Macro- and micro-scale investigation of suffusion in gap-graded soils under multiple factors using CFD-DEM

Internal erosion induces alterations in the initial microstructure of soils, simultaneously affecting physical, hydraulic, and mechanical properties. The initial soil composition plays a crucial role in governing the initiation and progression of seepage-induced suffusion. This study employs the controlled variable method to develop granular soil models with varying particle size ratios, initial fine particle contents, and coarse particle shapes. Seepage suffusion simulations coupled with microstructural analyses are conducted using the CFD-DEM approach. Results demonstrate that particle size ratio, fine particle content, and coarse particle shape exert distinct influences on cumulative erosion mass, fine particle distribution, contact fabric, and mechanical redundancy at both macroscopic and microscopic scales. This numerical investigation advances the fundamental understanding of internal erosion mechanisms and informs the development of micro-mechanical constitutive models. Furthermore, for binary granular media composed of coarse and fine particles, careful control of the particle size ratio and fine content is recommended when utilizing gap-graded soils in embankment and dam construction to improve structural resilience and resistance to internal erosion.