High gravity dams founded in hard rocks display settlements which are of the order of several millimeters and without any danger for the behaviour of the dam. Nevertheless care is necessary due to their influence on the behaviour of the adjacent powerhouse.
In general, the settlements of large gravity dams, founded on solid rocks, are negligible. Thus the settlements of the 95 m high Orlik dam in Czechoslovakia amounted 8 millimeters. Even when the compressibility of the foundation rock is not out of concern, the settlements are relatively small, as was the case of the Vír dam in Czechoslovakia, founded partly on rather decomposed mica — schist and displaying a settlement of the order of 10 millimeters. Excluding the case of the hanged blocks on the valley slopes in the course of construction, it can be said that the settlement does not endanger the structure of the dam as well as its operation.
Nevertheless cases appear when it is necessary to consider the influence of the settlement on the structure as well as on the operation of the adjacent powerhouse. Due to the large dimensions of the foundation surface of the rock and to the compressibility of rock even in depth, as well as due to the inclination of the resultant force, the settlement produced by the dam reaches also under the powerhouse. As the lower portion of the latter is a rigid structure as well as due to its large width, the structure behaves as a cantilever and a gap opens in the portion of the foundation surface adjacent to the dam (Fig. 1). Two features occur
(1) Fissures in the walls of the turbine shafts,
(b) A large vibration of the structure.
Both phenomena are of large concern and elaborate explications appear mostly concerning the rheological processes in the concrete. Nevertheless the only reasonable treatment is to fill the gap under the upstream portion of the foundation surface of the powerhouse by grouting it. For this purpose it is to be recommended to insert the grouting pipes into the structure during the construction. The grouting should begin still during the construction of the higher portion of the dam and proceed in the course of the filling of the reservoir.
Grands barrages — poids, fondés sur les roches solides produisent des tassements qui sont de l’ordre de quelques millimètres et sans danger pour la fonction du barrage. Néanmoins ils peuvent causer un fonctionnement inconvenant de l’usine accolée.
Hohe Gewichtsstaudämme weisen Setzungen von einigen Millimetern auf, welche ohne Einfluss auf das Verhaltendes Dammes sind. Sie können aber das Verhalten des anliegenden Kraftwerkes beeinflussen.