Bridging the Micro and Macro Mechanical Behaviour of Granular Materials

Understanding the underlying physics and mechanisms responsible for the loss of stability of granular systems is crucial to the mitigation of geohazards such as landslides and earthquakes. We use a combination of in situ testing under X-ray micro-computed tomography (micro-CT) and the hybrid finite and discrete element method (FDEM) to investigate the mechanical behaviours of granular materials from the microscopic to the macroscopic scales. We conduct a miniature triaxial test on a granular column sample that is imaged with X-ray micro-CT at incremental strain steps. Then, spherical harmonic (SH) analysis is performed to characterize and reconstruct the multi-scale morphological characteristics of particles, which was used to create the digital twin of the tested sample. FDEM simulation quantitatively agrees with the overall response observed in the experiment. We find that the granular material deforms plastically through spatially localized zones of large nonaffine displacements, and the spatiotemporal evolution of these zones controls the macroscopic responses of the system. Our method sheds light on bridging length scales from microscopic scale to macroscopic granular systems.