The general characteristics of the works and of the rock in which the excavations have been carried out are described, emphasizing the importance of prior investigation of the site and planning of the final works, that have been utilised to widen knowledge on the foundation behaviour. Remarks are made on the difficulties found during excavation and how these have been solved.
Les caracteristiques generales de l'ouvrage et du massif ou les excavations ont ete realisees sont decrites et l'on souliqne l'importance de l'investigation prealable du site et l'ordonnation des travaux definitifs, lesquels ont ete utilises pour elargir la connaissance du comportement les difficultes trouvees lors de la realisation des excavations et la manière dans laquelle elles ont ete surmontees.
Wir beschreiben Ihnen die allgemeinen Merkmale der Baustelle und des Massivs, wo die Ausgrabungen durchgefuehrt worden sind, wobei die Bedeutung der vorangegangenen Erforschungen des Ortes, sowie auch die Organisierung der endgueltigen Arbeiten hervorgehoben wird, die dazu verwendet wurden, die Kenntnisse ueber die Merkmale des Felsmassivs zu erweitern. Es wird auf die Schwierigkeiten bei der Durchfuehrung des Ausgrabungen und auf die Art und Weise, auf die diese gelost wurden, hingewiesen.
The Cortes-La Muela Hydro power project is located in the province of Valencia (Spain) in the river Júcar. It comprises two different functional elements: the Cortes II hydro power plant and the La Muela pumped storage project. The Cortes II hydro power plant is a conventional installation with a hydro power station rated at 240,000 kW, replacing the previous 30,000 kW plant, built in 1922. La Muela is a pure pumped storage system utilising favourable geomorphology, as the difference in elevation between the upper plane and the bed of the river Jucar is 600 metres, whereas the horizontal distance is only 800 metres. The favourable topography is completed by a geological frame of great tectonic serenity, only broken by a major fault parallel to the river that, on being impermeable, has allowed the underground plant to be brought close to the lower reservoir, thus reducing the length of tunnels and galleries. The underground pumped storage plant of La Muela houses three reversible pump-turbine units with a compound rating of 540 MW for pumping and 630 MW as turbines, requiring excavation of a complex system of shafts, tunnels, galleries and caverns.
The underground works were carried out in a massif comprising cretacean rocks ranging from the Coniacian (C-7) to the lower Aptian (C-l), with the most important and largest excavations located in the latter. Two blocks with different characteristics are distinguished in the rock mass separated by the Cortes fault. The outer block, Northern block, has fallen some 200 m, following the fault plane and is only crossed by the excavations for access tunnels and draft tubes.(Fig. No.1). The fracturing data taken therein show a high degree of dispersion. The same is not true of the inner block, a block in which all of the major works are carried out; this appears to be tranquil with a smooth inwards dip. In the stratigraphic column obtained in the preliminary investigation up to 36 different levels were identified within the lower Aptian (C-7), including the so-called C.l.7 comprising loose sandstone, greywackes and marly clays of 12 metres thickness. This is a highly interesting level as it is different to those predominating in the area. The petrographical analysis of the samples taken in this layer define it as sub graewackian, with fundamental components of quartz, feldspar, moscovite, sericite and chlorite. Given its special nature and location, it has been called the guide layer. Rock fracturing shows no significant singularities and there are three main systems. Even though is should be emphasized that this classification was used with the following reserves. During the rock investigation work the presence of seven levels of confined sub-horizontal aquifers was detected, that were later shown to be intercommunicated by open preferential pathways in the vertical diaclases and fractures, which has facilitated execution of the excavations, as the filtration flows have outcropped in the excavated zones through them and have not exceeded 50 l/s. The main conclusions of the extensive surveys carried out on the rock can be summarised as follows:
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Existence of the Cortes fault and confirmation of its impermeability.
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Detection of the so-called -guide layer-, with a practically zero load bearing capacity.
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Existence of confined water tables, with minor flow rates.
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The practical absence of residual stresses in the rock, except for gravitational stresses.
