Study on the Effect of Continuity and Load Angle of Prefabricated Cross-Flaws on Crack Initiation and Coalescence

Abstract

In this study, a model that is closer to the state of fracture presentation in natural rocks has been developed, which is different from the previous. The cross-flaws can be characterized by the joint persistency (k) and the angle between the primary flaws and axial load (α). The two parameters were varied individually and, by combining them, nine specimens with different nodal parameters were formed. Laboratory specimens and numerical simulations were performed on these specimens to investigate the crack extension process and the variation of crack initiation and coalescence stresses. It is found that a new category of crack coalescence is discovered according to the experimental results besides those reported before, and the angle α affects whether tensile-shear cracks appear. Also, α has an impact on the location where crack first occurs. The joint persistency k alters rock failure mode and has a substantial effect on crack initiation stress. However, the effect on the aggregation stress is not significant. The crack initiation stress decreases in the case of cross-flaws in contrast to flat fissures. In addition, the flat-joint model in PFC2D is used for numerical simulation. It is possible to conduct a study that is difficult to achieve experimentally by using simulations, i.e., only changing one macroparameter without changing others and thus studying the changes in the effect on cracking during fracture. The simulation results are in good agreement with the experimental results. At the same time, the connection mode and the width of the crack coalescence zone of the primary defect, which is difficult to observe in the experiment, are found out from the numerical simulation.