VAN BUREN STREET TUNNEL, CHICAGO.
The Van Buren Street tunnel, built to carry a double-track street railway under the Chicago River, was completed in 1894 by the cofferdam method. The special features of the tunnel[14] are: (1) the unusually large dimensions of the cross-section of 30 ft. × 15 ft. 9 ins.; (2) its construction inside of cofferdams of great length and width; (3) the construction under some very high buildings calling for great care and very strong temporary and permanent supports.
[14] “Eng. News,” April 12, 1892.
The special feature of the work for our present purpose was the construction of the tunnel across the river. To accomplish this a cofferdam was built out from the west shore of the river to its middle, and the tunnel constructed within it like the building of any other structure within a cofferdam. Transverse and longitudinal sections of this cofferdam are shown by [Fig. 141]. As will be seen, it was a simple double-wall cofferdam, with a clear width between the walls of 58 ft., and braced transversely as shown. Inside of this a single-wall cofferdam of piles was constructed, with a clear width just sufficient to allow the construction of the masonry within it. When the tunnel end reached the channel end of the cofferdam, a crib-wall was built over the end of the completed tunnel, as shown by the drawings. This crib-wall was intended to form the end wall of another cofferdam, which was built out from the east shore, and within which the remaining half of the tunnel was built as the first half had been. The drawings show the character of the tunnel masonry and of the centering upon which it was built.
TRANSVERSE SECTION OF COFFERDAM AND TUNNEL
SECTION SHOWING METHOD OF CONSTRUCTING CRIB DAM.
Fig. 141.—Sections of Cofferdam, Van Buren St. Tunnel, Chicago.
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The Van Buren Street tunnel was the last of the three tunnels under the Chicago River, constructed according to the cofferdam method. At the time the tunnels were constructed the bed of the river was 17 ft. deep. In connection with the harbor and river improvements, the Federal Government ordered the Chicago River to be lowered so as to give a depth of 26 ft. of water. This necessitated the lowering of the tunnel roof and the excavation for a deeper floor which was a very difficult operation. This work was described in “Eng. News,” Sept., 1906.