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Bertha, tunnel, SR99
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Bertha reaches one-mile mark

Bertha has now bored more than a mile of tunnel under Seattle. (WSDOT)

Bertha, the SR 99 tunneling machine, has now bored more than one mile of the tunnel under Seattle that will replace the Alaskan Way Viaduct.

Crews with Seattle Tunnel Partners passed the 5,290-foot mark on Thursday morning, according to the Washington State Department of Transportation.

There is now less than 4,000 feet of soil between Bertha and the final receiving pit near the Space Needle. The machine is located 200 feet below First Avenue, north of Stewart Street.

Below: Operators show how crews precisely steer Bertha.

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