Post-peak mechanical property and a new strain softening model for rocks subjected to freeze–thaw cycles

In this paper, the mechanical properties and strain softening model of rock in cold regions after the peak were investigated. Freeze–thaw cycle tests and triaxial compression tests were performed on green sandstone to obtain stress–strain curves for rocks under different freeze–thaw cycles. The deformation, strength, and post-peak characteristics of rocks under freeze–thaw cycles and triaxial compression were analyzed, including brittleness and drop degree. On this basis, the experimental data were used to draw the Mohr stress circle and its corresponding envelope under different freeze–thaw cycles and confining pressure conditions. It also determines the generalized cohesion c̅ and the generalized internal friction angle φ̅ under different freeze–thaw cycles and confining pressure conditions. Least square surface fitting was used to obtain the softening law of post-peak strength parameters of frozen–thawed rock. Finally, a constitutive model was established that accurately reflects the post-peak strain softening behavior of rock under freeze–thaw cycles. The model uses the maximum principal strain ε_1 as the softening parameter and subjects the strength parameters (generalized cohesion c̅ , generalized internal friction angle φ̅ ) to piecewise linear evolution according to the Mohr–Coulomb criterion. The paper concludes by comparing and analyzing the influence of each strength parameter on the post-peak strain softening behavior of rock.