A novel analytical approach for 3D stability of unsaturated soil slopes with cracks under rainfall infiltration

Rainwater infiltration in unsaturated soil slopes with crest cracks can trigger two distinct threedimensional (3D) failure modes: shallow translational failure along the slope face and deep-seated rotational failure at the crack tip. This study employs the upper-bound limit analysis method to present an analytical framework for the 3D stability analysis of unsaturated soil slopes with cracks under rainfall infiltration. Two kinematically admissible failure mechanisms are constructed: a novel composite mechanism combining a 3D horn-shaped block with an oblique cylinder to characterize translational failure, accounting for boundary effects at slope crest, toe, and lateral constraints; and a rotational failure mechanism based on the horn-shaped block. The wetting front model is adopted to capture the transient process of rainwater infiltration. The proposed method enables a unified evaluation of both shallow and deep-seated stability for slopes with arbitrary crack depths at the crest, and its effectiveness is validated by existing literature. Parametric studies are conducted to investigate the effect of slope geometry (width-to-height ratio) on stability and the controlling factors of the translational and rotational failures.