Bertha to Resume Excavating

July 21, 2015



The tunnel-boring machine (TBM) dubbed “Bertha” could resume excavation beneath downtown Seattle in late November 2015, following repairs to its latest mechanical hitch, reports ENR.

According to ENR, crews discovered damage to the seal system and the main bearing of the machine earlier this year. The cause of that damage is unconfirmed. To access Bertha for repairs, project contractor Seattle Tunnel Partners (STP) dug an access shaft in front of the machine and lifted the TBM's front end from the 120-ft-deep pit in March.

In addition to the main bearing, STP crews installed portions of a new seal system, which includes the addition of reinforced steel, a new monitoring system and, to help prevent clogging, upgrades to the soil-conditioning system.

Inside the machine, bigger openings in the cutterhead, longer mixing arms to stir dirt, a heavier bearing, and steel rods and plates to reinforce the front end will give Bertha a new robustness.

STP released a completion date of Spring 2018, nearly three years after its original completion date. STP predicts that once Bertha is up and running again it will take approximately one year to dig the remaining 8,000 ft to the projects north end point, reports ENR.

However, the Washington Department of Transportation said they can not verify STP's project schedule.