DEM investigation into triaxial compression behaviour of gap-graded soil-rock mixture subjected to internal erosion: from contact forces to critical state evolution

Internal erosion significantly alters the mechanical properties of gap-graded soil-rock mixture (SRM), posing considerable risks to the stability of granular structures. However, our understanding of the mechanisms driving this phenomenon remains limited, particularly regarding the influence of confining pressures during the internal erosion process. This study employs three-dimensional discrete element method (DEM) simulations to investigate the mechanical behaviour of gap-graded SRM subjected to internal erosion. The results reveal that fine particle loss leads to substantial increases in void ratios, especially under low confining pressures. Notably, a transition from strain-softening to strain-hardening behaviour occurs as erosion progresses, with a 12% reduction in fine content resulting in a 12%–17% decrease in peak shear strength. Additionally, the analysis demonstrates that internal erosion induces significant changes in both deviatoric and volumetric responses of the SRM. The shear secant modulus (E 50) consistently decreases with increasing erosion, illustrating the essential role of fine particles in maintaining stiffness. This study established a clear relationship between the extent of erosion and the evolution of critical state parameters. This research not only contributes to the existing body of knowledge but also provides valuable insights for the development of constitutive models applicable to scenarios involving internal soil erosion.