Stability analysis of unsaturated fractured rock slopes considering water‒air flow induced by rainfall infiltration

This study delves into the stability analysis of unsaturated fractured rock slopes under rainfall infiltration, focusing on the intricate dynamics of water and air flow within fractures. The research emphasizes the importance of two-phase flow models in accurately predicting slope stability, particularly in scenarios where rainfall-induced infiltration triggers complex hydrological and mechanical processes. The study introduces a novel two-phase flow framework that explicitly considers air entrapment, fracture-dominated infiltration, and realistic boundary transitions, offering a more precise prediction of unsaturated flow behavior and its mechanical implications. It also explores the impact of different relative permeability models, such as the Corey model, on the infiltration dynamics and slope stability. The research includes a comprehensive analysis of three types of fractured rock slopes—single-fracture, anti-inclined, and randomly fractured slopes—under various rainfall intensities. The study concludes that the two-phase flow model significantly delays the infiltration of rainwater into domains, affecting the evolution of slope stability. The Corey model, in particular, reduces fracture permeability and slows the infiltration process, highlighting the critical influence of relative permeability models on slope stability during rainfall. The research also underscores the dominant role of fracture spatial distribution in determining the potential instability modes of rock slopes, which differ significantly from soil slopes. A case study of the GS Hydropower Station illustrates the practical application of the proposed model, demonstrating how prolonged atomized rainfall can weaken the stability of outlet slopes and potentially trigger landslides or collapses. This study provides valuable insights into the stability analysis of fractured rock slopes under rainfall infiltration, offering a more accurate and comprehensive understanding of the complex interactions between water, air, and rock mechanics.