Shear strength and damage model of silty sand in Daxing 'anling under freeze-thaw cycles

Abstract This study examines the evolution of mechanical properties in silty sand from the Daxing' anling region under coupled freeze-thaw cycles and confining pressure using triaxial testing. The results demonstrate that under low confining pressure and with zero or limited freeze-thaw cycles, the stress-strain response exhibits strain-softening behavior, indicative of brittle failure. In contrast, under high confining pressure or after multiple freeze-thaw cycles, the behavior transitions to strain-hardening, characterized by plastic failure. Freeze-thaw cycling markedly degrades the soil's mechanical performance. The first cycle causes a 30%–40% reduction in failure strength, elastic modulus, and internal friction angle. Subsequent cycles lead to progressively slower degradation, with properties stabilizing after approximately 30 cycles. Although increasing confining pressure enhances mechanical behavior by promoting soil densification, this beneficial effect becomes less pronounced as the number of freeze-thaw cycles rises. Based on experimental data, a damage model incorporating the elastic deformation phase was developed. By linking Weibull distribution parameters with test variables, a coupled freeze-thaw and loading damage variable was formulated. Model validation shows close agreement between predicted and experimental results, accurately capturing the effect of freeze-thaw cycles on strength degradation and damage evolution during loading. These findings offer a reliable theoretical basis for the safety design of engineering structures in cold regions.