'Bertha' Does The Heavy Lifting In Seattle Tunnel Project

The world's largest tunnel boring machine in a few months will begin digging a new double-decker highway tunnel under downtown Seattle. If all goes according to plan, Bertha will start digging this summer. It'll emerge again late next year on the other side of downtown, not far from the Space Needle.

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DAVID GREENE, HOST:

And let's turn from walking the earth to tunneling under it. The world's largest tunnel-boring machine is being assembled in the city of Seattle, and in a few months it will begin digging a new double-decker highway tunnel under the city's downtown. NPR's Martin Kaste got a look with one of the men running the project.

MARTIN KASTE, BYLINE: This being radio, it's going to be really frustrating trying to convey the sheer bigness of this thing. But let's start with the launch pit. That's where they're getting ready to assemble the machine on the south side of downtown Seattle. The pit is 80 feet wide and 80 feet deep. Matt Preedy peers down at the ant-sized guys working at the bottom.

MATT PREEDY: You have to assemble a 6,800-ton boring machine in that hole.

KASTE: Preedy is with the Washington State Department of Transportation, which named the machine Bertha. It's in honor of a former mayor, but everyone here is thinking Big Bertha. Preedy points to the tunneling machine's business end - the cutting head, lying on its side near the pit.

PREEDY: If you look at this from the air from a downtown Seattle high-rise, it would almost look like a very large green flying saucer that's parked itself in the middle of the work zone here. It weighs in at about 670 tons.

KASTE: It actually looks more like a circular cheese grater - a six-story-tall cheese grater. And as to that green paint job? It's doomed.

PREEDY: Probably within the first few hours of the tunnel-boring machine drive, all that nice bright shiny green paint will be gone. In fact, by the time we complete the 1.7-mile tunnel bore and it comes out the north end, we will have lost about nine ton's worth of steel just from abrasion of the ground.

(SOUNDBITE OF MACHINERY)

KASTE: As Bertha worms its way under downtown Seattle, it'll be towing a tunnel-building factory, including rolling buildings with restrooms and a kitchen for the crew. And if Bertha breaks down, no matter how catastrophically and no matter how deep it is, it'll have to be fixed where it sits.

PREEDY: There's only one direction on these things, and that's forwards. Because behind the machine, the machine is also constructing a two-foot-thick concrete liner. And the machine is pushing off that ring. You can't back up.

KASTE: So, enormousness plus claustrophobia - it's not a job for the faint-hearted. If all goes according to plan, Bertha will start digging this summer and it'll emerge again late next year on the other side of downtown not far from the Space Needle. Martin Kaste, NPR News, Seattle.

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