The so-called "Stainzer Platten" gneiss is part of a regional ductile shear zone within the metamorphic Koralm core complex and has some practical importance due to its perfect fissility. Investigations on the rock fabrics revealed a characteristic mi-crocrack pattern besides a distinct mineral alignment. Rock mechanics laboratory tests which were performed at core samples drilled at 30° direction intervals along the principal fabric planes resulted in a pronounced anisotropy for the determined elastic parameters. In particular the orientation and distribution of existing microfractures, as well as their readiness for activation under load are crucial for the interpretation of the obtained results.
Le "Stainzer Plattengneis" fait partie d'une zone regionale ductile de cisaillement dans le cristallin de la chaîne de Koralm et, roche en dalles de c1ivage prononce, porte un certain interêt pratique. L'etude de la texture granulaire a demontre, outre un alignement mineral distinct, une structure caracteristique de microfissures. Les essais effectues sur des carottes remontees à des inter-valles d'angle de 30° le long des plans principaux de la texture ont montre une anisotropie très nette des paramètres èlasttque.s determines. Ces resultants s'expliquent en particulier par l'orientation et la distribution des microfissures presentes des la roche ainsi que par leur tendance à la mobilisation sous charge.
Der "Stainzer Plattengneis" entstammt einer regionalen duktilen Scherzone im KoralmkristalIin und ist als Gestein mit ausgepragter plattiger Spaltbarkeit von gewissem praktischem Interesse. Untersuchungen des Korngefueges ergaben neben einer deutlichen Mineralregelung ein charakteristisches Mikrorißmuster. Beim Test von Kernproben, welche in Winkelabstanden von 30° entlang der Hauptebenen des Gefueges erbohrt wurden, konnte eine deutliche Anisotropie der ermitelten elastischen Parameter festgestellt werden. Die Ergebnisse lassen sich insbesondere ueber die Orientierung, Verteilung und Aktivierung der vorhandenen Mi-krorisse im Gestein erklaren.
There is ample knowledge on rock anisotropy and petrophysics available in textbooks and scientific papers (e.g, Peres- Rodrigues 1966, Willard 1969, Barla 1974, Amadei 1983, Wit-tke 1984, Montoto 1985, Gottschalk et al. 1990, Siegesmund 1994, Ersoy& Waller 1995,)
In certain cases, however, up to 21 independent elastic constants could have to be determined just to characterise anisotropic behaviour comprehensively. This fact evidently makes it too laborious for most applications. Both mineral shape and/or lattice preferred orientation (MPO, LPO) and defect frequency/ orientation (DFO), as well as their distributions in space are thought to be decisive for the observable behaviour of the rock material. In a practical 'sense it is a mere scale problem Whether we speak of rock mass and/or rock material: It takes only a step down in the size of the region of interest to consider the so-called intact rock specimen as a mechanical system consisting of at best elastically deformable elements (minerals, components), bounded by discontinuities (grain boundaries, cleavage, microfractures, voids), and including fluids.
In analogy to rock mass inferred performance investigation via discontinuity analysis, and in order to assess both the magnitude and the directional pattern of the fabric-induced mechanical anisotropy, we selected a gneiss type of practical importance for a preliminary textural analysis and concomitant rock mechanics laboratory tests series.
