Analysis on characteristics and mechanism for rock fracture in deep rock with cracks under dynamic-static coupling effect

The mechanical behavior and fracture mechanisms of deep fractured rocks under explosive dynamic loads are critical for understanding rock instability in engineering applications such as blasting operations. This study aims to investigate how the presence of pre-existing cracks and different stress states affect the mechanical properties and fracture patterns of rock-like specimens under dynamic loading conditions. We utilized a Split Hopkinson Pressure Bar (SHPB) with an active confining pressure loading device to conduct impact compression tests on rock-like specimens containing pre-existing cracks. These tests were performed under uniaxial and triaxial stress states to simulate various in-situ stress conditions. The study revealed three key findings: (1)The dynamic compressive strength of specimens with pre-existing cracks exhibited a non-monotonic relationship with crack inclination angle under uniaxial stress, contrasting with an increasing trend under confining pressure, highlighting the significant effects of confining pressure and strain rate. (2)Confining pressure significantly altered the failure modes, with specimens failing predominantly in axial tension at 0° and 90° crack inclinations, and a mix of axial tension and shear at 30° and 60°, indicating complex failure mechanisms. (3)The pre-existing crack angle under confining pressure influenced the propagation path and fractal dimension of the specimen, with an increasing angle correlating to higher fractal dimensions and a positive impact on compression peak stress. The research provides valuable insights into the complex fracture behavior of fractured rocks under dynamic loads, which can inform the design of blasting parameters in deep engineering. It also offers critical knowledge for preventing rock instability-related disasters, thus holding significant theoretical and practical importance in the field of rock mechanics and engineering.