Yaocheng Lv

Reservoir landslides pose a persistent threat to the safe operation of hydropower projects, particularly where altered rock masses within water-level fluctuation zones undergo repeated wetting–drying and seepage-induced deterioration. This study investigates the mechanical behavior and long-term strength evolution of altered granite from the Guobu Slope near the Laxiwa Arch Dam in Qinghai, China. Rock masses with four alteration degrees, ranging from complete to slight alteration, were examined through an integrated experimental program involving torsional shear tests, hydro-mechanical coupled triaxial tests, large-scale direct shear and ring shear tests, Brazilian splitting tests, and long-term P-wave velocity monitoring. The results demonstrate that increasing water content progressively weakens the shear strength of altered granite, while elevated seepage pressure further reduces its strength and deformation resistance under hydro-mechanical coupling. Residual shear behavior also shows a clear dependence on water content, indicating that post-peak strength deterioration should be considered in slope stability assessment. Long-term P-wave monitoring further reveals that mechanical degradation is more pronounced during the early stage and gradually approaches a relatively stable state, suggesting a site-specific decelerating deterioration process rather than unlimited strength loss. Based on the experimental results, empirical relationships between shear-strength parameters and water content are established, and long-term lower-bound strength parameters are proposed for altered granite with different degrees of alteration. These findings provide experimental support for understanding the hydro-mechanical deterioration and long-term deformation behavior of reservoir-bank altered rock masses and offer a basis for parameter selection and stability assessment when combined with rock-mass reduction, field calibration, and sensitivity analysis.

Reservoir-bank landslides may become unstable after reservoir impoundment and generate impulse waves, posing serious threats to hydropower hub structures, reservoir navigation, and downstream safety. The H1 landslide, with a volume of approximately 5.35 million m³, is located on the left bank of the near-dam reservoir area of Yangqu Hydropower Station. Reservoir operation and water-level fluctuations may affect the stability of the H1 landslide; if instability occurs, rapid water entry could generate impulse waves that threaten the hydraulic structures. To evaluate the impulse-wave hazards associated with the H1 landslide, a three-dimensional physical model was constructed at a geometric scale of 1:200. Representative experiments were conducted under landslide instability volumes of 100 × 10⁴, 200 × 10⁴, and 500 × 10⁴, reservoir water levels of 2710.0 m and 2715.0 m, and the corresponding prototype-oriented water-entry conditions. The generation, propagation, opposite-bank run-up, and wave responses in front of the hydraulic structures were investigated. The results show that both the initial wave height near the water-entry point and the wave height in front of the hydraulic structures increase with increasing landslide volume. At the water-entry point, the maximum wave height increases from 3.10–3.27 m for the 100 × 10⁴ m³ landslide to 4.50–4.64 m for the 200 × 10⁴ m³ landslide and further to 7.18–7.21 m for the 500 × 10⁴ m³ landslide. In front of the hydraulic structures, the maximum wave height at the spillway reaches 5.61 m for the 200 × 10⁴ m³ landslide under the ecological restricted water level of 2710 m. After superposition with the wind-wave run-up, the corresponding total wave elevation is 2718.8 m, which remains below both the dam crest elevation of 2721.0 m and the wave-wall crest elevation of 2722.2 m. However, under the normal pool level of 2715 m, the total wave elevations at the spillway and power station intake after superposition with wind-wave run-up exceed the wave-wall crest elevation, indicating a potential overtopping risk. The research results provide a scientific basis for reservoir impoundment scheduling, landslide-generated impulse wave risk prevention, and the safety protection of key hydraulic structures at Yangqu Hydropower Station.