Effects of freezing temperature and confining pressure on strain-dependent modulus of frozen sandstone

The mechanical behavior of frozen rock under in situ stress conditions is critical to the stability and successful operation of underground refrigerated rock caverns. In this study, triaxial compression tests were conducted to investigate the mechanical behavior of sandstone under the coupled effects of freezing temperature and confining pressure. The results show that both peak strength and the corresponding axial strain generally increase with decreasing temperature, whereas the elastic modulus decreases in saturated sandstone but increases slightly in dry sandstone. Frozen saturated sandstone exhibits a characteristic convex initial stress–strain response, associated with suppressed pore compaction and progressive ice–rock interface debonding. Analysis of the strain-dependent tangent modulus identifies two concise parameters, the initial tangent modulus E tA and the interface debonding coefficient λ int , to characterize the initial stiffness and its progressive degradation during loading. These results demonstrate that freezing-induced changes in strength and stiffness are not necessarily consistent and highlight the importance of initial nonlinear deformation in evaluating frozen rock. The proposed parameters provide a quantitative framework for characterizing stiffness evolution and ice–rock interfacial effects in underground refrigerated rock caverns.