Mechanical properties of sandstone under freeze-thaw cycles and studies on meso-damage constitutive model

To address the freeze-thaw problems of rocks in cold-zone rock engineering, the sandstone is selected as the specimen and analyzed for mass loss, microstructure and mechanical properties by conducting the cyclic indoor freeze-thaw tests, scanning electron microscope observations and triaxial compression tests. Then, based on the Lemaitre strain equivalence hypothesis theory, the meso-scale freeze-thaw damage variables and force damage variables are introduced to reflect the process of freeze-thaw damage of the rocks to describe the degree of deterioration of rock materials and the damage evolution law. Using the continuous damage mechanics theory, the damage evolution equation and the meso-scale damage constitutive model for the rocks under the coupling of freeze-thaw and cofining pressure are established. The theoretical derivation method is used to obtain the required expressions for model parameters. Finally, the rationality and accuracy of the model are verified by the triaxial compression test data of freeze-thaw of the rocks. The peak points of the test curve are compared with those of the theoretical curve by the model, and the results show that they are in good agreement. The damage constitutive model can better reflect the stress-strain peak characteristics of the rocks during triaxial compression, which verifies the rationality and reliability of the proposed model and the relevant method for determining the model parameters. This model expands the damage model for the rocks under the coupling of freeze-thaw and confining pressure and further reveals their damage mechanism and failure law.