It isn’t so much the time we’ve all been waiting for, but it is a milestone over a year in coming: Bertha’s front end is on a repair platform.
Sure, there are plenty of other milestones those in favor of seeing the 1.7-mile-long bored tunnel beneath downtown Seattle would rather see than the 57.5-ft-dia front of Bertha, the tunnel-boring machine doing the digging, sitting unattached on the top of Seattle’s surface, but nonetheless, there Bertha now sits. In parts.
On Tuesday, March 31, a Mammoet crawler crane—At 116 ft wide, 90 ft long and 105 ft tall, the distance between the towers is 75 ft as it straddles the access pit and the crane legs sit on 48 hydraulic cylinders instead of directly on the track rails—finished placement of the 2,000-ton front end of Bertha on a repair platform just south of the access pit.
The set-down marked the end of a lift that started early Monday, March 30.
By noon on Monday, Seattle Tunnel Partners had started lifting the five-story-tall cutterhead to the surface. The day started with tests and a few hours after noon the piece was visible at the surface. Crews rotated the section into a horizontal position as they hoisted it from the pit. When the rotation was complete, the crane rolled southward on its rails toward the platform. The piece sat suspended above the repair platform overnight as Seattle Tunnel Partners decided to wait for a fresh crew on Tuesday to finish the setting of the Bertha piece.
This was the fourth and final—and easily the largest—of the four Bertha lifts as part of this repair sequence.
As with the majority of this project, especially since the machine stopped tunneling in December 2013, the unknowns will rise again as crews start the repair work.
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.