Influences of particle size ratio and fines content on the suffusion characteristics of gap-graded soils

Suffusion severely threatens the stability of granular soils supporting infrastructure. While the geometric conditions of the granular soils are intrinsic to their mechanical behavior, their influences on the suffusion characteristics have not been fully understood. This study presents a micro-macro investigation of the suffusion characteristics of gap-graded soils with different fines contents and particle size ratios using the coupled computational fluid dynamics and discrete element method (CFD-DEM). The severity of the suffusion was quantified by both the loss of fines by mass and the volumetric deformation of the specimen. Meanwhile, Voronoi tessellation and weighted Delaunay method were employed to analyze the evolution of pore structures. The evolution of different contact types was used to analyze the rearrangement of the specimen skeleton. The simulation results show that suffusion is aggravated under otherwise identical conditions with an increase in particle size ratio and fines content. The particle size ratio influences the local pore difference between coarse and fine particles, while the fines content influences the fines’ contribution to the soil skeleton. The evolution of the distribution of local void fractions, constriction size distributions, stress-reduction factors, different types of coordination numbers, and different types of contact forces provides useful insights into the microscopic mechanism of the suffusion process.