岩体掉块是在地下洞室开挖过程中容易遇到的破坏灾害之一.为客观评价爆破开挖引起的地下交叉洞室岩体掉块的微震活动及震源机制,在白鹤滩水电站母线洞安装了6个单轴加速度计和8个单轴检波器,开展原位微震监测试验.在时域上,生产爆破的微震活动响应表明,爆破后3 h内,微震活动处于活跃阶段.在空间域上,随着工作面的推进,开挖区周围的应力集中分布,岩体的破坏和劣化逐渐加剧.微震事件的活动区域与应力集中区域一致.基于矩张量反演法分析破裂机理可知,地下交叉洞室岩体掉块的破裂机理以拉张断裂为主.研究结果可为类似地下洞室围岩的稳定性分析、爆破开挖及支护优化等问题的重新思考提供重要参考依据.
Block falling is a rock mass damage disaster that is easily encountered during the excavation of underground caverns. To objectively assess the microseismicity and focal mechanism of block falling of underground intersecting chamber induced by blasting excavation, an array of six uniaxial accelerometers and eight uniaxial geophones were installed around the busbar chamber of underground cavern group of the Baihetan Hydropower Station in China. In the time domain, the seismicity response to production blasting reveals that within 3 h after blasting, microseismicity is in an active phase. In the spatial domain, with the advance of working face, the concentrated stress is distributed around the excavation region, and the damage and deterioration of the rock mass are gradually intensified. The active area of microseismic (MS) events is consistent with the stress concentration region. By analyzing the fracture mechanism based on the moment tensor inversion method, it can be seen that the fracture mechanisms of block falling of the intersecting chamber are dominated by tensile fracture. The research results could provide crucial guiding reference for stability analysis, as well as for rethinking the blasting excavation and support optimization of rock masses in similar large underground cavern.