Suffusion of irregular concave gap-graded sand with resolved CFD-DEM

The complex morphologies of particles are a crucial factor influencing suffusion in gap-graded granular soils. However, the micro-mechanism of soil suffusion composed of irregular concave particles remains unclear. To this end, a systematic numerical simulation that considers particle concavity and aspect ratio is performed with the resolved discrete element method (DEM) and computational fluid dynamics (CFD) approach. The macro responses of suffusion of particles with varying morphologies, e.g., cumulative eroded particle mass and sample profile, are revealed and interpreted from a microscopic view, e.g., particle rotation, average number of contact points, and moment. It is found that the rotation of irregularly shaped particles during suffusion requires overcoming the moment applied by the surrounding particles. Particles with bigger contact force or irregularity require a higher moment to be overcome, thus significantly increasing their suffusion resistance. Irregularly shaped particles can adjust their orientation to reduce the moment and drag force applied to them. At the same aspect ratio, particles with larger concavity are more likely to interlock with each other, with increasing the average number of contact points of the soil packing and shrinking the pore channel for particle migration. A shape parameter considering both concavity and aspect ratio is finally proposed to characterise the influence on suffusion.