Model test study on natural frequency evolution and early warning of reservoir landslides under water level fluctuations

Reservoir water fluctuation is the key factor affecting the stability of reservoir landslides. Existing research on the evolution of landslides under cyclic reservoir water fluctuations is limited. However, further research is needed focusing on the evolution of the first-order natural frequency of reservoir landslides. In this study, model tests were conducted to investigate the evolution of the stress, displacement, inclination angle and first-order natural frequency of reservoir landslides under different rates of water level fluctuations during cyclic reservoir water fluctuations. The tests demonstrated that cyclic fluctuations in the reservoir water level resulted in oscillatory increases in the pore water pressure and soil pressure; while, the effective stress exhibited an oscillatory decrease, leading to a reduction in the landslide stability. The landslide displacement and inclination angle exhibited periodic increases, without distinct stages of initial deformation, uniform deformation, or accelerated deformation. Regarding landslide failure below the water surface, the inclination angle was more sensitive than the displacement. Changes in the inclination angle preceded changes in the displacement, making this approach highly suitable for early warning of reservoir landslide instability. Before the occurrence of landslide failure, the development and connection of cracks led to fragmentation of the sliding mass into multiple smaller blocks with reduced masses, resulting in a drastic increase in the first-order natural frequency of the landslide. Changes in the first-order natural frequency preceded changes in the inclination angle and displacement, rendering this approach very suitable for early warning of reservoir landslides.