Study on mechanical properties and failure mechanism of single-fractured granite under impact load

Fractured granite is a predominant geological medium in underground mining, tunnel excavation, and rock mass reinforcement. Its mechanical behavior under complex loading conditions directly controls engineering stability and long-term operational safety. However, systematic research on single-fractured granite remains insufficient, particularly regarding the influence of geometric characteristics (e.g., fracture inclination angle, length, and width) on its mechanical properties, failure mechanisms, and energy dissipation. This knowledge gap impedes accurate stability assessment and risk mitigation in practical engineering applications. This research employs a microcomputer-controlled electro-hydraulic servo universal testing machine and a split Hopkinson pressure bar to conduct quasi-static and dynamic compression tests on single-fracture granite of three different strengths. Simultaneously, LS-DYNA is used to establish numerical models of single-fracture granite with different fracture geometries to deeply investigate the specific impacts of fracture angle, length, and width on the mechanical properties and crack propagation characteristics of single-fracture granite through numerical simulation. The results show that intact granite under stress waves forms axial shear-tensile cracks, while single-fractured granite generates wing-shaped cracks from the prefabricated fracture tip. Lower strength in single- fractured granite leads to higher energy efficiency. Crack initiation shifts clockwise along the fracture edge with increasing inclination, involving oblique shear cracks along the fracture and diagonal shear cracks from the vertices. For fracture lengths < 20 mm, stress concentration is balanced. For fracture lengths ≥ 20 mm, stress focuses at the upper end, causing upward shear cracks. Wider fractures reduce shear cracks along the prefabricated fracture but intensify damage from vertex-initiated shear cracks. The critical fracture parameters (20 mm length, 45° inclination) and energy dissipation laws derived from this study provide a quantitative basis for stability assessment of fractured rock masses, optimization of support schemes, and early warning of rock burst risks in underground engineering.