Bertha fix will likely require big access shaft
The plan to fix Bertha probably won’t be finalized before the end of the month, but Seattle Tunnel Partners is making arrangements to unearth the idled boring machine.
STP, the Highway 99 Tunnel Project’s lead contractor, is working closely with Bertha’s manufacturer, Hitachi Zosen Corp., to determine the fastest way to get at and replace a set of five damaged seals that protect the machine’s main bearing. The seals are located behind Bertha’s 57.5-foot-diameter “cutter-head,” which, along with the rest of the machine, sits idle some 60-feet beneath Pioneer Square, near South Main Street.
The contractor has been in touch with companies that would help with accessing and working on the machine from above ground, via a shaft. Reaching the bearing assembly from inside the machine is possible but complex, and would require removing a large number of parts. “It’s looking fairly certain that a shaft is going to be the preferred option,” Seattle Tunnel Partners project manager Chris Dixon told reporters on Friday.
While the exact shaft requirements are not definite, Dixon said the rectangular hole would likely be about 80 feet wide and extend some 20 to 30 feet in front of Bertha’s cutter-head. To reach all the way to the bottom of the roughly five-story boring rig, the shaft would need to be around 120-feet deep.
To keep the surrounding gravelly soil from collapsing, and water from Elliott Bay and groundwater from flowing into the work area, the shaft will be walled on three or four sides. If the contractor chooses the four-walled option, operators will drive the ailing machine forward slightly to break through the side closest to the cutter-head.
Dixon said that Seattle Tunnel Partners staff would meet with the firm Brierley Associates on Tuesday to discuss the shaft’s design. Brierley specializes in underground engineering. The two companies haven’t yet signed a contract for any shaft work.
Hitachi Zosen hasn’t confirmed whether fixing the bearing seals will involve removing Bertha’s 745-ton cutter-head, which weighs the same as about seven locomotives. Seattle Tunnel Partners has contacted Barnhart Crane & Rigging, the company that assembled Bertha last year. For the assembly, Barnhart used a “modular lift tower,” which relies on hydraulic jacks to pick-up and rotate objects weighing up to 1,000 tons. Dixon said it’s possible that the tower could be used for the upcoming repairs, but that a large crane might also suffice.
In Japan, where Bertha was manufactured, Hitachi Zosen has assembled a task force that is looking to remedy the machine’s problems. In recent weeks Hitachi Zosen had as many as 30 employees, including principals, here in Seattle. Three Seattle Tunnel Partners staff members are now in Japan working with the task force. One of the STP employees was in Japan while the machine was manufactured; another is a project manager who has worked on the Highway 99 Tunnel Project since 2010.
Hitachi Zosen is also coordinating with Rothe Erde, the company that manufactured Bertha's bearing, to ensure that the part was not compromised when the seals failed. The bearing allows Bertha’s cutter-head to spin. If it is damaged, there is a spare on standby in Europe. Preliminary inspections by Seattle Tunnel Partners indicate that the bearing is still in good shape.
Washington State Department of Transportation officials said that the access shaft should not weaken the nearby Alaskan Way Viaduct. David Sowers, WSDOT Engineering Manager, allowed that one of the viaduct's support columns did sink about .2 of an inch earlier in the project as water was pumped from underground. but he added that the “the viaduct is certainly stable.” The agency is monitoring the ground around the overpass.
WSDOT and Seattle Tunnel Partners continue to say that it's too early to know how long the repairs will take, or how the delay will affect the project’s overall schedule or budget. Dixon did say last Tuesday that it could still be possible to finish digging the tunnel, as scheduled, around Sept. 30. The machine is about 1,000 feet into the roughly 9,000-foot (1.7-mile) tunnel path, which will end in South Lake Union. Until Bertha makes it to 1,300 feet, Seattle Tunnel Partners do not have to pay Hitachi Zosen the last 10 percent of the machine’s nearly $90 million pricetag.