'Bertha' stopped after reaching obstruction


by KING 5 News


Posted on December 9, 2013 at 8:57 PM

Washington state's biggest construction project, the Highway 99 tunnel, has hit a bump. "Bertha," the giant tunnel boring machine under downtown Seattle has stopped in its tracks because of some kind of obstruction.

Bertha hit the the obstruction on Friday and has been stopped in her tracks 60 feet underground between South Jackson and South Main streets for three days.

"We don't know what the obstruction is. Our contractor, Seattle Tunnel Partners, is working on that now," said KaDeena Yerkan with the Washington State Department of Transportation.

Project officials are trying to determine how to proceed, but it’s not clear yet how long Bertha will be stopped.

"The tunnel boring machine was experiencing resistance and eventually came to a stop," said Yerkan. "We're being really cautious to make sure we don't damage this 80 million dollar machine."

Efforts to diagnose the problem are being hampered by loose silt and soil above the obstruction. The tunnel route was tested before boring began, but test shafts didn't strike an object.

The obstruction could be a big piece of timber or wood debris from a century ago, but that's just speculation. WSDOT is talking to outside experts, possible to extract whatever it is.

Work continues on the site as engineers try to figure out how to move forward.

WSDOT, which maintains Bertha's official Twitter page, tweeted Monday:

Bertha began tunneling at the end of July, but was stopped for several days due to a labor dispute.

The machine is scheduled to finish digging by the end of the next year.