A week after Seattle’s Highway 99 tunnel machine overheated and came to a grinding halt for a second time, transportation officials have identified what’s causing Bertha’s fever.
The Washington State Department of Transportation and Seattle Tunnel Partners, the project's contractor, on Friday said a clogged cutter head is what’s causing the overheating. They said there’s also some damage to the main bearing seal. When that happens, they say an intrusion of mud gets into the cutter head.
WSDOT said workers spent 158 hours of hyperbaric inspections and found cutter head openings clogged with dirt and other material. Crews concluded the clogged cutter head, not a major obstruction like a pipe or a boulder, was causing Bertha's problems.
WSDOT posted multiple YouTube videos of crews inside the tunnel working to unclog the cutter head. (Story continues below).
Repair costs and timetable were unavailable, but transportation officials plan to present their plan on Monday on how to fix the problem and how long it will take to get the world's largest tunnel boring machine back online.
The viaduct tunnel project was stalled for seven weeks after Bertha hit an underground pipe in December, but both WSDOT and STP have repeatedly said there were other issues that may have caused it to heat up and grind to a halt.
WSDOT announced outside experts would be brought in to meet with state and STP project teams to "review the situation and determine the best path forward."
The machine is only one-tenth of the way toward completing a 1.7-mile tunnel. The tunnel will carry Highway 99 traffic and allow the removal of the aging Alaskan Way Viaduct along the Seattle waterfront.
The total viaduct replacement is estimated to be a $3.1 billion project.
Watch a full report by KING 5's Gary Chittim tonight on KING 5 News at 5pm.
KING 5's Gary Chittim and Liza Javier and the Associated Press contributed to this report.