Effects of uniaxial and triaxial compression tests on the mechanical properties of frozen sandstone samples using real-time CT scanning technique

To explore the mechanical properties of frozen sandstone, the medical X-ray and self-designed triaxial equipment were applied to conduct the real-time uniaxial and triaxial compression scanning tests at room temperature of 20 degrees C and different freezing temperatures of -2 degrees C, -6 degrees C and -10 degrees C. Moreover, computed tomography (CT) scanning images of dry sandstone samples, saturated sandstone samples and saturated frozen sandstone samples were employed to compare and analyse their mechanical features. On the basis of the stress-strain curves and CT scanning images of frozen sandstone samples under different stress states, the influences of confining pressure and freezing temperature on the mechanical properties of frozen sandstone are explored, and the relationships between the average CT value and its variance of the three selected regions and the corresponding stress states are also analysed. In addition, a new damage variable of frozen sandstone based on the volume mean and variance of CT values of the whole sample is proposed to consider the evolving meso-structures in the loading process, and a damage constitutive model for frozen sandstone under uniaxial compression conditions is also formulated. Finally, comparing the experimental results with theoretical ones, the proposed damage model is verified to be capable of describing the stress-strain relationship of frozen sandstone.