Segmental Tunnel Lining Meets `Buy American'by Mohammad Irshad, (M.ASCE), Chief Structural Engineer; DeLeuw, Cather Company, 600 5th St. N.W., Washington, DC 20001,
Serial Information: Civil Engineering—ASCE, 1989, Vol. 59, Issue 10, Pg. 59-61
Document Type: Feature article
Segmental concrete tunnel lining is the other innovation proven during construction of the Washington Metropolitan Area Transit Authority (`wmata'). Although `wmata's' use of the New Austrian Tunneling Method has drawn most of the attention, some 4 miles of single-pass, bolted and gasketed segmented concrete lining mark a new state of the art in U.S. tunneling technology. Between 1983 and 1988 the option to use the 10 in. thick, 4 ft wide segments attracted a succession of low bids on five separate contracts representing a total construction cost of $120 million. The only stipulation was to honor `wmata's' general Buy American clause, so the segments were produced in the U.S.A. rather than being imported. The segmental lining system provides circular tunnels 16 ft 8 in. i.d. and 18 ft 4 in. o.d. Seven segments, including a key, combine to form one 4 ft wide coffered tunnel lining ring. Construction is advanced ring by ring behind a tunnel boring machine. Among the system's advantages: The single pass installation eliminates the need for temporary tunnel support; one 4 ft wide ring can be erected in less than an hour; and the immediate ground support minimizes surface settlement and assures optimum interaction between lining and ground.
Subject Headings: Tunnels | Linings | Concrete | Tunneling | Construction equipment | Soil settlement | Concrete construction | Innovation | Washington | North America | United States
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