Routine maintenance on Bertha, the SR 99 tunneling machine currently working on Seattle's Alaskan Way viaduct project, includes inspecting and replacing the 700+ steel cutting teeth that chew through whatever gets in her way - concrete, clay, etc.
The Ballard Marine Construction and Seattle Tunnel Partners crews are making good progress as they continue performing routine maintenance on this stop that began June 23. The work is done 120 feet below ground in hyperbaric conditions similar to those found in an underwater dive. Crews can spend only about one hour working in this increased air pressure which is about 2.6 times atmospheric pressure, or 35 pounds per square inch. Five crews of seven people take turns replacing the tools and performing other work in the space behind the cutterhead.
Bertha was originally built with a retractable front end to give divers 18 inches of elbow room, but when the damaged main bearing was replaced in 2015, engineers from the boring machine's manufacturer, Hitachi Zosen, made the front rigid.
This new video captured by STP shows that performing maintenance on the cutterhead is no easy task. In addition to working in hyperbaric conditions, crews must complete their work in a confined space. The steel cutting tools shown in the video weigh approximately 75 pounds.
Bertha will resume digging again by late summer. STP plans two more planned maintenance stops as the project continues.