Strength and Failure Properties of Preflawed Granite under Coupled Biaxial Loading and Unloading Conditions

In this study, numerical simulations of uniaxial compression, biaxial compression, and biaxial unloading were performed on granite specimens that contained different prefabricated defects. The microscopic parameters in numerical models were verified by the uniaxial compression experiments on the intact standard cylindrical granite specimen and the square granite specimens with prefabricated defects. The influences from different stress paths, different shapes of prefabricated defects, different numbers of defects, and different distribution of defects on the strength, deformation, and crack initiation stress characteristics of the rock specimens were investigated. Furthermore, the initial cracking and cracking stage distributions, cumulative crack amounts, ultimate failure modes, and crack propagation fractal dimensions of specimens with different prefabricated defects under biaxial unloading conditions were analyzed and compared. The experiment was divided into three stages to analyze crack evolution mechanisms. The results show that most cracks appeared after peak strength, and different shapes, the number of defects, and the relative defect positions significantly affected crack initiation, crack propagation, and crack coalescence.