A Constitutive Model to Reveal the Anchorage Mechanism of Fully Bonded Bolts

To better understand the bonding failure at the contact between the bolt shank and anchoring agent, we developed a constitutive model of fully bonded rock bolts, in which the relative movement of the contact was considered. A bond coefficient factor was proposed to calculate the longitudinal displacement of the anchoring agent at the contact between the bolt shank and anchoring agent. The credibility of the developed model was demonstrated with three independent experimental pulling tests. A highlight of this model is that most input arguments can be acquired and calibrated directly from the experimental pulling data. Based on the developed model, a sensitivity analysis was performed. The influence of the bond coefficient and residual bond strength on the anchorage performance of bolt shanks was evaluated. The results revealed that the bond coefficient had a direct relationship to the anchorage performance of bolt shanks. The larger the bond coefficient is, the higher the bond capacity of the bolt shanks. However, there was a certain influencing range for the bond coefficient. Once the bond coefficient was beyond that range, the bond coefficient had a marginal effect on the anchorage performance of the bolt shanks. Moreover, when the residual bond strength equalled the bond strength, fully bonded bolts were likely to show constant resistance behaviour.