The Gravagna Viaduct was designed in the 1970s as a prototype high-span bridge, connected by a Gerber saddle.

The truss spans and the consequent construction system with cantilevered advancement by successive segments, were chosen following a study of the area and the observation that the ground on which it rests is generally in motion, except for some areas where it was planned to position the piers.

In 1993, following local interventions, extraordinary maintenance was carried out in order to guarantee the practicability of the work and the restoration of its full efficiency since, already at the end of the original construction works, the performance response was not in line with the design forecasts, so much so that specific monitoring was required.

The unique renovation work carried out made it possible to cope with the vertical loads acting on the viaduct by means of large steel portals whose imposts, as they move apart, rest on the same bases as the piers. Metal reinforcements placed in twin alignment on the axis of each carriageway, provide elastic support to the three intermediate spans.

The renovation of the Gravagna Viaduct also aimed to pursue innovation in the field of static restoration of large road structures by preserving the decks and ensuring, during construction, minimum traffic interruption times to protect users and operating needs.

Photos of the first restoration, planimetry and viaduct elevation with arches and arch details.

Action was taken on the viaduct again in 2001 when the slab was reinforced transversally by laying reinforced concrete screed in order to be able to install new safety barriers. In another intervention dating back to 2006, the lateral approach spans were rebuilt with new decks in a mixed steel-concrete structure; the intervention was necessary because of the interaction between the deck and abutments at the parapets, which showed critical issues in particular on the La Spezia side abutment, located, like the rest of the viaduct, at the paleolandslide called San Rocco.