Local seismic amplification as a key factor in the instability of dangerous rock masses during earthquakes: a case study

Dangerous rock masses pose a widespread threat to hydraulic and hydropower engineering. This study investigates the seismic response and progressive failure of a dangerous rock mass on a reservoir bank using field surveys, high-resolution satellite imagery, and numerical simulations. A 3D geological model was developed to assess the rock mass stability, with the Factor of Safety (FOS) indicating that it is in a state of limit equilibrium under static conditions. The dynamic analysis was validated through shake table tests, revealing that the rock mass failed in four stages under seismic loading: tilting toward the free face, disintegration, sliding, and accumulation on the lower platform. The seismic response exhibited significant amplification of the dangerous rock mass area, particularly at its boundaries, which is a key reason for the instability of the dangerous rock mass under seismic loading. This amplification is attributed to two mechanisms: (1) the reflection and refraction of seismic waves at undulating terrain, leading to localized energy concentration, and (2) the generation of surface waves at unloading and free surfaces, which interacted with incident waves, further amplifying the effects at the rock edges. These findings provide valuable insights and theoretical guidance for assessing the dynamic stability of dangerous rock masses.