Engineering Wonders of the World
Volume I

110 ENGINEERING WONDERS OF THE WORLD. Fig. 9.—FRONT FACE OF A HUDSON TUNNEL SHIELD at the end of its journey. (Its battered condi- tion testifies to its hard service.) Fig. 10.—con- crete-lined APPROACH SECTION IN ROCK, LOWER HUDSON TUNNELS. Fig. 11.—SURFACE VIEW OF A tunnel cave-in in soft ground. (This occurred in the Weehawken or west approach section of the Pennsylvania Hudson River Tunnel, where it passes under the Erie Railway freight yards.) cutting away as much of the balloon as had settled into the opening, could build a chamber, with the help of 42 lbs. air pressure. Then the shield was erected ; soon it was pushing ahead toward New York, and a substantial cast-iron lining was erected behind it as it proceeded. The work progressed rapidly, as much as ten feet in a day. By the fall of 1891 the north tunnel had been extended to nearly 4,000 feet from the New Jersey shore. Then suddenly the great Baring Brothers’ failure in London cut off the money supply, and the work stopped. Another period of ten years of idleness followed, and again new hands took up the work. In 1902 Charles M. Jacobs, who eight years before had directed the East River Gas Tunnel, took the Mud. charge. His skill was soon tested, for the shields encountered rock—a submerged peak near the New York shore. To blast out the sloping rock in the lower part of the face, while the top of the shield was still in flowing mud, was a task of the same kind as recounted above for the Gas Tunnel. By extending the horizontal plat- form forward at mid-height of the shield to form a protecting apron (Fig. 7), the work was accomplished successfully, though very slowly. On a part of this rock work also the novel plan of baking the mud face with torches, to prevent it from flowing, was used. Dump- ing clay in the river to form a thicker and less porous cover over the tunnel was also necessary at times. In 1904 the shield of the north tunnel met the short heading which had been driven west from the New York shaft. A beautifully effective method marked the progress of the south tunnel, which had mean- while also been taken in hand. When its shield was well started in the j .v . Phenomenal river mud, the engineers con- i • ceived the bold idea that it would not be necessary to cjig out the soft