This fall’s hoist of the damaged, 2,000-ton front end of the tunnel boring machine Bertha will happen a bit later than planned, because workers are having difficulty digging a 120-foot deep retrieval shaft just ahead of the big drill.
The state Transportation Department hasn’t released details of the problem, but is expected to do so within the next few days, and pass along an updated schedule from contractors.
Installation of a concrete ring that is part of the retrieval shaft was going along briskly in late June, but work then began to slow down. A similar but smaller pit in Sarnia, Ontario in 1994 wound up taking two months longer to dig and reinforce than engineers had expected.
Once the retrieval shaft is completed, the contractor, Seattle Tunnel Partners, will bring in a massive crane to hoist the entire front end of the tunnel machine to street level, then lay the components on the surface. Workers will replace the main bearing and its leaky seals, add steel plates to reinforce Bertha’s interior and carve out larger gaps in the disc-shaped cutterhead for dirt to pass through.
Despite any delay, the state says Seattle Tunnel Partners is still capable of restarting the Highway 99 tunnel excavation by March as has been announced, because STP built extra days into the overall repair schedule.
Matt Preedy, deputy Highway 99 director for the WSDOT, mentioned the slow down at a City Council waterfront committee meeting last week. Preedy said the March restart is still likely, unless some kind of unexpected damage is found when Bertha’s drive parts are disassembled.
When Councilman Mike O’Brien asked whether the front end of the tunnel drill will be brought up sometime in September or October, Preedy replied: “The contractor is currently updating their schedule at this time. It’s probably going to be a little later in the year than that.”
STP director Chris Dixon recently said he hoped Bertha could drill again as soon as December, but that no longer appears possible.