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
by a 1-1/2-in. by 7-ft. bolt, inserted through the bolt holes nearest
the broken flange. The long bolt acted in the nature of a bow string,
and was provided at its ends with two nuts set on opposite sides of the
cross-joints to replace the standard bolts removed for its insertion.
Fig. 4, Plate LXXIII shows one of these bolts in place. In addition, all
broken plates remaining in the tunnel were reinforced with 1-in.
twisted-steel rods in the concrete lining, also shown in Fig. 4, Plate
LXXIII.

_Special Construction at River Shield Junctions._--Dismantling the
shields was started as soon as they came to rest in their final position
with the cutting edges together. The plans contemplated their entire
removal, with the exception of the cylindrical skins and cast-steel
cutting edges. Inside the former the standard tunnel lining was erected
to within 4 ft. of the heels of the cutting edges. Spanning the latter,
and forming the continuous metal tunnel lining, the special construction
shown by Fig. 2 was built. This consisted of a 1-1/4 in. rolled-steel
ring, 7 ft. long, erected inside the cutting edges, with an annular
clearance of 1 in., and two special cast-iron rings shaped to connect
the rolled-steel ring with the normal lining. One flange of the special
cast-iron rings was of the standard type, the other was returned 9 in.
in the form of a ring, the inside diameter of which was the same as the
outside diameter of the rolled-steel ring to which it was bolted.

The space between the standard