Numerical study on the dispersion of mechanical characteristics of granites: Based on a three-dimensional grain-based model and force chain analysis

In this paper, a novel three-dimensional grain-based model based on particle flow code (GBM3D-PFC) is proposed, in which both the geometric division and mechanical property distinction of minerals are realized on the three-dimensional scale. A batch of cylindrical numerical samples with different sizes are constructed based on this model, and the uniaxial loading is then carried out. The position of mineral grains is variable within these samples. In addition, multilevel classification and quantitative analysis of a force chain network are also realized. The dispersion of mechanical characteristics of granites is explained from the point of microscopic mechanism information. This study found: the variation trend of stress-strain curves of the samples is consistent, and the dispersion of compressive strength and elastic modulus decreases with the increase in sample height L. The average value of force chains gradually approaches a stable value. The dispersion of it is almost the same as that of the macroscopic mechanical parameters. With the increase in L, the dispersion of the resistance to rupture of intragranular structures and intergranular structures decreases, that is, the stress level required to produce a single micro-crack is gradually stable, which is the fundamental reason for the decrease in the dispersion of the macro-mechanical parameters. With the improvement of computational efficiency, the quantitative analysis of a multilevel force chain network on the three-dimensional scale can be used in various engineering cases, such as the characterization of stress evolution of surrounding rocks during excavation and the strength estimation of damaged rock mass.