Mesoscopic Freeze-Thaw Damage Evolution Characteristics of Fractured Sandstone at Different Saturations

To study the effect of saturation on the freeze-thaw damage of fractured rocks in cold regions, five prefabricated oval double-hole red sandstones with different saturations were prepared. Three-dimensional images of rock fractures were obtained by CT technology. The freeze-thaw damage mechanism and critical saturation of the red sandstone were explored through the fracture propagation evolution and quantitative characterization of the pore structure. The experimental results show that the pore size distribution can reflect the complex pore structure. Pores can be divided according to their sizes: small pores, mesopores, and macropores; mesopores account for the largest proportion and more than 70% of the total, and the proportion of mesopores in high-saturation sandstone (90% or 100%) increases under the action of freeze-thaw cycle. This is also accompanied by a small increase in the proportion of macropores. An 80% critical saturation of the sandstone was obtained. In addition, prefabricated cracks make the ice separation mechanism more likely to occur. The low-saturation sandstone mainly damaged the fracture area during freeze-thaw cycles, while the prefabricated cracks provided a good seepage channel for high-saturation sandstone. The corresponding rock bridge area eventually demonstrated a connectivity trend. This study more realistically reflects the freeze-thaw damage of actual rock masses in cold regions and provides a theoretical basis for the prediction of rock mass engineering disasters in cold regions.