In the paper the influence of stress induced anisotropy on failure conditions or rocks is studies. This is done through the development of an anisotropic damage-rate elastic constitutive law (ADRECL), based on a phenomenological incremental damage model. This law has been validated by using an experimental program of uniaxial and triaxial tests on a soft limestone (Pietra Leccese) and a sandstone (Rothbach sandstone). The evolution law of the component of the anisotropic damage-rate tensor has been determined for the two rocks. The behaviour of a hollow cylinder and a deep cavity have been simulated. It is shown that the model can reproduce correctly the behaviour of the two rocks considered and the elastic instability associated with the brittle behaviour of Rothbach sandstone.


Dans cet article nous etudions l'effet de l'anisotropie induite par l'etat des contraintes sur Ie conditions de rupture des roches. Pour cela nous avons developpe une loi de comportement incrementale elastique endommageable formule clans le cadre d'un modèle d'endommagement incremental phenomenologiquc. Cette loi a ete valide à partir d'un programme d'essais de compression uniaxial et triaxial sur line calcarenite (Pictra Leccese) et sur un grès (grès de Rothhach) pour lesquels les lois d'evolution des composantes du tenseur d'endommagement incremental ont ete determinees. Ce modèle à ete utilise pour simuler Ie comportement d'un cylindre creux et d'une cavite cylindrique profonde. Les resultats de ces simmulations Montrent que ee modèle reproduit correctement Ie comportement des deux roches ainsi que l'instabilite elastiquc associee au compartement frtagile du grès de Rothbach.


In dieser Arbeit wird derEinfluß der durch Belastungszustande induzierten Anisotropie auf das Bruchverhalten von Felsen Unitersucht. Insbesondere wird ein inkrementales Gesetz zur konstitutiven Anisotropie (ADRECL) entwickelt, das auf ein Beschaidigungsmodell Bezug nimmt. Dieses Gesetz wird durch labortests zur ein- und dreiachsigen Kompression an Weichkalksandstein ("'Pietra Leccese") und an Sandstein (Rothenbach) ueberprueft. Fue diese beiden Steinarten werden im Einzelmen die Komponenten der BeschaHdigungsspannung bestimmt. Außerdem werden das Problem des Hohlzylinders und das der tiefliegenden Rundhöhlung simuliert, wobei nachgewiesen wird, daß das Model in der lager its, das Verhalten der beiden Test-Gerstein zoo reproduzieren und insbesondere die elastische instabilitat im Bruchverhalten des Rothbach-Sandsteins.

It is well known that brittle failure at cavity wall is largely influenced by the boundary conditions. This question has been addressed by an ISRM commission (Maury, 1987) which clearly stated that the orientation of the cavity with respect to the in situ stress field is of first importance for the development of failure. This sensitivity to the relative orientation of the stress field is related to the stress induced anisotropy of the rock. In order to study the stress induced anisotropy of rocks and the development of damage in preferred directions, an experimental program of uniaxial and triaxial compression rests has been carried out. Emphasis has been given to the effect of boundary conditions applied to the specimen, in order to avoid inhomogenenous strain field inside the specimen. The slenderness of the specimen and the conditions of contact between the specimen and the platens have a great influence on the apparent strength of rock cylinders (Hawkes and Mellor, 1970; Vukuturi et al, 1974; Paterson, 1978; Brady and Brown, 1985; Bridell, 1991; Labuz and Bridell, 1993). At constant diameter, more slender specimens fail earlier than less slender ones. This phenomenon is attributed to the friction between platens and the specimens (Drescher and Vardoulakis, 1982) and to the contrast of the elastic properties of rock and steel plates (Brady, 1971 a and 1971 b). The effect of the friction is to restrain the specimen near the ends and to prevent it from uniform deformation.

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