Research on the fracture properties and collaborative mechanism of hole-bolt composite structures using discrete element analysis

The stability of the hole-bolt composite structure (HBCS) is crucial for controlling the surrounding rock in engineering. Based on the experimental results, the discrete element analysis was employed to investigate the fracture properties and collaborative mechanism of HBCS. Initially, the theoretical analysis indicates that the stress within the surrounding rock around the pressure relief hole is influenced by the rock mass’s properties and the spatial distance. The mechanical response observed in the models is consistent with the results from physical tests. Observations of fracture suggest that a higher bolt pre-tightening force promotes the coalescence of tensile cracks between the hole and bolt. In contrast, increased hole-bolt spacing leads to more discontinuous cracks. Data monitored using measuring balls show that the stress around the pressure relief hole initially increases as hole-bolt spacing rises, while it will diminish on the upper and horizontal sides of the hole. Furthermore, stress nephograms illustrate a proportional relationship between the stress around the bolt and the bolt pre-tightening force, with an expanding low-stress area occurring as hole-bolt spacing increases. The variations in bolt force further corroborate that larger hole-bolt spacing enhances the reinforcement capacity of the bolt. These findings demonstrate that the hole-bolt collaborative mechanism enables the bolt to achieve optimal reinforcement effectiveness, while maximizing the pressure relief capabilities of the pressure relief hole, thereby enhancing the strength and stiffness of the HBCS. This research provides critical insights for controlling the stability control of surrounding rock in high-stress roadways.