The Washington State Dept. of Transportation has qualified four design-build teams that will vie for a $1-billion contract to construct a deep-bore tunnel replacing the seismically unsound Alaskan Way viaduct in Seattle. The winner will begin work on the four-lane, 2-mile-long double-decker tunnel on state Route 99 after the award in late 2010. + Image A new tunnel (inset) will replace waterfront viaduct. WSDOT on Dec. 18 announced the qualified joint-venture teams: Seattle Tunnel Partners, which includes Dragados USA Inc., Coral Gables, Fla., and HNTB Corp., Kansas City, Mo.; Seattle Tunneling Group, which includes S.A. Healy Co., Lombard, Ill., FCC
Arch dams, classically curved monoliths situated in narrow valleys, are not as common as other types of dams, such as embankment dams and gravity dams. ENR takes a look at some of the biggest arch dams in the world, both completed and under construction.