Simulation Study on Strength and Failure Characteristics for Granite with a Set of Cross-Joints of Different Lengths

The strength and failure characteristics for granite specimen with a set of cross-joints of different lengths were studied using PFC2D software. The results show that when the included angle of alpha between the main joint and loading direction is 30 degrees or 45 degrees, no matter what the included angle of beta between main and secondary joints is, the main joint controls crack propagation and failure of granite specimen, which occurs the shear failure propagating from main joint tips, and the corresponding uniaxial compressive strength is low. Meanwhile, the secondary joint is the key joint for crack propagation and failure at alpha of 0 degrees and 90 degrees except when beta is 90 degrees. The granite specimen occurs the shear failure propagating from secondary joint tips. And, the shear failure crossing upper tips of main and secondary joints is found at alpha of 0 degrees or 90 degrees and of beta 90 degrees. Their uniaxial compressive strengths are large. Also, the combined actions of main and secondary joints determine crack propagation and failure at alpha of 60 degrees except when beta is 90 degrees. The granite specimen occurs the hybrid failure, including shear failure propagating from main joint tips and tensile failure propagating from main and secondary joints center or secondary joint tips. And, when alpha is 60 degrees and beta is 90 degrees, the granite specimen occurs the shear failure along secondary joint plane direction, and its uniaxial compressive strength is small. Generally, when alpha or beta is a fixed value, the uniaxial compressive strength firstly decreases and then increases with the increase of beta or alpha. Additionally, when alpha is 60 degrees and beta > 45 degrees, the uniaxial compressive strength represents a decreasing trend. The uniaxial compressive strength at alpha and beta between 30 degrees and 60 degrees is generally small. Finally, the microdisplacement field distributions of granite specimen were discussed