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<p>The intersection angle between the tunnel axis and the strike of rock mass exerts a profound influence on the stability of the surrounding rock, especially when tunneling through steeply dipping layered rock masses. This study investigates the stability of spillway tunnels at the GS Hydropower Project, which intersect steeply dipping layered rock masses at unfavorable small angles. To examine the influence of different intersection angles on tunnel stability, we developed four numerical models based on field investigation data to explore the effects of alignment at parallel (0°), small (25°), large (70°), and perpendicular (90°) angles to the strike of the rock mass. Simulation results indicate that the small intersection angle (25°) yielded the greatest deformations and the poorest stability. Quantitative analysis reveals that the horizontal displacements and plastic zone depths at small intersection angles are approximately 3 times those at large angles. Similarly, parallel alignments also demonstrate relatively poor surrounding rock stability. Consequently, it is recommended to avoid parallel alignment or small-angle intersections with layered rock masses during tunnel design and construction whenever possible. When such alignments are unavoidable, rigid support measures, particularly heavy steel sets combined with consolidation grouting, are recommended to mitigate potential large deformations and ensure structural stability.</p>

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Deformation Risks of Tunnels with Small Intersection Angles in Layered Strata: Numerical Analysis and Field Evidence from a Hydropower Project

  • 期刊论文

  • 发表日期：

    2026年1月21日

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  • Ming Li,
  • Hui Deng,
  • Hanhan Liu,
  • Wei Cheng,
  • Junyao Luo

摘要

The intersection angle between the tunnel axis and the strike of rock mass exerts a profound influence on the stability of the surrounding rock, especially when tunneling through steeply dipping layered rock masses. This study investigates the stability of spillway tunnels at the GS Hydropower Project, which intersect steeply dipping layered rock masses at unfavorable small angles. To examine the influence of different intersection angles on tunnel stability, we developed four numerical models based on field investigation data to explore the effects of alignment at parallel (0°), small (25°), large (70°), and perpendicular (90°) angles to the strike of the rock mass. Simulation results indicate that the small intersection angle (25°) yielded the greatest deformations and the poorest stability. Quantitative analysis reveals that the horizontal displacements and plastic zone depths at small intersection angles are approximately 3 times those at large angles. Similarly, parallel alignments also demonstrate relatively poor surrounding rock stability. Consequently, it is recommended to avoid parallel alignment or small-angle intersections with layered rock masses during tunnel design and construction whenever possible. When such alignments are unavoidable, rigid support measures, particularly heavy steel sets combined with consolidation grouting, are recommended to mitigate potential large deformations and ensure structural stability.