Confortement de digue. Darse de l’usine d’eau potable. Orly | France

Protecting Paris against flooding by strengthening the dock dike

EAU DE PARIS has been providing water to Paris for over 20 years from groundwater and river water taken from the Marne and the Seine before being treated. In 1961, the Paris city council decided to build a new surface water treatment plant to cope with the constant increase in drinking water demand. 

Inaugurated in 1969, the facility occupies 52 hectares on the banks of the Seine on the site of an old ballast pit. The originally flood-prone land was filled, except for the basins which, covering over 5 hectares, form a dock with a capacity of 300,000 m3 of water, providing the plant with 24-hour autonomy at full capacity in case of river contamination.

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To avoid long-term ruin, a new reinforcement project has been launched. It involves the implementation of a main sheet pile curtain and an anchoring curtain, each 390 meters long, capable of ensuring the stability of the dike for normal use and in case of Seine flooding with an empty dock, for a lifespan of 100 years.

In order to preserve as many trees as possible, additional geotechnical tests were carried out. These tests led to new, more favorable calculation hypotheses, which made it possible to bring the anchoring curtain closer. The chosen optimization includes AZ 36-700N sheet piles of 14.0 meters in the main curtain and AZ 17-700 sheet piles of 5.0 meters in the anchoring curtain, with the top of the sheet pile respectively at 20.5 NGF and 28.5 NGF.

The work involved filling the dock with water, excavating the dike path fill, and cutting or drilling the existing curtain for the installation of tie rods. Sheet piles were then driven using vibrators and pile driving was carried out when necessary. 

Tie rods were installed 2.5 meters apart, and the gap between the new and old curtains was filled with lean concrete. The final phase was the construction of a concrete crown beam and the dike was reconstructed to its original state. 

The project was completed between June 2012 and January 2013, using a total of 925 tons of sheet piles.