The SR 99 tunneling machine digs again
Bertha is back at it.
At 4:48 a.m. on Sept. 23, after a monthlong stoppage and several days of startup time, the world’s largest tunneling machine resumed digging at the south end of downtown Seattle. Over the next two days, Bertha dug more than 20 feet and was preparing to install the first of 1,450 permanent concrete rings that will fit together to form the tunnel walls.
The rings Bertha has installed to date are temporary, which, as we explained previously, take longer to build than the permanent rings. Production should speed up considerably after permanent ring installation begins. By the time Bertha is under the heart of downtown, she is expected to dig an average of 35 feet per day.
Crews used the break in mining to optimize Bertha and make sure she’s operating as efficiently as possible when she tackles the difficult work ahead. Our contractor, Seattle Tunnel Partners (STP), will have opportunities to make up time as tunneling progresses. Crews can work longer shifts, for example, and take advantage of improvements made to the machine over the last month.