Calibration of tensile strength of a rock model in PFC2D by using distribution function of micro-cracks and clumping method

Ability of discrete element method to simulate initiation and propagation of cracks enables researchers to investigate different topics in the field of fracture mechanics, which is not possible with using finite element and boundary element methods. Study of micro-cracks and failure threshold in rocks with high compression strength help better understanding of brittle behavior under real conditions. PFC2D is based on discrete element method and its special features in modeling the propagation of cracks are compared with other numerical methods. The problems which researchers are faced with this software are mismatch in tensile strength and failure mode of numerical modeling in real samples with high compression strength. In this study, experimental results were used to calibrate numerical models. Petrographic thin sections and cubic samples of granite were prepared for SEM studies. Necessary information about the grain distribution and distribution of micro-cracks in rock samples with microscopic studies were obtained for using in numerical model. In addition, in this study, a clumping method was used. The clumps size is controlled by known influence radius to achieve correct failure pattern of models in accordance with lab samples. Using this type of clumping, showed that ratio of tensile to compressive strength decreases from a mount of 0.5 (without clumping) to less than 0.1 and the tensile strength in numerical models were almost equal to lab samples in high compressive strength.