The characteristics of rock instability precursors and the principal stress direction are very crucial for the prevention of geological disasters. This study investigated the qualitative relationship between rock instability precursors and principal stress direction through wave velocity in rock acoustic emission (AE) experiments. Results show that the wave velocity variation exhibits obvious anisotropic characteristics in 0%–20% and 60%–90% of peak strength due to the differences of stress-induced microcrack types. The amplitude of wave velocity variation is related to the azimuth and position of wave propagation path, which indicates that the principal stress direction can be identified by the anisotropic characteristics of wave velocity variations. Furthermore, the experiments also demonstrate that the AE event rate and wave velocity show quiet and stable variations in the elastic stage of rock samples, while they present a trend of active and unstable variations in the plastic stage. It implies that both the AE event rate and wave velocity are effective monitoring parameters for rock instability. The anisotropic characteristics of the wave velocity variation and AE event rate are beneficial complements for identifying the rock instability precursors and determining the principal stress direction, which provides a new analysis method for stability monitoring in practical rock engineering.

岩石失稳前兆的特征和主应力方向对地质灾害的防治至关重要。本研究通过岩石声发射 (AE) 实验中的波速研究了岩石不稳定前兆与主应力方向之间的定性关系。结果表明，由于应力诱发微裂纹类型的不同，波速变化在峰值强度的0%~20%和60%~90%范围内表现出明显的各向异性特征。波速变化的幅度与波传播路径的方位角和位置有关，这表明主应力方向可以通过波速变化的各向异性特征来识别。此外，实验还表明，AE 事件率和波速在岩石样品的弹性阶段表现出平静而稳定的变化，而在塑性阶段则呈现出活跃和不稳定变化的趋势。这意味着声发射事件率和波速都是岩石失稳的有效监测参数。波速变化和声发射事件率的各向异性特征是识别岩石失稳前兆和确定主应力方向的有益补充，为实际岩石工程中的稳定性监测提供了一种新的分析方法。这意味着声发射事件率和波速都是岩石失稳的有效监测参数。波速变化和声发射事件率的各向异性特征是识别岩石失稳前兆和确定主应力方向的有益补充，为实际岩石工程中的稳定性监测提供了一种新的分析方法。这意味着声发射事件率和波速都是岩石失稳的有效监测参数。波速变化和声发射事件率的各向异性特征是识别岩石失稳前兆和确定主应力方向的有益补充，为实际岩石工程中的稳定性监测提供了一种新的分析方法。