Research On The Damage Evolution Characteristics And Gas Flow Law Of Structurally Anisotropic Coal

At present,China's coal mining has gradually entered the deep mining mode.In the actual underground mining process,it often encounters different bedding structural coal seams.Due to the differences in the coalbed bedding structure,the deformation characteristics of the coal seam and the gas flow law are significantly different,affecting the occurrence of various coal and rock power disasters in mines.However,the systematic research on the damage evolution characteristics and gas flow law of structural heterogeneity coal is still lacking,and it needs to be further studied and perfected.Therefore,the study of damage evolution characteristics and gas flow law of structural heterogeneity coal has practical value in understanding the mechanical deformation damage characteristics of the structural heterogeneity coal,grasping the gas flow law,increasing gas extraction efficiency,and simultaneously revealing various types of coal seams.The mechanism of dynamic disasters and the effective prevention and treatment of disasters provide theoretical support and scientific evidence.In this paper,on the basis of a comprehensive analysis of the research results of structural heterogeneity coal bodies at home and abroad,the coal bodies with obvious bedding structure are pressed to five different bedding inclination angles samples of raw coal at 0??30??45??60??90?.First,the damage process of the coal before and after the clinker was added to the uniaxial loading bar by using a pressure loading system,a strain acquisition system,and an acoustic emission acquisition system.Dynamic monitoring,a more comprehensive study of the structural heterogeneity of coal body strength,deformation characteristics and acoustic emission characteristics,compared before and after the cracking structure of the heterogeneity of the coal body strength characteristics,deformation characteristics and acoustic emission characteristics of the difference;Second,through the establishment of 0??30??45??60??90??120??135??150? numerical models of bedding dip coal were used to reveal the defects of traditional numerical models that did not consider the bedding structure of coal,and the results of physics experiments of structural heterosexual coals were well verified and improved.Finally,structural heterogeneity was included.The establishment and solution of multi-field coupling theoretical model and geometric model of gassy coal seam reveals the characteristics of coalbed gas anisotropy that are different from the traditional isotropic,and studies the temporal and spatial evolution of permeability and gas pressure around the borehole of the coal seam.The actual problem of engineering provides an important basis.The main research results are as follows:(1)The physical and numerical experimental studies on the mechanical properties of coal with structural heterogeneity were carried out,and the variation of the mechanical properties with the bedding angle was analyzed.The results show that the heterogeneity of the mechanical properties of the heterotopy coal with bedding structure is obvious.The compressive strength and elastic modulus of the coal are presented as decreasing and then increasing with increasing bedding angle.The maximum and minimum values of compressive strength appear at the bedding dip angle of 0??70?(complete coal),0??73?(borehole coal),the maximum and minimum elastic moduli appear at the bedding dip angle of 0??55?(complete coal),0??65?(borehole coal);The strength of the coal body after the kerf is weakened obviously,and the magnitude of the weakening of the coal is affected by the bedding structure of the coal.With the increase of the bedding dip,the weakening of the coal body strength decreases first and then increases.(2)Physical experiments and numerical experiments on acoustic emission characteristics of structurally heterogenous coal bodies were carried out to analyze the differences in acoustic emission activities.The results show that there are differences in the acoustic emission characteristics of the structural heterogeneity coal body.With the increase of bedding angle,the duration of the “development period” of the acoustic emission activity of the coal body decreases first and then increases gradually,but the “evolution period” acoustic emission activity gradually Frequently;and with the increase of bedding angle,the peak abrupt change of acoustic emission in the “active phase” of the acoustic emission is gradually weakened,and the hysteresis effect of the maximum acoustic emission intensity increases first and then weakens,and to a certain extent,due to the external factors Acoustic emission signal acquisition interference can be avoided,so the acoustic emission results of numerical experiments are better than physical experiments.(3)The physics experiments on the damage evolution of structural heterogeneity coal bodies are in good agreement with the numerical experimental results,and the mutual verification between physical experiments and numerical experiments is realized.The traditional numerical models without considering the coal body bedding structure are used to characterize coal.There are major defects in body strength and deformation characteristics.(4)Through the numerical experiments of damage evolution of coal with structural heterogeneity,the process and difference of damage propagation in coal with different bedding dip angles are supplemented from the microscopic point of view.The results show that there are differences in the microcrack propagation curves of coal bodies with different bedding dip angles,but all of them are roughly in the form of “slow”-emergent-slow “S” curves,and the coal body failure is mainly caused by tensile stress.Tensile type failure is the main type;secondly,the total number of damage cracks in coal seams with different bedding angles after cutting is reduced to different degrees,indicating that the severity of damage and damage of coal after cutting is significantly reduced.(5)The multi-field coupling model of gas-bearing coal seams with structural heterogeneity was studied,and the law of gas flow around boreholes was analyzed.The results showed that the difference and the traditional mathematical model concluded that the gas pressure and permeability around the boreholes in the coal seam gas have obvious anisotropy,they are vertical “8”-shaped and horizontal “8”-shaped,respectively,and the gas is distributed over time.The pressure vertical “8” shape distribution gradually shrinks inward,and the transverse “ 8 ” shape distribution of the permeability expands outward.With the increase of the drilling distance from the drainage,the change trend of the two is opposite.