Restoring hydraulic functionality: the ameliorative GRP solution chosen to ensure strength and durability

The new project for the restoration of the hydraulic functionality, commissioned by the contracting authority Consorzio di Bonifica Friulana to the design of Ing. Blasone and to the construction company Adriacos srl with the support of P-TREX, is located in Fossalon di Grado (UD) and, due to the peculiarity of the context, represents an important turning point in the implementation of GRP applicative solutions.

 

 

Fossalon is a fertile agricultural area created by land reclamation in the first half of the 20th century. The hydraulic network and the Vittoria water drainage system (designed in 1908 and built in the 1930s) were built to ensure water retention during heavy rains, prevent hydrogeological instability, and encourage agricultural activity, representing a significant state intervention for the entire area.

Due to its conformation, the basin requires a water collection network made up of artificial earth canals (main and secondary) that are able to collect and remove rain and surface water and convey it to the mechanical lifting plant located in the most depressed area. Here the plant lifts and discharges excess water over the embankment toward the sea.

The urbanisation that began in the second half of the last century and climate change have led to an increase in flood flows, with the acceleration of landslide phenomena resulting in the slopes sliding towards the canal’s bottom.

 

The removal of the sediment from the canal’s bottom is indispensable to ensure the functionality of the entire hydraulic system. In fact, earthen artificial canals require continuous maintenance, removal of bottom sediment, and consolidation of the embankments.

Moreover, in the Vittoria basin, which is rich in natural mercury, sediment management is particularly problematic since it can only be reused within the same water body to improve the watercourse’s hydraulics and management, with a view to a circular economy.

 

Geotechnical-structural design in response to authority expectations

The basic design hypotheses envisaged the re-profiling of the edges of the collector canal of the plant’s arrival basin, originally modelled in earth and subject to local landslides and instability, through the construction of an edge piling to contain the upstream soil and at the same time allow for dredging of the canal bottom to bring it back to the original hydraulic levels.

The intervention, approximately 640 m long and planned on both banks of the canal, consists of the construction of a double wooden piling; in the tender design, the displacement resistance at the head of the two rows of piles was obtained with a metal structure connecting and distributing the piles’ heads.

In the interspace between the two pilings, after the placement of a geotextile sheet, is placed the soil reclaimed from the excavation of the canal bottom; the same is provided upstream of the retaining structure, in order to restore the original soil profile near the edge of the canal.

 

 

The originally planned metal partition structure was made of weathering steel, consisting of longitudinal beams straddling the two rows of piles, transversally connected.

During the tender, among the evaluation criteria of the Technical Offer, was precisely evaluated the possibility of providing an improved solution “for the realisation of the transversal connection between the two pilings with respect to the protection against corrosive phenomena and towards aggressive agents considering the environmental conditions of the work (atmospheric agents, presence of water, contact with the ground, etc.)”.

The solution that has been awarded by the contracting authority (Consorzio di Bonifica Pianura Friulana) is the one proposed by the Contractor Adriacos S.r.l. of Latisana (Ud) through the use of GRP profiles under the P-TREX brand produced by FIBRE NET S.p.A., as it provides a guarantee of durability as well as meeting the project’s resistance requirements.

 

 

Conclusions

It can be pointed out that:
– the structural geotechnical solution adopted was much more economical than traditional systems, considering also the exponential cost of wooden piles with lengths of more than 8 metres (in these soils the lengths were around 12 metres);
– the solution of reusing the sediment, in a circular economy perspective, transformed it from a “problem” into a resource;
–  the use of innovative tie rod materials has eliminated the problem of corrosion of classic metal anchors by increasing their durability and offering effective head protection;
– Protecting the GRP connection beam (installed with the flanges upwards) with a wooden trunk combined with the excellent mechanical properties of the profiles, also allows the transit of mechanical vehicles above the structure, minimising the costs of watercourse management;
– the prefabrication of the tensioning system allowed for more than a halving of the construction time, resulting in lower costs;
– the ‘weak’ element of the system, which determines the service life of the entire construction, remains the wooden part in the foreshore area.

 

 

Authors: Ing. Massimo Blasone, Ing. Maurizio Ventulini, Ing. Enrico Zanello

The article, of which this is an excerpt, has benefited from the technical contribution to the drafting of the structural and geotechnical designer Massimo Blasone, the Deputy Technical Director of the Friulian Land Reclamation Consortium, Engineer Maurizio Ventulini, and Engineer Enrico Zanello, P-TREX Technical Office Manager.