Quantitative investigation of the cracking mechanism of 3D sand-printed rock containing a fold flaw

Abstract

Natural discontinuities originating inside rocks are often distributed in folds rather than simple straights. To represent the details of fold-shaped flaws, rock-like specimens containing a fold flaw are created by 3D sand printing, and cases involving four undulation angles (α) are considered. Uniaxial compression tests, digital image correlation (DIC), and the extended finite element method (XFEM) on rock-like models are conducted to investigate the influence of undulation angles on the cracking mechanism of the specimens. The 3D sand-printed specimen has obvious advantages in simulating natural rocks. Two types of crack initiation modes are observed: tip cracking and nontip cracking. DIC-based measurements and XFEM simulations show that the maximum value of maximum principal stress and strain occur near when α = 0° and 10°, while they appear in the flaw inflexion when α = 20° and 30°, which explains the difference in crack initiation. Two types of cracks are identified based on the displacement vector analysis: tensile and horsetail cracks. The crack initiation position of these two cracks is precisely determined by extracting strain data around the flaw tip. The undulation angle cannot alter the final coalescence, which is induced by the connection of horsetail cracks with the flaw.