Study on the Reactivation Mechanism of Typical Reservoir Bank Deposits under High Water Level and Large Fluctuation Conditions

The historical activity of the Xianshuihe fault has resulted in the formation of numerous large to giant landslide deposits along both banks of the Xianshuihe River. The impoundment associated with the hydropower project has significantly altered the hydrological environment of these deposits. To investigate the reactivation mechanisms of landslide deposits under high water level and large fluctuation conditions，this study uses the Jiaowu landslide deposit in the Xianshuihe reservoir area of the Lianghekou Hydropower Station as a case study. Through field engineering geological surveys，drone-based aerial photography，satellite remote sensing interpretation，and numerical simulations，this study identifies the spatial structural characteristics and failure mechanisms of the Jiaowu deposit. This research elucidates the deformation characteristics and reactivation mechanisms of the landslide deposits under high water level and large fluctuation conditions. The results indicate that the deformation characteristics of the Jiaowu landslide deposit exhibit significant spatial and temporal variation. Geological conditions serve as the primary drivers of landslide deposit formation，with rock mass structure acting as the controlling factor，while high water level and large fluctuation conditions as the primary trigger for reactivation. The Lianghekou Hydropower Station reservoir experiences an unusual water level difference of 80 meters，from the dead water level to the normal storage level. These high water levels primarily impact the front slope by inducing extensive softening due to saturation，which results in a reduction in shear strength and instability at the toe of the rock-soil mass，leading to sliding，creating a free face，and inducing sliding of the rear part of the deposit under the influence of gravity. Comprehensive analysis suggests that the deformation mode of the Jiaowu landslide deposit involves sliding failure driven by frontal traction along the base-cover interface and gravity at the rear under high water level and large fluctuation conditions. This process occurs in three distinct stages: (a) Front-edge deformation stage，(b) Front-driven and rear-driven stage，and (c) Reactivation sliding stage. The primary reactivation mechanism occurs under high water level with large fluctuations, where prolonged reservoir water infiltration and erosion weaken the soil structure at the slope toe. This process induces localized loosening, crack expansion, and the formation of tensile fractures, ultimately leading to the loss of support at the slope front and resulting in slope instability and sliding.