The work and the technique: Rome Metro Line C, Italy
The Line C project, awarded to the Metro C S.c.p.A. consortium of which Webuild Group is the lead company, posed a considerable engineering challenge given the unique nature of the area involved, a UNESCO World Heritage Site, the innovative construction technologies used, and the monitoring of the historical assets and monuments on the surface and along the underground route. Line C doubles the current length of Rome's metro system, connecting the city from the south-east to the north-west, linking the suburbs to the center and creating a significant “network effect” thanks to the intersections with Rome’s other metro lines.
The line starts from the municipality of Monte Compatri and follows part of the pre-existing Termini Pantano overground railway route. Just before the Grande Raccordo Anulare motorway ring road, it enters a tunnel and continues towards the city center, crossing it completely.
The project is being executed in functional sections. The section from the terminus to San Giovanni (19 km with 22 stations and a workshop depot) has been completed and is already operational. The next stations to be connected will be Porta Metronia, Colosseo - Fori Imperiali and Venezia. Planning for the final stations, Chiesa Nuova, San Pietro, Ottaviano and Clodio/Mazzini, is underway. The project also includes 4 interchange stations: San Giovanni and Ottaviano (with the A line), Colosseo (with the B line) and Pigneto (with the local FL1/FL3 railways).
The studies on the interaction between the metro line and Rome’s historical monuments, and the techniques to be employed for their protection took about four years, and covered 13 sites and 40 historic buildings. A specific monitoring system, implemented on an SDD platform, was developed ad hoc for the project.
The tunnels were excavated mainly with four EPB (Earth Pressure Balance) TBMs, chiefly in soft or medium/soft terrain with a high clay content. To ensure safe working conditions in the tunnels below the existing San Giovanni Line A station, use was made of the artificial ground freezing method, a waterproofing and/or consolidation technique employed for underground excavation work in loose terrain or fractured rock.