Debonding mechanisms of fully grouted rock bolts driven by adhesive-ring cracking

Interface debonding is the primary failure mode of fully grouted rock bolts, yet the role of adhesive-ring cracking remains insufficiently understood. This study proposes a mechanics-based framework coupling bolt-adhesive interfacial shear with crack initiation and propagation, deriving stage-dependent load-displacement relations. We identify four evolutionary stages: initial elastic coupling, transient shearing hardening, hardening with radial crack growth, and softening after full-depth cracking. A criterion is established to determine the governing interface: debonding occurs at the bolt-adhesive interface if rock tensile strength surpasses that of the adhesive, whereas it shifts to the adhesive-rock interface (or rock detachment) if the adhesive is stronger. The predicted debonding propagation is qualitatively validated via laboratory pull-out tests and acoustic emission monitoring. Our findings demonstrate that adhesive tensile strength and bolt-borehole geometry govern stage-wise crack evolution and load-transfer behavior. The proposed framework provides valuable insights into the debonding mechanisms of fully grouted rock bolts, which could inform adhesive selection and the design of anchorage systems under specific conditions. Further empirical validation is needed to confirm its applicability in a wider range of geological and dynamic environments.