The subterranean odyssey continues for Big Bertha. The tunnel boring machine opened up a 7-foot-deep sinkhole in the ground Thursday.
The 15-by-20-foot hole opened up between the Alaskan Way Viaduct and the Seattle waterfront, near South King Street.
The hole was quickly filled with no damage.
The Seattle Times reports rotten timbers dumped a century ago may have left the soil in the area unstable.
Bertha had recently resumed drilling after a two-week break for adjustments and to receive a new set of cutting teeth.
Bertha had one of her better days on Thursday, advancing over 33 feet. Bertha has drilled more than 460 feet since July 30. It's scheduled to move under downtown Seattle next year, creating a new Highway 99 route to replace the Alaskan Way Viaduct.
The Associated Press contributed to this report.