Here's how the tunnel boring machine, or TBM, works: As the 200-ton TBM moves forward, a round cutter head studded with titanium teeth grinds into the tunnel face and splits large chunks off the rock.

Mechanism: A Gripper TBM uses a rotating cutterhead equipped with disc cutters that apply significant pressure (up to 32 tonnes per disc) against the tunnel face. The machine’s design includes gripper ...