Dynamic true triaxial compressive micro-macro fracture model in brittle rocks

To address the dynamic instability problem caused by the coupling of the true three-dimensional high in-situ stress and dynamic impact in deep underground engineering, this paper develops a micro-macro cross-scale mechanical model for brittle rock under combined true triaxial static and dynamic compressive loading. Based on a quasi-static microcrack mechanical model under true triaxial stress, the dynamic fracture toughness is introduced, and a toughening formula along with the applicability boundaries of the toughening effect is proposed. The rationality of the model is systematically verified by experiments. The boundary conditions for the transition from “compaction-toughening” to “damage-degradation” induced by axial pre-stress σ 1pre are thoroughly investigated. Furthermore, the asymmetric regulatory function of true triaxial lateral confinement is analyzed, revealing the inhibitory effect of the intermediate principal stress σ 2 on the shear slip of crack surfaces, as well as its synergistic mechanism with the minimum principal stress σ 3 in regulating lateral dilatancy, elucidating the strength enhancement and anisotropic characteristics induced by σ 2 . Finally, the coupling laws of strain rate effects and complex stress states are summarized. The results provide a unified description of the non-linear dynamic response characteristics of deep rock under complex loading paths, offering theoretical support for dynamic stability evaluation and disaster prevention in deep tunnels subjected to high in-situ stress and strong dynamic disturbances.