Hydraulic reconfiguration and risk mitigation works for the terminal reach of the Rio Ranzi, including construction of a reinforced-concrete box culvert to increase hydraulic capacity along the Genova–Ventimiglia railway line, in the Municipality of Pietra Ligure (SV).

Project objective

The intervention aimed to mitigate the previous hydraulic risk conditions affecting the terminal reach of the Rio Ranzi between the roundabout on SS 1 “Via Aurelia” and the sea outlet, where the stream crossed the Genova–Ventimiglia railway line beneath a masonry arch underpass with a clear width of 5.50 m.
A general widening of the channel cross-section along the above reach was therefore designed, together with construction, alongside the existing structure, of a new reinforced-concrete box culvert to be installed using the “jacked monolith” technique.

Main works

Reinforced-concrete box culvert
Reinforced-concrete box structure, 16.80 m long, with finished internal clear dimensions of 4.00 × 2.60 m; slab and side wall thickness is 50 cm.
Cast off-line upstream of the railway and subsequently jacked beneath the railway formation by hydraulic pushing, after installation of temporary steel girders type “Verona” supporting the tracks resting on handling beams.
Additional temporary works were required as preparatory measures for construction of the box and its subsequent jacking, and were removed at completion (reinforced-concrete base slab with guide profiles, reaction block, temporary shoring wall protecting the railway embankment).

Embankment walls
With alignment constrained by the presence of adjacent buildings on both the left and right orographic banks, the works required prior execution of temporary micropile shoring walls supporting the excavation faces, either founded on them or used as their front facing.
Additional L-shaped retaining works were provided at the inlets/outlets to close the gap between the box culvert and the abutments of the existing underpass and to tie in with the already-existing retaining walls.