Investigation on the mechanism of size effect on suffusion via CFD-DEM simulations

Suffusion is a critical issue in geotechnical engineering. Despite extensive studies, the effect of soil specimen dimensions on suffusion remains unclear. In this paper, a coupled computational fluid dynamics and discrete element method (CFD-DEM) approach is employed to study the suffusion of gap-graded soils with varying aspect ratios, and the underlying physical mechanisms are discussed. The results indicate that as the aspect ratio increases, erosion degree, mechanical coordination numbers, and unevenness in the fines distribution decrease, while the likelihood of fine particles integrating into the soil skeleton rises. Before suffusion, specimens with lower aspect ratios show higher peak strengths. After suffusion, peak strength decreases with erosion degree. However, all specimens exhibit comparable residual strengths. The mechanism behind different suffusion behaviors in specimens with varying aspect ratios is primarily governed by their unique suffusion boundary conditions. Accounting for suffusion boundaries significantly modify erosion laws and eroded soil mechanics behaviors. A standardized specimen size is proposed to account for suffusion boundary effects, thereby minimizing errors attributed to variations in outlet sieve aperture sizes and inconsistencies in specimen dimensions. The results obtained highlight the influence of specimen size on suffusion, advancing our precise understanding of eroded soil behavior.