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<p>Twin-tunnel excavation in urban areas posed challenges for predicting surface settlement when excavation sequence, tunnel diameter, and center-to-center spacing interacted. Previous studies considered these parameters individually or used two-dimensional models, leaving their combined three-dimensional influence unresolved. Three-dimensional finite-element models were constructed using the Mohr–Coulomb constitutive law and validated against empirical superposition and independent benchmark cases (maximum deviation &lt; 10%). Parametric analyses included tunnel diameters of 6.5–9.5&#xa0;m, center-to-center spacing of 1.25D–3.8D, and lagging distances of 0–2 TBM lengths (9&#xa0;m). Simultaneous excavation produced the highest surface settlement. Sequential excavation with a lagging distance of 2 TBM lengths reduced maximum settlement by up to 2.8-fold (64–71% lower) compared with simultaneous excavation. Increasing tunnel diameter from 6.5&#xa0;m to 9.5&#xa0;m amplified settlement by 28.6%, whereas increasing center-to-center spacing from 1.25D to 3.8D reduced settlement by 37.5%. Interaction effects became negligible beyond approximately 3D spacing. The results revealed the combined effects of construction sequencing, tunnel geometry, and soil behavior on longitudinal and transverse ground deformation, establishing quantitative relationships that enable safer, more predictable mechanized twin-tunnel excavation beneath sensitive urban infrastructure and guiding optimal design and construction practices for minimizing settlement.</p>

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Influence of Lagging Distance and Geometric Parameters on Surface Settlement in Mechanized Twin Tunneling

  • 期刊论文

  • 发表日期：

    2026年3月17日

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  • Sogol Azizzadeh Ashrafi,
  • Adel Asakereh

摘要

Twin-tunnel excavation in urban areas posed challenges for predicting surface settlement when excavation sequence, tunnel diameter, and center-to-center spacing interacted. Previous studies considered these parameters individually or used two-dimensional models, leaving their combined three-dimensional influence unresolved. Three-dimensional finite-element models were constructed using the Mohr–Coulomb constitutive law and validated against empirical superposition and independent benchmark cases (maximum deviation < 10%). Parametric analyses included tunnel diameters of 6.5–9.5 m, center-to-center spacing of 1.25D–3.8D, and lagging distances of 0–2 TBM lengths (9 m). Simultaneous excavation produced the highest surface settlement. Sequential excavation with a lagging distance of 2 TBM lengths reduced maximum settlement by up to 2.8-fold (64–71% lower) compared with simultaneous excavation. Increasing tunnel diameter from 6.5 m to 9.5 m amplified settlement by 28.6%, whereas increasing center-to-center spacing from 1.25D to 3.8D reduced settlement by 37.5%. Interaction effects became negligible beyond approximately 3D spacing. The results revealed the combined effects of construction sequencing, tunnel geometry, and soil behavior on longitudinal and transverse ground deformation, establishing quantitative relationships that enable safer, more predictable mechanized twin-tunnel excavation beneath sensitive urban infrastructure and guiding optimal design and construction practices for minimizing settlement.