Excavation of a tunnel with conventional method in urbanized context – A case study from Line 15 South of Grand Paris Express

As part of the Grand Paris Express project, the work package of Metro Line 15 South Lot T2C is situated near Villiers Sur Marne in the south‐eastern outskirts of Paris. It consists in two mechanized tunnels, principal as well as maintenance and storage site lines, respectively 4.7 and 2.2 km long, connected by a shaft approximately 180 m long (O807), 92 m of which is characterized by a traditional tunnel. This article presents the study carried out for the detailed design of the conventional tunnel which is excavated in the Calcaire de Champigny formation, a succession of layers with typical characteristics of a heavily fractured rock mass alternates with marly others, sometimes showing dissolution phenomena due to the presence of gypsum. Due to the urbanized context and the workface planning, a particular construction stage was also foreseen: the lower part of the section has been excavated by tunnel boring machine when the upper was finalized. The discussion is completed with the results of the monitoring activity, designed to check the correct behavior during and after the excavation process.