Mechanical Behavior Evolution Of Mining Stope And Gas Control Technology

Mining protective coal seam is the most efficient method for regional gas controlunder the condition of coal seam group. But the mechanical behavior evolutioncharacteristics of the stope and the influence mechanism on gas three dimensionalflow had no system theoretically studies all the time, especially the thin protectivecoal seam, which makes the regional gas control to be lack of guidance. Thedissertation studied how the three dimensional stress affects the three dimensional gasflow and the outburst riks by the method of numerical simulation, field experimentand theoretical analysis. The dissertation also built the spatial distribution model ofthe stope and divided the coal seam group to be far and close coal seam groups bystudying the three dimensional stress evolution with space and time of mining theupper thin protective coal seam. At last the efficient exploitation mode of coal seamgroup was built, and the problem of gas control under close coal seam group and theproblem of stress relief under far coal seam group were solved. The main conclusionsare as follows:The statistical analysis of in-situ stress distribution characteristics pointed outthat the maximum and minimum principal stresses are tend to be along the horizontaldirection, the intermediate principal stress is tend to be along the longitudinaldirection, and the maximum principal stress is2times of the minimum principal stress.It was found that the direction of the maximum stress is the key factor to control theoutburst risk when driving a roadway in an outburst risk coal seam, which highlightsthe coal and gas outburst prevention concept to a new heights. The study found thatsignificant stress concentration appears in front of the roadway face when the drivingroadway is perpendicular to the direction of the maximum stress, while there is nostress concentration in front of the roadway face when the roadway drives along thedirection of the maximum stress. The outburst risk is much higher when the roadwayis perpendicular to the maximum stress than parallel to. It was also found that thedifference of coal seam strength is the key factor to generate stress concentration, theoutburst are higher when the roadway drives from one strength coal seam to anotherno matter what direction the roadway drive along.The “stress-fracture–permeability” constitutive model was established for theformer stress peak stage, and then the three dimensional stresses differences of thestope surrounding rock mass and how they control the gas three-dimensional flow atdifferent positions was studied by the numerical simulation and field experiment. At the same time, the space time evolution mechanism of the abutment stress, pressurerelief angle, O-shaped stress relief area during the thin coal seam mining process wereinvestigate. Then the rock mass under the mined coal seam was divided into threebelts and five zones, and the stope surrounding rock mass was divided into fourspaces. At last the coal seam group was firstly divided into far and near groups fromthe perspective of mechanics, which is the theoretical basis for regional gas control ofthe coal group.The gas flow characteristics of mining the upper thin coal seam under close coalseam condition was investigated, which proved the stope division to be crrect. Inorder to prevent the pressure relief gas of the close coal seam group from flowing intothe thin coal seam and cause the gas overrun, the gas drainage hole sealing technologyfor strong disturbed mining area and gas three dimensional drainage technology areinvented according to the stope surrounding rock mass migration and gas flowenrichment regularity. The technologies enhanced the drilling damage resistanceability and efficiently control the relieved gas of the closed coal seam group.A new technology of regional gas control was initiated based on the stressdirection. Most of the roadway should be designed parallel to the direction of themaximum stress in order to reduce the stress concentration and then reduce theoutburst risk, which was proofed to be right by the field experiment. The technologyis a new regional gas control technology beside the two technologies of protectivecoal seam and regional gas pre-drainage.The main results published3papers in SCI journals,5papers in EI journals and1journal in ISTP journals, authorized12patents, and6first prizes about progress ofscience and technology including the Shaanxi Province, China Coal IndustryAssociation.The results lay an important foundation of theory and technology for gas controlwhen mining the protective coal seam, and have the important theory significance andpractical value for future mine gas control and prevention design.