深埋隧洞TBM掘进微震与岩爆活动规律研究

Activity laws of microseisms and rockbursts in deep tunnels by TBM tunneling

以锦屏二级水电站TBM开挖的深埋隧洞为工程背景,基于微震监测数据和岩爆实例,研究了深埋隧洞TBM掘进过程中微震与岩爆时空分布特征及岩爆孕育过程微震演化规律。结果表明:(1)微震活跃期和岩爆高发期处于TBM作业时段及停机后的1 h以内;微震活动范围主要介于掌子面后方3倍洞径至前方0.4倍洞径之间,其峰值位于掌子面后方0.8倍洞径附近;而岩爆主要发生在掌子面后方2倍洞径以内,尤其是掌子面后方1倍洞径以内是岩爆高发区;可见,微震与岩爆具有良好的时空相关性。(2)在时间序列上,微震能突增现象,以及累积视体积快速上升而Schmidt数急剧下降的现象均属微震活动异常,属岩爆前兆。(3)在空间序列上,微震事件逐渐向某个区域高度集结且大震级高能量事件不断增多的现象属微震活动异常,预示高岩爆风险,属岩爆前兆。

For the deep tunnel of Jinping II Hydropower Station excavated by TBM, based on the seismic monitoring data and rockbursts, the temporal and spatial distribution characteristics of microseismic events and rockbursts and evolution laws of microseismicity information during the preparation process of rockbursts are studied. The conclusions are drawn as follows： （1） The active period of microseisms and the peak period of rockbursts are the working time and within one hour after stopping working for TBM. The microseismic activity mainly ranges from 3 times the tunnel diameter behind working face to 0.4 times ahead, and its peak value is located at 0.8 times the tunnel diameter behind working face. The rockbursts mainly occur within the region 2 times the ttmnel diameter behind working face, especially the high-risk zone of rockbursts lies in the region as large as 1 times the tunnel diameter behind working face. Therefore, there is certain space-time relativity between the microseisms and the rockbursts. （2） A sudden increase of microseismic released energy or the steep rise of cumulated apparent volume （CAV） with a sharp drop of Schmidt number in the time sequence is an microseismic anomaly, which is a premonition of rockbursts. （3） The spatial distribution pattern of mircroseismic events shows a transformation from random to clump distribution in certain zone with time, and the degree of their clump dispersion pattern gradually increases, simultaneously accompanied by a growing number of microseismic events with large magnitude and high energy, that is, it is an microseismic anomaly and also a premonition of rockbursts.