Tunnel Update: Tentative Repair Plans and an Archaeological Scavenger Hunt
State officials announce tentative plans for accessing—and hopefully fixing—the stalled tunnel-boring machine.
After announcing late last month that repairs to the stalled deep-bore tunnel will take six months, under the most "optimistic" scenario, to complete, the Washington State Department of Transportation said today that Hitachi-Zosen, the Japan-based subcontractor that built the tunnel-boring machine, has arrived at a tentative plan to dig a shaft in front of the machine and repair whatever is ailing it.
The machine, known as "Bertha," would tunnel a few feet forward and break through the concrete-piling wall of the shaft with its digging cutterhead, allowing workers to access it from above.
What remains to be seen is whether that repair is as simple as replacing the seals that protect the massive bearing that helps turn the machine's cutterhead, or whether it will require workers to pull the cutterhead itself out to the surface from its curent location, 120 feet below ground.
Hitachi had initially considered three different sizes of shafts—approximately 10, 13, and 20 feet in diameter—but ultimately has narrowed in on what WSDOT deputy tunnel project manager Matt Preedy called "closer to the smaller size," which will be faster and less expensive to build than the largest shaft. The shaft Hitachi is proposing would also be circular, instead of the square shaft originally proposed.
While Hitachi comes up with a final plan for building a shaft to access the machine (Preedy said the tunnel team expects to announce a proposal next week), WSDOT's archaelogical division will be digging 60 four-inch-wide holes borings into the ground around where the shaft will be located, which is closer to the surface than the tunnel dig, where the ground predates human settlement. As a result, it's possible that WSDOT will find historical artifacts.
The digging process, according to WSDOT cultural resources manager for megaprojects Steve Archer, will take about a week and shouldn't slow down the project, even if WSDOT finds artifacts. "There is nothing in the law that says if you find something historical the project stops," he said.