Most of the valleys, including narrow ones, in humid tropical regions, present covers of residual soil that sometimes are very thick. In the case of Funil dam site, in Brazil, the sound rock in the upper level of the right bank was discovered 60 meters below the surface. However the geological studies, the borings, the geophysical tests, the opening and tests of galleries made it possible to map the levels of sound rock and to establish the surface of the foundation taking into consideration the mechanical properties of the rock mass. The excavations now completed for the foundation of the dam fully confirmed the predictions, which indicates that the methods of prospection and tests used were satisfactory. The correlations established between different physical properties of the rock including its deformability, obtained by various tests were very important for the definition of the data necessary for the design of this important shell-dam.
Dans la plupart des vallees,même etroites, des regions tropicales et humides, les roches se presentent avec une couverture de sol residuel, quelques fois très epaisse. Dans le cas du site du barrage du Funil, au Bresil, où le rocher sain se trouvait à 60m audessous dans la partie la plus elevee de la rive droite, des etudes geologiques, des sondages, des essais geophysiques, et le percement et essai des galeries, ont permis l'etablissement du niveau de la surface de fondation et les caracteristiques des roches. Les excavations qui viennent d'être achevees ont complètement confirme les previsions faites, ce qui indique que les methodes de prospection et essai utilisees sont satisfaisantes. Les correlations etablies entre differentes proprietes physiques du rocher, les caracteristiques de deformation inclues, obtenues par des essais ont ete decisives pour la definition des elements necessaires au projet de cet important barrage-voûte.
In der grossen Mehrheit der Taler der feuchten Tropengegenden, wenn sie auch schmal sein mögen, zeigt sich der Fels mit einer manchmal auch sehr dicken Erdbedeckung. Im Fall der Funilstaumauer, in Brasilien, befand sichdasfeste Gesteinin einer Tiefe von höchstens 60 m in dem höher gelegenenTeil des rechten Ufers. Sowohl die geologischen und geophysikalischen Untersuchungenalsauch diegewohnlichenSondierbohrungen, neben derEröffnung vonVersuchsstollen, gestatteten die Festlegung der Felsoberflache, wie auch die Ermittelung der Felseigenschaften. Die soeben beendete Entfernung der Erdoberschicht hat die vorherigen Untersuchungen vollkommen bestatigt, was andeutet, dass die verwendeten Untersuchungsverfahren zufriedenstellend waren. Die festgestellten Zusammenhange zwischen den verschiedenen physikalischen und Verformungseigenschaften des Felsens, die durch die genannten Untersuchungen gewonnen wurden, waren zur endgueltigen Gestaltung dieses Wichtigen Staumauerprojektes von entscheidender Bedeutung.
In humid tropical regions it is frequent to find, in the upper elevations of the valleys, a thick cover of residual soil above rocks, sometimes with large boulders. However the total thickness of the transition zones between the soil, the altered and the sound rock is frequently short. The case of Funil dam foundation, in Paraiba River in Brazil, now under construction by ELETROBRAS (Government Agency of Electricity) is typical of that situation. In fact, in the right bank above the crest of the dam, the total thickness of residual soil and altered rock attains 60 meters. In this case, although the superficial reconnaissance was not possible, borings, galleries and geophysical investigations allowed a good prediction of the convenient foundation level, which was confirmed in the actual excavation (Fig. 1 and 2) with a difference not greater than one meter almost everywhere. As Rock Mechanics today is a discipline basically empirical, the establishment of correlations between geotechnical rock properties is a very important guide for the design of large concrete dams. In the case cited, tests were carried out in the inspection galleries and in the laboratory which allowed sufficient correlations to be established for a convenient design of the foundation and of the structure. Extensive construction of large darns and hydroelectric undertakings in Portugal, Spain and Brazil allowed the development of Rock Mechanics studies in these countries [Ref. 1 to 6]. This paper deals with aspects of such studies in the case of a gneiss formation, covered by altered rock and residual soil and serving as foundation of a thin but wide shell dam.
As is known, for the design of a large concrete dam, including its foundation, it is necessary to know the contours of altered and sound rock, the patterns of the discontinuities, the fabric of the mass, the deformability and shear strength for various possible situations of decompression and, sometimes, the residual stresses in the rock mass [7]. Under these circumstances the strategy for attacking the problem of the study of the foundations of a large dam consists, as described elsewhere [8], in investigations on the mapping of the joints, strata and techtonics, on the properties of the rocks themselves, and eventually of the material filling the seams, joints or faults.