Study On Macro Micro Damage Mechanism Of Gas Adsorbed Coal

With the continuous development of coal resource mining,the number of high-gas mines has increased significantly,and the exploitation of high-permeability high-gas coal seam is easy to be prominent.Studying the mechanical mechanism of gas adsorption to coal rock can explore the evolution mechanism of coal rock dynamic disaster.According to the insufficient quantitative analysis and action mechanism of coal damage,the parameters and the coal damage parameters were quantitatively analyzed.The important conclusions of this article are given below:(1)Due to the complexity and danger of in-situ test,the indoor test method is used to study the damage law of coal body,and the physical and mechanical parameters of coal body in single-phase and multi-phase coupling state are monitored and obtained.There are a lot of cracks and pores in coal.The structure of coal determines its ability to absorb CH4,CO2 and other gases.Using the "visual constant volume solid gas coupling test system" independently developed by the research group,the damage and failure laws of coal and rock with different adsorption gas properties and different stress stages were studied.Under he condition,the compressive strength is the highest,which is 15.63mpa,while under CO2 condition,the compressive strength is the lowest,which is 11.26mpa,and the deterioration rate reaches 27.96%;The maximum elastic modulus of the same coal sample is 1720.95mpa under he condition,and 705.07mpa under CO2 condition,indicating that gas adsorption can reduce its bearing capacity;The fractal analysis of coal sample images in different stress stages is carried out by using MATLAB software.The fitting correlation coefficient is in the range of 0.99276-0.99868.The fractal dimension is 1.2376 when the peak strength is 40%,and 1.4288 when the peak strength is 80%,and the increasing proportion is 15.45%.The larger the fractal dimension is,the more complex the fracture is.(2)The macro properties of materials are determined by their microstructure.The material composition and microstructure characteristics of coal samples determine the adsorption and desorption capacity of coal samples.At the same time,the microstructure characteristics of coal samples will change after adsorption and desorption.Mercury injection test and scanning electron microscope are used to analyze the microstructure of coal.The mercury injection and mercury withdrawal curves of coal samples obtained from mercury injection test data have the phenomenon of pore hysteresis loop.Under the conditions of he,N2,CH4 and CO2,the hysteresis loop of coal sample increases gradually,which indicates that the open pores of coal sample increase with the increase of gas adsorption capacity.Analysis of mercury intrusion data shows that the pore size distribution of coal samples is different under different adsorption gas conditions.Under he and N2 conditions,the sum of micropores and micropores in coal samples is more than 75%.Under CH4 conditions,accounting for 20.39%and 40.13%respectively.Under CO2 adsorption conditions,the proportion of macropores in coal samples increases significantly,accounting for 53.78%of the total pore size distribution;When the peak strength is 40%and 60%,the pore size is mainly concentrated in small holes and micropores,accounting for more than 30%.When the peak strength is 80%,the proportion of mesopores and macropores is 12.38%and 26.31%respectively.In the peak stage,the pore size increases to a certain extent,especially in the micro holes and macropores,A part of the micropores and micropores expanded into mesopores and macropores,and the micropores and micropores were still developing.The proportion of mesopores and macropores was 20.23%and 36.34%respectively.It can be observed by scanning electron microscope that the adsorption and desorption of coal samples play the role of "pore thinning","pore expanding" and "pore increasing",which changes the micro pore structure.Based on the fractal theory,the mercury intrusion data of coal samples are studied.Under the conditions of adsorbed gases he,N2,CH4 and CO2,the fractal dimension increases continuously.The minimum is 3.26 under he and the maximum is 3.36 under CO2 The larger the fractal dimension is,the coarser the surface of coal samples is(3)From the point of view of damage mechanics,the damage mechanics mechanism of coal and rock under different external conditions is studied and verified by numerical simulation.The damage deterioration mechanism of coal and rock is analyzed from the perspectives of physicochemical adsorption theory,Griffith strength criterion and Mohr Coulomb strength criterion.Based on the damage mechanics theory,the macro and micro fractal dimensions of coal and rock are established Based on the statistical damage evolution model of coal and rock,GDEM numerical simulation software is used to simulate the damage state of coal and rock at different stress stages,and the simulation analysis of macro variables such as strength,deformation and fracture expansion degree is realized from the point of view of continuous and discontinuous coupling.