Microseismic activity law and control methods in mega-fault structure area under the influence of extensive mining

To provide a reference for rock burst prevention and control in mega-fault structure area under the influence of extensive mining, the Balipu Fault (i.e. the drop reaches up to 100 meters) in Jining No. 2 Coal Mine has been selected as the engineering background for the study. The microseismic behavior of the entire mine as well as the footwall and hanging wall of the Balipu Fault was studied, and the fault activity was analyzed based on the accumulated microseismic energy. Additionally, the control methods of microseismic activities in mega-fault structure area were explored, and then the engineering application was carried out. Results show that: Under the influence of extensive mining, low-energy-level microseismic events were uniformly distributed in the mining face and roadway areas in the Jining No. 2 Coal Mine, which principally come from regular roof strata movement. There were no concentrated, continuous, and widely distributed microseismic events observed along the Balipu Fault plane. The microseismic events increased with the decrease of distance between the mining face and fault plane. It means that the mining can disturb the fault plane, but the current mining intensity was not enough to induce the fault activation. The highest cumulative energy of microseismic in the fault structure area exhibited an overall stable trend, but the concentrating position continuously varied as changing the mining conditions, particularly influenced by the mining speed and intensity. The effective solution is to leave a wide protective coal pillar for mitigating microseismic activity and achieving safe mining in mega-fault structure area, accompanied with reasonable roof pre-fracturing and coal pressure relief. Engineering practice was carried out in the 103_lower03 mining face of the Balipu Fault area based on the rock burst control strategy of different fault types. It was observed that the intensity of microseismic activity was noticeably weakened during the mining process. The total microseismic energy of one day decreased, while the microseismic frequency increased, indicating that a high frequency-low intensity of energy release.