Research on influencing factors of permeability change for outburst-prone coal

According to permeability test investigation of outburst-prone coal, permeability properties of outburst-prone coal specimens are analyzed systematically for different confining pressures, different gas pressures, and different stress-strain conditions. Quantitative and qualitative relations between outburst-prone coal permeability and confining pressure, gas pressure and stress-strain curve are established respectively. The controlling mechanism and changing law of outburst-prone coal permeability under variable loading conditions are discussed. The results show that the loading condition has an important impact on outburst-prone coal permeability, and the details are: (1) For fixed gas pressure condition, outburst-prone coal permeability decreases with increasing of confining pressure; and the decreasing rule obeys an exponential law. (2) For fixed confining pressure condition, the relation between permeability and gas pressure is showed a "V" curve approximately in shape affected by Klinkenberg effect, which happens in the gas pressure range of p < 1 MPa. (3) During the whole stress-strain process under triaxial compression, the change trends of outburst-prone coal permeability versus strain curve for different loading conditions are almost uniform, which are showed a "V" curve. At the stage of microfissure closing and elastic deformation, the coal specimen permeability decreases with the increasing of stress; after entering into the yield stage, the coal specimen permeability reaches the minimum and anti-exceeding is accomplished before reaching the peak strength. The permeability increases continuously until the end of test after reaching the peak strength. The outburst-prone coal permeability after anti-exceeding changes more mildly than before anti-exceeding.