The Bertha saga took a step—or dig—in the proper direction. Downward.

Seattle Tunnel Partners started digging the circular repair pit this week, the same pit that crews will use to access the front of North America’s largest tunnel-boring machine in order to make needed repairs to get the State Route 99 tunnel under Seattle moving again.

Bertha hasn’t tunneled since December 2013 after Bertha started overheating. To fix the machine, complete with a new $5 million main bearing, they’ll enter Bertha from the front. A 120-ft-deep, 80-ft-wide pile-supported pit will allow Seattle Tunnel Partners to get in front of Bertha, remove the cutterhead and make the necessary fixes.

In order to clear the waterfront area of groundwater, crews have installed wells, which will help when they excavate approximately 20,000 cu yards of soil. Because a variety of construction activities are competing for space near Pier 48 in downtown Seattle, excavation won’t occur nonstop. During the process, truck or barge will haul all contaminated soil to a disposal facility and any non-contaminated soil will get stored and reused to fill the pit once Bertha is ready to dig again.

On Oct. 23, archeologists monitoring the dig discovered “shell material” that could signify cultural materials. Further evaluation will determine the next course of action.

Also ongoing is the construction of a 2,000-ton modular lift tower crane needed to lift pieces of Bertha from the pit. Two cranes are needed to assemble the tower crane. Many of the repair pieces will arrive from a manufacturing facility in Japan, getting stored in a Seattle warehouse until needed.

With no ongoing tunneling work, crews went ahead and started building the structures that will support the roadway inside the tunnel. Bertha has moved about 1,000 ft since it started tunneling, so crews expect to build approximately 450 ft of structure before tunneling resumes, likely in March 2015. 

Tim Newcomb is Engineering News-Record’s Pacific Northwest contributor. He also writes for Popular Mechanics, Sports Illustrated and more. You can follow him on Twitter at @tdnewcomb or visit his website here.