On non-coaxiality and fabric evolution of granular media in circular shear simulated by DEM

The non-coaxiality of monotonous loading for granular materials has been studied in laboratory tests and simulations using the discrete element method (DEM). However, the non-coaxiality and its relation to the fabric evolution under the stress path of circular rotational shear in the deviatoric plane remain largely unanswered. To address this issue, we report a series of true triaxial DEM simulations on initial isotropic samples to investigate the effects of stress-induced anisotropy on non-coaxiality and its fabric evolution. The mechanical behavior was captured by continuously changing the Lode angle \(\theta _\sigma\) under a wide range of confining pressure \(\sigma _c\), while the deviatoric stress q remains constant. In addition, the role of inter-particle friction on the non-coaxial response has been explored to elaborate on the effects of the changing of micro-structure on the macro-mechanical performance. Simulation results indicate that the non-coaxiality is the function of the stress ratio \(\eta\), confining pressure \(\sigma _c\), and inter-particle friction, which could be related to the orientation variation of contact fabric. The deviation of \(\theta _{\text {d}\varvec{\varepsilon }}\) from the loading direction \(\theta _{\text {d}\varvec{\sigma }}\) gradually increase as the rise of stress ratio \(\eta\), while it shows an obvious decrease trend with the increase of confining pressure \(\sigma _c\) and inter-particle friction coefficient \(\mu\). As for fabric evolution, it verifies the correlation between the non-coaxial response and fabric evolution in rotational shear. The directional evolution of incremental fabric \(\theta _{\text {d}\varvec{F}}\) are sensitive to stress ratio \(\eta\), while it is insensitive to confining pressure \(\sigma _c\) and inter-particle friction coefficient \(\mu\) than the non-coaxial response.

Graphical Abstract