Slope Stability Analysis under Heavy Rainfall Conditions Based on a Modified Green-Ampt Model

The analysis of rainwater infiltration is crucial for the prevention and early detection of rainfall-induced landslides. Under the assumption of saturated-unsaturated stratification, and considering the influence of saturated layer seepage and air pressure on infiltration, a modified Green-Ampt model (SRGA model) suitable for slope rainfall infiltration is established. A corresponding slope safety factor expression is derived for the model. The results show that the SRGA is demonstrated to accurately describe dynamic expansion of the wetting layer throughout the heavy rainfall infiltration process; it is also applicable under weaker rainfall conditions. Validation against experimental data confirms the model’s accuracy, with an error of approximately 21% compared to Chen-Young’s model. The instability time predicted with the SRGA model during the slope stability analysis emerges approximately 7.2% earlier than measured, significantly outperforming Chen-Young’s model. Air pressure and seepage force influence infiltration depth through different mechanisms. The influence of air pressure is more significant in the early control stage of soil infiltration capacity, while seepage force is more significant in the later stage. Rainfall infiltration is affected by slope length to greater extent than slope stability. The SRGA model is versatile, and can be simplified into existing models under certain conditions. The results of this work may provide theoretical support for slope control under rainfall infiltration conditions.