ABSTRACT:

For a fractured rock, the coupling between thermal, hydraulical and mechanical behaviour requires alternative means of evaluation in discontinuous rocks than the ones used for porous media. In this paper, the case of a gallery containing high level nuclear waste and connected with a single fracture is considered. Priority is given to a global two-dimensionnal analysis of the existing connections between the heat released, the joint closure and the transient flow in the fracture. A software entitled CAFEC has then been developed on these bases using the finite difference method. Its originality resides in its integrated modularity which lets the different interactions to be either activated or not activated. CAFEC's major features are presented. A sensitivity analysis to evaluate the influence of the joint mechanical behaviour is also presented.

RESUME:

Contrairement aux milieux poreux, dans un massif rocheux fracture, l'etude des couplages entre les comportements thermique, hydraulique et mecanique du massif necessite une approche de milieu discontinu. Dans cet article, on considère Ie cas d'une galerie contenant des dechets radioactifs et connectee avec une fracture. Les priorites seront donnees à une analyse bidimensionnelle des relations entre I' echauffement du massif par les dechets, l'ouverture de la fracture et l'ecoulement du fluide dans la fracture. Un code de calcul par differences finies nomme CAFEC a ete developpe pour ce cas specifique. Son originalite reside dans des fonctions integralement modulables qui donnent la possibilite d'activer ou de desactiver les differents couplages. Après une presentation des principales fonctions du logiciel, on presentera les analyses parametriques des influences du comportement mecanique de la fracture.

ZUSAMMENFASSUNG:

Das rissige Gebirge ist als ein Non-kontinuierliches Medium zu halten bei der Untersuchung der Kupplung zwieschen den thermischen, hydraulischen und mechanischen Verhalten des Gebirges gegenueber dem loechrigen Medium. In dieser Arbeit ist ein Tunnel, in dem hoch radioactive Atomabfaelle gespeichert werden, untersucht worden. Mit Hilfe von einem zwei-dimensionalen Modell sind hauptsaechlich die Wechselwirkung zwieschen der freigegebenen Waerme, der Entwicklung der Risse und der Fluechtigkeit analysiert worden. Aufgund der Ergebnisse ist dann ein Programm - CAFEC mit Hilfe von dem Finit- Differential-Methode entwickelt worden. Dieses Programm, dessen Besondheit die verschiedene Wechsel wirkungen activieren orde nicht activieren lassen kann, ist in dieser Arbeit vorgestellt. Die Analysierung der Einfluesse des mechanischen Verhaltens der Risse ist hier dazu dargestellt.

1. INTRODUCTION

The modeling of fractured rock lies in two major alternatives: the continuous approach, where the rock is considered as an equivalent homogeneous porous media, and the discontinious approach, which attemps to represent every single joint individually. However, both approaches failed to correctly repre- sent the coupled behaviour of the geological barrier, especially as far as flow modeling is concerned [Jing, 1994]. The Decovalex benchmark showed evidence of a strong need to associate the two approaches within a multi-scale framework in order to better represent in-situ behaviour: at the far field scale, a distinction is likely to occur between fractures of large extension on the one side, which will be explicitely represented in the model, and a secondary network of discontinuities on the other side, impossible to identify in practise, but still important to be accounted through homogeneization techniques. Prior to this ambitious goal, the understanding of the physical interactions involded is necessary, in order to possibly simplify the problem. Nevertheless and for the same reasons as quoted above, such a "coupling assessment" requires alternative means than the ones derived from an homogeneous porous media theory [Coussy, 1991]; [Giraud, 1993].

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