Workers might have to dig a hole up to 115 feet deep to reach and repair the damaged drive system of tunnel-boring machine Bertha, contractors now say.
Once the pit was dug, the 630-ton cutter head would be detached and lifted using a crane, supported by wide footings as if on duck feet so it wouldn’t sink into the soft waterfront soils.
Chris Dixon, director for Seattle Tunnel Partners (STP), said Monday his team is weighing “four or five options” for a front-end mission, and coordinating the use of waterfront surface space with the city’s nearby Elliott Bay Seawall project.
He said a decision isn’t made yet, and STP might be able to deliver parts from the rear, depending on what inspections this week show.
In a news release Monday evening, the Washington State Department of Transportation said either way, the repairs will take months. The tunnel project is already four months behind.
It appears the tunnel and seawall projects won’t conflict, even though they are only a few feet apart, Dixon said.
For now, the tunnel team needs a few weeks to spend on engineering design, giving the seawall crews time to set their own concrete seawall components, rock riprap and grout, before salmon migrations begin, Dixon said.
Then STP would take over and establish its pit and crane by April.
Add several weeks or more to actually fix the broken bearing seals, rev up the motors and run tests, and it could be summer before Bertha starts moving again.
In its news release Monday, WSDOT said STP “have not shown any evidence that suggests the state or taxpayers will be responsible for cost overruns associated with these repairs.”
Lee Newgent, executive secretary of the Seattle Building & Construction Trades Council, said Monday workers have been told to expect a long operation.
“What we’re talking about is, they’re going to excavate the shaft, drive 60 or 70 piles, then lift up the cutterhead,” Newgent said.
“They’re looking at least six to seven months.”
Depending on the strategy, some kind of deep piles or walls must be inserted to keep soil and groundwater from sliding into the workers and Bertha’s open front end.
Dixon said there’s been no such official notice given to workers.
“We’ve got a few hundred people on site, so it’s difficult to know who said what to whom,” he said.
Newgent said there are about 200 workers on the tunnel project and they expect to continue on the job, building the Sodo and South Lake Union entrances.
The $80 million tunnel machine has damage to the seals that lubricate and protect the $5 million main bearing. This bearing enables the ring-shaped drive shaft to turn the cutter, at about one rotation per minute.
Sand was found in the seal grease, and high temperatures have occurred in the main bearing, according to WSDOT interviews and quality-inspection records.
Bertha has traveled 1,025 feet since drilling began July 30. After a shutdown Dec. 7, the machine advanced 4 feet during experimental restart efforts Jan. 28-29.
An investigation into what caused the seal damage, and possible fixes, is still under way, STP’s Dixon said.
Dixon said it’s not known whether the entire $5 million bearing must be replaced. “As far as we can determine now, the bearing is OK.”
That question will get a closer look when senior managers from Hitachi Zosen, the tunnel-machine manufacturer, meet with STP on Wednesday, Dixon said.
“Hitachi Zosen needs to tell us. That’s going to dictate the size and location of that surface access.”
The seal and bearing have about a 25-foot diameter, impossible to deliver through the rear unless either the parts or the tunnel machine are disassembled.
Matt Preedy, the state’s deputy Highway 99 administrator, said Friday that Hitachi Zosen has a bearing on standby in Europe.
A similar incident happened in the early ’90s at the Sarnia rail tunnel, between St. Clair, Ontario, and Port Huron, Mich., where bearing-seal troubles required crews to remove a cutterhead from a machine, made by Lovat of Canada. Insurers wound up paying $29.5 million, reported Tunneltalk.com, an industry website. Despite months of delay, the seals were fixed and the tunnel opened in April 1995.
Reporter Andrew Garber contributed to this article.
Mike Lindblom: 206-515-5631 or firstname.lastname@example.org