FORI IMPERIALI STATION WORK AND ACTIVITIES IN PROGRESS
The Fori Imperiali station is located below the street of the same name in the area between the Colosseum and the area in front of the Basilica di Massenzio. It is a unique and complex work, both for the position in which it is located, involving an archaeological and monumental area declared among the most famous in the world by UNESCO World Heritage Site, and for the characteristics inherent in the construction such as the connection of the atrium of Line C with the atrium of the existing Line B Colosseo station.
The body of the station, inserted in a structure excavated between diaphragms (supporting walls), has a variable plan width between 30 and 50 metres and a total length of about 240 metres. The structure reaches a depth of 32 metres from street level and is divided into five levels: the atrium floor, of over 6,100 square metres which also allows the connection with the platforms of Line B by means of a mezzanine level, two floors dedicated to technical rooms of about 3,900 square metres each, a platform floor and an under-platform floor.
The functional scheme of the Fori Imperiali station is a central platform, 110 metres in length and 4 metres wide. There are 2 accesses to the station, positioned one on each side of the Via dei Fori Imperiali. Each access is equipped with a pair of lifts and a system of both fixed stairs and two escalators. The excavation of the station has been designed to minimize interference with the road surface. Once the perimeter diaphragms and the roof covering had been built, in alternating traffic phases the site was reduced and construction continued in top-down mode. This method of excavation consists of the construction of the floors from top to bottom, with jet grouting against the soil which allows the contrast of the perimeter bulkheads already put in during the construction phase. The connection with the platform level of Line C takes place by means of a single large staircase with fixed and intertwined mobile stairs, located in the centre of the atrium floor. The accesses of the two lines B and C remain separated, while the underground connection with the Colosseo station takes place by means of a pathway at the atrium level which arrives directly on the platform of Line B in the direction of Termini and by means of a mezzanine level pathway which reaches the other platform, thanks to an underground connecting pedestrian walkway that runs over the existing station.
The excavation of the station has been designed to minimize interference
with the surface road system.
THE CONNECTION WITH LINE B
The pedestrian connection (currently under construction) between the station of Line C and the existing Colosseo station of Line B, will occur by means of a corridor which crosses over the Line B and will allow access to both platforms of the Colosseo station, on both the Laurentina and Termini sides. For this work to be completed, some interventions have been necessary at the platform tunnel of Line B. The work only concerns the lining structures of the central station tunnel located under the Colosseum. The other structures of the existing station Colosseo station are not affected by the works for the connection with Line C.
The crossing structure, jointed to the vault of the existing tunnel, is placed on curbs based on micropiles and forms an underground pedestrian walkway, the covering of which is located just below road level. All the works have been organised with the aim of minimizing the inconvenience for those using the Colosseo station of Line B and allowing the most delicate phases of the construction of the structures to be carried out during night time interruptions to the line’s service. The phases and methods of execution of the works, their duration and their temporal succession have been approved by and shared with a tecnical body including the Mobility and Transport Department of the Municipality of Rome, ATAC, USTIF, Lazio Region and Roma Metropolitane. The schedule of works is organised with time windows for early closure at 9pm of the line in operation and with some weekends of complete closure.
In order to keep interference with the line in operation to a minimum, the usable part of the existing 150 metre long platform of Line B has been reduced to 110 metres, so that a partitioning structure can be installed in the area being intervened, with the aim of physically separating the work areas and those which are in service. The structure is composed of a reticular system of metal beams and pillars on which a corrugated sheet parallel to the tunnel shell cap is mounted on the top. The area of the tunnel piers has been delimited by a structure of wooden pannelling connected to the metal structure, leaving only a gate that allows access for site workers directly from the platform. Only after the assembly of the above mentioned structure was it possible to proceed with the subsequent phases that involve the cutting of the tunnel shell section and the piers , for a width of about 8 metres, and the construction of 4 plinths based on micropiles, on which the final overpass structure will be laid.
Once the cutting of this segment of the existing tunnel was completed, assembly of the overpass structure began. The first step was the installation of two longtitudinal beams that act as the load-bearing framework of the structure, put into place during the nights between 22 and 23 April. The implementing of the prefabbricated structures, (predalles) and the completion of the bottom floor is in progress. The steel bracing will then be positioned, the upper predalles will be put into place and the box roof covering will be laid. Only afterwards parts of the existing tunnel will be demolished in order to create the accesses to the platforms of the Colosseo station. The crossing will then be completed with the installation of side glass walls and interior finishes.
22-23 April: launching of the longtitudinal beams that form the load-bearing framework of the pedestrian connection with Line B.
THE CURRENT PHASE OF THE WORK.
To date, the Fori Imperiali station is divided into three macro-areas of the construction site, each of which is managed autonomously with designated vehicles and personnel. In the area on the Clivo di Acilio side, excavation and construction work is underway on the structures of the part of the station above the “dispari” track tunnel; at the atrium floor the area is currently connected with the adjacent station complex, while on the subsequent technical levels it is separated by the diaphragms at ground floor level which determine its perimeter. This compartmentalisation of the area has been designed to allow the rapid execution of excavation down to the TBM tunnel level and the early start of radial consolidations, to be carried out on the tunnels themselves, preparatory to excavation in the traditional way for subsequent extensions.
Why is it necessary to widen the tunnels at the Fori Imperiali station with the traditional method?
The presence of the superstructures on Via dei Fori Imperiali has strongly limited the space to operate an excavation from above. In particular, at the “dispari” track of Line C, the current configuration of the Clivo di Acilio bounded by the Muro di Munoz made it possible to excavate from above (top-down) only a part of the structure necessary for the insertion of the station platform. It was therefore necessary to widen the tunnels built with the TBM by means of traditional excavation, preceeded by the consolidation of the excavated ground to increase the geotechnical characteristics of resistance and impermeabilty. The widenings are about 50 metres long in the direction of San Giovanni and about 30 metres in the direction of Venezia, which together with the part of the station that could be built from above, will provide the 110m needed for the platform. This activity allows the areas to proceed with excavation of one meter at a time, followed by the laying of the centering rib (provisional circular metal structure that supports the tunnel’s vault) and subsequent spritz breton concrete surface (cement projected with accelerant to create a solid and uniform surface.
The construction site for the drillings, carried out by the TBM tunnel, has been started, after which it will be possible to proceed with the injection of cement and chemical mixtures that will make the soil solid and not very permeable, in order to proceed with the excavation of the tunnel widenings. The second technical level and the laying of the contrasting metal structures, located just above the TBM tunnel, are also underway. Only after the completion of the mechanised tunnels and the dismantling of the equipment will it be possible to proceed with further study and the start of the planned consolidations.
In the external area of the worksite, the final lining in brick of the Muro del Munoz is being carried out by a company specializing in restoration, after having studied and sampled the most suitable types of lining with the Superintendence. In the area on the Clivo di Venere side, where the worksite is more extensive, the assembly of the injection system has been completed and consolidation has begun at the TBM tunnel preparatory to the excavation of the “dispari” track platform tunnel. As far as the station structure of Line C (the site on Clivo di Venere side) is concerned, the roof, atrium and first technical floor slabs have been completed and excavation is in progress between the latter and the mezzanine floor. Work is also underway on the station linings between the atrium and the first technical floor.
Particular attention is paid to the third macro-area of the construction site (the Colosseo shaft), which concerns the connection between the Fori Imperiali station and the Colosseo station of the existing Line B. The overpass structure described above ends in a shaft, built at the foot of the Colosseum, which provides access to the platforms in the direction of Termini. The shaft was excavated thanks to a double bulkhead of micropiles and to a system of metal struts that has allowed the emptying of the structure in an archeological mode. Currently the excavation activities have been completed and the bottom floor of the structure is under construction after which the linings and the roof covering will be underway. The section of the structure between the Fori Imperiali station and the existing tunnel of Line B is under construction; among the parts of the work already finished are the roof and floor coverings, (with the exception of the section closest to Line B), and part of the perimeter linings.
THE FORI IMPERIALI STATION AND ARCHAEOLOGY
The construction of a metro station, in a city like Rome, is also an opportunity for historical/archaeological discovery of inestimable value. The works for the construction of the Fori Imperiali station with the new extensive excavations have provided the opportunity to document the archeological stratigraphies saved from the excavation of the Velia Hill in the last century during the building the Via dei Fori Imperiali,which has allowed a reconsideration of the previous data in order to reassemble an overall picture of the archaeological evidence of this very important sector of the central area of Rome.
The archaeological investigations have been carried out in a multi-layered manner since 2014 and have recently been completed. Initially, preliminary archaeological interventions were carried out during the construction of the piling supporting the Velia on the Clivo di Acilio side and the bulkheads of the station. Subsequently it was possible to excavate extensively inside the station body and thus also with the nearby Q18 shaft which has a connection function with Line B. The archaeological investigations involved various sectors of intervention. On the Clivo di Acilio side the temporary removal of part of the Muro del Munoz brought to light the archaeological structures left behind by the cutting down of the Velian Hill, most of which were the residential buildings that during the Imperial and late antique age were located on the south-eastern side of the hill.
Archaeological surveys have been carried out on several occasions, starting in 2014, and have recently been concluded.
On the side of the Clivo di Venere Felice, the excavation and levelling of the western slopes of the Velia carried out in 1932, had led to the removal of a complex system of structures that supported the slopes of the hill, articulated on several levels along the south-east side. Archaeological excavations have highlighted the remains of these buildings, which can be dated beteen the late Repubblican and the early Imperial age and preserved only at the foundation level and a few inches from street level. The station building is located on the Via dei Fori Imperiali in the stretch where orginally was the summit of the Velia, and where the archaeological levels were completely removed during the excavations of 1932, with the exception of the numerous archaic and repubblican wells that descend deep into the geological bank and which today can be fully explored. The corridor connecting the Line B and the Q18 shaft is located in the piazzale of the Collsseo. Here, the southern slopes of the Velia slope down towards the original valley bowl within which the Flavian Amphitheatre was built.
In this case the conservation of the archeological structures has been more consistant. In fact new and important elements have emerged that integrate the archaeological knowledge about the topographical structure of this sector, from the Repubblican age to the arrangement linked to the construction of the Colosseum. Below the floors of the Flavian age, the mighty foundations of the Neronian period accomodation have come to light again, preceded by the remains of the older buildings, which represent an important testimony of the late Repubblican and early Imperial age housing. As has already happened for other archaelogical excavations related to the construction of Line C, so too in the case of the Fori Imperiali station and the works on it, the cement bulkheads have allowed an extensive and safe archaelogical exploration down to very deep and not otherwise reachable levels.