Balancing act

When operated in earth pressure balance mode, the Lovat TBMs can regulate the flow of soil into the face of the machine via controllable 'flood doors' and pressure-relieving gates. This is then discharged by an enclosed Archimedes-screw conveyor onto an open belt conveyor in the machine back-up.

The machine is thus balanced against the pressure imposed by the surrounding water-bearing strata. The spoil removed from the face is depressurised by the screw conveyor belt and removed to the surface. Operating a TBM in EPB mode increases the static and dynamic forces acting on it, which in turn increases the wear rate of the moving parts.