Pullout response and failure characteristics of anchorage system in hard rocks

The axial load-bearing capacity of grouted anchorage systems is critical for rock reinforcement and reflects the interactions among system components. Hence, the mechanical response and failure characteristics of the anchorage system under axial loading are of vital importance. They serve as the foundation for establishing the mechanical model of the anchorage system and provide significant guidance for the optimization design of bolts and the assessment of anchorage conditions. However, as the most widely used research method, current pullout tests have not paid sufficient attention to simulating actual rock mass stiffness, have not fully revealed the radial mechanical response during the pullout process, and have not clarified the locations and modes of pullout failure. To address these issues, a testing method simulating hard rock stiffness and strength was developed using elasticity and stiffness equivalence theories. Tests revealed three anchorage failure modes under equivalent hard rock stiffness: tooth cutting, sliding, and sliding-tooth cutting composite failure, with the composite failure being dominant. The pullout load-displacement curves exhibited bimodal patterns for composite failure and single peaks for tooth cutting and sliding failures. Post-peak softening showed up-convex curves for tooth cutting and down-concave curves for sliding failure, while bolt yielding displayed distinct plateaus. The radial stress trends at the rock-grout interface paralleled pullout load curves, with sliding failure exhibiting approximately 10 MPa lower peak radial stress compared to tooth cutting failure. Anchorage length most strongly affected peak load, while grout properties predominantly governed failure mode.