Permeability of coal samples containing methane under cyclic loading-unloading of axial stresses
SUN Guangzhong1,2,3,JING Yongbin2,3,ZHANG Ruilin2,3,WANG Liguan1
(1. School of Resources and Safety Engineering,Central South University,Changsha,Hunan 410083,China;
2. School of Safety Engineering,Henan Institute Engineering,Zhengzhou,Henan 451191,China;
3. Key Laboratory of Coal Mine Safety Training Base in Henan Province,Henan Institute Engineering,Zhengzhou,
Henan 451191,China)
Abstract:In order to investigate the response of tectonic coal to cyclic loading-unloading of axial stresses,experimental study and analysis of dynamic model of permeability were carried out with experiment facility developed in-house for triaxial seepage test considering the fluid-solid-heat coupling in gas filled coal. The results show that the relation between the permeability of gas filled coal and the strain presents a trend of inclined letter ‘V’. The permeability of tectonic coal samples increases obviously after peak strength and the growth rate is greater than the reduction rate of permeability in the initial stage of compression. The permeability of coal samples and the axial stress presented a relation of negative exponential function during unloading. The permeability decreases under loading and recoveres a bit under unloading. The permeability and the effective stress does not form a closed curve. The reduction of permeability increases and the sensitivity of permeability to the effective stress decreases because that pores of coal sample are more compressed under cyclic loading- unloading. A factor in reduction of permeability sensitivity when loading and another factor in reduction of permeability when unloading were introduced,and then the dynamic evolution model of permeability and effective stress under cyclic loading-unloading was established. The comparison of experimental data with theoretical results verified the applicability of this model.
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