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.

Particle breakage is an important factor affecting the mechanical properties of granular materials. In this study, the influence of particle breakage under different fine particle content is investigated by DEM. Through 3D scanning and Voronoi tessellations, the breakable particle model with realistic shape is constructed. A series of confined cyclic loading tests were performed at different fine particle content. Then, the particle breakage characteristics, including the degree of breakage and the breakage pattern, were evaluated. In addition, the compaction deformation was analyzed according to the evolution of porosity. Finally, the influence mechanism of particle breakage is explained from two perspectives of particle contact and particle motion. On the one hand, with the increase of fine particle content, the number of contacts on the coarse particles is increasing. Hence, the coarse particles can withstand greater forces without breaking. On the other hand, the displacement of coarse particles and the porosity decrement have very similar evolution curve. This indicates that the Z-axis displacement of coarse particles can directly reflect the variation of sample porosity. In addition, particle breakage has little effect on particle rotation. The effect of particle breakage on porosity is mainly realized through the effect of particle translation rather than particle rotation.