The TBM's with face support are those machines which can control the pressure on the excavation chamber and balance the pressure
of the ground. There are two different types of TBM's with face supports:
With an hidroshield, the balance is achieved through the pressure that the water or bentonite suspension is inyected
on the excavation chamber.
The bentonite suspension also is used for the transport of the material from the excavation chamber to the separation
plant outside the tunnel in the surface.
In an EPB shield, the pressure balance is achieve by filling the excavation chamber with material, and controlling the
extraction of it, by increasing or decreasing the rotatory speed of the screw conveyor.
