ABSTRACT
The D&B contract realized by Società Italiana per Condotte d’Acqua is part of the largest infrastructure project in Norway, named Follo Line. It includes the construction of several tunnels in hard rock (gneisses) in an urban site and it has required a large use of special excavation methods, like the Drill & Split; furthermore, the great attention to minimize the excavation effects on the water table, demanded a great use of high pressure cement injection named pre-grouting. Other challenges were the excavation of a large cavern of over 400 sqm with variable geometry, named Three Track Tunnel as well as many important interferences with existing underground infrastructures like the Oil Depot (17 big caverns in which petrol and others oil products are stocked), the Alna river tunnel and the E6 Motorways Tunnels. These interferences required other special works like water curtain and the installation of temporary big steel pipe in the Alna river tunnel.
