基于微震信息的硬岩新生破裂面方位特征矩张量分析

Moment tensor analysis of attitude characterization of hard rock newborn fracture surface based on microseismic informations

为了更清晰直观地了解高应力下硬岩破坏(岩爆、片帮、应力型塌方等)孕育过程中岩石破裂演化过程,根据岩石破裂面的特点,依据微震监测数据的矩张量结果,推导并得到了岩体破裂面空间方位计算方法,在此基础上给出了根据运动夹角来判断岩石破裂类型的确定方法。借助此方法,在实例研究中进一步证明了深埋隧洞矩张量分解判断破裂类型分析方法的可靠性。依托锦屏二级水电站深埋引水隧洞这一典型工程,依据破裂面的方位角、倾角特征和岩爆宏观破坏情况,初步探究了即时性应变-结构面滑移型岩爆的孕育过程:在岩爆孕育初期,以张拉破裂为主,由于硬性结构面的存在,在开挖扰动应力调整初期,破裂面由岩体浅层往岩体较深层硬性结构面扩展,张拉破裂面尖端接近硬性结构面时,硬性结构面上发生剪切滑移,若较深层岩体内部还有其他硬性结构面存在,则在该硬性结构面尖端,除随着岩体浅层切向应力的持续增大,往开挖面扩展外,继续以张拉破裂面型式往深层扩展,至较深层硬性结构面上剪切破裂产生,最终以剪切滑移面为破坏面边界往开挖面发展,并最终将岩体抛掷而出。

For understanding rock crack initiation, propagation and development in hard rock destruction （rockburst, spalling, collapse etc.） pregnant process under high in-situ stress clearly, according to the observation and description of the characteristics of rock fracture surface, a method for calculating its attitude is presented here based on the moment tensor theory. The estimation of the fracture type using the motion angle is also conducted in this method. This method is applied to analyzing the formation mechanism of rockbursts encountered in the deep headrace tunnels in the Jinping II hydropower station. In the case study, in the estimation of rock fracture type, the technology of moment tensor decomposition is proved accurate. Based on the comprehensive study of the strikes and dips of rock fracture surfaces and the representation features of the pit of rockburst, it is concluded that strain-structure slip rockburst forms tension crack firstly; and cracks develop from the shallow into the deep in rock mass at the beginning of the excavation disturbance because of the surface of the rigid structure. When tensile crack tip is close to the surface of the rigid structure, the surface of the rigid structure will slide; and if there is the surface of the other rigid structure in the relative deeper rock mass, the first surface will continue to the deeper rock mass based on tensile cracks, except continuing to the excavation wall because of the tangential stress increase in the shallow rock mass. When tensile cracks deepen into the second surface, the surface slides. At last, the damaged rock mass is thrown out from the failure boundary which is assembled by the shear slip planes.