Engineering Wonders of the World
Volume I

THE RIVER TUNNELS finished, its slope was lumpy, irregular, and in places too steep. Now, the design did not include a thick concrete lining as in the Pennsylvania tubes, and the leeway for divergence from true line was small. In short, the conditions were such that it was necessary to make an attempt to straighten the tubes. Mr. W. I. Aims was the contractor’s engineer. An ingenious plan of doing this was schemed out and successfully executed. It consisted in cutting away, as it were, the humps of the OF NEW YORK CITY. 121 been excavated deep enough (only a few feet in the worst case), a strong concrete bottom, reinforced with steel rods, was put into the desired new outline. A more serious difficulty was encountered at one point where it was desired to raise the top for a short distance. This was accom- plished by forcing the plates upward (after unbolting) by means of powerful jacks, and simultaneously loosening and washing out the sand above by water streams and stirring rods through holes in the plate. TUNNEL WITH CONCRETE-FILLED FOUNDATION PILES. TUNNEL IN ROCK AND SHIELD-DRIVEN PORTIONS. Fig. 23.—CROSS-SECTION OF BATTERY Fig. 24.—SECTIONS OF THE STEINWAY bottom down to a new bottom line corre- sponding to the parts which had sagged most. This necessarily produced an irregular and varying outline of tunnel ; but that was no disadvantage, as the reconstructed tunnel could be lined with a thin layer of concrete so distributed as to produce a fairly regular outline all along. The process of cutting down the bottom was briefly this: A bottom segment of lining having been unbolted and broken to pieces by heavy hammers, the air pressure was raised to balance exactly the soil pressure at that point. Then the bottom plate was taken oat, and, under the perfectly balancing air pressure, the soil could be dug away without dr nger. The whole length of a hump was treated in this way, and after the soil had. Finally, another remarkable thing was done in this tunnel. A belief gained ground that the tunnel would be unstable, being in quick- sand, and it was decided to sink foundation piles under it, to give a firm support. The plan was carried out, several hundred feet of length being thus underpinned. Bottom plates were broken out just as for reconstruction, and then large vertical iron pipes were “ jetted ” down—that is, were pressed down by jacks while a stream of water, forced through a small pipe attached to the bottom of the pile, washed away the sand below it. When the pile finally rested on rock or firm ground, it was cleaned out and filled with concrete, and then a con- crete “ cradle ” was built around the top of the pile to support the tunnel. Two such