Experimental and Theoretical Study on Frost Deformation and Damage of Red Sandstones with Different Water Contents

Volumetric expansion of water by 9% in saturated pores and cracks causes substantial frost deformation in rock masses. Frost deformation is an important index reflecting the frost resistance of rocks; however, water saturation has a great influence on the frost deformation characteristics. In this research, the frost strains and acoustic emission activities of red sandstone with different water saturations are monitored under freeze–thaw conditions. The experimental results show that both the peak and the residual frost heaving strains greatly increase for sandstone beyond 85% water saturation. However, there is no significant frost heaving strain that occurs in low-saturation red sandstone (less than 85% water saturation). The acoustic emission activities show the same change trend and further confirm the existence of this critical saturation. In addition, the pore size distribution also has a great influence on the frost heaving strain and freeze–thaw damage. All the liquid pore water in this red sandstone is frozen at − 20 °C because the pores are larger than the critical freezing radius (2.58 nm at − 20 °C) according to the measured pore size distribution. Based on the pore micromechanics and Gibbs–Thomson equation, a developed frost heaving model is proposed considering the effects of water saturation and the pore size distribution. The proposed model can be used to predict the frost heaving strain at any freezing temperature for unsaturated red sandstone. This study thus provides the frost deformation characteristics of red sandstone and contributes to a better understanding of the freeze–thaw damage mechanism of unsaturated sandstone.