Abstract: To study the mechanical properties and damage evolution of sandstone after the synergistic action of stress and freeze-thaw cycles,uniaxial compression tests were conducted on sandstone samples under different stress levels and number of freeze-thaw cycles.The variation characteristics of stress-strain threshold,elastic modulus,and fracture mode of sandstone were analyzed,and a segmented damage constitutive model of rock under load after the synergistic action of stress and freeze-thaw cycles was proposed.The results indicate that as the number of freeze-thaw cycles increases,the uniaxial compressive strength,crack closure stress,crack initiation stress,and elastic modulus of sandstone decrease,while the peak strain first decreases and then increases,and the crack closure strain and crack initiation strain generally increase.As the stress level increases,the uniaxial compressive strength,crack initiation stress,and elastic modulus decrease.The rock fracture mode shifts from axial splitting to multi tensile shear fracture with the repeatedly freezing-thawing cycles.Higher stress levels promote the accumulation of rock freeze-thaw damage,while lower stress levels are also conducive to the damage.The reason may be that the superposition of frost heave force parallel to the loading direction and external stress is more likely to exceed the tensile strength of the rock,leading to the initiation and propagation of cracks.Considering the nonlinear deformation characteristics caused by pore-crack compaction and the relationship between pore-crack strain and axial strain,a rock damage constitutive model is established with the crack closure stress as the segmented point.The proposed model can reasonably describe the deformation and failure process of sandstone under load after the synergistic action of stress and freeze-thaw cycles.