Influence of freeze-thaw cycles on the degradation of sandstone after loading and unloading

The physical and mechanical properties of rocks in cold regions are strongly affected by temperature fluctuations and stress states. In this study, the deterioration of sandstone subjected to freeze-thaw (F-T) cycles and different stress states was investigated. To do so, the physical and mechanical properties of sandstone experiencing different loading-unloading paths were studied after 45, 90, and 135 F-T cycles. The results show that after applying F-T cycles, the porosity of the sandstone samples increased, demonstrating a degradation in physical properties. In addition, the saturated mass showed an increase in 0–90 F-T cycles and a decrease in 90–135 F-T cycles, while for sandstone experiencing different loading-unloading paths, the variation rate varies. The uniaxial compressive strength is proven to decrease in sandstone samples subjected to different F-T cycles. Most degradation was found in the sample that experienced a stress state within the unstable crack propagation stage. A decay model implied that the strengths were more easily deteriorated by F-T cycles after loading to a higher stress state. The effects of F-T cycles on strain energy development were also investigated, demonstrating that both the peak strain energy and the elastic strain energy decreased to different extents after the F-T cycles were applied. Finally, a freeze-thaw resistance index was proposed to describe the frost-resistivity ability of sandstone subjected to F-T cycles.