The anisotropic behaviour of "Athens Schist" has been brought out through the testing of specimens with varying orientation of schistosity with respect to the major principal stress under uniaxial, triaxial and dynamic conditions. A large number of results from tests on intact rock specimens of the "Athens Schist" were statistically analysed and evaluated.

Le comportement anisotropique des roches du système "Schistes d' Athènes" a ete determine sur des epreuves avec une orientation differente de la schistosite par rapport à l'axe de chargement sous des conditions axiales, triaxiales et dynamiques. Un grand nombre des resultats a ete statistiquement analyse et discute.

Zur Bestimmung der anisotropen Eigenschaften der Athen Schiefer wurden einaxialen, dreiaxialen und dynamischen Kompressionsversuchen an Gesteinskernen durchgefuehrt, bei denen die Belastungsachse verschiedenen Neigungen gegen die Schieferung hat. Die Messreihen an anisotropen unzerreissbaren Fels Samplen von Athen Schiefer wurden statistisch analysiert.

Introduction

The term "Athens Schist" describes a geological formation comprising a variety of low-level metamorphic and sedimentary (non-metamorphic) weak rocks (Marinos G et al.). Significant spatial variability in the degree of weathering exists ranging between slight weathering, where the material resembles a heavily crushed rock mass, and high weathering, where the material forms rock blocks "floating" in a completely weathered soft matrix.

Consequently the "Athens Schist" is a heterogeneous formation that includes soil and rock like members of different composition, grade of weathering and anisotropy.

Experimental Work

Two types of schist, namely graphitic and calcitic schist were obtained in their intact rock state from surface excavations in Pagrati and Ilisia area of Athens. Both types retain low metamorphism characteristics, well-developed schistosity planes and have significant amount of quartz in crypto-crystallised form or in veins. They are typical samples from categories D and E as classified by Marinos et al. (1994) and explained in a following paragraph.

The testing of numerous rock samples included: determination of physical properties (dry density, porosity), dynamic properties (longitudinal and transverse wave velocity on air dried 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 trimmed with their sides perpendicular to each other to facilitate coring at different inclinations, using a special frame fitted to the base of the conventional laboratory-drilling machine. About 50 specimens of length to diameter of 2 to 3 having a 5.4 cm diameter (NX-size) at different orientation angles β relevant to the core axis (0°, 15°, 30°, 45°, 60°, 75°, and 90°) were obtained 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.

(Table in full paper)

Wave Velocity anisotropy

The ultrasonic pulse method was used to determine the anisotropy of P- and S-waves of intact schist. The correlation of these two follows the expression Vp = 1.84· Vs with a correlation coefficient r = 0.84.

This content is only available via PDF.
You can access this article if you purchase or spend a download.