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Changes in Frequency of Electromagnetic Radiation from Loaded Coal Rock

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Abstract

To understand the relationship between the frequency of electromagnetic radiation (EMR) emitted from loaded coal rock and the micro-crack structures inside it, and assess the stress state and the stability of coal rock by analyzing frequency changes in characteristics of its emitted EMR, we first experimentally studied the changes in time sequence and the frequency spectrum characteristics of EMR during uniaxial compression, then theoretically derived the relationship between the principal frequency of EMR signals and the mechanical parameters of coal crack and analyzed the major factors causing the changes in the principal frequency, and lastly verified the results at Nuodong Coal Mine, Guizhou Province, China. The experimental results showed that (1) EMR intensity increased with the applied stress on loaded coal rock during its deformation and failure and could qualitatively reflect the coal’s stress status; (2) with the applied stress increasing, the principal frequency gradually increased from near zero to about 60 kHz and then dropped to less than 20 kHz. During this period, coal rock first stepped into the linearly and elastically deformed stage and then ruptured around the peak load. Theoretical analysis showed that there was a negative correlation between the principle frequency and the size of internal cracks. Field detection showed that a lower principle frequency was generated from coal rock applied by a greater load, while a higher principal frequency was generated from coal rocks suffering a weaker load.

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Abbreviations

ω :

Angular frequency

b :

Crack width

V R :

Rayleigh wave speed

K I :

Stress strength factor of Type I cracks

σ s :

Yield stress

E :

Elastic modulus

μ :

Poisson’s ratio

σ :

Applied stress

a :

Half length of initial crack

V s :

Speed of the transverse wave

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Acknowledgments

This work is supported by the Youth Science Foundation of the National Natural Science Foundation of China (51104156), the China Postdoctoral Science Foundation (2014T70678) and the Priority Academic Program Development of Jiangsu Higher Education Institutions.

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Authors and Affiliations

  1. School of Safety Engineering, China University of Mining and Technology, Xuzhou, 221116, China

    Dazhao Song, Enyuan Wang & Liming Qiu

  2. Postdoctoral Research Station, Yongcheng Coal and Electricity Holding Group Co. Ltd., Yongcheng, 476600, China

    Dazhao Song

  3. Key Laboratory of Gas and Fire Control for Coal Mines, Xuzhou, 221008, China

    Enyuan Wang

  4. College of Applied Science and Technology, China University of Mining and Technology, Xuzhou, 221008, China

    Xiaoyan Song

  5. School of Municipal and Environmental Engineering, Jilin Jianzhu University, Jilin, 130118, China

    Peijian Jin

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  1. Dazhao Song
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  2. Enyuan Wang
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  3. Xiaoyan Song
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  4. Peijian Jin
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  5. Liming Qiu
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Correspondence to Enyuan Wang.

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Song, D., Wang, E., Song, X. et al. Changes in Frequency of Electromagnetic Radiation from Loaded Coal Rock. Rock Mech Rock Eng 49, 291–302 (2016). https://doi.org/10.1007/s00603-015-0738-6

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  • DOI: https://doi.org/10.1007/s00603-015-0738-6

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