Metro C participated in the Conference with a total of 7 articles, out of which 3 were accepted for oral presentations and 4 were accepted as e-posters. Here is a list of the contributions:
- Line C in Rome: San Giovanni, the first archaeological station. This article was developed entirely by Metro C and was selected for an oral presentation.
- The archaeological findings are changing Amba Aradam station design in Rome Metro C Line C. This article was developed entirely by Metro C and was selected for a poster presentation.
- The T3 stretch of Line C in Rome: TBM excavation. This article was developed entirely by Metro C and was selected for a poster presentation.
- The management of the soil conditioning process for the excavation of the Rome Metro C line. This article was developed in collaboration with the University La Sapienza and Astaldi and was selected for an oral presentation.
- Line C in Rome: strain measurements in precast TBM lining segments using an embedded smart wireless monitoring system. This article was developed in collaboration with IMG and was selected for a poster presentation.
- Embedded barriers as a mitigation measure for tunnelling-induced settlements: a field trial for the Line C in Rome. This article was developed in collaboration with the University of Tor Vergata and was selected for an oral presentation.
- Ground response to micro-tunnelling plus ground improvement in the historical city center of Rome. This article was developed in collaboration with the University La Sapienza and was selected for a poster presentation.
Engineer Eliano Romani “Line C in Rome: San Giovanni, the first archaeological station”
In the context of the construction of Line C of the Rome Metro, the San Giovanni station required the adoption of construction techniques to address geological, geotechnical, archaeological, and territorial challenges, given the high density of buildings and underground services. The execution methods for this station were significantly constrained by unexpected archaeological layers found at the start of construction, particularly the presence of displaced archaeological layers in the backfilled soil to a depth of 18 meters below ground level.
The design choices for the construction of this station were strongly influenced not only by pre-existing conditions and the geological-geotechnical scenario mentioned above but also by the unexpected discovery of displaced archaeological layers in the backfilled soil to a depth ranging from 14 to 18 meters, with a water table level at approximately 8 meters below ground level.
Following the results of the preliminary archaeological investigations conducted before the execution of perimeter diaphragm walls and jet grouting for ground consolidation, the Archaeological Superintendency of the Municipality of Rome imposed the following construction constraints:
- It was not possible to carry out ground consolidation without prior archaeological excavation.
- All excavations had to be conducted archaeologically until reaching the “virgin” soil.
These obligations required a comprehensive revision of the Line C project in the historic center of the city of Rome, starting from the San Giovanni Station, to safeguard archaeologically sensitive layers.
Along the T4 section of Line C, from San Giovanni to Malatesta, archaeological findings necessitated an alteration in the elevation of the track starting from the Lodi Station. This involved deepening the underground line tunnels beneath the archaeological layers and creating natural tunnels to pass under the existing station. This deviated from the original plan from the 1970s, which had the Line A platform above the station’s ceiling. This change resulted in the excavation of the San Giovanni station being approximately 14 meters deeper than the project initially proposed.
The study of the new construction phases, heavily influenced by archaeology and not wanting to forgo the advantages of the “top-down” approach, with downward construction of the slabs serving as support for perimeter walls, led to the definition of the following construction sequence, which, for each slab, includes:
- Excavation using archaeological methods to a depth of approximately 3.00 meters below the underside of the slab;
- Construction of the slab using self-supporting prefabricated structures and subsequent casting and consolidation.
This phased approach, known as the “modified top-down method,” eliminates front excavation typical of the classical “top-down” methodology, which involves casting slabs against the ground. Instead, it allows for the deepening of excavation in horizontal layers while preserving ancient structures.
During the construction of the San Giovanni station, approximately 50,000 m3 of soil were excavated using archaeological methods, resulting in the discovery of around 40,000 artifacts. The most significant discovery was undoubtedly the Roman-era reservoir, measuring 35×70 meters, found at a depth of approximately 15 meters below the ground surface, between the second and third intermediate levels. The exceptional nature of this discovery led the Archaeological Superintendent’s Office to prescribe a comprehensive revision of the architectural design of the station. Metro C, in collaboration with the Department of Architecture at the University of La Sapienza in Rome, designed and implemented an exhibition that takes visitors on a journey through history, from modern times to prehistory.
The Line C tunnels pass beneath the existing Line A station for a length of approximately 40 meters each. These tunnels were constructed using traditional excavation techniques under the water table, involving soil consolidation and waterproofing using the freezing method.
The method of artificial ground freezing involves freezing water within a known volume of soil using heat exchangers that circulate a low-temperature liquid, which extracts heat from the soil and dissipates it outside. The complexity of the project required a mixed system, utilizing liquid nitrogen in the initial freezing phase to reduce construction times, and brine during the maintenance and tunnel excavation phases.
Around the perimeter of each tunnel to be excavated, there are 36 freezing probes for the circulation of refrigerant fluids and 15 thermometric probes for continuous real-time monitoring of the ice wall’s evolution. The spacing between freezing probes varies, approximately 75-80 cm on the pillars and up to 3 meters at the keystone due to the presence of piles. The average length of the probes is approximately 36-39 meters.
The underpass beneath the existing San Giovanni station represents an exceptionally unusual and technically challenging intervention due to the surrounding conditions and constraints, as well as its placement in a complex stratigraphic context with challenging geotechnical modeling. These conditions have given the freezing technique characteristics of absolute technical and conceptual complexity.
Ing. Marco Cervone “Line C in Rome: the archaeological findings are changing Amba-Aradam station design”
The article describes the modifications made to the Amba Aradam/Ipponio Station project due to archaeological findings discovered from the preliminary project phase to the implementation phase.
During the deep excavations, a series of ancient Roman structures were found inside the station diaphragm walls at depths ranging from 8 to 15 meters below the ground surface. The exceptional historical and archaeological significance of these structures, combined with their good state of preservation, led the Archaeological Superintendent’s Office to request a complete redesign of the station’s architectural project to ensure the widest possible valorization and use of the ancient structures within the future station.
During the first-phase archaeological investigations conducted since 1999, wall structures were discovered in the backfill soils along the T3 Line. As a result of these investigations, the Archaeological Superintendent’s Office prescribed that the tunnel excavation works for the section from mid-Via La Spezia to Largo Amba Aradam must be carried out in the open air, using archaeological methods until reaching the sterile subsoil located at approximately 18-20 meters below the ground surface. This is because these excavations affect the backfill layers with very high archaeological risk. Furthermore, the use of jet grouting, a technology considered “extremely invasive, destructive, and therefore incompatible in areas with complex archaeological interests,” is excluded.
To overcome the archaeological challenges described above, the solution adopted was to place the metro line tunnels entirely within archaeologically sterile soils, limiting interference with the backfill layers to the station structures alone.
Regarding the Amba Aradam/Ipponio Station, it was necessary to relocate the station in a way that allowed for the use of a fully enclosed box-type structure confined within impermeable diaphragm walls, creating a “watertight” structure without the need for soil consolidation (jet grouting).
The construction phases and technological choices for the station’s realization were borrowed from the recent experience of excavating the San Giovanni Station, where a excavation methodology called “Modified Top – Down” was developed.
This sequencing allows for the benefits of “Top – Down” excavation while ensuring the preservation of archaeological pre-existing structures. After the perimeter diaphragm walls are constructed, excavation begins using archaeological methods, reaching a depth of approximately 3 meters below the cover slab. Subsequently, once the cover slab is completed, intermediate slabs are progressively constructed down to the foundation level, with each phase deepening the excavation by at least 3 meters below the intrados of the individual slab. This deepening ensures that the excavation progresses from top to bottom in successive horizontal excavations, typical of archaeological excavation methods.
The cover slabs and atriums that fall within the “archaeological layer” cannot be constructed using the soil as temporary support, except for limited portions. For these structural elements, the widespread use of self-supporting prefabricated structures was chosen to minimize the use of temporary elements such as shoring.
The slabs of the first technical level and mezzanine, located below the archaeological layer, are constructed using reinforced concrete structures, with the soil serving as a temporary support element before the concrete sets.
During the second-phase archaeological excavations conducted between 2015 and 2017 within the perimeter diaphragm walls of the station, at a depth of approximately 9 meters below ground level, a complex of structures dating back to the first half of the 2nd century AD, specifically the Hadrianic period, was discovered. These structures can be functionally identified as a barracks-camp.
The exceptional historical and archaeological significance of this discovery, along with the good preservation state of the ancient structures as a whole, led the Archaeological Superintendent to request a complete redefinition of the architectural design of the Amba Aradam – Ipponio station. This involved authorizing the temporary dismantling of the discovered structures with the condition that they would be subsequently relocated to ensure their maximum protection and extensive valorization and use within the future station, creating a museum space functionally separated from the operation of the metro.
Ing. Valerio Foti “The management of the soil conditioning process for the excavation of the Rome Metro C line”
The article describes the results of research conducted through the collaboration between Metro C, Astaldi, and the Department of Structures and Geotechnics at La Sapienza University in Rome. The research aimed to deepen the analysis of various aspects of the soil conditioning process during the excavation of a tunnel with an EPB TBM in the delicate context of the underground of a historic city like Rome.
The research focused on the interaction with the soils crossed by the TBMs in the T3 section, between San Giovanni Station and via dei Fori Imperiali. In this section, the machines enter the historic center of Rome, which itself, along with its numerous important monuments, is a UNESCO World Heritage Site.
For the preservation of this heritage, Metro C has created a specific Technical-Scientific Committee to ensure high-quality research methods and to analyze in advance all possible interactions between the construction works and the cultural heritage.
This research article fits into this context, as it represents the conditioning of soils as a fundamental element for minimizing the effects of tunnel boring machine (TBM) excavation on the surrounding environment.
The research has also served as a valuable tool in selecting conditioning products and balancing basic parameters in the operational management of the machines.
The laboratory activities consisted of:
- A preliminary testing phase
- Characterization tests of soils (performed on representative samples of the various lithotypes present in the T3 section) to define granulometry, plastic behavior, adhesive behavior, and mechanical resistance
- Characterization tests of different conditioning products (chemical-physical and stability over time), provided by Metro C in completely anonymous form
- Tests on soil samples conditioned with the proposed products to verify their effectiveness in improving the characteristics (especially adhesiveness and undrained resistance) of untreated soils
- A back-analysis and field effects verification phase
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The comparison of the results from the second analysis phase with the data obtained from preliminary tests allowed for satisfactory representation, taking into account differences induced by some typical operational conditions that have not yet been perfectly reproduced in laboratory tests, such as the actual temperature and pressure values in the excavation chamber.
It is therefore believed that further research could enhance this representation, thus providing useful tools for the prior identification of the correct conditioning products and the design of appropriate operational excavation parameters. This is crucial to minimize the effects of TBM excavation activities on the surrounding elements, especially in particularly sensitive contexts such as the historic center of a city like Rome.
On Wednesday, May 8th, a Press Tour took place with a guided visit to the Rome Metro C Line, the capital’s third metro line and the first fully automated one that passes through the historical and archaeological heart of the city. The T3 section, currently under construction, stretches from San Giovanni to the Imperial Forums, covering approximately 2.9 kilometers and includes the two stations of Amba Aradam/Ipponio and Fori Imperiali, as well as the two ventilation shafts Celimontana and Sannio. The tunnels run beneath the archaeological layer without interfering with it, while the two stations are located near the Colosseum and the Aurelian Walls.
The press tour allowed access to the construction sites of the T3 section, with visits to the Amba Aradam/Ipponio station and a visit to the TBM tunnel up to the excavation front, as well as the Celimontana shaft.
Finally, on May 9th, technical visits were dedicated to offering participants the opportunity to visit some of the most significant construction sites currently underway in Italy.
Inside the Celimontana shaft construction site, there was a welcoming briefing for over 40 participants, where Eng. Claudio Ottaviani on behalf of Roma Metropolitane S.r.l. provided a general overview of the project and some useful information highlighting the complexity of the work.
Eng. Eliano Romani (Head of Metro C Design) delved into the technical and logistical aspects related to the construction of underground works. In particular, he illustrated the construction technologies of the stations and tunnels, which are planned for most of the route with mechanized TBM (Tunnel Boring Machine) EPB (Earth Pressure Balance) excavation, except for the section between San Giovanni station and multifunctional shaft 3.3, where tunnel excavation is carried out traditionally by widening the pilot tunnel already constructed using the Ø3000 microtunnel technology lined with prefabricated segments.
Following the presentations, the group of conference guests was accompanied by the responsible Project Managers, Eng. Marco Cervone and Eng. Valerio Foti, to the Celimontana site (Shaft 3.2) and subsequently to the Amba Aradam/Ipponio site, where they could see one of the two TBMs and witness a tunnel excavation phase that will connect Amba Aradam/Ipponio Station to the future Fori Imperiali station.
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