The Seattle Times reported a delay on fiberglass strands that became stuck near the cutting face of the drill and a now a labor dispute has disrupted the excavation along Seattle's waterfront.
Officials say the pace is about two weeks behind what the team expected.
Before drilling began, state officials estimated it would progress at 6 feet per day to start, and eventually accelerate to 35 feet per day in good soil under downtown.
The 1.7-mile dig is supposed to be finished by fall 2014, and the new Highway 99 tunnel to open at the end of 2015.
Officials say they aren't worried, at this early stage, about missing the schedule.
The project's 250 workers, at the launch pit in Sodo, are still performing tasks such as putting the arc-shaped tunnel segments into position, and adjusting the drill.
"We're not laying off, we've shortened some shifts and are canceling some others," said Chris Dixon, project director for the Seattle Tunnel Partners team.
After the July 30 start, bunches of fiberglass strands, 2 feet long and as much as an inch thick, began to clump at the bottom of the machine, just behind the cutting face, Dixon said.
That spot is where the dirt is scooped up by a red screw conveyor that spins within a big tube, nudging the soil toward the rear of the machine -- where it's dropped onto a conveyor belt headed to Terminal 46.
Fiberglass jammed the screw.
Contractors anticipated some difficulty, but the fiberglass caused more trouble than expected. Bertha has bigger openings in the cutter head than most drills, so it didn't chew the fiberglass into manageable pieces, Dixon said.
Seattle transportation officials expect a slow start, said spokesman Rick Sheridan. The $2 billion tunnel is the most difficult segment of the state's $3.1 billion replacement for the 1950s Alaskan Way Viaduct, which is at risk of failure in a severe earthquake.
Information from: The Seattle Times, http://www.seattletimes.com
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