en.Wedoany.com Reported - A 8.18-metre diameter Earth Pressure Balance Tunnel Boring Machine (TBM) manufactured by Terratec has been selected to excavate the final section of the Politeama–Notarbartolo Phase II contract for the Palermo underground metro in Italy. Equipped with 12 motors delivering a total cutterhead power of 1,320 kW, the TBM will complete an 817-metre tunnel drive beneath Palermo's historic centre.
After launching from the starting shaft, the TBM will advance along Via Malaspina, passing beneath Piazza Virgilio and Via Brunetto Latini. It will then negotiate one of the tightest curves on any metro project currently under construction in Europe—a curve with a 180-metre radius—to enter Via Paternostro, before finally breaking through at the Politeama Theatre. Terratec states that the TBM's ability to navigate such a small radius curve is due to an optimised articulation system, compact shield geometry, and a high-torque cutterhead drive capable of stable excavation even under asymmetric loading conditions.
The TBM's steering system precisely controls the thrust distribution across the shield and articulation joints, enabling smooth turning without imposing excessive stress on the segmental lining or causing significant ground disturbance. The Earth Pressure Balance working principle ensures face stability on curved sections by maintaining uniform chamber pressure and controlled spoil flow. To withstand the high lateral forces generated by small radius turns, the TBM incorporates a reinforced main bearing and a robust shield skin design. The back-up system and segment erection equipment are configured to handle the construction of lined tunnels on tight curves, including the installation of wedge segments where necessary, ensuring precise ring build and long-term lining integrity on curved alignments.
The drive also presents numerous additional engineering challenges. Beyond the small radius curve, the TBM must manage gradients of up to 1.45% uphill and 2.93% downhill, while passing directly beneath one of Palermo's most densely built-up and heavily trafficked urban districts, not far from the city's port. The geological conditions along the route are highly variable, comprising mixed formations of clay, silt, sand, and sandy gravel. Site preparation works are currently underway, with TBM launch scheduled for the second quarter of 2027.
Once Phase II is completed, it will close the Palermo underground metro ring, connecting Notarbartolo station with the port area and the historic centre at Politeama. The new line will provide a rapid urban connection between the city centre and the Passante Ferroviario, the strategic north-south rail line crossing Palermo from Palermo Centrale station to Falcone-Borsellino (Punta Raisi) Airport. Gianguido Babini, Production Director of D'Agostino Costruzioni, stated that the Palermo rail ring is one of Sicily's most anticipated public works. The project is expected to alleviate chronic urban traffic congestion for the city, improve air quality, and connect Palermo's strategic civic, cultural, and transport hubs.
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