Experts say a steel pipe is at least partly to blame for halting a massive tunnel-boring machine beneath downtown Seattle.
The state Department of Transportation said Friday the 8-inch-diameter pipe was discovered protruding through an opening in the machine's cutter-head. Officials say the pipe is a well casing installed by the department in 2002 to monitor groundwater.
The tunneling machine, known as "Bertha," is digging a new path for State Route 99, one of the region's primary north-south arterials. It's been halted since encountering a mysterious obstruction Dec. 6.
The DOT says it's still not sure whether the pipe is the only thing blocking Bertha. There could be other obstructions that aren't yet visible, and changing soil conditions might have caused excessive wear of cutting tools.
Officials say the location of the pipe was included in materials provided to the contractor.