Multi-scale analysis of fracture mechanisms in granite: the influence of mineral spatial distribution, size, and content via a 3D grain-based model

The heterogeneous internal structure of crystalline rocks governs their mechanical behavior. This study employs a three-dimensional Grain-Based Model (GBM3D) within the Particle Flow Code (PFC) to replicate the heterogeneous structure of granite by controlling the spatial distribution, geometric size, and volume fraction of mineral grains. The model is employed to systematically investigate the influence of these microstructural heterogeneities in macroscopic mechanical properties and microcracking behavior. Good agreement between experimental and simulated results validates the proposed model. The main findings are as follows: The model successfully reproduced the heterogeneous structure arising from the random distribution of mineral grains. With increasing grain size, the uniaxial compressive strength (UCS) of the specimen increased, accompanied by a higher proportion of intragranular cracks. As intragranular contacts possess higher bond strength than intergranular contacts, their fracture requires a greater stress concentration, ultimately necessitating a higher external load for macroscopic failure. Similarly, an increase in the volume fraction of quartz led to more intragranular cracks within the quartz grains. Given the exceptionally high bond strength of quartz, an even greater stress concentration is required to fracture these contacts, thereby necessitating a further increase in the UCS.