A new Cayenne River crossing in French Guiana

Egis has been awarded the programme management contract for the Larivot Bridge between Macouria and Matoury (near Cayenne), a structure that is outstanding in both its size and is environmental setting.

Built on behalf of the French Guiana Environment, Planning and Housing Directorate (DEAL), this new crossing will run alongside the existing bridge, as part of the DEAL’s plans for the redevelopment of highway RN1 between Balata and the RD51 junction. Egis is also conducting the preliminary studies for this project.

The initial design of the bridge was produced by the consultancy Lavigne-Chéron Architectes and the CEREMA.

The new bridge will measure 1,312 metres in length. It will carry two lanes of traffic running from Cayenne towards Kourou (the old bridge will carry traffic running in the opposite direction) and a segregated lane for bikes and pedestrians.

It will be made of a pre-stressed concrete box deck. Depending on whether the chosen height of the deck is fixed or variable, the deck will be supported by 19 or 20 piles sunk into the riverbed and in the mangrove swamp on the riverbanks.

Soil, wildlife, marine environment: technical and environmental factors

The construction of the new Larivot Bridge, located in the remarkable natural site of the River Cayenne and close to the Atlantic Ocean, involves a number of challenging technical and environmental factors: the presence of mangrove, protected fauna and flora, tides, a rainy season, a particularly corrosive environment for concrete, highly compressible soils, a very resistant, abrasive and highly irregular granite bedrock, and the relocation of high voltage electricity pylons.

To deal with these requirements, Egis will deploy all its relevant expertise in the fields of the environment, geotechnical engineering and geology, but also in materials, earthworks and road surfacing.

The programme management assignment, scheduled to last for five years, include the optimisation and finalisation of detailed design drawings (to be performed using BIM), the award of works contracts and the supervision of construction works. The project is due for delivery in 2023-2024.