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

This study examines the evolution of mechanical properties of silty sand from the Daxing' anling region under coupled freeze-thaw cycles and confining pressure, using triaxial testing. The results show that at low confining pressure and with zero or limited freeze-thaw cycles, the stress-strain response exhibits strain softening, indicative of brittle failure. In contrast, at high confining pressure or after multiple freeze-thaw cycles, the behaviour transitions to strain hardening, characterised by plastic failure. Freeze-thaw cycling markedly degrades the soil's mechanical performance. The first cycle causes a 30-40% reduction in peak deviator stress, elastic modulus, and internal friction angle. Subsequent cycles lead to progressively slower degradation, the degradation rate decreased and approached stabilization within the investigated range of 30 cycles. Although increasing confining pressure enhances mechanical behaviour by promoting soil densification, this benefit diminishes as the number of freeze-thaw cycles increases. Based on experimental data, a damage model incorporating the elastic deformation phase was developed. By linking Weibull distribution parameters to 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 provide a reliable theoretical basis for the safety design of engineering structures in cold regions.