A study on mechanical properties and damage model of rock subjected to freeze-thaw cycles and confining pressure

red sandstone was tested in the freeze-thaw cycle under open and saturated conditions, and the mechanical properties of samples after different freeze-thaw cycles (0, 5, 10, 20, and 40 freeze-thaw cycles) were tested under the four kinds of confining pressures (0 MPa, 2 MPa, 4 MPa, 6 MPa). The whole process characteristics of deformation and failure of red sandstone were analyzed, and the effects of freeze-thaw cycles and confining pressure on red sandstone mechanical properties were studied. According to the characteristics of rock material non-uniformity and randomness, the effect of freeze-thaw and load coupling effect on the total damage was quantitatively expressed, and established a damage model can reflect the whole process of rock deformation. The theoretical expression of model parameters were derived by using the multivariate function to obtain total differential method, and the damage mechanical properties of rock were analyzed. The results has shown that: With the increase of the freeze-thaw cycles and confining pressure, the compressibility of rock is continuously enhanced, the peak strain is gradually increasing, the plastic yielding section is becoming more and more obvious, the post-peak stress reduction rate slows down, and the failure mode is transformed from brittleness to ductility. Meanwhile, the elastic modulus, peak stress and residual strength increase with the increase of confining pressure, and decrease with the increase of freeze-thaw cycles. The damage model reflects the process of deformation and failure of frozen-thawed rock under the action of load, especially the characteristics of post-peak strain softening and residual strength. The rock total damage evolution path reflects that the meso-mechanical response was consistent with the macro-deformation and failure characteristics, and the nonlinear influence characteristics of freeze-thaw and load on the rock total damage propagation are described. Furtherly, the deformation failure of rock is revealed by the mechanical damage mechanism.