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 and special construction was of varying
width at the various shields, and was filled with a closure ring cast to
the lengths determined in the field. Fig. 2 shows the completed
construction.

Hook-bolts, screwed through threaded holes and buried in 1 to 1 Portland