Tags: home

Lots to see inside the tunnel launch pit

You can’t see much from the surface, but there’s a lot of work happening in the launch pit where tunneling started last summer. Last week, Seattle Tunnel Partners removed the giant steel frame that Bertha, the SR 99 tunneling machine, pushed against to start her drive into the tunnel. The frame is now on its way to be recycled.

Work is also well underway to dismantle the temporary concrete tunnel rings Bertha installed to give her additional leverage at the start of her journey. Each ring consists of 10 segments of reinforced concrete that together weigh 360,000 pounds! One by one, the rings have been pulled to the ground and then hoisted out of the launch pit for recycling. Here’s some video of the process, and here’s a photo that shows the launch pit before and after the temporary ring removal. The last temporary ring should be out of the pit by St. Patrick’s Day.

The launch pit serves many purposes. It’s where Bertha was assembled, but it also provides critical access into the tunnel for materials and supplies. That’s why removal of these temporary structures is necessary – crews need to make room to build a double-deck highway inside the tunnel. You can see a preview of what that highway will look like from the work that’s occurring just south of the launch pit, where the southern portion of the upper and lower decks of the new SR 99 are being built.

Removal of temporary structures in the launch pit was originally scheduled to take place during a pre-planned maintenance stop for the tunneling machine before it tunnels under the viaduct and the city. Doing the work now, while Bertha awaits repairs, is a way to save time later on.