Rome’s Metro C: hydrofraise completes the First Diaphragm at Piazza Venezia

For the first time, a machine has reached the depths of Rome, reaching down 85 meters in one of the symbolic places of the city’s history and present: Piazza Venezia. On February 15th, the excavation of the first diaphragm has begun, the first excavation of those pillars that, side by side, will constitute the box inside which the station of Metro C of Piazza Venezia will rise.

An exceptional, unique station in the world will be developed at a depth of 40 meters with eight underground levels and three entrances that will allow travelers to reach the major museums of the square (Palazzo Venezia, Vittoriano, and the Imperial Forums) without ever emerging on the surface. A museum station destined to become a symbol of a strategic infrastructure for the city, namely the underground line that from Pantano (the far eastern periphery of the capital) is destined to reach and surpass the historic center.

The project is currently being worked on by the Metro C Consortium led by the Webuild Group and Vianini Lavori, which puts at the service of the work the experience gained in the construction of large underground railways around the world. From the New York subway to the Cityringen ring in Copenhagen passing through the Grand Paris Express, the new and vast underground network that will change the mobility of Paris.

Just as in the case of Piazza Venezia, many of these works have to do with the protection of artistic, historical, and architectural heritage. This happened in the construction of Milan’s M4, partly already inaugurated; in the construction of the subway in Thessaloniki, Greece, and in the construction of the subway in Naples, where some stations like Toledo have become real open-air works of art.

Behind the realization of the first diaphragm in the construction site of Piazza Venezia, there is a unique and considerable-sized machinery. For weeks now, tourists strolling between Via del Corso and the Vittoriano have been curiously observing this giant, 25 meters tall, with an arm 22 meters long and weighing up to 185 tons.

A tricolor giant, named hydrofraise, which moves delicately, like an elephant in a china shop, and digs deep holes up to 80 meters. The machine is equipped with two rotating drills capable of excavating soil portions 2 meters and 80 centimeters long and one meter and fifty wide. In this way, the hydrofraise digs the diaphragm, or one of the many underground pillars that will make up the boundaries of the box. Once one diaphragm is finished, the next one is started, and the operation is repeated until the station walls are completed.

The activities of the hydrofraise at Piazza Venezia have been going on for weeks. Every time the machine starts, a pre-excavation of a few meters filled with mud is made, so that the hydrofraise pump is completely submerged. At that point, the excavation begins. When it finishes, reinforcement cages are slid into the hole, inside of which concrete is poured to form the underground pillar. Step by step, the wall of the future station takes shape.

The hydrofraise is now an essential machine for the construction industry. Almost all subway stations are excavated with these modern and safe giants. Their history begins in Japan in the 1980s when the first machine was designed. Concurrently with Japan, the idea of the hydrofraise also took hold in Germany, where machinery suitable for the construction of the Brombach reservoir walls was studied. The Bauer Maschinen GmbH was then commissioned to design one of the first hydrofraises. Initially, these machines could dig up to 40 meters deep, but over the years, they have undergone profound technological evolutions that, as in the case of Piazza Venezia, have allowed them to exceed 80 meters.

The Metro C is currently the largest urban mobility project in the Italian capital. To date, there are 22 completed stations with 19 kilometers in operation, stations that start from the Pantano terminus and reach up to San Giovanni. At the completion of the work, there are 7 stations missing, three of which (Piazza Venezia, Colosseo-Fori Imperiali, and Porta Metronia) are already under construction, while the final design is being prepared for the other 4 stations.

According to the project, the new subway should cross the historic center to reach Piazzale Clodio in the Prati district. A long journey that will put 800,000 people in motion every day, reducing harmful CO2 emissions by up to 34,000 tons per year just for the central section from San Giovanni to the Colosseum. Piazza Venezia is certainly the symbolic station of this great work, destined to become not only a strategic infrastructure but also a new symbol of beauty for the Eternal City.