Anisotropy is a characteristic of intact foliated metamorphic rocks (slates, gneisses, phyllites, schists). Τesting was used to establish the anisotropic behaviour of selected gneissic rocks. The effect of anisotropy on various mechanical properties (strength, deformation) and dynamic properties (wave velocity) was examined. The rock samples were also tested at successively higher confining pressures in order to evaluate the effect of anisotropic behaviour at high overburden pressures.

L' anisotropie characterise les roches foliees (schistes, gneiss, phyllades). Dans ce travail des essais en laboratoire ont ete executes afin de determiner le comportement anisotropique des roches gneissiques. L' effet de l'anisotropie a ete examine par rapport aux proprietes mechaniques (resistance, deformation) et proprietes dynamiques (velocite ultrasonique). En outre des essais des roches ont ete executes a des compressions laterales successivement plus grandes afin de determiner le comportement des roches sous grands charges.

Anisotropie ist eine Eigenschaft der geschieferten Gesteine (TonSchiefer, Gneis, Phyllit, Marmor). Versuche wurden durchgefuehrt, um anisotrope Verhalten von gneis Gesteinen zu ermitteln. Der Einfluss von Anisotropie auf mechanische (Festigkeit, Dehnung) und dynamische Eigenschaften (Wellegeschwindigkeit) wurde bestimmt. Die Dreiaxialversuche wurden unter grossem allseitigen Druecken entnommen, um das anisotrope Verhalten auf grösse herrschende Spannung zu bestimmen.


The factors that influence the strength and deformation of the intact rock are the mineral composition, the fabric, the grain size and the degree of alteration and weathering.

The current paper deals with the pronounced effect of the fabric of anisotropic rocks on the strength and deformation characteristics of intact rocks. It is part of ongoing research in the Sector of Geotechnics, National Technical University of Athens.

Experimental Work

Two types of gneissic rocks were examined and were collected from rock exposures of slope cuts and tunnel portals of the Egnatia Highway, Veroia - Polymylos Section in Northern Greece.

Attention was given that the rocks blocks selected were from mechanically excavated slopes in order that minimum disturbance existed. Gneiss A is banded gneiss with finesized grains and light-coloured minerals. The petrographic composition is actinolithic gneiss.

Gneiss B is typical gneiss to schistous gneiss with mediumsized grains and dark-coloured minerals. It characterised as epidotitic, actinolithic schistous gneiss. Both gneisses originate from low to medium metamorphic conditions.

The testing of numerous rock samples included: determination of physical properties (dry density, porosity), dynamic properties (longitudinal and transverse wave velocity on dry samples) and mechanical properties including point load tests, unconfined compression tests, indirect tensile tests and triaxial tests, according to ISRM (1981).

Large size blocks were cored at different inclinations, using a special frame fitted to the base of the conventional laboratory-drilling machine. About 60 specimens of length to diameter of 2.0 to 2.5 having 5.4 cm diameter (NX-size) at different orientation angles β (0°, 15°, 30°, 45°, 60°, 75°, and 90°) were cored from the rock blocks.

An attempt was made to drill cores with different values of β from the same block to minimize the lithological differences. The specimens meeting the tolerance limits were first oven dried at 105°C for 24 h.

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