Abstract: The underground powerhouse of Lianghekou hydropower station is located in the high geostress area. Under the influence of excavation, a series of problems, such as surrounding rock instability and rock burst, are prone to occur. Based on the ESG monitoring system of the underground powerhouse, this paper analyses the laws of micro-seismic (MS) events during excavation by comparing with data from the regular stress monitoring system, to provide timely warning for rock mass instability. The results show that: (1) the excavation of bus tunnels No. 3 and No. 4 has triggered a large number of MS events, and the sudden increase of the number of MS events could be seen as a sign of surrounding rock deformation; (2) during the process of rock deformation, the central frequency of MS events goes down first and then up. These characteristics, indicating the development of micro fractures in rock mass, can be used as an important index for prediction of rock mass damage. The results can provide reference for excavation and support of underground caverns of hydropower stations.

Key words: micro-seismic monitoring, underground cavern, frequency characteristics, S transform

摘要： 两河口水电站地下厂区位于高地应力区，受工程开挖影响，易发生围岩失稳、甚至岩爆等一系列工程安全问题。基于两河口水电站地下厂房的微震监测系统，分析开挖过程中工程岩体破裂微震信号特征的变化规律，并结合锚杆应力计的应力监测数据，为工程岩体失稳及时提供预警。研究结果表明：（1）微震事件活动特征与工程开挖密切相关，3、4号母线洞开挖引发了大量微震事件，微震事件数目的突增可以作为围岩变形预警的前兆；（2）在岩体发生变形的过程中，微震信号的中心频率呈现先下降后上升的特征，预示了岩体内部微裂隙的产生与不断发展，逐渐形成大裂纹的过程，该特征可作为岩体破坏预警的重要指标。研究结果可为水电站地下洞室开挖与支护提供新思路。

关键词: 微震监测, 地下洞室, 频率特征, S变换