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<p>The stability of the quasi-rectangular shield tunnel face is a critical safety concern in urban underground construction. To address the lack of understanding regarding the failure mechanisms of non-circular tunnel faces, this study systematically investigates the instability behavior of quasi-rectangular shield tunnel faces in sandy soil through a combination of transparent sand model tests and finite difference method (FDM) numerical simulations. By conducting transparent sand model tests under burial depth ratios (<i>C</i>/<i>H</i> = 0.5, 1.0, 2.0, and 3.0), this research quantitatively analyzes the progressive failure process, the expansion pattern of the sliding zone, and the critical support pressure. Furthermore, FLAC3D-based numerical simulations are performed to explore the influence of the tunnel cross-sectional aspect ratio (<i>L</i>/<i>H</i>) on the failure mode. The results reveal that: Failure Mechanism: The instability of quasi-rectangular tunnel faces exhibits distinct progressive characteristics, forming a “wedge-prism composite sliding mode” in sandy soil. When <i>C</i>/<i>H</i> ≤ 2.0, widening the tunnel significantly promotes the upward propagation of the sliding zone at a specific inclined angle, resulting in an 80% increase in longitudinal failure extent. Support Pressure Characteristics: The limit support pressure ratio (<i>P</i>/<i>P</i><sub>0</sub>) demonstrates an approximate linear positive correlation with <i>L</i>/<i>H</i> (R² = 0.89), indicating heightened sensitivity of quasi-rectangular tunnel faces to support pressure variations. Predictive Model: A fitting formula for the limit support pressure of quasi-rectangular tunnels is proposed. The findings confirm that quasi-rectangular shields face elevated instability risks under shallow burial conditions (<i>C</i>/<i>H</i> ≤ 2.0), emphasizing the necessity of dynamic support pressure regulation during construction. This study advances theoretical frameworks and technical solutions for stability analysis and reinforcement design of complex-section shield tunnels.</p>

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Face stability analysis of quasi-rectangular shield tunneling within sandy material

  • 期刊论文

  • 发表日期：

    2025年10月23日

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  • Huayang Lei,
  • Bohan Guan,
  • Yingnan Liu,
  • Changyuan Ma

摘要

The stability of the quasi-rectangular shield tunnel face is a critical safety concern in urban underground construction. To address the lack of understanding regarding the failure mechanisms of non-circular tunnel faces, this study systematically investigates the instability behavior of quasi-rectangular shield tunnel faces in sandy soil through a combination of transparent sand model tests and finite difference method (FDM) numerical simulations. By conducting transparent sand model tests under burial depth ratios (C/H = 0.5, 1.0, 2.0, and 3.0), this research quantitatively analyzes the progressive failure process, the expansion pattern of the sliding zone, and the critical support pressure. Furthermore, FLAC3D-based numerical simulations are performed to explore the influence of the tunnel cross-sectional aspect ratio (L/H) on the failure mode. The results reveal that: Failure Mechanism: The instability of quasi-rectangular tunnel faces exhibits distinct progressive characteristics, forming a “wedge-prism composite sliding mode” in sandy soil. When C/H ≤ 2.0, widening the tunnel significantly promotes the upward propagation of the sliding zone at a specific inclined angle, resulting in an 80% increase in longitudinal failure extent. Support Pressure Characteristics: The limit support pressure ratio (P/P0) demonstrates an approximate linear positive correlation with L/H (R² = 0.89), indicating heightened sensitivity of quasi-rectangular tunnel faces to support pressure variations. Predictive Model: A fitting formula for the limit support pressure of quasi-rectangular tunnels is proposed. The findings confirm that quasi-rectangular shields face elevated instability risks under shallow burial conditions (C/H ≤ 2.0), emphasizing the necessity of dynamic support pressure regulation during construction. This study advances theoretical frameworks and technical solutions for stability analysis and reinforcement design of complex-section shield tunnels.