The Miranda hydroelectric development is located in river Douro in Portugal. This development made It necessary to construct in a first phase, a massive-head buttress dam, three independent underground hydraulic circuits and an underground powerhouse. Recently, a decision was made to carry out works for the power increase of this hydroelectric power station. A monitoring plan was established for the new structures of the Miranda development, which implied also reactivation of some observations for the old power station. The observations established in the plan concern also the characterization of the deformability and strength of the rock mass and of the concrete of the supports, and in situ stress measurements. Some results referring to observations made during the beginning of construction are presented.
Le projet hydroelectrique de Miranda est situe sur le fleuve Douro au Portugal. Ce projet a rendu necessalre la construction, dans une première phase, d'un barrage à contreforts de chute massive, trois circuits hydrauliques independants et une usine souterraine. Recemment, on a decide d'effectuer des travaux d'elargissement de l'usine. Un plan d'observation a ete etabli pour les nouvelles structures du projet de Miranda, ce qui a aussi comporte la reactivation de quelques observations pour I'usine ancienne. Les observations etablies dans le plan concernent la caracterisation de la deformation et de la contrainte du rocher et du beton des appuis, et la mesure contrainte in situ. On presente quelques resultats concernant les observations.
Das hydroelektrische Projekt von Miranda befindet sich am Fluβ Douro in Portugal. Dieses Vorhaben erforderte in einer ersten Phase den Bau eines massivkopfigen Stuetzdamms drei unabhangiger unterirdischer wasserkreislaufe und eines unterirdischen Maschinenhauses. Erst vor kurzem wurde die Entscheidung getroffen, das Kraftwerk zu vergröBern. Der Beobachtungsplan, der fuer die neuen Strukturen des Miranda-Projekts aufgestellt wurde, beinhaltete auch die Reaktivierung einiger Beobachtungen, die im Bezug auf das alte Kraftwerk gemacht wurden. Die im PIan aufgestellten Beobachtungen betreffen unter anderem die Charakterisierung von Verformbarkeit und Widerstand der Felsmasse und den Beton der Auskleidung, sowie Feldspannungsmessungen. Es werden auch einige Beobachtungen, die wahrend des Beginns der Bauarbeiten gemacht wurden, dargestellt.
The Miranda hydroelectric power scheme is located on the river Douro, in the northern border between Portugal and Spain (Figure 1). The Douro, one of the most Important rivers of the Iberian Peninsula, has a length of approximately 850km and a total catchment area of 97,000km2. It is located in a site where the course of the river suddenly changes its direction, forming an elbow at an angle of 45°. The profile of the valley is shaped like a very open V the slope of the banks is not very pronounced. The nature of the ground on the site of Miranda plant is complex. It is a zone of general metamorphisms, the rock mass consists of rocks like micaschists, migmatic rocks and anatexy granites. During the initial exploitation phase, that started in 1961, a diamond-shaped massive head buttress dam was built, with maximum height above lowest foundation of 80m and a developed crest including the abutments of 263m. The spillway with four openings is located in the central zone of the dam. Three independent hydraulic circuits were formed for each set, comprising the intake, penstock, draft tube and tailrace tunnel (Figure 2). The powerhouse is a cavern with 80m long, 19.6m wide and 42.7m height of excavation with a horse shaped profile.
