The design of a hydro dam has required the determination of the strength and deformability of the adjacent schistous rock mass. Large scale triaxial tests were performed on specimens, which had schist-planes parallel or normal to the maximum principal stress. The strength and deformability of the discontinuities were investigated in direct shear tests with a close-to-joint measuring equipment. The behaviour of large specimen with a joint dip of 45° was simulated by numerical tests using the FEM. It can be shown, that laboratory tests, combined with a numerical simulation of triaxial tests give satisfactory results of the strength and deformation parameters for a transversal isotropic rock mass model.


Dans le cadre du projet d'un barrage, it s'agissait de determiner la resistance et la deformabilite d'une roche schisteuse. Pour l'investigastion des paramètres du massif rocheux, on a realisβ des essais triaxiaux à grande echelle aur des echantillons avec des plans de schistosite orientes parallèlement ou perpendiculairement à la direction de la contrainte principale maximale. Les paramètres des discontinuites sont obtenus par des essais de cisaillement avec mesure des deformations proche du plan de discontinuitÜ. Le comportement mecanique des echantillons fissur°s sous 45° etait simule par des essais triaxiaux numeriques selon la methode des elements finis. On a montre, que par la combinaison d'essais physiques et d'essais numeriques, it etait possible d'evaluer les paramètres de resistance et de deformation pour un modèle transversal isotrope.


1m Rahmen eines Talsperrenprojektes bestand die Aufgabe, das Festigkeits- und Verformungsverhalten eines geschieferten Gebirges zu bestimmen. Zur Ermittlung der Gebirgskennwerte wurden Triaxialgroβversuche an Proben durchgefuehrt, deren Schieferungsflachen parallel bzw. senkrecht zur gröβten Hauptspannung orientiert waren. Durch kleinmaβstabliche direkte Scherversuche mit kluftnaher Scherdeformationsmessung wurden die Trennflachenkennwerte gewonnen. Das Festigkeitsund Verformungsverhalten von unter 45° orientierten Groβproben wurde durch numerische Triaxialversuche nach der Methode der finiten Elemente simuliert. Es wird gezeigt, daβ sich durch die Kombination von physikalischen Versuchen mit numerischen Triaxialversuchen die Festigkeits- und Verformungsparameter fuer ein transversalisotropes Gebirgsmodell bestimmen lassen.


The foundation of a planed dam for a water supply scheme required the investigation of the mechanical behaviour of the bed rock. The rock type was a quartzite schist with high strength and stiffness of the intact rock. The system of discontinuities consisted of the steep inclined schistosity S1: 310/80 (dip direction/dip angle) having a average spacing of 20 cm, the bedding SS: 070/16 and a joint set AC: 216/77. Due to the pervasive jointing of the rock mass a strong scale effect could be expected. Amongst the discontinuities the planes of schistosity were dominant. Thus a transversal isotropic behaviour was assumed. The investigation of the strength and deformability of a transversal isotropic material requires to perform compression tests in three different orientations to the material axis. Figure 1.1 shows one possibility of orientations which was selected in this case. The testing was done by large scale triaxial tests with radialsymetric boundary conditions on cylindrical and prismatic samples having a diameter or edge length of 60 cm and a height of 120 cm. As described in section 2, it was only possible to get samples having an orientation of the planes of schistosity normal and parallel to the stress axis. The inclined orientation could not be sampled in a 60cm diameter specimen. Instead of this a combined procedure was chosen which allowed to perform a numerical triaxial test on a 45°orientation. The material parameters needed were gained from direct shear test on samples of the foliation, midsize uniaxial tests of 25 × 25 × 50 cm samples having an angle of 30° between schistosity and the loading direction, standard triaxial and uniaxial tests of small cores from investigation drillings.

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