Investigation of the effect of particle size non-uniformity on the stress-force-fabric relationship for granular materials

Abstract

The traditional stress-force-fabric relationship (SFF relationship) assumes that contact forces and branch vectors are independent, linking between the macro- and micro-scale behaviors of granular materials. However, both experimental results and numerical simulations indicate that this assumption does not hold for granular materials with high particle size non-uniformity. This study investigates the effect of non-uniformity on the SFF relationship for granular materials via 3D discrete element method (DEM). A series of drained triaxial tests was conducted on dense granular materials with continuous and gap gradations, varying the non-uniformity coefficient (C_u). The results show that as C_u increase, the stress ratios predicted by the traditional SFF relationship gradually deviate from that DEM data. This deviation is attributed to the correlation between contact forces and branch vectors, which can be characterized using a lower-order Fourier series expansion. Based on the traditional SFF relationship and incorporating this correlation, a modified SFF relationship is proposed. Verifications show that stress ratios from the modified SFF relationship align well with the DEM data. Finally, an anisotropic analysis provides insights into the microscopic mechanisms underlying the dependence of shear strength on C_u.