Heterogeneous Frost Deformation of Partially Saturated Sandstones Due to the Freeze–Thaw Cycle

Understanding the frost deformation characteristics of rock with varying water contents under freeze–thaw conditions is of great significance to engineering construction activity in cold regions. In this study, sandstone samples with different degrees of water saturation were first prepared and then submitted to cyclic freeze–thaw experiments. Temperature sensors and strain gauges were attached to the samples so as to trace the temperature and strain changes. The changes in the major principal strain and minor principal strain against the temperature were individually explored. It is found that the sandstones exhibit heterogeneous frost deformation behaviors during the freeze–thaw cycle, and the heterogeneity of frost deformation is more considerable in terms of the sandstone with a higher degree of saturation based on the strain ellipse analysis. The coefficient of linear thermal expansion (CLTE), maximum frost heave strain and residual frost heave strain tend to increase exponentially with increasing the degree of saturation. These three parameters, however, are different from one another along the minor and major principal strain directions, which further gives evidence of the heterogeneous frost-heaving features of the sandstone. Finally, the crystallization pressures within a single pore and over the entire sandstone volume were theoretically calculated. It is verified that the resulting stress translated by the crystallization pressure for the 80% or higher saturation degree exceeds the tensile failure threshold, which explains the mechanisms that more considerable frost-heaving damage and heterogeneous behaviors are caused in the sandstone with a saturation degree of 80% or higher. The findings in this study help schedule feasible ways of alleviating the freeze–thaw-induced damage of rock mass in cold regions.