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<p>The acceleration of deep resource exploitation has led to challenges in deep resource development, deep engineering geological disaster prevention, and healthy operation and maintenance, where the stress changes in surrounding rock under different conditions present varying stress loading and unloading rates. To investigate the mechanical properties of deep rock under different loading and unloading rates, several tests were conducted via a multifunctional true triaxial geophysical apparatus. The results indicate that the principal strain of specimen is not directly related to the loading rate but depends on the relative changes in three-dimensional principal stresses caused by complex loading‒unloading conditions. In horizontal maximum principal stress unloading (HMAU) tests, the true triaxial strength of specimen gradually decreases with decreasing the rate of change of <i>σ</i><sub>h,max</sub>, with the corresponding failure mode shifting from shear failure to tensile failure, intensifying tensile plastic failure. In horizontal minimum principal stress unloading (HMIU) tests, the true triaxial strength also gradually decreases with decreasing the rate of change of <i>σ</i><sub>h,min</sub> (<i>v</i><sub>h,min</sub>), transitioning from tensile‒shear failure mode to a more complex failure mode, exacerbating specimen fragmentation. In horizontal minimum principal stress loading (HMIL) tests, the true triaxial strength of specimens shows no significant change with increasing <i>v</i><sub>h,min</sub>, and the failure mode remains unchanged, resulting in tensile‒shear failure characterized by layering and less fragmentation. A calculation method for elastic strain energy and dissipation energy applicable to different true triaxial stress loading‒unloading conditions is proposed, revealing the characteristics of energy evolution. Furthermore, based on the Drucker‒Prager criterion, the stress results under different loading–unloading conditions are compared with those under normal conditions, elucidating the variations in mechanical parameters of specimens and establishing the relationship between loading and unloading rates and strength reduction, thereby revealing the mechanism of strength reduction in true triaxial tests. This research provides guidance for deep underground engineering.</p>

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Effect of True Triaxial Loading and Unloading Rates on the Mechanical Properties of Deep Rock

  • 期刊论文

  • 发表日期：

    2025年4月27日

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  • Heng Gao,
  • Heping Xie,
  • Ru Zhang,
  • Zetian Zhang,
  • Mingzhong Gao,
  • Jun Lu,
  • Mingyang Wu,
  • Yihang Li,
  • Hongxin Xie

摘要

The acceleration of deep resource exploitation has led to challenges in deep resource development, deep engineering geological disaster prevention, and healthy operation and maintenance, where the stress changes in surrounding rock under different conditions present varying stress loading and unloading rates. To investigate the mechanical properties of deep rock under different loading and unloading rates, several tests were conducted via a multifunctional true triaxial geophysical apparatus. The results indicate that the principal strain of specimen is not directly related to the loading rate but depends on the relative changes in three-dimensional principal stresses caused by complex loading‒unloading conditions. In horizontal maximum principal stress unloading (HMAU) tests, the true triaxial strength of specimen gradually decreases with decreasing the rate of change of σh,max, with the corresponding failure mode shifting from shear failure to tensile failure, intensifying tensile plastic failure. In horizontal minimum principal stress unloading (HMIU) tests, the true triaxial strength also gradually decreases with decreasing the rate of change of σh,min (vh,min), transitioning from tensile‒shear failure mode to a more complex failure mode, exacerbating specimen fragmentation. In horizontal minimum principal stress loading (HMIL) tests, the true triaxial strength of specimens shows no significant change with increasing vh,min, and the failure mode remains unchanged, resulting in tensile‒shear failure characterized by layering and less fragmentation. A calculation method for elastic strain energy and dissipation energy applicable to different true triaxial stress loading‒unloading conditions is proposed, revealing the characteristics of energy evolution. Furthermore, based on the Drucker‒Prager criterion, the stress results under different loading–unloading conditions are compared with those under normal conditions, elucidating the variations in mechanical parameters of specimens and establishing the relationship between loading and unloading rates and strength reduction, thereby revealing the mechanism of strength reduction in true triaxial tests. This research provides guidance for deep underground engineering.