Bertha – Largest tunnel boring machine
Named after Seattle’s first woman mayor, Bertha is what is known as a soft rock TBM, as opposed to a hard rock TBM. The latter, as the name suggests, is essentially a big rock drill designed to bore through solid granite or something equally nasty. That’s not to say that Bertha had an easy time of things. Far from it. Soft rock TBMs have to contest with sand, which can be as damaging to machinery… more