Experiment Research On Evolution Process And Mechanism Of Coal And Gas Extrusion

With the increase of mining depth, stress and gas pressure is becoming higher and higher,the coupling effect of stress, gas, coal and others is more and more complicated. And the coaland rock dynamic disasters occurrences are on the rise, so does their harm. The coal and gasextrusion disaster which happened ever less is recently on the rise, but researches on itsmechanism is rare. In this paper, the coal and rock dynamic phenomenon simulation systemwas established, the behavior characteristic of different coal and rock dynamic phenomenawas studied; the variation laws of stress and gas pressure and the influence factors during theextrusion process were analyzed. The layer-crack structure formation process ofgas-containing coal was studied, and the layer-crack damage evolution model of coal and gasextrusion was established. The key influence factors of coal and gas extrusion disaster in fieldwere analyzed, rank division of the working face hazard area was carried out, so did theprevention measures. The main research achievements are as follows:The coal and rock dynamic phenomenon simulate testing system was established andused to study the behavior characteristics of different coal and rock dynamic phenomena. Thereason of different behavior characteristics of the dynamic phenomenon was discussed. It isfound that thrown distance of coal and gas extrusion is smaller, and the dynamic effect isunobvious. Both the coal fragmentation degree and the thrown distance of coal and gasoutburst reach the maximum with obvious directivity. As to gas-containing coal burst, the coalmass bursts into blocks without obvious directivity. The main reason the behaviorcharacteristics of dynamic phenomena are different results from the difference of coalproperties and the release ratio of coal elastic energy and gas potential energy.The variation rule and influence factors of coal and gas extrusion were studied. It isfound that coal extrusion is a relatively slow mechanics process, the stress deceases afterearlier increase; the release speed of gas pressure tends slower with the distance deeper fromthe extrusion outlets. The layer-crack damage happened in coal mass which makes the coalmass fracture further into blocks. With the increase of gas pressure and stress, residual cavityoccurs from nothing and becomes bigger gradually and the coal destruction is increasinglyviolent. With the increase of coal strength, the residual cavity reduces gradually and tends todisappear. The higher the roof and floor rocks’ strength is, the more serious the coaldeformation and fracture will be.Through the numerical simulation of mining process, the variation laws of stress, gaspressure and coal plastic deformation zone were studied, the impact of burial depth, coal seam parameters and initial gas pressure on the extrusion risk was analyzed. Research shows thatwith the increasing of the burial depth, gas pressure and the decreasing of thickness, strengthof coal seam, the danger of coal extrusion gradually increased.Based on the elastic-plastic fracture mechanics, the critical extension angle and theazimuth angle of gas-containing coal crack were calculated. The coal strength criterionconsidering the free and adsorbed gas was derived and the relation between crack extensionlength and three directional stresses was analyzed. Take the limit equilibrium zone forwardthe working face as the study object, the coal layer-crack formation process and the differenteffects of disturbances on the stability of coal body were researched. The critical rupture loadof the layer-crack structure was calculated, and the failure form of coal extrusion wasanalyzed. The―layer by layer‖failure form and variation law of stress and gas pressure duringthe coal extrusion process were obtained in the research, the reason for cavity formation incoal body was analyzed, and the instability mechanism of―layer by layer‖failure during thecoal extrusion process was revealed.The key influencing factors of coal and gas extrusion disaster were analyzed, based onwhich, the working face danger zones division was made. For ensuring the safety productionof working face, specific dynamic disaster prevention measures for different danger zoneswere formulated.Research findings provides theoretical foundation and scientific basis for furtherunderstanding the coupling effects of stress, gas, coal mass and the others during the deepmining process, and for the prevention and controlling of coal and gas extrusion disasters.