| Fangshan coal mine mainly mines single II＿1 coal seam,which does not have a protective layer.The coal is soft with a high gas content and low permeability.It is difficult to control coal seam gas and it seriously restricts the safe production of the mine.As a pressure relief and permeability enhancement method,hydraulic punching technology can effectively and quickly eliminate the risk of gas outburst compared to conventional measures,and is widely used in soft outburst coal seams.However,after the on-site application of this technology,the plasticity of the coal body is reduced,which is easy to cause coal wall spalling.Therefore,it is of great significance to investigate the effect of hydraulic punching on pressure relief and permeability enhancement,and to find a suitable control measure for coal wall spalling.Based on this,the thesis takes the Fangshan coal mine as the engineering research background,which analyzes the gas adsorption characteristics of the coal seam and the physical and mechanical characteristics of the coal seam,the roof and floor by means of laboratory tests,theoretical analysis,numerical simulation,and on-site measurement.It clarifies the characteristics of the II＿1 coal seam,the roof and floor;Based on the gas-solid coupling model of coal and gas,COMSOL Multiphysics was used to numerically simulate the effect of hydraulic punching on pressure relief and permeability enhancement,and a suitable construction layout of drill is determined;Based on numerical simulation,An industrial test of hydraulic punching was conducted on site and its pressure relief and transparency enhancement effects were investigated;Aiming at the problem of coal wall spalling caused by the reduction of coal plasticity after the application of hydraulic punching technology,corresponding control measures for coal wall spalling are proposed.The work and results obtained in the thesis are as follows:(1)Samples were conducted on site,and parameters such as compressive strength,elastic modulus,Poisson’s ratio,adsorption constant,density,and solidity coefficient of II＿1 coal seam were tested in the laboratory.The characteristics of soft coal seams,low permeability,and difficult gas extraction were identified.(2)Based on the gas-solid coupling model of coal and gas,the strength of the effective radius of gas extraction affected by the coal output,borehole inclination,suction negative pressure,and mining time was studied.The stress and gas distribution evolution laws under different coal output,borehole inclination,and borehole spacing were analyzed,and a more suitable borehole construction layout scheme was obtained.(3)The gas flow method and the stress method were used to investigate the effective pressure relief radius and the effective impact radius of gas extraction for hydraulic punching under different coal outputs(0.5t/m,1t/m,and 1.5t/m).The on-site inspection results combined with the numerical simulation results determined the regional outburst prevention drilling construction plan,and the hydraulic punching effect was evaluated through the actual measurement and evaluation of residual gas pressure and residual gas content in the area.(4)Aiming at the serious problems of coal body plasticity reduction and coal wall spalling after the application of hydraulic punching technology,grouting reinforcement and control measures for coal wall spalling were proposed.Based on COMSOL Multiphysics,the impact of grouting pressure and borehole diameter on grouting effect was analyzed,and appropriate grouting pressure,grouting time,and borehole diameter were determined.Field application was conducted to investigate the control effect of this technology for coal wall spalling.This thesis contains 65 figures,23 tables and 106 references. |
PDF Full Text Request