Analysis Of Floor Fault Activation Induced By Mining And Its Risk Of Water Inrush

During the mining process of fault-bearing coal seam on confined water,due to the combined action of mining mine pressure and confined water,the floor faults are activated,which makes it extremely easy for the confined water to enter the mining area through the faults and the risk of water inrush occurs,the water inrush problem of the floor faults seriously threaten the mining of coal resources and the safety of people and property.Therefore,this paper takes the 4104 fault-bearing working face of Guangxi Heshan No.3 Mine as the engineering background.Through the combination of theoretical analysis and numerical simulation,and analyzes the influence of mining on the activation of the floor fault and assesses the risk of water inrush.The results are as follows:(1)The mechanism of fault activation water inrush and the law of fault fracture propagation under the action of confined water are theoretically analyzed.By establishing a mechanical model of fault activation,the distribution of normal stress and shear stress of the fault under water pressure is derived.According to Mohr-Coulomb criterion,activation occurs when the shear stress of a fault exceeds its shear strength,the presence of confined water accelerates the activation of faults.Furthermore,based on the rule of mining pressure manifestation,a determination criterion for water inrush from the fault is established,and it is concluded that the smaller the fault inclination,the more likely it is to occur water inrush.By analyzing the activation of fault fractures by confined water,the activation and extension rules of tensile-shear and compression-shear composite fractures under different fracture angles and stress states are obtained.(2)The activation of faults with different dip angles of the floor during the mining process of working face under confined water is simulated and analyzed.Based on the theory of fluid-solid-damage coupling,the COMSOL Multiphysics numerical simulation software is used to simulate the effects of mining on the stress field,displacement field,damage evolution,and seepage field of floor faults with different dip angles.It is found that the smaller the dip angle of the fault affected by mining,the more likely it is to activate.Under the condition of the working face passing through faults with different dip angles,under the action of the first principal stress and additional shear stress,deformation and consequent damage to the floor fault,the damage area continues to expand along the fault to the coal seam,the A28°fault is damaged at a distance of 27.63 m from the coal seam,the B86°fault is damaged at a distance of 14.94 m from the coal seam,and the damaged areas are not connected with the confined aquifer.Affected by fault activation,the confined water flows along the fault to the coal seam,and the location of the sudden increase of the permeability coefficient of the two faults is consistent with the location of the damage.The water inflow of the floor reaches a maximum of10 m~3/h when the working face is advanced to the A28°fault,which does not exceed the drainage capacity of the mine.(3)Combining with the simulation results,the risk of water inrush on the faults is evaluated based on the critical conditions.According to the vertical stress distribution law of the floor,the damage depth of the coal seam floor and the distance between the peak stress line and the fault intersection with the floor near the fault.The difference of the A28°fault was-0.42 m,and the difference of the B86°fault was-23.11 m,it is found that none of them reach the conditions of the fault water inrush,so the working face will not have water inrush during the mining process.However,as the distance between the mining face and the fault decreases,the fault with small dip angle is gradually in the critical state of fault water inrush conditions,which is more prone to water inrush accidents.