ROAD CONSTRUCTION: Bertha to restart tunneling this week

Seattle Tunnel Partners is expecting to restart operations of the S.R. 99 tunneling machine this week, the Washington State Department of Transportation announced yesterday.

Crews were expected to finish inspections of the excavation chamber and cutter head by this morning. This will mark the completion of the hyperbaric intervention work at this time. As of Sunday evening, Jan. 26, crews had performed 36 hyperbaric interventions, totaling 134 hours over 10 days.

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

Once mining resumes, the next critical milestone will be arriving at the third and final safe haven. This safe haven is approximately 500 ft ahead of the machine’s current location and was proposed by the contractor as a controlled environment for maintenance prior to mining under the Alaskan Way Viaduct and downtown Seattle. WSDOT plans to close S.R. 99 while tunneling occurs under the viaduct.

“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,” the agency said. “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.”