Study On Mechanical Behavior And Energy Evolution Characteristics Of Gas-solid Coupling Containing Gas Under Triaxial Compression

Coal seams in my country generally have the characteristics of high gas,low permeability and strong adsorption.In-situ stress,gas pressure and gas content continue to increase with the depth of mining.Gas migration,adsorption and desorption will significantly change the physics,mechanics and energy of coal structure.The nature of evolution affects dynamic disasters and engineering behavior characteristics such as coal and gas outbursts,gas explosions,and gas drainage.Therefore,the research on the deformation and failure mechanism of gas-containing coal under the coupling action of ground stress,gas pressure and adsorption and desorption has very important scientific and engineering significance.The microscopic pore structure of gas-bearing coal has typical nonlinear characteristics,coupled with the amplification of pore gas pressure,makes the heterogeneity of gas-bearing coal more prominent than that of ordinary rocks,resulting in laboratory test results often showing greater dispersion It is difficult to monitor the internal cracks of the sample and the distribution and evolution of gas pressure in real time.Therefore,this paper developed a new gas-solid coupling numerical realization method,based on the triangulation method to build a gas permeation network,real-time correction of the particle diameter to simulate the adsorption expansion and desorption shrinkage process,through the application of physical force to characterize the pore gas pressure effect,achieved the whole process of gas-solid coupling simulation of the compression failure of gas-containing coal has obtained the following main developments and conclusions:(1)Based on the Delaunay triangulation,a gas migration network is constructed to realize the gas migration process driven by changes in pore pressure and pore structure.The analysis found that the effect of adsorbed gas on the physical and mechanical properties of coal and rock mass is mainly caused by the structural expansion caused by adsorption on the coal wall.A particle expansion model based on gas pressure was established.(2)According to the established gas migration network and particle expansion model,triaxial compression simulation tests of gas-containing coal under different gas pressures were carried out.By monitoring the stress,pore pressure,and crack distribution in the process of deformation and failure,the microscopic deformation and failure characteristics of gas-bearing coal were obtained,and the three showed stage changes.The distribution of cracks in the process of deformation and failure was extracted and tested for permeability.It was found that the permeability first decreased and then increased,and an inflection point appeared at the crack propagation stage before the peak.(3)Carrying out compression tests of gas-containing coal under different confining pressures,and it is found that the existence of confining pressure will significantly change the deformation and failure characteristics of gas-containing coal.The overall trend changes from brittleness to ductility,and the angle between the crack and the horizontal plane decreases from 90° at 45°,the macroscopic cracks that cause overall instability evolve from a single through crack to two cross through cracks.As the confining pressure increases,the peak stress and residual stress of gas-containing coal increase approximately linearly.(4)Through the comparative analysis of energy evolution theory under discrete element system and triaxial stress,the evolution characteristics of elastic energy and dissipated energy of gas-containing coal are obtained.A damage constitutive equation based on the number of cracks is established.The number of cracks contains more complete damage information,and it is more comprehensive and effective to construct the damage constitutive equation based on the micro-crack feature information.At the same time,according to the energy index of the impact tendency of coal,the impact tendency of gas-containing coal under different conditions is obtained.It is found that as the gas pressure increases,the impact tendency of gas-containing coal will show a characteristic change from weak to no.As the confining pressure increases,the overall impact tendency of coal and rock increases nonlinearly.This paper has 36 pictures,3 tables,and 140 references.