cu. yd.) mixed in one plant per hour was
about 35; the largest number per day of 10 hours was about 240; but the
apparatus was never worked to its full capacity, the quantity of
concrete which it was possible to use being limited by other
considerations.
[Illustration: Fig. 11.
_A_ CROSS-SECTION OF HAINS MIXER INSTALLATION, AT WEEHAWKEN SHAFT
_B_ CROSS-SECTION OF HAINS MIXER INSTALLATION,
STONE AND SAND BINS ABOVE AND SCREEN OF CRUSHER, AT HACKENSACK
PORTAL]
The concrete for the foundations was hauled in steel, =V=-shaped,
dumping cars holding about 1 cu. yd., and the concrete for the
bench-walls and arches in Stuebner, 1-yd., bottom-dumping buckets placed
on small flat cars, as shown by Fig. 1, Plate XXIV. Rock packing was
handled in Allison 4-yd. cars and also in the cars shown by Fig. 5,
as well as in the Stuebner buckets, the latter, however, being most
generally used. Mules were used for a short time at the Weehawken end to
haul the concrete in, but proved entirely inadequate to haul the loaded
cars up the 1.3% grade, and locomotives were substituted after the
headings were holed through. At the western end the cars were allowed to
coast in, and, up to the time the headings were holed through, were
hauled back by mules; after that they were pushed out by a locomotive
which had gone in ahead of them. As a rule, from 8 to 10 cars of
concrete and rock packing were sent in, one after the other, in proper
order, a boy riding on each car and stopping it at the proper place; all
these cars were pushed out together when empty.
[Illustration: Plate XXIV.
Fig. 1: K 131. P.R.R. Tunnels, N. R. Div. Sect. K. (Bergen Hill
Tunnels) Weehawken Shaft, North Tunnel. Rear view of conveyor for
concrete, showing method of hoisting bucket from car on track in
hopper over belt. June 7, 07.
Fig. 2: K 130. P.R.R. Tunnels, N. R. Div. Sect. K. (Bergen Hill
Tunnels) Weehawken Shaft, South Tunnel. View showing waterproofing
(extreme left) portion of completed sand wall, sand wall forms,
traveller and end of conveyor overhead. July 22, 07.
Fig. 3: K 148. P.R.R. Tunnels, N. R. Div. Sect. K. (Bergen Hill
Tunnels) Weehawken. View showing method of placing concrete in
forms. Hoisting apparatus and bucket in background. Sept. 24, 07.
Fig. 4: K 154. P.R.R. Tunnels, N. R. Div. Sect. K. (Bergen Hill
Tunnels) Weehawken Shaft, North Tunnel. Method of placing concrete
in bench walls. Top of waterproofing suspended from top of sandwall.
Oct. 21, 07.]
During the time the excavation was being carried on simultaneously with
the lining at the Weehawken end, the rock packing was loaded at the
working face and sent out to the point where it was to be used; after
that the rock packing was sent in from outside from the reserve pile on
the north side of Baldwin Avenue.
At the western end the larger part of the rock packing was sent in from
outside, but occasionally, during the time the excavation was going on,
the cars from the heading were stopped at convenient points, generally
under the gantries, where the lining was being placed, and whatever
stone could be utilized was sorted from the top and passed up to the
platforms above.
After the headings were holed through, there was considerable difficulty
at times in getting a sufficient supply of concrete and rock packing
into the tunnel at the time it was required, and while undoubtedly the
transportation facilities may have had some influence in this, the
principal trouble lay in the difficulty of securing a sufficient supply
of proper stone for rock packing, and for the crusher.
While the excavation was progressing, the cars of muck, as they came
from the headings, were taken directly to the crusher and dumped into
it, the proportion of fine material being fairly constant and the supply
regular. At this time, also, a portion of the rock not required at the
crusher was dumped along the edge of the bank on the south side of the
approach, the larger stones rolling to the bottom where they were easily
available to be loaded into cars for rock packing, being entirely free
from the fine material; as this stone at the bottom of the bank was used
up, the supply was renewed, the rock suitable for rock packing being
automatically separated from the fine material as it rolled to the foot
of the slope.
After the excavation was completed, however, it was necessary to go into
the bulk of the storage piles to get material for the crusher and for
rock packing, and then the difficulties were materially increased by the
large quantity of fine material encountered, the proportion remaining
after the rock packing had been sorted out being too large to send
through the crusher. It was not only the handling over of this fine
material which caused delay, but the difficulty of disposing of it. On
rainy days the trouble was increased by the difficulty of getting men to
work in the open.
The delays due to transportation were usually caused by derailments,
which were more numerous than they should have been, and were due to the
condition of the rolling stock rather than to that of the track. These
delays, especially when they occurred in the early part of the day,
greatly increased the cost, by necessitating over-time work; a delay of
1 hour in the forenoon generally meant 2 hours' work after 6 o'clock to
finish the day's work.
The average number of cars handled (round trips of 1 car) during a day
(two 10-hour shifts) at the Hackensack end during January, 1908, when
the excavation and lining were in full swing, was about 125 cars of muck
and 200 cars of lining material, the former being hauled by locomotives
and the latter by mules.
_Methods of Handling Concrete in the Tunnels._--The concrete for the
floor, ditches, and foundations, was brought into the tunnel in
=V=-shaped steel, dumping cars, and dumped as near as possible to the
place it was to occupy.
The concrete for the arches and bench-walls was loaded at the mixers
into 1-yd., Stuebner, bottom-dumping buckets which just held a 4-bag
batch. These buckets were placed on small flat cars, hauled into the
tunnel, placed beneath the traveling gantry, as shown by Fig. 1, Plate
XXIV, and hoisted to the platform above.
These traveling gantries, the details of which are shown by Fig. 12,
consisted essentially of platforms at each end of which an =A=-frame was
erected; the latter supported at their apexes two =I=-beams, from the
lower flanges of which was suspended a traveling block, shown at _A_,
Fig. 12, and through which the hoisting rope was rigged. The buckets
were hoisted through an opening in the platform and then moved along to
where they could be dumped. The platforms were supported on wheels
traveling on rails laid on the concrete of the foundation (for the
bench-wall gantries) or on top of the bench-wall (for the arch
gantries).
Each of the first two of these traveling gantries used was equipped with
a belt conveyor working on a cantilever arm, as shown by Figs. 3 and 4,
Plate XXI, and Figs. 1 and 2, Plate XXIV. In using these belt conveyors,
the concrete was dumped from the Stuebner bucket into a hopper, Fig. 1,
Plate XXIV, with an adjustable slot in the bottom, under which the belt
ran.
[Illustration: Fig. 12. [Full Page]
DETAILS OF TRAVELING GANTRY USED IN THE CONSTRUCTION OF THE TUNNEL
LINING:
SECTIONAL ELEVATION
CROSS-SECTION
A. DETAIL OF TRAVELING BLOCK
B. DETAIL OF TOP SHEAVE
C. DETAIL OF LOWER SHEAVE.]
It was the original intention, in designing the conveyor, that the end
of the cantilever arm should be swung from one side of the tunnel to the
other, and that the traveler should be moved backward or forward, as
might be required, and thus deliver the concrete from the end of the
belt directly over the place in which it was to be deposited in the
bench-walls. As a matter of fact, it was found impractical in operation
to move the gantry readily, owing to its great weight, which was
supported on only four ordinary car wheels and their bearings, and it
was found more convenient to leave the arm in one position near the
center, letting the concrete drop on the platform above the bench- or
sand-wall forms, whence it could be shoveled into place, than to attempt
to move it as had been intended. Both of these difficulties might
possibly have been overcome by modifications in the design of the gantry
and conveyor, had this method of handling the concrete seemed otherwise
desirable.
The principal difficulty with its use, however, was the inability to
take care of more than one batch of concrete at a time. When one batch
had been dumped into the hopper, a second could not be disposed of until
the first had nearly all run through on the belt, and this took from 7
to 20 min., varying with the consistency of the concrete, etc. In a few
instances, where there happened to be some fairly dry batches, the
concrete could not be started through the slot at all, and had to be
shoveled out of the hopper. On the other hand, it is stated that some
batches, under favorable conditions, passed through in about 2 min., but
this was quite exceptional, and the operation was irregular and
uncertain.
Before the final method of handling the concrete was adopted, a trial
was made of two forms of cars and buckets, to be used on the top
platform, as shown by Figs. 3 and 4, and Plate XXIV. In the method shown
by Fig. 3, Plate XXIV, the concrete was hoisted in the regular Stuebner
buckets, one of which can be seen suspended in the background of this
photograph, and dumped into the car shown, which was mounted so that it
could be revolved in a horizontal plane. It was intended to move this
car on the tracks to the point at which the concrete was required, and
dump it directly through a chute into the bench-walls. This car was
abandoned, as there was a great deal of difficulty in turning it when it
was loaded, and in several instances it had to be dumped straight ahead
in the middle of the platform and the concrete shoveled into the forms.
This method was also objectionable when the bucket was dumped, inasmuch
as the force of the impact of a whole batch of concrete dumped from such
a height into the forms, not only tended to throw the conduits out of
line, and to break them, but also caused considerable strain on the
forms.
The bucket shown by Fig. 4, Plate XXIV, was next tried. It had a
slanting bottom and a door opening at the side. It was filled at the
mixer, came into the tunnel on a small flat car, and was hoisted and
placed on a similar car on top, as shown. This bucket was not
successful, as its great weight made it difficult to handle, and it
generally required a man to shovel the concrete out, which latter, of
course, had been pretty well compacted in the bottom of the bucket by
its trip from the mixer. All these cars were hauled backward and forward
on the top platform by a rope running to the winch on the hoisting
engine on the traveling gantry.
Aside from the fact that neither type was a success, neither of these
schemes was much improvement over the belt, inasmuch as only one batch
could be handled at a time, owing to the necessity of using the engine
to haul the cars back and forth on the platform. The final solution was
found in the use of the traveling gantry, shown by Fig. 12 and Fig. 1,
Plate XXVI, the latter being one of the arch gantries. The gantry used
for the bench- and sand-walls was supported on framed bents on wheels
running on rails laid on the foundation; that for the arch was the same,
except that the high-framed bent was dispensed with, the side-sills
resting directly on the journals of wheels traveling on rails on top of
the finished bench-wall.
These gantries were used only as a means of hoisting the buckets and
moving them along to where they could be dumped directly on the
platform, whence the concrete was shoveled into wheel-barrows, which
could be dumped directly into the bench-walls; or, in the case of the
arches, shoveled from the platform of the gantry to the intermediate
platform on the arch ribs, and thence directly into the arch. This use
of wheel-barrows, though apparently a somewhat crude method and a
retrogression from the use of the belt conveyor, proved very successful,
and really involved no more labor than did the conveyors, although this
might not have been the case had these latter worked as they were
originally designed to.
The method finally adopted allowed as many as four buckets to be dumped
on the platform on one end of the arch gantry at one time, and eight on
one end of that used for the bench-walls, the workmen handling about
three of these latter into the forms by the time the last of the eight
was dumped. It required about 1½ min. to place a car under the gantry,
hoist the bucket, dump, close it, and return it to the car below.
Rock packing was stored at the other end of the platform, for use as
required, when it was not handled directly from the end nearest the
work. This method allowed the concrete and other materials to be brought
in in trains at infrequent intervals, and provided a sufficient supply
of material on hand so that the men handling it on top could be kept
steadily at work.
Each hoisting engine on these gantries had 7 by 10-in. cylinders, and a
double drum; some of them were Lamberts and some Mundys, operated by
compressed air.
_Ditches, Floor and Foundations._--The first method of building the
foundation was that shown by Fig. 13, _A_; no attempt was then made to
build the ditch, or floor, the intention being to leave these until the
completion of the remainder of the lining. In building the bench-wall on
this foundation, however, it was found difficult to secure the bottom of
the forms properly (Fig. 2, Plate XXV), so as to prevent any give, as
the material under the track was not solid enough to brace against. It
was decided, therefore, to build the whole of the ditch (see Fig. 13,
_B_) so that the bottom of the forms could be braced against the solid
concrete. At the beginning of the work, the face of the bench-wall was
built up to the level of the bottom of the conduits with the foundation;
if, therefore, in placing the concrete above this level, extreme care
were not taken to get a tight fit between the bench-wall form and the
lower face, and then to hold it rigidly in place, the result was a
rather unsightly horizontal joint high enough to be plainly visible. The
position of this joint may be seen in Fig. 2, Plate XXV, which shows the
first section of bench-wall built. Several subsequent sections showed an
overhang above this joint, amounting in one or two cases to as much as ½
in., due to the fact that the bench-wall form moved or did not fit
tightly. This defect was obviated by building the foundations with an
offset on the face, shown by Fig. 13, _B_, so that the joint came at the
level of the top of the flagging over the ditches, and therefore was
almost entirely concealed; at the same time this allowed a sufficient
surface, on the plane of the face of the bench-wall, against which the
bench-wall forms could be braced and lined up.
[Illustration: Fig. 13.
PLAN SHOWING VARIOUS METHODS OF BUILDING FLOOR AND FOUNDATION,
AND DETAILS OF FORMS]
The ditch forms were set very carefully to line and grade by the
alignment corps, as this formed the starting point of all the rest of
the work, the only other thing which was necessary was to give a level
at the front end of the bench-wall form, after it was set, for the
elevation of the top of the bench, and to check up the stations of the
ends of the sections occasionally to see that they were at the even
25-ft. points (that is +08, +33, +58, and +83).
After a short length had been built with the ditches only, it was
thought desirable to try and put in the floor as well, so that the whole
of the concrete would be put in place as the lining advanced, and leave
less cleaning up to be done over the end of a single track, in the
restricted spaces between the bench-walls. Fig. 13, _C_, shows the
method finally adopted. In this may be seen the three stages in which it
was put in, the details of the ditch forms being shown by Fig. 13, _D_.
In that part of the tunnel where sand-walls were built, a hollow tile
drain was built into the foundation, as shown in Fig. 13, _A_ and _B_,
along the foot of the water-proofing and connected at intervals with the
drains by 4-in. cast-iron pipes. When the sand-walls and water-proofing
were not built, however, the concrete of the foundations was sloped from
the neat line back to the rock, as shown by Fig. 13, _C_3, so that in
case any water found its way down through the rock packing, its tendency
would be to flow back against the rock, or to follow the low part of
this concrete to 4-in. cast-iron pipes leading to the side ditches,
rather than to find its way through the joint between the foundation and
the bench-wall and so into the lower duct lines.
_Sand-Walls._--The sand-wall forms first used are shown in Fig. 2, Plate
XXIV, with a section of the finished sand-wall. As this work was only
intended to give a comparatively smooth surface against which to place
the water-proofing, no particular care was taken with the surface,
except to avoid sharp projections which might cut through the felt and
pitch used for this purpose. A rather porous concrete (with all the rock
which could be safely embedded in it and have the wall stand) was used,
so that it would not act as a dam, but rather tend to allow the water to
find its way to the bottom of the tunnel, and so into the drains.
The traveling gantry for placing the concrete in the sand-walls, as
first designed, with the belt conveyor, could of course only deliver the
concrete at one end. Before setting the forms for a new section, it was
necessary, therefore, to move the gantry ahead, before the cross-bracing
between the tops of the forms, which also held the top platform, could
be placed in position. Fig. 2, Plate XXIV, shows the end of the conveyor
over the top of the cross-braces. In order to hold the bottom of these
forms, small wooden blocks were embedded in the foundation concrete,
against which they could be wedged, as shown by Fig. 13, _A_; these
blocks were cut out after the sand-wall had been built.
After the forms had been filled, the conveyor could not be moved back to
the bench-wall until the concrete had set sufficiently so that these
cross-braces could be removed, and, on account of the overhang at the
top, the set had to be fairly good in order to prevent this overhang
from breaking off. This arrangement, therefore, for placing the concrete
was found to be impractical, if the proposed schedule of a section of
bench-wall and a section of sand-wall to be built on alternate days, was
to be carried out. In a few instances, where the sand-wall was finished
fairly early in the afternoon, the forms were released next morning, and
the conveyor was moved back, but, even then, 2 or 3 hours at least were
lost at the beginning of the shift. The conveyor, however, was
abandoned, for the reasons previously given, and the traveling gantry
was rearranged to allow concrete to be delivered at either end; it was
then only necessary to move it backward and forward between the bench-
and sand-wall forms instead of through these forms. This permitted the
construction of the much more substantial type of forms shown by Fig.
14.
After being moved ahead on the track on top of the foundation, the form
was first blocked up to grade, and then adjusted to line by the screws
and slotted cleats shown at _B_, Fig. 14, after which it was secured by
the braces from the ditches, as shown. The face lagging was placed in
separate pieces and held against the uprights by lightly nailing every
third or fourth piece; the whole was removed each time the form was
moved, and built up again as the concrete was placed.
Considerable care was taken to slope the top of the sand-wall back
toward the rock, as shown by Fig. 14, and to allow free drainage along
the top (which ran parallel to the grade of the tunnel) to the 4-in.
cast-iron drain pipes which carried the water from the rock packing
above the arch to the drains beneath the track.
Sand-walls were built for a length of about 1,100 ft. in each tunnel at
the Weehawken end, and about 700 ft. in each tunnel at the western end,
the remainder of the work, with the exception of a few short stretches,
not being considered wet enough to require water-proofing.
[Illustration: Fig. 14.
TRAVELING FORM FOR BUILDING SAND-WALL;
DETAIL SHOWING METHOD OF HANGING WATER-PROOFING FROM TOP OF SAND-WALL]
_Conduits._--The arrangement of the conduit lines is shown in the
general cross-section.[3] On the core-wall side there are 48 lines for
telegraph and telephone cables, built of 4-way multiple conduit, each
piece of which is 3 ft. long and about 10 in. square outside. On the
other side there are the high- and low-tension lines, built of single
conduit 18 in. long and a little more than 5 in. square outside.
Manholes or splicing chambers are built every 400 ft., and are about
8 ft. long and 4 ft. wide. General views of the conduits as built are
shown in Fig. 4, Plate XXV, which shows all the lines in one tunnel, and
in Fig. 1, Plate XXV, which shows the telegraph and telephone lines,
with the expanding mandrels used in laying them.
[Footnote 3: Plate VIII in the paper by Mr. Jacobs.]
[Illustration: Plate XXV.
Fig. 1: K 173. P.R.R. Tunnels, N. R. Div. Sect. K. (Bergen Hill
Tunnels.) Hackensack Portal and Approach. Telephone and Telegraph
ducts and mandrels. Nov. 20, 08.
Fig. 2: K 125. P.R.R. Tunnels, N. R. Div. Sect. K. (Bergen Hill
Tunnels) Weehawken Shaft, North Tunnel. View showing general
construction of tunnel lining forms, and clearance to allow disposal
of excavated material. June 17, 07.
Fig. 3: K 156. P.R.R. Tunnels, N. R. Div. Sect. K. (Bergen Hill
Tunnels) Weehawken Shaft, South Tunnel. North side looking East,
showing method of placing waterproofing. Oct. 22, 07.
Fig. 4: K 147. P.R.R. Tunnels, N. R. Div. Sect. K. (Bergen Hill
Tunnels) Weehawken. General view showing center and first section of
arch and completed lining, North Tunnel. Sept. 24, 07.]
In attempting to plan the work of placing the lining, two methods of
building the bench-wall were considered. One was to build the wall in
longitudinal sections, each section separated by a line of ducts; and
the other was to attempt to build the wall in the manner called for by
the specifications, which required the concrete to be carried up in
layers as the conduits were laid. In this latter method, it was proposed
to bond the concrete together with the forked bonds, the details of
which are shown by Fig. 15, _A_, but, as it might have been impractical
to use these if the wall had been built in sections, provision was made
in the contract to place expanded metal, as shown by Fig. 15, _B_, if
this was thought advisable. The method of construction necessary, if the
wall had been built in sections, is shown graphically by the five
sketches, Fig. 15, _B_, 1, 2, 3, 4, and 5.
The form and details of the expanding mandrel which was finally designed
to meet the conditions, and proved so satisfactory in every way, are
shown by Fig. 15, _C_. The mandrel consisted of two triangular pieces of
hard pine, separated by wedges attached to one piece which fitted into
slots in the other; these, when expanded, practically filled the whole
of the inside of the ducts. One of these mandrels was placed in each
line of single ducts and two in each 4-way duct, placed diagonally, as
shown in Fig. 1, Plate XXV. This required 60 mandrels at each working
point, or 240 for the whole work. The mandrels were 35 ft. long, so that
they easily covered the whole of a 25-ft. section, projected
sufficiently far back into the previously finished work to assure the
continuity of the alignment, and allowed the ends to be racked out at
the forward end to secure proper breaks between the joints.
In laying the single conduits, as a rule, the (collapsed) mandrels were
pulled ahead from the previous section as each line was laid, and the
conduits were strung on it until the whole length was completed; the
conduits were then pushed up tight together, so as to close the joints
as tightly as possible, and then the mandrel was expanded. The conduits
were thus held firmly in position, and the forward end of the line was
lifted slightly so that the wraps could be placed around the joints. The
4-way conduits were generally laid in the ordinary way, except that no
laying mandrel was necessary. One dowel was used between each of the
pieces of conduit, at the center, and the joints were wrapped. When a
line was finished, two mandrels were placed diagonally in each line and
expanded simultaneously, so that any inequalities in the ducts
themselves were divided as far as possible. In connection with the use
of these mandrels, one of the points which was most carefully watched
was that they projected back into the last completed section, thus
insuring the continuity of the alignment.
It was originally intended to wrap the joints of the 4-way ducts only,
but it was found to be impractical to keep the grout from the wet
concrete entirely out of the single ducts, and, after a short trial, it
was decided to wrap these also. The expanding mandrel kept out a great
deal of the cement, and, in the sections laid without wraps, the only
difficulty from this cause seemed to be that a slight film of grout,
from 1/16 to 1/8 in. thick, was deposited on the bottom of the inside of
the ducts at some places, and although this was not considered a serious
defect, it was thought that the slight extra cost of placing the wraps
would undoubtedly be justified by the practically perfect results
obtained by using them.
Considerable attention was given to breaking the joints of the ducts
properly, so as to maintain throughout the conduit lines the greatest
break possible. The joints in each superimposed line were broken at half
the length of the individual pieces of conduit, the joints in lines in
the same horizontal plane being broken at one-quarter the length, thus
preventing any joints from touching one another either at the sides or
corners, which tended to prevent a burn-out on one line from being
communicated to another. There was some little difficulty at first in
maintaining the breaks, owing to slight variations in the lengths of the
conduit, but after a very short time both the workmen and the inspectors
became very expert at this and in the proper use of short lengths to
maintain the spacing; after the first few weeks there was little if any
difficulty in attaining at all times almost perfect results. The method
of making the breaks is shown in the photographs and by the isometric
sketch at _F_, Fig. 15.
All the conduits used on this work were furnished by the Great Eastern
Clay Company, and were made at its factory at South River, N.J., where
they were inspected before shipment.
The mandrel used in the final rodding was made as shown at _G_, Fig. 15,
the larger size being used for all lines. The rods for pushing it
through the conduit lines were made of 6½-ft. lengths of ordinary 1-in.
wrought-iron pipe with extra long (3-in.) couplings. The lines were
rodded in both directions from alternate manholes, thus avoiding
uncoupling the rods and allowing every pull to be effective in pushing
the mandrel through the ducts.
[Illustration: Fig. 15. [Full Page]
ELECTRICAL CONDUITS: METHODS OF LAYING, RODDING, ETC.
A. FORK ENDED STEEL BONDS FOR CONDUITS.
B. SEQUENCE OF METHODS OF BUILDING BENCH-WALL PROPOSED WHEN USING
EXPANDED METAL BONDS.
C. ISOMETRIC DRAWING OF EXPANDING MANDREL.
D. DETAILS OF "WEASEL" Used for gripping disconnected pipe rods in
conduit
E. CUTTER FOR REMOVING OBSTRUCTIONS IN CONDUITS.
F. ISOMETRIC SKETCH SHOWING METHOD OF BREAKING JOINTS AND POSITION
FORKED BONDS.
G. PLAN AND SECTIONS OF EXPANDING MANDREL.
INDEX
+-----+------------+----------------+
| | Multi-Duct | Single-Duct |
| | Mandrel | Mandrel |
+-----+------------+----------------+
| _A_ | 3¼" | 3-3/8" |
| _B_ | ¾" | 7/8" |
| _C_ | 2½" | 2-5/8" |
+-----+------------+----------------+