Bertha Cutter Head Going Back Underground for Seattle Tunnel Digging

Digging scheduled to resume on Seattle's new state Route 99 tunnel on November 23

August 26, 2015

Seattle PI

Crews worked Monday, Aug. 24, 2015 to begin one of four crane operations to lower Bertha's cutter head and drive unit back into the ground. Once the giant tunnel boring machine is back together and tested, it will start tunneling again Nov. 23, nearly two years after it stopped 1,000 feet into the nearly two-mile tunnel project. This wide shot shows the giant "super crane" used to first pull the 4-million-pound cutter head out of the ground and now to lower it back in.

A crane is lowering the approximately 4-million-pound cutter head and drive unit for the boring machine — known as Bertha — that has been digging the new state Route 99 tunnel beneath Seattle's waterfront. Bertha broke down in 2013 and repairs on the cutter head began this year once it was freed from the tunnel. Digging is now scheduled to resume on November 23.

Bertha has been outfitted with a new seal system and main bearing, steel reinforcements on the cutter drive unit and new shields, more than 100 extra cutter teeth, modification and additions to the soil processing ports and upgrades to the monitoring system.

The current crane lift is just one of four that will be required to get the cutter head back into place before crews can reattach its parts and test it over the coming months.

(more on reattaching Bertha's cutter head for the tunnel construction...)