The Aguayo hydroelectric system has a head of 320 m between the Aguayo reservoir and the reversible plant at Alsa. As penstocks, two parallel pipes of 3,800/3,400 mm diameter were designed without expansion joints. Each pipe is almost 1,300 m long with six fixed points which have to withstand the forces due to its own weight, water load and thermal variations. In the foundations of the four intermediate fixed points, and in order to do away with enormous volumes of concrete, great prestressed forces had to be applied by means of permanent anchors grouted into the ground.


Le système hydroelectrique de Aguayo a une chute de 320 m entre le barrage de Aguayo et la centrale reversible de Alsa. Pour la conduite forcee on a prevu deux tubes parallèles de 3.800/3.400 mm de diamètre sans joints de dilatation. Cette conduite de presque 1.300 m de longueur a 6 points d'appui fixes où il faut absorber les charges dues aux poids propre, charge d'eau et variations thermiques. Pour les fondations des quatre points fixes intermediaires, et afin d'eliminer. d'enormes volumes de beton, il a ete necessaire d'appliquer de grands efforts de precontrainte, au moyen de tirants definitifs ancres au terrain.


Das Wasserkraftprojekt von Aguayo verfuegt ueber ein Gefalle von 320 m zwischen dem Aguayo Stausee und der Alsa Umkehrzentrale. Die Druckleitung wurde als zwei parallel liegende Röhren ohne Dehnungsfugen projektiert, die einen Durchmesser von 3.800/3.400 mm haben. Die Leitung hat eine Lange von ca. 1.300 m und ist an 6 Punkten fixiert. Diese Punkte muessen das Eigengewicht der Röhren, die Wasserlast und die Lasten infolge thermischer Unterschiede aufnehmen. Fuer die Fundierung von 4 Fixierpunkten wurden allzu große Volumen von Beton dadurch vermieden, daß man große Vorspannkrafte mittels Daueranker aufbrachte.


The Aguayo Project, in Spain, is a reversible hydroelectric development, promoted by ELECTRA DE VIESGO, S.A. in the municipal districts of Barcena de Pie de Concha and San Miguel de Agua yo, in the Cantabria region, north-west of - Spain. The Alsa reservoir, in existence since 1920, forms the lower basin the capacity of which has been raised to 22 Hm3 by increasing the height of the dam 7 m aprox. The upper basin with 10 Hm3 capacity is an artificial reservoir located on a plateau to the south of Ano Peak, formed by a rock-fill dam abutted against the Peak, and constructed with the material excavated from the floor of the basin itself. The dam, whose length at crest is 3,000 m, has a maximum height of 32 m. The dam upstream face has an asphalt membrane, whereas the slopes cut in the rock and the basin bottom have no lining whatsoever, relying for water tightness on the nature of the rock, Triassic sandstones and lutites (Bundsandstein). The power-plant is-located next to the old Alsa dam and is connected to the upper basin by two telescopic high pressure penstocks 3,800/3,400 mm in diameter and 1,300 m long, and to the Alsa reservoir by means of four low pressure pipes, one for each group, 3,500 mm in diameter and approximately 70 m long. The gross mean head is 320 m an the total power capacity of the plant is 424 MVA. The path of the high pressure pipelines crosses the above mentioned Triassic sandstones, except for a short stretch, approximately 300 m long, which passes through a Keuper zone, with outcrops of ophites, severely affected by spheroidal weathering.


The two 1,300 m long penstock pipelines were designed parallel along the centre axis and with out expansion joints. Their foundations have six fixed points to take up the forces due to their own weight, water load and thermal variations du ring assembly and the later operating period. Fig. 1 shows the penstocks in construction phase. Based on these hypothesis, the normal force N, the moment M and the tangential force T (see Fig. 2) acting on the basis of the fixed points were calculated. As a result of these forces, if classic, gravity blocks had been used for the foundations of the se fixed points, enormous volumes of concrete - would have been required. The result would have been an uneconomical and virtually unfeasible solution.


The solution adopted for the foundation of the four intermediate fixed points consisted of installing permanent prestessed anchorages in such a way that for the two most unfavorable hypothesis, the resultant forces RI and RII (see Fig.3) passed through the ends of the central third part of the supporting base, and with symmetrical dips in respect of it. The total anchorage force, F, to be applied as well as its position and orientation, defined by eccentricity "d" and angle "ß", as shown in Fig.3 was calculated. The summary of these values is presented in Table II.

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