Mechanical Behavior Analysis of Fully Grouted Bolts under Axial Cyclic Load

Fully grouted bolts are widely used in engineering. In order to deeply understand the load-transfer mechanism of a fully grouted bolt, it is necessary to analyze and study its mechanical behavior under axial cyclic load. First of all, based on the idea of discretization and the force balance analysis of each mass spring element, this study proposes a method for analyzing the force of the bolt—the spring element method. Second, the load-transfer model of the fully grouted bolt is established by using the spring element method, assuming that the bolt and the sidewall rock and soil are connected by tangential linear springs. The analytical solutions for the displacement, axial force, and shear-stress distribution of the bolt before and after the damage of the sidewall spring are given. It is found that the analysis results of the analytical model proposed in this paper have a great relationship with λ, which is the square root of the ratio of sidewall spring stiffness k′u to bolt stiffness ku. Further analysis found that this model is more suitable for the two working conditions of λ ≈ 0 and λ ≈ 1, and the relationship between sidewall spring stiffness k′u and pull-out stiffness K of the bolt was established under these two working conditions. Finally, the rationality and accuracy of the analytical model proposed in this study are verified by an analysis of two typical test cases under the two working conditions of λ ≈ 0 and λ ≈ 1.