| Coal and gas outburst is one of the serious hidden dangers in coal mining. The outburst mechanism is a popular issue in the mining field, and peoples have not made a thorough study about it. It is of great importance to study the interaction between coal seam deformation and gas migration in coal seam, to explore effective computational method of coal seam deformation and gas migration coupling system, and to analyze the structural stability and Lyapunov's stability of the system.The initial state of coal seam and its surrounding rock was disturbed by mining, and violent change in both the deformation state of coal seam and the motion state of gas migration follows. At the same time, Lyapunov's instability or structural instability would occur. Gas migration (adsorption/desorption, diffusion and seepage) is effected by the deformation state of coal seam; and the change of porosity, deformation state, displacement, velocity, acceleration, strain and stress of coal seam were effected by the change of gas content and gas pressure. So the interaction between coal seam deformation and gas migration in coal seam is of extreme complication.The behaviors of dynamic system were researched by using theory, experiments and numerical calculation from the point of view of Dynamics of Systems with Variable Boundaries (DSVB). The main innovative results are listed as follows(1) Permeability parameters of coal samples in complete stress-strain process were obtained by experiments, those samples came from a low gas mine, a high gas mine and an outburst mine, respectively. The result shows that the permeability of coal sample from low gas mine monotonously increase with strain after failure. The permeability of coal sample from high gas mine does not fluctuate drastically after failure. The permeability of coal sample from outburst mine has a valley atε=1.4%, and leaps fromε=2.7%. The permeability of sample from low gas coal mine is larger than that of sample from high gas mine, and the later is higher than that of sample from outburst mine under a same strain. The non-Darcy-flowβfactor and acceleration coefficient change in a contrary manner to permeability.Permeability parameters of granular coal sampled from a low gas mine, a high gas mine and an outburst mine are obtained by test, respectively. The test results show that the permeability, non-Darcy-flowβfactor and acceleration coefficient can all be expressed by power function of porosity.(2) The failure modes and deformation states of coal seam were discussed, flow rules after both shear yielding and tensile failure were studied, the conversion condition of deformation states were presented, and the effect of gas pressure on material constants in both D-P criterion and Lagrange criterion was considered. Based on all these, the constitutive relation of coal seam was constructed.(3) The relationship between coal seam deformation and gas migration is connected by porosity and gas pressure. A dynamic system, coal seam deformation and gas migration coupling system, was modeled. In the establishment of dynamic model, three deformation state (elastic deformation, shear yielding, tensile failure) and three gas migration (adsorption/desorption, diffusion and seepage) were involved.(4) A numerical method for calculation of the response of the dynamic system is constructed by Fast Explicit Finite Difference Method based on Lagrangian description. Gas pressure, diffusion velocity and porosity of coal seam need to be defined on both nodes and elements.(5) A algorithm program for calculation of response of the dynamic system was programmed by Fortran. The mechanical properties of Daxing Coal Mine, Cuijiagou Coal Mine, and Qinan Coal Mine are used as control parameters to calculate the dynamic response of low gas coal seam, high gas coal seam and outburst coal seam, respectively. The deformation state of coal seam, permeability, non-Darcy-flowβfactor and acceleration coefficient are given by surface. The time history plot of gas emission was also given, and the state transition of deformation was obtained.
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