The work and the technique: Naples Metro - Art Stations, Italy
The Art Stations in Naples form part of an urban mobility system that now comprises three interconnected underground lines. A common goal shared by all the works was urban regeneration, linking highly populated areas - often in decline - with the city centre, as well as transforming hectic places that are typically purely transitional, such as metro stations, into fully fledged art galleries.
The first section of the works were on the stretch of Line 1 from Piazza Vanvitelli to Piazza Dante. The construction of these first 10 kilometres - which represented a significant challenge given that the area was both geologically difficult and of great archaeological interest - was achieved using traditional excavation, specifically with the Austrian method known as NATM, which involves the use of steel ribs and the insertion of rivets and anchors into the rock. This stretch also includes four other stations, namely Quattro Giornate, Salvator Rosa, Materdei and Museo.
Work then began on the extension of Line 1 from Piazza Dante to the Centro Direzionale. This section of approximately 5km, which passes through the historical centre, involved the construction of five new stations: Toledo, Municipio, Università, Duomo and Garibaldi.
The two separate tunnels required for the extension of the line - running for a total combined length of 7,760 m at 35 m below sea level, through sandy and tufaceous soils - were excavated using two EPB tunnel boring machines with a diameter of 6.74m, with the excavation face being supported using foams and polymers, and the pressure balance being maintained.
The excavated material was transported away using carriages and trains. The excavations were carried out in close collaboration with the Superintendencies of Archaeology and Architecture in order to identify and document, by means of preliminary geo-archaeological surveys and archaeological excavation campaigns, any materials of historical interest in the construction site areas.
A great many technological challenges arose during the construction of the new stations, both because of the area they were built in and because of the existing archaeological features unearthed. One of these - Toledo Station - required the construction of a 40m-deep tunnel and the use of advanced technologies to minimise its environmental impact. It is the deepest of the stations currently in operation on Line 1 and has garnered awards for its design (Emirates Glass LEAF Award 2013) and its innovative use of underground space (ITA International Tunnelling Award 2015). Similarly, Università Station - another winner of the Emirates Glass LEAF Award for design in 2011 - required the use of an artificial ground freezing technique to consolidate the subsoil.
In August 2015, work began on Line 6, specifically the Mergellina - San Pasquale - Municipio section, which runs for 5.5km and covers eight stations, connecting the populous area of Fuorigrotta with the central Piazza Municipio. One of the eight along this stretch is the breathtaking San Pasquale Station, located in the heart of Riviera di Chiaia. The interior consists of a 100m-long, 35m-deep reinforced concrete structure spread over five levels, built from the top down with the use of a double overhead crane to speed up the excavation phase. The executive phases proved particularly complex due to the present of an exceptionally aggressive, corrosive water table. Overcoming this particular obstacle required the use of a hydromill to construct perimeter retaining diaphragms, formed into an unusual T shape (achieved by placing two rectangular panels perpendicular to one another), intended to better counteract the pressure from the soil and the water table. Additionally, before the diaphragms were constructed, the ground was consolidated to prevent the leakage of bentonite muds, which would have compromised the safety of operations.
A further complicating factor was the use of TBMs for the construction of the line tunnel within the body of the station, requiring further retrofitting works with the use of fibreglass diaphragm reinforcement cages to facilitate their transition and ensure the continuity of the reciprocal works.
Another of the city’s famed Art Stations is Monte Sant’Angelo Station on Line 7, which has been constructed entirely within a natural cave. The tunnels have been lined with an approximately 50cm-thick layer of shotcrete, so as to maintain the effect of the original cave. The station reaches a maximum depth of 40m and features two monumental sculptures by artist Anish Kapoor, one made from Corten steel that stands 19m high and weighs 220 tonnes, and another made from aluminium at 11m high and 42 tonnes. The two pieces are located at the Università and Traiano exits, respectively.
The last project in chronological order is the extension of Line 1 from Piazza Garibaldi to Capodichino, spanning a distance of 3.2km and including the construction of four additional stations, including a station named after the international airport. The project required the team to dig down to a depth of approximately 50 metres, with an exposed atrium being built at street level. The circular segment, with an internal diameter of around 33m, is a single open-plan space with eight central lifts and four spiral staircases ascending along the walls and up towards the surface. The lift landing area is connected by three bypasses to the station’s two tunnels, which are each 110m long and 8.9m in diameter. Looming over the station is a hangar roof 8m above street level that consists of a steel web covered with prefabricated elements and glass windows, for a total weight of 450 tonnes. Throughout the entire excavation phase, there was a particular focus on the issue of environmental sustainability. As such, more than 200,000m³ of soil was transported and reused within the district of the metropolitan city of Naples, in former open-pit tuff quarries, for the urban and landscape redevelopment of the area.