Front-End Of Tunnel-Boring Machine Freed From Seattle Pit

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Engineers have removed the cutter head from the enormous tunneling machine nicknamed Bertha. The malfunctioning part had been stuck for more than a year in a highway project under the city's downtown.

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Transcript

STEVE INSKEEP, HOST:

The saying holds that if you want to get out of a hole, stop digging. This, however, is not an option for the world's largest tunneling machine. The machine dug its way under Seattle and then got stuck more than a year ago. There's no way out except for the machine to keep tunneling. And last night, engineers in Seattle completed a major step in the effort to salvage it. NPR's Martin Kaste reports.

MARTIN KASTE, BYLINE: Seattle's waterfront has become the site of the world's biggest engine overhaul. The tunneling machine's mechanical problems are deep inside the cutter head. That's the front end of the tunneling machine which does the actual digging. It seems its seals failed, letting grit into the mechanism and making it overheat. To get at the problem, workers had to dig down 11 stories, then detach the cutter head, which has now been lifted out to be rebuilt - lifted out very slowly, says Matt Preedy. He's with the state's Department of Transportation.

MATT PREEDY: So there's a basic law of physics - things at rest tend to stay at rest. And things in motion tend to stay in motion. When you're moving 2000 tons, you want to go slow because if it starts moving the wrong way, you've got to be able to control that load at all times.

KASTE: Two-thousand tons - to give you some idea, that's the weight of five 747s. As the cutter head emerged, rush-hour drivers gawked from the nearby elevated highway. That's the highway this tunnel project is supposed to replace. And it is a strange sight - a tunneling machine coming out into the light part way into its job. And it really can't happen again either because after it's fixed here, the machine will make its way under the buildings of downtown. And they can't dig another rescue pit there. Preedy says that shouldn't be a worry though because the machine's seals will be rebuilt better than they were.

PREEDY: If something were to happen to the seals again, which is highly unlikely - but if they were, the seal array is being constructed so that it can be replaced or repaired much more easily.

KASTE: The more complicated matter may be figuring out who pays for this massive repair job. The contractor, the state and the Japanese company that built the tunneling machine are nowhere close to settling that. Martin Kaste, NPR News, Seattle. Transcript provided by NPR, Copyright NPR.