ABSTRACT
In the frame of the high speed railway line Napoli-Bari, it is foreseen the realization of a cut and cover tunnel which partially develops below the ground water level. The top down construction will be performed using the compressed air in order to achieve a dry base during the soil excavation and the cast of the internal structures. All the benefits of this technology are discussed, including the aspects related to the environment. The practical application of the technique has revealed numerous detailed problems from a structural point of view: together with the additional load on structures, the limitation of the air losses has been a relevant topic. The measures implemented for the maintenance of the prescribed pressure are presented in the paper describing the solution developed to minimize the dissipation of compressed air through production joints. The air losses are estimated after a brief survey of the formulations available in literature.
