lining, cast-steel bore segments were designed, and placed in the invert
at 15-ft. centers; these are of such a design as to permit the blade and
shaft of the screw-pile to be inserted without removing any portion of
the lining. Fig. 11 is a typical cross-section of the river tunnel, as
originally planned, with these pile supports.

After the shields had met and the iron lining was joined up, various
experiments and tests were made in the tunnel; screw-piles, and 16-in.
pipes, previously referred to, were inserted through the bore segments
in the bottom of the tunnel, thorough tests with these were made, levels
were observed in the tunnels during the construction and placing of the
concrete lining, an examination was conducted of the tunnels of the
Hudson and Manhattan Railroad Company under traffic, and the result of
these examinations was the decision not to install the screw-piles. The
tunnels, however, were reinforced longitudinally by twisted steel rods
in the invert and roof, and by transverse rods where there was a
superincumbent load on the tunnels; it might also be noted that on the
New York side, where the tunnels emerge from the rock and pass into the
soft material, the metal shell is of cast steel instead of cast iron.
Fig. 12 is a typical cross-section of the river tunnels as actually
constructed.

[Illustration: FIG. 11.--(Full page image)

CROSS-SECTION OF TUNNEL SHOWING TRACK SYSTEM AND SCREW-PILE.]

[Illustration: FIG. 12.--SUBAQUEOUS TUNNELS CROSS-SECTIONS]

During the investigations in the tunnels, borings were made to determine
exactly the character of the underlying material, and it was then found