Rock and Soil Mechanics ›› 2019, Vol. 40 ›› Issue (2): 481-488.doi: 10.16285/j.rsm.2017.1646

• Fundamental Theroy and Experimental Research • Previous Articles     Next Articles

Characteristics and generation mechanism of low-frequency magnetic field generated during the damage of coal under static load

LI Cheng-wu, FU Shuai, XIE Bei-jing, LI Guang-yao, WAN Tian-yu   

  1. College of Resource and Safety Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China
  • Received:2017-11-02 Online:2019-02-11 Published:2019-02-13
  • Supported by:
    This work was supported by the National Natural Science Foundation of China (51274206) and the National Science Foundation for Young Scientists of China (51404277).

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Abstract: The aim of this paper is to study the characteristics and generation mechanism of the low-frequency magnetic field generated during the damage of coal under static load, and to complete the monitoring and warning technology of dynamic disasters in coal mine. Laboratory and field experiments were conducted to analyse the characteristics in time and frequency domain of low-frequency magnetic signal. Laboratory experiment results show that the strength of the generated magnetic field is in the range of 19-156 nT. Both the maximum amplitude and magnetic field energy have a positive correlation with the intensity of coal and loading speed. It also shows that the magnetic field perpendicular to crack surface is the strongest, while the magnetic field parallel to the crack surface is the weakest. Then, by combining with the micro-seismic signal, generation mechanism of the low-frequency magnetic field was proposed. Results reflect that the magnetic signal and micro-seismic signal are synchronous in the time and frequency domain, and oscillation of crack surface with charge leads to low-frequency magnetic field. Field test results indicate that the magnetic signal includes the cluster pulse signal and small amplitude oscillation signal. The cluster pulse signal is caused by the crack surface vibration generated from blasting. The small amplitude oscillation signal is the result of lateral tensile failure generated during the formation process of the new stress equilibrium in coal wall, and migration, friction and rotation of coal particles with charge.

Key words: damage by static load, low-frequency magnetic field, micro-seismic signal, characteristics in time and frequency domain, generation mechanism

CLC Number: 

  • TD 324
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