Mechanical properties and permeability evolution of gas-bearing coal under phased variable speed loading and unloading

  • Chengpeng Xin
  • Kai WangEmail author
  • Feng Du
  • Xiang Zhang
  • Gongda Wang
  • Yilei Liu
Original Paper


It is of great significance for the analysis and prediction of coal-gas outburst disasters to understand the mechanical properties and permeability evolution of coal and rock under conditions of stope stress evolution. In this study, mechanical tests were conducted on gas-bearing coal under four stress paths, including conventional triaxial compression (CTC), phased variable speed triaxial compression (PVSTC), unloading confining pressure (UCP), and phased variable speed unloading confining pressure (PVSUCP), simultaneously measuring the permeability in mechanical tests. The mechanical properties and permeability evolutions in gas-bearing coal under four different stress paths were compared. The obtained results show that the deviatoric stress-strain curves of gas-bearing coal under four stress paths could be divided into five stages: compaction, linear elasticity, plastic deformation, stress drop, and residual stress stage. The permeability-strain curves under four stress paths could also be divided into five stages: fast drop, slow decrease, slow increase, sharp increase, and slowed growth. Compared to the CTC conditions, the peak strain and strength of coal under PVSTC conditions increased. Furthermore, the stress drop and energy release under PVSTC were more intense at the moment of instability failure. Compared to both loading paths, the coal was damaged more rapidly under unloading paths and the damage was stronger. Additionally, among both unloading paths, the time required for the failure of coal under PVSUCP was shorter than that under UCP, while the damage under PVSUCP was stronger. The strength characteristics of the gas-bearing coal under PVSTC and PVSUCP still met the Mohr–Coulomb criterion. This preliminary study has guiding significance for the understanding of the co-occurrence mechanisms of coal-gas outburst disasters.


Gas-bearing coal Triaxial compression Unloading confining Phased variable speed Mechanical properties Permeability 



Conventional triaxial compression


Phased variable speed triaxial compression


Unloading confining pressure


Phased variable speed unloading confining pressure



This research is financially supported by the State Key Research Development Program of China (2016YFC0801402, 2016YFC0600708), National Natural Science Foundation of China (51474219, 51604153, 51874314), the Open Funds of Hebei State Key Laboratory of Mine Disaster Prevention (KJZH2017K02), the Joint Fund Project of Guizhou Science and Technology Department and Bijie Science and Technology Bureau and Institute of Circular Economy (LH[2017]7520), the Guizhou Science and Technology Support Program ([2017]2820), and the Yue Qi Distinguished Scholar Project, China University of Mining & Technology, Beijing. Feng Du would like to acknowledge the Fund of China Scholarship Council (CSC) for his study in Department of Civil Engineering and Engineering Mechanics, Columbia University.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.


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Copyright information

© Saudi Society for Geosciences 2018

Authors and Affiliations

  • Chengpeng Xin
    • 1
    • 2
    • 3
  • Kai Wang
    • 1
    • 2
    • 4
    Email author
  • Feng Du
    • 1
    • 2
  • Xiang Zhang
    • 1
    • 2
  • Gongda Wang
    • 5
  • Yilei Liu
    • 3
  1. 1.Beijing Key Laboratory for Precise Mining of Intergrown Energy and ResourcesChina University of Mining and Technology (Beijing)BeijingChina
  2. 2.School of Resource & Safety EngineeringChina University of Mining & Technology (Beijing)BeijingChina
  3. 3.School of Mining EngineeringGuizhou University of Engineering ScienceBijieChina
  4. 4.Hebei State Key Laboratory of Mine Disaster PreventionNorth China Institute of Science and TechnologyBeijingChina
  5. 5.Mine Safety Technology BranchChina Coal Research InstituteBeijingChina

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