Discrete Element Simulation and Monitoring Analysis of Different Construction Methods of the Shallow Buried Bias Tunnel

Affected by the bias stress, the mechanical properties of shallow buried bias tunnel construction are complex. The influence of different construction methods on the stability of the portal section of the shallow buried bias tunnel has received significant attention in past studies, but the microscopic mechanism of it has not been properly analyzed. In this study, the discrete element method is used to simulate the construction steps of the three-step method and the single side heading method with and without systematic bolt supports taking Qijiazhuang tunnel as the research object. The tunnel surrounding rock stress, vertical displacement, and surface deformation results under different working conditions are analyzed, and the mechanism of systematic bolt supports is analyzed from microscopic perspective. The results show that the single side heading method can gradually release the load and deformation and better play the supporting capacity of lining; the existence of systematic bolt improves the shear capacity of surrounding rock and enhances the arching effect, thus significantly reducing the vertical displacement of surrounding rock and surface deformation. Finally, compared with the field monitoring data, it is recommended to adopt the single side heading method with systematic bolt support for the construction of the portal section.