Study On Reactivation Characteristics Of F16 Fault In Gengcun Coal Mine Under Mining Disturbance

Fault is a common geological structure.Fault activation instability may be affected by mining disturbance,resulting in serious mine pressure,and even lead to rock burst,coal and gas outburst accidents.Gengcun coal mine is located in the western Yima coalfield,F16 fault runs through the southern coalfield.The possibility of activation and instability of F16 fault increases with the coal mining face approaching.Therefore,taking F16 fault of Gengcun Coal Mine as the research object,this paper makes an in-depth study on the activation characteristics of F16 fault in the mining process of 13200 coal mining face.It provides theoretical guidance for the safe mining of Gengcun Coal Mine and adjacent mines in Yima mining area.The paper adopts the method of combining theoretical analysis,FLAC^3D numerical simulationand field measurement,and takes the F16 fault of Gengcun Coal Mine as the background,establishes a two-dimensional fault mechanics model and analyzes the influence of mining stress on the activation of the fault.Based on the Mohr-Coulomb criterion and Perturbation-Response criterion analyze the effect of shear stress and normal stress on fault activation instability.Using the FLAC^3D numerical simulation software,the numerical model under the condition of the oblique intersection of the F16 fault and the 13200 coal mining face was established,and the mining stress distribution law during coal mining,the normal stress,the shear stress,the ratio of shear stress to normal stress,and the slip of the F16 fault plane were studied.the critical distances for activation and instability of the fault plane at 160 m and 280 m in the coal mining face were analyzed.The"anchor cable tension+measuring tube displacement"monitoring method of fault activation characteristics was designed and applied in the field,and the sliding amount of the coal-rock interface of the F16 fault and the change law of the fault anchor cable tension during the mining process of the 13200 coal mining face were studied.The research results show that the fault stability is proportional to the buried depth of the coal mining face and the stress concentration factor of the stope,and is inversely proportional to the lateral pressure coefficient;the relative increase of shear stress and the relative decrease of normal stress can make the fault in a state of activation and instability.During the coal mining of 13200,a large advance support pressure is formed in the lower coal seam of the direct top of Jurassic system and the lower coal seam of the bottom end of F16 fault plane,and the advance support pressure in the extremely thick coal seam belt is relatively small;the mining stress distribution is discontinuous at the F16 fault plane,and the stress at the F16 fault plane is obvious lower than the surrounding rock mass.The normal stress of F16 fault plane in front of coal wall increases first and then decreases,and the shear stress of F16 fault plane decreases gradually.Taking the ratio of shear stress to normal stress greater than 0.27 as the fault activation instability index,When the coal mining face is recovered 120～160 m,the fault plane at 160 m of the coal mining face may be in a state of activation instability,and the critical distance of the activation instability of the fault plane at 160 m of the coal mining face is 40 m;when the coal mining face is recovered of 240～260m,the middle of the fault plane of 280 m of the coal mining face may be in a state of activation instability,the bottom of the fault plane is relatively lagging 20 m in the activation instability state,and the critical distance of the activation instability in the middle of the fault plane at 280 m of the coal mining face is 40 m.The critical distance for activation instability at the bottom of the fault plane is 20 m..The F16 fault was in an unstable state during the monitoring period,resulting in a significantly higher growth rate of the tensile force value of the fault anchor cable B than that of the coal seam anchor cable A;In the upward trend,the cumulative value of the slip of the coal-rock interface of the F16 fault is 100 mm;during the monitoring period,when the coal mining face is about 40 m away from the monitoring point,the slip of the monitoring point increases significantly,with an increase of 50 mm,and the fault is in an unstable state.The paper has 43 figures,5 tables,and 61 references.