Abstract: Grout bolting is widely used as an economical reinforcement of surrounding rocks in underground engineering. However, the mechanism of bolt and rock interaction is not yet fully understood, and analytical evaluation of the reinforcement effect is still underway. This paper derives analytical expressions for the stress, displacement and yield depth at the medium interface for elastic bolts fully embedded into a plastic zone of homogeneous surrounding rock, using the elastic-brittle-plastic model and Mohr-Coulomb yield criterion. This analytical model takes into account the inhibition effects of bolt shear stress ?b on rock. The simulation results of the Kielder test tunnel are in good agreement with measurements. Comparison analyses using different bolt lengths for this tunnel indicate that an anchor length of 1.8 m is appropriate and the benefit of longer bolts is insignificant. Our analytical model is applicable to non-axisymmetric underground caverns and its solutions are simple and clear, helping identify parameters and evaluate support load and support effect in preliminary design phase.

Key words: underground engineering, grouted rock bolt, grouted annulus, interface, deformation modulus after yielding