Tunnel machine Bertha is showing damage to seals around its main bearing, an important piece that houses the axle that turns the world-record 57-foot, 670-ton cutterhead, the state Department of Transportation (DOT) said today.
DOT didn’t speculate on how long the machine will be shut down, but said it will take perhaps two weeks for contractors to finish diagnosing the problems and issue a repair plan.
Sand mixed with grease was found within the seals, and could damage moving parts if Seattle Tunnel Partners (STP) were to drill without fixing the seals first, said Matt Preedy, deputy Highway 99 administrator for DOT. He said STP is doing the right thing by taking time to carefully investigate.
Bertha has already been stalled two months, except for advancing 4 feet during test runs last week.
Preedy also said the stoppage in early December was caused by soil that clogged the cutterhead at the same time temperatures spiked in the bearing.
The main bearing is a $5 million part that houses a ring-shaped axle that turns the cutter. The bearing took 10 months for drill-maker Hitachi-Zosen to design and build, according to contractor documents. It would be difficult to replace, if that’s necessary, near the front of the 330-foot-long machine. Preedy said it’s unlikely the whole bearing must be replaced, and STP hasn’t reported any bearing damage. Replacing the rubberized seals would take less time, Preedy said.
Meanwhile, public records show that sand got into the bearing grease on the afternoon of Dec. 7. The high temperature caused the machine to shut down several times that day, according to a routine DOT quality-control report.
Bertha had moved forward only 4.4 feet on Dec. 6. Then on Dec. 7, operators spent the afternoon “trying to move forward with little success,” as executives from contractor Dragados USA were in the control room, said that day’s report, released under public-records requests to KIRO-TV and The Seattle Times.
The morning of Dec. 7, workers were starting to drill shafts down into the soil from the surface to look for obstructions, but stopped “because the underground crew was going to try to advance the machine, regardless of what was happening on the surface,”‘ the report says.
Among other issues, workers apparently were using extra grease to try to flush out the main bearing, because sand was found mixed with grease, the report says. Project managers at DOT previously said temperatures reached 140 degrees in early December, then again in restart tests last week.
Project engineers have said for weeks that the $80 million machine didn’t show major damage and is capable of finishing the long bore from Sodo to South Lake Union. Bertha is now 60 feet below street level, next to Pioneer Square.