Abstract
As a result of deposition process and particle characteristics, granular materials can be inherently anisotropic. Many researchers have strongly suggested that the inherent anisotropy is the main reason for the deformation non-coaxiality of granular materials. However, their relationships are not unanimous due to the limited understanding of the non-coaxial micro-mechanism. In this study, we investigated the influence of inherent anisotropy on the non-coaxial angle using the discrete element method (DEM). Firstly, we developed a new DEM approach using rough elliptic particles, and proposed a novel method to produce anisotropic specimens. Secondly, the effects of initial specimen density and particle characteristics, such as particle aspect ratio Am, rolling resistance coefficient β and bedding plane orientation δ, were examined by a series of biaxial tests and rotational principal axes tests (RPAM). Findings from the numerical simulations are summarized as: (1) The peak internal friction angle ϕp and the non-coaxial angle i both increase with the initial density, Am and β, and they both increase initially and then decrease with ϕ in the range of 0 - 90°; (2) Among the particle characteristics, the influence of Am is the most significant; (3) For anisotropic specimens, the non-coaxial angle can be calculated using the double slip and rotation rate model (DSR2 model). Then, an empirical formula was proposed based on the simulation results to depict the relationship between the non-coaxial angle and the particle characteristics. Finally, the particle-scale mechanism of non-coaxiality for granular materials was discussed from the perspective of energy dissipation.