This paper presents the results of a project for developing a methodology for empirically determining some of the mechanical properties of the rock mass at the Äspö Hard Rock Laboratory, Southern Sweden. Using the equations available in the literature, the deformation modulus, friction angle, cohesion and unconfined compressive strength of the rock mass were estimated. A comparison of the results using different classification methods (Q, RMR, GSI, RMi, Ramamurthy's) was made to estimate the range of variations in the mechanical properties with the considerations of:

  • the quality/quantity of the geological data;

  • the technique for partitioning of the rock mass into homogeneous domains;

  • the sensitivity and subjectivity of the empirical methods; and

  • the need for validating the empirical methods against a test case.

Cet article presente les resultats d'un projet visant à etablir une methodologie, pour determiner, de façon empirique, les proprietes mecaniques de la masse rocheuse. En utilisant les correlations disponibles dans la litterature, quelques-unes des proprietes de la masse rocheuse ont pu être determinees (module de deformation, angle de friction, cohesion, force de compression illimitee). Une comparaison des resultats obtenus par differentes methodes (Q, RMR, GSI, RMi, de Ramamurthy) a permis d'etablir une echelle de variations des proprietes mecaniques et de formuler une serie de recommandations concernant:

  • la qualite/quantite des donnees geologiques;

  • la technique de partition de la masse rocheuse dans des domaines homogènes;

  • la sensibilite et la subjectivite des methodes empiriques;

  • la necessite de valider les methodes empiriques à l'aide de nouvelles etudes de cas.

Dieses Paper prasentiert die Ergebnisse eines Projekts mit dem Ziel, eine Methodik fuer die empirische Festhellung von mechanischen Eigenschaften im Gesteinmassiv zu etablieren. Durch Verwendung der in der Literatur zuganglichen Korrelationen, wurden einige Eigenschaften des Gesteinmassivs festgestellt (Entstellungsmodul, Reibungswinkel, Kohasion, unbeschrankte Kompressionsstarke). Ein Vergleich der Ergebnisse unterschiedlicher Methoden (Q, RMR, GSI, RMi, Ramamurthy's) wurde durchgefuehrt und dies erlaubte die Feststellung der Variationsskala von den mechanischen Eigenschaften, sowie eine Reihe Empfehlungen fuer:

  • Qualitat/Quantitat der geologischen Dateien;

  • die Technik fuer Teilung des Gesteinmassivs in homogene Domane;

  • die Empfindlichkeit und Subjektivitat der empirischen Methoden;

  • das Bedarf die empirische Methoden gegen neue Fallgeschichten zu validieren.

Introduction

To estimate the overall properties of fractured rocks during site investigation, design and performance/safety assessment of nuclear waste repositories is a task of major importance. One possible approach is the use of empirical methods. Due to non-existence of closed-form solutions and difficulties in direct large-scale in situ measurements, the rock classification systems are very often used as a means to get a first-hand estimation of the mechanical properties and strength parameters, as applied in many rock engineering projects. This is done without considering issues such as the existence of a representative elementary volume (REV) (Cunha, 1990), reliable constitutive models for fractures and intact rock, and properly defined boundary/initial conditions, which all are required for the numerical schemes.

Characterisation by means of empirical methods has recently been used for predicting the mechanical properties of large-scale rock masses to perform feasibility studies for underground constructions of environmental importance, such as nuclear waste repositories. This is done as a first estimate because more in-depth understanding of the mechanical behaviour and reliable constitutive models of the fractured rocks are not available at the start of site investigation.

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