Bertha making progress, Highway 99 tunnel taking shape under Seattle

SEATTLE -- The tunnel-boring machine Bertha is chugging along and is now 70 percent complete on her way from Sodo to Denny Way, according to the Washington State Department of Transportation.

Ever since crews repaired Bertha’s cutter-head in July, the machine has dug out more than a mile of new tunnel.

WSDOT and the contractor, Seattle Tunnel Partners (STP), said Bertha has made big progress after a costly and lengthy delay last summer. In addition, crews so far haven't found new sinkholes.

“There’s virtually no movement of the ground around the TBM as we’re tunneling northward and there’s negligible settlement at the surface,” said Chris Dixon with STP.

Engineers feared the ground in front of Bertha’s massive cutter-head would face large boulders but instead she’s been hitting a mixture of clay, silt and sand.

“The machine is capable of handling all the ground conditions we’ve encountered so far,” said Dixon.

Bertha has so far tunneled more than 6,500 feet but she still has more than 2,700 to go before surfacing near Denny Way. The tunnel-boring machine is currently under Belltown near 3rd and Blanchard.

The shape of the new double-decker highway is also beginning to taking shape. The upper decking will be for southbound traffic while northbound traffic will drive underneath.

Corridors for utilities and exits are also being built alongside the roadways.

Workers put up Christmas lights at the tail end of the TBM as they get ready to take a break for the holidays. Project managers said crews will get back to tunneling in the new year.