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Experimental Study of the Seepage Characteristics of Loaded Coal Under True Triaxial Conditions

  • Jiajia Liu
  • Jianliang Gao
  • Xuebo Zhang
  • Gaini Jia
  • Dan Wang
Original Paper
  • 93 Downloads

Abstract

Gas-bearing, coal-bearing rocks are affected by geological structures and mechanical disturbances. A stress environment exists in an unequal three-way pressure state. To determine the mechanisms of stress change that influence the fissure evolution in stratified coal under true triaxial conditions, different stratifications (vertical, horizontal and oblique stratifications) are experimentally studied based on coal gas permeability. The coal samples are investigated using scanning electron microscopy and transmission electron microscopy to analyze the microstructure differences of the coal samples before and after loading. The results show that the permeability of the different stratified coal samples is exponentially related to the maximum principal stress, the intermediate principal stress, the minimum principal stress and the effective stress. The initial permeability of the vertically stratified coal samples is only 13.5%, which is 22.2% of that for skewed bedding. The bedding direction has a significant effect on the seepage characteristics of the coal samples. In the past, most scholars ignored the influence of bedding when conducting permeability tests. The results of this paper have important theoretical and practical value for optimizing the parameters of gas drainage, increasing the gas drainage rate and reducing the “greenhouse effect” caused by gas emissions.

Keywords

True triaxial test Layer structure Gas seepage Microstructure Coal damage 

List of Symbols

\({\sigma _1}\)

Maximum principal stress

\({\sigma _2}\)

Intermediate principal stress

\({\sigma _3}\)

Minimum principal stress

Dm

Permeability loss of coal samples

k0

Permeability of the initial coal sample during loading

km

Permeability of the coal sample at the end of the loading

kb

Minimum permeability value of the coal sample during the entire loading process

\(\varepsilon _{{\text{v}}}^{{\text{P}}}\)

Volumetric strain increment

\({\varepsilon _{{\text{v}}i}}\;(i=1,2,3 \ldots ,n)\)

Volumetric strain

\({\varepsilon _{\text{v}}}\)

Volume strain

\({\varepsilon _1}\)

Direction of the maximum principal stress

\({\varepsilon _2}\)

Direction of the intermediate principal stress

\({\varepsilon _3}\)

Direction of the minimum principal stress

\(\tau\)

Shear stress

\({\sigma _{\text{m}}}\)

Average normal stress

\({\tau _\psi }\)

Shear stress on the \(\psi\) plane

\({\sigma _\psi }\)

Normal stress on the \(\psi\) plane

Notes

Acknowledgements

This work was supported by National Natural Science Foundation of China (51604101, 51704099, 51734007, 51774119, and 51604092), the National Key Research and Development Program of China (2018YFC0808103), the Doctoral Fund of Henan Polytechnic University (no. B2018-59), the State Key Laboratory Cultivation Base for Gas Geology and Gas Control (Henan Polytechnic University) (WS2017B06), the Henan Postdoctoral Foundation, and the Open Research Fund Program of Hunan Province Key Laboratory of Safe Mining Techniques Of Coal Mines (Hunan University of Science and Technology) (201502), the Open Research Fund Program of Hunan Province Key Laboratory of Safe Mining Techniques Of Coal Mines (Hunan University of Science and Technology) (201502).

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Copyright information

© Springer-Verlag GmbH Austria, part of Springer Nature 2019

Authors and Affiliations

  1. 1.State Key Laboratory Cultivation Base for Gas Geology and Gas ControlHenan Polytechnic UniversityJiaozuoPeople’s Republic of China
  2. 2.School of Safety Science and EngineeringHenan Polytechnic UniversityJiaozuoPeople’s Republic of China
  3. 3.State and Local Joint Engineering Laboratory for Gas Drainage and Ground Control of Deep MinesHenan Polytechnic UniversityJiaozuoChina
  4. 4.The Collaborative Innovation Center of Coal Safety Production of Henan ProvinceJiaozuoChina

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