The terrain that characterizes the surroundings of the Sicilian city of Catania is unique due to the omnipresence of Mount Etna. The eruptions over time have shaped a capricious and highly variable subsoil.
In this environment, we will develop a major railway project: the Metropolitana di Catania expansion, with a budget of nearly 800 million euros. The extension covers almost 14 km of line, of which eight and a half are underground sections of various kinds. This expansion will connect several towns in the metropolitan area.
Ferrovia Circumetnea (FCE), an agency under the Italian Ministry of Infrastructure and Transport, awarded SIS—a permanent consortium formed by Finninc (51%) and Sacyr (49%)—a section between the towns of Misterbianco and Paternò in September 2023, and in December 2024, a complementary section between Monte Po (Catania) and Misterbianco, connecting with the currently operational line.
This project will feature the use of a new and uncommon tunnel boring machine known as the Variable Density TBM (VD-TBM). Only about 20 machines of this type have been ever operated worldwide.
It stands out for its adaptability to the area’s changing geological conditions. Additionally, due to the frequent seismic activity generated by the volcano, it is necessary to comply with strict seismic standards for both permanent and temporary works.
“A few years ago, the city already undertook a metro project using a conventional TBM, and it ran into significant difficulties due to the unfavorable geological conditions”, explains Miguel Ángel Montón, tunnel manager for this project.
“The ground is extremely complex due to its heterogeneity; there are fissures, cavities, and frequent alternations between basaltic rock—lava—and softer soils. Our TBM is highly adaptable to current conditions; its operating mode can be changed on the fly using four different excavation modes, allowing us to respond in real time to the terrain. It is more complex to operate, but offers that flexibility”, Montón adds.
This isn’t the first time that Montón faces this kind of challenge, as he had a similar experience on Line 3 of the Guadalajara Metro (Mexico). “It was more complicated than usual, but not as challenging as this project,” he states.
The TBM began manufacturing in August 2024 and operational testing started in May this year. Disassembly and transport to the construction site are scheduled to begin in June, with arrival expected in July.
The heaviest components will be transported across the Alps using special convoys to the port of Ravenna (Italy), from where they will be shipped to Catania. The smaller components will be transported by truck to across the Strait of Messina to reach Sicily.
On-site assembly of the machine will take around three months, followed by approximately two weeks of commissioning and testing. Excavation is expected to begin by the end of December or early 2026.
“We will excavate around 5 km of tunnel with this TBM. The initial contract was for 3,200 meters, and with the most recent award, an additional 2 km were added,” Montón explains.