Study On The Evolution Characteristics And Its Applications Of Permeability In Working And Goaf When Using The Cutting Roof And Release Pressure Technique

The technology of roof cutting and pressure relief self driving has changed the way of roof pressure transmission and the characteristics of rock collapse,which has caused the change of the law of permeability evolution in the goaf,leading to the great difference between the law of air flow movement in the goaf and the traditional mining mode.Through theoretical analysis,numerical simulation and statistical analysis of field measured data,based on the analysis of the movement law of overlying strata in goaf and the change law of stress in goaf,this paper constructs the evolution model of porosity and permeability of porous media in goaf under the mode of top cut pressure relief self forming roadway.On this basis,the "Z-type" ventilation of top cut pressure relief self forming roadway is simulated Under the mode,the law of air flow movement in goaf is studied.The influence of measures such as air distribution volume,air inlet corner account and shotcreting on the law of air flow movement is studied.The main conclusions are as follows:Based on the analysis of the deformation of the surrounding rock,the stress of the supporting structure and the monitoring data of the mine pressure in the roadway,it is considered that after the working face is pushed over 40 m,the collapsed coal and rock fill the goaf;when the working face is pushed forward 0-40 m,the void ratio in the goaf is determined by the filling degree of the goaf and the coefficient of rock fragment expansion;when the working face is pushed forward 40-160 m,the void ratio in the goaf is determined by the coefficient of rock fragment expansion,The coefficient of dilatancy changes with the change of roof stress;when the advancing distance of working face is more than 160 m,the void ratio in goaf tends to be stable.Based on this understanding,the porosity evolution model of the goaf is established based on the filling degree and the coefficient of rock crushing expansion.Based on the permeability evolution model of goaf constructed,the air flow field of goaf under the "Z-type" ventilation mode of roof cutting and pressure relief self forming roadway is simulated by FLUENT software.The research shows that: along the direction of the working face tendency,there is air flow exchange between the working face air flow and goaf.Due to the inertial effect of air flow,the air flow in the corner of the working face 0-10 m is large The air flow in the 10-45 m section,45-80 m section and 80-135 m section of the working face returns to the working face from the working face,but the return air volume decreases gradually;the air flow in the 135-190 m section and 190-280 m section of the working face escapes into the working face from the working face,of which the exchange strength of the air flow in the 135-190 m section and the goaf is weak,190-28 The exchange intensity between air flow and goaf is strong in 0m section.The 0-10 m section and 190-280 m section of the working face are areas with strong air flow exchange.Along the direction of the reserved lane,the air flow escapes from the goaf,of which the air flow escapes from the 0-50 m section behind the working face has the largest intensity,accounting for 56-58% of the total amount of escapes;the air flow escapes from the 50-100 m section behind the working face is the second,accounting for 13% of the total amount of escapes;the air flow escapes from the 350-400 m section behind the working face takes up 9% of the total amount of escapes;the air flow escapes from the100-350 m section behind the working face takes up 56-58% of the total amount of escapes The escape intensity is small.With the increase of air distribution in the working face,the air flow into the goaf increases gradually.The comprehensive measures of reducing the air distribution in the working face,hanging the air account at the air inlet corner and spraying in the reserved lane can effectively reduce the air flow exchange intensity between the working face and the goaf,between the goaf and the reserved lane.The field test data proves that the air reduction and pressure reduction,corner hanging accounts and spraying in the reserved lane can change the goaf The law of air flow movement reduces the air leakage in goaf.