(1) A full-face circular mechanized shield machine, usually of Man-Entry diameter, steerable and with a rotary cutting head. For pipe installation it leads a string of jacked pipes. It may be controlled from within the shield or remotely. (2) (Mole, Tunneling Head) A mechanical excavator used in a tunnel to excavate the front face of the tunnel.

a machine used to drill through the ground to create a tunnel.

The machine that excavated the tunnels of the Metro do Porto network. There are two machines in reality: “Micas” and “Micas II”, both of which are more than 70 metres long and weigh over 20 tons. They were operational for close to four years and put an end to the myth that it was not possible to dig tunnels underneath Oporto.