Oct. 31 project update: Bertha resumes mining

Posted on Oct 31 2016 3:45 PM
Seattle Tunnel Partners resumed mining Monday following a week of tunneling machine maintenance. Crews working in hyperbaric conditions changed approximately 100 cutterhead tools during the maintenance stop, which began on Oct. 22.
The machine has more than 700 cutterhead tools in all, but crews only inspect and replace a portion of them each time they stop for maintenance. This post explains more about the different types of tools and the methods crews use to replace them.
Bertha, the SR 99 tunneling machine, is more than 200 feet beneath First Avenue, approaching Stewart Street. Before mining started Monday morning, crews had mined 5,085 feet and installed 774 concrete tunnel rings.