Evaluation of the effect of adsorbed gas and free gas on mechanical properties of coal

  • Shouqing Lu
  • Yongliang ZhangEmail author
  • Zhanyou Sa
  • Shufang Si
Original Article


The mechanical properties of coal are important parameters for coalbed methane (CBM) extraction and gas outburst control. However, the effect of adsorbed gas on strength cannot be evaluated quantitatively yet. To better understand the weakening mechanisms of free and adsorbed gas on the strength of coal, normal coal, and deformed coal are chosen to test their mechanical properties of CH4-saturated and non-gas-saturated specimens under different conditions. Under the same effective stresses, the peaks of strength of CH4-saturated specimens with high-pressure gas are lower than those with low-pressure gas, implying that the adsorbed gas can also weaken the peak strength of coal. Then, a new model for the weakening values of strength induced by free and adsorbed gas was developed, and the effects of free gas and adsorbed gas on the strength of coal were assessed by our model. The results show that the free gas and adsorbed gas can weaken the strength of coal for different weakening mechanisms. The ratio of weakening value of strength due to free gas to that of adsorbed gas of the normal coal is 1.3–3.4, and that of the deformed coal is 8.4–19.8. These results can help us to better understand why the weakening effect of adsorbed CH4 in the laboratory is ignored in earlier studies.


Gas-saturated coal Strength of coal Weakening mechanisms Free gas Adsorbed gas 



Financial support is provided by the Open Funds (WS2017B05) of State Key Laboratory Cultivation Base for Gas Geology and Gas Control (Henan Polytechnic University), the Natural Science Foundation of Shandong Province (ZR2018PEE001, ZR2018MEE002, 2017GSF20113), the National Science Foundation of China (51804176, 51574153, 51874187 and 51504140) and a Project of Shandong Province Higher Educational Science and Technology Program (J18KA187). The authors would like to thank Longyong Shu for his help and suggestion on modification of this paper.


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Copyright information

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

Authors and Affiliations

  • Shouqing Lu
    • 1
    • 2
    • 3
  • Yongliang Zhang
    • 1
    • 3
    Email author
  • Zhanyou Sa
    • 1
    • 3
  • Shufang Si
    • 4
  1. 1.Department of Safety EngineeringQingdao University of TechnologyQingdaoChina
  2. 2.State Key Laboratory Cultivation Base for Gas Geology and Gas Control (Henan Polytechnic University)JiaozuoChina
  3. 3.Shandong Key Industry Field Accident Prevention Technology Research Center (Non-ferrous Metallurgy)QingdaoChina
  4. 4.Qingdao Hongan Certified Safety Engineer Firm Limited CompanyQingdaoChina

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