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<p>The construction of new tunnels in proximity to existing operational tunnels has become increasingly common in dense urban environments, raising concerns regarding tunnel–tunnel interaction and structural safety. This paper presents a three-dimensional finite element investigation of the underpassing of Tehran Metro Line 6 beneath the existing Line 1 tunnel, with a vertical clearance of approximately 5.5&#xa0;m. The analysis is based on a real case study. It incorporates realistic construction staging, nonlinear soil behavior, and advanced constitutive models for tunnel linings, including a user-defined hardening soil formulation for the ground and the concrete damaged plasticity model for concrete linings. The interaction effects are evaluated in terms of internal forces, deformations of the existing tunnel, and ground surface settlement. Results indicate that the most critical response occurs when the top-heading excavation of Line 6 enters the intersection zone, where asymmetric loading induces peak axial forces and bending moments in Line 1. The maximum vertical displacement of Line 1 was approximately 8&#xa0;mm, remaining below the allowable limit of 12.5&#xa0;mm; subsequent bench excavation had a negligible additional impact. The presence of the stiff overlying tunnel significantly reduced deformation of Line 6 and limited surface settlement.</p>

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Tunnel–tunnel interaction in underpassing excavation: a case study

  • 期刊论文

  • 发表日期：

    2026年6月22日

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  • Abbas Pourdeilami,
  • Mehdi Ebadi-Jamkhaneh,
  • Mohammadreza Asgarpanah

摘要

The construction of new tunnels in proximity to existing operational tunnels has become increasingly common in dense urban environments, raising concerns regarding tunnel–tunnel interaction and structural safety. This paper presents a three-dimensional finite element investigation of the underpassing of Tehran Metro Line 6 beneath the existing Line 1 tunnel, with a vertical clearance of approximately 5.5 m. The analysis is based on a real case study. It incorporates realistic construction staging, nonlinear soil behavior, and advanced constitutive models for tunnel linings, including a user-defined hardening soil formulation for the ground and the concrete damaged plasticity model for concrete linings. The interaction effects are evaluated in terms of internal forces, deformations of the existing tunnel, and ground surface settlement. Results indicate that the most critical response occurs when the top-heading excavation of Line 6 enters the intersection zone, where asymmetric loading induces peak axial forces and bending moments in Line 1. The maximum vertical displacement of Line 1 was approximately 8 mm, remaining below the allowable limit of 12.5 mm; subsequent bench excavation had a negligible additional impact. The presence of the stiff overlying tunnel significantly reduced deformation of Line 6 and limited surface settlement.