Seattle tunnel machine back to work after maintenance

SEATTLE – Bertha the tunnel machine is rolling again.

The massive machine boring a tunnel to replace the State Route 99 Alaskan Way Viaduct stopped drilling on June 23 to undergo scheduled maintenance. Seattle Tunnel Partners said Bertha resumed mining Monday.

During the maintenance period, which included more than 40 shifts of work under hyperbaric conditions, workers changed the cutting tools and performed other maintenance behind the cutterhead.

Laura Newborn, spokeswoman for the Washington state Department of Transportation, said Bertha is one-third of the way through the project. Bertha is about 120 feet below Spring Street tunneling toward First Avenue. At its deepest point near Virginia Street, Bertha will be more than 200 feet deep.

The machine is on a 9,270-foot trek from the stadium area to South Lake Union. Officials hope Bertha finishes by December.