Characteristics of tremor time-space evolution and Coulomb stress distribution along the fault during workface excavation

In order to study the Coulomb stress variation along a fault face and the tremor distribution features under the mining disturbance,the elements which have effects on Coulomb stress of fault face were theoretically analysed on the basis of the geological and mining conditions of 1303 top-caving workface in Zhaolou Coal Mine,China. With nu- merical simulation and laboratory test,the Coulomb stress of different location along a reverse fault face was calculated as the distance between mining face and fault face decreasing. Additionally,the in-situ tremor data was collected and statistically analysed. The results show that the Coulomb stress ( f) of a fault face point is determined by the mining disturbance (including σx ,σy ,τxy and τyx ),the angle of the fault ( θ) and the frictional coefficient ( μ) of the fault face. If the mining disturbance and frictional coefficient are fixed,the most dangerous angle of the fault for sliping could be obtained by df / dθ = 0. Stress disturbance circle and displacement disturbance circle are formulated as the coal excavating,and the symmetry of the stress disturbance circle and the continuity of the displacement disturbance circle are broken because of the existence of fault. Numerical simulation data and laboratory test data all show that the upper zone of the fault face is influenced by the mining firstly,and the slipping liability of fault increases first and then decreases as the workface mining forward to the fault face. The daily frequency of tremors was about 20 per day as the workface located in footwall and increased to approximately 35 per day when the workface located in the hanging wall. However,the average energy for each tremor declined from 22 kJ before workface reach the fault to 4 kJ after the work- face passes the fault,which demonstrates that the tremor disturbance is severe as the workface moving forward to the fault,what is more,the concentration zone of tremor focus transfers from upper zone of the fault to down zone when the mining face mining through the fault face.