Posted on Sep 8 2016 4:25 PM

Seattle Tunnel Partners is continuing to change large cutting tools on the cutterhead of Bertha, the SR 99 tunneling machine. Crews have inspected 12 tools – replacing 10 of them – during the current maintenance stop. They could change up to four additional tools before they resume mining.

This is a normal part of tunnel mining. Cutting tools wear down over time and must be replaced regularly. Bertha recently transitioned from soft clay to a more abrasive mixture of sand and gravel, resulting in greater tool wear.

The tools STP is focused on during this maintenance stop are the first parts of the cutterhead that contact the ground, making them crucial to the machine’s ability to excavate soil. Replacing them now will preserve the cutterhead and keep the machine in good working order as it continues mining north beneath downtown.