ABSTRACT
This paper deals with the construction of two tunnels connecting the existing Municipio Station Line 6 main shaft (interchange node between Metro Line 6 and Metro Line 1 extension project in Naples, Italy) to the TBM extraction shaft located nearly 40 m far from it. The two short tunnels, whose construction in sequence was completed at the beginning of 2018, underpass archaeological findings consisting in fortification walls built in the sixteenth century, through a subsoil composed by loose silty sand overlying a soft and sometimes fractured rock. The groundwater table is close to the ground surface. The excavation phases have been carried out adopting a mix of different ground improvement technologies as cement and chemical grouting at the sides and inverts in tuff and Artificial Ground Freezing at the crowns in the sandy layer. To preserve a unique archaeological site, part of the cultural heritage in the city of Naples, compensation grouting technique was also introduced at the design stage to partially compensate predicted subsidence. In this work, monitored displacements have been back-analysed with a FEM 2D numerical model. The focus of the back-analysis is a better understanding of the effects of volume changes due to AGF adoption on the above historic walls foundations. This experience and the obtained knowledge are a contribution to a better implementation of the technique for future similar projects.
