Abstract: In order to predict the mechanical behavior of a fully grouted bolt in tunnels,a novel interfacial model with hyperbolic tangent function to describe the relationship of shear stress and interfacial slip has been proposed in this study.Using this model,the loadtransferring equation of a fully grouted bolt that undergoes the surroundingrock deformation is formulated,and the calculation method for its mechanical behavior is developed by combining the finite difference scheme and Newton iterative formula.The correctness of the proposed interfacial model and calculation method is verified by the testing results of the bolt in a typical tunnel.Then,the distributions of the axial force and shear stress of the bolt induced by the surroundingrock deformation are studied,and the influence from the bolt length,interfacial shear strength and initial shear stiffness as well as the deformationreleasing coefficient are illustrated and discussed.The results indicate that the proposed interfacial model with hyperbolic tangent function can effectively characterize the nonlinear relationship between the shear stress and interfacial slip as well as the evolution of the interfacial stiffness,so that it can predict the mechanical behavior of fully grouted bolt in tunnels.Increasing the length of the bolt can increase the anchoring force of the bolt,but there is a critical length for a bolt;Once exceeding this value,the change in the length of a bolt has insignificant influence on its anchoring force.With increases in the interfacial shear strength and initial stiffness,the anchoring force of the bolt gradually increased and the neutral point moves towards the tunnel.Simultaneously,the interfacial shear stress gradually accumulates toward both the tunnel and the far end of the bolt.The smaller the displacementreleasing coefficient is,the greater the anchoring effect provided by the bolt is.In the engineering practice,it is advisable to reasonably determine the supporting time and the bolt length according to the stability of the surroundingrock and the required anchoring force.

Key words: tunneling engineering,fully grouted bolt,load transferring mechanism,mechanical behavior,nonlinear analysis method