| During the "14th Five-Year Plan" period,China’s demand for coal will continue to increase.Scientific research to reasonably define the protection range of coal pillars is an important method to liberate coal under three pressures and improve coal recovery rate.Based on the engineering geological background of the Yuchang Coal Industry3116 comprehensive mechanized working face,this study used methods such as data collection and collation,site investigation,laboratory experiments,numerical simulation,and mining subsidence prediction calculations to optimize the reasonable size of the protected coal pillars of the return air shaft,analyze the failure characteristics of the surrounding rock and shaft during mining,analyze the law of surface subsidence,and provide protection measures for the shaft during the coal pillar recovery process based on mine production conditions.The main research results are as follows:(1)By measuring the mechanical parameters of coal-rock samples,including the natural block density and mechanical properties such as uniaxial tensile,shear,and compressive strength,it was determined that the direct roof of the 3116 fullymechanized mining face is moderately stable,and the old roof belongs to the mediumhardness roof,with good stability.The protected coal pillar range of the return air shaft was preliminarily divided using the vertical profile line method and the vertical line method.(2)Through the study of the reasonable width of the protected coal pillar in the return air shaft,it was determined that the width of the coal pillar left along the direction of the working face in the return air shaft should not be less than 96 m.Combining theoretical analysis and other methods,the main modes of deformation and failure of the shaft under the geological conditions of Yuchang Coal Industry were determined.Firstly,the return air shaft mouth is easily affected by the mining,resulting in significant horizontal displacement and sinking.Secondly,due to the significant difference in mechanical properties between the bedrock and loose layers of Yuchang Coal Industry,the slip between layers causes deformation and damage to the shaft.Finally,under the condition of single-side mining of the protected coal pillar,the stress on the inner wall of the shaft is much higher than that on the outer wall,which may cause single-side damage to the inner edge of the shaft.The advance stress generated by the mining face will increase the vertical stress at the bottom of the shaft,but due to the strong compressive strength of the concrete material,the deformation of the shaft in this section is generally small before the yield strength is exceeded.(3)The probability integral method was used to predict the surface subsidence caused by the mining of the 3115 and 3116 working faces,and the damage level of surface buildings under different mining degrees was evaluated.Based on the numerical simulation results,it was finally determined that leaving a 100m-wide protected coal pillar along the direction of the working face in the return air shaft can meet the requirements of safe production.(4)Based on the engineering characteristics of Yuchang Coal Industry,protective measures for the return air shaft were proposed,including strengthening the monitoring of stress and strain on the inner wall of the shaft,timely reinforcing the fractured shaft wall,optimizing the mining speed of the working face,and adopting the mining method of only mining the bottom coal seam at the end of the working face mining and leaving the upper roof coal to naturally collapse as the caving zone to prevent the shaft from shifting and being damaged during the final stage of the working face mining.This thesis contains 56 figures,28 tables,and 84 references. |
