Update 4:15 p.m.:
Tunnel-boring machine Bertha’s cutterhead is within about three feet of drilling all the way to open air, which ought to happen this evening.
Chris Dixon, project manager of Seattle Tunnel Partners (STP), said the team is aiming to replace the damaged bearing seals and other parts, to resume excavating toward South Lake Union, by late summer.
He said the entire four-lane highway tunnel is expected to open for traffic by late 2017. That’s two years later than the original schedule.
As of 3 p.m., he said the machine is halfway through a 6-1/2 foot thrust forward, which will expose the front end to the deep repair vault and allow the next tunnel ring to be put in place. In all, Bertha has about 40 feet to go before it will halt for spring repairs, but it will move faster since there is no longer resistance (a concrete wall) in front, he said. The giant drill has spent not quite two days grinding through the 20-foot-wide south wall of the vault, so a crew can detach and hoisted the 4-million pound front end for repairs.
The state has posted time-lapse video of today’s breakthrough at this YouTube page.
Concrete dust continues to rise from the job site, but it’s tapering off. There could be occasional pauses in the next couple days to scoop rubble from the floor of the 120-foot-deep access vault, Dixon said.
Bertha hasn’t overheated this week — and in fact, it reached only 86 degrees, far below STP’s limit of 140 degrees Fahrenheit for the inner parts around the bearing, Dixon said. Grit was discovered in the seal area in December 2013 and the entire main bearing for the rotary cutting head is to be replaced.
Why did it run cool? Dixon said based on a plan by machine builder Hitachi-Zosen, the operators ran Bertha forward at only 1 foot per hour, compared to its designed pace of 6 feet per hour. That reduced the pressure and heat up front. The machine was slowed by reducing the force in the hydraulic thrusters. The cutter rotation was also slowed.
STP and the Washington State Department of Transportation declined to be too specific about restart schedules.
Update 12:17 a.m.:
WSDOT has issued another update on Bertha’s progress, confirming the cutterhead’s breakthrough into the repair pit.
The update notes that crews will continue to mine two more feet before stopping Bertha to build another tunnel ring. Afterward, the machine will continue to advance into the pit.
“The machine will continue to move forward in 6 ½ foot increments, stopping to build rings on its way into the pit,” the update states. “When the front end of the machine is fully exposed, crews will begin the disassembly process. STP has told us that taking the machine apart and lifting it to the surface will take significant time and effort.”
Update 11:59 a.m.:
WSDOT now says the top of Bertha’s cutterhead has broken through the repair pit’s wall.
The machine will dig two more feet before it stops to build a ring, WSDOT has tweeted.
Update 11:33 a.m.:
WSDOT construction cameras appear to be capturing dust clouds over Bertha’s repair vault.
But WSDOT spokeswoman Laura Newborn said that the machine has not broken through the pit’s interior wall.
Bertha is now more than halfway through its trek to a repair vault.
The damaged Highway 99 tunnel-boring machine has moved another eight feet since the six feet it had moved by Wednesday afternoon, according to a Thursday morning update from the Washington State Department of Transportation (WSDOT).
“Bertha has travelled 14 feet since mining resumed late Tuesday evening and work is proceeding as planned,” the statement issued at 10:19 a.m. said.
After being stalled for more than a year, project contractors Seattle Tunnel Partners started operating Bertha at 10:15 p.m. Tuesday as part of a rescue plan that requires the machine to mine through 20-feet of concrete on its way to a 120-foot deep access pit. Once the machine makes it to the pit, crews are expected to lift Bertha’s broken front end to the surface for repairs. (Here’s our story about Bertha’s progress as of Wednesday.)
Bertha, as the tunneling machine is nicknamed, first overheated on Dec. 6, 2013. Since then, it has mostly been stalled about 60 feet underground near Pioneer Square with damaged rubber seals and a main bearing. Because the machine is prone to overheating, its trek to the repair pit is expected to go slowly. WSDOT has said Bertha might have to take periodic breaks to guard against overheating.
“Crews from STP and manufacturer Hitachi Zosen are continuing to use caution to protect the machine from overheating or further damage as they mine through 20 feet of unreinforced concrete to reach the interior of the pit, WSDOT’s Thursday morning update said.
Laura Newborn, a WSDOT spokeswoman for the project, had not returned a telephone call seeking additional information as of 11 a.m.
“I really don’t know more at this point than what was posted and what I said in the email update,” she said in an email to The Times.
Among the questions that project officials have not answered is whether Bertha has overheated during its latest restart and what specific precautions crew members are taking on the machine while mining toward the repair pit. WSDOT also has refused to say when they expect Bertha to arrive inside the pit and how long it will take to repair the machine.
Also Thursday, state Labor & Industries spokeswoman Elaine Fischer said the agency’s investigation of last week’s accident involving four construction workers injured on the tunnel project remains ongoing. The investigation involves Central Steel, the employer of the injured workers, and STP. The investigation will likely take months to complete, Fischer said.
Seattle Times staff writer Christine Clarridge contributed to this blog post.