Development of Anisotropy in Sandstone Subjected to Repeated Frost Action

In cold regions, the anisotropy of sedimentary rocks is modified by repeated frost action, potentially increasing the risks of rock engineering. Hence, a deep understanding of the development of rock anisotropy due to frost action is essential. In this work, two sets of sandstone samples were cored and used in experiments, which contained bedding planes either perpendicular or parallel to the height direction. The P-wave velocity, uniaxial compressive strength, tensile strength, and shear strength of samples were tested after different numbers of freeze–thaw cycles. Several anisotropic indexes were defined by the above parameters and their variations with freeze–thaw cycles were analysed. The results demonstrate that (1) the P-wave velocity, uniaxial compressive strength, tensile strength, and shear strength of both sets of sandstone samples decayed with increasing freeze–thaw cycles; however, (2) the initial values and decay rates of these parameters differed significantly between the two sets. (3) Sandstone bears strong inherent anisotropy and (4) it is enhanced by repeated frost action. Based on direct observations of bedding structures by magnetic resonance imaging, we suggest that the enhancement of anisotropy in sandstone results from a combination of its inherent anisotropy and anisotropic frost damage accumulation. Both originate from sandstone’s structure of interbedded coarse- and fine-grained layers.