The concept of ageing of dams and their appurtenant works as a class of deterioration is presented. The major ageing scenarios concerning the rock mass foundations of concrete dams are indicated, with particular reference to scenarios of erosion and dissolution of rock masses, and of degradation of grout curtains and drainage systems. Methods developed to control such scenarios in Portuguese dams are referred to.
Le concept de vieillissement des barrages et leurs ouvrages annexes en tant qu'une classe de dete-rioration est presente. Les scenarios de vieillissement majeurs concernant les fondations en massif roeheux des barrages en beton sent indiques, avec une reference particulière a des scenarios d'erosion et dissolution des massifs roeheux, et de degradation des voiles d'injection et systèmes de drainage. Des methodes develop-pees pour contrôler de tels scenarios dans des barrages portugais sont mentionnees.
Das Konzept der Alterung der Talsperren und ihrer Nebenanlagen als eine Ver-fallsklasse wird vorgestellt. Die die Felsfundamente von Betonstaumauern betreffenden Hauptalterungsszenari-en werden angegeben, mit besonderer Erwahnung der Szenarien der Erosion und Lösung von Felsen, und des Verfalls von Injektionsschirmen und Dransystemen. Zur Kontrolle solcher Szenarien in portugiesisehen Talsperren entwickelte Methoden, werden angefuehrt.
Dams are important structures for water management, therefore their safety and performance is a major concern for those involved in their design, construction and operation. This subject has been also a major concern for the International Society for Rock Mechanics (ISRM), the International Commission on Large Dams (lCOLD) and other entities [1 to 7]. Dams should be safe, to prevent accidents and suited for the intended use, to prevent incidents. Safety and performance should be fulfilled along the lifetime (durability) at acceptable cost of construction, operation and maintenance [8, 9. 10]. Deterioration (accidents and incidents) may be caused by exceptional unforeseen events (floods, earthquakes. etc.) or may accumulate with time under normal operation conditions, owing to use, material alterations and environment. Deterioration occurring until the end of the initial period of the operation stage (5 years) is assumed to be congenital or first age and attributed to malfunctions of design, construction and operation. Deterioration which occurs after this initial period is considered ageing [6, 9]. To prevent and control ageing it is necessary to understand the phenomena (through its causes-effects and possible consequences) leading to the development of ageing i. e.. the ageing scenarios. The causes of the ageing scenarios are associated to initial conditions, design, construction, operation and maintenance of the works. They act through structural properties (geometric. hydraulic, thermic, chemical and mechanical) and actions, and originate direct effects (seepage through the dam and foundation, flow, temperature variations, forces, strains and displacements) as well as the eventual corresponding consequences (erosion and dissolution, abrasion, cavitation, thermal degradation). The above indicated mechanical direct effects (applied forces, strains and displacements) originate in turn indirect structural effects (displacements, strains and stresses) and the corresponding eventual consequences (overturning, heaving, settlement, cracking, crushing or sliding) [6. 9]. In this paper, the major ageing scenarios concerning concrete and masonry dam foundations are presented. Particular attention is given to scenarios of erosion and dissolution of the rock mass foundations and of degradation of grout curtains and drainage systems. A brief mention is made to the Portuguese experience in monitoring such scenarios.
The major ageing scenarios of dams and appurtenant works (concrete, masonry, earthfill and rockfill structures) were selected, illustrated and characterized by the ICOLD Committee on Ageing of Dams . The work of this Committee was based on the analysis of 980 case-histories on ageing of dams, obtained by adding new information to that assembled in previous ICOLD reports.