SR 99 Tunnel Making Machine Bertha Blocked by Pipe

Jan 3, 2014

Big Bertha is halted by a metal pipe.
Credit WADOT

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 today (Friday) that an 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. Chris Dixon is the Seattle Tunnel Partners Project Manager.  “A cutter head won't line through and cut up steels.  Very good with clay and sands and boulders and gravels but …not good with metal.” He said.

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 December 6th. The DOT says it's still not sure whether the pipe is the only thing blocking Bertha. There could be other obstructions, 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.