The tunnels constructed under the Hudson River for the Pennsylvania Railroad, consist of two parallel tubes driven side by side 14 ft. apart. The tubes are of circular cross-section, 23 ft. exterior diameter, and are lined with cast-iron rings. The tunnels were driven from two shafts, one on the eastern shore of the Hudson River near 32nd St. and 11th Ave., New York; the other at Weehawken, New Jersey, near the piers of the Erie Railroad. The horizontal distance between the shafts was 6550 ft. The permanent one at Weehawken was built on a square plan, 130 ft. to a side. It was lined with concrete masonry and the walls were battered in such a way as to become the shape of an inverted frustum of a pyramid. It was provided with five openings at the bottom, four of these are used by trains that run in the open, the fifth one leads to a power house near by. During the construction of the tunnels one-third of this shaft was used for the land portion of the tunnel under Bergen Hill, while the remaining two-thirds were devoted to the construction of the tunnel under the river. The working shaft on Manhattan Island was a side shaft of rectangular plan 30 ft. by 22 ft., the tunnel proper being connected by two drifts 10 ft. by 10 ft. each. The shield rooms 23 ft. long, were situated on both sides of the river just in front of the shafts. On the New York side, the shields, one for each tube, were built inside the iron lining of the shield chamber, and the hoisting tackle was slung from the iron lining. The erection on the Weehawken side was done in the bare rock excavation where timber falsework was used. After the shields were finished and in position, the first two rings of the lining were erected in the tail of the shield. These rings were firmly braced to the rock and the chamber lining; then the shields were shoved ahead by their own jacks, another ring was built and so on.

[13] Condensed from paper by James Forgie, “Eng. News,” Vol. LVI, and by H. B. Hewett and W. L. Brown, “Proc. Am. Soc. C. E.”, Vol. XXXVI.

Rear Elevation of Shield.

Vertical Section.

[Larger illustration]

Half Section A-B.

Half Section C-D.

Horizontal Section.