Confortement de digue. Saint-Laurent-du-Var | France

Reinforcement of the dike to protect Saint-Laurent-du-Var from floods

The State and the Departmental Council of Alpes-Maritimes (CD06) signed a convention in July 2009 on the Flood Prevention Action Program (PAPI) of the lower Var River valley. This first PAPI made it possible to carry out and engage in the most priority protection work. Action 5.5 of PAPI 1 provided for the protection of a priority section of about 500 meters to contain overflow for a reference flood of Q = 3,800 m3/s. 

The linear protection consisted of creating a 1 meter high dike, resistant to overflow and erosion. The approval of the Flood Risk Prevention Plan (PPRI) in April 2011 highlighted the need to review the protection of Saint-Laurent-du-Var. In this sense, Action 7.2 of PAPI 2, signed in October 2013, aims to protect the dike over an additional 1,100 linear meters.

The work concerns nearly 2,000 inhabitants, an artisanal activity zone, sports and cultural facilities, and the city center. The reinforcement of the Saint-Laurent-du-Var dike is part of the complementarity of the embankment system on both sides. 

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Coupe type Confortement de digue
Retouchée_Saint-Laurent-du-Var, France_Digue
Détail ancrage excentré
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The reinforcement work on the dike marked by the metropolitan road 95 represents a length of 1.6 km. The reinforcement is carried out using a double curtain of sheet piles for sectors with sufficient footprint: AZ 23-800 from 12.7 m to 14.5 m in the main curtain and AZ 18-800 from 2.5 m to 7.5 m in the anchor curtain, in steel grade S 355 GP, for a total of 2,315 tonnes. 

The distance between the two curtains is 12 m, and the tie rods are installed with a spacing of 1.6 m. The reinforcement extends from the Jean Aicard roundabout parking lot upstream to the Pierre de Coubertin roundabout downstream, and must ensure the stability of the protection structures against the risk of rupture (external erosion, internal erosion, overflow, and overall instability) for an exceptional flood of Q = 5,000 m3/s.

The reinforcement work on the dike marked by the metropolitan road 95 represents a length of 1.6 km. The reinforcement is carried out using a double curtain of sheet piles for sectors with sufficient footprint: AZ 23-800 from 12.7 m to 14.5 m in the main curtain and AZ 18-800 from 2.5 m to 7.5 m in the anchor curtain, in steel grade S 355 GP, for a total of 2,315 tonnes. The distance between the two curtains is 12 m, and the tie rods are installed with a spacing of 1.6 m. 

Initiated in July 2016, the reinforcement of the banks also included the implementation of protections with riprap and gabion mattresses, the redevelopment of the outlets of the rainwater hydraulic structures, and landscaping, creating a green space along the entire dike.

The pressuremeter tests showed a layer of fill with low to medium mechanical characteristics, followed by a layer of alluvium made of gravel and pebbles in a sandy matrix. The values of the limit pressure of this layer were higher than 3 MPa and exceeded 5 MPa in some places.

Another specificity of the construction site was the installation of an eccentric anchorage with GEWI bars with a diameter of 32 mm, requiring a particular design based on a calculation method developed by ArcelorMittal in collaboration with the Institute of Steel Structures of the Civil Engineering Department of the Polytechnic School of Aix-la-Chapelle. The work began in 2016 and was completed in 2017.