After a final, Feb. 28-March 6 maintenance stop, the world’s largest-diameter tunnel-boring machine has moved less than two blocks away from the disassembly pit in Seattle. TBM “Bertha,” churning a 1.7- mile-long tunnel for a state Route 99 replacement of the Alaskan Way Viaduct, required a stop less than 1,000 ft from the pit to confirm that the 57.5-ft-dia machine was 6 in. off course alignment.
To get just over a quarter of a mile from the finish of the 1.7-mile-long bored tunnel under downtown Seattle, Bertha had to dig under another State Route 99 tunnel.
The holiday season provided some rest for Bertha, the tunnel-boring machine roughly three-quarters of the way through its route to bore a new State Route 99 tunnel under downtown Seattle, but that doesn’t mean crews have had it so easy.
The vast majority of 2016 Bertha news has fallen into the positive category, a welcome respite for the $3.1 billion project to replace Seattle’s aging Alaskan Way Viaduct with a 1.7-mile-long bored tunnel.
After years of struggles with Bertha, the world’s largest diameter tunnel boring machine, resulting in a roughly three year delay and $220 million cost overrun on a plan to replace Seattle’s aging Alaskan Way Viaduct with a bored downtown tunnel, the project has hit the halfway point of the dig.
