Layered rock (LR) exhibits significant weakness plane structures, with anisotropic properties in strength, deformation, and failure modes that vary according to the orientation of the weakness planes. In cold regions, these weakness planes make the rocks more sensitive to freeze–thaw (FT) weathering, potentially increasing engineering risks from repeated FT cycles. This study investigates the changes in anisotropic strength, deformation characteristics, brittleness, and failure modes of LR induced by FT cycles, as well as the underlying mechanisms of FT degradation. Triaxial compression tests were conducted on LR specimens at five different orientations of weakness planes (0 \(^\circ\) , 22.5 \(^\circ\) , 45 \(^\circ\) , 67.5 \(^\circ\) , and 90 \(^\circ\) ) under four confining pressures (0, 5, 10, and 15 MPa) after various numbers of FT cycles (0, 25, 50, and 75). Subsequent morphology analysis of the weakness planes was performed, while X-ray computed tomography was used to capture the internal development of defects during FT cycles. The results reveal that (1) increasing FT cycles significantly reduces the strength, elastic modulus, and brittleness of LR under triaxial compression. However, (2) the initial values and decay of these parameters vary significantly across different inclination angles of the weakness planes, with inherent anisotropy contributing to anisotropic FT damage. (3) FT cycles notably affect the frictional properties of the weakness planes, diminishing surface roughness and thereby degrading strength. (4) The defect network structure in LR can be conceptualized as a “weakness plane-microcrack” model, with three potential FT damage modes playing critical roles during repeated FT cycles. These insights provide a comprehensive understanding of the mechanical behavior of LR after FT cycles and reveal the FT degradation mechanisms.
