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<p>The mining-induced boundary is a crucial tool for ascertaining the stress relief characteristics of protected coal seam. The damage and failure of coal near the boundary leads to stress relief boundary displacement,&#xa0;which complicating precise determination&#xa0;procedure. To investigate the mechanical response of coal specimens subjected to cyclic loading, the MTS 815 was utilized to conduct increasing variable-frequency multistage uniaxial cyclic compression tests with varying stress levels. The laws of elastic moduli, strain energy and acoustic emission evolution under cyclic loading were derived. The experimental results indicated that coal specimens displayed distinct cyclic hysteresis under high stress levels when subjected to different loading frequencies. The application of cyclic loading significantly improved the coal specimen’s strength at relatively lower stress levels, and the coal specimen’s peak strength increased from 29.3 to 37.4 MPa. Prior to the attainment of maximum strength in coal specimens, a modest decline in elastic moduli was observed when stress levels remained sufficiently low. The elastic moduli exhibited heightened sensitivity to the frequency of loading, particularly at lower stress levels. The gap of the elastic moduli becomes stable when applied stress increases. Besides, Poisson’s ratio decreases with increase in cyclic number and the gap of Poisson’s ratio immediately show decrease when loading frequency increase. In addition, strain energy is the dominant energy in different loading stress loading conditions, However, the strain energy decreases at lower stress levels. The acoustic emission signal becomes pronounced when applied stress approaches crack closure stress, and the <i>b</i>-value serves as an effective measure for ascertaining crack closure stress. The research provides a comprehensive analysis of coal mass crack closure stress, offering a theoretical framework for the analysis of prevention of dynamic disasters.</p>

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Mechanical Response of Coal Exposed to Variable-Frequency Multistage Uniaxial Cyclic Loads

  • 期刊论文

  • 发表日期：

    2025年7月6日

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  • Zhang Bichuan,
  • Fu Junhui,
  • Feng Zengchao,
  • Zhu Nannan,
  • Li Guofu,
  • Guo Jizhe,
  • Liang Yunpei,
  • Zou Quanle,
  • Ran Qican,
  • Li Xuecheng,
  • Liu Jiaqi

摘要

The mining-induced boundary is a crucial tool for ascertaining the stress relief characteristics of protected coal seam. The damage and failure of coal near the boundary leads to stress relief boundary displacement, which complicating precise determination procedure. To investigate the mechanical response of coal specimens subjected to cyclic loading, the MTS 815 was utilized to conduct increasing variable-frequency multistage uniaxial cyclic compression tests with varying stress levels. The laws of elastic moduli, strain energy and acoustic emission evolution under cyclic loading were derived. The experimental results indicated that coal specimens displayed distinct cyclic hysteresis under high stress levels when subjected to different loading frequencies. The application of cyclic loading significantly improved the coal specimen’s strength at relatively lower stress levels, and the coal specimen’s peak strength increased from 29.3 to 37.4 MPa. Prior to the attainment of maximum strength in coal specimens, a modest decline in elastic moduli was observed when stress levels remained sufficiently low. The elastic moduli exhibited heightened sensitivity to the frequency of loading, particularly at lower stress levels. The gap of the elastic moduli becomes stable when applied stress increases. Besides, Poisson’s ratio decreases with increase in cyclic number and the gap of Poisson’s ratio immediately show decrease when loading frequency increase. In addition, strain energy is the dominant energy in different loading stress loading conditions, However, the strain energy decreases at lower stress levels. The acoustic emission signal becomes pronounced when applied stress approaches crack closure stress, and the b-value serves as an effective measure for ascertaining crack closure stress. The research provides a comprehensive analysis of coal mass crack closure stress, offering a theoretical framework for the analysis of prevention of dynamic disasters.