The state Department of Transportation (WSDOT) announced today that after nearly six weeks with the tunnel-boring machine, "Bertha,"* out of commission, it plans to send crews down into the machine's excavation chamber—a process that will require workers to go into a special pressurization chamber to adjust to the increased air pressure underground, where the machine is stuck. (The air pressure is higher down there because the soil is full of groundwater, making the atmosphere similar to what you'd find at an equivalent depth of water).
The announcement means another delay for the boring machine, which has been stuck underground for nearly six weeks. Initially, WSDOT thought an eight-inch-diameter steel pipe, left over by a contractor 11 years ago and discovered in early January, was causing the problem; now they say they don't fully know what's causing the stoppage.
WSDOT has not said how much the extra delay will cost, who they expect will pay for cost overruns (a week ago, Republican state Sen. Mark Schoesler, R-9, proposed putting Seattle on the hook if costs increase beyond the $2 billion the state has pledged to pay, and the state has just $40 million in reserve), or whether they have more specific guesses about what they expect workers to find.
Before the workers go down into the machine, they'll fill up the foot-wide space between the earth in front of the machine and the machine's cutter head with the soil conditioner bentonite to create a barrier between the machine and the ground, and fill the chamber with compressed air, creating an air bubble in the chamber to allow workers to take a look around. Once they're there, they'll try to figure out what's keeping the machine from running.
Back in December, tunnel project manager Chris Dixon with Seattle Tunnel Partners said building the "protective membrane" of bentonite could take weeks.
Each crew will stay in the excavation chamber for about three hours, then come back into the pressure chamber for about an hour—a process similar to what scuba divers go through when they're ascending from deep water.
"We recognize that this process isn't moving as quickly as some would like," WSDOT said in a statement. "The reason for this is that, like going hyperbaric, none of this is easy. On the contrary, tunneling is incredibly complicated, Bertha is incredibly complicated, the ground conditions where she's located are incredibly complicated – you get the idea. This is challenging work. The safety of our workers and the success of our work are paramount. A thoughtful approach is just what the doctor ordered."
A theory: Bad news about "Bertha" is inversely proportional to the cutesiness of WSDOT's proclamations about it—I mean, "her."