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.
A tunnel boring machine (TBM) also known as a "mole", is a machine used to excavate tunnels with a circular cross section through a variety of soil and rock strata. They can bore through anything from hard rock to sand. Tunnel diameters can range from a metre (done with micro-TBMs) to 19.25 m to date. Tunnels of less than a metre or so in diameter are typically done using trenchless construction methods or horizontal directional drilling rather than TBMs.