Crack growth mechanism in granite specimens with non-persistent joints under punch shear through test

Experimental and numerical methods (Particle Flow Code) were used to investigate the effect of echelon notches on the shear behavior of the joint’s bridge area in granite. A punch-through shear test was used to model the granite cracks under shear loading. Granite samples with dimension of ۲۰ mm×۱۵۰ mm×۴۰ mm were prepared in the laboratory. Within the specimen model and near the edges, four edge notches were provided. Nine different configuration systems were prepared for notches. In these configurations, the length of each notch was taken as ۳ cm, ۴cm and ۵ cm. Assuming a plane strain condition, special rectangular models were prepared with dimensions of ۱۰۰ mm×۱۰۰ mm using the particle flow code in two dimensions (PFC۲D). Similar to those joints’ configuration systems in the experimental tests, i.e. ۹ models with different rock bridge lengths and different rock bridge joint angles were prepared. The axial load was applied to the punch through the central portion of the model. This testing showed that the failure process was mostly governed by the rock bridge length and the rock bridge angle.  Shear strengths of the specimens were related to fracture pattern and failure mechanism of the discontinuities. It was shown that the shear behavior of discontinuities is related to the number of the induced tensile cracks which are increased by increasing the rock bridge angle.  The strength of samples decreases with increasing the joint length. The failure pattern and failure strength are similar in both methods, i.e. the experimental testing and the numerical simulation.

Keywords:

punch-through shear test , rock bridge length , rock bridge inclinations , PFC۲D