On Saturday,the world's largest tunnel boring machine was dedicated in the city of Seattle. “Bertha,” as it’s known, will spend the next 14 months boring a 1.7 mile (2.7 km) tunnel under the city to replace a viaduct damaged in a 2001 earthquake. Gizmag took a look inside the giant machine.
More than 150 feet below the streets of Seattle, Bertha presses on, boring a 57.5-foot diameter tunnel underneath the city. The largest tunnel boring machine (TBM) in the world when it was built, Bertha weighs a gargantuan 6,700 tons and stretches 326 feet long.
Bertha is a giant marvel of engineering, both literally and metaphorically. Currently, Bertha is the largest diameter tunnel boring machine in the world, though a slightly larger one (by about a quarter foot) was used last year in China for a short section of tunnel before it was converted back to a smaller machine for the rest of the work. http://www.popularmechanics.com/technology/infrastructure/news/a24895/seattle-big-bertha-tunnel-boring-machine/