Line C and the Preservation of a Unique Heritage in the Protected World of UNESCO.
Along its route the C line interacts with historical palaces and monuments of great value, from the Colosseum to the Palazzo della Cancelleria passing the Palazzo Venezia. To ensure the protection of a unique heritage in the world protected by UNESCO, specific studies have been developed to analyse the possible interactions with the historical and monumental heritage during the construction of the line.
To this end, in 2007, Metro C scpa set up a Scientific Technical Committee chaired by Professor JAMIOLKOWSKI which is composed of world-renowned professors working in the field of geology, geotechnical and structural engineering as well as in heritage conservation and monument restoration.
These studies of interaction have proved an essential phase for the design of the historic centre section in its high-quality level of the methodological approach applied. They have proved essential too for the conclusions reached by the activities of 5 geotechnical and structural engineering working groups, also appointed by the General Contractor, who have developed interaction studies starting from the survey and investigation phase and ending with defining specific monitoring plans and safeguard interventions for each monument, all based on results obtained by the complex numerical modelling they implemented.
For each building the architectural history has been reconstructed, verifying if and how the structural interventions carried out in the past may have modified its stability. Facades and internal structures have been inspected to detect the presence of any cracks while the typology of the foundations and its structural support has been examined.
Line-monuments interaction analysis has been developed for about 4 years involving 13 monuments and 40 historical buildings among which are the crumbling ones in the baroque loop within a bend in the Tiber which face along the Corso Vittorio Emanuele.
In 2007 the General Contractor Metro C spca established a permanent Technical Table with officials from the Ministry of Cultural Heritage and Activities in order to jointly analyse and share the design process followed for the preservation of monuments as well as the conclusions reached by the Scientific Technical Committee from the analyses acheived by the Working Groups.
Safeguard interventions can essentially be traced back to 2 macro-categories:
- Provisional or definitive interventions to be put in place before the start of the excavation activities. This category includes executing structural consolidation measures aimed at remedying previous problems or pronounced states of deterioration thus those not directly correlated to the effects induced by the construction of Line C’s works. By way of example, we point out the final structural consolidation interventions of the Basilica di Massenzio or of the Chiesa di Santo Stefano Rotondo and the temporary interventions of the Colonne del Foro di Nerva. The results of the analyses carried out by the Structural and Geotechnical Engineering Working Groups, and the current level of widespread deterioration of the ancient walls of the Basilica di Massenzio or of the Chiesa di Santo Stefano Rotondo, brought the Scientific Technical Committee to suggest the need for definitive structural consolidation interventions. This consists of longitudinal and transversal chaining carried out on several levels both inside and outside the Basilica di Massenzio, in the tambour of the dome’s drum and the second ring of the Chiesa di Santo Stefano Rotondo together with the final consolidation of the masonry of the third ring with weathering cor-ten steel crutches. In the latter case, given the presence of an artistic heritage of inestimable value, the General Contractor also arranged for a conservative restoration of the frescoes and mosaics in the church and in the Cappella dei Santi Primo e Feliciano together with temporary interventions of preservation in order to avoid any coming apart of the frescoes from the ancient walls.
- Interventions to be carried out during the excavation phase aimed at counteracting the induced subsidence simultaneously containing it below pre-set thresholds. This category includes geotechnical interventions such as the Compensation Grouting envisaged in the T3 section during the passage of the line tunnels under the Aurelian Walls at Porta Metronia and at the existing Colosseum station of the Line B. Here the results of the analyses carried out by the Structural and Geotechnical Engineering Working Groups as well as the current level of widespread deterioration of the Aurelian Walls have in fact enforced the need to arrange a geotechnical intervention to reduce active subsidence with the aforementioned Compensation Grouting. This process consists of the injection of cement mixtures into the ground during the development of the activity which induces subsidence such as in the excavation of the tunnels. This operation will be carried out from within a specifically designed temporary shaft in the gardens of Largo dell’Amba Aradam, with an internal diameter of 8 metres and an excavation depth of about 20 metres from street level. This intervention consists of the consolidation of land of a surface area of about 3600 square metres carried out by means of cementitious grout injections below the level of the foundation of the Walls with a margin of about 4 metres with respect to the ancient walls, within the layer of recent floods at the bottom of the valley. The technologies put in place for the aforementioned intervention are extremely avant-guarde, in fact, guided drilling is used which reaches distances of between 40 and 70 metres. Precision during the drilling operations is a fundamental requirement for the success of the intervention. In all phases of the processing it is planned to install extremely precise monitoring equipment such as levelling gauges, in order to know exactly the deformation state of the antique structures and to correctly modulate both the injection quantities and the area to inject.
Prior to the journey of the TBMs, a test field is underway from inside the shaft, specifically in the direction of the Walls, to verify on a real scale both the quality of the consolidation mixtures and the deformation state of the ground.
Considering the development of the T3 section of the Line C with its urban fabric, as well as some buildings considered ordinary, is so rich in UNESCO’s unique historical and monumental buildings, the monitoring plays a major role. The controlling of the processes, the consideration of the design parameters, in addition to their technical value and support to the decisional processes, it assumes a primary importance in the management of the execution of the works. In this context, the observational method represents an indispensable control tool that is used to verify the correct design hypothesis, for any refinement of the models and design parameters-applying the methods of the back analysis-and for the verification of the effectiveness of any project actions to be made during the executive phases.
Monitoring is performed with laser and optical techniques, inclinometers, electric meters, thermometers and accelerometers for vibration control. The results of the monitoring flow into a specifically created usable database, accessible to all operators enabling them to follow the evolution of deformation phenomena and to therefore be able to promptly make any changes necessary to the working process.
The monitoring has therefore been conceived as an innovative system, based on automation, and with the linking of the technology-mediated service, their computerisation and publication on the WEB-GIS platform allows operators to have access to monitoring data through the web in enough time to manage critical issues, and therefore in time to provide support to the building sites.
The instrumentation was installed well before the beginning of the works, in order to acquire the necessary reference base with respect to the variations produced by seasonal and daily thermal cycles. This also provided the opportunity to keep under careful control damage already present and to observe possible unfavourable changes of the mechanisms already activated or those that can be activated.
The Line-Monuments studies have provided a useful contribution for the designer regarding the preservation of the historical, artistic and monumental heritage along the line. Among the activities carried out particular attention has been dedicated to the finalisation of a geotechnical, topographical and structural monitoring plan in progress to protect the monuments.
As part of the verification of the results in the on-going monitoring of the monuments of the T3 section-such as the Aurelian Walls, the Chiesa di Santo Stefano Rotondo, the Chiesa di Santa Maria in Domnica, the Acquedotto Celimontano, the Colosseo, the Basilica di Massenzio, the Colonnacce del Foro di Nerva and the Colonne del Foro di Cesare, the General Contractor Metro C has signed a specific agreement with the Department of Structural and Geotechnical Engineering of the University of Rome La Sapienza for support in the construction phase of the works of the T3 section and in the analysis and interpretation of the aforementioned monitoring data. This has placed them in close and constant correlation with the results of the Line-Monument interaction studies carried out in the design phase, validating and calibrating the models developed by the Working Groups and, if necessary, performing further numerical analyses to correlate the monitoring data acquired with the conclusions reached by the Working Groups in the modelling field. This has given continuity to the complex interaction studies carried out.
The studies of Line-Monument interactions have represented a work of exceptional scientific interest for the multidisciplinary methodological approach and for the complexity and quality of the analyses and results achieved, which is the first and only example in the world.
Metro C spca conveys a heartfelt thanks to all the professors of the Scientific Technical Committee, to the Managers and all the members of the Working Groups for the professionalism with which they have developed the aforementioned analyses over the years.
Eliano Romani – Head of Engineering of Metro C ScpA