INVESTIGATION ON CHANGE RULE OF PERMEABILITY OF COAL CONTAINING GAS UNDER COMPLEX STRESS PATHS

According to experimental investigation on permeability property of coal containing gas,the change rule of permeability of coal containing gas is analyzed systematically under complex stress paths.Quantitative and qualitative relations of the permeability of coal containing gas with axial pressure,confining pressure,gas pressure,loading-unloading of confining pressure and complete stress-strain process are established respectively.The controlling mechanism and change law of permeability of coal containing gas under different stress paths are discussed.The results show that the stress path has an important impact on the permeability of coal containing gas:(1) The permeability of coal containing gas decreases with the increase of axial pressure and confining pressure,while increases with the increase of gas pressure.(2) The relationships of permeability of coal containing gas with axial pressure,confining pressure and gas pressure obey approximately an exponential law.(3) During the loading-unloading process of confining pressure,the permeability of coal containing gas is damaged to a certain extent and this damage can be represented by the maximal damage rate and damage rate of permeability.At the same time,the results show that the second-compacting effect of coal containing gas will happen under the condition of triaxial compression.(4) During the complete stress-strain a test process under triaxial compression,the change trend of permeability of coal containing gas versus strain curve is V-shaped approximately.The permeability of coal sample decreases first,then increases with strain,and reaches its maximum finally.The increasing amplitude is less than the decreasing amplitude.