DEM-CFM Analysis of Undrained Cyclic Behavior in Transversely Isotropic Granular Soils under True Triaxial Loading Paths

True triaxial and hollow cylinder tests are among the best alternatives to explore the effects of stress paths oriented along different Lode angles on soil behavior. However, those experiments are not easy to conduct in the laboratory, especially for cyclic loading. This study investigates the undrained cyclic behavior of granular soils under true triaxial loading conditions using the discrete element method (DEM) coupled with fluid method (CFM). Numerical specimens with elongated particles oriented along three different bedding planes and in an isotropic condition were prepared and subjected to constant volume cyclic loading. Loading direction effects on the liquefaction potential were considered, applying the deviatoric stress amplitude along different Lode angles. The impact of initial fabric orientation and stress anisotropy on the micro- and macro-scale response of particulate assemblies was intensively studied. The results show the significant effect of the Lode angle on the liquefaction susceptibility and inclination of the phase transformation line of granular assemblies. It can be concluded that particulate assemblies become more prone to the onset of liquefaction by alternating the Lode angle. The inherent anisotropy and Lode angle influence the number of cycles to reach liquefaction, the slope of the phase transformation line, and the failure line.