| Being one of the serious natural disasters threatening the safety production of coal mine at home and abroad, coal and gas outburst is a kind of extremely complex dynamic phenomena which happens during the process of coal mining. With the increasing of mining depth in recent years, the in-situ stress and gas pressure are enlarging, besides, the geological and technical conditions of coal mining are growing more complex, thus the numbers of coal and gas outbursts increase at the same time. The in-situ stress in coal changes with the mine mining activities, and the “three area” is formed by stress relaxation zone, stress concentration zone and original stress zone on the heading face and the working face, which brings more difficulties to the prevention and control of coal and gas outburst.Based on the combined effect hypothesis, after the measurement of the basic physical and mechanical parameters of briquette, physical simulation experiments were conducted by coal and gas outburst simulation test device which is independently researched and developed by the State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, and the PCI-2 acoustic emission system which is produced by the acoustics and physics company of the United State. These experiments simulate the influence on coal and gas outburst with different stress concentration coefficients under deep mining-induced stress. The gas pressure, the coal seam temperature, the acoustic emission characteristics, the deformation of coal, the strike force, the outburst strength, the sorting of pulverized coals and the outburst hole models were studied. The main results are shown as follows:(1) In the whole process of coal and gas outburst, the gas pressure and coal seam temperature have the similar rules in temporal and spatial evolution: The gas pressure declines while coal seam temperature decreases in vacuum pumping; The gas pressure grows while coal seam temperature grows in the process of charging gas into the coal; The gas pressure and coal seam temperature drops rapidly in the early stage and then tends to be stable, and the closer to the outburst mouth the faster gas pressure and temperature drop at the same time,inside, the gas pressure nearby outburst mouth rises up and down in many times. The AE counts and AE energy are weak in the inoculation stage while they are large in the burst stage, and they are not obvious when the gas pressure and coal seam temperature becomes steady.(2) The development of outburst is a process of coal breakage in cavity wall from start part to surrounding which is paroxysmal. Pulverized coals are threw out by intermittent type and the gas pressure rises up and down in many times; Pressure isobaric surface distributes at the spherical center of outburst mouth during outburst. The gas desorption area expandes outwards with the shape of spherical shell and the gas gradient nearby is greater. The sorting of pulverized coals in coal and gas outburst is significant: After coal and gas outburst, the ratio of large particle pulverized coals mass decreases, while the ratio of small particle pulverized coals increases and small particle pulverized coals mass is mainly distributed in the middle of the outburst area.(3) The stress concentration coefficient( K) has a significant impact on coal and gas outburst: The larger the value of K is, the larger coal strain is in stress loading stage; The larger the value of K is, the slower gas pressure decreases in outburst stage; The larger the value of K is, the bigger the peak value of AE counts and AE energy are in outburst stage; The larger the value of K is, the bigger the peak value of strike force is in outburst stage; The larger the value of K is, the bigger the outburst strength is; The larger the value of K is, the bigger the volume of outburst hole model is; The larger the value of K is, the more thoroughly pulverized coals are broken; While the value of K has has less to do with coal seam temperature. |
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