Failure mechanism and reliability analysis of soil slopes under rainfall infiltration considering spatial variability of multiple soil parameters

The current reliability studies on slope stability under rainfall infiltration only consider the spatial variability of saturated hydraulic conductivity of soils, while ignores that of shear strength parameters. An infinite slope model is taken as an example, and a modified Green-Ampt model is developed to determine the distribution of moisture content of soils and the wetting front depth within the slope under different rainfall durations. The failure mechanism of the infinite slope considering the interaction of the spatial variabilities of multiple soil parameters and the rainfall infiltration is investigated. Then the probabilities of slope failure under different rainfall durations are compared. The results indicate that a smaller coefficient of variation of saturated hydraulic conductivity induces a smaller probability of slope failure during the initial period of rainfall. However, it will result in a larger probability of slope failure as the rainfall sufficiently progresses. Additionally, during the initial period of rainfall, the uncertainty of slip surface location due to the spatial variability of shear strength parameters of soils will greatly affect the slope stability. In this case, the slope will fail along the weak zones induced by the spatial variability of shear strength parameters besides along the wetting fronts and impermeable layers. As a result, the probability of slope failure is larger when the spatial variability of shear strength parameters is considered. In contrast, the advance of the wetting front is the crucial factor that affects the slope stability during the late period of rainfall. In this case, the slope will fail mainly along the wetting fronts, and consequently the probabilities of slope failure will be similar no matter whether the spatial variability of shear strength parameters is taken into account.