Engineering Wonders of the World
Volume I

THE RIVER TUNNELS OF NEW YORK CITY. 109 double-track tunnel, though he later changed over to two single-track tunnels of elliptical shape, 16 feet by 18 feet. This early project, which we now consider foolhardy, seemed to be opposed by the very fates. Five years were first consumed in litigation over rights. Then, The Old -n iggø, after work was again Hudson River x , , , ,. T , Tunnel ” started at the New Jersey end, a disastrous “ blow-out ” oc- curred close to the shore shaft. The roof of •the tunnel, lined only with thin steel plates, caved in suddenly under the pressure of the water-charged soil above and blocked the air-lock, the tunnel was flooded by the in- rushing water, and twenty men who. could not escape through the air-lock were drowned. The greatest interest in the early work in this tunnel lies in the fact that, though lacking the aid and protection of shields, the engineers actually succeeded in building some 1,800 feet of the north tube and 600 feet of the south tube. This was accomplished during the period 1881 to 1887 in several stages, interrupted by money troubles and other mischances. The method of excavation first used was -simply to start at the top, dig out a small space, put in a section of plating one quarter of an inch thick, and continue downward until the whole ring was in place. Meanwhile, how- ever, the next ring had been started at the top, etc., so that the face was a series of terraces. One great trouble with this method was that it allowed the plating to settle before the ring was completed and the 24-inch brick lining was laid. The clay face, being so large in area, had to be watched very carefully to detect holes—which the compressed air tended to produce—and seal them before they could grow. Then the “ pilot tunnel ” method was in- troduced by Mr. J. F. Anderson, and there- after used (Fig. 8). It employed a small 6-foot steel-plate tunnel, 50 or 60 feet long, with half its length in advance of the main A Pilot Tunnel. face, on the precise axis of the main tunnel. The small tunnel was very much easier to construct, and its rear part served as a support for radial braces supporting the lining of the main tunnel. As the brickwork of the main tunnel set, the radial strutting could be taken out and the rear of the pilot removed plate by plate and re-used at the forward end. Fig. 8.—SKETCH ILLUSTRATING THE PILOT TUNNEL METHOD, BY WHICH THE OLD HUDSON RIVER TUNNEL WAS BUILT FOR 1,800 FEET. While the “ pilot ” method did much to prevent settlement out of line, it did not keep the tunnel satisfactorily straight, and later on much cutting and patching had to be done on this account. Also, it was not nearly so safe, rapid, and cheap as shield work. A new stage began in 1889 with new blood both as to money and as to engineers. An ex- perienced English firm of contractors, S. Pear- son and Son, took charge, and immediately prepared for working by the shield method. A wonderful achievement marked the com- mencement of their work. The enter the abandoned tunnel, and end, one-third (he way across the river, dig out a chamber in the mud large enough to enable their shield had caved in ; and followed from the became impossible. an engineer for the contractors, made a large canvas balloon filled with hay and clay, and dropped it from a scow into the hole in the river bottom. This blocked the gap success- fully, and the workers in the tunnel, after men had to at its outer Stopping a Hole. to be set up. The mud as they dug away, more river bottom till work Then Mr. E. W. Moir,