1.--4-way duct, for telephone and telegraph cables,
2.--2-way duct, for telephone and telegraph cables,
3.--1-way duct, for high- and low-tension cables,
4.--Plug for closing open ends of ducts,
5.--Plug for closing open ends of ducts in position,
6, 7, and 8.--Cutters for removing obstructions,
9.--Hedgehog cutter for removing grout in ducts,
10.--Rodding mandrel for multiple ducts,
11.--Laying mandrel,
12.--Rodding mandrel, with jar-link attached,
13.--Laying mandrel,
14 and 15.--Rubber-disk cleaners, used after final
rodding,
16 and 17.--Sectional wooden rods used for rodding,
18.--Section of iron rods used for rodding,
19.--Jar-link,
20.--Cotton duck for wrapping joints of multiple ducts,
21.--Hook for pulling forward laying mandrel,
22.--Top view of trap for recovering lost or broken
rods left in ducts.
[Illustration: PLATE XXXV. TRANS. AM. SOC. CIV. ENGRS. VOL. LXVIII, No.
1155. HEWETT AND BROWN ON PENNSYLVANIA R. R. TUNNELS: NORTH RIVER
TUNNELS. FIG. 1. FIG. 2.]
Ordinary ¾-in. gas pipe was used for the rod, and a cutter with
rectangular cross-section and rounded corners was run through ahead of
the mandrel: following the cutter came a scraper consisting of several
square leather washers, of the size of the ducts, spaced at intervals on
a short rod. The mandrel itself was next put through, three or four men
being used on the rods. All the ducts in a bank were thus rodded from
manhole to manhole. When a duct was rodded it was plugged at each end
with a wooden plug. A solid wooden paraffined plug was used at first,
but afterward an expansion plug was used.
Very little trouble was met in rodding the power conduits, except for a
few misplaced ducts, or a small mound of mortar or a laying mandrel left
in. At such points a cut was made in the concrete and the duct replaced.
In the subgrade telephone and telegraph ducts east of the Manhattan
Shaft, much trouble was caused by grout in the ducts. The mandrel and
cutters were deflected and broke through the web of the ducts rather
than remove this hard grout. Trenches had to be cut from the floor to
the top of the water-proofing, the latter was then cut and folded back,
and the ducts replaced. To do this, a number of ducts had to be taken
out to replace the broken ones and get the proper laps. The
water-proofing was then patched and the concrete replaced. This grout
had not penetrated the water-proofing, but had got in through the ends
of the ducts where they had not been properly plugged and protected. The
duct gang, both for laying and rodding, generally consisted of
1 Foreman, at $3.50 per day,
and 9 laborers, at $1.75 per day.
When laying: 4 men were laying, 2 men mixing and carrying mortar, and 3
were transporting material. When rodding: 4 men were rodding, 2 men at
adjacent manholes were connecting and disconnecting cutters and
mandrels, 1 was joining up rods, and 2 men assisting generally.
The cost of this work is shown in Table 17.
Transportation and Disposal.
The track on the surface and in the tunnels was of 20-lb. rails on a
2-ft. gauge.
The excavation was handled in scale-boxes carried on flat cars, and the
concrete in 1¼-cu. yd. mining cars dumping either at the side or
end.