Mechanical responses and failure mechanisms of anchorage systems under pullout load in soft rock stiffness conditions

The pullout performance of the anchorage system is a key indicator for assessing the effectiveness of rock mass reinforcement. However, existing pullout tests, though widely used, fail to accurately simulate the stiffness of the actual rock mass, reveal the radial mechanical response, and analyze failure modes. To address these issues, this study designed a combination of aluminum sleeves and rock to simulate a soft rock environment and conducted pullout tests on the anchorage system under the stiffness conditions of a soft rock environment. Results indicate two dominant failure modes in a soft-rock environment: rock-splitting failure and unsplit failure, with the corresponding pullout curves showing post-peak sharp drop and post-peak gradual drop, respectively. A significant correlation exists between radial stress and failure mode: peak radial stress ranges from 4 MPa to 10 MPa for rock-splitting failure and 2 MPa to 4 MPa for unsplit failure. Moreover, the anchorage length has the most significant impact on the peak load, while the anchorage length and grout strength are the main factors affecting the failure mode of the anchorage system.