分幅开挖方式下高应力硬岩地下洞室的微震特性及稳定性分析

高应力硬岩大型地下洞室开挖卸荷导致围岩片帮、塌方事故频发，严重威胁现场施工人员及设备的安全。从降低围岩局部破坏风险的角度考虑，白鹤滩水电站右岸主变室第Ⅳ层采用分幅开挖方案。通过构建微震监测系统，研究分幅开挖下岩体的微震特性及稳定性，监测结果表明：上游半幅开挖诱发的微震事件、能量大于下游半幅诱发的，且上、下游半幅开挖均表现出了掌子面贯通前微震事件、能量增大的特性，这主要受两相向掘进掌子面前方支承压力叠加的影响；上游半幅开挖诱发微震事件频发且出现了丛集现象，下游半幅开挖诱发的微震事件较少且事件空间分布离散，规律性不明显；采用Schmidt数、事件活动率与累积视体积、能量指数与累积视体积评价研究区域的稳定性，结果显示，较之于应变硬化阶段，处于应变软化阶段的岩体发生不稳定变形破坏的风险较大。研究结果可为白鹤滩水电站地下洞室施工方案的优化提供重要参考，同时也可为其他类似工程的施工提供借鉴。

Analysis of microseismic characteristics and stability of underground caverns in hard rock with high stress using framing excavation method

Excavations of large-scale hard-rock underground caverns with high stress often result in rib spalling and collapse of surrounding rock, threatening the safety of on-site builders and equipment. From the perspective of reducing the risk of local failure of surrounding rock, framing excavation method was adopted in the fourth floor of the right transformer chamber of the Baihetan hydropower station. In order to study the microseismic (MS) characteristics and stability, MS monitoring was carried out in the right transformer chamber. The results show that: By the excavation of upstream rock, the number of MS events and energy release were greater than the downstream rock. In the process of working face advancing, the number of MS events and the energy increased, which was in accordance with the overlay abutment pressure. When the upstream rock was excavated, the excavation unloading induced seismic events and the cluster phenomenon. In contrast, the excavation of downstream rock only induced few MS events. The Schmidt number, the activity rate, the cumulative volume, and the energy index were combined to evaluate the stability of the study area. The study found that compared with the strain hardening phase, the rock mass in the stage of strain softening has a greater risk of unstable deformation and failure. The results can provide valuable reference to the optimization of construction scheme of the Baihetan hydropower station. At the same time, the results can also provide reference to other similar projects of construction.