SEATTLE — Bertha, Seattle’s tunnel machine, achieved what officials called “a significant milestone” on Thursday when it broke through a 20-foot-thick concrete access pit wall into a shaft so that it can be pulled out and repaired.
Hoses strapped to fences shot streams of water into the pit and plumes of dust wafted into the air as the cutterhead clawed through the concrete and emerged from underground into the 120-foot-deep rescue pit, where workers will remove the front of the machine, pull it to the surface and repair its broken parts.
“It’s a very significant milestone but there’s still a lot of work ahead,” said Matt Preedy, transportation department deputy administrator of the Alaskan Way Viaduct Replacement Project, which stalled in December 2013 when Bertha hit a pipe that caused it to overheat and quit after traveling about 1,000 feet on its 2-mile trip under the city.
The tunnel was the project of choice to replace the viaduct, which was damaged in a 2001 earthquake. Crews spent much of 2014 digging the pit to reach the front of the machine.