Safety of existing arch-dams [La sûreté des barrages-Voûtes existants]
Résumé
There are about a hundred arch dams in France, essentially built between 1935 and 1980. These elegant, often majestic, structures testify to the knowledge of a generation of brilliant engineers. These engineers dared to draw pure and thin lines by optimizing the material placement to reconcile the structures safety with the projects costs. The mechanical operating mode ideally depends on the transmission of the efforts to their foundation by mobilizing arch effects. So it seems safe provided that the rock supports resist. In practice the behavior of these structures is complex, especially for geometries which are far from the standard design: arch dams settled in wide or expanded flat-bottom valleys, unfavorable slopes of banks. Due to the number of projects becoming scarce (set apart in some countries), it is essential to assess the safety of existing dams taking into account incidents and accidents analysis of these structures, as well as experiences gained through their behavior analysis carried out for more than 50 years. These experimental lessons allow identifying the main failure modes, by distinguishing what come from a normal adaptation of the structure, from located cracks due to structure hyperstatic design, or from more global mechanisms. The present development of risk analyses and the regulatory requirements to take into account low frequency events require the search for analysis methods and if necessary for solutions (monitoring, remedial works) adapted to possible failure kinematics. In this context, a working group of the French Committee of Dams and Reservoirs, consisting of experts coming from consulting firms, operational groups and monitoring department, has introduced an approach centered on the analysis of the existing arch dams portfolio. This article presents the first results in terms of recommendations of behavior analyses, failure modes, performance criteria and adapted monitoring. In addition, Coyne and Bellier / Tractebel and Artelia, two French engineering consulting firms present their innovative practices on two specific topics, respectively: - concrete abutments behavior and modeling through three examples; - dam modeling taking into account the loading history on structures by “cyclic calculations”. The full text of this article is available in English: http://barrages-cfbg.eu/IMG/pdf/gtvoute_vienne2018.pdf. © 2018 ICOLD/CIGB, Paris, France.
Mots clés
Abutments (bridge)
Accidents
Arch dams
Arches
Concretes
Foundations
Lanthanum
Monitoring
Numerical models
Reservoirs (water)
Risk analysis
Risk assessment
Behavior analysis
Behaviour
Engineering consulting
Global mechanisms
Innovative practices
Performance
Performance criterion
Regulatory requirements
Structural design