Upgrading and realignment of State Road No. 28 “del Colle di Nava” between km 130.4 and km 132.7.

Project objective

The road variant was constructed to improve ride quality and safety along the infrastructure, which carries a high volume of heavy vehicles travelling to and from the Alpine pass of “Colle di Nava”, connecting the Liguria Region with southern Piedmont.

Main works

Tunnel “Madonna degli Angeli”
The excavation, approximately 676 m long, affected a rock mass locally characterised by very poor geomechanical properties; to overcome these conditions, also with low overburden, specific construction measures were required to ensure safe excavation, adopting a half-section advance method with pre-consolidation works.
For the excavation faces at the portals, given the presence of cover deposits and altered rock horizons, stabilisation works were required consisting of anchored retaining walls with tiebacks.

Viaduct over the Impero stream
In the section between the south portal of the tunnel and the end of the lot, a viaduct over the Impero stream was built (Viaduct “Impero 1”, L = 268 m, 9 spans).
The viaduct deck consists of precast prestressed reinforced-concrete beams, with reinforced-concrete piers and abutments.
For the foundations it was necessary to adopt piled foundations (indirect foundations).

Interchanges
For the two interchanges, one near the north portal of the tunnel and the other at the end of the lot, earth-retaining works were built consisting of reinforced-concrete retaining walls and a two-span bridge (Viaduct “Impero 2”, L = 60 m).
For the foundations it was necessary to adopt piled foundations (indirect foundations).