Excavation of an artificial tunnel using compressed air

The High Speed/High Capacity (HS/HC) railway line between Naples and Bari is currently under construction in Southern Italy. The Napoli-Cancello stretch, at the beginning of the line, includes the Casalnuovo artificial tunnel, excavated through coarse-grained uncemented pyroclastic soil, mostly under the ground water level. The excavation will be carried out using a top-down approach, with the aid of compressed air to counterbalance the pore water pressure. This technique was chosen as an alternative to dewatering or execution of jet-grouting columns due to its reliability, flexibility and negligible impact on the pre-existing pore pressure regime. The design of the Casalnuovo tunnel excavation using compressed air is presented in this paper.