Crack growth and coalescence mechanism in granite material containing two surface flaws under uniaxial compression

The main purpose of this study is to investigate the crack growth process and the coalescence mechanisms of two parallel pre-existing 3-D surface flaws under uniaxial compression in real rocks. In this study, the flaw angle, flaw length and the distance between two surface flaws (bridge length) are fixed. The bridge angle (the relative inclination between two flaws) is varied from 45° to 90°. Two observation systems (CCD camera and acoustic emission (AE) system) were used to study the propagation of cracks in the specimen. It was observed that petal cracks initiated along the interior surface of the flaw front. The propagation of the petal cracks is in three-dimensional curve shape towards to the surface of the specimen and extended to the bridge area. The coalescence mechanism depends on the bridge angle and bridge length. When the bridge angle is 90° with the bridge length equal to the flaw length, coalescence occurred. The coalescence crack is formed by the mixed mode of tensile cracks and petal cracks. But when the bridge angle is 45° with the same bridge length, no coalescence occurred. Further experimental study is required for coalescence mechanism of variables not fully investigated in the current study.