Triaxial creep test and damage model study of layered red sandstone under freeze-thaw cycles

To examine the creep behavior and degradation of stratified rock in cold areas, triaxial creep experiments and microscopic analyses were performed on layered red sandstone specimens under freeze-thaw (F-T) cycles. This study revealed the deterioration characteristics and damage mechanisms of red sandstone's creep behavior under the influence of F-T cycles and bedding inclination. The test results showed that: (1) The steady-state creep rates with bedding angles beta=30 degrees after 0, 40, 80, and 120F-T cycles were 0.0168 x 10(-2)<middle dot>h(-1), 0.0224 x 10(-2)<middle dot>h(-1), 0.0289 x 10(-2)<middle dot>h(-1), and 0.0368 x 10(-2)<middle dot>h(-1) respectively. The instantaneous deformation, creep deformation, and steady-state creep rates increased gradually with the increase of F-T cycles, while the long-term strength exhibited a decreasing trend. (2) After 40F-T cycles, the long-term strengths with bedding angles of 0 degrees, 30 degrees, 45 degrees, 60 degrees and 90 degrees were 121.17 MPa, 65.47 MPa, 46.28 MPa, 77.64 MPa and 124.78 MPa, respectively. The bedding angle of 45 degrees has the greatest influence on the triaxial creep properties of red sandstone, followed by the bedding angles of 30 degrees and 60 degrees, and the bedding angles of 0 degrees and 90 degrees have the least influence. (3) As the F-T cycles increases, the longitudinal wave velocity gradually decreases, and the pores and cracks on the sample surface continue to expand, leading to increased damage. The failure mode evolves from a single oblique shear plane to an "X"-shaped tensile splitting. Additionally, the bedding angle has a significant effect on the longitudinal wave velocity. As the bedding angle increases, the longitudinal wave velocity exhibits a "V"-shaped distribution, initially decreasing and then increasing. Based on the test results, a creep damage model of layered rock considering the influence of F-T cycles was established, and the rationality of the model was verified by test data. The research results can provide a scientific basis and technical reference for the long-term stability of layered rock engineering in cold regions.