正、逆断层下盘开采断层及其附近煤层应力时空分布的数值模拟

Numerical simulation of spatiotemporal distributions of stresses on the fault and coal seam in the vicinity of the fault for mining in the footwall of the normal and reverse fault

研究采动条件下断层及其附近煤层应力的时空分布规律对于矿震和断层冲击矿压的机理分析及预防具有重要意义.针对兖矿集团济三煤矿6303工作面,建立了正断层下盘开采的FLAC3D数值模型,并建立了相应的逆断层下盘开采的数值模型以进行对比.通过计算分别获得了正、逆断层下盘开采断层及其附近煤层应力的时空分布规律.得到了下列结果.对于逆断层下盘开采,松动区的范围最大约为127 m,最小约为21 m.根据松动区切应力上升会增加断层滑动危险的认识,当工作面煤壁距断层的水平距离分别为100 m、60 m、40 m和10 m时,处于滑动危险增加的测点通常位于松动区两端.对于正断层下盘开采,松动区的范围最大约为113 m,最小约为64 m,处于滑动危险增加的测点通常位于松动区前端.对于逆断层下盘开采,断层不容易滑动,断层附近积累的能量越来越高,发生断层冲击矿压的危险性较高.对于正断层下盘开采,断层更容易滑动,正断层附近不会积累较高的能量,发生断层冲击矿压的危险性较低.可通过考察断层附近煤层的应力差来评价断层阻隔效应强弱.对于正、逆断层下盘开采,当工作面煤壁距断层的水平距离相同时,断层对垂直应力的阻隔效应最强,对水平和切应力的阻隔效应较弱.

Studies on stress distributions of the fault and the coal seam in the vicinity of the fault are especially important to predict and prevent mining earthquakes and rockbursts induced by fault slip and to analyze their mechanisms induced by mining.A numerical model of mining in the footwall of a normal fault was built in FLAC3 D,which is based on the 6303 working face of Yankuang Group Jisan Coal Mine.A corresponding numerical model of mining in the footwall of a reverse fault was built for contrast.In each model,thirteen rock strata and one fault whose dip is 45°are included.Interface elements are used to model fault and strata contact surfaces.Twenty-two monitored nodes are arranged at the hanging wall of the fault.Spatiotemporal distributions of stresses of the fault and the coal seam in the vicinity of the fault were obtained as the working face advanced from the footwall of the normal and reverse fault,respectively.The following numerical results were obtained.For mining in the footwall of the reverse fault,the maximum and minimum sizes of loosening zones are about 127 m and 21 m,respectively.For mining in the footwall of the reverse fault,according to the viewpoint that an increase shear stress in the loosening zone will increase the dangerous extent of fault slip,dangerous fault segments are mainly at ends of loosening zones when the horizontal distance between the fault and the coal wall of the working face is 100 m,60 m,40 m,and 10 m.For mining in the footwall of the normal fault,the maximum and minimum sizes of loosening zones are about 113 m and 64 m,respectively,and dangerous fault segments are mainly in the front of loosening zones.For mining in the footwall of the reverse fault,high strain energy is accumulated in the vicinity of the reverse fault hard to slip,and the risk of rockbursts induced by fault slip is high,but not vice versa for mining in the footwall of the normal fault.Stress differences of the coal seam in the vicinity of the fault were used to assess the extent of the fault barrier effect.For mining in the footwall of the normal or reverse fault,fault barrier effects on horizontal and shear stresses are weaker than on the vertical stress effected greatly for the same distance between the coal wall of the working face and the fault.