Construction of a new offshore road on geotextile reinforced embankment

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La Reunion - France

TenCate Geosynthetics

On Indian Ocean Island, La Réunion, the « Nouvelle Route du Littoral » is a 12 km offshore road, with more than 6 km long dike. This major infrastructure uses widely geosynthetic solutions: geotextile filter within the structure between different materials, and reinforcement geotextile in a 60 000 m² reinforced earth wall.

The old coastal road between Saint-Denis and La Possession, is regularly exposed to climatic hazards (southern and cyclonic storms) and rock falls from the cliff. A landslide occurred in 2006 and completely blocked the traffic on this axis. The new secure link from Saint-Denis (to the east) to La Possession (to the west), consisted of a mixed marine project alternating dikes (1450m and 5150m long) and viaducts (8400m and 300m long). The project is located at the foot of the cliff, at the sea, and in the erosion zone subject to southern swells.

The cliff side of the dikes is a stiffened slope, reinforced by TenCate Geolon® PET geosynthetic with mineral gabion facing. The reinforced slope acts as a support for the roadway and as a mean of retaining any isolated blocks in the event of a rock falls. It has a height between 9 and 15m, for a cumulative length of more than 6 km.

The design carried out according to the approach of the limit states defined by the Eurocodes must meet for the case of the fundamental Ultimate Limit States (ULS) and considering a work sensitive to deformations (SLS) due to its large dimensions, and the importance of the sustained traffic lane.

Different grades of TenCate Geolon® PET reinforce the dike, with a vertical spacing of 0.50m. Ultimate tensile strength varies from 100 to 400 kN/m and anchorage length from 5 to 15m, depending on their position in the slope. The reinforcement layers are wrapped around at the facing behind the mineral gabion cladding and then fully support the slope.

The use of geosynthetic reinforcement technique allowed the construction of a support structure of unusual dimensions combining reliability and implementation speed, meeting the sustainability and budget requirements of the project.

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