Seattle's massive tunneling machine on move again

SEATTLE — Bertha has reached her goal.

The cutterhead on Seattle's troubled tunnel boring machine broke through the 20-foot-thick wall of a rescue pit around 11:15 a.m. Pacific Thursday. Video from a television helicopter showed a big plume of dust coming from inside the pit as the machine emerges.

After beginning its drive under the city in mid-2013, the machine was forced to stop after creating 1,000 feet of tunnel. It's believed that seals designed to keep grit and water from reaching the bearings failed.

Last week, four workers were injured at another part of the project when a elevator shaft collapsed. One of the four is still in the hospital.

Seattle Tunnel Partners, the contractor building the new Highway 99 tunnel under downtown Seattle, is trying to repair Bertha — the world's largest tunneling machine — so it can finish mining its way forward.

In preparation for the short dig, the Seattle Tunnel chipped a circle into the pit's wall. That work was completed Tuesday.

State transportation officials say Bertha moved forward about 6 feet by Wednesday night; it stopped so crews could build two concrete tunnel rings before resuming Thursday morning.

Chris Dixon with the Seattle Tunnel Partners said Bertha has another 40 feet to go where it needs to be inside the rescue pit. Once there, crews plan to remove the front of the machine and pull it out of the pit with cranes so crews can replace its bearings and seals.

"These subsequent shifts will go much quicker because we're not excavating, we're just pushing the machine forward," said Dixon.

The tunnel, which will run about 2 miles under the city, is designed to replace the Alaskan Way viaduct, damaged in a 2001 earthquake. The project is two years behind schedule, and transportation officials did not have a clear date for when Bertha will resume SR 99 tunneling.