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<p>Cyclic loading and unloading are common in rock engineering and natural environments, particularly in geo-engineering projects where stress conditions are highly dynamic. Existing studies often neglect the nature of unloading amplitudes, limiting realistic understanding of rock behavior. Therefore, this study examines the influence of unloading stress levels on the mechanical response, damage evolution, and failure mechanisms of sandstone. Experiments were performed using a high-precision dynamic testing system and acoustic emission (AE) monitoring, with four unloading stress levels (25, 50, 75, and 100% of peak stress). Mechanical parameters, energy evolution, and AE characteristics were systematically analyzed. Results suggest that higher unloading stress tends to delay damage, enhances energy storage and elastic recovery, and shifts failure from tensile-dominated to shear or mixed-mode. Lower unloading stress accelerates microcrack initiation, stiffness loss, and tensile failure. Rock fatigue progresses through cumulative irreversible strain, modulus reduction, and increasing Poisson’s ratio. Energy analysis reveals rapid dissipated energy growth as a pre-failure signal, while AE monitoring confirms intensified crack activity, tensile-to-shear transitions, and spatial clustering. Loading–unloading response ratio further indicates stronger early recovery but faster irreversible damage accumulation at higher unloading levels. These findings highlight the regulatory role of unloading stress in rock fatigue and provide valuable insights for predicting failure and improving stability assessment in rock engineering.</p>

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Effects of Unloading Stress Variations on Mechanical and Acoustic Emission Properties of Rock Under Cyclic Loading

  • 期刊论文

  • 发表日期：

    2026年5月26日

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  • Yanhao Ning,
  • Chunfeng Ye,
  • Shiyue Zhang,
  • Xiao Song,
  • Jiajia Zhao,
  • Xujing Tan,
  • Qican Ran

摘要

Cyclic loading and unloading are common in rock engineering and natural environments, particularly in geo-engineering projects where stress conditions are highly dynamic. Existing studies often neglect the nature of unloading amplitudes, limiting realistic understanding of rock behavior. Therefore, this study examines the influence of unloading stress levels on the mechanical response, damage evolution, and failure mechanisms of sandstone. Experiments were performed using a high-precision dynamic testing system and acoustic emission (AE) monitoring, with four unloading stress levels (25, 50, 75, and 100% of peak stress). Mechanical parameters, energy evolution, and AE characteristics were systematically analyzed. Results suggest that higher unloading stress tends to delay damage, enhances energy storage and elastic recovery, and shifts failure from tensile-dominated to shear or mixed-mode. Lower unloading stress accelerates microcrack initiation, stiffness loss, and tensile failure. Rock fatigue progresses through cumulative irreversible strain, modulus reduction, and increasing Poisson’s ratio. Energy analysis reveals rapid dissipated energy growth as a pre-failure signal, while AE monitoring confirms intensified crack activity, tensile-to-shear transitions, and spatial clustering. Loading–unloading response ratio further indicates stronger early recovery but faster irreversible damage accumulation at higher unloading levels. These findings highlight the regulatory role of unloading stress in rock fatigue and provide valuable insights for predicting failure and improving stability assessment in rock engineering.