The concrete segments that will line the tunnel. Bertha will dig 6 feet at a time, lay a ring of these, and proceed—averaging 35 feet of progress a day.
A Closer Look at Bertha
Go behind the scenes of this big tunnel-boring machine
At the media preview on Saturday, July 20, Seattle magazine editor in chief Rachel Hart toured Bertha's dig site with photographer Stuart Isett. The 57.5-foot diameter cutterhead can swallow boulders 3 feet in diameter.