Crews on the Highway 99 tunnel project were drilling a second vertical shaft Wednesday, in hopes of breaking and removing the steel pipe that has blocked tunnel-boring machine Bertha for more than a month.
The first 5-foot-diameter shaft was finished Tuesday, without hitting steel, said Laura Newborn, spokeswoman for the state Department of Transportation (DOT). Because the machine is descending, any objects near the bottom of the 57-foot-diameter cutting face will be difficult to reach through straight vertical drilling, she pointed out. The top of the machine, at 60 feet below street level, is farther forward than is the bottom half of the rotary cutting face. Bertha is buried near the central waterfront, near South Main Street.
After a shaft strikes some steel, workers might try to extract pieces by lowering a clamshell-shaped picker into the shaft. Or, an auger might be inserted to grind or break the buried pipe. The team will not send a worker down one of the dark tubes, Newborn said.
DOT revealed Friday that Bertha has been obstructed since early December by an 8-inch-diameter well casing, left behind by one of the Highway 99 project’s own research crews in 2002. DOT says the well was shown in reference drawings given to contractor Seattle Tunnel Partners, while STP says it expected that all steel would have been removed years ago.
Workers removed about 55 feet of the 119-foot-long pipe last month, after Bertha first hit the steel and pushed some of it to the surface.
State officials posted pictures of that pipe segment this week, along with fragments of pipe and boulders. Tunnel-boring machines can grind through rock and concrete, but steel will become wrapped around cutting blades or rotating parts.
The infamous pipe length still sits in a yard at the job site, as shown in the DOT photo to the left. Officials haven’t decided what to do with it. The state’s Milepost 31 interpretive center is a few blocks away, with just enough ceiling space to maybe anchor a mobile.
“We haven’t had that discussion yet,” Newborn said.