Bertha picking up speed
It was a good first week back on the job for Bertha, the SR 99 tunneling machine.
Bertha dug 64 feet between Sept. 23 and the end of the month, averaging about 11 feet of excavation per work day. Add that to the 24 feet she traveled prior to the monthlong stoppage in mining, and Bertha had traveled a total of 88 feet by the start of October.
The end of September brought with it an important milestone: installation of the first permanent tunnel ring. Now that Bertha is building rings underground, instead of in the launch pit, crews no longer need to install the elaborate system of bracing that was used to reinforce the temporary rings.
Also, with Bertha’s shield now fully underground, crews were able to create a seal behind her. The seal allows Bertha to begin pushing toward full speed, using the pressure underground to her advantage without having to worry about muck escaping through the unsealed ground that surrounds the newly installed tunnel rings.
Crews hope to speed up production in the coming weeks. Once Bertha gets beneath downtown, she should dig about 35 feet a day.