Blame—at least in part—an 8-in-dia steel pipe for Bertha’s nearly month-long standstill just over 1,000 ft into its 1.7-mile tunnel bore beneath downtown Seattle.
North America’s largest tunnel-boring machine—it is 57.5 ft in diameter—has been at a standstill since Dec. 6 and crews from joint-venture contractor Seattle Tunnel Partners have struggled to figure out why, all but dismissing the idea that a large boulder was in the way. The boulder idea was the leading theory early on during the investigation before crews got a look inside the chamber.
But on Thursday, Jan. 2, with the information released to the public on the afternoon of Friday, Jan. 3, Washington State Dept of Transportation and Seattle Tunnel Partners found the steel pipe “protruding through an opening in the machine’s cutterhead.” Probes, there were 17 in total, from the surface also detected metal in front of the machine.
The steel pipe is a well casing installed in 2002 following the 2001 Nisqually earthquake to help geologists better understand how groundwater moves in the area, WSDOT says in a release. The location of the pipe was included in reference materials in the contract they were quick to point out.
Ironic that the 2001 earthquake that rocked the Seattle area and showed the extreme vulnerability of the Alaskan Way Viaduct, which this new Highway 99 tunnel will replace, is coming back to haunt this project only 1/10th into the tunnel bore.
Matt Preedy, the project’s deputy administrator says finding the pipe in the top half of the cutterhead is just the first step in the process to figuring out the total obstruction. “We need to investigate further to see if there are other factors that could have contributed to the blockage,” he says.
Right now WSDOT isn’t saying if this delay, which will easily stretch past a month, will push the project well off schedule and budget, instead saying they will continue to inspect the blockage and replace damaged cutter tools earlier than planned, another possible cause of the slowdown.
The case of Bertha’s obstruction continues. WSDOT just hopes there isn’t a second chapter later on.
Tim Newcomb is Engineering News-Record’s Pacific Northwest contributor. He also writes for TIME, Popular Mechanics, Sports Illustrated and more. You can follow him on Twitter at @tdnewcomb or visit his website here.