Crews have filled in about 80% of nine voids leftover from a 2-mile tunneling job through Seattle’s Beacon Hill. Japan’s Obayashi Corp. did not discover the voids while boring the parallel, 1-mile tunnels as part of its $280-million contract, which has since increased to $312 million. Owner Sound Transit contends the contractor is at fault. Photo: Sound Transit Crews pump low-density concrete into tunnel voids found by drilling. The new, $2.6-billion, 16-mile Link Light Rail from downtown Seattle south to Seattle-Tacoma International Airport required tunnels and a station 180 ft deep beneath Beacon Hill. Obayashi in 2004 won the contract
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.