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<p>Boulders exhibit random burial locations, variable dimensions, and anomalous strength properties, which, during shield tunnelling operations, lead to abrupt increases in overturning moments and thrust forces, potentially triggering passive instability of the tunnel face. Current research inadequately addresses boulder-induced face instability, resulting in unclear failure mechanisms in boulder-laden strata. Based on the Zhuhai Xingye Express Tunnel project, this study systematically investigates face stability through field monitoring, numerical simulation, and theoretical modeling, establishing limit equilibrium models (NI-model for <i>D</i><sub><i>b</i></sub> = 0&#xa0;m, LI-model for 0 &lt; <i>D</i><sub><i>b</i></sub> &lt; <i>D</i><sub><i>c</i></sub>, and GI-model for <i>D</i><sub><i>c</i></sub> ≤ <i>D</i><sub><i>b</i></sub> &lt; <i>D</i>) that consider boulder diameter and positions, where <i>D</i><sub><i>b</i></sub>, <i>D</i><sub><i>c</i></sub>, and <i>D</i> represent boulder diameter, critical boulder diameter, and tunnel diameter, respectively. Key findings include: (1) Unblasted boulder-laden strata significantly impair shield performance, reducing penetration rates by 40%, increasing peak overturning moments by 300%, and elevating thrust forces by 30%, with exceptionally large boulders exacerbating these effects; (2) increasing boulder diameter induces a transition from localized to global passive failure mechanisms, with limit support pressure (<i>σ</i><sub><i>p</i>,max</sub>) showing negligible variation when 0 &lt; <i>D</i><sub><i>b</i></sub> &lt; <i>D</i><sub><i>c</i></sub> but a monotonic reduction when <i>D</i><sub><i>c</i></sub> ≤ <i>D</i><sub><i>b</i></sub> &lt; <i>D</i>; (3) comparative analysis of normalized parameters confirms agreement between the proposed model and numerical results, demonstrating that <i>σ</i><sub><i>p</i>,max</sub> increases with greater clearance between boulder top and tunnel crown while larger boulders exhibit stronger position-dependent instability effects; (4) parametric analysis reveals no significant correlation between <i>c</i>, <i>C</i>/<i>D</i>, or <i>D</i> with <i>D</i><sub><i>c</i></sub>/<i>D</i>, while <i>φ</i> shows a positive correlation with <i>D</i><sub><i>c</i></sub>/<i>D</i>.</p>

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Passive instability mechanisms in mega-diameter tunnel faces induced by boulder-laden strata: an integrated field-theoretical-numerical framework

  • 期刊论文

  • 发表日期：

    2026年3月23日

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  • Qilong Song,
  • Dong Su,
  • Weihong Yang,
  • Xiangsheng Chen

摘要

Boulders exhibit random burial locations, variable dimensions, and anomalous strength properties, which, during shield tunnelling operations, lead to abrupt increases in overturning moments and thrust forces, potentially triggering passive instability of the tunnel face. Current research inadequately addresses boulder-induced face instability, resulting in unclear failure mechanisms in boulder-laden strata. Based on the Zhuhai Xingye Express Tunnel project, this study systematically investigates face stability through field monitoring, numerical simulation, and theoretical modeling, establishing limit equilibrium models (NI-model for Db = 0 m, LI-model for 0 < Db < Dc, and GI-model for Dc ≤ Db < D) that consider boulder diameter and positions, where Db, Dc, and D represent boulder diameter, critical boulder diameter, and tunnel diameter, respectively. Key findings include: (1) Unblasted boulder-laden strata significantly impair shield performance, reducing penetration rates by 40%, increasing peak overturning moments by 300%, and elevating thrust forces by 30%, with exceptionally large boulders exacerbating these effects; (2) increasing boulder diameter induces a transition from localized to global passive failure mechanisms, with limit support pressure (σp,max) showing negligible variation when 0 < Db < Dc but a monotonic reduction when Dc ≤ Db < D; (3) comparative analysis of normalized parameters confirms agreement between the proposed model and numerical results, demonstrating that σp,max increases with greater clearance between boulder top and tunnel crown while larger boulders exhibit stronger position-dependent instability effects; (4) parametric analysis reveals no significant correlation between c, C/D, or D with Dc/D, while φ shows a positive correlation with Dc/D.