TY - JOUR
TI - Permeability evolution of unloaded coal samples at different loading rates
AU - Zhang Ze-Tian
AU - Zhang Ru
AU - Liu Jian-Feng
AU - Liu Xiao-Hui
AU - Li Jia-Wei
JN - Thermal Science
PY - 2014
VL - 18
IS - 5
SP - 1497
EP - 1504
PT - Article
AB - As coal mass is often at unloading status during mining process, it is of  great significance to push on the research on permeability evolution of  unloaded coal samples at different loading rates. A series of triaxial  unloading experiments were conducted for initially intact coal samples using  an improved rock mechanics testing system, and the permeability was  continuously measured by the constant pressure differential method for  methane. Permeability evolution law of unloaded coal samples and the  influence mechanism of loading rates on that were studied. The results of  triaxial unloading experiments indicate that the permeability of coal samples  increases throughout the whole testing process without a descent stage, which  is different from the permeability evolution law in conventional triaxial  compression tests. The maximum permeability of unloaded coal sample, which is  4 to 18 times to its initial permeability, often appears before reaching the  peak stress and increases with the decrease of axial loading rate. Stress  state corresponding to the surge point of permeability of the unloaded coal  samples is also discussed.