Group-tunnel Mechanical Effect of PBA Method in Metro Stations Bidirectional Excavation

Abstract

［Objective］ The group-tunnel effects induced by multi-pilot tunnel construction by PBA (pile-beam-arch) method and the mechanical characteristics of ingates during breakthrough excavation pose significant threats to the construction safety of underground metro stations. Thus, it is essential to investigate the group-tunnel mechanical effects in metro station bidirectional excavation process using PBA method. ［Method］ FLAC3D software is employed to establish a three-dimensional numerical calculation model for PBA pilot tunnel construction. Through this model, the deformation patterns of ground and the mechanical characteristics of ingates under different bidirectional pilot tunnel construction sequences are analyzed, leading to the identification of optimal bidirectional pilot tunnel construction sequence. ［Result & Conclusion］ The group-tunnel effects of bidirectional PBA pilot tunnel construction are significant, with the influence degree as follows: two-way four-pilot tunnel excavation > two-way double-pilot tunnel excavation > two-way single-pilot tunnel excavation. For ingates, the maximum tensile stress after breakthrough occurs at the arch bottom, while the maximum shear stress is observed at the sidewalls and arch foot. The stress levels of both go with the following trend: two-way single-pilot tunnel excavation < two-way double-pilot tunnel excavation < two-way four-pilot tunnel excavation. Additionally, the maximum shear stress of the ingate exhibits a leap-like increase with excavation progress and gradually stabilizes in the later stages of construction. From the perspective of improving the stress state of the ingates and ensuring safe breakthrough, the two-way single-pilot tunnel construction sequence is more advantageous.

Keywords

• metro station
• pba method
• group-tunnel effect
• numerical simulation