A new damage constitutive model for frozen-thawed sandstone under triaxial conditions: Considering the characteristics of pre-peak compaction and post-peak residual strength

The study of the constitutive model under stress loading for rock after undergoing freeze-thaw weathering cycles (FTWCs) treatment has important theoretical significance for the site operation and numerical calculation of rock mass engineering in cold regions. In this work, a series of FTWCs treatment tests of sandstone were carried out, and the evolution characteristics of the T2 spectrum distribution curve for sandstone before and after FTWCs treatment were analyzed utilizing nuclear magnetic resonance (NMR) technology. The schematic diagram of freeze-thaw damage evolution for sandstone was drawn, and the damage evolution mechanism was analyzed. Evolution laws of the stress-strain curves, peak and residual strength, peak and residual strain, and Young's modulus of sandstone under different FTWCs and confining pressures were analyzed by conventional triaxial compression tests. A piecewise constitutive model under triaxial stress loading for sandstone after undergoing FTWCs treatment was established, and the model considered the significant influence of FTWCs on the nonlinear deformation in the compaction stage and residual strength. By introducing error analysis indexes, the proposed model and published models were compared with the experimental data, it was found that the proposed model's performance is better than the published models, which indicated that the proposed model has good performance and strong universality.