Study on underlying coal seam stress distribution and failure characteristics in slicing mining of extra-thick coal seams

For the extra-thick coal seam layering mining,grasping the stress distribution law and deformation characteristics of the underlying coal seam after coal mining can provide some theoretical basis for studying the evolution law of permeability distribution of the underlying coal seam and accurately determining the gas enrichment area in gob. Therefore,in order to clarify the stress distribution law and deformation characteristics of coal seam under inclined extra-thick coal seam,the numerical simulation calculation of coal seam mining with different coal seam inclination was carried out. First,based on the theory of gob compaction,the stress-strain relationship of caving rock mass in gob was obtained,and then the mechanical parameters of caving rock mass in caving zone were determined by trial and error. On this basis,through numerical simulation calculation and analysis,the influence law of coal seam inclination change on the stress distribution and failure characteristics of the underlying coal seam was obtained. The results showed that:in the scope of gob floor，with the increase of coal seam inclination，theO ring of gob stress recovery is no longer distributed symmetrically in the central strike line of gob,but migrated to the lower part. Along the dip,the lateral stress concentration coefficient at both the upper and lower ends of the gob decreases with the increase of the coal seam dip angle,but the lateral stress concentration coefficient at the upper dip end is always smaller than that at the lower dip end. Along the strike,in the working face floor,the stress concentration coefficient of advance support increases with the increase of coal seam dip Angle. Finally，through the analysis of the distribution of the plastic failure zone of the underlying coal seam，it can be seen that the plastic failure depth of both the working face and the upper inclined floor increases with the increase of the coal seam inclination,but the failure depth of the upper inclined floor is always smaller than that of the lower inclined floor. The location of the maximum plastic failure depth of the gob floor is gradually away from the middle of the gob，and tends to the lower end.