The EOLE (Est-Ouest Liaison Express) project consist in the extension of the RER (Réseau Express Régionale) Line E from the current terminus station of Haussmann Saint-Lazare in Paris to Mantes-la-Jolie in the west of Ile-de-France. The project involves the construction of a series of underground structures in a particularly densely built area with underground buildings and infrastructures in the 8th arrondissement of Paris. The underground works include the interconnection to the west of the Haussmann Saint-Lazare station, a tunnel excavated by TBM, and other tunnels to the east and west of the Gare de la Défense, located under the CNIT (Centre des Nouvelles industries et technologies). Lombardi has been entrusted with the final design of the interconnection of the HSL Station with the new line on behalf of the Engineering Joint Venture Alliance, consisting of the construction companies NGE Génie Civil, Guintoli, Demathieu Bard, Pizzarotti, Franki Foundations Belgium and Atlas Fondations. The construction of the interconnection consists of three main elements. The interconnection itself consists of a series of caverns about 10 m high and between 13 and 20 m wide, extending over 170 m from west to east. A vertical shaft is provided for access to the interconnection area during construction and for rescue operations during operation. The connection between the shaft and the caverns is constructed by access tunnels in a Y-shape. The complex of these new underground structures is located close to several existing metro lines (L3, L13 and L14). Moreover, the surface above the excavation area is built on, with the presence of historic buildings. Limiting the excavation-induced settlement on the surrounding structures was the most stringent design requirement to be met. The calculation of the interference between the excavations and the existing structures was carried out using three-dimensional numerical modeling.