ABSTRACT:

The stability of an excavation cut in a rock mass comprising a regular network of joints is analyzed within the framework of a homogenization method. This method relies upon an explicit formulation of a macroscopic strength condition for the jointed rock mass considered as a homogeneous anisotropic material. Making use of two different kinds of failure mechanisms on the homogenized structure, upper bound estimates are then derived for the stability factor, which prove better than those obtained from a direct approach in which the intact rock material and the joints are considered separately.

RESUME:

On s'interesse à la stabilite d'un talus excave dans un massif ruche traverse par un reseau regular de fractures, analyses par une methode d'homogeneisation, Celle-ci repose sur une formulation explicite du critère de resistance macroscopique de la roche fracturee consideree comme un milieu homogène anisotrope. Mettant en oeuvre deux differents types de mecanismes de ruine de I'ouvrage homogeneise, on obtient alors des bornes superieures du facteur de stabilite, qui se revèlent meilleures que celles provenant d'un calcul direct. dans lequel la roche intacte et les joints de fracture sont consideres separement.

ZUSAMMENFASSUNG:

Man interessiert sich an die Standsicherheit einer Böschung in einem felskörper, d'er von einem regelmassigen Kluftnetz durchgequert ist. Diese Arbeit stuetzt sich auf dip Homogenisierungstheorie, die von der ßestimmung der anisotropischen und homogeny makroskopischen Grenzbedingung des gekluefleten Folsmaterials aught. Zweig verschiedenen Bruchmechanismen der Böschung werden beruecksichtigt. Sie fuehren zu Berechnungen des Standsicherheitsfaktors, die sich besser erweisen als diejenigen, die man aus einer unmittelbaren Methode erhaltet., in der das felsmaterial und die Klueften getrennt betrachtet werden.

1 INTRODUCTION

Taking into account the mechanical behaviour of joints in jointed rock masses has always been of paramount importance to civil or mining engineers involved in the failure design of structures built In such materials. Most usual approaches either refer to the well known "block theory" (Goodman and Shi (1985); Goodman (1995)) which attempts to identify the possible failure patterns along the joints through geometrical and kinematical considerations (concept of key-block), or to the "distinct element method" (Cundall (1988); Hart et al. (1988)) which regards the jointed rock mass as an assemblage of rigid or deformable blocks of intact rock in mutual interaction through discontinuities. However, for a dense network of joints, the numerical treatment generated by the application of such methods is getting rapidly untractable as the number of block elements increases, so that a homogenization approach seems far more advisable for dealing with such a situation. The aim of the present contribution is to put the implementation of such an approach into practice on the particular example of a jointed rock excavation whose stability analysis is carried out by means of the upper bound kinematic method of yield design. As a preliminary, it requires the determination of the global strength properties of the jointed rock mass regarded as a homogeneous medium, which has been recently performed by Bekaert and Maghous (1996). Results of this analysis are discussed and compared with those derived from a direct approach in which joint surfaces and blocks of intact rock are treated separately.

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