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Damage and Permeability Development in Coal During Unloading

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Abstract

One of the key issues in protective seam mining is the pressure relief and permeability improvement effect. In this paper, the results of X-ray CT scanning experiments and permeability experiments using reconstituted coal specimens subjected to the same stress path and the same effective confining pressure (confining pressure minus pore pressure) are combined using the stress–strain relationship to study the damage to reconstituted coal specimens and its influence on permeability during the unloading process. When the effective confining pressure (σ 3 − p) is unloaded from 8 to 6 MPa and the deviatoric stress increases, the damage variables will increase by 0.0351 and 0.084, respectively, compared with the unloading point under the fixed axial displacement with unloading confining pressure (FADUCP) and fixed deviatoric stress with unloading confining pressure (FDSUCP) stress paths. At the same time, the permeability increased by 1.7 and 16.7 %, respectively. Therefore, the damage variable and permeability increased notably little in this process. After the effective confining pressure is unloaded to approximately 5 MPa, together with the decrease in the deviatoric stress, the growth of the damage variable and permeability begins to accelerate. In addition, the relative decrease in the deviatoric stress with appearing damage cracks, and the relative increase in permeability with the same amount of effective confining pressure being unloaded, shows that the damage to specimens under the FDSUCP stress path is larger than that from the FADUCP stress path.

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Acknowledgments

This research was supported by the Natural Science Foundation for the Youth of China (No. 51204173), the National Basic Research Program of China (973 Program, No. 2011CB201204) and the Natural Science Foundation for the Youth of China (No. 41202118).

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Authors and Affiliations

  1. National Engineering Research Center for Coal and Gas Control, China University of Mining and Technology, Xuzhou Jiangsu, 221116, People’s Republic of China

    Hai-Dong Chen, Cheng Yuan-Ping, Hong-Xing Zhou & Wei Li

  2. State Key Laboratory of Coal Resources and Mine Safety, China University of Mining and Technology, Xuzhou Jiangsu, 221116, People’s Republic of China

    Cheng Yuan-Ping

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  1. Hai-Dong Chen
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  2. Cheng Yuan-Ping
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  3. Hong-Xing Zhou
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  4. Wei Li
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Correspondence to Cheng Yuan-Ping.

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Chen, HD., Yuan-Ping, C., Zhou, HX. et al. Damage and Permeability Development in Coal During Unloading. Rock Mech Rock Eng 46, 1377–1390 (2013). https://doi.org/10.1007/s00603-013-0370-2

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  • DOI: https://doi.org/10.1007/s00603-013-0370-2

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