Investigating the Resilience of Fiber-Reinforced Clay Under Freeze–Thaw Cycles

In cold-region engineering, freeze–thaw (F–T) cycles act as a critical stressor on soil stability, where the recurring transition between frost heave and thaw settlement can drastically alter geotechnical properties and threaten long-term structural integrity. Yet, while the static characteristics of frozen soils are well documented, the dynamic impact of repetitive thermal cycling on long-term soil behavior remains a significant and relatively underexplored challenge in the field. This study investigates the effectiveness of polypropylene fiber (FPP) as a sustainable and environmentally benign reinforcement for high-plasticity clay. The research examines FPP’s influence on stress–axial strain relationships (unconsolidated undrained (UU) compressive strength) and its ability to mitigate frost heave and volumetric changes during F–T cycles. Laboratory-prepared FPP–clay samples were subjected to ten closed-system F–T cycles and tested using a UU triaxial machine. Results showed a 51% decrease in UU strength for unreinforced samples after ten cycles, while samples reinforced with 1% FPP exhibited only an 18.4% reduction. FPP reinforcement reduced frost heave and thaw settlement by 30% and significantly enhanced UU strength, increasing it by 60% before F–T cycles and 167% after exposure. The findings highlight FPP’s effectiveness in improving soil strength, minimizing volumetric changes, and mitigating frost-related damage, making it a viable solution for enhancing soil performance in cold regions.