ABSTRACT
The paper presents the methodology and results from the construction design analysis of the Route des Nations 491m tunnel in Geneva, Switzerland. This high visibility 12m diameter urban tunnel, is excavated using conventional methods under 6.5 to 18m cover, within heterogeneous glacial till containing multiple confined aquifers, requiring cautious predictions of settlements. The method consists in excavating adits, header and subsequently, bench and invert. Soil reinforcement is ensured by a pipe umbrella and face bolting. The complexity and stakes involved implies the use of a 3D numerical model, to calibrate the 2D models, and to extrapolate the short-term trough settlement predictions as a function of the tunnel excavation face advancement. The paper evaluates the influence of the adits being excavated with differing productivity. It investigates the Peila approach to face bolting, and assesses its impact on settlement predictions. Finally, implementation of the determined thresholds in the monitoring procedure is discussed.
