Evolution and hysteresis of K0 in granular soils under repeated loading: the role of particle shape

The coefficient of earth pressure at rest ( K 0 ) is a fundamental parameter in geotechnical analysis and design. Its evolution under repeated loading remains inadequately understood, particularly concerning the effects of particle shape. This study systematically investigates the combined influence of particle morphology and relative density on the evolution and hysteresis of K 0 using the discrete element method. Five granular assemblies with distinct, realistic particle shapes but identical particle size distributions are examined across three density states (loose, medium dense, and dense). The results show that denser specimens composed of more irregular particles exhibit lower K 0 values during virgin loading. During unloading and reloading, pronounced hysteresis is observed, which becomes more significant with non-spherical particles. The unloading and reloading coefficients display clear linear correlations with various particle shape descriptors. Micromechanical analyses reveal that the hysteresis of K 0 cannot be fully explained by changes in the coordination number alone but is primarily governed by the anisotropic evolution of contact force networks. The stress–force–fabric framework effectively captures the evolution of K 0 , emphasizing the dominant role of normal force anisotropy, while contact normal and branch vector anisotropies play a lesser role. A unified exponential relationship between K 0 and normal force anisotropy is identified, which is independent of density, stress history, and particle shape. These findings offer new insights into the micromechanical origins of K 0 hysteresis and its dependence on particle morphology under repeated stress paths.