The Naples metro Line 1: the service tunnel at Toledo station

Abstract This paper is concerned with the analysis of a 13 m wide, 17 m high and 40 m long service tunnel execution at Toledo Station within the Metro Line 1 extension project in Naples (Italy). From the terminal of Dante Station, the new stretch of the underground is composed of five new stations and two twin rail tunnels with a length of 5 km. Four stations out of five have the access shaft centered with the twin rail tunnels. On the contrary, Toledo Station, situated in the deeply urbanized historical centre of the city, has the shaft located laterally and a large size service tunnel connects it to the rail and pedestrian access tunnels, starting from the access shaft. The subsoil concerned can be divided schematically into two main layers: a top loose silty sand overlying the soft and sometimes fractured Neapolitan Yellow Tuff, with a hydrostatic head of 27 m above the tunnel invert. In this work, a more refined and thorough back analysis of the full construction process of the service tunnel was implemented starting from the drift construction and passing through the freezing process of the soil with the pore water, the excavation with the soil removal and the final thawing step. To this purpose a 3D model was built into the general purpose DFM software package named Flac3D