Engineering Wonders of the World
Volume I

THE RIVER TUNNELS the idea probably never had much promise. Multiple-unit trains of electric cars now run through the tunnels. The only main-line railway tunnels now building or planned to be built at New York are the Pennsylvania Rail- road tunnels, and these were not designed for steam locomotive traction. The entire ter- • minal extension, crossing the meadows west of the Weehawken heights and thence passing through the tunnel under the Hudson to New York, or still further through the cross- town tunnels and the East River tubes to Long Island, will be operated by the electric third-rail system. THE PENNSYLVANIA TUNNELS (HUDSON RIVER AND EAST RIVER). The Pennsylvania R.R. tunnels are by far the most daring tunnelling enterprise of the entire New York group, in their engineering perhaps even more than in their financial as- pect. The real estate and construction cost of the entire project will approximate, say, $100,000,000; and as the extension will do little for the railway’s freight service, the cost must be paid for by the passenger traffic. The railway manager who made the decision to commit his company to so costly a project needed to have a long sight to see the return- ing profits, and undaunted courage to fight his beliefs through. Mr. A. J. Cassatt, late president of the Pennsylvania Railroad, pos- sessed these qualities. The Pennsylvania development includes, besides the tunnels, a considerable extent of new line and other improvements on the New Jersey side and on Long Island, and a magnificent terminal station within the city connected with the river tubes by rock tunnels under the city streets. A very large book would be required to recount the story of the whole enterprise. Our interest at present is centred on the river tunnels, the shield-driven work. At the outset of this project the gravest (1,408) OF NEW YORK CITY. 113 doubts, perhaps, concerned the question of the stability of the Hudson River mud or silt. This material is physically little better than a stiff jelly ; The Two yet the tunnels must rest in it, and must be secure against Tunnels all possibility of being strained by the load and the vibration of heavy express trains passing through it. To ensure this security, the engineers laid plans for a pile foundation, consisting of strong cast-iron hollow piles to be sunk from the bottom of Fig. 14.—CROSS-SECTION OF PENNSYLVANIA RAILROAD HUDSON RIVER TUNNEL TUBE, WITH SCREW-PILE FOUNDATION AS PLANNED. the finished tunnel down to hard soil, and then filled with concrete and anchored to the tunnel shell. The cross-section drawing (Fig. 14) shows this pile arrangement, which, was to be re- peated every fifteen feet along the tunnel. There are screw piles fitted with a broad-winged helical ^crew Piles, disc at the bottom and twisted down through the mud. To enable the piles to be passed through the tunnel shell, highly ingenious special bottom plates for the tunnel were designed, and built in at the proper intervals. But since the early stage of the enterprise, views have changed somewhat, and the people in charge have apparently reached the con- clusion that the piles are not necessary. The upper Hudson tunnels, in which a train service 8 vol. II.