Transactions of the American Society of Civil Engineers, vol. LXVIII, Sept. 1910 / The New York Tunnel Extension of the Pennsylvania Railroad. / The East River Tunnels. Paper No. 1159

by James H. Brace; Francis Mason; S. H. Woodard

Iron Lining.

The standard cast-iron tunnel lining was of the usual tube type, 23 ft. in outside diameter. The rings were 30 in. wide, and were composed of eleven segments and a key. The webs of the segments were 1-1/2 in. thick in the central portion, increasing to 2-3/8 in. at the roots of the flanges, which were 11 in. deep, 2-1/4 in. thick at the root, and 1-1/2 in. at the edge, and were machined on all contact faces. Recesses were cast in the edge of the flanges, forming a groove, when the lining was in place, 1-1/2 in. deep and about 3/8 in. wide, to receive the caulking. The bolt holes were cored in the flanges, and the bosses facing the holes were not machined. The customary grout hole was tapped in the center of each plate for a standard 1-1/4-in. pipe. In this work, experience indicated that the standard pipe thread was too fine, and that the taper was objectionable. Each segment weighed, approximately, 2,020 lb., and the key weighed 520 lb., the total weight being 9,102 lb. per lin. ft. of tunnel. [Fig. 1] shows the details of the standard heavy lining.

In addition to the standard cast-iron lining, cast-steel rings of the same dimensions were provided for use in a short stretch of the tunnel, when passing from a rock to a soft ground foundation, where it was anticipated that unequal settlement and consequent distortion and increase in stress might occur, but, aside from the small regular drop of the lining as it passed out of the tail of the shield, no such settlement was observed.

Two classes of lighter iron, one with 1-in. web and 8-in. flanges and the other with 1-1/4-in. web and 9-in. flanges—the former weighing 5,166 lb. per lin. ft. of tunnel and the latter, 6,776 lb.—were provided for use in the land sections between East Avenue and the Long Island City shafts. Two weights of extra heavy segments for use at the bottom of the rings were also furnished. The so-called XX plates had webs and flanges 1/4 in. thicker than the standard segment and the YY plates were similarly 1/2 in. heavier. The conditions under which they were used will be referred to later. All the castings were of the same general type as shown by [Fig. 1].

Rings tapering 3/4 in. and 1-1/2 in. in width were used for changes in alignment and grade, the former being used approximately at every fourth ring on the 1° 30' curves. The 1-1/2-in. tapers were largely used for changes in grade where it was desired to free the iron from binding on the tail of the shield. Still wider tapers would have been advantageous for quick results in this respect.

No lug was cast on the segments for attachment to the erector, but in its place the gadget shown on [Fig. 4, Plate LXX], was inserted in one of the pairs of bolt holes near the center of the plate, and was held in position by the running nut at one end.

In the beginning it was expected that the natural shape of the rings would not show more than 1 in. of shortening of the vertical diameter; this was slightly exceeded, however, the average distortion throughout the tunnels being 1-7/16 in. The erectors were attached to the shield and in such a position that they were in the plane of the center of the ring to be erected when the shove was made without lead and just far enough to permit placing the segments. If the shield were shoved too far, a rare occurrence, the erection was inconvenienced. In driving with high vertical leads, which occurred more frequently, the disadvantage of placing the erector on the shield was more apparent. Under such conditions the plane of the erector's motion was acutely inclined to the plane of the ring, and, after placing the lower portion of the ring, it was usually necessary to shove the shield a few inches farther in order to place the upper plates. The practical effect of this action is referred to later.

At first the erection of the iron in the river tunnels interfered somewhat with the mucking operations, but the length of time required to complete the latter was ample for the completion of the former; and the starting of a shove was seldom postponed by reason of the non-completion of a ring. After the removal of the bottom of the diaphragms, permitting the muck cars to be run into the shield and beyond, the two operations were carried on simultaneously without serious interference. The installation of the belt conveyor for handling the soft ground spoil in Tunnel A was of special benefit in this respect.