Multi-scale DEM Investigation of the Effects of Particle Shape and Size Characteristics on the Direct Shear Response of Granular Materials

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This study investigates the impact of particle shape, size, and size distribution on the shear behavior of granular materials using a multiscale Discrete Element Method (DEM) approach. A DEM model validated against direct shear test data from the literature was first developed, and seven models with systematically varied particle properties were analyzed. To assess the influence of particle shape, models with equal-volume particles but different sphericity and roundness were used. The effects of particle size and size distribution were investigated through models containing particles of various diameters and gradation coefficients (Cᵤ). The results demonstrated that particle shape exerts the most significant influence on both macro- and microscale behavior. Decreasing sphericity and roundness increased peak shear strength but led to a faster breakdown of contact networks during shearing. Particle size was the second most influential parameter; its effect intensified as size decreased but diminished below a threshold diameter. Particle size distribution showed a minor effect, with a slight increase in dilatancy observed as uniformity decreased. Correlating macroscale stress–strain responses with microscale coordination number changes confirmed that particle shape is the dominant factor controlling the strength and deformation mechanisms of granular systems.