Improving geological models of projects by risk management: the Ponserand tunnel

The tunnel project of Ponserand (Aigueblanche, Savoie, France) includes several variants. The longer ones go across the mountain with good geological conditions whereas the latter one goes between the national road RN90 and the existing tunnel. The latter variant cuts across scree slopes that represent unfavorable geological conditions. Thus costs of the longer variants are better estimated than the ones for the shorter alignment alternative. In order to choose the right variant, a risk management has been performed leading to the characterization of specific geological investigations. Based on these investigations, the first uncertain geological model has been modified in order to get a more reliable one. The updated cost projections of the project leads to lower cost that eventually shows that the shorter variant is a better solution. Based on a real example, this article highlights the interest of using risk management to improve the geological model.