<p>The pile-beam-arch (PBA) method is a new type of metro station construction method in which the pilot tunnel construction phase produces a relatively large amount of surface settlement. The pilot tunnel excavation sequence is one of the most critical factors affecting surface subsidence during the construction phase of the pilot tunnel. Therefore, adopting appropriate excavation sequences for different groups of pilot tunnels in metro stations is particularly important for reducing surface subsidence. This paper analyzes the optimal excavation sequence of three kinds of pilot tunnel groups in metro stations based on surface subsidence control through theoretical analysis, numerical simulation, and field monitoring. The results show that the group tunnels can be categorized into X-symmetric group tunnels, Y-symmetric group tunnels, and XY-symmetric group tunnels based on the range of stress redistribution after the pilot tunnel excavation. The surface subsidence curves of the three types of group tunnels are parabolic, and all of them have the largest amount of surface subsidence at the center of the guide tunnel group. The optimum excavation sequence for X-symmetric group tunnels and Y-symmetric group tunnels is to excavate the lower and upper pilot tunnels from the center to the edge. The greater the number of pilot tunnels, the greater the surface subsidence. The optimal excavation sequence of XY-symmetric group tunnels is to excavate the lower pilot tunnel and the upper pilot tunnel in the order of alternation excavation. The reliability of numerical simulation is verified by the field monitoring data of a subway in Chengdu.</p>

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Influence of Pilot Tunnel Excavation Sequence on Surface Subsidence in Metro Stations Constructed Using the Pile Beam Arch Method

  • Ziyan Fan,
  • Junfu Fu,
  • Jintao Fu,
  • Junru Zhang

摘要

The pile-beam-arch (PBA) method is a new type of metro station construction method in which the pilot tunnel construction phase produces a relatively large amount of surface settlement. The pilot tunnel excavation sequence is one of the most critical factors affecting surface subsidence during the construction phase of the pilot tunnel. Therefore, adopting appropriate excavation sequences for different groups of pilot tunnels in metro stations is particularly important for reducing surface subsidence. This paper analyzes the optimal excavation sequence of three kinds of pilot tunnel groups in metro stations based on surface subsidence control through theoretical analysis, numerical simulation, and field monitoring. The results show that the group tunnels can be categorized into X-symmetric group tunnels, Y-symmetric group tunnels, and XY-symmetric group tunnels based on the range of stress redistribution after the pilot tunnel excavation. The surface subsidence curves of the three types of group tunnels are parabolic, and all of them have the largest amount of surface subsidence at the center of the guide tunnel group. The optimum excavation sequence for X-symmetric group tunnels and Y-symmetric group tunnels is to excavate the lower and upper pilot tunnels from the center to the edge. The greater the number of pilot tunnels, the greater the surface subsidence. The optimal excavation sequence of XY-symmetric group tunnels is to excavate the lower pilot tunnel and the upper pilot tunnel in the order of alternation excavation. The reliability of numerical simulation is verified by the field monitoring data of a subway in Chengdu.