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<p>The freeze‒thaw (F-T) damage mechanism and evolution model of saturated gray sandstone specimens under uniaxial compression were systematically studied based on acoustic emission (AE) and nuclear magnetic resonance (NMR) technology. The results indicate that the F-T cycles can lead to the deterioration of the internal structure of specimens by observing the T<sub>2</sub> spectrum and NMR images. The peak strength and elastic modulus of the specimens decreased gradually as the number of F-T cycles increased, and the peak strain showed an obvious increasing trend. The decrement rates for the peak strength and elastic modulus of the specimens are 95.49% and 88.92%, respectively, and the increment rate peak strain is 43.06% when the F-T cycles increase from 0 to 60. In addition, the strength decreased from 27.5&#xa0;MPa to 11.2&#xa0;MPa after 20&#xa0;F-T cycles, a decrease of 59.27%. However, the strength at 20 cycles did not decrease significantly, and the strengths at 40 cycles and 60 cycles were 5.5&#xa0;MPa and 1.3&#xa0;MPa, respectively). The failure modes of the specimens changed into splitting failure, shear failure, cone failure and multicrack composite failure modes with the increase in the number of F-T cycles. F-T cycles have a significant effect on the AE response characteristics during the progress of loading process. With the increase in F-T cycles, the AE events gradually increase, and the AE response is violent. AE localization technology can not only accurately reflect the internal damage evolution trend during loading, but also evaluate the early signs of brittle failure of sandstone. Kernel density estimation (KDE) results show that under the lower F-T cycles, the tensile crack has a higher AF (acoustic shear/mixed cracking phenomenon occurs after the higher F-T treatment.Damage evolution can be divided into three typical stages based on the damage variable D<sub>AE</sub>: Microscopic damage accumulation stage, Damage accelerated development stage, Damage stable growth stage. A damage model considering the F-T cycle effect was adopted based on fitted AE counting, which can reflect the damage evolution process under unconfined compression conditions.</p>

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Study on the freezing-thawing damage mechanism and evolution model of saturated gray sandstone based on NMR and AE technology

  • 期刊论文

  • 发表日期：

    2025年10月31日

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  • Shuailong Lian,
  • Yanlin Zhao,
  • Wen Wan,
  • Qiuhong Wu,
  • Rugao Gao,
  • Min Wang

摘要

The freeze‒thaw (F-T) damage mechanism and evolution model of saturated gray sandstone specimens under uniaxial compression were systematically studied based on acoustic emission (AE) and nuclear magnetic resonance (NMR) technology. The results indicate that the F-T cycles can lead to the deterioration of the internal structure of specimens by observing the T2 spectrum and NMR images. The peak strength and elastic modulus of the specimens decreased gradually as the number of F-T cycles increased, and the peak strain showed an obvious increasing trend. The decrement rates for the peak strength and elastic modulus of the specimens are 95.49% and 88.92%, respectively, and the increment rate peak strain is 43.06% when the F-T cycles increase from 0 to 60. In addition, the strength decreased from 27.5 MPa to 11.2 MPa after 20 F-T cycles, a decrease of 59.27%. However, the strength at 20 cycles did not decrease significantly, and the strengths at 40 cycles and 60 cycles were 5.5 MPa and 1.3 MPa, respectively). The failure modes of the specimens changed into splitting failure, shear failure, cone failure and multicrack composite failure modes with the increase in the number of F-T cycles. F-T cycles have a significant effect on the AE response characteristics during the progress of loading process. With the increase in F-T cycles, the AE events gradually increase, and the AE response is violent. AE localization technology can not only accurately reflect the internal damage evolution trend during loading, but also evaluate the early signs of brittle failure of sandstone. Kernel density estimation (KDE) results show that under the lower F-T cycles, the tensile crack has a higher AF (acoustic shear/mixed cracking phenomenon occurs after the higher F-T treatment.Damage evolution can be divided into three typical stages based on the damage variable DAE: Microscopic damage accumulation stage, Damage accelerated development stage, Damage stable growth stage. A damage model considering the F-T cycle effect was adopted based on fitted AE counting, which can reflect the damage evolution process under unconfined compression conditions.