Strain-Softened Elastoplastic Analysis of Surrounding Rocks in the Deep Tunnel under Pre-Stressed Anchor Support Conditions

In order to investigate the mechanical state of pre-stressed anchors for tunnel support under water-rich ground conditions, an elastoplastic analysis of the tunnel surrounding rock was carried out based on the three-dimensional Hoek-Brown failure criterion, considering the effects of hydraulic coupling and strain softening of the surrounding rock, and considering the pre-stressed anchors as a passive anchor model with anchor pads and non-zero strain at both ends. The numerical calculation method of shear stress distribution and end prestress of prestressing anchor was established by using bond-slip theory. Through the comparison and analysis of the calculation results of relevant engineering cases, the rationality of the calculation method in this study is verified. At the same time, parametric analysis is carried out on the change law of surrounding rock stress and displacement under the influence of different factors by relying on the actual project. The results show that: The maximum values of anchor shaft force, tunnel surface force, and anchor neutral point are well-fitted with the monitoring values of the selected engineering cases. When the anchor shear stress reaches the peak stress of the tunnel wall, the decoupling phenomenon occurs between the anchor and the surrounding rock near the tunnel wall. The actual project reflects that the method of this study can effectively solve the design calculation problem of pre-stressed anchors in the deep tunnel, and the pre-stressed anchors can effectively reduce the surrounding rock deformation after installation. Compared with the passive anchor, its support effect is better. The study results can theoretical guidance for the design of the deep tunnel support under similar engineering geological conditions.