Seattle's Tunnel Machine Chokes On Dirt

State officials said Friday afternoon that the tunneling machine known as Bertha had to stop, not because it hit foreign objects, but because it clogged with dirt.

Bertha is digging an underground highway to replace Seattle's Alaskan Way Viaduct. Officials could not say why the $80 million tunnel boring machine would choke on dirt.

Bertha has been largely stuck since early December, when it was stopped after running into a steel pipe.

Washington State Department of Transportation officials said on Friday it was not the pipe — or a boulder or any other large objects that underground inspections have discovered — that forced Bertha to halt.

Todd Trepanier with WSDOT said Bertha also suffered damage to the seal around its main bearing.

Bertha's five-story-tall cutter head revolves around that bearing.

"The bearing is a key part of the machine," said Trepanier. "Just because the seals have been compromised, it does not imply that the bearing has been compromised."

WSDOT officials said they don't know whether the main bearing itself is damaged.

Tunnel machine operators restarted Bertha and dug two feet forward in late January. During that brief experiment, they found that the machine overheated again, as it had in early December. Workers discovered damaged areas in the bearing seal afterward.

Trepanier provided little detail to reporters in a conference call Friday afternoon. He said investigations were ongoing.

Trepanier said it's up to the contractor, Seattle Tunnel Partners, to decide how to fix the damaged seal, either by digging up the machine or by sending workers inside it to make repairs.

Seattle Tunnel Partners project director Chris Dixon could not be reached for comment Friday afternoon.

Trepanier declined to say how much the two-month delay has cost, or when North America's largest tunnel machine might get back to work.

WSDOT video of worker removing dirt from Bertha’s cutter head:

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