SEATTLE -- The State Route 99 deep-tunnel boring machine has been stalled since Dec. 6. State transportation officials said Friday that clogged cutterhead openings and high
temperatures within the machine are causing the problem, and that one of Bertha's seals has been found to be contaminated by sand, dirt and water.
The machine has been plagued by problems since it began tunneling in 2013. Bertha is already behind schedule in the digging of the SR 99 tunnel.
Officials do not yet know when work is expected to resume.
Tunnel workers performed 158 hours of hyperbaric inspections on the machine between Jan. 17 and Jan. 28. They found that many of the cutterhead openings were clogged with dirt and other material. A clogged cutterhead can affect the tunneling machine’s performance in the same way that a major obstruction would affect its performance, officials said.
Once the hyperbaric work was completed, it was determined that a major obstruction was not the cause of the mining difficulty. The more likely cause was the clogged cutterhead.
After the cutterhead was unclogged, the contractor moved the machine forward an additional 2 feet and installed one of the concrete rings that line the tunnel. On Jan. 28 and 29, higher-than-normal heat sensor readings appeared like they did on Dec. 6, 2013. In the course of investigating the temperature readings, STP discovered damage to the seal system that protects the tunneling machine’s main bearing.
STP is working with experts to determine the best fix for the issue, officials said.