Numerical Simulation Of Spatiotemporal Distributions Of Stresses On The Normal Fault And In The Vicinity Of The Fault Induced By Coal Extraction

Studies on stress distributions of the fault and the coal and rock strata in the vicinity of the fault are especially important for us to predict and prevent mining earthquakes,rockbursts induced by fault slip and to analyze their mechanisms induced by coal extraction.A numerical model was built in FLAC^3D,which is based on the geological condition of the 6303 working face of Yankuang Group Jisan Coal Mine.In the model,thirteen rock strata and one normal fault whose dip is 45°were included.Interface elements were used to model fault and strata contact surfaces.Twenty-two monitored nodes were arranged at the hanging wall of the fault.Spatiotemporal distributions of stresses on the fault were obtained as the working face advanced to the normal fault from the footwall and the hanging wall,respectively,and a numerical model which include a reverse fault was built for contrast.Spatiotemporal distributions of vertical,horizontal and shear stress fields including the stresses of the coal seam were obtained as the working face advanced to the normal fault from the footwall and the hanging wall,respectively.The following results are obtained.As the working face advances to the normal fault from the footwall,the maximum size of the loosening zones is about 113m,and the minimum size is about 64m.As the working face advances to the normal fault from the hanging wall,the maximum size of the loosening zones which are above the compressing zone is about 78m,and the minimum size is about 35m.As the working face advances to the reverse fault from the footwall,the maximum size of the loosening zones is about 127m,and the minimum size is about 21m.As the working face advances to the normal fault from the footwall,the decreasing normal stresses are found once each excavation is completed instantaneously.The determined dangerous fault segments after each instantaneous excavation are mainly in the front of the loosening zone according to a decrease of the safety factor.According to the viewpoint that an increase shear stress in the loosening zone will increase the dangerous extent of the fault slip,the determined dangerous fault segments are mainly in the front of the loosening zone between two excavations.As the working face advances to the normal fault from the hanging wall,fault segments in the loosening zones which are above the compressing zone become dangerous when the coal wall of the working face is close to the fault.As the working face advances to the reverse fault from the footwall,the determined dangerous fault segments are mainly at the ends of the loosening zones between two excavations when the horizontal distance between the fault and the coal wall of the working face is 100m,60m,40m or 10m.As the working face advances to the normal fault from the footwall,the vertical,horizontal and shear stress concentration regions in the vicinity of the working face are close to the fault and begin to be influenced by the fault barrier effect when the horizontal distance between the fault and the coal wall of the working face is 40m-50m.As the working face advances,these stress concentration regions progressively extend toward the hanging wall.For the same distance between the coal wall of the working face and the fault,usually,the fault barrier effects on vertical,horizontal and shear stresses are weakened in due order.When the distance decreases to 20m from 50m,the fault barrier effect is enhanced.As the working face advances to the normal fault from the footwall,usually,the maximum vertical and horizontal stresses of the coal seam or their peak stresses in the vicinity of the coal wall of the working face when the distance between the fault and the coal wall of the working face is 20m or 30m are 10.5m and 11.5m-13.5m ahead of the coal wall of the working face,respectively.The maximum value of the shear stress is 11.5m-14.5m ahead of the coal wall of the working face.As the working face advances to the normal fault from the hanging wall,the peaks of vertical,horizontal and shear stresses of the coal seam in the vicinity of the coal wall of the working face in the hanging wall firstly increase and then decrease,and their locations are 7.5m-10.5m,10.5m-15.5m and 11.5m-12.5m ahead of the coal wall of the working face,respectively.In this paper there are 26 Figures,6 tables and 60 references.