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 macromechanical 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(d epsilon) from the loading direction theta(d epsilon) 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(dF) 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.