Fabric anisotropy in cyclic liquefaction: DEM-CFM analysis of pre- and post-liquefaction response

This study investigates the interplay between inherent and load-induced fabric anisotropy in the pre- and post-liquefaction behavior of granular soils. To this end, the Discrete Element Method (DEM) is combined with the Coupled Fluid Method (CFM) to simulate the undrained response of granular assemblies under cyclic true-triaxial loading conditions. Transversely anisotropic samples with bedding plane orientations of 0°, 45°, and 90° are modeled using elongated particles. These samples undergo continuous shearing along paths with varying Lode angles, ranging from 0° to 60°. The results indicate that both the initial fabric and the Lode angle influence the number of cycles required to reach liquefaction and the evolution of deviatoric strain in the post-liquefaction state. To further elucidate these macroscale behaviors, the study tracks the evolution of microscale entities, including inter-particle contact fabric, particle orientation fabric, coordination number, and redundancy index. Across all assemblies, changes in inter-particle contact fabric correlate strongly with progressive excess pore water pressure accumulation. In the post-liquefaction stage, the mean effective stress remains low, and the stress path is largely constrained. Continued movement, often in a butterfly-shaped trajectory, promotes pronounced disruption, reorientation, and rearrangement of particles and their contacts, leading to substantial microstructural evolution.