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Line C Compensation Grouting Aurelian walls at Porta Metronia

Line C T3 stretch is presently under construction and will run under the historic city center of Rome, an area with a high density of monuments and archaeological buildings included in the UNESCO World Heritage sites.
Metro C constituted a specific Scientific Technical Committee (STC) in order to safeguard all the monuments and to ensure high quality research methods meant to analyze the potential interactions between the tunnels and the monuments and archaeological buildings. Among these interactions, Line C tunnels intersect Aurelian Walls crossing Porta Metronia approximately 28 m below ground level.
The monument shows various regular crack patterns, mainly affecting the attachment sections between the curtain walls and the towers. The results of subsidence and structural analyses predict an increase in the existing cracks and possible openings of new cracks.
Compensation Grouting works has been therefore implemented from a temporary shaft with an internal net diameter of 8 m and an excavation depth of 20 m from ground level.


The 77 drillings were video-guided, as depths between 40 and 70 m must be reached and the precision of perforation is an essential requisite for the success of the intervention. In all stages of the process, an integrated monitoring system was implemented and this real time monitoring was the most important key aspect during TBM excavation which allowed a proper management of tunneling activities and determined the project construction success. All the data were stored to be analyzed immediately in order to allow adopting mitigation actions during tunnel construction. Simultaneously settlements are measured by 48 H-Level gauges for the precision monitoring, 48 settlement gauges and 74 prisms surveyed by 4
total station. A complex geotechnical monitoring system was implemented for
ground deformations control as well. Before the passage of the TBMs a field trial was carried out within the shaft, in the opposite direction to the Walls, to check on a real scale both the quality of the consolidation admixtures and the deformative response of the soil.

Metro C S.c.p.A.’s member companies