Creep properties and model of fractured sandstone under freezing environment

Creep is an important mechanical property of fractured rock. To explore the creep mechanical properties and damage evolution law of surrounding rock mass under long-term external load during freezing construction, triaxial graded loading creep and CT tests are conducted under a freezing environment (-10 degrees C) on sandstone with different fracture dip angles. The test results reveal that the prefabricated fracture have a significant impact on the creep of sandstone under freezing environment. As the fracture dip angel increases, the creep duration, creep deformation, and long-term strength all decrease first and then increase, with lower values at 15 degrees and 45 degrees . At 0 degrees , 15 degrees and 45 degrees dip angles, the rocks exhibit integrated shear through failure, whereas rocks with a dip angle of 75 degrees and 90 degrees exhibit the mode of tensile shear through failure. Notably, no microcracks or secondary cracks are observed in the rock samples. Finally, a nonlinear viscoelastic - plastic constitutive model of fractured sandstone is established via fractional calculus. Fitting the experimental curve with the theoretical model reveals that the proposed creep damage model could accurately describe the creep behavior of fractured sandstone under freezing, especially in the accelerated creep stage, which validates the reliability of the parameters.