Macroscopic behaviour and properties of rocks are dependent on their microstructure. In particular, the grain-grain interfaces and pre-existing cracks are of great importance as they act as flaws in the rock matrix and, based on their distribution, length, and orientation, can induce significant and variant effects on the macroscopic properties of the rock. Another level of complexity is the mechanism that forms pre-existing cracks which can result in smooth or rough surfaces along the grain boundary. In this study, we used the grain-based modelling (GBM) approach within the combined finite-discrete element method (FDEM) to demonstrate the importance of the friction of grain-grain interfaces on the macroscopic rock behavior. This approach discretizes grains making intergranular and intragranular cracks easily traceable. The results of the simulation indicated that for rough fractures, the effect of fracture intensity was minor and only affected the uniaxial compressive strength. For smoother fractures, the effect was more predominant on both stress-strain curves and macroscopic strength properties. As frictional values and fracture intensity decreased, the sample exhibited yielding on loading. These findings indicate the importance of understanding the frictional behavior along pre-existing cracks and suggests that it should be extended into macro-scale modelling.

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