Study On The Stress Transfer Mechanism Of Sandwiches Coal-rock Pillar In Steeply Inclined And Extra Thick Coal Seam

The inter-layer rock pillars between two adjacent coal seams in a steeply inclined coal seam group have a special“role",that is,not only the floor of the upper coal,but also the roof of the lower coal.When two adjacent coal seams are arranged on the same working face,that is,when they belong to the same two adjacent working faces,the stress-environment deteriorates due to the double stress from the upper and lower coal seams,and the rock pillars are easily deformed to the free surface,forming stress concentrations locally or may even causing total or partial breaks,which may create dynamic shocks and deteriorate the mining environment.Therefore,it is of great scientific and practical significance to carry out the research on the mechanism of stress transmission of rock pillars between the steeply inclined and extremely thick coal seams to improve the safety and high efficiency of steeply inclined coal seams.The purpose of this study is to explore and reveal the stress transfer mechanism of rock pillars between layers in steeply inclined and thick coal seams,and to obtain the basic physical and mechanical parameters of coal rock through field investigations and rock mechanics experiments.The use of drilling peeks,acoustic emission,loosening rings and other monitoring means found that the partial coal and rock mass structure in the 45#coal seam roof at the +575 level is relatively complete,and the position of the dynamic impact disaster prone to occur(stress concentration)is preliminarily determined.The analysis of the calculation results of the mechanical model shows that with the increase of mining depth,the stress concentration level of the +575 level 45#coal seam roof is intensified,and the possibility of occurrence of dynamic disasters is greatly increased.Numerical model calculations show that under the joint action of gravity and mining stress,the interlayer rock pillars are deformed towards the 45#coal seam,and the suspended area under the mining roof continues to increase,and the intense pressure of the roof tends to increase,which resulting in deterioration of stress environment in stope coal rock.The prevention and control measures of "waterflooding-bursting" coupling-induced cracking surrounding rock were formulated for the coal seams in the 43#coal seam and the +600 horizontal south alley and the 45#coal seam and the +575 horizontal south rock lane stress concentration zone.The research results provide reference for prevention and treatment of dynamic disasters under similar mining settings.