Abstract: 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.

Key words: rock fracture, fracture surface, movement direction, moment tensor, strain-structural plane slip rockburst, pregnant process, microseismic monitoring