Several days at the dentist: new teeth will give Bertha more bite

Posted on Nov 7 2013 11:08 AM

It’s been a little over a week since Bertha, the SR 99 tunneling machine, stopped near South King Street for scheduled maintenance. Crews have been thoroughly testing Bertha’s various systems and examining things like hoses and belts to see how well they weathered the first 430 feet of tunneling. The consensus so far is that Bertha is turning out to be the efficient workhorse we’d all hoped for.

Still, as you might imagine, chewing through concrete, rebar, soil and timber hasn’t exactly made Bertha the model dental patient. Crews are swapping out 24 of Bertha’s giant teeth so that she’ll have a stronger bite when she resumes digging next week. Our contractor, Seattle Tunnel Partners, had initially planned to resume tunneling this week, but decided to change out more teeth now rather than waiting until Bertha’s next scheduled maintenance stop just south of Yesler Way.      

Bertha’s dental visit is about more than just dealing with wear and tear. Her new rectangular teeth are better suited for the glacial soils she’ll soon encounter than the round teeth she’s been using to tunnel through the much harder grout-injected soils along the early part of the tunnel route.

Overall progress through Nov. 7:

  • Feet traveled since tunneling started: 430
  • Rings built since tunneling started: 58