Mechanical performance analysis of fully grouted bolts considering yield and hardening characteristics

This study presents a coupling numerical method to study the mechanical performance of fully grouted bolts under the yield state. In this study, the tri-linear bond-slip model was utilized for modeling the damage characteristics of the bolt-grout interface and the yield characteristic of bolt was simulated using the bi-linear plastic-hardening model. A series of pull-out tests were conducted to validate the efficacy of this numerical model. Subsequently, this numerical model was adopted to analyze the mechanical performance of fully grouted bolts in high-stress tunnel by considering the effects of the support timing, dilation angle and endplate force. The results reveal that the installation timing of bolts depends not only on the bonding strength at the anchoring interface, but also on the yield strength of bolts. Installing the bolts too early may cause the yield failure of the bolts, resulting in a reduction in the support capacity of the bolts. In addition, the influence of the dilation angle on the mechanical behavior of bolts is also related to the installation timing of the bolts. The endplate can effectively enhance the support capability of the bolts. However, once the bolt enters the yielding state, the endplate only has a slight impact on the support capability of the bolts. This study offers meaningful insights into the mechanical behavior of fully grouted bolts under the yielding state, which contributes to uncovering the interaction mechanism of the bolt-grout interface when bolts yield and providing a guidance for the design of fully grouted bolts in high-stress tunnel.