Seattle's TBM Bertha gains a new set of "teeth"

11/12/2013 | Engineering News-Record

Bertha, the 7,000-ton tunnel-boring machine working on Seattle's State Route 99 tunnel, has already chewed through 430 feet of soil, concrete, rebar and timber. At a scheduled maintenance check, 24 of her massive round "teeth" were exchanged for rectangular ones deemed more suitable for boring through the glacial soils it will encounter of the next stage of its journey.

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