DEM Simulations of Critical State Behavior of Sand Under Triaxial Compression and Extension

This study focuses on examining the behaviors of dense and loose sand subjected to drained triaxial compression and extension using DEM. The research involved performing drained tests on samples, manipulating them under both traditional (constant confining pressure) and constant mean stress conditions using servo-control. The observed drained behavior qualitatively aligns with previously published laboratory findings. It is demonstrated that the void ratio of sand samples remains unaffected by initial packing densities and applied stress paths (CT/CP). The critical state (CS) line is unique regardless of the stress path (CT/CP) conditions, though it shows dependence on whether triaxial compression or extension is applied. Drawing upon the DEM results, a comparison and discussion of various failure criteria are presented. The Matsuoka criterion emerges as the most suitable at the CS. To describe structural anisotropy, a generalized microscopic fabric parameter is proposed, which appears to be unique regardless of the stress paths (CT/CP) conditions.