[Illustration: FIG. 6.--15' 4" Span Twin Tunnels. Rock Roof.] [Illustration: FIG. 7.--19' 6" Span Twin Tunnels.] [Illustration: FIG. 8.--21' 6" Span Twin Tunnels] [Illustration: FIG. 9.--PROPOSED SHIELD FOR SUBAQUEOUS TUNNELING GENERAL ELEVATION] [Illustration: FIG. 10.--RESTORATION OF PIER 72 (OLD 62) NORTH RIVER TRANSVERSE SECTION AT CENTER OF PIER] In order to permit the screw-piles to be put in place through the 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]