At least one Seattle tunnel-boring machine should churn earth this summer.
While Bertha, the continent’s largest TBM, will remain idle and await for repairs in order to tunnel again by the end of March 2015, a smaller TBM digging a Sound Transit tunnel will get dedicated today and start moving in June.
Sound Transit needs to bore twinned tunnels, 3.6 miles long, for new light rail track from Northgate to the University of Washington’s Husky Stadium as part of its Northgate Link light rail extension project. Twin tunnel-boring machines will do the job, with the first, dubbed Brenda, launching in June and the second unnamed TBM set for a fall 2014 release.
Sound Transit will dedicate Brenda April 28 before sending her underground for the job.
The $2.1 billion project to extend light rail north includes a 4.3-mile-long stretch—mostly tunnel, but with some track at surface and more track elevated—to move light rail north of Seattle for the first time.
Brenda has a 21-ft-dia cutter head, less than half the size of Bertha’s 57.5-ft-dia head, but has proven successful already, having dug Sound Transit tunnels in 2011 and 2012 as part of the University Link extension. Part of that tunneling job, performed by Jay Dee Contractors as part of the JCM joint venture, included an ENR Newsmaker-award winning dig just feet under Seattle’s Interstate 5.
Brenda will take off from Northgate and head south toward the university. Tunneling is scheduled to finish in 2016 with the new tracks in service in 2021.
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.