煤层气运移过程中损伤效应对煤强度的弱化影响

During coalbed methane mining, the gas pressure interactions within the matrix- fracture cause damage effects in the coal seam, resulting in a reduction on the strength of the coal. To investigate the damage effect of the coal strength, a conceptual model of matrix and fracture geometry deformation was proposed, and then, a permeability model with coupled damage constitutive parameters was deduced. The strength post-processing calculations for the permeability model considering gas action were also carried out by the COMSOL live link with MATLAB program. The results show that the permeability model obtained from the pore fundamentals is suitable for different boundary conditions, and that the new model matches the experimental data well under uniaxial strain and constant stress conditions while the Palmer-Mansoori(P-M) model is only suitable for uniaxial strain boundary conditions. Compared to the control coal samples, the strengths of the samples with Young's modulus ratios of 1/3, 1/5, 1/7 and 1/10 decrease by 46.6%, 32.0%, 27.9% and 26.4% respectively after gas action. The damage effect of gas transport on the strength of the coal sample contributes to the porosity of the coal in the form of damage-induced strain, and pore development changes the extension trace of the main fracture after uniaxial loading. Post-processing calculations of the permeability model were programmed to realize the evaluation of the damage effect on the coal strength arising from coal bed methane transport.