SEATTLE -- Bertha, the world's largest tunnel boring machine, has resumed digging its way under downtown Seattle.

Transportation Department spokeswoman KaDeena Yerkan says work resumed at 4:48 a.m. Monday, after being shut down since Aug. 20 by a labor dispute. The Longshore union had put up a picket line in a dispute with another union over four jobs moving excavated dirt.

WSDOT says Bertha has bored through three feet since restarting early Monday morning. The tunnel boring machine faces 100 feet of grouted ground, which can harden inside the machine.

The drillings contractor wants to average 39 feet a day and hopes for a drilling completion date in November 2014.

The National Labor Relations Board (NLRB) decision on the tunnel labor dispute could still affect the tunnel in the future. There's no estimated time when that decision could come, but for now work has resumed on the tunnel.

The tunnel project is part of the state's overall $3.1 billion plan to replace the Alaskan Way Viaduct, the double deck highway along the downtown Seattle waterfront.

The $80 million machine began digging July 30 on a nearly 2-mile tunnel expected to take 14 months. The 58-foot diameter tunnel is scheduled to open in late 2015.

WSDOT officials say the Alaskan Way Viaduct would be shut down as a precaution for 1 to 2 weeks as Bertha passes through, but has no estimation on when that would be. They promise to give the public plenty of notice ahead of time.

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