Measuring the evolution of contact fabric in shear bands with X-ray tomography

Numerous studies have shown that the fabric of granular materials plays a fundamental role in its macroscopic behaviour. Due to technical limitations, this fabric remained inaccessible in real experiments until recently when X-ray tomography became accessible. However, determining the fabric from tomographic images is relatively challenging, due to various inherent imaging properties. Triaxial experiments on natural sands are chosen to investigate the contact fabric evolution. Two different observation windows in the specimen are chosen for the contact fabric analysis: one inside and another one outside a shear band. Individual contact orientations are measured using advanced image analysis approaches within these windows. The fabric is then statistically captured using a second-order tensor, and the evolution of its anisotropy is related to the macroscopic behaviour.