Terzo Valico Project: Geological challenges and solutions in high‐speed railway tunnel construction

In the realm of modern infrastructure development, tunnels play a key role, serving as vital channels for transportation, utilities, and various other applications. Ensuring the successful construction and operation of tunnels is dominant in maintaining the efficiency and safety of these essential passageways. However, challenges arise when tunnels intersect with the intricate geological characteristics of the surrounding rock mass, particularly in tectonic regions. The stability and performance of tunnels can be significantly affected by various factors, necessitating a thorough understanding of their behavior when excavated within complex geological structures, such as those at the Alps–Apennines contact zone. In these areas, the energy accumulated from tectonic‐induced stresses can play a crucial role in tunnel design and construction, influencing stability conditions and determining the most appropriate excavation and support strategies. The article examines the construction of the Terzo Valico dei Giovi high‐speed railway line, focusing on the geological challenges encountered during tunnel excavation. Special attention is given to clay formations and complex tectonic zones that impact tunnel stability. The technical solutions adopted are described, including the use of high‐performance steel ribs equipped with a semiautomatic locking system, designed to counteract rock mass pressures, mitigate risks, and ensure safety. These engineering solutions were applied for the first time globally in a delicate tectonic passage between the Alps and the Apennines, known as the Sestri–Voltaggio Zone. Monitoring data analysis is conducted to assess the effectiveness of the various engineering approaches. Finally, the document presents a repair intervention carried out on a tunnel section that sustained damage due to the use of a deformable rib, which proved unsuitable for this specific context.