What are TBM moles

The full section mechanical cutter called mole or mechanical mole (ingl. Tunnel boring machine from which the abbreviation TBM) is a machine that allows the complete mechanization of the excavation of the tunnels and the realization of the lining of the same.
This machine can work in rock, even very resistant, or below groundwater.
By “shield” (shield in English) we mean the metal cylinder that closes the machine on which, at one end, the rotating head carrying the actual excavation tools is mounted.
The head rotates at 1-10 revolutions per minute (depending on its size of the material it digs into) and removes small flakes of material.
Inside the cylinder behind the head there is a chamber in which the excavated material is collected which, depending on the TBM type, can be extracted as it is or mixed with mud ("slurry shield"), the choice depends on the conditions of the heap in which it is excavated.

The material leaves the chamber on an auger, or worm, and is placed on a conveyor roller.
The machine moves like an earthworm: hydraulic jacks point on the rock (if sufficiently healthy, otherwise on the just positioned coating) and push the shield forward; the rear part of the TBM is also anchored to the mouth of the tunnel to contribute to the thrust.
Once the head is repositioned, the rest of the machine is dragged forward.
All services run inside the shield, from electricity for the control chamber to conduits for the mixing sludge. Also inside the shield is the positioning system of the precast concrete segments for the lining