Under the port of Genoa, the largest in Italy, there is a machine that aims to devour the sea floor meter by meter. And it does so from the bowels of the earth, 45 meters deep and without interrupting the traffic that passes above it every day. The key is a 16 meter diameter tunnel boring machine that is drilling into the seabed like butter. This is how Italy is solving one of its most entrenched mobility problems, and in the process building the first underwater tunnel of the history of the country.
A problem that has been unsolved for decades. Genoa is a city trapped between the Mediterranean Sea and the foothills of the Apennines. It has no room to grow. Its historic center is a labyrinth of narrow streets, and east-west traffic has always been a headache. The solution adopted in the 1960s was to build a gigantic elevated highway, the Sopraelevata Aldo Moro, which crosses the city like a concrete scar.
for her About 80,000 vehicles pass through each daybut at a high price: it blocks the view of the sea, generates constant noise and, for many citizens, is a barrier that separates the city from its own port. Its demolition has been stalled for years because no one knows what to do with that traffic in the meantime.
Tragedy. The tunnel project was born from an agreement between Autostrade per l’Italia, the Italian Ministry of Transport and local administrations as compensation to the city after the collapse of the Morandi bridge in 2018. That collapse, which claimed 43 lives, left Genoa without one of its main accesses and put the highway concessionaire company under the spotlight.
As part of the repair agreement, signed in October 2021, Autostrade per l’Italia, the Liguria Region, the Western Ligure Sea Port System Authority and the Municipality of Genoa agreed to build this underwater tunnel. It is, in practice, the great work of compensation for a city that suffered a tragedy.
What is being built. The total route is 4.2 kilometers, of which 3.4 run under the sea floor. It will consist of two separate galleries, one in each direction, each 16 meters in diameter, and will reach a maximum depth of 45 meters below sea level. When completed, it is expected to be Italy’s first underwater tunnel, the largest in Europe (with pardon is being built between Germany and Denmark) and the fourth largest in the world by diameter. Next to nothing.
The key: a Hydroshield TBM. Excavating under an active port without interrupting its activity is a monumental challenge. The solution is a TBM tunnel boring machine (Tunnel Boring Machine) Hydroshield type. Each of the two main galleries will be constructed by mechanized excavation with a Hydroshield type back-pressure armored TBM milling cutter, with an excavation diameter of approximately 16 meters.
Why this type and not another? In a Hydroshield TBM, the balance in the excavation chamber is maintained through the pressure of water or bentonite slurrywhich stabilizes the excavation face. The extracted material is mixed with these sludge and transported to the surface through pipes. It is the ideal technology for unstable terrain with the presence of water: it allows you to continue drilling without the sea floor crumbling and without the sea entering the gallery. The port above is still working.
The gallery measures 15.4 meters in diameter on the outside, but the useful space for circulation is somewhat less, 14.3 meters, because the walls are considerably thick. These walls are built by assembling prefabricated pieces of concrete, as if they were the staves of a giant barrel, joined together with screws and sealed with rubber gaskets so that water does not enter.
As if that were not enough, an additional layer of concrete is added inside that further reinforces the impermeability, especially in the sections that are just below the port. The result is a practically airtight tube capable of withstanding the pressure of the sea on its walls.
lto logistics of the work. You can’t just place a tunnel boring machine on the seabed and run it. First you have to prepare the ground. The tunnel boring machine was thrown from an attack pit in the San Benigno areaon the west side of the city. To free up that space, Autostrade first had to move a port railway line that ran through there. The railway route, about 700 meters long, has been moved about 70 meters to the south with respect to its previous position, running parallel to the port sopraelevata until passing under it in its final section.
Deadlines. Preparation works started in 2023, and work began in March 2024. However, the full tender for the construction of the two main galleries was not approved until January 2026. The specifications set a period of 75 months to complete the entire work. According to the latest Autostrade documents, the TBM will complete excavation work in October 2030, with full completion of the work planned for 2031.
Budget. The project started from a budget of 700 million euros, although the mayor of Genoa, Silvia Salis, confirmed that Autostrade now places the cost at more than 1,129 million euros. An escalation of costs that, according to the original agreement between the parties, is covered by a mechanism linked to national highway tolls.
Transformation. When the tunnel is completed, it will allow the creation of new green areas (10 hectares, distributed in three public parks) and pedestrian routes that reconnect the city center with the sea. In the San Benigno area, on the new railway gallery already in use, the Lantern Park will be built, which will connect that sector with the city’s historic lighthouse through a bicycle and pedestrian path.
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