ABSTRACT
After decades of failed attempts, the excavation of the 8.5km long Pavoncelli Bis water tunnel in Southern Italy has been successfully completed by the Joint Venture formed by Ghella S.p.A, Vianini Lavori S.p.A. and Giuzio. The tunnel is one of the largest and most important underground civil works in Southern Italy, with its variety of grounds and tectonic movements. It has probably been one of the most challenging excavations, completed without any accident or injury. The main strategy has been the selection of an extremely sophisticated Earth Pressure Balance Tunnel Boring Machine (EPB TBM)specifically designed to accommodate the variety of grounds: compact limestone, chaotic rocks such as the Flysch of Materdomini, multi-coloured clays with swelling characteristics and heavily tectonized sandstones as well as compressing grounds. The tunnelling teams have coped with large amounts of methane, some of it at pressure, and significant inflows of water. The precast segments have been designed specifically to cope with compressing ground, high-water pressures and an area subject to seismic activity. During the initial phases of excavation, the presence of methane proved to be not occasional as expected, but quite constant and larger than foreseen. This has required quick adaptations to the boring machine together with a newly studied safety procedure, allowing excavation in presence of gas.
