Study on creep deformation behavior and constitutive model of filled fractured sandstone under freeze-thaw cycles

The time-dependent deformation and stability of fractured rock in seasonally frozen regions constitute a key scientific issue for engineering safety. To investigate the long-term deformation of fractured rock under the coupling of freeze-thaw (F-T) cycles and sustained loading, this study systematically examined the effects of F-T cycles and fracture dip angle on the creep behavior and damage evolution of sandstone through triaxial compression creep tests. The results indicate that F-T cycles significantly reduce the long-term strength and advance the onset of the accelerated creep stage. An increase in the fracture dip angle further reduces the long-term strength and markedly enhances the sensitivity of the steady-state creep rate. Computed tomography (CT) results reveal that pores and throats exhibit directional enrichment along the fractures. In addition, a nonlinear viscoelastic-viscoplastic creep damage constitutive model that couples initial F-T damage, fracture-structure damage, and time-dependent damage was established. Validation results demonstrate that the fitted model reproduces the measured creep responses under different F-T cycles and fracture dip angles. These findings provide laboratory-scale evidence and a constitutive framework for assessing time-dependent deformation in seasonally frozen fractured rock.