白鹤滩水电站地下厂房开挖过程微震特征分析

 白鹤滩水电站左岸地下厂房规模巨大，开挖卸荷导致局部围岩破坏问题突出。为研究开挖扰动下围岩破坏演化机制及变形机制，通过构建微震监测系统，开展地下厂房开挖卸荷过程微震实时监测。监测结果表明：(1) 微震活动与爆破开挖密切相关，地下厂房第一层开挖过程中，形成3个潜在失稳区域：主厂房4#与5#机组之间下游侧拱肩、主厂房6#与7#机组之间上游侧拱肩和主厂房8#机组顶拱至主变室顶拱的条带状区域。(2) 开挖强度以及断层构造主导下聚集的微震事件矩震级、Es/Ep等参数特征有所差异，由此引起的围岩潜在破坏形式不同，微震活动特征可为微震聚集区围岩提供针对性施工参考。(3) 局部围岩外观变形前的数日内，微震事件在该区域迅速聚集，同时视应力显着增加，累积视体积基本稳定。研究结果可为白鹤滩水电站左岸地下洞室群后期开挖和支护提供重要参考。

Microseismic characteristic analysis of underground powerhouse at Baihetan hydropower station subjected to excavation

Because of the large size of the underground powerhouse of Baihetan hydropower station at left bank，the local failures of surrounding rock occurred frequently subjected to excavation. To study the mechanisms of rock deformation and failure subjected to unloading caused by excavation，an ESG(Engineering Seismology Group) monitoring system was applied to monitor the microfractures in real time during the excavation processes in the underground powerhouse. Microseismic(MS) activity was found to be in good agreement with the excavation. Three potential failure zones of the underground powerhouse under the first layer excavation were revealed，i.e.，the downstream spandrel between unit 4 and unit 5 of the main powerhouse，the upstream spandrel between unit 6 and unit 7 of the main powerhouse，and the crown above unit 8 of the main powerhouse to the crown of the transformer chamber. The moment magnitudes and Es/Ep of microseismic clusters controlled by the excavation strength and faults were very different，resulting in the different potential failure modes of surrounding rock. The targeted supports should be adopted in the MS clusters based on the evolutional MS characteristics. Several days before the local deformation of the surrounding rock，the area manifested with the accelerated cluster of MS events，quick increase of the apparent stress，but rare change of the cumulative apparent volume.