If it weren’t for the traffic mess created by closing the Alaskan Way Viaduct many in Seattle would be ecstatic about the closure of the elevated and aging roadway for about two weeks. The closure of the viaduct means Bertha, the world’s largest tunnel-boring machine, is working in ground below the roadway.
As part of the effort to bore a 1.7-mile-long tunnel under downtown Seattle to eventually replace the Alaskan Way Viaduct, Bertha—still in early stages due to the roughly two-year shutdown and repair—must tunnel beneath the road that carries 90,000 vehicles each day.
The viaduct shutdown started on Friday, which was followed by Bertha digging out of its planned maintenance stop, essentially a block of concrete buried in the ground near Yesler Way. The machine had to dig through approximately 10 ft of concrete to exit the maintenance stop and enter the soil near the intersection of Yesler and Alaskan Way. Trucks carried away the excavated material as crews monitored the machine’s performance and the surrounding ground as Bertha moved forward.
The transition from concrete to soil was deemed “important,” forcing the slow and deliberate movements. By Friday evening, Bertha had moved just over six ft of the 385 ft needed before crews could reopen the Alaskan Way Viaduct. By Sunday at 2 p.m., Bertha had mined 39 ft and just over 24 hours later Bertha was up to 91 ft and 14 tunnel rings. Crews expected Bertha to continue to pick up the pace this week.
Getting Bertha back online was a monumental undertaking and one that came with years of delays and millions of dollars of mistakes. Even the restart earlier this year was fraught with problems, such as a suspended barge operation after excavated soil caused the barge to tilt and the state’s governor stepping in to suspend all operations after a sinkhole formed behind Bertha’s path.
The barging operation has since been revamped, allowing that to continue after two months of suspension and Seattle Tunnel Partners created a new soil monitoring plan to help alleviate some concerns about the sinkhole.
Up until now, though, mistakes have cost the project only time and money. Now that Bertha is moving under the viaduct and soon under the heart of downtown Seattle—and not just port property near the launch pit—mistakes will have much more dire consequences.
Follow Tim Newcomb on Twitter at @tdnewcomb.