THERMAL SCIENCE

International Scientific Journal

Thermal Science - Online First

online first only

Variation law of coal permeability under cyclic loading and unloading

ABSTRACT
In the excavation process, the coal pillar will undergo shear failure due to repeated loading and unloading from mining stress. Meanwhile, plastic flow will occur after shear failure. The permeability change of the coal pillar under plastic flow is closely related to the loading path. Through a permeability test of the coal sample after shear yielding under cyclic loading and unloading conditions, the variation law of permeability of a coal seam under plastic flow was obtained. The results show that the permeability of the coal sample increases as the axial strain decreases during the unloading phase. During the loading phase, as the axial strain increases, the permeability of the coal sample decreases. SEM (scanning electron microscope) tests show that the crack opening is larger at lower confining pressures. As the confining pressure increases, the crack opening decreases and moves toward the middle of the sample.
KEYWORDS
PAPER SUBMITTED: 2018-09-07
PAPER REVISED: 2018-12-12
PAPER ACCEPTED: 2019-12-25
PUBLISHED ONLINE: 2019-05-26
DOI REFERENCE: https://doi.org/10.2298/TSCI180907215G
REFERENCES
  1. Wu, G., et al., Studying Unloading Failure Characteristics of a Rock Mass Using the Disturbed State Concept, International Journal of Rock Mechanics and Mining Sciences, 41 (2004), 1, pp. 419-425
  2. Xie, H.Q., et al., Study of The Unloading Characteristics of a Rock Mass Using the Triaxial Test and Damage Mechanics, International Journal of Rock Mechanics and Mining Sciences, 41 (2004), 3, pp. 366-0
  3. He, M.C.,et al., Rock Burst Process of Limestone and Its Acoustic Emission Characteristics Under True-triaxial Unloading Conditions, International Journal of Rock Mechanics and Mining Sciences, 47 (2010), 2, pp. 286-298
  4. Mair, K., et al., Influence of Confining Pressure On the Mechanical and Structural Evolution of Laboratory Deformation Bands, Geophysical Research Letters, 29 (2002), 10, pp. 49-41
  5. Zheng ,J., et al., Relationships Between Permeability, Porosity and Effective Stress for Low-Permeability Sedimentary Rock, International Journal of Rock Mechanics and Mining Sciences, 78 (2015), pp. 304-318
  6. Zhang, Z., et al., The Relationships Among Stress, Effective Porosity and Permeability of Coal Considering the Distribution of Natural Fractures: Theoretical and Experimental Analyses, Environmental Earth Sciences, 73 (2015), 10, pp. 5997-6007
  7. Connell, L.D., et al., An Analytical Coal Permeability Model For Tri-axial Strain and Stress Conditions, International Journal of Coal Geology, 84 (2010), 2, pp. 103-114
  8. Liu, J. F., et al., Gas Permeability of a Compacted Bentonite-Sand Mixture: Coupled Effects of Water Content, Dry Density, and Confining Pressure, Canadian Geotechnical Journal, 52 (2015), 1, pp. 1159-1167
  9. Liu, J.F., et al., Experimental Research on Water Retention and Gas Permeability of Compacted Bentonite/Sand Mixtures, Soils and Foundations, 54 (2014), 5, pp. 1027-1038
  10. Wang, J.A., et al., Fluid Permeability of Sedimentary Rocks in a Complete Stress-Strain Process, Engineering Geology, 63 (2002), 3-4, pp. 291-300
  11. Zhao, Y., et al., Hydromechanical Coupling Tests for Mechanical and Permeability Characteristics of Fractured Limestone in Complete Stress-Strain Process, Environmental Earth Sciences, 76 (2016), 1, pp. 24-42
  12. Zhang, Q., et al., Coupled Thermal-Gas-Mechanical (TGM) Model of Tight Sandstone Gas Wells, Journal of Geophysics and Engineering, 15(2018), 4, pp. 1743-1752
  13. Liu, J.F., et al., Investigation into Water Retention and Gas Permeability of Opalinus Clay, Environmental Earth Sciences, 77 (2018), 5, pp. 5213-226
  14. Guo, J.N., Experimental Study on Permeability Evolution of Coal Samples under Plastic Flow, China University of Mining and Technology.2015.