In its day, tunnel-boring machine Excalibore was the pride of Canada, 3 stories high and churning merrily westward through the port city of Sarnia, Ontario.
Just before it was to reach the St. Clair River, with Michigan on the horizon, inspectors in late 1993 found tiny particles of clay in the grease that lubricated the bearing seals. Rather than risk a breakdown under the river, the team building the Canadian National Railway tunnel stopped for repairs a mere 820 feet from the starting line.
Subcontractors dug a deep vault in front of the machine, lifted the cutterhead away, and fixed the damaged seal parts a few feet inside.
After seven months, Excalibore resumed digging, and the one-mile tunnel got done before the end of 1994.
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Seattle will probably learn a lot this year from the chronicles of Sarnia.
Contractors here will need months to fix Highway 99 tunnel-boring machine Bertha, after seal damage allowed sand into the bearing assembly that steadies and spins the cutterhead.
Seattle Tunnel Partners will soon announce whether the difficult task of reaching and replacing the damaged seals will be accomplished by entering through the front of the stalled machine — the most likely option, and the one used in Canada — or from the rear.
Last week, the state Department of Transportation (DOT) and STP disclosed the $80 million machine is damaged, after weeks of concealing news that sand in the grease was noted in a DOT quality-control report Dec. 7.
Bertha’s manufacturer, Hitachi-Zosen, and the bearing and seal makers, are helping STP investigate what caused the damage and how to fix it.
There have been many examples of bearing failures and ruptured seals, said Shani Wallis, editor of Tunneltalk.com, and the key is to get the job done and worry about liability later.
The DOT understood that bearings can fail and required STP to have a spare.
A front-end attack in Seattle probably entails inserting concrete pilings several feet ahead of Bertha, then scooping out dirt to form a vault that’s roomy enough to remove the cutterhead and accommodate large parts and equipment.
If STP lifts the cutterhead all the way to the surface, as in Sarnia, the world-record 57.3-foot disc would offer a circular tourist attraction to rival the Great Wheel several blocks away.
Matt Preedy, DOT’s deputy tunnel administrator, insists a vault can be built in Seattle’s watery fill soil. He noted that STP already built a bigger pit in bad fill soil, where the machine was launched July 30 in Sodo.
“It’s basically a vertical square shaft that’s supported on all sides,” he said, perhaps 75 feet wide, 120 feet deep and surrounding Bertha’s bow for about 30 feet.
A few feet inland, STP built a buried concrete wall to protect the Alaskan Way Viaduct from vibrations, so maybe that can perform double duty, Preedy said.
Holding back groundwater will be tough, as was learned this winter when water flooded the machine’s cutting chamber. Workers installed 10 pumping wells, to allow a cutter inspection.
In Sarnia, squishy clay made it difficult to set new concrete pilings for the Excalibore’s vault. Another time, drillers were vexed by “saturated, collapsing ground,” said a retrospective written by the engineers.
Another problem with the tunnel-boring machine spooked the team:
“The TBM in its parked position was settling.”
Eventually, engineers decided to add more pilings to make the vault more stout when the machine arrived. They wound up making a doughnut-shaped cluster, rather than a thin ring.
The original design called for 120 pilings. By the end there were 227.
Excalibore burrowed forward through one wall, into its protective vault — some 10 inches lower than it should have been. Operators steered the machine upward, and a steel sheet was spread beneath to support it.
“Due to the adverse conditions encountered, the sinking of the shaft proved considerably more difficult than anticipated,” said the retrospective, by vault engineer Brian Isherwood of Ontario, who did not respond to interview requests this week.
Though Bertha has moved only 4 feet since Dec. 7, it could chew through a concrete wall to reach the safe repair vault, as in Sarnia, insists Preedy.
“The machine is capable of mining forward. Clearly they wouldn’t want to do it for very far, because the seal system is compromised,” he said. “You don’t want to be creating further issues for the machine.”
To be more blunt, the state worries about damage that might cause a stall later this year, below the old Alaskan Way Viaduct.
Bertha has traveled 1,025 of the 9,270 feet from Sodo to South Lake Union. The warranty for Hitachi-Zosen runs through 1,300 feet — which was supposed to be reached Jan. 16, the original schedule says.
The $36 million bill
What if a bearing assembly fails later in the project, say, beneath Pike Place Market?
The contract requires that a bearing can be delivered through the back, said Todd Trepanier, DOT tunnel administrator. Rear entry would avoid having to dig a pit 20 stories deep.
But it’s not easy.
To bring a 35-foot-diameter bearing forward, STP would need to disassemble trailing gear, the metal arms that lift the concrete segments forming the tunnel, or the conveyor tube that pushes muck from front to back.
Also, if a rear attack were attempted now, with the machine alongside Pioneer Square, that might slow workers building the nearby highway entrance in Sodo.
Preedy emphasized the role of the “design-build” contracting system. The DOT lacks tunneling expertise, so it provided the contract requirements and soil research, leaving bidders to choose tools and methods.
The state won’t tell its contractors what to do, Preedy said, because interfering could bring greater financial responsibility to taxpayers. But the DOT has consulted with Rick Lovat of Ontario, whose company manufactured Excalibore.
Arguments over costs in Sarnia dragged on until 2008, when the Supreme Court of Canada decided who must pay $36 million for repairs and delays — the CN Railway’s insurers.
By then, double-stacked trains had been using the tunnel between Canada and the U.S. nearly 14 years, and the seven-month delay was long forgotten.
Mike Lindblom: 206-515-5631 or firstname.lastname@example.org. On Twitter @mikelindblom