Seepage Test And Numerical Simulation Of Coal Under True Triaxial Stress

Gas-bearing coal seams can be regarded as solid-fluid multiphase media with complex and irregular fissures,and they are in a stable equilibrium under the combined effects of overburden pressure,tectonic stress and gas pressure.Under the influence of mining activities,the original state of stress balance in the coal seam was broken,resulting in a redistribution of stress in the coal seam.With the pore connectivity and fissure expansion of the coal,the gas occurrence status changes.The redistribution of stress in surrounding rock and the change of gas pressure in the coal body will all have a certain impact on the mechanical properties and permeability of the coal body,which in turn may trigger a coal mine dynamic disaster.Therefore,it is necessary to study the influence of stress and gas pressure on the coal body damage deformation and seepage characteristics,and further improve the gas-solid coupling mechanism that can accurately express the damage and deformation characteristics of coal,and define the transport characteristics of gas in coal.Firstly,in order to realistically simulate the three-dimensional unequal stress state of the underground coal and rock mass,and study the mechanical properties and seepage law of the coal and rock under the true triaxial gas-solid coupling conditions.A true triaxial gas-solid coupling coal seepage test system was developed by our research team.The system consists of a true triaxial pressure chamber,a hydraulic servo system,a gas seepage system,and a monitoring and control system.The three-dimensional stress ?₁,?₂,and ?₃ can be independently applied without interfere with each other.The problem of seepage sealing of coal body under true triaxial stress is solved,which provides a reliable test platform for studying the damage and deformation and gas seepage of coal under the action of true triaxial stress conditions.Secondly,the conventional triaxial stress loading and unloading conditions under the coal body compression seepage test were performed by using the true triaxial gas-solid coupling coal seepage test system.By analyzing the stress-strain curve and permeability-strain curve of the test results,the deformation and gas flow characteristics of the rectangular coal specimen under the conventional triaxial stress conditions are obtained.The damage and deformation and gas seepage test results of coal specimen under conventional triaxial compression were compared and analyzed.The reliability of the system was verified.It provided a reliable method for studying the damage and deformation of coal and gas seepage under the effect of true triaxial stress.Thirdly,based on the conventional triaxial stress loading and unloading test,the compressive seepage test of coal under the action of true triaxial stress were carried out by changing the intermediate principal stress,and the stress-strain curves and permeability-strain curves of the coal were analyzed.The influences of intermediate principal stress,gas pressure,adsorption,and particle size on the damage and deformation and seepage characteristics of coal have been studied.It provided a reliable experimental basis for studying the damage and deformation of coal and gas seepage under the effect of true triaxial stress.Finally,the PFC^3D particle flow simulation software was used to simulate the coal damage and gas flow under the true triaxial stress.The damage characteristics,gas flow law and crack evolution characteristics of coal were analyzed and compared with the physical test.The results were compared to reveal the mechanism of deformation and failure of coal.