ABSTRACT
The construction of Pavoncelli bis tunnel, started in 1990 and stopped after about 580 m (5% of the route) due to uncontrollable groundwater flows that imposed work’s abandonment, was completed in October 2017. This paper describes the innovative solutions that allowed for tunnel completion by solving complex excavation problems, hence opening new perspectives for small diameter TBM-EPB tunnelling in difficult ground conditions. Thanks to a new construction design, which introduced several innovative solutions, in 2014 Caposele S.c.a.r.l. resumed tunnelling works with a small diameter TBM-EPB (4.6 m), successfully facing the difficult geological, hydrogeological and geostructural conditions (faults, continuous and important methane gas and water inflows from the surrounding formations). Pavoncelli bis construction was made possible thanks to the study, design and implementation of innovative technical, technological and procedural solutions to: (I) guarantee high advance rates and maximum safety conditions in the excavation through gassy formations, thanks to special ATEX equipment, a novel gas drainage system and specific safety procedures; (II) rescue the TBM-EPB from the stoppage determined by crossing a regional fault and in presence of firedamp.
