The Line C: From Its Origins to the International Tender for Awarding to the General Contractor
In the early 1990s, the City of Rome initiated a feasibility study to implement a third metropolitan subway line for the capital city. The objectives of the project included reducing private traffic, expanding pedestrian zones in the central archaeological area, and fully enhancing the historical and monumental heritage of the capital. Therefore, the assignment to carry out the preliminary design was given to STA, a company that was “in-house” with the City itself. The preliminary design of Line C was funded by Law No. 211/1992, “Interventions in the field of rapid mass transportation systems.” In 1995, with Resolution No. 351 of December 4, the City Council approved the overall project for the Pantano – Vigna Clara route (divided into two fundamental sections, “Pantano – Giglioli” and “Giglioli – Vigna Clara”) and requested government funding; however, these funds were only made available starting in 1997, well beyond the deadline to complete the project by the Jubilee of 2000.
Between 1995 and 2000, following further project developments by STA, the overall route was modified to include a branch line to Tor Vergata and the construction of a new railway depot near the Graniti station. The resulting route was also divided into additional sub-sections: Tract T3 from San Giovanni to Venezia, Tract T6 from Torrenova to Alessandrino, and Tract T7 from Torrenova to Pantano. In 2001, CIPE, with Resolution No. 121/2001, included Line C among the priority works of national interest, incorporating it into the 1st Program of Strategic Infrastructure as per Law No. 443/2001, also known as the “Objective Law.” An Operational Agreement was signed between the three funding entities (Ministry of Transport, Lazio Region, and City of Rome). On June 17, 2002, the Preliminary Project of the entire Line C, which involved over 90 entities, including Municipal Offices, Authorities, and private companies, was approved by the City Council with Resolution No. 67.
The Line C: From its Origins to the International Tender for General Contractor Assignment
In the early 1990s, the Municipality of Rome developed a pre-feasibility study to initiate the implementation of local public transportation, resulting in the planning of a third metropolitan subway line for the city. The project’s objectives included reducing private traffic and expanding pedestrian areas in the central archaeological zone, as well as fully enhancing Rome’s historical and monumental heritage. The Municipality assigned the task of developing the preliminary design to STA, a company that was an in-house entity of the Municipality itself. Funding for the preliminary design of Line C was provided through Law No. 211/1992, “Interventions in the Rapid Mass Transit Sector.”
In 1995, with Resolution No. 351 of December 4th, the City Council approved the preliminary project for the Pantano – Vigna Clara route (divided into two fundamental sections: “Pantano – Giglioli” and “Giglioli – Vigna Clara”) and requested funding from the government. However, the funds were only made available starting in 1997, well past the deadline to complete the project in time for the Jubilee of 2000.
Between 1995 and 2000, following further project developments by STA, the preliminary route was modified to include a branch to Tor Vergata and the construction of a new railway depot near the Graniti station. The resulting route was further divided into additional subsections: Tranche T3, from San Giovanni to Venezia; Tranche T6, from Torrenova to Alessandrino; and Tranche T7, from Torrenova to Pantano. In 2001, with Resolution No. 121/2001, the Interministerial Committee for Economic Planning (CIPE) included Line C among the priority works of national interest, incorporating it into the first Program of Strategic Infrastructure, as provided by Law No. 443/2001, the “Objective Law.” An Agreement of Procedure was signed among the three funding entities (the Ministry of Transport, the Lazio Region, and the Municipality of Rome).
On June 17, 2002, the City Council approved the Preliminary Project for the entire Line C, and the Conference of Services involved over 90 entities, including Municipal Offices, Institutions, and private companies.
On February 15, 2005, the tender for the assignment to the General Contractor was finally published.
The tender was awarded on February 28, 2006, to the Temporary Association of Companies formed by Astaldi S.p.A. – Vianini Lavori S.p.A. – Consorzio Cooperative Costruzioni – Ansaldo Trasporti Sistemi Ferroviari S.p.A. As stipulated by the tender, these same companies subsequently established the Metro C S.c.p.A. Project Company on April 3.
In the spring of 2006, the first campaign of supplementary archaeological investigations was initiated in preparation for the development of the definitive designs for sections T2, T3, T6A, and T7, as well as the executive designs for sections T4 and T5. In the spring of 2007, the first areas for the construction of works for sections T4 and T5 were delivered.
Section T2
Regarding section T2, from Venezia (exclusive) to Clodio/Mazzini (inclusive), the contract signed stipulates that the General Contractor shall:
- Provide the Definitive and Executive Design, execution, and Works Management of the archaeological investigations and excavations necessary for the preparation of the definitive project;
- Provide the Definitive Design for compensatory and integrative works;
- Provide the Definitive Design;
- Provide the Executive Design, construction, and Works Management of the section and integrative and compensatory works;
- Supply the rolling stock necessary for the line’s commissioning.
The contract bound the execution of the services mentioned in points four and five above to the approval by CIPE of the Definitive Project and the subsequent acquisition of the corresponding funding.
Archaeological Investigations Leading to the Definitive Design
During the preparation of the Preliminary Project, section T2 underwent various and in-depth archaeological investigations conducted by Roma Metropolitane initially and later by Metro C. The campaign of investigations initiated by Metro C from 2006 to 2010, under the scientific direction of the Soprintendenza for Archaeological Heritage of Rome, complied with the prescriptions formulated by the latter regarding the Preliminary Project for the entire route in 2003. In particular, it was prescribed: “…. all areas of interference with archaeological stratigraphy (technical rooms of stations, exits, ventilation shafts, processing shafts, etc.) must be fully excavated according to the agreed technical methods, from time to time, with the Soprintendenza.” The note also provides instructions on the operative methods for the investigations to be carried out, recommending that “excavations be carried out with caution, using small mechanical means, under the constant supervision of archaeologists provided by the entity performing the work.”
In 2009, in order to deepen the knowledge of the archaeological sub-stratum, a campaign of in-situ geognostic investigations was carried out using core drilling with core recovery and archaeological reading, as well as a campaign of geo-archaeological investigations. Overall, preventive investigations were carried out at 12 archaeological sites:
- Site no. S01 in Viale Giuseppe Mazzini;
- Site no. S02 in Viale Angelico – Viale delle Milizie;
- Site no. S03 in Via Barletta;
- Site no. S04 in Piazza Pasquale Paoli;
- Site no. S05 in Piazza della Chiesa Nuova;
- Site no. S07 in Piazza Sant’Andrea della Valle;
- Site no. S9 in Via Cesare Battisti;
- Site no. S9 bis in Largo Santi Apostoli;
- Site no. S21 in Via Sforza Cesarini;
- Site no. S22 in Via Sora;
- Site no. S25 in Piazza Risorgimento;
- Largo Giovanni XXIII.
The Archaeological Superintendent of Rome did not authorize the implementation of preventive archaeological investigations in the area where the Argentina Station was planned, and as a result, this station was eliminated from Section T2. As part of the contract, a Commissioner Delegate was appointed by the Presidency of the Council of Ministers to oversee the continuation and completion of the new metro lines in Rome and Naples. This commissioner promptly established a multidisciplinary technical committee responsible for evaluating, based on the results of the archaeological campaigns conducted, the feasibility of the central section stations. The aforementioned technical committee authorized the construction of the stations by signing a handbook of archaeological excavations, which was endorsed by the Commissioner, the Director General for Antiquities, and the Superintendent of Archaeological Heritage of Rome. The guidelines outlined in this handbook must be incorporated into the Definitive and Executive Project and serve as the basis for the construction activities of these stations.
The Study of Line-Monument Interaction
Along its route, Line C interacts with historic buildings and monuments of immeasurable value. Therefore, Roma Metropolitane tasked the General Contractor with preparing a study on the interaction of Sections T2 and T3 with the monumental heritage and historic buildings for the preparation of the Definitive Project. Given the significance of the heritage intersected by the Line, a multidisciplinary Technical-Scientific Committee (TSC) was established, consisting of a group of university professors with expertise in various disciplines: Conservation and Restoration, Structural Engineering, Gallery Construction Techniques, Geotechnical Engineering, and Geology.
Construction Technologies
Both containment structures are excavated using the hydrofraise. This technological choice is related to various factors:
- the need to create milled joints between the diaphragms, ensuring adequate hydraulic sealing, especially in relation to pressures reaching 4 bars at the bottom of the excavation;
- the need to create a circular crown with interlocking panels to ensure adequate transfer of compression forces in a circumferential direction, resulting from radial pressures exerted by the soil and groundwater on the external walls of the structure;
- the need to limit deviations from the vertical of the panels, given the significant depth of the diaphragms; excessive panel deviations from the vertical would reduce the contact area between the diaphragms, leading to increased transfer stresses at the joints between the diaphragms.
The choice to construct the shaft in a “bottom-up” manner, combined with the need to cover significant spans with horizontal structures and the impossibility of erecting intermediate supports for the floors (due to interference with the switchgear park at the platform level), has led to the extensive use of prefabricated structures, which are as self-supporting as possible during assembly and casting of the floors.
This choice offers clear advantages, especially in terms of execution speed.
The studies conducted have analyzed the interaction between tunnel excavation and existing buildings, taking into account their state of conservation, the geotechnical conditions of the subsoil, and the excavation method used. They have allowed for the preparation of a building monitoring scheme, identifying monuments and historic buildings that require safeguarding measures, preferably of a temporary and reversible nature.
The Final Design
The project for Route T2, which formed the basis of the tender, involved a route of approximately 4 km, from Piazza Venezia to Piazzale Clodio/Piazza Mazzini, with 6 stations: Argentina, Chiesa Nuova, San Pietro, Risorgimento, Ottaviano, Clodio/Mazzini. The Final Design of Route T2 was developed by Metro C based on the Preliminary Project approved by CIPE in 2003 and in compliance with the prescriptions of the guidelines approved by the Extraordinary Commissioner in agreement with the Ministry for Cultural Heritage and Activities.
The design choices made benefited from the experience gained in the construction of the more external routes that were already in progress at the time. In particular, the main modifications compared to the Preliminary Project for the tender were as follows:
- reduction in the diameter of the line tunnels;
- consequent change in the type of construction of station structures;
- revision of the planimetric and altimetric layout of the 2 line tunnels;
- new technological choices for the construction of the work.
Going into more detail, regarding the Venice – San Pietro sub-section, the route was modified due to the following factors:
- State of conservation of buildings of particular artistic value: It became necessary to move the planimetric-altimetric route to minimize subsidence induced by the excavation of the line tunnels, shafts, and stations.
- Location of the Chiesa Nuova station: This necessitated the redefinition of the alignments required for the platform tunnels.
- Location of the inter-section shafts: They were relocated to Piazza San Pantaleo and Largo Tassoni, areas with lower archaeological risk and less impact on city traffic.
Regarding the San Pietro – Clodio/Mazzini sub-section, the main modifications consisted of:
- Eastward shift of the tunnel galleries exiting from the San Pietro station: This made it necessary, given the new position of the station, to eliminate the Risorgimento station.
- Consolidation of the 4 inter-section shafts into a single structure located on Via Properzio.
- Functional optimization of the Ottaviano station structure: The achieved optimization allows for the construction of a single common atrium for both stations, avoiding the need for a pedestrian tunnel connection between the two stations.
- Location of the San Pietro station: It was necessary to reposition it adjacent to Castel Sant’Angelo, on the opposite bank of the Tiber River, due to discoveries made during preventive archaeological excavations and the challenges of managing the traffic disruptions resulting from the construction site openings on Lungotevere (the Tiber River waterfront).
With reference to the diameter of the underground line tunnels, it should be noted that the preliminary project for the T2 and T3 sections, which served as the basis for the tender, originally envisaged the construction of tunnels with a diameter of 10.10 meters. Metro C, based on the design constraints set by the Archaeological Superintendence following the archaeological investigations and the results of numerical modeling carried out to assess interaction with the historical and monumental heritage, proposed to reduce the tunnel diameter from 10.10 meters to 6.70 meters. Below are the key reasons for this design choice.
The Preliminary Project included stations located in contexts where it was impossible to excavate entirely in open air. The section of the tunnel excavated with a Tunnel Boring Machine (TBM) of 6.70 meters in diameter did not allow both the train and the platform to fit inside the tunnel. However, using a TBM with a larger diameter effectively eliminated the need to carry out traditional cut-and-cover tunneling for each station, especially in complex hydrogeological contexts and interactions with the historical and monumental heritage. Following the constraints imposed by the Archaeological Superintendence at the end of the initial archaeological investigations, which required archaeological excavation methods up to approximately 15-20 meters below ground level and prohibited the use of any ground consolidation and waterproofing techniques in the absence of preventive archaeological excavation, the stations had to be relocated to larger contexts and transformed into the “box” typology. This typology allowed open-air excavation, incorporating the platforms directly into the structure, without the need for traditional tunneling. Once this constraint was overcome, it became preferable to use smaller-diameter tunnels, with clear benefits in terms of subsidence that tunnel excavation could induce on the historical and monumental heritage. On March 11, 2010, Roma Metropolitane ordered the suspension of the design activities for the T2 section, also considering the absence of “higher determinations by the Municipal Administration.”
The Venezia Station of the T3 Section
In 2009, Metro C delivered the Final Project for the T3 section to Roma Metropolitane, and in 2010, the CIPE approved funding for its construction. In 2011, Metro C delivered the Executive Project, which was finally approved in February 2013. The first construction sites for the T3 section opened in March 2013. In October of the same year, Roma Metropolitane requested the development of a Final Project for the Venezia station alone, as the terminal station of Line C. The Final Project developed by Metro C was delivered in April 2014. Also in 2014, in November, Roma Metropolitane requested that Metro C prepare a new Final Project for the Venezia station, considering its configuration as a passing station within the functional section Ottaviano – Colosseo/Fori Imperiali, and therefore no longer as a terminal station. This request aimed to extend Line C beyond Piazza Venezia through the construction of the T2 Section. This new project was delivered to Roma Metropolitane in December 2015.
