25 / 2021-10-26 22:29:01

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

Old reservoir bank landslide; Soil-water characteristic curve; Unsaturated hydraulic conductivity; Bayesian method; Reliability analysis

If a reservoir bank landslide happened in the history, the safety factor of slope stability will approach to the critical value, 1.0, which cannot indicate the realistic stable situation of the reservoir bank slope. In addition, the old landslide carried away a large amount of coarse-grained soil, which was separated from the bedrock. The residual soil retained in the slope is mainly the fine-grained clay. Physical and mechanical test results of the geotechnical parameters are relatively comprehensive, but the variability of the unsaturated hydraulic conductivity is less considered. Based on the combined random (field) statistical characteristics of the hydraulic parameters, which consist of the Soil and Water Characteristic Curve (SWCC) and the saturated hydraulic conductivity, a reliability analysis method of 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 by the laboratory measurements. Secondly, combining the random field characteristics of the saturated hydraulic conductivity with the random characteristics of the SWCC models, 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. Results indicate that the safety factor 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 continuing.