Study on permeability characteristics of coal rock in complete stress-strain process

Nine standard coal samples with dimensions of 50 mm in diameter and 100 mm in height,which were taken from Zhangji Coal Mine in Huainan City of Anhui Province,and tested on gas flow regularities of complete stress-strain process and the X-ray industrial CT.The results of the permeability tests show that the permeability-strain curves are similar to stress-strain curves of the coal rock,and stress hysteretic nature is shown in permeability-strain curves,which indicates that the close relativity between the character of gas flow in the coal samples and the damage evolution of coal samples during the loading processes.The permeability is decreased with the developing of confining pressure which causes consolidation in the gas thoroughfare of coal samples.Tests by the X-ray industrial CT before and after the permeability tests show that there are rare micro-porosity and micro-fracture observed before the permeability tests,and clear cracks found after the permeability tests which indicate sharp rising of permeability after the peak of stress-strain curves.