Mechanical response characteristics and failure evolution law of anchorage body under different confining pressure gradient and anchorage length

To investigate the synergistic mechanism of confining pressure and anchorage length on anchorage body bearing capacity, this study examined the mechanical response and failure evolution under varying confining pressures and anchorage lengths using laboratory pull-out tests, acoustic emission monitoring, and ABAQUS numerical simulation. A high-precision confining pressure loading system and acoustic emission monitor were used to synchronously acquire pull-out load–displacement curves, acoustic emission energy and ring count parameters, and interface failure modes. A numerical simulation framework incorporating a nonlinear bond-slip model discretized the anchorage interface behavior with virtual spring elements to verify test reliability. Results show the bolt pull-out process comprises four stages: elastic deformation, plastic yield, post-peak softening, and friction slip. Increasing confining pressure from 0 to 15 MPa raised the ultimate bearing capacity of long anchorage specimens by 62%, 37%, and 15%, and short specimens by 61%, 37%, and 27%, respectively. Higher confining pressure enhances bearing capacity, but the increase rate diminishes with pressure. Under long anchorage conditions, increased confining pressure significantly influences the anchorage body failure mode.