Dual Mode machines are a combination of single-shield EPB and hard rock TBMs, and are intended for projects with highly variable and non-homogeneous geotechnical formations. A Dual Mode TBM provides active support for the excavation face in soft soil formations and can therefore be used in EPB mode. Alternatively, it can be utilized in standard single-shield mode (not under pressure) when facing stable rock formations.
In EPB mode, the material is extracted by a screw conveyor, while in "rock" mode the latter is replaced by a conveyor belt. The material collecting hopper is designed to accommodate both the screw auger and the belt conveyor.
The other parts of the TBM and the back-up remain unchanged in both operating modes, so the transition between the 2 modes can be carried out in a short time.
