Study on Mechanical Mechanism and Pull-out Bearing Capacity of Cylindrical Reaming Anchorage

Abstract

To address the engineering challenges of low anchorage capacity, easy shear debonding failure at the anchorage interface, and the difficult long-term stability control of the roof in deep coal mine soft-rock roadways, a refined 3D numerical model was established in Abaqus based on the bolt-adhesive-surrounding rock collaborative bearing theory and the interfacial shear transfer theory. The influence of cylindrical straight reaming diameter on bolt pull-out behavior was systematically investigated. Seven reaming diameters (24, 30, 40, 50, 60, 70, and 80 mm) were used to analyze the peak pull-out force, load evolution characteristics, stress distribution of the anchorage agent, interfacial load transfer characteristics, and the evolution of anchorage failure modes. Results show that the peak pull-out force exhibits a three-stage trend: rapid increase, slight decrease, and gradual rise with rising reaming diameter. At a 40 mm reaming diameter, the anchorage agent stress distribution is relatively uniform, local stress concentrations are low, and the collaborative bearing state is ideal, yielding a peak pull-out force of 143 kN, which can be used as a reasonable engineering reaming diameter. When the reaming diameter exceeds 50 mm, the effective bearing thickness of the surrounding rock is insufficient; the borehole wall rock gradually enters a plastic softening state; the effective shear capacity decreases; and the pull-out force declines. Within 60–80 mm, the gain from increased contact area compensates to some extent for the weakening of the surrounding rock, and the pull-out force continues to rise. However, surrounding rock damage is severe, construction costs increase significantly, and the engineering practical value is limited. This study can provide a sufficient theoretical basis and reference for mechanism analysis, parameter optimization, and engineering design of reaming bolt support.