Surface movement detection and stability evaluation of a loose fine‐grained soil slope during reservoir operation: A case study in NE reservoir

Abstract Landslide in reservoirs imposes challenges to reservoir operation and dam safety management practices. The understanding of the landside mechanism during reservoir operation is crucial to landslide‐related risk migration. During the reservoir operation from 2018 to 2021, a massive landslide occurred with over 107 m3 in total volume on the bank of the NE reservoir. The surface movement characteristics before and after the occurrence of landslides in the NE reservoir in the region scale were detected and interpreted by Sentinel‐2 time series images. Experimental studies were conducted to investigate the geotechnical properties of the fine‐grained soil. The slope stability was evaluated for a typical slope profile considering the rising water level using the extended Bishop's simplified method, which was implemented in the code STAB‐UNSAT. It can be found that the landslide in the fine‐grained soil occurred simultaneously when the water level rose. The cumulative area of soil slope failure on the left bank of the NE reservoir increased continuously during the reservoir operation from 2018 to 2020, especially had a remarkable increment from August to October in 2019. The extended Bishop's simplified method provides a more rational method to evaluate the soil slope stability. The slope failure mechanism of the studied soil, that is, collapse–erosion–slide upon the rising reservoir water has been proposed.