Influence of cross-flaws on crack initiation and failure modes around a horseshoe-shaped cavity

Cross-flaws are frequently encountered in practical rock engineering projects near horseshoe-shaped cavities, and their presence can significantly impact the failure mode of these cavities. This study utilizes a combination of laboratory experiments and numerical simulations to investigate the influence of cross-flaws on the failure mode of a horseshoe-shaped cavity. During the experimental tests, we varied the length of secondary flaw and the angle of the cross-flaws in the specimens, followed by subjecting them to biaxial compression. Our experimental results show that when the angle a between the primary and the secondary flaws is small (0 and 45), only one crack is initiated at the vault of the cavity, resulting in a shear failure mode. Conversely, when the angle a is large (90 and 135), two cracks are more likely to initiate at the vault of the cavity, leading to the failure mode of falling blocks in the surrounding rock. Furthermore, the circumferential stress at the cavity vault from numerical simulations results is consistent with this observed phenomenon. When the angle a is small, only one circumferential tensile stress concentration is observed at the cavity vault, resulting in the initiation of a single crack. In contrast, when the angle a is large, two stress concentrations appear at the vault of the cavity, leading to the initiation of two cracks from these locations.