Tunnel lining design in multi-layered grounds

Multi-layered grounds are usually encountered during tunnel excavations. However, tunnel design methods often adopted the homogeneous ground assumption for the sake of simplicity. This paper focuses on improving the performance of the Hyperstatic Reaction Method (HRM), which is part of the numerical method category, in the case of multi-layered grounds. A special attention is paid to the change of the weaker ground layer's position over the cross-section of the tunnel and of the ground layer's thickness. The numerical HRM model was validated based on a comparison with monitoring data from a real site and with those of finite element (FEM) models for different cases of multi-layered grounds. The results indicated that a reduction of the upward pressure applied on the lower half of the tunnel for the HRM model needs to be considered. Using the HRM model, a parametric study was conducted to highlight the significant dependency of the tunnel lining to the position and the thickness of the weaker ground layer.