TBMs

A tunnel boring machine (TBM), also known as a "mole" or a "worm", is a machine used to excavate tunnels. TBMs are an alternative to drilling and blasting methods and "hand mining", allowing more rapid excavation through hard rock, wet or dry soil, or sand. TBM-bored tunnel cross-sections extend up to 17.6 meters (58 ft). TBM tunnels are typically circular in cross-section, but may also be square or rectangular or U- or horseshoe-shaped. Much narrower tunnels are typically bored using trenchless construction methods or horizontal directional drilling rather than by TBMs.