Influence of hydraulic and geometric conditions on the early stages of the filtration process in idealised granular soils comprising spherical particles

The early stages of particle-scale filtration in idealised granular soils were investigated using coupled Computational Fluid Dynamics and Discrete Element Method. Filtration simulations were conducted for assemblies of finer base particles underlying coarser filter particles with upward seepage flow perpendicular to the base-filter interface. A wide range of size ratios that covered the complete spectrum of filtration behaviours were considered, along with different ramping accelerations for seepage flow to investigate the combined influence of geometric characteristics and hydraulic loading. The influence of flow conditions and size ratios on the time-dependent infiltration depth of transported base particles was observed to be universal with respect to a newly proposed dimensionless time parameter. The susceptibility to filtration during the early stages was quantitatively investigated with the number of infiltrating base particles and the filling degree of pores within the filter. The susceptibility during the early stages was shown to have a strong correlation with pore space geometry at the filter boundary, which was also reflected by the maximum pore filling degree of the filter. While filter susceptibility has been conventionally evaluated by the size ratio of the assembly, the consideration of the pore space geometry at the filter boundary provided an alternate approach of evaluating local filter susceptibility.

Automated summary

The early stages of particle-scale filtration in idealised granular soils were investigated using coupled Computational Fluid Dynamics and Discrete Element Method. A wide range of size ratios and different ramping accelerations for seepage flow were considered to investigate the combined influence of geometric characteristics and hydraulic loading. The susceptibility to filtration during the early stages was shown to have a strong correlation with pore space geometry at the filter boundary.