Boring is unlikely to resume on the Highway 99 Tunnel for at least six months, the project's main contractor said on Friday.
Repairing Bertha, the machine digging the tunnel, will involve constructing an 11-story deep, concrete lined access shaft near South Main Street, west of the Alaskan Way Viaduct. The contractor, Seattle Tunnel Partners, is working closely with the machine's manufacturer, Hitachi Zosen, to choose one of three size options for the shaft, which would extend 36, 42, or 65 feet in front of the ailing rig. The shaft would be about 80-feet wide.
The six-month estimate, according to Seattle Tunnel Partners project manager, Chris Dixon, is "slightly optimistic." Still, it is in-line with a report issued yesterday by an independent expert review panel assembled to keep the governor and Legislature updated on the project. That report projected that Bertha would be mining again in late summer or early fall. Building the shaft, Dixon said, would probably take about two months.
"We would be obviously pleased to start tunneling earlier than that," he said. "but this isn't the time to try to accelerate things or take shortcuts, we need to go step-by-step."
The repair operation will involve removing the machine's 57.5-foot diameter, 745-ton "cutter-head," which cuts through rock and soil in front of the machine. That will allow crews to access and replace a set of damaged seals that protect Bertha's main bearing assembly. Depending on the final repair plan, the machine's "cutter drive" unit, which turns the cutter-head might also be removed.
The 35-foot diameter main bearing allows the cutter-head to spin. Dixon said that it's still unclear whether or not the bearing was damaged when the seals failed, but a spare is standing by at a Hitachi Zosen facility in Osaka, Japan.
A final decision about the shaft configuration will probably be made in the next 10 to 14 days, Dixon said. If the contractor and manufacturer decide to go with the smallest shaft size, then they'll take the parts out of the pit and place them on the ground for repairs. The medium-sized version would allow for workers to fix the parts while they are standing upright in the shaft. The largest configuration would allow parts to be layed down horizontally on the shaft's floor.
Seattle Tunnel Partners is waiting for Hitachi Zosen to confirm that each of the shaft sizes will provide enough space for workers to replace the machine's main bearing in the event that further inspection reveals that the $5 million part is in fact damaged. "We know they're all viable for the seal repair," Dixon said. "I feel comfortable with the options."
Nothing to see here. The site where Seattle Tunnel Partners will dig an access shaft to repair Bertha. Photo: Bill Lucia
The Washington State Department of Transportation said Friday that portions of the Alaskan Way Viaduct will be closed this weekend in both directions for regularly scheduled inspections. The tunnel will eventually replace the aging concrete overpass. When the project began it was scheduled to open in December 2015. The expert panel report issued yesterday predicts that the opening date will be pushed back to summer or fall of 2016.
The machine is currently about 1,000 feet along the 9,300-foot tunnel path, which runs from Sodo to South Lake Union. Since early December Bertha has moved about 4-feet. Under the terms of a contract between Seattle Tunnel Partners and Hitachi Zosen, until Bertha reaches 1,300 feet the contractor will not pay the manufacturer the final 10 percent of the cost for the nearly $90 million machine.
There was no new information on Friday about the root cause of the bearing seal failure. And Dixon said Seattle Tunnel Partners and Hitachi Zosen were still discussing how they would divide repair costs. State officials have said repeatedly that they've yet to see any evidence that indicates taxpayers will be on the hook for any cost overruns associated with the delay or the repairs.
Like what you just read? Support high quality local journalism. Become a member of Crosscut today!