Rhône Canal Modernization, Sète, FR | 2012

This ambitious project is not only economically significant, but also environmentally important. The canal runs through sensitive areas along its route that must be preserved during the works, such as the Hérault coastal ponds, the wetlands of the Gard Camargue, and classified sites.

The work related to the Aresquiers crossing zone began in October 2011 for a duration of approximately 16 months. The verticalization of the banks will locally widen the navigation rectangle to 34 m from the canal ceiling over a length of 650 ml on the left bank and 540 ml on the right bank. The transit of larger commercial boats will increase from 900/1000 tonnes today to 2300/2500 tonnes.

A bit of history... Under the reign of Louis XIV, Vauban and Pierre-Paul Riquet respectively undertook the construction of the port of Cette (Sète) and the Canal du Midi. While wealth was developing in the west of the province, the decision was made to develop the eastern part with a navigable canal to connect Sète to the Rhône. The current Canal du Rhône à Sète is the result of the merger of the three former canals: Etangs, Radelle, and Beaucaire.

The presence of an indurated horizon (limestone and marl) at a shallow depth (about -8 m NGF) directed the choice of the bank support type towards a combined wall solution. The support curtain is made from steel tubes and 3 intermediate PU 10R steel sheet piles. The tubes constitute the main elements of the mixed wall; they take the horizontal forces corresponding to the earth pressure and hydrostatic pressure as well as the vertical loads of the structures. The intermediate sheet piles transmit the horizontal forces to the tubes.

The first excavation phase involved purging the bank rocks within the curtain's footprint. Then, the curtains were implemented using two driving workshops, one on land and the other on a barge. After installing the two-level driving guide, driving was carried out in the following order: one tube, 3 intermediate sheet piles, then 1 tube, using a PTC 25 H2 vibratory hammer and an ICE 416 both mounted on a cable crane. The tubes are then anchored at the bottom, at the level of -10.0 m NGF on the left bank and -9.5 m NGF on the right bank, using a diesel Delmag D22 pile driver. In the more strongly indurated area to the west of the bridge, drilling inside the tube is necessary to reach the design level. The verticality of the wall is constantly monitored during the driving operation. 

To ensure a 50-year service life for the structure, the sheet piles are coated on one side and along their entire length with an ACQPA anticorrosion paint system of the Im2A NI 631 type. The tubes are protected by this paint system for a length of 5 m.

After trimming the curtain, a reinforced concrete coping beam is constructed at the top of the wall. To integrate this element into the protected environment (classified site), a bush-hammered concrete facing was implemented. Cast steel mooring bollards and elastomer fendering will complete the structure. Throughout the construction period, navigation on the canal is maintained. 

The work was interrupted on April 1, 2012, to ensure the tranquility of the colony of Mediterranean coastal heritage birds for whom this area is the main nesting site. Work resumed on July 31, 2012.