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<p>This study investigates the impact of constructing parallel overlapping shield tunnels in water-rich sandy gravel strata beneath an existing overpass. Underpinned by the actual case of Shenyang Metro Line 6, the research utilizes a combined approach of numerical simulation and field monitoring to assess the mechanical responses induced in the existing second ring overpass and the underlying tunnel. The analysis focuses on a ‘bottom-up’ excavation sequence, with an additional evaluation of the efficacy of implemented control measures. The data shows that in the process of constructing the overlapping tunnels, the existing overpass exhibits a three-stage settlement deformation evolution of ‘uplift-settlement-stabilization’ and horizontal deformation concentrated in the tunnel excavation direction, while the lower tunnel is primarily affected by unloading, resulting in vertical elliptical uplift deformation. During the construction of overlapping tunnels, the maximum monitored settlement and horizontal deformation of the existing overpass are − 2.92&#xa0;mm and − 2.51&#xa0;mm, respectively, while the maximum monitored vault uplift, arch bottom uplift, and horizontal clearance convergence of the lower tunnel are 3.0&#xa0;mm, 1.75&#xa0;mm, and − 1.2&#xa0;mm, respectively, all meeting the control requirements of the project, thereby demonstrating the safety of the second ring overpass and the lower tunnel. For ‘bottom-up’ overlapping tunnel projects, the focus of internal support reinforcement for the lower tunnel should be on the horizontal direction to improve its structural design, thereby reducing material usage, installation difficulty, and space occupation.</p>

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Impacts of overlapping tunnels underpassing an existing overpass in water-rich sandy gravel strata

  • 期刊论文

  • 发表日期：

    2026年7月27日

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  • Geng Wang,
  • Zhaoping Li,
  • Zihan Zhao,
  • Yi Zhao,
  • Yuhang Lin

摘要

This study investigates the impact of constructing parallel overlapping shield tunnels in water-rich sandy gravel strata beneath an existing overpass. Underpinned by the actual case of Shenyang Metro Line 6, the research utilizes a combined approach of numerical simulation and field monitoring to assess the mechanical responses induced in the existing second ring overpass and the underlying tunnel. The analysis focuses on a ‘bottom-up’ excavation sequence, with an additional evaluation of the efficacy of implemented control measures. The data shows that in the process of constructing the overlapping tunnels, the existing overpass exhibits a three-stage settlement deformation evolution of ‘uplift-settlement-stabilization’ and horizontal deformation concentrated in the tunnel excavation direction, while the lower tunnel is primarily affected by unloading, resulting in vertical elliptical uplift deformation. During the construction of overlapping tunnels, the maximum monitored settlement and horizontal deformation of the existing overpass are − 2.92 mm and − 2.51 mm, respectively, while the maximum monitored vault uplift, arch bottom uplift, and horizontal clearance convergence of the lower tunnel are 3.0 mm, 1.75 mm, and − 1.2 mm, respectively, all meeting the control requirements of the project, thereby demonstrating the safety of the second ring overpass and the lower tunnel. For ‘bottom-up’ overlapping tunnel projects, the focus of internal support reinforcement for the lower tunnel should be on the horizontal direction to improve its structural design, thereby reducing material usage, installation difficulty, and space occupation.