TOPOLOGICAL MECHANISM OF THE STRESS ANISOTROPY INFLUENCE ON THE THREE-DIMENSIONAL STRENGTH OF GRANULAR MATERIALS

In practical engineering applications, granular materials in geotechnical systems are often subjected to complex three-dimensional anisotropic stress conditions. The initial anisotropy of the stress state can exert a significant influence on the mechanical behavior of granular materials during loading and unloading process at both macro and micro scales. In this study, a series of numerical specimens with varying degrees of initial anisotropic stress were generated using the Discrete Element Method (DEM). These specimens were then subjected to true triaxial tests under the condition of constant mean principal stress, with loading applied in different directions. Based on the simulation results, strength envelopes on the π plane were constructed for specimens with different initial stress anisotropies. In order to further investigate the internal mechanical evolution, the microscopic structural changes during loading towards a specific point on the strength envelope were compared across specimens with different initial stress states before reaching peak strength. Furthermore, the topology of strong contact networks was analyzed for specimens at both pre-peak and post-peak stages under the same initial anisotropic stress conditions. The results demonstrate that initial stress anisotropy has limited impact on the strength envelope of samples before reaching the peak strength. However, post-peak strength envelope exhibits a similar shape to pre-peak strength envelopes but with reduced yield strengths. As loading progresses towards a specific point on the strength envelope, differences in the internal microstructure caused by different initial stress conditions tend to diminish rapidly and converge gradually as loading continues. Despite being at the same macroscopic stress state, specimens with the same initial anisotropic stress display notable differences in their internal contact distribution and the topology of strong contact network before and after the peak strength. These differences in contact network evolution are likely critical factors governing the three-dimensional strength behavior and failure mechanisms of granular materials.