Freeze–thaw (FT) alternation can severely affect the properties of fine–grained soils, often leading to the failure of foundation backfill projects, such as open canals and roads in cold regions. To address these problems, a water–soluble anionic polyacrylamide (APAM) was used to improve the properties of fine–grained soils, particularly silty clay. This study aims to analyze the effects of the APAM polymer on the physico–mechanical and microstructural properties of silty clay under both unfrozen and FT cycles. For this purpose, different addition dosages and FT cycle numbers were determined, and then a series of zeta potential, thermal conductivity, permeability, triaxial compression, and scanning electron microscopy (SEM) tests were conducted on the soil samples. Additionally, a unidirectional freezing test was constructed to investigate the coupled thermo–hydro–mechanical processes of APAM–treated soil samples. The results showed that the addition of the APAM polymer significantly enhanced the macroscopic engineering properties and microstructural characteristics of silty clay. This improvement was attributed to the charge neutralization, adsorption bridging effect, and hydrophobic interaction provided by the APAM polymer. However, all the soil samples showed a significant deterioration in their engineering properties during FT cycles, especially after the third FT cycle. It was notable that APAM–treated soil samples were superior to the untreated sample in terms of FT resistance. During the unidirectional freezing process, the pore water migrated from the unfrozen zone towards the freezing front due to the temperature gradient. The treated sample's pore water migration volume was considerably lower than that of the untreated sample, resulting in a 55.25% reduction in total frost heave when the APAM dosage was 0.30%. The findings of this paper may be utilized to mitigate the risk of frost damage to foundation backfill projects in cold regions, as well as to get a better understanding of the stabilization mechanism of the eco–friendly APAM polymer.

冻融（FT）交替会严重影响细粒土的性质，常常导致地基回填工程失败，例如寒冷地区的明渠和道路。为了解决这些问题，使用水溶性阴离子聚丙烯酰胺（APAM）来改善细粒土壤，特别是粉质粘土的特性。本研究旨在分析 APAM 聚合物在未冻结和 FT 循环下对粉质粘土物理机械和微观结构特性的影响。为此，确定了不同的添加剂量和FT循环数，然后对土壤样品进行了一系列zeta电位、导热系数、渗透性、三轴压缩和扫描电子显微镜（SEM）测试。此外，还构建了单向冷冻试验来研究经 APAM 处理的土壤样品的热-水-机械耦合过程。结果表明，APAM聚合物的添加显着增强了粉质粘土的宏观工程性能和微观结构特征。这种改进归因于 APAM 聚合物提供的电荷中和、吸附桥效应和疏水相互作用。然而，在 FT 循环期间，特别是在第三次 FT 循环之后，所有土壤样品的工程性能均显着恶化。值得注意的是，经 APAM 处理的土壤样品在耐 FT 性方面优于未处理的样品。在单向冻结过程中，由于温度梯度的作用，孔隙水从未冻结区向冻结前沿迁移。处理后的样品孔隙水迁移量明显低于未处理样品，当APAM用量为0.30%时，总冻胀减少了55.25%。本文的研究结果可用于减轻寒冷地区地基回填工程的冻害风险，并更好地了解环保型 APAM 聚合物的稳定机制。