The Multifunctional Shaft 3.3
The Multifuctional Shaft named 3.3 is located between the Amba Aradam/Ipponio and San Giovanni stations, in a garden area adjacent to the historic local market in Via Sannio, on the Piazzale Appio side.
This is the shaft into which the TBMs (Tunnel Boring Machines) were lowered after being extracted from the San Giovanni station, which began excavating the tunnels going in the Fori Imperiali direction in March 2018. The overall planimetric dimensions are 64.40×25.65m. The track level varies between +8.940 and +9.120m above sea level inside the shaft. The structure is composed of 3 horizontal levels:
- Technical Floor at +25.47m above sea level (finished)
- Intermediate Floor at +16.54m (finished) This floor has the sole structural function of bracing the retaining structures of the shaft.
- Platform Floor at a variable level depending on the Iron Floor level between +10.007m on the Sannio side and +10.127m on the San Giovanni side.
The excavation technique used is of the ‘top-down’ type, which consists of building structures downwardly, in order to minimise the impact of the site on the external environment.
On the basis of the guidelines received from the Archaeological Superintendency, the excavations up to the levels involved in the archaeological investigations (+18.52m above sea level) were carried out in the archaeological excavation mode in successive horizontal layers. The floors within the “archaeological layer” were built only after ensuring an adequate height between the excavation surface and the roof intrados, the height necessary for the transit of excavation and material handling equipment. The use of prefabs made it possible to avoid shoring the horizontal levels during the construction phase, with added advantages in terms of construction speed.
The first functional phase of the T3 section involves the activation of Shaft 3.3 in Via Sannio and a new section of track equipped with two pairs of rail switches. This will allow trains to pass quickly and efficiently from one track to the other, creating the so-called “San Giovanni terminus turnaround”, which will reduce the waiting times between trains. At present, the line in operation has a reduced use of the last four stations before the Shaft (San Giovanni, Lodi, Pigneto, Malatesta), as trains cannot reverse direction by changing tracks, so on the same platform both trains run in the direction of the centre and in the direction of the termins of Monte Compatri/Pantano, unlike the other stations where the two platforms are each dedicated to a train direction.
With the addition of the crossover at Shaft 3.3, the optimum configuration for the railway operation will be acheived and signalling and station use can be simplified and streamlined. The project’s operating schedule envisages trains every 9 minutes with 9 trains in operation. Shaft 3.3 is the first on Line C in which, in addition to the “traditional” ventilation function, there is a room for ATC signalling (SER: Signalling Equipment Room). The ATC electronic devices enable the new crossover switches to be operated and interfaces with the line in operation.
The construction of Shaft 3.3 is substantially finished. All reinforced concrete and internal finishing works are complete. The flooring, the assembly of the external domes and the connection to the sewer are currently under construction. Work on the landscaping of the surface area of the so-called “Via Sannio gardens” is nearly completed.
The archaeological excavations of Shaft 3.3, located in the gardens of Via Sannio, were carried out by Metro C ScpA under the scientific direction of the Special Superintendence for the Colosseum, the National Roman Museum and the Central Archaeological Area of Rome. This excavation has provided new and important data to reconstruct the topography of the area, in particular that relating to the most ancient times, which are difficult to document through superficial tests, given the depth at which the evidence is located and the presence of a layer of acquifer. This has significantly expanded the knowledge framework about the occupation and exploitation of the area from pre-anthropic times. In Roman times the area was bordered by two roads, one exiting from Porta Asinaria (via Asinaria) and the other from a postern (a small access door hidden in the walls), located to the west (perhaps via Tuscolana), and crossed by a ditch called Acqua Mariana since Medieval times. On the Lateran hill, two late 1st-2nd century domus are known to have been documented in the area of the basilica, demolished in the Severan age for the construction of the castra ova equitum singularium, barracks dismantled by Costantine for the construction of the basilica dedicated to the Saviour.
The construction of a terracing wall in listed work with a NE-SW orientation, 0.60m wide and identified at a length of about 62m refers to the time of Septimius Severus. The structure, flanked to the South-East by a masonry channel, seems to have the function of a terracing with a difference in height of about 1.50m between the walkway upstream (on the Mura side) and that downstream (on the Sannio side). The construction of the listed wall is preceded by a sequence of levels of garden datable between the late Flavian and Antonine ages. The oldest is characterised by the presence of a trench that crosses the entire excavation area filled with three rows of almost 300 perforated ollae (garden earthernware pots). The garden of ollae obliterates the structures pertaining to a portico for which at least three phases of life between the middle of the 1st century a.d and the Flavian age can be recognised. Inside the Shaft the man-made terrain, documented to be 16m thick, can be dated to between the Repubblican and Contemporary Ages.
The first 4.50 m of subsoil can be attributed to the 20th century, related to the construction works of the Appio-Tuscolano district, below which are layers datable to the second half of the 17th and 19th centuries, linked to the agricultural use of the area outside the Aurelian Walls (about 2.50m thick). Between the 7th and 16th century no activities are documented in the construction site area. It is known however, the existance in this period of a ditch called Acqua Mariana, the first evidence of which dates back to the pontificate of Callisto II (1119-1124), a watercourse already existing in a pre-anthropic phase.
For the most ancient period it was possible to bring to light the NW bank of a paleolithic ditch from the pre-anthropic era and two tufa block walls from the beginning of the 3rd century b.c. An interesting piece of information concerns the construction in the second half of the 3rd century of a catchment basin at the side of the river. This arrangement is related to what has been documented in the excavation of the San Giovanni station.
The surface arrangement of the area.
The design for the surface arrangement of the area affected by the construction site of Shaft 3.3, commonly known as the “via Sannio gardens”, was developed by Metro C ScpA in close collaboration with the Special Archaeological, Fine Arts and Landscape Superintendence of Rome, whose guidelines were adhered to.
In particular, the Superintendency felt that the landscaping of the Shaft area, which will return to its original use as a public garden, should be used as an opportunity to recount some of the discoveries made during the excavations. It therefore requested to reproduce on the ground the dimensions of the wall structures and the traces of the river, without reconstructions, but with materials suitable for the design of a public park.
With regard to the vegetational project for the area, the Superintendence requested that the choice of tree species be based on the Palaeobotanical data discovered during the excavations, which showed the presence in ancient times of characteristic tree and shrub species, such as cypress, plane tree, manna ash, rosmary, bay laurel etc
The Superintendency also requested that planting be avoided in the area between the garden and the walls, to allow a full view of the walls themselves, and that a didactic panel be placed containing information about the archaeological subsoil investigated, with particular regard to the portico phase.