The Evolvement Rule And Percolation Mechanism Of Coal And Gas Outburst

Coal and gas outburst is a serious hazard threated to mine safety. With the increase ofmining depth, complex multi-field coupling effects, structural changes in the original system, thepossibility and intensity of coal and gas outburst are both greatly increased. The mechanism ofcoal and gas outburst is still unclear. Therefore, it is still serious natural disasters on productionprocess of the worldwide coal mine. Based on the basic theory of mining science, rockmechanics, multiple-dimensioned dynamics, and permeation fluid mechanics, using laboratoryexperiments, theoretical studies and numerical analysis method, according to macroscopic andmicroscopic experiment, the whole process of coal’s destruction by the stress field is observatedand analysed. The relation of basic parameters of percolation and environment parameters isfound. And the CT images of internal microstructure on the whole process of evolution accessare received. The paper researches the percolation transition conditions and criterion on thepotential phase and occurrence phase of coal and gas outburst. Considering the whole process ofthe percolation and coal and gas outburst evolution laws, coal and gas outburst percolationmechanism is obtained. The main results are:Through equipment modifications, there are the physical and mechanical propertiesexperiments of coal containing gas under conditions of stress and temperature. The results showthat the peak strength increases with the decrease with gas content in coal containing gas;Young’s modulus decreases with increasing of gas content; permeability increases with thereduce of gas content, but temperature will create new effects on the seepage rate. The resultsfrom a different angle shows gas produced a variety of macro effects on coal. All of the effectswill happen mainly through occurrence and development of pore and fissure by the pressure,temperature, and pore pressure.Describes the coal pores and fissures structure that contains classification, research methods,models, pore size distribution, coal rank and seepage rate. Clarify the fractal characteristics ofcoal depends on the non-homogeneous distribution of pores and fissures. The high-precision CTscan should be used for pores and fissures occurrence and development under real conditions.Coal and gas outburst percolation mechanism could be created.Through the study of materials and structures, Micro-testing machine for miniaturecylindrical coal specimen’s demagement measured uniaxial compressive strength is successfully developed. The testing machine coupled with three-dimensional CT could be used forobservating the internal laws of crack propagation and damage. The testing machine fills theempty part of microscopic research of rock mechanics. It will achieve truly reflect themicro-loading of coal and rock deformation during the various stages. The conclusion candeepen the relevant theory of coal failure laws.Using self-designed micro-testing machine coupled with the CT system, uniaxial damageCT scan experiment at real-time loads is carry through. Experimental results show: at thelinear-elastic phase, coal has emerged within the micro-cracks; in the yield phase, the existingmicro-cracks within the coal were expanding, new cracks emerge; after peak intensity, theporesand fissures are large connectivity in the coal. The experimental results reveal with thestress-strain phase of the change, porosity of each section within the coal continued to increase,the correlation length increases at first and then decreased, the development of main cracks aredescribed, explained the occurrence of pores and fissures conducive to percolation transitionoccurs.Two-dimensional and three-dimensional percolation process and law of coal is systematicstudied. The results showed that: As heterogeneous distribution of pores, before the percolationtransition, the expansion of largest pore group is much faster than the ideal model, theoccurrence of percolation threshold points generally less than ideal model results, which greatlyreduces the occurrence difficulty of percolation transition. Threshold and the correlation lengthchange laws explain the degree of percolation transition will be significantly enhanced if themain fissure occur and complete the development of coal body.Three-dimensional percolation process of coal analysis showed that: pore points in the mainfracture zone increases along to all stress-strain phase change. Largest connected group of coalshift from original pore developed regions to the new fissure by the internal stress. It willeventually be extended to the confluence with the main fissure, the percolation group is formed.The development of the fissures within coal will avoid high-density waste rock area, but willsqueeze the waste rock area, narrow the scope of its area. The starting position of fissure often isa pore developed area; the percolation parameter variation is different with the other positions.Analysis results show cracks led to the destruction of coal in advance, the percolation probabilityincreases; and percolation phenomena will increase the connectivity of pores and cracks, so that gas can be brought together, the main fissure zone is high risk zone of the percolation transitionand coal and rock unstable. There is prominent likely of.coal and gas outburst in the zone.Coal and gas outburst is a mechanical process. Distinguish into breeding, latency,occurrence, development and termination five stages. The adsorbed gas erosion completesbleeding process. In-situ rock stress and disturbance outside urge the development of cracks,porosity of coal exceeded the threshold, the percolation phenomenon occured; gas assembles andcompletes latency process. After percolation transition, the external disturbance leading toinstability of coal, energy release. Spall and powder alternately finish development phase. Coalwall is covered by broken coal spall, coal and gas outburst finished.In this paper, coal and gas outburst percolation mechanism is conducive to find out themechanism of coal and gas outburst. And then, coal and gas outburst happened criterion will bebuild, the occurrence of the theory is formated. Coal and gas outburst technology research andimplementation will be guided. It has greater practical value for reducing and avoiding theprominent disasters, ensuring safe production of coal, and avoiding casualties.