Study on low-frequency disturbance damage mechanism of sandstone based on AE wave velocity change

Accurate evaluation of surrounding rock bearing capacity deterioration is essential to ensuring the operational safety of closed or abandoned mines converted into underground pumped-storage hydropower (UPSH) stations. In this study, uniaxial compression tests were conducted on sandstone subjected to various static prestress levels under low-frequency disturbance. Coupled with acoustic emission wave velocity and microcrack evolution analysis, the degradation mechanism of sandstone strength under disturbance conditions was systematically explored. The results indicate that with the increase of static prestress levels, the wave velocity along the loading direction increases logarithmically, whereas the velocity perpendicular to the loading direction exhibits a nonmonotonic trend—first increasing and then decreasing. The change of wave velocity in the vertical loading direction shows greater sensitivity to damage induced by static prestress. After low-frequency disturbance, the sandstone strength degradation rate (SDR) initially decreases and then increases as static prestress increases, which correspond closely to the trend in the absolute value of wave velocity change rate along the loading direction. The smallest SDR of sandstone occurs at a static prestress level of 48.98% of the uniaxial compressive strength (UCS), while the minimum rate of change in wave velocity along the loading direction is observed at a static prestress level of 42.20% UCS. Furthermore, an empirical relationship between the SDR caused by disturbance and the wave velocity change rate along the disturbance loading direction was obtained. These findings provide a theoretical basis for the application of real-time seismic source wave velocity field inversion imaging techniques to quantify disturbance-induced damage in the surrounding rock of underground engineering such as UPSH stations.