What stopped earth’s biggest-diameter tunnel boring drill?

Transportation West
The south end of the tunnel. (WSDOT; Flickr.)

The south end of the tunnel. (WSDOT; Flickr.)

It was early December in Seattle when the world’s biggest-diameter tunnel boring machine, called Bertha, came to a stop underneath Seattle. It was plowing through the city’s underground as part of the two-mile project to bring SR 99 underground and replace the Alaskan Way Viaduct. Overnight, it seemed as if the whole of Seattle and beyond was curious: was it buried treasure from the gold rush days? Or bootlegger artifacts?

Last week officials determined the frustrating cause of the blockage: an 8-inch wide, 119-foot long steel pipe originally placed by a state groundwater research team back in 2002. The Washington State Department of Transportation is currently drilling shafts to grind and remove the pipe.

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