Each Tunnel, 950 meters long, excavated by mining methods with maximum overburden above tunnel crown of about 45 meters is a twin tube tunnel 9.2 meters wide and 9.3 meters high, having shape of a horseshoe with a slightly rounded invert; the distance between the walls of the twin tunnels is 15.3 meters, that is 24.6 meters between the two axes.The excavation area of each tube ranges between 78 and 89 square meters.
The first phase lining is made of radial steel bolds placed at the crown, steel ribs and a reinforced shotcrete layer of 15÷20 cm. The totally waterproofed final lining has an uniform thickness along the tunnel, equal to 30 cm at the crown and at the invert, while at the sides it becomes variable up to approx. 60 cm.
The twin tunnels are connected with by-passes each 250 meters where all service systems are lodged; in case of fire the by-passes serve as a safe place and as emergency exits.
Particularly interesting is the eastern portal of the tunnels, where it was impossible to approach from outside, hence the portal was created by underground excavation up to the end of the tunnel. In this area there were some issues due to the morphological formation and to the presence of rock blocks possibly unstable while opening the portal. In order to govern this kind of problems, before opening the portal using underground excavation, an hexagonal mesh wire-net was placed on the slope anchored to the ground and a protection against falling rock blocks was placed at the boundary of the involved area.