Assessing the annual probability of three-dimensional fractured rock slope failure induced by rainfall, considering preferential flow

The annual probability of slope failure is an important indicator for quantifying landslide risk under rainfall conditions. However, the current assessment methods for three-dimensional (3D) fractured rock slope fail to consider the effect of preferential flow, which may cause large errors in the results. We propose a discrete summation method to calculate the 3D safety factor of slopes by combining the numerical solutions of rainfall infiltration considering preferential flow with the 3D failure mechanism. The joint distribution of rainfall intensity and duration was fitted based on the long-term rainfall data from the Fushun area. The critical rainfall pattern curves were derived from multiple seepage and stability analyses, which divide the possible rainfall patterns into stable and unstable zones. The effects of preferential flow and 3D failure on the annual probability of the northern longwall slopes' failure were investigated through comparative analyses. The results indicate that preferential flow accelerates rainwater infiltration into the depths and significantly reduces the critical duration of slope failure at different rainfall intensities. The preferential flow increases the annual probability of 3D slope failure by 8.32 times, and the probability of 3D failure over 30 years reached 84.69%, which is more consistent with the facts of slope failure.