Joints orientation and properties are between the major factors at the origin of the anisotropic behavior of rock masses. This paper stresses the role of joint orientation, with respect to the loading direction, in determining the deformational behaviour of a rock mass by means of some numerical simulations. As a consequence, it is stressed that rock mass characterization requires particular care to give a complete assessment of rock mass conditions and to correlate joint pattern and deformational behavior.


L'orientation et les caracteristiques des discontinuites rocheuses sont a I'origine du comportament anisotrope d'un massif rocheux. Le but de ce travail est I'orientation des discontinuites, au regard de la direction de charge, pour determiner les parametres de deformation avec des simulations numeriques. II est done une consequence de reconnaitre l'Importance d'une precise caracterisation des conditions du massif rocheuse, pour etablir un raport entre la distribution spatiale des discontinuites et la deformabilite de la roche.


Die Orientierung der Klufte und ihre Eigenshaften sind unter den Ursachen der Anisotropie im Verformbarkeitsverhalten zu zahlen. Unsere Ergebnisse heben die Rolle hervor, die die Orientierung del Klufte, gelen die Richtung der Belastung, in der Bestimmung der Verformbarkeits Parameter durch Computer simulation spielt. Es wird daher die Bedeutung einer genauen Charakterisierung des Zustands des Felsmassivs erkannt, damit man die Orientierung del Klufte mit den Verformbarkeitseigenschaften korrelieren kann.


The anisotropic rock mass behavior is an important concept in rock mechanics. At the origin of such anisotropic behavior, involving both rock mass deformation and strength, there could be some intact rock (intrinsic anisostropy) and rock mass features (acquired anisotropy) like foliation, schistosity, stratification, jointing, weathering and alteration. It is known, in fact, that for a intact rock homogeneous material the anisotropic rock mass response is the results of the contribute by many different factors: geometrical, like joint spatial distribution, orientation and aperture, and physical factors, like friction, normal and shear stiffness (Pinto, 1966, 1970; Barla, 1974; Bieniawski, 1978; Nova, 1980; Amadei, 1983, 1988; Amadei & Savage, 1989; Chappel, 1989, 1990; Kulatilake et al., 1992a, 1992b). Between these properties, joint properties cover an important role and are strongly influenced by scale effects. A certain importance could also be attributed to an external factor like the direction of applied loads with respect to joint pattern, joint distribution and the size of the application area or the stressed volume of material (Heuze, 1980). To imagine the consequences of such an anisotropic behavior thought to the foundations of a dam or any other large structure able to distribute its load in different directions on a rock mass and then think to the miscomputation of the deformation on the basis of a unique or multiple uni-directional loading tests. With the purpose to check such influences, a series of numerical simulations, by the distinct element method (UDEC), have been performed to verify the importance of rock mass anisotropy and the need to take in account, during the computation of the rock mass modulus of deformation (Chappel, 1990), the local joint distribution at the scale of the structure (Kulatilake et al., 1992a, 1992b) and the relative loading direction. Few simulations has been carried out till now introducing confining loads even if their effects could be very important on deformational behaviour. The main differences of this work from the deeper research conducted by Kulatilake et al. (1992a, b) is the adoption of samples with persistent joints (fig. 1a), instead of non-persistent joints, and subjected to uniaxial loads only.

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