First application of the Pretunnel system for the construction of a tunnel in the high-speed railway line in Italy

The first Pretunnel application is a double-track railway tunnel, part of the new high-speed railway line under construction between Rome and Naples in Italy. The major constraints on the selection of excavation and support technique are presented by the low overburden (<10m) and the presence of a historical site along the tunnel route. The excavated ground consists of pyroclastic and tuffaceous material with medium to low cohesion and very low bearing capacity. To both minimise surface settlements and guarantee the stability of the excavation face, the jet-grouting arch technique was used. In the detailed construction phase, the Pretunnel system was applied. The basic concept of the Pretunnel, developed by Trevi, involves the execution of a structural lining in advance of the excavation phase. A slot of required thickness is excavated along the tunnel contour by a continuous cutting machine. This ingenious machine injects the concrete lining immediately after excavation of the slot. In the following sections the site geology is described along with the characteristics of excavation system: the slot-cutting machine and the sequence of construction phases.