There's more than one way to change a cutterhead tool

Performing regular maintenance on Bertha, the SR 99 tunneling machine, is critical to the success of the tunnel drive. During each of Seattle Tunnel Partners’ three planned maintenance stops in 2016, crews have spent time checking and maintaining various systems throughout the machine. Specific maintenance needs vary with each stop, but one maintenance item is always on STP’s to-do list: inspection and replacement of cutterhead tools.

Bertha’s rotating cutterhead has more than 700 tools that scrape away the earth in front of the machine. Not all of these tools are the same. Some can be accessed and replaced during routine weekend maintenance, while others are only reachable in hyperbaric conditions. Click through the photo slider below to learn more about how these tools work, and how crews maintain them during the tunnel drive.

During STP’s most recent maintenance stop – which lasted from Oct. 5-11 – crews replaced three pre-cutting bits from within one of the machine’s spokes. The photo below shows an STP crew member at work inside a spoke.

Spoke photo

Crews also inspected approximately 40 scrapers under hyperbaric conditions and determined that none of them needed to be replaced. The video below shows crews replacing a scraper during an earlier hyperbaric maintenance stop.

With no significant damage or wear noted during their inspection, STP chose to continue tunneling north beneath First Avenue on Oct. 11. They will continue to inspect and replace pre-cutting bits during routine weekend maintenance. Future hyperbaric stops will be scheduled by STP as needed, based on the condition of the cutterhead tools and other maintenance needs.