白鹤滩柱状节理玄武岩隧洞开挖微震活动时空演化特征

TEMPERAL-SPATIAL CHARACTERISTICS OF MICROSEISMIC ACTIVITY IN COLUMNAR JOINTED BASALT IN TUNNELLING AT BAIHETAN HYDROPOWER STATION

金沙江白鹤滩水电站导流洞III1类柱状节理玄武岩发育,开挖过程中松弛破坏明显,对施工人员安全及施工进度造成严重影响。基于微震监测技术对白鹤滩柱状节理玄武岩导流洞开挖全过程进行研究,沿隧洞轴向方向,柱状节理玄武岩微震活动集中于开挖掌子面附近,服从三参数Logistic分布。掌子面附近及其后方微震活动分布可分为3个区域:开挖强卸荷区、综合影响区和时效松弛区,在开挖强卸荷区范围内应完成锚杆支护。隧洞开挖过程中,柱状节理玄武岩微破裂由隧洞边墙快速向围岩内部发展,当掌子面距离较远时,边墙内微破裂活动较微弱,微破裂集中区最终稳定在距边墙6 m范围内。降低开挖速率能有效减弱开挖卸荷对柱状节理玄武岩的影响。所得认识和结论对微震监测技术的应用以及柱状节理隧洞开挖方案和支护措施的优化具有参考意义。

Due to the developed columnar joints in basalt III1 around the diversion tunnel at Baihetan Hydropower Station along the Jinsha River,the relaxation and failure of basalt with columnar joints during the excavation had the severe influence on the personnel and construction progress. Microseismic monitoring technology was utilized during the excavation of columnar jointed basalt. Along the tunnel,the microseismic activity in columnar jointed basalt was found to obey the Logistic(3P) distribution. Three typical microseismic activity zones in columnar jointed basalt along the tunnel near the working face were obtained, i.e., a strong unloading area, a comprehensively influenced area and a time relaxation effect area. Rock bolting should be completed in the strong unloading area. In the period of working face around the researched area,the fractures developed rapidly into the inner rockmass. When the working face was far away,the microseismic activity in the sidewall was weak. Meanwhile,the area of micro-fracture concentration stabilized in the ranges of 6 meters in sidewall finally. A low excavation rate weakened the influence of unloading of excavation on columnar jointed basalt.