Study on the mechanical properties and failure evolution of multi-fractured rock based on AE and DIC techniques

To investigate the mechanical properties and failure evolution of multi-fractured rocks, gypsum-based rock-like materials are employed to fabricate specimens with different fracture numbers and fracture inclinations. Uniaxial compression tests are carried out in conjunction with acoustic emission（AE） monitoring and digital image correlation（DIC） techniques to systematically analyze the effects of fracture number（3 and 9） and fracture angle（0°, 30°, 45°, 60°, 90°） on the mechanical behavior and failure evolution of the specimens. Experimental observations show that both fracture number and fracture inclination have a pronounced influence on the compressive strength and failure modes. The uniaxial compressive strength of the specimens varies with fracture angle in a clear V-shaped pattern: the minimum strength occurs at a fracture angle of 30°, whereas the maximum strength is observed at 90°. However, specimens with fractures oriented at 90° exhibit the strongest sensitivity to fracture number, and increasing the fracture number from 3 to 9 results in the most significant strength degradation at this angle, with a maximum reduction of 23%. AE monitoring reveals distinct angle-dependent energy release behaviors during the loading process. For specimens with fracture angles of 0° and 90°, fracture propagation is relatively slow and the released energy is distributed over a longer period. In contrast, specimens with fracture angles between 30° and 60° experience rapid crack propagation accompanied by concentrated energy release. The highest AE ring-down count peak is recorded at a fracture angle of 45°, indicating the most intense fracture activity. Moreover, interactions among multiple fractures further increase the complexity of the energy release mechanisms, particularly in specimens with high fracture angles. Full-field strain analysis based on DIC indicates that strain localization consistently initiates at fracture tips and subsequently evolves along paths controlled by fracture geometry. Compared with specimens containing fewer fractures, specimens with higher fracture numbers exhibit more complex strain field distributions and significantly larger maximum principal strain values, increasing from approximately 2.1% for specimens with 3 fractures to 4.6% for those with 9 fractures. This behavior suggests that increasing fracture density accelerates material integrity degradation and promotes synergistic failure. The failure mode is predominantly governed by fracture inclination. Tensile-dominated failure is observed at low fracture angles, which gradually transitions to tensile-shear composite failure at intermediate angles, and finally returns to tensile-dominated failure at high angles. These results provide deeper insight into the mechanical behavior and failure mechanisms of multi-fractured rock masses and offer important theoretical support for stability evaluation and support design in engineering applications such as coal mine underground reservoirs.