ABSTRACT
The paper describes the case of Lercara tunnel in Sicily (Italy) belonging to Palermo–Agrigento railway line. Lercara is a single-track tunnel, 10 m in diameter, with a total length of 2800 m, a maximum overburden of 150 m, excavated with conventional methods in clay formations. The excavation began in 2006. As soon as the excavation reached the central part of the stretch, unexpected convergences caused shotcrete cracking, producing the deformation of steel ribs and failure mechanisms. Besides, due to unexpected levels of gas emission, in 2009 works were interrupted by the authorities. In 2010 the new project design was assigned to Italferr with the aim of solving the critical issues emerged. The tunnel excavation re-started on April 2014 and successfully completed on August 2016: all the construction phases were accompanied by an intense program of monitoring about the effects of the tunnel excavation and the presence of gases.
