Effect of Stress‐Induced Anisotropy on the Stability of Infinite Sandy Slopes

Abstract

Reliable assessment of infinite sandy slope stability requires accounting for anisotropic in‐situ stress state imposed by slope geometry and self‐weight. This study presents a mechanics and state‐based analytical framework that introduces stress‐induced anisotropy through the effective principal stress ratio and quantifies its influence on shear resistance and factor of safety using standard soil parameters. Upper and lower bounds of are derived to determine the admissible slope stress‐state domain. The formulation links to slope geometry and provides a closed‐form evaluation without requiring complex anisotropic laboratory testing for routine applications. Parametric analyses were performed to assess the effect of anisotropy on soil and slope parameters. Stress‐path triaxial tests were conducted to examine consistency with the analytical trends. Clean river sand at different relative densities and a residual sandy soil from the 2024 Wayanad landslide site were tested under isotropic and anisotropic consolidation. Compared with isotropic consolidation, anisotropic consolidation produced 30%–40% reduction in peak deviatoric stress, greater contractive volumetric response, and earlier strain localization. Complementary undrained tests showed rapid pore‐pressure generation and contractive effective stress paths consistent with intense rainfall conditions. The framework is applied to published case studies as well as to the 2024 Wayanad landslide. Incorporating stress‐state anisotropy reduces the computed stability margins and can shift marginal slopes across commonly adopted screening thresholds. Generalized design charts relating , , and are developed to support screening‐level assessment and interpretation of proximity to commonly adopted stability thresholds for infinite sandy slopes.