Research On Technology Of Pressure Relief And Permeability Increment Caused By Nearly Whole Rock Upper Protective Seam Mining

The direction of coal mining has gradually shifted to the deep part,resulting in more and more mines facing the problem of high gas and low permeability coal seam mining,and the form of gas control is becoming more and more serious.Protective layer mining is the most effective way to reduce coal seam gas pressure and improve coal seam permeability.In view of the high gas and low permeability coal seam mining with no suitable coal seam as protective layer,this paper innovatively proposed that mining nearly whole rock seam?thin coal seam and thick coal gangue?as protective layer to realize the pressure relief and penetration enhancement of the protected coal seam.On the basis of systematic analysis on the principle of pressure relief and penetration enhancement in nearly whole rock protective layer,the effect of thickness and spacing of protective layer on the pressure relief and permeability increment of protected layer is studied by means of theoretical analysis and numerical simulation,and verified by field measurement.The main research results of this paper are as follows:?1?The basic principle of pressure relief and permeability increment for protective seam mining is explained from the angle of stress change and movement deformation of surrounding rock in protective seam mining.The main process of pressure relief and permeability increment in the whole rock protective seam mining is introduced.In addition,the key points of pressure relief and permeability increment technology in the nearly whole rock protective layer mining are analyzed,and the evaluation indexs of the pressure relief and permeability increment effect are summarized.?2?Based on the analysis of the stress variation and Plastic zone development characteristics of the surrounding rock of the stope.According to the theory of elastic mechanics and the theory of floor failure plasticity,the computational mechanics model of abutment pressure distribution and the mechanical calculation model of crack growth depth are established respectively.The formula for calculating the vertical stress at any point of the underlying coal rock mass and the maximum depth calculation formula of the limit plastic failure area of the bottom coal rock are derived.Effect of different protective layer thickness and spacing on the underlying coal rock mass stress and plastic zone development are analyzed.?3?Based on the engineering geological conditions of Pingdingshan No.12 mine,the effects of thickness and spacing of protective layer on the characteristics of vertical stress change,vertical displacement and plastic zone development of protective floor are analyzed.The reasonable mining thickness and spacing of the Ji-₁₄ protective layer is obtained through comparative analysis.?4?The occurrence characteristics of coal and rock thickness in the Pingdingshan No.12 Mine working face of nearly whole rock protection are analyzed.The mining technology and gas drainage system of the nearly whole rock protective seam are designed.The pressure relief and permeability increment effect of the nearly whole rock upper protective seam mining has been measured and analyzed.