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<p>To investigate the effects of single-tunnel inclination angle (<i>α</i>) and double-tunnel offset distance (<i>d</i>) on mechanical properties and fracture mechanisms of tunnel specimens, sandstone-like tunnel specimens were fabricated via 3D printing technology. Digital image correlation (DIC) technology was employed to classify cracks into tension-dominated cracks (TDC), shear-dominated cracks (SDC), and mixed-mode cracks (MC). All specimens exhibited a four-stage deformation process: elastic stage, micro-crack initiation stage, peak strength stage, and residual stage. For strength characteristics, the peak stress of single-tunnel specimens exhibited fluctuating variations with increasing <i>α</i>, whereas that of double-tunnel specimens increased initially and subsequently decreased with increasing <i>d</i>; the elastic modulus showed a consistent variation trend with peak stress. PFC2D numerical simulations exhibited high consistency with experimental results. After reaching peak load, strain energy was rapidly converted into dissipated energy: specifically, at <i>α</i> = 15°, the dissipated energy reached 2.7260&#xa0;kJ with an energy conversion rate of 50.91%, corresponding to slow multi-directional crack propagation; at <i>d</i> = 2.5&#xa0;mm, the boundary energy of double-tunnel specimens reached 4.0070&#xa0;kJ, representing an optimal balance between energy storage and dissipation. Stress distribution analysis revealed that varying <i>α</i> altered the symmetry of strain concentration zones, thereby influencing crack propagation paths; varying <i>d</i> interfered with the inter-tunnel stress superposition effect, which further modified the failure mode. This study offers a theoretical foundation for design optimization, stability analysis, and hazard prevention of underground double-tunnel engineering.</p>

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Study on the Influence of Tunnel Inclination Angle and Offset Distance on Its Mechanical Properties and Fracture Mechanisms

  • 期刊论文

  • 发表日期：

    2025年12月24日

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  • Hesi Xu,
  • Shuyang Yu,
  • Jun Yu,
  • Yifei Li

摘要

To investigate the effects of single-tunnel inclination angle (α) and double-tunnel offset distance (d) on mechanical properties and fracture mechanisms of tunnel specimens, sandstone-like tunnel specimens were fabricated via 3D printing technology. Digital image correlation (DIC) technology was employed to classify cracks into tension-dominated cracks (TDC), shear-dominated cracks (SDC), and mixed-mode cracks (MC). All specimens exhibited a four-stage deformation process: elastic stage, micro-crack initiation stage, peak strength stage, and residual stage. For strength characteristics, the peak stress of single-tunnel specimens exhibited fluctuating variations with increasing α, whereas that of double-tunnel specimens increased initially and subsequently decreased with increasing d; the elastic modulus showed a consistent variation trend with peak stress. PFC2D numerical simulations exhibited high consistency with experimental results. After reaching peak load, strain energy was rapidly converted into dissipated energy: specifically, at α = 15°, the dissipated energy reached 2.7260 kJ with an energy conversion rate of 50.91%, corresponding to slow multi-directional crack propagation; at d = 2.5 mm, the boundary energy of double-tunnel specimens reached 4.0070 kJ, representing an optimal balance between energy storage and dissipation. Stress distribution analysis revealed that varying α altered the symmetry of strain concentration zones, thereby influencing crack propagation paths; varying d interfered with the inter-tunnel stress superposition effect, which further modified the failure mode. This study offers a theoretical foundation for design optimization, stability analysis, and hazard prevention of underground double-tunnel engineering.