Note
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.
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.