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  • Greg Stump

This week, a huge portion of the paper is given over to detailed examination of the politics and technology surrounding the construction of a tunnel through downtown to replace the state highway along the water. You have probably read a lot about this already, but you probably haven't read anything this thorough. It's called What Could Possibly Go Wrong, and it's required reading. Here are a few paragraphs:

A massive cylinder with a rotating face covered in blades that gnash away rock and soil, a tunnel-boring machine churns everything in its path to paste, which cargo cars then haul to the surface. Each machine is custom-made just for the width of the tunnel it needs to dig. Our tunnel-boring machine (TBM) will cost around $80 million to build, and, at 56 feet in diameter, it will be the widest TBM ever constructed.

"I've been talking about a 56-foot-wide machine for a long time," says Council Member Mike O'Brien. "Then I looked at a building about five stories tall and thought, 'Holy shit, that is 56 feet. That is one big-ass fucking machine.'"

Our TBM will confront a mixture of sedimentary elements in soft soil, which are the most difficult conditions to penetrate because the loose material tends to cave in behind the machine. So as the machine grinds forward, it must simultaneously create a concrete tunnel lining behind it to hold up the earth. Those cement slabs narrow the diameter of the hole, preventing the TBM from backing up. Tunneling machines can't travel in reverse. And if the TBM's blades break, the machine can't move forward. It's stuck.

This is not only the most expensive thing that could go wrong, it's also a fairly common thing that goes wrong.

Two TBMs recently got stuck underground in King County. One was 320 feet below an elementary school in Bothell and another is still stuck at the same depth under Lake Forest Park... One was immobilized for nine months, and the other hasn't budged in over a year.

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The soil conditions that the Brightwater TBMs encountered—the soil conditions that disabled two of the TBMs—appear to be the same soil conditions underneath downtown Seattle.

Plus: where the money is coming from, the big question-mark about the port's contribution, the bigger question about Seattle having to pay cost overruns on a state highway, the city council's response to the risks (silence), the mayor's response to the risks (certainly hasn't been silent), how to deal with tunnel-boring machines when they do get stuck (it isn't pretty), what happens if the ground caves in under the Federal Building, and much more. You just gotta read it.