Experimental evaluation on rock failure mechanism with combined flaws in a connected geometry under coupled static-dynamic loads

Flaws in different geometries are widely existed in rock masses and play a significant role in the stability of rock engineering structures. To investigate the failure mechanisms of rock block with combined flaws under coupled static and dynamic loads, a series of experiments were conducted on granite containing pre-existing fissures in the vicinity of a circular opening by using a modified split Hopkinson pressure bar (SHPB) device. Digital image correlation (DIC) method was applied to record the real-time cracking processes. The results show that the fissure inclination angle and the number of fissure are important factors affecting the mechanical properties and cracking processes. The strength of specimens shows a decrease trend with fissure inclination angle increasing, and the localized strain of fissure tip can be used to identify and reveal the crack initiation in the experiments. Based on the temporal and spatial evolution rules of principal strain field obtained by DIC technique, the crack sequences and crack paths of typical specimens are summarized in the paper, especially the crack initiation position. The roof, floor of the opening and the fissure tip are the critical zones where the new cracks usually initiate from. The crack types of the specimens can be categorized as wing crack, coplanar secondary crack, oblique secondary crack, tensile crack and shear crack based on the observation of the failure processes.