Bertha is now tunneling under buildings in downtown Seattle
As Bertha continues to dig a tunnel underneath Seattle it is moving into a whole new region far different than what it has passed under before. Now the machine enters a region of the city populated with more structures on the surface than it has crossed under in the past.
Bertha — once the world’s largest tunneling machine constructing a tunnel to replace the Alaskan Way Viaduct — has moved 2,255 feet out of its 9,270-foot journey as of May 26. The machine is now in Zone 3. There are 10 zones.
Bertha recently tunneled under the Columbia Street on-ramp to the viaduct and is currently under Western Avenue, nearly to Marion Street.
Before the on-ramp, Bertha tunneled under two concrete buildings constructed in 1910. After crossing under the on-ramp, Bertha tunneled under a parking lot and a building constructed in 1906. Bertha will soon cross under the edge of an apartment building erected in 2013. After Marion Street, Bertha will move under an office building built in 1932.
Bertha was about 50 feet below the Columbia Street on-ramp. As it moves forward under buildings in downtown Seattle, Bertha is about 100 feet below the surface, according to the Washington State Department of Transportation.
The material that the machine is digging through is also much different than before, according to WSDOT. Bertha is primarily digging through clay at this point. Unlike the other soils in its wake, which were more loose, the clay is is dense and more uniform.