Prediction of likely response to excavation, and production of final designs for the rock reinforcement, require realistic descriptions of the components of rock mass behaviour. This article explores some of the methods that have proved reasonably successful in describing and modelling rock joints and rock masses, despite the complexities involved. Index testing of rock joints and rock mass characterisation, including geophysical methods, are the essential activities in preparation for two- and three-dimensional distinct element modelling. Recent improvements are described.
La prevision de la reponse vraisemblable d'un massif rocheux lors de la realisation d'une excavation, ainsi que Ie dimensionnement des renforcements necessaires, necessitent une description realiste du comportement des composants de ce massif. Cet article explore quelques unes des methodes qui se sont montrees raisonnablement satisfaisantes pour la description et la modelisation des massifs rocheux et de leurs joints, en depit de la complexite que cela suppose. Les essais sur joints et la caracterisation du massif (y compris par les methodes geophysiques) sont les elements essentiels prealables a une modelisation en deux ou trois dimensions par elements discontinus. Des developpernents recents sont decrits.
Die Vorhersage der wahrscheinlichen Gebirgsreaktion auf das Auffahren von Untertageraumen und das Design von Felsverstarkungen verlangt die wirklichkeitsnahe Beschreibung der einzelnen Komponenten des Felsverhaltens. Dieser Artikel beschreibt einige Methoden, welche trotz ihrer Komplexitat, erfolgreich zur Kluft- und Felsmodellierung und Beschreibung angewandt werden. Das Indextesten von Klueften und die Gebirgsklassifizierung, geophysikalische Methoden eingeschlossen, sind wesentliche Bestandteile in der Vorbereitungsphase von zwei und dreidimensionalen bestimmten Elemente Simulierungen. Neuere Entwicklungen werden beschrieben.
This article explores some of the methods which appear to be having some success in realistic modelling and design for jointed rock masses. Key techniques are joint index testing, rock mass characterisation, seismic measurements and distinct element modelling. At NGI, these methods can be represented by the following basic symbols: JRC, JCS, r Q, Vp, UDEC and 3DEC. The first three are the index parameters for the joint sets of concern (Barton and Bandis, 1990). The Q-values give estimates for rock mass moduli and rock reinforcement, following Grimstad and Barton, 1993. The two- and three dimensional distinct element models UDEC and 3DEC conceived by Cundall and refined by Itasca Inc. provide the final essential link to reality. Spatial variability within the rock mass which is reflected to some extent by the statistics for JRC, JCS, r and Q, is further described by the seismic measurements which provide a means of extrapolation between mapping locations (i.e., exposures or drill core). In its optimal form (cross-hole seismic tomography), it gives detailed information that can be approximately correlated to Q-values and to deformation modulus, using recent developments.
Direct shear tests of rough-walled tension fractures developed in weak model materials, that were performed many years ago when the author was a student, indicated the importance of both the surface roughness and the uniaxial strength (of the rock. The empirical relation for peak shear strength given in Equation 1 was essentially the forerunner of the subsequent JRC-JCS or Barton-Bandis model, where the joint roughness coefficient (JRC) was equal to 20 for these rough tension fractures. The joint walI strength (JCS) was equal to (the unconfined compression strength).