Suffusion of Gap-Graded Soil with Realistically Shaped Coarse Grains: A DEM–DFM Numerical Study

Suffusion refers to the phenomenon in which fine particles in internal unstable soil are carried by seepage through skeleton pores. It is a type of internal erosion that can lead to major hazards for hydraulic and geotechnical engineering. In this study, the suffusion process is reproduced in gap-graded soil with realistically shaped coarse grains by coupling the discrete-element method (DEM) with dynamic fluid mesh (DFM), which can reproduce the pores formed by coarse particles and adapt to the deformation of the soil skeleton by changing the mesh according to the movement of coarse particles. Realistically shaped clumps are generated according to 49 Leighton Buzzard sand grains and applied to be the coarse grains in the gap-graded soil numerical model. We examine the roles of relevant parameters and compare the results with the model formed by spherical coarse grains. Two mechanisms (interlock effect and retention effect) hindering fines migration are identified at the pore-scale. The realistically shaped grains can better interlock, reducing porosity and squeezing fine particles. In addition, fines migration can be better prevented due to the roughness of the particle surface. Sensitivity analysis shows that the erosion mass increases with increasing hydraulic head, fine content, and the rising rate of the hydraulic head. Our results show that the erosion weight of the spherical particle model is much larger than that for the model of realistic grain shape; however, no evident difference in the suffusion pattern is observed between these two models.