Résumé
Granular materials have macroscopic behavior that is intricately tied to the mesoscale and microscale dynamics of constituent particles. In particular, it is well established that their strength properties arise from the buildup of various anisotropic structures at the particle scale induced by grain connectivity (fabric), force transmission, and frictional mobilization. More fundamentally, these anisotropic structures work collectively to define the shear strength at the macroscale through the Stress-Force-Fabric (SFF) relationship. Although SFF has been extensively verified by means of discrete numerical simulations, an experimental verification has remained elusive due to the challenge of measuring both normal and frictional contact forces. In this study, we analyze experiments performed on a photoelastic granular system under two different loading conditions: compression and shear. During these experiments, we record particle locations, contacts, and normal and frictional forces vectors at various points in the loading history. We are able to reconstruct the angular distributions of these force vectors, and thus extract the corresponding anisotropies for each of the corresponding networks. Finally, we show that macroscopic resistance to load is well described by the sum of these anisotropies as predicted by SFF, closing the gap between experiments and numerical simulations.