ABSTACT:

The evaluation of the elastic constants contained in the deformability matrix using diametral compression tests has been the main subject of some papers presented in the ISRM Congresses. In this work, new expressions are proposed for the determination of elements of the deformability matrix and the stress concentration factors that appear due to the anisotropic character of the deformability of most rocks and the rock masses.

RÉSUMÉ:

La evaluation des constants elastiques contenues dans la matrice de deformabili te par des essais de compression diametral on ête le principal sujet de quelques tra- vaux presentes dans le Congrès de la SIMR. Dans ce travail, pour la determination d'ele ments de la matrice de deformabilite des nouvelles expressions sont proposees. Dû au caractère anisotropique de la majorite des roches et des massifs rocheux, les coefficients de concentration de tension apparaitrent.

ZUSAMMENFASSUNG:

Die Bestimmung der in der Verformungsmatrix enthaltenen, elastischen Konstanten mit Hilfe von diametralenDruckversuchen ist das Hauptthema einiger, auf IGF- -Kongressen vorgestellter Referate gewesen. In dieser Arbeit werden neue Formeln fuer die Bestimmung von Elementen der Verformungsmatrix vorgeschlagen, sowie auch fuer die Bestimmung der Spannungskonzentrationsfaktoren, die wegen des anisotropischen Charakters der Verformbarkeit der meisten Gesteine und Felsen erscheinen.

1 INTRODUCTION

Since the first steps of Rock Mechanics, one of its major subjects and concerns has been the study of the anisotropy of differ ent characteristics of rocks and rock masses.

When dealing with foundation problems of large power plants and civil works the in- fluence of the anisotropy of the deforma- bility characteristics and of the unconfined compressive strenght; can play an import- ant role. One can easily find bibliogra- phic references of strong losses in bearing capacities of rock masses of about 1:4; in some highly altered schists it can go up to 1:10.

The developments that computers have un dergone in the last decade enabled an ex- tensive use of numerical methods in the field of Rock Mechanics. Numerical methods, like the finite and boundary element methods, for instance, made possible to model the behaviour of rock masses in a three- -dimensional way and taking into account heterogeneity, anisotropy, non-linear behaviour, failure criteria and time-dependent properties. Therefore the proper determination of rock deformability is an up-to-date problem, because, even numerical methods have a great ability to perform parametric calculations, the elastic constants of the rock mass are some of the basic data required.

The relations between strains and stres- ses of an anisotropic body can be defined using a total of 21 elastic constants. The testing techniques proposed in the litera ture to determine some of these elastic constants can be reviewed in Loureiro-Pin to (1985) and Amadei (1982). The use of - diametral compression tests was first pro posed by Loureiro-Pinto (1979)and further developed by Amadei, Rogers, Goodman (1983). This method makes it possible to determine 15 of the 21 elastic constants and its main advantage is that it can be performed.

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