DEM investigation of particle gradation effect on the stress-dilatancy behavior of granular soil

Particle gradation effect on the shear-dilatancy of granular soils was studied through a series of drained triaxial tests using the discrete element and finite difference methods (PFC^3D-FLAC^3D). Spherical particles with different coefficients of uniformity C_u and median particle sizes D₅₀ were assembled to exclude the strong size-shape correlation in natural sands. Four groups of C_u and four groups of D₅₀ at the same void ratio e_c prior to shearing, and seven more groups with the same void ratio e₀ prior to isotropic compression were tested. Various mechanical behaviors were analyzed, including the stress–strain response, the stress-dilatancy response, friction angle, and fabric anisotropy. C_u significantly influences the peak friction angle, the maximum dilation angle, and the anisotropies of normal contact force and contact normal, whereas these are almost independent of D₅₀. The contribution of the maximum rate of dilation to the excess friction angle is largely independent of C_u and D₅₀ for spherical particles.