CFD-DEM modelling of suffusion in multi-layer soils with different fines contents and impermeable zones

Suffusion in broadly graded granular soils is caused by fluid flow and is a typical cause of geo-hazards. Previous studies of it have mainly focused on suffusion in homogeneous soil specimens. In this study, the coupled discrete element method (DEM) and computational fluid dynamics (CFD) approach is adopted to model suffusion in multi-layered soils with different fines contents, and soils with one or more impermeable zones. The parameters of the CFD-DEM model are first calibrated with the classic Ergun test and a good match with experiment is obtained. Then suffusion in multi-layered soils with different fines contents and impermeable zones is simulated and discussed. The simulation results show that, for soils with multiple layers, the cumulative eroded mass is mainly determined by the fines content of the bottom layer. In general, the higher the fines content of the bottom soil layer, the higher the cumulative eroded mass. In addition, suffusion is more severe if the fines content of the layer above is decreased. Impermeable zones inside soil specimens can increase the flow velocity around those zones, facilitating the migration of fine particles and intensifying suffusion.