Micro- and macro-mechanical analysis of rev in sheared polydisperse granular samples

A representative elementary volume (REV) is key to ensuring accurate estimations of the mechanical behaviour of granular materials. Guidelines given by testing standards and laboratory equipment restrictions define limits on the maximum particle size (dₘₐₓ) in a triaxial test. The recommended aspect ratio (a = D/dₘₐₓ) varies from 5 to 20. However, particle size polydispersity is often ignored in the standards, and its effects on REV estimation are poorly understood. This work studies the combined effects of α and particle size distribution (PSD) on the critical shear strength of granular materials through drained triaxial tests DEM simulations. We found that shear strength increases with α to a maximum value and it stabilizes, indicating a REV. However, better-graded samples stabilize earlier. At the microscopic level, the fraction of particles contributing to stress transmission (N*ₚ) shows an effect on shear strength. Finally, for our samples, when α > 12.5 and N*ₚ > 3000, a REV state is achieved regardless of gradation.