Currently under construction, the Nouvelle Route du Littoral (NRL) in Reunion Island will be one of the most important road infrastructures in the world. The flagship structure of this multimodal communication axis, the viaduct is a remarkable 5.4 km structure intended to link Saint-Denis and the Grande Chaloupe along the coast at more than 20 meters above water level.
Cadden won, in March 2016, the call for tenders relating to the monitoring system for the laying of the piles of this gigantic sea viaduct, the largest on French territory.
The deck of the structure will be based in particular on 48 sea piers, each made up of several elements. These are, one by one, transported and placed in their final location by a self-propelled and self-lifting barge with extraordinary dimensions specially designed for this Reunion site.
The operations of laying the piles from the overhead crane of the barge present in particular two types of constraints. The first concerns the level of positioning requirements: absolute precision to within 8 centimeters and perfect verticality, for massive pieces placed on the ocean floor at a maximum depth of 17 meters. The second stems from the need to bring together all the measurement sensors on the barge in order to dispense with measurement or control equipment from the ground, for many reasons: to secure the measurement system, to maintain it more easily, move it as construction progresses …
To meet this double challenge, Cadden proposed an original solution never implemented before, based on a total laser station (laser tracker) compensated in attitude and orientation and georeferenced in RTK (Real time kinematic). Mounted at a point on the barge, this system points to a staff placed on the deck pier element to be installed and measures its displacement with absolute centimeter precision. Integrator of the complete system, the Nantes-based company has also developed a special interface for dialogue between the stack and the barge, including control tools, real-time visualization of the position deviation from the theoretical position and calibration tools.
Guarantor of the proper functioning of the system and of the final contractual precision, Cadden intervened on site at the end of July for the turnkey delivery to the consortium holding the sea viaduct contract (VINCI Construction Grands Projets, Dodin Campenon Bernard, Bouygues Travaux Publics and Demathieu Bard Construction) and user training.
Started in August, the pile installation operations will be spread over 2 years, at the rate of 2 piles installed per month on average. The first measurements show a positioning accuracy of +/- 5cm, in accordance with the initial need.
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