Numerical Analysis of Tunnel Displacement Profiles with Pipe Umbrella Support: Parametric Study of Selected Umbrella Parameters

Ensuring the stability of tunnels excavated in weak rock masses poses significant engineering challenges, particularly in controlling deformations of the excavated rock-mass. This research represents a conceptual analysis aimed at exploring the effectiveness of pipe umbrella support systems across various configurations, without being tied to a specific tunnel project. The study also investigates the possibility of using simplified Finite Element Method (FEM) modelling for such purpose. Specifically, analysis focuses on findin the correlation between selected design parameters and support system performance. A numerical model incorporating the Hoek-Brown failure criterion, was employed to simulate the interaction between the pipe umbrella and surrounding rock mass. Key parameters analyzed include the length of the pipe umbrella segments, overlap between segments, and the stiffness of the pipe umbrella material. The results demonstrate the potential in reducing both radial and axial displacements as the segment length of the pipe umbrella and overlap increase, with diminishing returns observed for higher umbrella’s stiffness values. This study despite being based on theoretical case scenario also highlights the practical advantages of a simplified axisymmetric FEM model for conducting parametric analyses, significantly reducing computational complexity while maintaining sufficient accuracy.