The cutterhead's disc rollers crush the rock face as the machine pushes forward under axial thrust and spins at a set RPM. Two lumped engineering relations drive the whole scene:
advance (m/h) = max(0.2, thrust·rpm / (strength·0.86 + 25))
cutter load (%) = min(100, strength / (thrust·0.024 + rpm·1.1))
Higher thrust and RPM push the advance rate up; harder rock (higher MPa) pushes it back down and raises cutter load. Cutter wear accumulates over time in proportion to load, and precast rings assemble behind the shield whenever "Tube installation" is on.