The sheer size of Bertha, the world’s largest tunnel-boring machine at 57.5 ft in diameter can prove hard to grasp. And even as the machine moves less than two blocks away from the disassembly pit near Seattle’s Space Needle, about two months away from a final stop at the end of a 1.7-mile-long bore under downtown Seattle, the owner, the Washington State Dept of Transportation, wants to give the public one more unique view inside the machine.
Using a 360-degree camera, Alaskan Way Viaduct Program Administrator Joe Hedges offers up a virtual tour and the lets the viewer steer the direction. Check out the video here. Along the way, WSDOT says they hope the video can give people a sense of the enormity of the work happening underneath Seattle and out of sight to the general public.
The new view of Bertha comes days after the TBM launched forward on the final 1,000 ft of mining on the total 9,270-ft job. In Zone 10, the final zone from Denny Way to the finish line of the disassembly pit, the cutterhead now rests less than 100 feet below the surface and the conveyor belt carrying the tunnel muck out of the machine has extended more than a mile and a half long.
With less than two blocks remaining until Bertha pokes through the final destination—and a concrete wall—near the intersection of Sixth Avenue North and Thomas Street into the north receiving pit, the machine still needed a readjustment to make it on the correct path.
Bertha was stopped on Feb. 28—the machine started again on March 6—to conduct additional survey work to verify the machine’s position based on data that indicated the machine may have slipped off path. Following the investigation, three independent surveys confirmed Bertha was roughly 6 inches off alignment, requiring contractor Seattle Tunnel Partners to adjust the course. This was the second time a course adjustment was needed for Bertha, with the first coming after the machine mined out of the access pit following repairs that lasted roughly two years.
Crews steer Bertha based on information received from its onboard guidance system, now set to the new tunnel alignment.
The most recent schedule calls for Bertha to reach the north receiving pit in May, but WSDOT cautions that date may still change based on any maintenance needs or unexpected ground conditions. Once Bertha reaches the pit, crews will spend months removing the machine in small pieces, hauling the parts by truck. At the same time, the double-deck highway will continue to take shape inside the tunnel. Currently the roadway deck sits at the southern edge of Pike Place Market, nearly 50 percent complete.
Crews also much continue to install mechanical, electrical and plumbing systems, work expected to last into 2018. It all comes with the goal of a 2019 opening of the tunnel to traffic.
Follow Tim Newcomb on Twitter at @tdnewcomb.