Multi-Field Responses and Failure Mechanisms of Loess Slopes under Engineering Disturbance and Extreme Rainfall: Implications for Sustainable Slope Management

Understanding the stability of loess slopes under the combined effects of engineering activities and extreme rainfall is essential for sustainable land use and infrastructure development in loess regions under climate change. In this study, a 1:20 large-scale physical model test was conducted to investigate the multi-field responses and deformation–failure mechanisms of loess slopes subjected to coupled surcharge loading, slope excavation, and continuous rainfall. The spatiotemporal evolution of the stress, moisture, pore-water pressure, and deformation fields was systematically monitored throughout the entire loading–excavation–rainfall process. The results indicate that: (1) Engineering disturbances induce pronounced stress concentration zones within the slope, which are further intensified and migrate downward during rainfall infiltration. The maximum vertical stress exceeded 150 kPa in the late rainfall stage, reflecting substantial stress redistribution under combined actions. (2) Rainfall infiltration exhibits apparent spatial and temporal heterogeneity, with rapid saturation of the shallow soil layer and delayed water migration and pore-pressure buildup in deeper zones. After approximately 15 h of rainfall, pore-water pressure increased sharply, concentrating in the middle–lower part of the slope toe and significantly reducing effective stress. (3) Slope deformation and failure evolve progressively from local initiation to through-going instability, characterized by a rapid chain-type process of “shallow softening → shallow mudified sliding → toe-shear failure → flow-plastic and liquefied sliding.” Shallow flow slides dominate the early stage and serve as precursors to more profound instability. These findings reveal the intrinsic mechanisms of coupling between engineering disturbances and rainfall infiltration that control loess slope instability. The experimentally identified failure processes and critical response characteristics provide scientific support for sustainable slope management, early warning, and risk mitigation strategies in loess regions facing increasing extreme rainfall under climate change.