Related Links: Steel Pipe Found Stuck in Bertha's Cutterhead When North America's largest tunnel-boring machine pushed a 50-ft-long, 8-in.-dia steel pipe seven feet out of the ground on Dec. 3, joint-venture contractor Seattle Tunnel Partners and Washington State Dept. of Transportation officials didn't think much of it."Bertha," the 57.5-ft-dia machine, kept churning its state Route 99 tunnel path below Seattle at faster-than-predicted paces. But only for three more days.Now, that pipe—a well casing put in place in 2002 to measure groundwater movement following the 2001 Nisqually earthquake, the very same earthquake that serves as the catalyst for Bertha boring a
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.