Experimental study of deformation localization characteristics of sandstone under seepage-stress coupling based on 3D digital image correlation technology

In order to study the localized failure characteristics of sandstone deformation under the coupling of seepage and stress, the three-dimensional digital image correlation (3D-DIC) technology was applied to the visualized three-axis servo control test system, and the triaxial compression tests under different seepage pressures were carried out on the sandstone. The results show that, under the coupling of seepage and stress, the cloud image of the sandstone surface deformation field has undergone an evolutional process from uniform to non-uniform. The deformation before the peak is relatively uniform, the strain concentration appears at the peak, and a deformation localized zone is formed rapidly in a short time after the peak. With the increase of seepage pressure, the peak strength and elastic modulus of the rock exhibit exponential nonlinear attenuation, the peak strength weakening coefficient and elastic modulus weakening coefficient both increase, the permeability gradually increases, and the earlier the maximum permeability appears. With the seepage pressure increases, the deformation localization zone of sandstone transits from shearing to tension-shearing, the internal and external strains of the axial and radial deformation localized zone show large differences within a short time after the peak, and the in-band strain is much larger than the out-of-band strain. With the increase of seepage pressure, the higher the starting stress level of deformation localization, the earlier the starting time point. The seepage pressure is linearly associated with the stress level of the sandstone deformation localization start-up stress. The axial deformation localization start-up level is more significantly affected by the seepage pressure than the radial direction.