The project to upgrade State Road No.260 "Picente", belonging to the "Rieti-Amatrice-L'Aquila-Navelli" itinerary, consisted in upgrading the current roadway, with platform adaptation to regulatory standards (Ministerial Decree 05/11/2001 type "C2"). In particular, Lot IV of this intervention, which extends for approximately 6.40 km from Marana to Cavallari, envisaged the design of a long stretch in tunnel below the Marana built-up area, and the execution of geological and geotechnical studies and surveys.
The Marana tunnel is characterized by a single tunnel tube with a single carriageway with one lane in each direction, an area (in section) of 130 sq.m. and an overall length of 1200 m (1140 m to be excavated). The remaining sections, in artificial tunnels, are located at the two entrance and have been designed considering the terrain morphology and in full compliance with environmental requirements. At the center, two parking areas were planned (one for each direction) whose the final position was adapted according to the presence and position of "good" rock masses.Continue
Parallel to the tunnel, at a distance of 18 m on the downstream side, an emergency tunnel is planned to guarantee the evacuation of the main tunnel in case of accident. The connections between the two tunnels are ensured by 4 pedestrian bypasses about 250 m apart. The emergency tunnel excavation will be carried out with a single-shaft TBM with an excavation 4 m diameter and lined with 20 cm thick prefabricated ashlars. The excavation will start from the southern entrance advancing northwards with a longitudinal gradient of 1.8% and a total length of 1'076 m. From a geological and lithological point of view, the tunnel mainly crosses Scaglia Cinerea rocky masses (marls with limestone in the lower layers) and of the Scaglia Rossa e Variegata (mainly marly limestone with flints) that alternate several times along the route. The Scaglia Cinerea first mass was identified only after the in-depth investigation campaign carried out in the context of the Final Design. The maximum coverage is about 100 m in the sections characterized by Scaglia Rossa and 60 m in those with Scaglia Cinerea. The excavation inside the Scaglia Cinerea masses is planned with an umbrella of threading with pre-consolidation of the excavation front. Within the Scaglia Rossa, a cylindrical section of the first phase is planned with shotcrete, radial bolting and ribs; in the fault sectors, consolidation involves the use of fiberglass bars longitudinal to the face, again with a cylindrical section.
The portals of the Marana tunnel and the relative emergency tunnel were built (totally or partially) in a trench with tie-rods anchored to a micropiles line to stabilize the slope. The portals are completed by artificial sections that were then filled in, thus restoring the slopes original morphology. Finally, the southern entrance was designed to ensure the necessary space for a bicycle path and a plant room at the service of both the main tunnel and the emergency tunnel.
Marana Tunnel (Length 1'200 m, of which 1'140 m excavated): single tube tunnel (A=130 sq m) with two parking areas in the middle. The emergency tunnel is connected to the main one by 4 bypasses. The portals are realized in trench with tie-rods anchored to a micropiles berlin.