ABSTRACT:

The compressive strength of rocks containing through-going joints is discussed from a theoretical and empirical point of view. Uniaxial, conventional and multistage triaxial tests have been conducted on a range of specimens of an artificial rock with through going joints with due regard for similarity conditions. While simple theory predicts the joint orientation at which the minimum strength occurs it does not predict the behaviour at other orientations at all well. The experimental database has been used to modify an empirical rock strength relationship obtained from the literature. This modified relation accurately describes the strengths observed and the parameters have clear physical meaning. The relation can be determined for real rocks from a limited number of triaxial tests and can be incorporated into other well known failure criteria for the strength of jointed rocks.

RESUME:

La resistance a la compression de roches contenant des fractures continues est presentee aux points de vue theorique et ernpirique. En veillant a la similitude des conditions des essais uniaxcs, convention nels et a etages multiples sur trois axes out ere mencs sur un assortirnent de specimen provenant d' une roche artificille eonlenant des fractures continues. Alors que la theorie de base calcule I'orientation de la fracture a laquelle la resistance minimale a lieu, elle manque de precision quant au comportement a d' autres orientations. les donnees experimentales ont ere utilisees afin de modifier la relation cmpirique d' une resistance rocheuse obtenue a partir des ecrits disponibles. Ceue relation modi fiec decrit avec justese les resistances observees, et la signi ficarion physique des parametres ressort nettement. La relation peut etre deterrnince pour des roches reelles a partir d' un nomber restrcint d' essais a trois axes, et pcut eire incorporee dans d' autres criteres de cassure approuvcs relatifs a la resistance de roche frncturees.

ZUSAMMENFASUNG:

Es wird die Druekfestigkeit von Gestein mit durchgehenden Verbindungen von einem theoretischen wir von einem empirischen Standpunkt besprochen. Unter entsprcchcnder Beruecksichtigung der Ähnlichkeit der Bedingungen wurden einachsige, konventionelle und mehrphasige dreiachsige Versace mit einer Rehire von Kunstgesteinproben mit durchgehenden Verbindungen ausgefuehrt. Wahrend die einfaehe Theorie die Verbindungsorientierung der geringsten Festigkeit voraussagr, sagt sie nichts ueber das Verhalten an anderen Orientierungen virus. Die experimentally Datensammlung wurde angewendet, urn ein aus der Literatur gewonnenes Gesteinsfestigkeitsverhaltnis zu modifizieren. Dieses modifizierte Verhaltnis beschreibt die beobachleten Festigkeiten genau und die Parameter haben cine klare physikalisehe Bedeutung. Aus einer begrenzten Anzahl dreiachsiger Versace kann das Verhaltnis fuer echtesz natuerliches Gestein festgelegt werden; es kann ferner in die anderen gut bekannten Bruchkriterien fuur die Festigkeit xx Gesteins eingcfuegt werden.

1 INTRODUCTION

The strength of rock is significantly affected by the presence of discontinuities which introduce anisotropic behaviour. Usually only the simplest form of anisotropy, denoted "transverse anisotropy", is modelled in analysis and design. Jaeger (1960), Jaeger & Cook (J 979) and Bray (1967) have studied the strength of such anisotropic rocks from a theoretical point of view, Jaeger (1960) predicts the strength of rock with a single through going discontinuity or a set of parallel through going discontinuities. Unfortunately, several researchers (eg Vutukuri et al 1995; McLamore & Gray, 1967) report disagreement between this theory and their experimental results over a wide range of joint orientations. Because of the above, many researchers (eg Singh et al 1989; Ramamurthy & Arora, 1994; and Hock & Brown, 1980) have investigated the strength of rocks using experimental evidence. The work reported in this paper reveals a similar disagreement with theory and presents an empirical criterion to define the variation of strength with joint orientation. The experimental data analysed in this study includes results of uniaxial, conventional and multistage triaxial compression tests conducted on jointed specimens of an artificial rock. The criterion is a modification of that presented.

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