Soil conditioning for EPB tunnelling in coarse grained soils based on laboratory model tests

Earth Pressure Balance (EPB) tunnel boring machines (TBMs) are commonly used for tunnel construction in soft ground. Their application range has been extended through the use of soil conditioning to improve tunnel face stability and control of spoil flow through the TBM and screw conveyor. Effective conditioning is challenging for coarse grained soils, particularly with significant groundwater pressures. This paper presents results from laboratory tests undertaken with a model EPB screw conveyor on coarse grained soil samples with a range of gradings, conditioned with foam, polymers and fines addition. The tests modelled the EPB excavation process to assess the performance of different conditioning treatments. The results provide experimental support for published guidance on EPB TBM application ranges and conditioning requirements, and demonstrate the potential to expand the application range through the use of specialised water absorbent polymer conditioning treatments.