Research On Damage Evolution And Permeability Characteristics Of Coal And Rock Under Temperature And Stres

Coal is the basic energy to ensure the stable development of the country.The utilization of coal resources is not only limited to coal itself,but also the coal-bed methane(CBM)with exploitation and utilization value.CBM extraction can not only alleviate the shortage of natural gas supply in China,optimize the energy structure,but also effectively reduce the accident rate of coal and gas outburst under mining disturbance.Therefore,the analysis of coal mechanical response and permeability change under mining disturbance is the key issue to be solved urgently.Especially for deep mining,the problems of high ground stress,high ground temperature and high gas pressure make the evolution mechanism of coal damage and seepage more complicated.thus,it is of great practical significance to study the damage evolution and permeability characteristics of coal under the action of temperature and stress for CBM extraction and coal safety mining.Taking the raw coal of No.3 coal seam in Zhaozhuang Mine,Jincheng,Shanxi Province as the research object,triaxial seepage tests of coal under temperature and stress were carried out.The influence of temperature,gas pressure and confining pressure on coal damage and seepage characteristics is analyzed.Based on the interdisciplinary fusion theory of statistical damage theory,elastic-plastic mechanics and seepage mechanics,the coupling mechanism of coal damage and seepage is discussed.The research results are as follows:1)The changes of mechanical properties and permeability characteristics of coal under the action of temperature and stress were analyzed.The results show that the compressive strength and elastic modulus of coal decreased with the increased of temperature and gas pressure,but increased with the increased of confining pressure.Before the failure,the coal underwent compaction,linear elastic deformation and yield stages,and the permeability decreased in the first two stages and increased in the last stage.After the failure,the coal went through stress break stage and residual strength stage,and the permeability increased sharply.2)Based on the Mohr-Coulomb failure criterion,the coal micro-element expression was modified by using the relationship between cohesion and gas pressure,and the statistical damage constitutive model of coal under triaxial stress was established to analyze the damage evolution law.The results shown that the rationality of the model was verified by using the total stress-strain data under different gas pressures.The damage evolution curve of coal under triaxial stress was S-shaped,and the damage variables remain almost unchanged in the initial compaction and elastic stages.During the plastic deformation stage,the damage variable rises rapidly;Under the stress drop stage,the damage variable reaches the maximum and tends to 1.3)Considering the thermal expansion and gas adsorption effect,the elastic deformation was revised,and the damage constitutive relation of coal under the action of temperature and stress was established by combining the elastic-plastic theory and statistical damage theory,and then the permeability model considering damage was further constructed.1)The rationality of the new model was verified by using the seepage test data under different temperatures and different gas pressures,and the damage-seepage characteristics of coal under the action of temperature and stress are revealed.4)Based on the generalized plastic potential theory,the plastic strain was derived quantified,and the expression of the damage variable was modified by combining the stress-strain constitutive relation,and the modified damage variable was substituted into the simplified permeability model,and then the elastoplastic damage-permeability coupling model of coal was constructed.1)The new model was verified by the whole stress strain-seepage test data under different confining pressures,and the simplified model was still suitable for seepage simulation under different pore pressures and effective stresses.The coupling mechanism of damage and seepage was analyzed,and it was proved that the damage of coal was the fundamental cause of permeability surge,and the damage of coal can be induced by gas seepage...