Seattle’s ‘Bertha’ Pauses, Then Resumes Bore on Final Segment

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.