Seattle Tunnel Partners could still finish digging the Highway 99 Tunnel on schedule, a project manager said Tuesday. That’s despite the fact that Bertha, the machine boring the tunnel, has been largely idle for over two months and needs major repairs.
The immediate challenge facing the tunnel contractor is replacing a set of five damaged seals, which protect the machine’s main bearing assembly. Washington State Department of Transportation said on Monday the repair could take months to complete. Meanwhile, a disagreement is brewing between WSDOT and Seattle Tunnel Partners about whether chewing into an abandoned well pipe contributed the seal damage. For now, the contractor is not asking the state to pay for any of the repair or the stop-down costs.
Asked if Bertha could surface as scheduled, in South Lake Union around Sept. 30, Seattle Tunnel Partners project manager Chris Dixon said: “We believe it’s still possible.”
But replacing the 35-foot-diameter seals is not simple. The repair may involve digging a hole in front of the machine and detaching Bertha’s 57.5-foot-wide “cutter-head” so workers can access the bearing assembly. No easy task, given that the machine is 60 feet underground, submerged in gravelly, groundwater-sluiced soil. An alternative is to replace the seals from inside the machine, which is also complex and time consuming.
Seattle Tunnel Partners is consulting with Bertha’s manufacturer, Hitachi Zosen, to determine the best way to carry out the repair. Dixon did not offer specific estimates for when the seal replacement would begin or how long it will take.
“We’re sure that it can be fixed,” Dixon told reporters. “There’s been many, many tunnel projects where they’ve had to replace the seals, where they’ve had to replace the main bearings.”
Bertha’s mechanical woes began last December. On Dec. 3, the machine hit a 119-foot long, 8-inch diameter steel well pipe, which a WSDOT contractor left in the ground in 2002. Seattle Tunnel Partners stopped the machine a few days later and it has only moved about 4-feet since. WSDOT says the location of the pipe was included in project planning documents. Dixon has said that Seattle Tunnel Partners believed the pipe was removed when the well was decommissioned.
The investigation that followed the December stoppage revealed irregularly worn cutting teeth and soil-clogged cutter-head “spokes.”
“We believe the cutting tools were damaged by the pipe,” Dixon said. Whether the clogged spokes caused the bearing seals to fail remains unclear, but he said: “We haven’t ruled out the pipe as a contributing factor to the problem we’ve had.”
WSDOT Program Administrator Todd Trepanier said the agency “believes that the well casing has nothing to do with the seal issue.” He added that WSDOT’s teams of outside tunneling experts have said that the pipe could not have caused the patterns of wear exhibited by the cutting teeth.
“They have a right to feel that way because we haven’t presented a convincing case as of this point,” Dixon said. “At some point we’re going to reach agreement.”
Bertha’s $5.1 million main bearing assembly allows the cutter-head to rotate, typically at a speed of about one revolution per-minute. The bearing does not appear to be harmed, Dixon said. But Seattle Tunnel Partners has asked Rothe Erde, the German company that manufactured the bearing, to inspect and recertify it as a part of the repair process. The project’s contract says that Seattle Tunnel Partners needs to have a backup bearing available. While Dixon and Trepanier confirmed that the bearing exists, and is in Europe, they did not know its exact location.
Under Seattle Tunnel Partner’s supply contract with Hitachi Zosen, the machine’s manufacturer has some obligations to repair or replace parts that get broken or damaged during the tunnel drive. Determining whether a replacement part or repair is covered by Bertha’s “warranty” is determined on a case-by-case basis. Dixon said it is still unclear how much of the bearing seal replacement cost will be paid for by Hitachi Zosen.
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