, and a viaduct was erected to carry Ninth Avenue. The
length of this viaduct is about 375 ft., and the steelwork and its
erection was done apart from the North River Division work, but all
excavation and underpinning was included in this division. The contract
for this work on the Terminal Station-West was let to the New York
Contracting Company-Pennsylvania Terminal, on April 28th, 1906, and
included about 517,000 cu. yd. of excavation, about 87% being rock, the
construction of about 2,000 lin. ft. of retaining and face walls
containing about 18,500 cu. yd. of concrete, and a large quantity of
structural steel (1,475,000 lb.) for temporary use in underpinning Ninth
Avenue.

Fig. 4 shows cross-sections of the Terminal Station-West yard, and Fig.
5 shows the general method of underpinning the Ninth Avenue structures.

[Illustration: FIG. 4.--TERMINAL STATION WEST

TYPICAL SECTIONS]

_River Tunnels._--In the original plan a four-track tunnel was
contemplated from the east side of Tenth Avenue to the east side of
Eleventh Avenue, but, owing to the extension of the Terminal Yard,
previously noted, this plan was changed, and a two-track structure was
built having a central wall between the tracks. This was constructed in
tunnel, with the exception of 172 ft. about midway between Tenth and
Eleventh Avenues, where the rock dipped below the roof of the tunnel,
and there the construction was made in open cut. These tunnels were
lined with concrete with brick arches, Figs. 6, 7, and 8 being typical
cross-sections. This work was executed by the O'Rourke Engineering
Construction Company, under a contract dated November 1st, 1904.

It was possible to excavate in full rock cover about 250 ft. of the
tunnels eastward from the Weehawken Shaft and 225 ft. westward from the
Manhattan Shaft. At these points the rock cover was very thin, and there
shield chambers were made for the erection of two sets of shields, about
6,100 ft. apart. A typical cross-section of the Weehawken Land Tunnel is
shown on Plate VIII.

[Illustration: Plate VIII.--Typical Sections Between Manholes, Bergen
Hill Tunnels]

The Board of Engineers decided, and it was so stated in the contract and
specifications, that the river tunnels should be constructed by means of
hydraulic shields, but bidders were permitted to present to the Board
any scheme on which they might desire to bid, but, of course, the
decision as to the practicability of such plans rested with