Failure Mechanism of Soil Excavations Under Unsaturated Steady-State Flow Conditions Based on Slip-Line Method
摘要
Traditional methods for estimating active earth pressures often rely on predefined failure mechanisms, overlooking the influence of backfill properties, wall geometry, and boundary fluxes under unsaturated steady-state infiltration or evaporation conditions. Prolonged rainfall induces downward discharge, diminishing effective stress due to reduction in matric suction to increase risks of excavated slopes and retaining wall failures. This work presents a novel analytical slip-line framework that links hydro-mechanical responses via suction stress variations above the water table under infiltration, hydrostatic, and evaporation conditions. By employing a unified effective stress representation, the model captures the evolution of the critical slip surface—a feature previously ignored in static limit equilibrium methods. Validation against existing literature confirms the model’s efficacy in capturing matric suction effects on the active earth pressure coefficient (ka). Quantitative analysis reveals that moisture-induced changes are substantial: in clayey backfills, the ka increases by 62% when transitioning from evaporation to hydrostatic conditions, and by 81% under steady-state infiltration. Furthermore, vertical discharge conditions in sandy backfills were found to increase the ka by up to 86% for wall heights between 1 and 5 m. These results underscore the critical role of soil type and wall height in crack formation. The proposed model is the first to capture evolving critical slip surfaces, reliably predicting active earth pressures for mitigating rainfall-induced failures. This framework provides a practical tool for the design of resilient retaining structures and the forensic analysis of rainfall-induced failures in unsaturated earthen systems.