Seattle tunnel machine Bertha under tight schedule during viaduct closure

Apr 29, 2016, 8:47 AM | Updated: 12:22 pm

WSDOT, Bertha, Seattle, Tunnel, Viaduct...

Bertha has moved 385 feet and cleared the Alaskan Way Viaduct in Seattle. It is not stopped as planned, however. (WSDOT)


Update: Bertha has already begun boring forward toward the Alaskan Way Viaduct. Crews fired up the boring machine at 9 a.m. Friday morning. Read more.


Despite the rough start to the Seattle tunnel project, Deputy Project Administrator David Sowers expects better things for the next phase of work.

Sowers says the soil conditions Bertha the boring machine has been in since reaching King Street is, at least in some ways, “ideal.” The soil Bertha is in now isn’t as loose as when she first began tunneling.

Related: Commuters forced off viaduct and onto Seattle streets

“It’s not real loose and soft,” Sowers told KIRO Radio’s Jillian Raftery.

That’s good, because Bertha needs to dig about 27.5 feet per day in order to make it under the Alaskan Way Viaduct in the two-week time frame. The viaduct is closed to traffic during that time, forcing drivers to find alternate routes.

Digging at that rate is possible for Bertha. When she first began in January 2013, she was projected to dig up to 35 feet per day. However, soft soil prevented that from happening. Bertha is now in harder soil and that “makes conditions much easier to manage.”

Related: WSDOT monitoring ground around viaduct and downtown Seattle

In order to avoid a similar mishap to what occurred years ago when Bertha hit unexpected metal pipes, which was at least partially to blame for her shut down for two years, the state and contractor have double-checked that nothing is blocking the path. Sowers says “an exhaustive search” has been done.

The new tunnel, which will replace the viaduct, was supposed to open in 2015. That new schedule pushes the open date to 2018.

Bertha is expected to begin moving again sometime on Friday.

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Seattle tunnel machine Bertha under tight schedule during viaduct closure