Study On Gas-Solid Coupling Behavior And Mechanism Of Multi-scale Fractured Coal

Deep coal mining into the geological environment of high-stress, high-gas, strong-adsorption and low permeability, coal and gas extraction become more difficult, solid-gas coupling dynamic disasters are serious, and many catastrophic dynamic coupling factors, which make the hazard-formative mechanism more complicated. In order to reveal the solid-gas coal and gas coupling mechanism and kinetic behavior characteristics, this paper established a multidimensional unload strong coupling damage porous media seepage experimental system, carried out theoretical and applied basic research fractured gas-solid coupling dynamics of coal. Based on multi-scale structure of coal characteristics and temporal variability, carried out gas adsorption, desorption and diffusion experiments at different scales of coal particles, and meso-scale coal deformation and damage mechanics coupled seepage experiments, and the establishment of appropriate physical equations; developed for multi-scale fractured coal gas-solid coupling mathematical model of coal and gas coupling analysis, calculation methods and procedures, and successfully applied to engineering practice. Mainly achieved the following findings:Carried out liquid nitrogen adsorption experiment and mercury injection experiment of different kind of coal samples, revealed multiscale structural features of fractured coal, and the multifractal regularity of coal pore/fissure structure has carried on the quantitative research, and which is helpful for the mathematical physics model of gas in the coal and gas coupling research and laid the physical structure and scale boundary.Launched a gas isotherm adsorption experiments at different scales of coal particles and Methane emission test, revealed the scale features and control mechanism of coal particles of gas adsorption and desorption and diffusion law, and established the double pore diffusion numerical model of coal particles, from the micro, small and macro angle reveals the dynamic mechanism of gas emission of coal particles.Launched a coal containing gas uniaxial compression test, limit axial pressure swing adsorption expansion deformation and failure experiment and crack propagation damage and failure experiments, and AE positioning. Consider expansion stress and erosion of gas adsorption, An anisotropic effective stress equation of gas bearing coal was established. Based on fracture mechanics and microscopic damage mechanics, the influence of the temporal evolution of fracture mechanics properties of coal was stddied. Coal strength parameters changed because of gas adsorption, based on Mohr-Columb guidelines, the quantitative of adsorb non-mechanical effect of gas was made, and the established a dual porosity damage constitutive model. Combining custom physics module of Comsol Multiphysics software, developed a numerical model and calculation procedures for mechanical deformation and destruction of gas bearing coal.Build the multidimensional and uninstall porous media strong coupling damage seepage experiment system, simulated deep rock mass stress environment, to carry out limited confining pressure coal flow experiments, equivalent confining pressure flow experiments and true triaxial loading and unloading flow experiments. Study the coupling between the complex stress fracture damage evolution and temporal variability of flow field, and established matrix porosity and fracture stress-damage-seepage coupled equations. While carrying out a different pressure gradient helium seepage experiments to study the seepage mechanism during damage evolution process of coal fracture. The results showed that in the matrix porosity the presence of starting pressure gradient nonlinear Darcy flow, while the fissures in the low pressure gradient segments showed significant Klinkenberg effect, at high pressure gradient stage also exhibit a power-law flow rule.Established a multi-scale fissure gas-solid coupling mathematical physics model of coal(MSFM), and based on Comsol Multiphysics simulation software secondary development platform, developed specially suitable for large scale of coal seam gas seepage stress and damage field coupling numerical calculation program, and conducted a steeply inclined protective layer mining numerical analysis and engineering practice. MSFM model takes into account the real spatial distribution of crack damage to mechanical deformation and damage characteristics and the influence of seepage characteristics, it can be achieved under mining under stress(static and dynamic stress field) that crack extension and damage control accurately.The research results reveal the mechanism of gas bearing coal dynamic disasters, for timely and effective disaster prevention and build a multi-information fusion physics dynamic monitoring and early warning system to provide a scientific basis and theoretical support, but also to promote the development and use of shale gas resources, CO2 underground storage, the development of nuclear waste disposal and groundwater pollution, and other related subjects.The paper contains 94 figures, 17 tables, and 219 references.