Bertha to re-start digging; little said about problem-causing pipe

Bertha, the drilling machine used for the viaduct replacement tunnel, is expected to start digging again this week.

Bertha stopped Dec. 8 after hitting a pipe 8 inches in diameter, which was left by the Washington State Department of Transportation in 2002. It was part of an inspection after the Nisqually earthquake to monitor the Alaskan Way Viaduct.

The pipe was included in reference materials the contractor received, but the contractor, Seattle Tunnel Partners, told KIRO 7 Eyewitness News they thought the pipe had been removed by a WSDOT contractor doing the viaduct monitoring work.

WSDOT did not go into detail about who was responsible for removing the pipe.

“While we understand the interest in knowing the reasons why mining was stopped in December, it will take time to review the results of the hyperbaric interventions and consult with tunneling experts advising WSDOT,” WSDOT staff said in a statement. “We will continue to provide the public with information as we have it and work with the contractor to ensure that the machine is ready to begin mining under downtown Seattle.”

Crews will finish inspections of the excavation chamber and cutterhead by the Tuesday morning, marking completion of the hyperbaric intervention work, according to the State Department of Transportation. Crews had performed 36 hyperbaric interventions through Sunday, totaling 134 hours in 10 days.

“The first step after the hyperbaric interventions are completed is to advance the machine by 2 feet and build the next tunnel ring, which was in progress before the machine was stopped on Dec. 6. These 2 feet of mining and the ring build will be followed by an evaluation of the machine and its operating systems,” according to a WSDOT statement. “This is necessary because the machine’s systems have been idle for 7 weeks. The results of the initial mining and the extent of any required maintenance will determine when mining resumes”

When mining resumes, the next milestone is approximately 500 feet ahead of Bertha’s current location. WSDOT plans to close SR 99 while tunneling occurs under the viaduct.

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