Seattle Tunnel Partners completes digging of Bertha repair pit

The contractor building the new Seattle tunnel has finished digging the 120-foot pit it will use to access and repair Bertha, the SR 99 tunneling machine, the Washington Department of Transportation announced Friday.

Crews have removed nearly 20,000 cubic yards of material during the excavation since digging began in October.

Plans call for STP to launch Bertha and tunnel through the 20-foot-thick southern wall, exposing its damaged cutter head.

WSDOT says in a statement the amount of time that will take depends largely on her ability to “mine through and digest the concrete.”

If the world’s largest tunnel machine is unable to break through the wall, STP will create an opening from within the pit to create a clear path forward, WSDOT says.

STP will now begin construction of a concrete cradle at the bottom of the pit alongside the Alaskan Way Viaduct that will be used to support Bertha after it reaches the pit.

Once Bertha is inside the pit, crews will use a massive crane to lift the front of the machine to the surface for repairs and improvements.

Pumping of nearby groundwater believed to have caused some settling in the surrounding area will continue as STP proceeds with its repair plan, but settlement levels near the pit remain stable, WSDOT reports.

Crews building the highway inside the tunnel are gearing up for another project milestone: the first pouring of concrete on what will become the southbound lanes of the tunnel.

WSDOT released a time-lapse video of the entire excavation: