Thermal Science 2014 Volume 18, Issue 5, Pages: 1497-1504
https://doi.org/10.2298/TSCI1405497Z
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Permeability evolution of unloaded coal samples at different loading rates
Zhang Ze-Tian (Sichuan University, State Key Laboratory of Hydraulics and Mountain River Engineering, Chengdu, China + Sichuan University, College of Water Resource and Hydropower, Chengdu, China)
Ru Zhang (Sichuan University, State Key Laboratory of Hydraulics and Mountain River Engineering, Chengdu, China + Sichuan University, College of Water Resource and Hydropower, Chengdu, China)
Liu Jian-Feng (Sichuan University, State Key Laboratory of Hydraulics and Mountain River Engineering, Chengdu, China + Sichuan University, College of Water Resource and Hydropower, Chengdu, China)
Liu Xiao-Hui (Sichuan University, State Key Laboratory of Hydraulics and Mountain River Engineering, Chengdu, China + Sichuan University, College of Water Resource and Hydropower, Chengdu, China)
Li Jia-Wei (Sichuan University, State Key Laboratory of Hydraulics and Mountain River Engineering, Chengdu, China + Sichuan University, College of Water Resource and Hydropower, Chengdu, China)
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.
Keywords: permeability evolution, coal, loading rate, triaxial unloading experiment