Six Months, Under "Optimistic" Scenario, Before Tunnel Machine Gets Rolling
Tunnel contractor says it will be six months, optimistically, before the tunnel boring machine might start moving again.
Standing in front of the Alaskan Way Viaduct at downtown's Pier 48 this afternoon, viaduct replacement project manager Chris Dixon, with Seattle Tunnel Partners, told reporters that it could be six months or more before the tunnel-boring machine, "Bertha," is up and running again.
Dixon named a "slightly optimistic" date of September 1, 2014, when repairs to the TBM's damaged seals might be completed, allowing the machine to continue its path northward along the downtown waterfront. "I think it would be difficult to do a lot better than that," he said.
The machine has been idled since early December of last year because of damage to the seals around the bearing in its cutterhead, the 57-foot-wide part of the machine that does the digging.
Dixon said all seven of the seals that protect the machine's bearing will need to be replaced—"we're not going to go in and do a patch job here"—and that there could be damage to the bearing itself. "When they start taking things apart, the condition of the seals and bearing will be known," Dixon said. Hitachi-Zosen, which built the tunnel machine, has a replacement bearing in Osaka, Japan.
Repairs will require workers to build a 120-foot-deep reinforced shaft in front of the machine; the shaft, Dixon said, will be 11, 13, or 20 feet in diameter, depending on which option Hitachi-Zosen decides is best for getting down to the cutterhead and either replacing the bearings in place or removing the cutterhead and bringing it above ground, in pieces, for repairs.
Only the 20-foot pit would allow the contractor to bring the cutterhead out and lay it on the ground horizontally, a scenario that would make repair work easier but would also cost more and take longer than a smaller shaft. "Obviously the smaller shaft [allows] quicker design, quicker construction, less space is taken up—that would be preferred," Dixon said.
Hitachi-Zosen has told STP it will choose a repair strategy within 10 to 14 days, Dixon said, although he added that STP has asked them to try to come back with a proposal by next Friday.
Dixon said the contractor was fortunate the machine broke down where it did, near Pioneer Square—where workers can access the machine from the surface—instead of further north in the heart of downtown, where the machine wouldn't be accessible and "we'd have to report for work inside the tunnel."
Asked whether he was concerned that once the machine is fixed, it might just break again, Dixon said, "it performed well for 1000 feet and we really don’t have any concern that once we get it up and running that it [won't] peform well for the rest of the" length of the tunnel.
WSDOT is closing the viaduct for its quarterly inspection this weekend. WSDOT deputy tunnel project manager Matt Preedy said the state team will check on the size of the "hundreds and hundreds" of tiny cracks in the structure, and take measurements to see if the viaduct has settled further into the ground. A section near Yesler Way has sunk around 4/10 of an inch.