Rome Metro C Line is the longest urban underground railway line in Italy and it is the first metro line in Rome to stretch beyond the Great Ring Road, thus bridging the gap between the farthest suburbs and the Historical Centre. It is an original project, carried out mostly underground at a depth of 25/30 metres.
The main track put out to tender envisaged realization of a 25,6 km long line with 30 stations (10 of which resulting from the restyling of existing stations and 20 new underground stations).
Some important archaeological remains, brought to light during construction of the New San Giovanni Station, made it necessary to change the original project; the station was built at a depth of more than 30 metres and 2 traditional tunnels were excavated beneath Line “A”’s existing station.
Consolidation and impermeabilization of both excavated tunnels was achieved via the Artificial Ground Freezing Process, in order to ensure the greatest possible safety degree as far as both workers and existing surface structures were concerned.
The Underpass Project of San Giovanni Station - Line A presented many technical challenges related to restrictions imposed by the existing structures; in particular, due to the presence of line A’s foundation piles, the distance between each freezing pipe needed to be greater than 3 meters and a half. The complex stratigraphic and hydraulic conditions at the jobsite must be considered as well.