Modeling Grain Size Heterogeneity Effects on Mechanical Behavior of Crystalline Rocks Under Compressive Loading

Abstract

Strength and deformation behavior of intact rocks is influenced by a large number of factors, notably mineralogical content. If the constituent minerals are strong, the overall rock strength will be high, and vice versa. The prediction of rock properties of those composed of different types and amounts of minerals will be difficult. This paper presents a numerical approach to study the influence of material heterogeneity associated with the variation of grain size distribution and shape on the strength and deformation behavior of a felsic crystalline rock. By taking advantage of a grain-based modeling approach in two-dimensional Particle Flow Code, a heterogeneity index is defined and explicitly incorporated into the numerical models quantitatively. The numerical results reveal that the peak strength increases as the numerical model gradually changes the character of the rock from heterogeneous to homogeneous. The number of grain boundary tensile cracks gradually decreases and the number of intra-grain cracks increases at the moment of failure. The orientation of grain boundary micro-cracks is mainly controlled by the geometry of assembled grain structure of the numerical model, while the orientation of intra-grain micro-cracks is to a large degree influenced by the confinement. In addition, the development of intra-grain cracks (both tensile and shear) is much more favored in quartz than in other minerals. The findings of this study provide insights to the interpretation of rock properties, particularly those which are strongly influenced by the heterogeneous mineralogical composition.