Micro-mechanical analysis of cohesionless-frictional particulate materials considering principal stress rotation induced by moving surface loads

The principal stress rotation induced by moving surface loads has been extensively investigated, predominantly through hollow cylinder tests. In contrast to these element tests, residual stresses are generated within a structural component due to plastic strain accumulation during the loading and unloading process. Given the significant influence of residual stresses on principal stress distributions, it is essential to investigate the principal stress rotation at the structural scale rather than relying solely on element-scale analyses. In this study, a discrete element method model was developed to simulate the mechanical response of a cohesionless-frictional particulate structure subjected to moving surface loads. The macroscopic stresses responsible for principal stress rotation were analytically derived, and their behaviour was found to be significantly affected by residual stresses during the unloading process. Furthermore, a comprehensive micro-mechanical analysis was conducted, with particular emphasis on the evolution of fabric anisotropy. The results revealed a pronounced non-coaxiality between the principal directions of the fabric anisotropy. Finally, a stress-force-fabric relationship was employed to validate the concept of fabric anisotropy and to establish a connection between particle-scale contact mechanics and macro-scale stresses. The influence of branch vectors on macroscopic stresses was found to be negligible under conditions involving the principal stress rotation and irregular particle morphologies.