It took 80-ft-deep, dense soil for “Bertha,” the world’s largest-diameter tunnel-boring machine, to finally hit her stride. After three-plus years of delays, at least $220 million in cost overruns, and concerns about machine durability and ground movement, the past seven months have proven to be clear dirt-churning as the Washington State Dept. of Transportation attempts to replace the Alaskan Way Viaduct in downtown Seattle with a 1.7-mile-long bored tunnel.
Now halfway through the 9,270-ft-long journey to the north portal near the Space Needle and moving at a rate of about 15 millimeters per minute, Bertha’s path under First Avenue puts tunneling on track to finish in 2017, enabling the entire project to open to traffic in early 2019.