Constitutive model of sandstone under freeze-thaw and load coupling considering dynamic damage rate and confining effect

To reveal how confining pressure regulates rock mechanical behaviours under freeze-thaw and load and characterize dynamic damage rate evolution, this study develops a damage constitutive model for rock under coupled freeze-thaw and load conditions. The rock material is simplified into five components: freeze-thaw damage, confining pressure weakened damage, loading damage, coupled damage, and undamaged phase. With the intact portion carrying effective stress and damaged portion bearing residual stress, a model governed by dynamic damage rate is formulated and validated by triaxial tests. The model well captures full stress-strain curves and quantifies the confining pressure inhibition on damage. Dynamic damage evolves in four stages. Higher confining pressure slows damage accumulation and enhances strength and ductility, while extra freeze-thaw cycles weaken rock. The peak dynamic damage rate occurs near peak stress, and the final damage variable approaches 60%. This work supports cold-region rock mechanics analysis.