Study on structural deterioration characteristics and nonlinear dynamic damage constitutive model of freeze-thaw sandstone

The evaluation of the mechanical properties of rocks after freeze-thaw is crucial to the stability of rock engineering in cold regions, especially the prediction of rock strength under complex dynamic stress states. In this paper, Tongchuan sandstone in cold regions was used as the research object, and freeze-thaw, microscopic and mechanical tests were carried out. The study found that the porosity of sandstone increased after freeze-thaw, more than 90% of the internal pores and newly added pores are micropores. The triaxial dynamic compressive strength variation characteristics of sandstone under freeze-thaw were discussed. Based on the obtained mechanical data, a nonlinear damage dynamic constitutive model was constructed on the basis of the unified strength theory and the strength-strain rate model of thermal activation mechanism and viscosity mechanism, and the coefficient of determination R2 of the model was above 0.97. The model simultaneously considers the effects of freeze-thaw damage, strain rate and confining pressure. Based on the Sobol-QMC method, the global sensitivity analysis of 16 parameters in the damage dynamic constitutive model was carried out. The study found that under various strain rates and confining pressure conditions, the global sensitivity of micropore content, elastic modulus and saturation was always the largest.