Study On Mechanism Of Coal And Gas Outburst Based On Gas-Driven

With the increase of depth and intensity of coal mining,the gas occurrence features in coal seam become more complex,and the gas dynamic disaster based coal and gas outburst become more and more complicated.The mechanism of coal and gas outburst based on the comprehensive hypothesis has been accepted by most scholars,but the factors in this hypothesis play the different roles due to the diversity of geological conditions and mining methods,which lead to the differences of coal and gas outburst.Therefore,the analysis of the effect of the main controlling factors in the same type of coal and gas outburst is necessary.In this paper,the effect of gas on the outburst during the whole process occurred in the tectonic zone were analyzed thoroughly,which lays the foundation for the classification and quantitative research of coal and gas outburst mechanism based on the comprehensive hypothesis.In this paper,the self-made experimental system of coal and gas outburst based on gas-driven effect was employed to conduct coal and gas outburst test with the soft coal in tectonic zone and hard coal in non-tectonic zone under the action of methane and carbon dioxide,and then obtain the law of coal and gas outburst under gas-driven.The main conclusions are as follows:(1)By analyzing the controlling factors of coal and gas outburst occurred in tectonic zone based on the comprehensive hypothesis,it is considered that the coal and gas outburst is mainly affected by gas-driven.The core of the gas-driven is the high pressure gas enrichment area in tectonic zone that provides dynamic support for occurrence and development of outburst.The basis of gas-driven is cracked coal in tectonic zone which can reserves more gas and easy to damaged.The triggering condition of gas-driven is sudden decompression of gas enrichment area that caused by the rapid destruction of coal and rock mass due to the mining activities.(2)In order to systematically analyze the effect of gas-driven on coal and gas outburst,a set of test system based on gas-driven was developed independently.The test system can conduct coal and gas outburst test and delay outburst test with varisized of raw coal or briquette under triaxial loading conditions with different gas composition,gas pressure and temperature,in addition to the seepage and conventional mechanical tests.The variation of stress,strain,temperature,gas pressure,gas content and acoustic emission signal are collected and analyzed in real time.(3)The macroscopic and mesoscopic structural characteristics of soft coal in tectonic zone and hard coal in non-tectonic zone were analyzed.The results show that the two kinds of coal samples have a markedly difference in the material composition,pore structure and strength characteristics.According to the testing result,the NMR test technique provides a new method for the nondestructive testing and observation of pore structure of coal samples.(4)The coal and gas outburst test with soft coal and hard coal under the action of methane and carbon dioxide pressure were carried out.The damage law of gas on coal samples and the influence of gas on the outburst intensity were analyzed,and the evolution law of acoustic emission during outburst is highlighted.(5)The interaction between the gas(methane and carbon dioxide)and the coal samples was analyzed quantitatively in the preparation stage of outburst.The relationship between the adsorption capacity of the coal sample and the outburst intensity was established based on the experimental results.The dynamic deformation characteristics of the coal sample with gas adsorption were revealed.According to the surface physical chemistry and elasticity theory,a strain model of the coal sample after gas adsorption under three-dimensional stress was established.(6)Based on the mechanics criterion of crack propagation of coal samples and the desorption characteristics of coal samples,the failure mechanism of gas on coal was studied.The reason for the obvious destruction of carbon dioxide on the coal was also analyzed.It is found that gas pressure is the main driving force of crack initiation of soft coal and hard coal when the stress is low.Laboratory test,theoretical analysis and the field data were combined to confirm that crush effect of gas on the coal in the process of coal and gas outburst is limited,especially the micronized effect.(7)The evolution characteristics of coal and gas outburst under the action of gas-driven were revealed by summarizing the mechanism of gas in the various stages of outburst.The cases of coal and gas outburst were studied to verify the role of gas in the process of outburst.