Abstract: The geometric characteristics of soil (gap ratio, fines content, relative density, etc.) not only affect the internal stability of soil but also have an important influence on suffusion development. Based on the coupled method of discrete element method (DEM) and computational fluid dynamics (CFD), a three-dimensional computation model of suffusion for internally unstable soil is established, the coupled effects of fines contents and relative densities on the suffusion are investigated, and the mesoscopic variables including soil constriction size distribution (CSD), coordination number and internal force transfer mechanism are analyzed to reveal the microscopic mechanism of the coupled influence from fines content and relative density. The results show that the increase in relative density decreases the erosion mass ratio, which is also highly related to fines content; the higher the fines content, the more obvious the effect of relative density. The specimen after erosion can be divided into “upstream erosion zone”, “central stable zone” and “downstream erosion zone”. The increment of soil permeability during suffusion decreases with increasing relative density, while it increases with increasing fines contents. The influence of relative density on the suffusion process can be attributed to three aspects: differences in flow rates under the same hydraulic gradient, variations in the distribution of internal pore sizes, and variations in the contribution of fine particles to stress transmission within the soil. The results deepen the understanding of the influence of soil geometric characteristics on suffusion processes and provide a reference for the establishment of macroscopic erosion constitutive relationship.

Key words: suffusion, CFD-DEM, relative density, fines content, stress transmission mechanism