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<p>This study investigates the mechanisms and mitigation of surface settlement caused by twin-tunnel construction in water-sensitive coastal soft soils. We integrated field monitoring with 3D finite element modeling to analyze these phenomena. Our findings show that sequential tunnel excavation in low-permeability strata amplifies cumulative stress redistribution and hydro-mechanical coupling. Specifically, rapid pore pressure dissipation, driven by grouting pressure transients and groundwater fluctuations, is a key factor. This process accounted for 60–75% of post-construction settlements within the first 30 days. To address these settlement challenges, we evaluated several reinforcement strategies. A combination of grouting and structural anchorage reduced electric tower foundation displacements by 63%, from 12.7 to 4.69 mm. In another case, isolation piles and soil improvement effectively limited the horizontal displacement of high-speed rail bridge piers to 1.67 mm, staying within the 2.0 mm safety threshold. Numerical simulations provided further insights. The results indicated that increasing the tunnel spacing-to-depth ratio to over 2.5 can mitigate differential settlement by 42–58%. Furthermore, a dynamic grouting control protocol, maintaining pressure between 0.25 and 0.3 MPa, successfully balanced face stability with minimal surface uplift during shield advancement. Based on these results, we propose a graded monitoring framework with tiered alert levels, such as 5 mm for towers and 2 mm for rail piers. This framework enables proactive risk management through timely countermeasures. Our findings offer actionable guidelines for tunneling projects in coastal megacities. These include establishing pre-excavation grouting zones with a six-fold radius of the tunnel diameter and installing isolation piles at a spacing of 1.2 times the tunnel diameter. These measures collectively enhance the resilience of urban infrastructure in geotechnically sensitive environments.</p>

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Predicting and Mitigating Twin-Tunnel Settlement in Coastal Soft Soils: An Integrated Monitoring and Modeling Approach

  • 期刊论文

  • 发表日期：

    2025年9月18日

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  • Zheyuan Feng,
  • Bowen Cheng,
  • Yiming Shao,
  • Bing Zhang,
  • Xinping Li,
  • Xin Wang,
  • Peng Liu

摘要

This study investigates the mechanisms and mitigation of surface settlement caused by twin-tunnel construction in water-sensitive coastal soft soils. We integrated field monitoring with 3D finite element modeling to analyze these phenomena. Our findings show that sequential tunnel excavation in low-permeability strata amplifies cumulative stress redistribution and hydro-mechanical coupling. Specifically, rapid pore pressure dissipation, driven by grouting pressure transients and groundwater fluctuations, is a key factor. This process accounted for 60–75% of post-construction settlements within the first 30 days. To address these settlement challenges, we evaluated several reinforcement strategies. A combination of grouting and structural anchorage reduced electric tower foundation displacements by 63%, from 12.7 to 4.69 mm. In another case, isolation piles and soil improvement effectively limited the horizontal displacement of high-speed rail bridge piers to 1.67 mm, staying within the 2.0 mm safety threshold. Numerical simulations provided further insights. The results indicated that increasing the tunnel spacing-to-depth ratio to over 2.5 can mitigate differential settlement by 42–58%. Furthermore, a dynamic grouting control protocol, maintaining pressure between 0.25 and 0.3 MPa, successfully balanced face stability with minimal surface uplift during shield advancement. Based on these results, we propose a graded monitoring framework with tiered alert levels, such as 5 mm for towers and 2 mm for rail piers. This framework enables proactive risk management through timely countermeasures. Our findings offer actionable guidelines for tunneling projects in coastal megacities. These include establishing pre-excavation grouting zones with a six-fold radius of the tunnel diameter and installing isolation piles at a spacing of 1.2 times the tunnel diameter. These measures collectively enhance the resilience of urban infrastructure in geotechnically sensitive environments.