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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 S. H. Woodard;Francis Mason;James H. Brace
page 76 of 93 (81%)
0.42% of the total number erected. Of these, 52 were found and removed,
either before or immediately after a shove, by far the greater number
being broken in handling before or during erection. The remaining 267
are considered below.

_Repair of Broken Plates._--On the completion of a shove, the tail of
the shield lacked about 5 in. of covering the full width of the last
ring, and the removal of a plate broken during the shove, therefore,
would have exposed the ground at the tail of the shield. With a firm
material in the bottom, this introduced no particular difficulties, and,
under such conditions, a broken plate was usually removed at once. In
the sand, however, and especially on the Manhattan side where it was
quick and flowing, the removal of a plate was attended with some danger,
and such plates were usually left to be removed on the completion of the
tunnel. Many of these had been reinforced by the use of _XX_, _YY_, and
steel segments placed adjacent to the break in the following rings.

After the meeting of the shields, the postponed replacement of the
broken segments was taken up. The pressure was raised sufficiently to
dry thoroughly the sand outside the segments, which were drilled and
broken out usually in quarters as shown on Fig. 1, Plate LXXIII. A steel
segment was then inserted in the ring and drawn into place by
turnbuckles. The application of the draw-jack, with a pull of about 30
tons to each end successively, brought the plate to a firm bearing on
the radial joints at the ends.

Where the broken plate was isolated and was reinforced by steel or extra
heavy segments in the adjacent ring, the crack, if slight, was simply
caulked to insure water-tightness. If, however, the crack was opened or
extended to the web of the plate, the cross-flanges were tied together
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