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What’s Happening, Bertha!

The almost finished product (Photo: Courtesy of WSDOT)

Earlier this month, the Washington State Department of Transportation (WSDOT) announced Bertha as the new name for the SR99 tunnel boring machine. She was named after Seattle’s Mayor Bertha Knight Landes, the first woman to lead a major American city (served from 1926 to 1928). The name was chosen by students as part of a contest held by WSDOT in November. The winners were Darryl Elves’ fifth-grade class at Poulsbo Elementary School and Elijah Beerbower, a second-grader at Lincoln Elementary School in Hoquiam.

The machine’s cutterhead has bright colors to help distinguish the different components. The fixed cutters are painted in yellow and will score a groove in the soil as the machine moves forward. The black disc cutters grind boulders and rocks in the soil as the machine rotates. If one of these cutters wears out, it will be replaced from within the cutterhead’s arms. Lining the cutterhead’s arms are hundreds of red ripper teeth, helping guide the soil and other materials the machine’s cutters have broken up into the mixing chamber directly behind the cutterhead.

Up close and personal with the SR 99 tunnel boring machine cutterhead (Photo: Courtesy of WSDOT)

Bertha is a regular on Twitter; her latest post is her holiday wish list “1) Cruise to Seattle, 2) Dirt, preferably glacial till. Please, no sweaters. At my size, they never fit.” At 57.5 feet high, 326 feet long and 7,000 tons, she will dig an average of 35 feet per day once she starts work in Seattle.

Crews in Japan prepare the SR 99 tunnel boring machine for cutterhead installation. This area, directly behind the cutterhead, is the machine’s mixing chamber. The red spokes at the center work like a blender, mixing the excavated material into a consistency that can be easily removed by the machine’s screw conveyor belt. (Photo: Courtesy of WSDOT)

Crews in Japan are nearing completion of Bertha. The cutterhead has been installed and final testing of all components of the machine, including all motors, hydraulics, electrical and control systems is being performed. The machine will then be disassembled and shipped to Seattle across the Pacific Ocean – in more than 40 pieces!

The 57.5-foot-diameter cutterhead is hoisted up and rotated to be attached to the main body of the SR 99 tunnel boring machine. The cutterhead’s teeth will cut through the soil beneath Seattle as the machine moves forward. Most of the soil removed by the machine will be transported out of Seattle by barge from Terminal 46. (Photo: Courtesy of WSDOT)

Bertha will arrive in Seattle early next year. Keep an eye on the action with the construction cams at: more about how WSDOT is tunneling toward a new SR 99