Research on types of coal mine tremor and propagation law of shock waves

Aiming at the problems of the lack of quantitative indicators for the classification of coal mine tremor,the unclear propagation law of mine tremor,and the difficulty of identifying dangerous mine tremor. Methods of numerical simulation,theoretical analysis and field measurement are used in this study. Types of mine tremor are proposed. Through UDEC numerical simulation,the propagation process of shock wave in jointed rock masses is reproduced. Combined with micro-seismic monitoring data,the attenuation law of the peak velocity of the particle and the energy of the shock wave are analyzed during the propagation process. And the method of distinguishing dangerous mine tremor is discussed. The results show that:coal mine tremor can be divided into three types:induced by mining fracture,induced by broken of huge overlying strata and high-energy mine tremor. The high-energy mine tremor can be subdivided into failure of coal,roof instability,and fault activation. According to whether or not mine tremor is destructive,mine tremor can be divided into two categories:normal mine tremor and dangerous mine tremor. The propagation of shock wave in mines is affected by many factors,and the discontinuities in coal and rock masses have significant effects on the propagation of shock wave. The blocking mechanism of shock wave stress transmission on the discontinuous surface has been revealed:when the superposition of the stress transmitted by shock wave and original stress exceeds the strength of discontinuity surface,the discontinuity surface will failure and a certain displacement will occur,and the propagation of shock wave will be blocked because of discontinuity of the medium. During the propagation process of a mine tremor,there is an internal connection between the peak velocity of the particle and the energy of the shock wave,and there is a negative exponential relationship between the peak velocity or energy with the propagation distance. The velocity absorption coefficients of the solid coal area and the goaf area are 0.003 75 and 0.007 6,respectively,and the energy absorption coefficients are 0.007 5 and 0.015 2,respectively. There are obvious differences in the attenuation of shock wave in the two areas. The discontinuity has a significant impact on the propagation of shock waves,which verifies the correctness of the numerical simulation.