Reinforcement of the piers of the Stone Bridge

Context

The Bordeaux Stone Bridge is the oldest bridge in the city. It entered service in 1821 and remained Bordeaux’s only road bridge for nearly 150 years. Now an iconic landmark, its image has, over time, become inseparable from that of downtown Bordeaux.

However, the building is in danger: year after year, the bridge’s piers are sinking into the alluvial soils of the Garonne at a rate of a few millimeters per year. The river is also eroding the embankments around the piers, risking exposure of the foundations to strong currents and tidal forces.

To protect the bridge and ensure its long-term viability, Bordeaux Métropole has launched a new phase of work for the 2025–2029 period. This large-scale project involves:

– Reinforcing the bridge piers with drilled micropiles

– Restoring the rockfill protection along the piers’ banks

– Installing ring beams around the piers

– Repairing the bridge deck (waterproofing, drainage)

As part of a joint venture, Balineau has offered to install the rockfill protection, working alongside Solétanche-Bachy for the installation of the micropiles and Aevia (Eiffage Génie Civil) for the pile encircling, drainage, waterproofing, and road and utility infrastructure.

Location

Bordeaux, France

Client

Bordeaux Métropole

Project Management Assistant

Cerema sud-ouest

Project Manager

BG – 2BDM – VERDI

Joint venture

SOLETANCHE BACHY (mandataire)

BALINEAU

AEVIA – EIFFAGE GENIE CIVIL

Duration of the works

2025 / 2028

Works presentation

Balineau is therefore responsible for installing rockfill protection on the slopes around the bridge piers. The project will take place over four years (2025 to 2028) and calls for the placement of a total of 4,500 m³ of rock.

The purpose of the rockfill protection is to prevent the foundations of the bridge piers from being exposed to erosion. Over the long term, this erosion could create hollows around the piers, exposing the wooden piles and masonry, which would put the entire structure at risk of failure due to scouring.

Once they arrive at the bridge, the rocks are placed using an excavator equipped with a GPS system. The operator monitors the level and position of the rocks in real time and places them according to the plans provided by the 3D software.

Bathymetric surveys are conducted regularly to verify the correct positioning of the stones and to update the 3D model by indicating the areas where material needs to be added or removed.

The work requires great care and a thorough knowledge of the area, as the current between the bridge piers can be particularly strong. Coordination has also been established with river users to manage navigable passages. Finally, a permanent flood monitoring system has helped protect against various river hazards.

Historique

In 1996, Balineau helped reinforce piers 7 through 11 by installing gabion mattresses.

In 2004, during the preparation of piers 8 and 9 for the barges transporting A380 aircraft components, Balineau constructed four protective breakwaters around the piers.

In 2018, Balineau participated in a major repair project for the riverbed slopes, which involved, in particular, the installation of gabion mattresses.