Crews on the Highway 99 tunnel project spent Wednesday drilling a second vertical shaft, in hopes of breaking and removing the steel pipe that has blocked tunnel-boring machine Bertha for 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 rotary cutter, at 60 feet below street level, is farther forward than the bottom half.
Bertha is buried near the central waterfront, approaching South Main Street. Later this year it’s supposed to dive under the old Alaskan Way Viaduct, on the way to South Lake Union.
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Once a vertical 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 fragments. 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.
The well was shown in reference drawings given to contractor Seattle Tunnel Partners, according to the Department of Transportation, while STP says it expected that all steel would have been removed years ago.
Workers removed about 55 feet of the 119-footlong pipe last month, after Bertha first hit the pipe and pushed some of it to the surface Dec. 3.
State officials posted a picture of that pipe segment this week, along with a photo of steel fragments and boulders. Tunnel-boring machines can grind through rock and concrete, but steel can become wrapped around cutting blades or rotating parts.
The infamous pipe length still sits in a yard at the job site. Officials haven’t decided what to do with it. Who knows? It might show up as a kind of mobile in the state’s Milepost 31 information center a few blocks away.
Mike Lindblom: 206-515-5631 or firstname.lastname@example.org.