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<p>The interaction between seepage erosion and soil arching around existing tunnels poses significant challenges to the stability of underground infrastructure. While the mechanical shielding effect is recognized, the hydro-mechanical evolution under varying geometric constraints requires further investigation. In this study, a coupled CFD-DEM numerical framework is established to simulate the seepage-induced arching evolution within a trapdoor-tunnel system. Numerical models with varying vertical clearances (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(H_2/B\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>H</mi> <mn>2</mn> </msub> <mo stretchy="false">/</mo> <mi>B</mi> </mrow> </math></EquationSource> </InlineEquation>) and tunnel diameter ratios (<i>D</i>/<i>B</i>) are systematically examined to decouple the geometric effects on erosion kinetics and stress redistribution. The results illustrate that the vertical clearance dictates the continuity of the soil arch; a decrease in <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(H_2/B\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>H</mi> <mn>2</mn> </msub> <mo stretchy="false">/</mo> <mi>B</mi> </mrow> </math></EquationSource> </InlineEquation> triggers a transition from a stable bypass mode to a shadowing mode, leading to the formation of through-going hydraulic channels. Furthermore, the tunnel diameter exerts a significant bottleneck effect on the seepage field. The narrowing of the soil column amplifies local hydraulic gradients and reverses the crown stress state from unloading to concentration. The degradation process is further quantified by microscale parameters, including the topological evolution of force chains and fabric anisotropy. The results reveal that the loss of directional locking and the buckling of strong force chains are the fundamental mechanisms driving instability. These insights provide a quantitative basis for advancing the understanding of hydraulic stability in twin-tunnel systems.</p>

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Hydro-mechanical evolution of seepage-induced soil arching under geometric constraints: a CFD-DEM study

  • 期刊论文

  • 发表日期：

    2026年8月3日

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  • Hao Xiong,
  • Xiaoqi Fu,
  • Jianbo Fei,
  • Zhen-yu Yin,
  • Zengle Ren,
  • Xiangsheng Chen

摘要

The interaction between seepage erosion and soil arching around existing tunnels poses significant challenges to the stability of underground infrastructure. While the mechanical shielding effect is recognized, the hydro-mechanical evolution under varying geometric constraints requires further investigation. In this study, a coupled CFD-DEM numerical framework is established to simulate the seepage-induced arching evolution within a trapdoor-tunnel system. Numerical models with varying vertical clearances ( \(H_2/B\) H 2 / B ) and tunnel diameter ratios (D/B) are systematically examined to decouple the geometric effects on erosion kinetics and stress redistribution. The results illustrate that the vertical clearance dictates the continuity of the soil arch; a decrease in \(H_2/B\) H 2 / B triggers a transition from a stable bypass mode to a shadowing mode, leading to the formation of through-going hydraulic channels. Furthermore, the tunnel diameter exerts a significant bottleneck effect on the seepage field. The narrowing of the soil column amplifies local hydraulic gradients and reverses the crown stress state from unloading to concentration. The degradation process is further quantified by microscale parameters, including the topological evolution of force chains and fabric anisotropy. The results reveal that the loss of directional locking and the buckling of strong force chains are the fundamental mechanisms driving instability. These insights provide a quantitative basis for advancing the understanding of hydraulic stability in twin-tunnel systems.