Tensile Bearing Performance and Mechanical Transfer Mechanism of Coal-Rock Composite Anchor Bodies Under Different Height Ratios of Rock to Coal

In response to the problem of debonding failure of anchor rods crossing coal-rock interfaces in coal-rock roadways in Guizhou Province, China, based on bolt pull-out tests, the failure characteristics and bearing characteristics of coal-rock composite anchor bodies under different height ratios of rock to coal were analyzed. The results show that the bearing capacity of coal-rock composite anchor bodies gradually weakened with the height (proportion) of the coal, and that the load-bearing strength of the composite anchor body became closer to that of pure coal. Numerical simulation experiments were conducted using ABAQUS to reveal the debonding mechanism of coal-rock composite anchor bodies under different height ratios of rock to coal from the perspective of differences in coal-rock cooperative failure. The main stages included stress concentration zone expansion; coal failure and debonding while the rock still had bearing performance; the rock reaching critical gradual debonding; and residual strength. In addition, a load transfer model of bolts on coal-rock composite anchor bodies under different height ratios of rock to coal was constructed. This model could derive the pull-out load and displacement curves of coal-rock composite anchor bodies with different height ratios of rock to coal, which showed the same trend as the pull-out test and numerical simulation results and had high credibility. These findings can guide further theoretical research, engineering design, and on-site application of bolt support in coal-rock roadways.