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.

饱和孔隙和裂缝中水的体积膨胀 9% 会导致岩体发生大量的霜冻变形。霜冻变形是反映岩石抗冻性的重要指标；然而，含水饱和度对霜冻变形特性有很大影响。本研究在冻融条件下监测了不同含水饱和度红砂岩的霜冻应变和声发射活动。试验结果表明，当砂岩含水饱和度超过85%时，峰值和残余冻胀应变均显着增加。然而，在低饱和度红砂岩（含水饱和度低于85%）中没有发生显着的冻胀应变。声发射活动表现出相同的变化趋势，进一步证实了这种临界饱和的存在。此外，孔径分布对冻胀应变和冻融破坏也有很大影响。根据测量的孔径分布，该红砂岩中的所有液态孔隙水都在 - 20 °C 冻结，因为孔隙大于临界冻结半径（- 20 °C 时为 2.58 nm）。基于孔隙微观力学和 Gibbs-Thomson 方程，提出了一种考虑含水饱和度和孔径分布影响的冻胀模型。该模型可用于预测非饱和红砂岩在任意冻结温度下的冻胀应变。本研究由此提供了红砂岩的霜冻变形特征，有助于更好地理解非饱和砂岩的冻融破坏机制。孔径分布对冻胀应变和冻融破坏也有很大影响。根据测量的孔径分布，该红砂岩中的所有液态孔隙水都在 - 20 °C 冻结，因为孔隙大于临界冻结半径（- 20 °C 时为 2.58 nm）。基于孔隙微观力学和 Gibbs-Thomson 方程，提出了一种考虑含水饱和度和孔径分布影响的冻胀模型。该模型可用于预测非饱和红砂岩在任意冻结温度下的冻胀应变。本研究由此提供了红砂岩的霜冻变形特征，有助于更好地理解非饱和砂岩的冻融破坏机制。孔径分布对冻胀应变和冻融破坏也有很大影响。根据测量的孔径分布，该红砂岩中的所有液态孔隙水都在 - 20 °C 冻结，因为孔隙大于临界冻结半径（- 20 °C 时为 2.58 nm）。基于孔隙微观力学和 Gibbs-Thomson 方程，提出了一种考虑含水饱和度和孔径分布影响的冻胀模型。该模型可用于预测非饱和红砂岩在任意冻结温度下的冻胀应变。本研究由此提供了红砂岩的霜冻变形特征，有助于更好地理解非饱和砂岩的冻融破坏机制。