| The coal,roof and floor of the Luling Mine 883-1 top fully mechanized working face are all soft and the mining height is tall,the phenomenon of spalling and roof fall easily occur during coal mining and it seriously affects the safe and efficient.In order to achieve the stability control of coal wall,the Master's thesis,comprehensive methods including theoretical analysis,laboratory tests,numerical simulations,field tests,are employed to study failure forms and characteristics of coal wall in“three soft”thick coal seam,development law of plastic zone in front of coal wall,mechanism of water injection to strengthen the stability control of coal wall and design of water injection parameters.The main research conclusions are as follows:?1?The failure forms of coal wall in"three soft"thick coal seam was put forward and the criterion for determining the spalling of coal wall was formulated.The Mechanical calculation model of the“bending deformation”stage of coal wall and the mechanical model of“whole coal wall arc shear failure”were established to obtain the position of spalling,the depth of spalling and the critical stability height of coal wall based on the pressure bar theory and the sliding body theory.The depth of spalling and the critical stability height of coal wall were analyzed under the effect of inner friction angle,cohesion and the mining height.?2?Baesd on the D-P yield criterion to establish the mechanical calculation model of plastic zone of working face in"three soft"thick coal seam,which obtained the distribution law between abutment pressure and intermediate principal stress coefficient l,the width of plastic zone.The influence of mining height,mining depth,support protecting force,cohesion and inner friction angle of coal on the width of plastic zone was studied.The width of plastic zone of Luling Mine 883-1 working face was 5.29 m.It was revealed that the cohesion and inner friction angle of coal were two important factors affecting the stability of coal wall.The targeted technique to achieve the stability control of coal wall was put forward.?3?Theoretical analysis,laboratory tests and numerical simulations were comprehensively employed to analyze the mechanism of preventing from spalling of coal wall through water injection.Measured the raw moisture content of coal and obtained the variation law between the moisture content of coal samples and the time of drying through coal sample drying test,uniaxial compression and variable angle shear mechanical test of coal samples with different moisture content.It was revealed that the peak strength and elastic modulus decreased with rising moisture content while the cohesion,inner friction angle,shear strength,peak shear strain increased in varying degrees.The reasonable moisture content of coal wall was determined.The development law of plastic zone of coal samples with different moisture content was studied to verify the significance of preventing from spalling of coal wall through water injection in"three soft"thick coal seam.?4?The shallow hole dynamic pressure injection was put forward to achieve the stability control of coal wall based on the law of mechanical properties of water on coal samples and the development law of plastic zone of coal samples with different moisture content and carried out the selection of water injection equipment,the design of water injection parameters and process.The rationality of the theoretical value of water injection parameters and the moisture content of working face were confirmed.After using the shallow hole dynamic pressure water injection of coal wall,the depth of spalling decreased to 0.4m,the length of spalling reduced 50%,the operating rates of working face increased 38.7%,the monthly push progress increased 60 m,the monthly yield increased 26.53 kt,and created economic benefits up to 3 million 162 thousand and 600 yuan each month.The number of workers'support and the intensity of labor were reduced and the benefits of technical,economic and social are significant. |
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