Design substantiation of measures on stabilization of rock foundations of arch dams are considered. The determination of state of stress is made using the element method, the stresses being estimated on the basis of Mohr's theory of strength. Examples are given of filling a large tectonic fault with concrete and of rock foundation stabilization aimed at improvement of the state of stress in the foundation under the downstream toe of the Inguri arch dam.
Les problèmes des calculs concernant les mesures de consolidation de la fondation roche use des barrages-voûtes sont envisages. Le calcul de l'etat de contrainte s'effectue par la methode des elements finis, l'estimation des contraintes se fait sur la base de la theorie de resistance de Mohr. Sont donnes les exemples du remplissage par beton d'une fracture tectonique importante, ainsi que des mesures de comsolidation destinees pour l'amelioration de l'etat de contrainte de la fondation du barrage-voûte d'Ingouri près du parement aval.
Es werden die Probleme, die mit dem rechnerischen Nachweis der Sicherungsmassnahmen des Felsuntergrundes von Bogenstaumauern zusammenhangen, betrachtet. Die Berechnung des Spannunszustandes wird durch die Methode der finiten Elemente und die Einschatzung von Spannungen auf Grundlage der Mohrschen Festigkeitstheorie durchgefuehrt. Die Beispieile mit dem Einbetonieren eines grossen tektonischen Bruches sowie den Befestigungsmassnahmen zur Verbesserung des Spannungszustandes im unterwasserseitigen Untergrund der Bogenstaumauer der Wasserkraftanlage Inguri werden angegeben.
The Inguri arch dam, now under construction on the Inguri River in the western Part of the Georgian SSR, is 271.5 m high. The crest length (including 118 m in both abutments) is 758 m. The dam consist of the abutment pad, 50 m high, in the river bed and the arch dam proper, 221.5 m in height (Fig.1). The dam is a double-curvature arch of a polynometric shape. The dam has been calculated by the trial-load method and studied on elastic, brittle and geomechanical models. The shape of the dam has been selected so as to provide for uniform compression in its upper part. In this case the compression stress in arches amounts to 7 to 8 MPa, the reservoir level being at elevation of the NHWL. The compression stresses, taking the seismic action into consideration, are not in excess of 13 MPa. The arch dam foundation is composed of limestone and dolomite dipping steeply (under the angle of 50 to 70°) towards the downstream pool. The rock foundation is disturbed by a tectonic fault traversing the ringhbank abutment of the dam, by a number large fissures and by six sets of joints. The jointing diminishes considerably at the depth of 40 to 60 m from the surface. The rock foundation stability analysis has been carried out taking into consideration the forces transmitted into the foundation from the dam as well as filtration pressure and gravitational forces; the resistance of the arch dam to the virtual displacement of the foundation block has not been taken into consideration. In the opinion of designers, the absorbing by the rock foundation forces resulting from erection of the dam and impounding the storage reservoir, with a required stability factor (for the conditions of the Inguri Dam foundation the allowable stability factor has been assumed equal to 1.8), should provide for elastic behaviour of the dam. Special calculations of the foundation strength carried out on the basis of the given state of stress have demonstrated that zones of decompaction at the upstream face of the dam and plastic zones at the downstream face (at lower elevations in the areas of shallow foundation) are present and that the strength of the fill material in the tectonic fault and in five fissures is insufficient. It is practically impossible to prevent formation of decompaction zones and besides such a prevention is not necessary as the decompaction zones do not exert any substantial effect on distribution of stresses within the dam and its foundation. Taking into account the position of this zone the grout curtain has been arranged somewhat farther downstream. Formation of plastic zones in the foundation and insufficient strength of the fill material in the tectonic faults and fissures will result in local increases of the foundation deformability, which in its turn will affect unf'avourably the state of stress in the dam. In order to neutralize the effects of this phenomenon, consolidation measures in the lower third of foundation on both banks and measures on stabilization of the tectonic fault and fissures have been designed and calculated. Two problems are to be solved in the analysis of arch dam rock foundation stability. The first problem consists in determination of the state of stress and strain; solution of this problem involves great difficulties since the arch dam - foundation system should be considered as a three-dimensional system and at present the problem cannot be solved without introducing a number of simplifying assumptions.
