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Photo via WSDOT.

Bertha, the world’s biggest tunnel-boring machine currently underneath Seattle, has been stuck for nearly one month. Now, crews are close to figuring out what exactly is stopping her.

A steel pipe with an eight-inch diameter appears to be causing at least some of the stoppage. The Department of Transportation said it already knew of this pipe, as it was used for a 2002 groundwater study after an earthquake occurred one year earlier.

Now, it is protruding through one of Bertha’s openings:

Photo via WSDOT.

The Seattle Tunnel Partners, a contractor group, won’t say for sure whether the pipe is causing Bertha to be stuck. Other factors include changing soil conditions and objects in front of the cutterhead or excavation chamber that crews can’t quite see yet.

For now, there are no set plans for scheduling repairs or cost estimates. Construction on both the north and south ends of the tunnel are ongoing in the meantime.

At 57.5 feet in diameter and more than 300 feet long, Bertha is named after former Seattle Mayor Bertha Knight Landes, the first female mayor of a major U.S. city. The $80 million machine began digging from Sodo in July and will eventually make its way to South Lake Union. A four-lane underground tunnel is scheduled to open by 2016, when the current above-ground Alaskan Way Viaduct will be demolished.

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