The Line C from Project to Completion: Progress to Date

The Line C from Project to Completion: Progress to Date

The route of Line C of the Rome Metro, as initially conceived, aimed to connect the eastern quadrant of Rome, starting from the terminus of Pantano in the municipality of Monte Compatri, with the northwest quadrant (Clodio-Mazzini area), passing through the historic center. The original design of the route had the following objectives:

– Connect the areas at the northeastern edge of the city with those in the southwest.
– Increase the network effect with the two existing lines.
– Reduce surface vehicular traffic.
– Allow for the expansion of pedestrian zones in the central area.

Line C in Operation

The section of Line C that has been completed and is in operation today extends from the far eastern periphery to the San Giovanni station, the gateway to the historic center. It passes through the popular neighborhoods along Via Casilina before going underground at the Giardinetti station. From here, it serves the important neighborhoods of Alessandrino, Centocelle, and Pigneto. The center and the periphery become closer, bridging physical and social distances. The section currently under advanced construction, known as “Tratta T3,” starts from San Giovanni station, enters the historic center of Rome, and crosses an urban fabric characterized by unique archaeological and monumental pre-existing structures in the world, declared UNESCO World Heritage Sites.

Activities began in 2006 with initial archaeological investigations and the development of the final design. Currently, 22 stations and approximately 19 km of line are open to the public in the section between the Monte Compatri/Pantano station and the San Giovanni station. The latter, operational for passengers since May 12, 2018, is an important interchange node with the existing Line A. Line C is the first fully automated line built in Rome and one of the most technologically advanced subways in the world. In its current configuration, with the 13 trains delivered by Metro C ScpA to the operator, it can provide a train frequency of one every 7 minutes.

The construction of the Line C stations provided an opportunity to initiate a process of redevelopment for the squares where the stations are located and the surrounding areas. The new stations have ample spaces that can be used for various initiatives, turning these spaces from simple functional areas into real “places” in the city.

The first initiatives were carried out even before the start of operation, such as two concerts by the children’s choir from the Opera Theater. The first concert took place in the atrium of the Teano station, and the second at the San Giovanni station during its inauguration. Further initiatives took place, such as the one titled “Narrating Mothers,” which was held as part of the “Letterature Off” section of the Rome Literature Festival in June 2019. In San Giovanni, Pigneto, and Mirti stations, “spectacularized readings” were held, with mothers from different parts of the world reading fairy tales from their own cultural traditions. Starting from late June 2019 until early October, a series of free concerts were held at the Pigneto, Malatesta, Teano, Mirti, and Centocelle stations.

The construction of Line C also provided an opportunity for study and research, as evidenced by numerous discoveries made during archaeological excavations. It also offered a chance to improve the accessibility and utilization of Rome’s historical archaeological heritage. A comprehensive program of investigations was carried out through the collaboration between Metro C ScpA, the client Roma Metropolitane, and the Ministry of Cultural Heritage and Activities. This program was implemented by Metro C ScpA under the Operational Scientific Directorate of the Archaeological Superintendence of Rome. It not only led to the identification of numerous artifacts but also to the updating of archaeological maps in areas that had never been explored before.

The phases and execution methods of the works, their duration, and their temporal sequence were approved and shared within a technical committee that included the Mobility and Transport Department of the Municipality of Rome, ATAC, USTIF, the Lazio Region, and Roma Metropolitane. The work program is organized with time windows for early closure at 9:00 PM of the operating line and with some weekends of complete closure.

In order to minimize interference with the operating line, the usable part of the existing platform of Line B, which is 150 meters long, was reduced to 110 meters. This reduction allowed for the installation of a compartmentalization structure in the intervention area, physically separating the work areas from those affected by the service. The structure consists of a framework of metal beams and pillars onto which a corrugated metal sheet parallel to the vault is mounted. The area of the gallery’s piers was delimited with a system of wooden panels connected to the metal structure, leaving only a gate for access by construction workers directly from the platform. Only after the assembly of this structure was it possible to proceed with the subsequent phases, which involve cutting the vault and the piers to a width of about 8 meters and the construction of four piers founded on micropiles, on which the final crossing structure will be launched.

Once the cutting of the vault of the existing gallery was completed, the assembly of the crossing structure began. The first step was the launch of two longitudinal beams that represent the load-bearing framework of the structure, a launch that took place on the nights of April 22nd and 23rd. The prefabricated structures (predalles) are currently being installed, and the bottom slab is being completed. Steel bracing will then be positioned, the upper predalles will be launched, and the covering slab of the box will be cast. Only after that will the parts of the existing gallery be demolished to create access to the Colosseo station platform. The crossing will then be completed with the installation of lateral glass walls and interior finishes.

In the case of San Giovanni Station, the numerous findings have led to the decision to create a specific museum setup within the station. Meanwhile, the project currently awaiting approval for Amba Aradam/Ipponio Station includes the in situ enhancement of the archaeological complex found during the excavations. These interventions confirm how the construction of large urban infrastructures like Line C represents a tremendous opportunity for enriching historical and archaeological knowledge, as well as for the protection and promotion of new discoveries.

Line C under construction: San Giovanni – Fori Imperiali

The section known as T3 of Line C, currently under construction, covers a distance of approximately 2.8 km and includes 2 stations (Amba Aradam/Ipponio and Fori Imperiali) and 2 ventilation shafts (via Sannio and Piazza Celimontana). Construction work commenced on March 21, 2013. The T3 route starts from Piazzale Appio, where the line tunnels pass under San Giovanni station of Line A, entering the historic city center to reach the Fori Imperiali station. This route traverses an urban fabric characterized by unique archaeological and monumental remains. Starting from Piazzale Appio, the route runs parallel to the Aurelian Walls (the Amba Aradam/Ipponio station and the Multifunctional Shaft 3.3 are located in this initial section), then it crosses under the Aurelian Walls at Porta Metronia and continues toward the Celio hill. In Piazza Celimontana, a large-diameter ventilation shaft has been constructed, inside which a railway connection is established. In this section, the line tunnels reach the greatest depth ever reached in the context of Line C, penetrating approximately 15 meters into the Pliocene clay layer at an elevation of 55 meters above ground level with a hydraulic head, evaluated on the tunnel’s vault, exceeding 40 meters. Continuing along the route, you encounter the Fori Imperiali station, constructed beneath Via dei Fori Imperiali between the Basilica of Maxentius and the Colosseum square. The line tunnels follow the axis of Via dei Fori Imperiali, passing adjacent to the Forum of Caesar, crossing under the Cloaca Maxima, and skirting the Colonnades of the Forum of Nerva.

Tunneling with Mechanical Excavation (TBM) for the Tunnels

The tunnels are constructed using mechanical excavation with TBM (Tunnel Boring Machine) of the EPB (Earth Pressure Balance) type. These machines feature a 6.70 m diameter cutterhead, and the final tunnel lining consists of precast segments with a thickness of 30 cm.

In the external area of the construction site, the final lining with small bricks for the Muñoz Wall is underway. This work is being carried out by a specialized restoration company, following a study and sampling of suitable lining types in collaboration with the Superintendent. In the Clivo di Venere area, where the construction site is more extensive, the installation of the injection system has been completed, and consolidation work from the TBM tunnel has commenced, preparing for the widening of the platform tunnel on the odd-numbered track. Regarding the Line C station structure (Clivo di Venere side of the construction site), the roof slabs for the atrium and the first technical level have been completed, and excavation work is currently ongoing between the first technical level and the mezzanine slab. Activities related to station linings between the atrium and the first technical level are also in progress.

Particular attention is given to the third construction macro-area (Colosseo Shaft), which concerns the connection between the Fori Imperiali station and the existing Line B Colosseo station. The overpass structure described earlier terminates in a shaft located at the base of the Colosseum, providing access to the platform in the direction of Termini. The shaft was excavated using a double row of micropiles and a system of metal struts that allowed for the excavation in an archaeological manner. Currently, the excavation activities are complete, and the construction of the base slab of the structure is in progress, followed by the linings and the roof slab. The section of the structure between the Fori Imperiali station and the existing Line B tunnel is under construction. Among the completed parts are the roof slab and the base slab, except for the section closest to Line B, and part of the perimeter linings have been installed.

Tunnels: Traditional Excavation from San Giovanni Station to Sannio Shaft 3.3

In this section, spanning approximately 150 meters, the tunnels were constructed using a blind-hole excavation method for both tracks, carried out with the use of a shielded cutterhead with a diameter of 3000 mm (micro-TBM). The use of this excavation method was necessary for several reasons:

  • The TBM machines used for excavating all the Line C tunnels were unable to pass under the existing San Giovanni Station of Metro A.
  • It was impossible to carry out top-down consolidations due to the presence of archaeological layers.

Currently, the following activities are ongoing:

  • Excavation of the natural tunnel for the odd-numbered track on the San Giovanni side.
  • Preliminary work for the construction of the final lining for the even-numbered track tunnel.

In the near future, activities will commence to open the connecting passage between the odd-numbered track tunnel of the operational section and the one under construction. Additionally, the construction of the slab for the installation of railway tracks will begin.

Sannio Shaft 3.3

The multifunctional Shaft 3.3 is located between the Amba Aradam/Ipponio and San Giovanni stations, adjacent to a garden near the Via Sannio market on the Piazzale Appio side. This is the shaft from which the TBMs began excavating the tunnels towards the Fori Imperiali.

Currently, activities are underway to complete the bottom slab and the construction of perimeter linings and slabs for the three levels under the cover. Soon, work will proceed with the finishing of the technical floors for the plant and technological rooms, the construction of the slab for the track installation, and the construction of the metal platform.

Amba Aradam/Ipponio Station

It extends for approximately 120 meters in length and over 30 meters in depth and consists of 5 levels, including the roof and foundation. The urban context in which it is located, along with the limited dimensions of the construction site, dictated the choice of the Top-Down method as the excavation methodology for the station. This method involves excavation under the roof, creating intermediate floors as excavation progresses, and utilizing these structural elements as intermediate bracing for the perimeter diaphragm walls already during the excavation phase. Functionally, the station follows the typological pattern of Line C stations, with a central platform that extends for 110 meters in length and approximately 4 meters in width.

Important ancient structures were discovered at this site during the second-phase archaeological excavations, which began once the perimeter walls were constructed. The archaeological investigations at Amba Aradam/Ipponio Station of Line C covered an area of approximately 1753 square meters and led to discoveries of exceptional interest. As a result, the Archaeological Superintendence, in order to safeguard and enhance the findings, prescribed the redefinition of the architectural-functional project to relocate the ancient structures within the station in the same position and orientation, contextualize the discovered artifacts, and restore the visual relationship with the Aurelian Walls.

Following this prescription, Metro C ScpA requested three well-known architectural firms to develop concepts for the redefinition of the architectural-functional project. Based on the one chosen by the Archaeological Superintendence, the final project was developed and delivered to the client Roma Metropolitane in August 2018 and is currently awaiting approval.

After the approval of the aforementioned final project, it will be necessary to develop the executive and construction design, which must be submitted for approval by the client. Subsequently, construction work can resume. Currently, the station construction site is used for logistical support for all TBM excavation activities (introduction of segments, excavation material extraction, etc).

Celimontana Shaft 3.2

The shaft is located in a garden adjacent to Piazza Celimontana and has a circular plan with a diameter of 34.80 meters. The iron floor is at an elevation of -15.50 meters above sea level, resulting in a significant depth of excavation of about 59 meters from ground level.

The construction of the shaft, up to the levels involved in archaeological investigations (+19.00 meters above sea level), was carried out using archaeological excavation methods. During the archaeological excavation phases, the presence of reinforced concrete diaphragm walls allowed safe descent to otherwise unreachable depths. At a depth of approximately 17 meters from the current ground level, a Republican-era aqueduct was discovered, made of squared tuff blocks and connected to a large basin dating back to the 3rd century BC. Additionally, a burial site with accompanying items dating from the late 10th century to the early 9th century BC was found. Currently, the internal structures from level 5 (-45 meters from ground level) to level 1 (-8 meters from ground level) have been completed, as well as the lift structures and the forms for the level 1 floor. The construction of the technical level 1 floor, using prefabricated elements, is in progress. Excavation work will resume shortly, starting from an elevation of -45 meters from ground level.

Tunnels: Traditional Excavation from Stazione San Giovanni to Pozzo 3.3 Sannio

In this section of approximately 150 meters, due to constraints related to the profile of the track, the tunnels have been constructed using blind hole excavation for both tracks, performed with the use of a shielded cutterhead with a diameter of 3000 mm (micro-TBM). The use of this excavation method became necessary for several reasons:

  • The existing Stazione San Giovanni of Metro A could not be passed under by the TBM machines used for excavating all the tunnels of Line C.
  • Consolidation from above was not possible due to the presence of archaeological layers.

Currently, the following activities are underway:

  • Excavation of the natural tunnel for the odd-numbered track on the San Giovanni side.
  • Preliminary work for the construction of the final lining for the even-numbered track tunnel.

Activities will soon commence to open the connection gap of the odd-numbered track tunnel between the operational section and the one under construction, as well as the construction of the slab for laying the railway tracks.

Pozzo 3.3. Sannio

Multifunctional Shaft 3.3 is located between the Amba Aradam/Ipponio and San Giovanni stations, adjacent to a garden near Via Sannio, on the Piazzale Appio side. This is the shaft from which the TBMs began tunneling towards Fori Imperiali.

Currently, activities are ongoing for the completion of the bottom slab and the construction of perimeter linings and slabs for the 3 levels under the roof. Soon, work will proceed with finishing the technical floors designated for plant and technological rooms, the construction of the slab for laying the tracks, and the construction of the metal platform.

Currently, the following activities related to the station structure are underway:

  • Relocation of archaeological artifacts, as prescribed by the P.A.C. (Parco Archeologico Colosseo), aimed at safeguarding the structures.
  • Excavation beneath the roof between the atrium level and the first technical level.
  • Construction of the first technical level slab.

For the construction of the pedestrian connection between Fori Imperiali Station and Colosseo Station Line B, the relocation of systems and equipment has been carried out, as a prerequisite for the installation of a metal framework structure designed to contain the roof in the section where the future pedestrian underpass will be constructed. Currently, the following activities are ongoing:

  • Archaeological excavation of Pozzo Colosseo, which contains the connection to Line B.
  • Construction of the pedestrian connection tunnel.

Monitoring of Monuments and Historic Buildings and Intervention Safeguards

Along its route, Line C interacts with historic buildings and monuments of great value, from the Colosseum to Palazzo della Cancelleria and Palazzo Venezia. To ensure the preservation of a world-unique heritage protected by UNESCO, Metro C ScpA has conducted a series of preventive activities to accurately and reliably assess the state of historic buildings and monuments. The analyses of the interaction between the subway line and monuments have involved 13 monuments and 40 historic buildings, including those located in the Baroque bend of the Tiber that overlook Corso Vittorio Emanuele. The studies have been developed from the survey and investigation phase, leading to the definition of specific monitoring plans and safeguarding interventions for each monument, developed in collaboration with the Ministry for Cultural Heritage and Activities.

The safeguarding interventions can essentially be categorized into two main groups:

  • Provisional or definitive interventions to be carried out before the start of excavation activities: These are structural consolidation interventions aimed at addressing pre-existing issues or significant states of deterioration, not directly related to the effects induced by the construction of Line C. Examples include the definitive structural consolidation interventions for the Basilica of Maxentius or the Church of Santo Stefano Rotondo, as well as provisional interventions for the Columns of the Forum of Nerva.
  • Interventions to be implemented during the excavation phase, aimed at real-time mitigation of induced settlements, keeping them below predetermined thresholds: These are geotechnical interventions, such as Compensation Grouting, planned during the passage of the subway tunnels beneath the Aurelian Walls at Porta Metronia and the existing Colosseo Station of Line B.

Based on the results of the analyses carried out in the context of the T3 section, a series of structural and/or geotechnical safeguarding interventions, both provisional and definitive, have been implemented for the following monuments:

  • Aurelian Walls at Porta Asinaria: Temporary shoring of the walls, construction of a pile wall to safeguard Porta Asinaria, and geotechnical compensation grouting during the passage of the TBM.
  • Aurelian Walls at Porta Metronia: Temporary shoring of the walls and geotechnical compensation grouting during the passage of the TBM.
  • Church of Santa Maria in Domnica: Temporary shoring both internally and externally, as well as preservation interventions for the artistic heritage inside the church.
  • Church of Santo Stefano Rotondo: Drum encirclement and preservation interventions for the artistic heritage inside the church.
  • Celimontano Aqueduct Pillar: Temporary shoring.
  • Basilica of Maxentius: Temporary shoring of the external walls and definitive reinforcement interventions using cables and bars.
  • Columns of the Forum of Nerva: Temporary shoring.

All interventions, both definitive and provisional, have been completed. Furthermore, continuous monitoring of all monuments within the subsidence basin of Line C construction works is carried out using extensive vibrational, structural, geomatic, and geotechnical monitoring instrumentation.