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<p>Roadbeds in seasonally frozen regions are susceptible to frost-induced deformation and strength degradation during freeze–thaw (F–T) cycles, which severely impair the service performance of roads. Although fiber reinforcement has been widely applied to improve soil stability, the freeze–thaw durability and reinforcement mechanism of poly (p-phenylene-2, 6-benzobisoxazole, PBO) fiber-reinforced soil remain insufficiently understood. To investigate the engineering behavior of fiber-reinforced soil under F–T cycles, low-liquid-limit clay was used as the test material and PBO fiber was introduced as the reinforcement. The aim of this study is to evaluate the mechanical response and microstructural evolution of PBO fiber-reinforced soil under varying F–T cycles and moisture conditions and to clarify the mechanisms responsible for strength retention. Unconfined compressive strength (UCS) tests were conducted to examine the effects of F–T cycles, moisture content, fiber length, and fiber content on the mechanical and deformation characteristics of PBO fiber-reinforced soil. In addition, scanning electron microscopy (SEM) was employed to elucidate the corresponding microstructural evolution. The results indicate that the optimal fiber length and content are 12&#xa0;mm and 0.4%, respectively, yielding a UCS of 497.5&#xa0;kPa. Compared with plain soil under the same moisture condition, the fiber-reinforced soil exhibits significantly higher UCS. Under varying moisture conditions, both plain and fiber-reinforced soils exhibited a marked reduction in frost resistance at high moisture content (19.1%), mainly attributed to intensified ice lens formation and increased pore-water pressure during freezing. With increasing number of F–T cycles, strength, Young’s modulus, and resilient modulus of both plain and fiber-reinforced soils gradually declined; however, reinforced specimens remained consistently stronger than plain soils, indicating that PBO fibers restrain crack propagation and maintain soil skeleton integrity through fiber–soil interaction and bridging effects. This study provides a theoretical basis for the application of PBO fiber-reinforced soil in seasonally frozen roadbeds and offers guidance for designing frost-resistant subgrade materials.</p>

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Experimental Study on the Unconfined Compressive Strength of Fiber-Reinforced Soil Subject to Freeze–Thaw Cycles

  • 期刊论文

  • 发表日期：

    2026年3月31日

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  • Bingxin Cao,
  • Lina Xu,
  • Yuexin Gao,
  • Junjie Zheng,
  • Peiyi Yao

摘要

Roadbeds in seasonally frozen regions are susceptible to frost-induced deformation and strength degradation during freeze–thaw (F–T) cycles, which severely impair the service performance of roads. Although fiber reinforcement has been widely applied to improve soil stability, the freeze–thaw durability and reinforcement mechanism of poly (p-phenylene-2, 6-benzobisoxazole, PBO) fiber-reinforced soil remain insufficiently understood. To investigate the engineering behavior of fiber-reinforced soil under F–T cycles, low-liquid-limit clay was used as the test material and PBO fiber was introduced as the reinforcement. The aim of this study is to evaluate the mechanical response and microstructural evolution of PBO fiber-reinforced soil under varying F–T cycles and moisture conditions and to clarify the mechanisms responsible for strength retention. Unconfined compressive strength (UCS) tests were conducted to examine the effects of F–T cycles, moisture content, fiber length, and fiber content on the mechanical and deformation characteristics of PBO fiber-reinforced soil. In addition, scanning electron microscopy (SEM) was employed to elucidate the corresponding microstructural evolution. The results indicate that the optimal fiber length and content are 12 mm and 0.4%, respectively, yielding a UCS of 497.5 kPa. Compared with plain soil under the same moisture condition, the fiber-reinforced soil exhibits significantly higher UCS. Under varying moisture conditions, both plain and fiber-reinforced soils exhibited a marked reduction in frost resistance at high moisture content (19.1%), mainly attributed to intensified ice lens formation and increased pore-water pressure during freezing. With increasing number of F–T cycles, strength, Young’s modulus, and resilient modulus of both plain and fiber-reinforced soils gradually declined; however, reinforced specimens remained consistently stronger than plain soils, indicating that PBO fibers restrain crack propagation and maintain soil skeleton integrity through fiber–soil interaction and bridging effects. This study provides a theoretical basis for the application of PBO fiber-reinforced soil in seasonally frozen roadbeds and offers guidance for designing frost-resistant subgrade materials.