High-speed Naples-Bari: the dig using hyperbaric pressure begins

Using compressed air to drive away water, reaching a level of hydrostatic pressure that allows working in dry conditions, without the risks associated with cementitious mixtures and chemical additives used in excavation when they come in contact with the soil and groundwater. This is hyperbaric excavation, an innovative, safe and sustainable technique that is now being used in Italy as well on construction sites for the high-speed railway connecting Naples to Bari, one of the few times this technology has been used in Europe.

We are on the Naples-Cancello section, one of the stretches being constructed by the Webuild Group on behalf of Rete Ferroviaria Italiana (RFI), the main unit of the Polo infratrutture FS. Here, specialized workers and technicians are working on the construction of the artificial tunnel in Casalnuovo, which partially extends beneath the water table. This means that, right where the tunnel is being excavated, water presence is constant and massive. Hence the idea of ​​using the hyperbaric excavation technique, which precisely involves using compressed air to push away the water in the affected areas. It’s a complex and sustainable technique that requires high skills and specialized training for the workers who have chosen to contribute to this project.

To drain the groundwater from the Casalnuovo tunnel, the pressure will fluctuate between 0.3 and about 1.2 atmospheres. This means that workers, before being able to enter the work area, must gradually adapt to this difference in pressure in a dedicated compression chamber with a maximum capacity of 20 people per shift. Inside this chamber, a gradual compression phase takes place, lasting an average of 20 minutes. All activities naturally follow specific technical and health protocols that ensure maximum safety and health for the workers in all phases of work.

On the construction site, essential plant equipment is present for pressurization and regulating overpressure levels, managing worker entry, and ensuring maximum safety. A proven system that will be operational day and night because the workers selected for this project will be working in 7-hour shifts to cover the entire 24-hour period, 7 days a week. Along those 650 meters where the hyperbaric excavation technique will be applied, the construction site will never stop until the tunnel is completed.

The concept behind the technique applied on the Naples-Bari route is simple: using compressed air to push back the water. Its implementation, however, is more complex, as isolating the entire excavation area is necessary to ensure constant pressure. Compared to the total length of 3,300 meters that the Casalnuovo Gallery will measure, the section affected by the water table measures 650 meters, and it is precisely on these sections that the Gallery will be divided into watertight compartments, necessary to limit pressurization losses and groundwater infiltration during excavation.

To create these compartments and isolate them from each other, temporary diaphragms (actual walls) will be constructed, which will be successively demolished as excavation progresses. Essentially, for each compartment, all activities will be repeated, including lining, waterproofing, and installing the compression chamber. Once excavation in one compartment is completed, the next one will be tackled. Even the excavation waste material will be conveyed via conveyors into two Ground Locks, which are also watertight chambers under hyperbaric conditions. When the storage chamber is full, the conveyor is retracted, the window is hermetically sealed, and at that point, the door is opened to allow entry of vehicles for material removal.

The Casalnuovo tunnel, with all its innovative features, is just a small part of a large project, but it perfectly illustrates the sense of an ambitious project because it’s innovative, safe and sustainable, but also profoundly revolutionary for the territory it will affect. The Naples-Cancello section is part of one of the 4 sections of the AV/AC Napoli-Bari that the Webuild Group is constructing (Napoli-Cancello, Napoli-Hirpinia, Hirpinia-Orsara, Orsara-Bovino).

Overall, it consists of 74 kilometers of high-speed/high-capacity line, comprising 6 tunnels, 10 viaducts, and 6 new stations and stops, for the construction of which 8 large mechanical moles will be employed.

To complete the work on the 4 lots, Webuild currently employs over 1,700 people, while the production chain, since the beginning of the work, involves around 1,500 companies. It’s a major strategic project for Southern Italy. The Naples-Bari AV/AC line will allow trains to travel at a maximum speed of 250 km/h, significantly reducing the distances between Apulia, Campania, Lazio, and the rest of central-northern Italy, as well as connecting the country from east to west. In total, the future high-speed line between Naples and Bari will be 145 km long, with 9 tunnels (including the Hirpinia Tunnel, approximately 27 km long, which will contend with the Valico Tunnel in Genoa for the title of Italy’s longest tunnel), 25 viaducts, and 16 new stations and stops. After completion, the Naples-Bari route will be covered in 2 hours, compared to the current approximately 4 hours, while the Rome-Bari route will take 3 hours. The project will also promote the interconnection of the Southern railway infrastructure with the Core Corridor “Scandinavia – Mediterranean”, leading to an improvement in the integration of the railway route with facilities dedicated to intermodality and logistics, thus enhancing freight traffic connections between Southern Italy and Northern Europe.