Effect of stress difference and microfabric on the strength of deep granite

A multitude of subterranean engineering projects are established within granite bodies, where the mechanical properties of granite are predominantly influenced by the existing stress environment and inherent microfabric. As the depth of engineering projects increases, the characteristic stress differential becomes more pronounced, indicating a discernible distinction from the stress conditions encountered in shallow engineering applications. To elucidate the influence mechanism of microfabric and stress disparity on granite strength, a quantitative analysis is conducted on the microfabric of five types of granites. The results show that the strength of granite is primarily determined by initial damage, structural coefficient, biotite content, and quartz content. With an increase in stress differential, the impact of initial damage and biotite content on granite strength diminishes, while the influence of quartz content and structural coefficient on granite strength begins to intensify. A subjective and objective comprehensive evaluation model is established to quantify the weight ratio of microfabric on granite strength. The coupling mechanism of stress difference and microfabric on the granite strength is revealed from the rock fracture directional development induced by the increase of stress difference. The results can be used as a guide to understand the granite strength characteristics according to the lithofacies and true three-dimensional stress environment, and provide an effective theoretical basis for the safe construction of deep granite engineering.