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