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SEATTLE -- The Transportation Department says crews are drilling de-watering wells Thursday to relieve pressure on a machine that has become stuck while boring a highway tunnel under downtown Seattle.

Spokeswoman KaDeena Yerkan says the wells should make it easier to identify what's blocking the machine known as Bertha. Then contractors will determine how to proceed.

What's blocking 'Bertha' still a mystery

The machine was halted Friday by the mysterious obstruction. It may be a huge boulder, but so far WSDOT said it's all speculation until they are able to get eyes on the obstruction.

WSDOT wants to send men into the tunnel to see Bertha, but the area is not pressurized. So they have to set up hyperbaric chambers using specials divers. They then will drill down to it from above to help stabilize the soil so workers can get right next to Bertha.

The boring machine is 60 feet under the streets and about one-tenth of the way into the planned 1.7-mile tunnel that will carry Highway 99 traffic and replace the Alaskan Way Viaduct.

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