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Abstract The homemade triaxial servo-controlled seepage equipment was used to investigate the coal containing methane under the coupled action of thermo-fluid-solid. The gaseous loading-unloading tests under the different confining pressures and axial compressions were carried out to explore the process of the coal deformation and gas migration at different seam depths. During the loading process，the strain of coal decreases linearly with increasing gas pressures，while during the unloading process，the strain of coal increased with the decreasing of gas pressures. With the axial compression and the confining pressure increasing，the variations of the strain of coal under unit gas pressure reduce. As the gas pressure increases in the loading process，the permeability of coal decreases firstly then increases，which exhibits a V-shape. The permeability of coal has a turning point at the pressure about 1.2 MPa，which indicates that the expansion degree of coal porosity and the thickness of adsorption layer depends on the adsorption or the dominance of effective stress. As the gas pressure decreases during the unloading process，the permeability of coal decreases firstly then increases due to the effective stress or the effective stress dominance. With the effective stress increases，the permeability of coal decreases firstly then increases. The change of permeability caused by the effective stress is a logarithmic or exponential function in the different intervals. The gas pressure shows a typical of two-stage characteristics. The permeability and the volumetric strain are closely related to each other，indicating that the effective stress，the expansion due to absorption as well as the matrix shrinkage all affect the internal structures of coal.
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Received: 26 December 2013
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2014, Vol. 33 
