The lot involves the motorway construction works from km 0.00 to km 4+155, near the municipality of Courmayeur, allowing the elimination of the traffic passing through the urban areas.
The section includes an open-air section, between S.S. 26 in the area of Entrèves and the entrance to the “Dolonne” tunnel, and an underground section as far as the Lallà viaduct embankments, a work which is part of the next lot, downstream of the urban area of Courmayeur.
These works were conducted in a particularly delicate section from a geological-geotechnical aspect, in moraine ground directly below the Mont Blanc tunnel piazza. The works required prior Berlin type consolidation works on various levels and the construction of large diameter structural shafts in the centre section in order to stabilise the excavation fronts with regard to the deep sliding surfaces.
The entire open-air section has been protected against the risk of avalanche through the construction, upstream of the Val Veny cableway, of a reinforced earth dune topped with an avalanche protection structure and, downstream, of an avalanche prevention barrier.
The section passes through the route of the Dora di Veny River through two viaducts respectively 270 m long on the right side and 290 m on the left side. There are three spans, with the middle one being 110 m, in order to minimise the number of piers in the river bed.
In order to protect users in the case of avalanches, a bridge-tunnel solution has been adopted with the transverse section shaped like a hut, with the edges of the roof sloping (28° for the internal slope curve and 23° for the external slope curve).
The metal structure weighs approximately 5,785 tons in total.
From the bridge over the Dora di Veny you reach the entrance to the man-made tunnels (which are the extension of the two bores of the “Dolonne” tunnel), 129.95 m long on the left side and 102.80 m on the right side.
The Dolonne tunnel has two arches, respectively 2,847 m long on the left side and 2,902 m long on the right side; each bore features a section which has a structure with an internal spherical cap radius of 5.50 m. Taking into consideration the length of the tunnel and the aim of improving operating safety, six areas for the recovery and parking of vehicles have been included, located at a reciprocal distance of 750 m uphill and 1,200 m downhill.
The excavation of the tunnel took place using traditional methods, employing explosives in the rock sections and mechanised excavation in the debris and extremely fractured rock sections.
The waters in the Dolonne tunnel were disposed of through two cls D30 cm pipes positioned under the ground to side of the pavements. This way, as well as doubling the drainage capacity, any blockages can be repaired by closing only one of the tunnel bores.
|MAIN TECHNICAL DATA :|
- Excavations: 663,262 m³
- Excavations: 198,339 m³
A5 Mont Blanc-Aosta Motorway - Courmayeur- Morgex Section – Lot No 2