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<p>Freeze–thaw cycling and pre-existing fractures were key factors governing the mechanical degradation of cyan sandstone in cold-region tunnel engineering. Triaxial compression tests combined with nuclear magnetic resonance measurements were conducted on intact sandstone and prefabricated fractured sandstone subjected to different numbers of freeze–thaw cycles under various confining pressures. The results showed that freeze–thaw cycling caused a continuous reduction in peak strength, elastic modulus, and wave velocity. The presence of prefabricated fractures significantly accelerated mechanical deterioration, leading to greater strength loss compared with intact specimens under identical conditions. Increasing confining pressure partially mitigated the degradation by enhancing structural compaction and restraining lateral deformation. Nuclear Magnetic Resonance (NMR) analysis indicated that freeze–thaw action increased microporosity and improved pore connectivity, contributing to progressive internal damage accumulation. A damage evolution model based on elastic modulus degradation was established to quantify freeze–thaw-induced deterioration. The model captured nonlinear damage evolution under coupled freeze–thaw and stress conditions, and its predictions were consistent with experimental observations. The results demonstrated that the coupled effects of freeze–thaw cycles, confining pressure, and pre-existing fractures jointly controlled the mechanical response and failure behavior of cyan sandstone in cold environments.</p>

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Freeze-Thaw Effects and Prefabricated Fracture Strength Loss in Cyan Sandstone of Cold Region Tunnel Surrounding Rocks

  • 期刊论文

  • 发表日期：

    2026年7月9日

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  • Fugui Jia,
  • Ping Yin,
  • Guosheng Duan,
  • Kun He,
  • Hongfu Yang,
  • Xiuchao Cui,
  • Qingzhi Wang

摘要

Freeze–thaw cycling and pre-existing fractures were key factors governing the mechanical degradation of cyan sandstone in cold-region tunnel engineering. Triaxial compression tests combined with nuclear magnetic resonance measurements were conducted on intact sandstone and prefabricated fractured sandstone subjected to different numbers of freeze–thaw cycles under various confining pressures. The results showed that freeze–thaw cycling caused a continuous reduction in peak strength, elastic modulus, and wave velocity. The presence of prefabricated fractures significantly accelerated mechanical deterioration, leading to greater strength loss compared with intact specimens under identical conditions. Increasing confining pressure partially mitigated the degradation by enhancing structural compaction and restraining lateral deformation. Nuclear Magnetic Resonance (NMR) analysis indicated that freeze–thaw action increased microporosity and improved pore connectivity, contributing to progressive internal damage accumulation. A damage evolution model based on elastic modulus degradation was established to quantify freeze–thaw-induced deterioration. The model captured nonlinear damage evolution under coupled freeze–thaw and stress conditions, and its predictions were consistent with experimental observations. The results demonstrated that the coupled effects of freeze–thaw cycles, confining pressure, and pre-existing fractures jointly controlled the mechanical response and failure behavior of cyan sandstone in cold environments.