Mechanism analysis on anisotropic degradation of sandstone in freeze thaw environment based acoustic emission

In the freeze-thaw environments, the fracturing of bedding rock poses a significant threat to the stability of the projects in cold regions, leading to potential engineering accidents. In this paper, uniaxial compression and acoustic emission tests were carried out on parallel and vertical stratified sandstones after 0, 20, 40, and 60 freeze-thaw cycles. The mechanical properties of different stratified sandstones and the changes in acoustic emission characteristic parameters during rock deformation and failure were studied. The results show that with the intensification of freeze-thaw effects, both longitudinal wave velocities of the two sample groups gradually decrease, and the porosity increases gradually. The proportion of compressive strength decrease and strain increase of the parallel group of samples is greater than that of the vertical group, indicating a higher level of degradation in parallel group. The trend of acoustic emission ringing count evolution curve of the two groups of different stratified sandstones under freeze-thaw cycles is consistent and can be divided into three stages: a calm stage, a stepwise growth stage, and a sudden growth stage. Uniaxial failure modes of sandstones with different bedding directions are different. The change in acoustic emission b-values for parallel group samples presents an inverted “V” shape, while for vertical group samples, it shows a normal "V" shape. Based on the various characteristics of RA-AF values, it is suggested that the parallel stratified yellow sandstone primarily undergoes tensile failure, while the vertical stratified sandstone is mainly dominated by both tensile and shear failures in the untreated condition, and also mainly dominated by tensile failure after 60 freeze-thaw cycles. The research results provide a scientific basis for the safety assessment of geotechnical engineering in cold regions.