Up close and personal with the SR 99 tunnel boring machine cutterhead

Wed, Dec 12, midnight 2012

by WSDOT

Bright paint distinguishes the different components of the SR 99 tunnel boring machine’s cutterhead, and each one serves an important function. The large yellow pieces are fixed cutters that score a groove in the soil as the machine moves forward. As the machine rotates the black disc cutters grind boulders and rocks in the soil. Both of these types of cutters are replaceable and are accessed from within the cutterhead’s arms – when one wears out a new one is put in its place. Learn more about how we’re tunneling toward a new SR 99.