Earth pressure balance, or EPB, is a mechanized tunnelling method in which the excavated material is used to support the tunnel face whilst it is being plasticised using foam/slurry & other additives to make it transportable and impermeable. The excavated material is transported into the tunnel boring machine (TBM) via a screw conveyor arrangement which allows the pressure at the face of the TBM to remain balanced without the use of slurry.

EPB Tunnel Boring Machines are mainly designed for soft soils containing water under pressure. The EPB TBM can handle loose sedimentary deposits with large boulders and high water table.

The excavated material is then transported by a screw conveyor from the excavation chamber to the belt conveyor. The combination of the output of the screw conveyor and the advance rate of the TBM ensures that the support pressure in the excavation chamber can be exactly controlled. Continuous monitoring of the state of balance in the excavation chamber by means of earth pressure sensors, allows the operator to control and synchronize all tunnelling parameters. It allows high advance rates and reduces the risk of changes at the surface.

To improve the ground conditions for EPB tunnelling several conditioning materials can be injected through the cutter head and the bulkhead. By changing the ground conditions, tunnelling in soils containing gravel, sand, water or in unstable geology is also possible.

The cutter head of the machine will be designed especially for the ground conditions of the project. Depending on the requirements the head will be equipped with disc cutters or rippers, or a combination of both. All cutter heads will have an optimized opening ratio.