Influence of extremely rapid cyclic reservoir water level fluctuations on bank slope stability: Insights from model testing and numerical simulation of a pumped storage power station slope

The upper reservoirs of pumped storage power stations are subject to extremely rapid water level fluctuations, with daily variations of several tens of meters. These abrupt changes can trigger substantial slope deformations and failures, thereby threatening the structural integrity and operational safety of the facility. This study focuses on a representative slope within the upper reservoir of a pumped storage power station in eastern China. Physical model testing and numerical simulation are integrated to examine seepage behavior and deformation characteristics under extremely rapid cyclic water level fluctuations. Results show that water content, pore water pressure, and soil pressure respond synchronously with water level changes, while matric suction exhibits a delayed response. The groundwater line within the slope displays pronounced hysteresis relative to reservoir levels, and horizontal displacement initiates at the slope toe and propagates upward and inward. Slope stability deteriorates nonlinearly with increasing fluctuation cycles, and faster drawdown rates further exacerbate slope instability. The deformation and failure process of silty clay slopes under these conditions can be categorized into four progressive stages: (1) seepage-induced internal erosion, (2) accumulated shear creep, (3) accelerated damage coalescence, and (4) overall failure. These findings provide valuable theoretical guidance for the monitoring, prevention, and mitigation of geohazards in silty clay slopes under highly dynamic hydrological conditions.