Progressive failure behaviors and crack evolution of rocks under triaxial compression by 3D digital image correlation

In the study, a series of monotonic triaxial compression tests were carried out on Emochi andesite to evaluate the effects of confining pressure on progressive failure behaviors. The three-dimensional digital image correlation (3D-DIC) system consisting of six cameras was used to capture the images based on the transparent pressure cell. The effects of confining pressures on stress thresholds, energy evolution, field strain patterns and crack evolution were investigated qualitatively or quantitatively. The crack initiation (sigma(ci)), crack damage (sigma(cd))and peaks stress (sigma(c)) increased with confining pressure and the ratios sigma(ci)/sigma(c) and sigma(cd)/sigma(c) respectively varied from 57.74% and 75.11% to 64.02% and 85.33%. Total energy U, elastic energy U-e, and dissipation energy U-d at different characteristic points increased with confining pressures. Field strain patterns indicated that localization developed rapidly in the post-peak region due to the acceleration of crack propagation and damage evolution. The failure mechanisms of Emochi andesite under the uniaxial and triaxial condition are respectively tension-shear destruction and shear destruction. Furthermore, the stress-strain response inside and outside the localization zone are characterized by strain accumulation or inelastic unloading. Finally, a method of confirming the stress level of localization initiation is proposed based on the DIC technique. The stress level decreases with confining pressure. The study provides a useful reference for understanding the failure process of rocks and improving the stability and safety of underground structures.