Study on coal permeability characteristics under thermo-mechanical coupling

The increase of coal mining depth leads to the increase of ground temperature and stress, which affects the development of fractures and seepage characteristics. In order to study the variation characteristics of deformation and permeability of coal under thermo-mechanical coupling, the MTS815 test system was used to test the permeability of six groups of coal samples during the whole stress-strain process at 50 ℃ and 100 ℃. The results indicated that: when the temperature set to 50 ℃, the compressive strength of coal samples increased with the increase of confining pressure. The peak deviator stress of the coal sample reached to 3.6 MPa under the confining pressure of 4 MPa, and the axial and circumferential strains both reached more than 2%, showing high performance of malleability. The deformation resistance of coal samples decreased when the temperature set to 100 ℃; with the increase of confining pressure, the peak deviant stress increased to 4.9 MPa, and the rate of strain growth accelerated. When the test condition set to 4 MPa and 100 ℃, the peak permeability of coal sample reached to 3.5×10^-11 m². The original and new fractures expanded, and the pore connectivity was enhanced to form a complex fracture network during the loading process. Then, the volume of seepage fractures and permeability of coal samples was increased by thermal effect.