Developed and patented by NFM Technologies, the Benton’ Air® tunnel-boring machine (Slurry TBM) is used for tunnel-boring in highly permeable unstable terrain, or under civilian structures sensitive to ground disturbances.
When digging in highly unstable or liquid terrain, the pressure exerted by the terrain is directly governed by the depth at which digging is performed. It is therefore necessary to balance the pressure exerted by the terrain: the front shield of the Slurry TBM is filled with excavated material, with the exception of one air-filled part. The pressure within this air bubble is subject to fine control. Bentonite injection waterproofs the working face and improves its resistance.
NFM Technologies initiated the earth pressure with additive process in Europe. The EPB technology is suited for digging tunnels in unstable ground such as clay, silt, sand or gravel.
The front shield of the EPB TBM is filled with debris extracted by means of a screw conveyor. This screw compensates the pressure difference between the working face and atmospheric pressure. Foam injection renders the material more homogeneous, thus facilitating its excavation.