New railway bridge at km 0+229 of the Cuneo Gesso – Mondovì railway line, replacing the one previously damaged by flood events.

Project objective

This project concerned the reconstruction of a railway bridge with three arches and a composite structure made of brickwork and stone “bolognini”, largely collapsed due to a severe flood event.
As emerged from the hydraulic studies performed, with regard to flow conveyance issues the original structure was adequate under the current regulatory framework, but it was not verified with respect to scour of the in-river piers (in the absence of deep foundation elements).

Main works

Structure of the new bridge
The geometry of the original bridge was essentially replicated, with three arch spans of 26.0 m clear span; arches, piers and abutments are in reinforced concrete.
The piers feature a variable cross-section with a shape that facilitates flow conveyance; their height from the foundation footing level is 9.00 m.
The deck was built by placing self-supporting precast arch elements, in order to minimise construction time and occupation of the riverbed.

Abutments
In order to limit as much as possible the extent of the excavation area and to preserve and secure the building and structures located immediately upstream of the Cuneo-side abutment, adequate pre-support works for the excavation faces were designed, consisting of Berlin-type retaining walls; this also allowed traffic to be maintained on the private road on the left bank.

Foundations
To cope with the significant scour depth of the in-river piers predicted by the hydraulic study and to secure the foundations, caisson foundations were adopted, with a sub-foundation realised using soil column consolidation (jet-grouting), surrounded by a waterproofing ring made of interpenetrating columns, in combination with a small-diameter pile wall required both for excavation of the caissons and as protection against scour.