Abstract: Based on the special faults structure condition of Beipiao mining area and the gas leakage situation after mines were closed, the three-dimensional finite element model was established using ANSYS software. The variation of stress field and displacement field were simulated under the condition of considering the effect of faults structure or not before and after mining. The contour charts of stress field in fault section and vertical displacements of special horizontal section etc. were presented. Some novel valuable conclusions were drawn based on the analysis and summary about rules of stress field and displacement field before and after mining. Those are that faults structure affects the laws of stress field and displacement field before and after mining; the gob is the original gas source concentration region; the maximal stress values exist in the top and lower ends of the adjacent between faults and gob. This leads to the gob gas diffusing to the adjacent region. Then gas leaks to the ground surface through the continuous fractures. So the faults are the important pathway of gas transport; caving region, fractures region and bending region are regarded as the secondary gas source concentration region. The numerical simulation supplies the scientific reference for faults structure effect on gas leakage, the region determination of the original and secondary gas source. The results have instruction rule for the utilization and usage of gas.

Key words: faults structure, Beipiao mining area, gas, surface leakage, gas source concentration region