Excavation to Reach World's Largest Tunneling Machine Complete

Excavation crews have reached the 120-foot depth needed to repair Bertha.
Excavation to Reach World's Largest Tunneling Machine Complete
The world’s largest tunneling machine, Bertha, is lowered into a pit at the start of the tunneling project under Seattle for an underground highway. The tunneling machine broke down and needs to be repaired. Crews began excavating to its site in mid-October and finally reached the bottom of the pit on Jan. 30.

The Washington Department of Transportation announced Jan. 30 that the 120-foot-deep tunneling machine repair pit in Seattle is complete.

Approximately 20,000 cubic yards of material was removed from the ground over the course of the excavation, which began in mid-October, according to project manager Seattle Tunnel Partners.

Crews will now begin construction of a concrete cradle at the bottom of the pit that will support the machine. Crews will attempt to move the world’s largest tunneling machine into position so it can be repaired. Bertha, the tunneling machine, has not moved for more than a year since breaking down while working on the tunnel.

However, now it must dig through a 20-foot-thick concrete wall of the pit to get into position to be lifted out by a crane. The length of time it takes Bertha to reach the pit will depend on its ability to mine through and digest the concrete. If it’s unable to mine through the wall, Seattle Tunnel Partners will create an opening from within the pit to give it an unobstructed path.

Photo credit: Washington Department of Transportation


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