Quantifying Degradation Mechanisms of Loess under Wetting–Drying–Freezing–Thawing Cycles: A Box–Behnken Design Approach

Abstract

To address the degradation of dynamic properties in subgrade engineering of cold-region loess under wetting–drying–freezing–thawing (WDFT) cycles, this study quantifies the evolution of physical damage characteristics through mass loss rate and volumetric change rate under varying cycle numbers. Integrated with the Box–Behnken response surface methodology, systematic dynamic tests were conducted to investigate the interactive effects of WDFT cycles, confining pressure, and deviator stress on the dynamic resilient modulus and associated damage variables. Quadratic polynomial models were established to predict these parameters, with significance validated by analysis of variance (ANOVA). Quantitatively, confining pressure accounts for over 70% of the variance in the dynamic resilient modulus model, while the damage variable model reveals a significant interaction between cycle number and confining pressure ( P < 0.05). Key findings reveal that mass loss and volumetric change accumulate progressively with WDFT cycles, exhibiting distinct stage-wise characteristics. Significant nonlinear interactions among cyclic parameters dominantly govern both dynamic resilient modulus and damage variables. ANOVA-optimized models identify confining pressure as the dominant factor for resilient modulus, while damage variables highlight synergistic mechanisms in cycle–pressure interactions. This research elucidates the physicomechanical damage mechanisms of loess under WDFT cycles, providing quantitative tools for dynamic stability assessment of cold-region loess subgrades.