Stability analysis of old reservoir bank landslide by considering spatial random field characteristics of unsaturated hydraulic conductivity

If a reservoir bank landslide happenes in the history, the factor of safety of slope stability will approach the critical value 1.0, which cannot indicate the realistic stable situation of the reservoir bank slope. Based on the combined random (field) statistical characteristics of the hydraulic parameters, which consist of the soil-water characteristic curve (SWCC) and the saturated hydraulic conductivity, a reliability analysis method for the old reservoir bank landslide is established. Firstly, according to the limited laboratory test data of saturation-matrix suction, the statistical characteristics of the SWCC properties, such as VGM, VGB, VG, and FX model parameters, are calibrated by the Bayesian method, and the applied probabilities of SWCC model combination are determined through the laboratory measurements. Secondly, combining the random field characteristics of the saturated hydraulic conductivity with the random characteristics of the SWCC models, the spatial distributions of the unsaturated hydraulic conductivity are generated in the slide body. Finally, the reliability analysis will calculate the failure probability of the old reservoir bank landside only considering the random characteristics of the SWCC models, and the reliability index results of the spatial random field statistical characteristics of the unsaturated hydraulic conductivity. Under the conditions of heavy rainfall and rapid rise and fall of the Yangtze River water level in 2020, the reliability analysis of the old Shiliushubao landslide is carried out in the Three Gorges Reservoir area. The results indicate that the factor of safety of the slope stability is low, but the reliability index meets the minimum requirement of 2.70 according to the specification. None of the additional reinforcement measures are required. Nevertheless, the long-term slope monitoring program is suggested to be continued.