ABSTRACT
Egis and its partners are designing the eastern section of Line 15, which is one of the four new metro lines that will help develop the outer Parisian suburbs. This 23 km long underground section includes 11 stations, 21 technical shafts, two turnout structures and a service tunnel leading to the maintenance centre of the line. This article presents the challenges of the track alignment and how the designer has produced the optimum solution. Firstly, it describes the predetermined design constraints: the station locations, the operational requirements (maximum speed, user comfort), etc. It then focuses on the interactions between the tunnelling, its underground environment and the surface environment: the geological context with soft ground layers including risks of voids, sensitive buildings, other high capacity transportation infrastructure and the crossing of the Marne River. These have led to a deep, sinuous alignment with some structures over 30 m below ground level.
