Last week marked Bertha’s final push as a tunnel-boring machine. What was once the world’s largest machine of its kind churned through a final five-ft concrete wall and into the north receiving pit near the Space Needle, the end of its 1.7-mile-long underground bore under downtown Seattle. What started in 2013—and endured a two-year stoppage and repair—finally wrapped up on April 4, 2017.
But that isn’t the end of the effort to replace the aging and vulnerable Alaskan Way Viaduct. While finishing the bore 64 years to the day since the viaduct first opened to traffic, the Washington State Dept. of Transportation and contractors Seattle Tunnel Partners still have about two years of work to wrap up what Bertha accomplished in order to open the new State Route 99 route under downtown Seattle.
Sure, Bertha marked one of the most memorable and intriguing parts of the project, but plenty remains.
To start, crews needed to remove the steel support braces inside the 90-ft-deep disassembly pit. With the braces gone, Bertha could move forward into its final position in the pit, basically becoming a massive butcher’s block. Crews will saw apart Bertha’s four-million-pound cutterhead into small enough pieces to leave Seattle via truck. Along the way, some parts will get reused while others will end up in recycling. The backend of the 330-ft-long machine will hit the reverse button and get removed through the tunnel’s initial launch pit.
“We were always confident that we would successfully complete the tunnel drive,” says Chris Dixon, Seattle Tunnel Partners project manager, in a statement. “The dedication and commitment of everyone on the Seattle Tunnel Partners team has been exceptional and we wouldn’t be at this milestone without the hard work of our crews. We look forward to continuing this outstanding progress through project completion.”
During the disassembly process, which could take between four and five months, work will continue inside the tunnel to build a double-deck highway within the circular walls created by the machine. Mechanical and electrical systems, plumbing and safety features must also fall into place.
As work continues on installing systems to go around the roadway, the testing and commissioning process of the job will start too. Inspectors will individually test more than 8,500 separate components before testing each of the tunnel’s various systems as a whole.
“This truly is a remarkable feat of engineering,” says Roger Millar, WSDOT transportation secretary, in a statement. “There’s still work to be done, but the individuals working on this job should be proud of this accomplishment.”
Over the next several years, the City of Seattle’s Waterfront Seattle project will build new public space and a surface boulevard in the place of the double-deck viaduct, which will get removed in 2019 after the tunnel opens.
Follow Tim Newcomb on Twitter at @tdnewcomb.
