Discontinuities with a fractal distribution have become increasingly the focus of research in rock engineering. This paper begins by reviewing previous research on the assessment of in-situ block size distributions of a rock mass. The in-situ block size distribution with special reference to discontinuities with a fractal spacing distribution is investigated using a computer simulation of randomly generated artificial discontinuities with fractal distributions. Empirical equations are derived thus enabling the practical estimation of the in-situ block size distribution for these types of rock masses, A comparison with other typical spacing distributions is also presented. In addition, a grey correlation analysis technique is introduced to evaluate the goodness-of-fit between theoretical as compared with real spacing distributions.


Les discontinuites avec une distribution des fractal sont grandement devenues Ie centre d'interet de la recherche dans l'ingenierie de la roche. Ce document commence par faire la point des precedemtes recherches sur l'evaluation de la repartition des dimensions de blocs en place dans une masse recheuse. La repartition des tailles des blocs en place avec une reference particulière aux discontinuites avec une distribution d'espaces de fractal est recherchee sur ordinateur par une simulation de discontunuites generees artificiellement avec distribution des fractal. Des equations empiriques sont derivees pour rendre possible l'estimation pratique de la repartition des dimensions de blocs en place pour ces types de roches massives. Une comparaison avec d'autres distributions d'espaces typiques est egalement presentee. De plus, une analyse technique corollaire est introduite pour evaluer la concordance des resultats entre la theorie entre la theorie et la distribution reelle des espaces.


Diskontinuitaten mit fraktaler verteilung sind immer mehr ein wichtiges Forschungsgebiet der Felstechnik. Dieser Beitrag fangt mit einem Überblick ueber frueheren Schatzungen von Blockgrössevelteilungen in Gestein an. Die Blockgrössenverteilungen ist per Computersimulation, ausgehen von zufallsaugewahlten Diskontinuitaten mit besonderer Erwahnung Diskontinuitaten mit fraktaler Verteilung, untersucht. Empirische Gleichungen sind abgeleitet um in der Praxis Blockgrösseverteilungen solches Gestein zu schatzen, Ein Vergleich mit anderen typischen Verteilungen ist prasentiert. Zusatzlich ist ein Graucorrelationsanalyse eingeleitet um die Genauigkeit der Abatandeverteilungen zu schatzen.


The natural i.e. in-situ block size plays an important role in excavation by blasting, rock mass classification, stability analysis of excavations and fracture network flow modeling. The formation of individual blocks of intact rock of different sizes results from the mutual intersection of discontinuity sets with different spacing and orientation. The discontinuity spacing, together with the persistence of discontinuities and the number of discontinuity sets, are among the principal factors affecting the in-situ block sizes of a rock mass (ISRM 1978, Wang et aI. 1990), Several assessment methods of in-situ block size distribution (IBSD), including the Block Size Index method (ISRM, 1978), a simulation method (Hudson & Priest, 1979) and a computational method (Da Gama, 1983; JKMRC, 1991) have been proposed. Impressive developments in the IBSD assessment are presented by Wang and his co-workers (Wang et al, 1990, 1991; Wang 1992), who developed two techniques of predicting the IBSD parameters. One is the so-called. Dissection Method, which uses a computer programme to determine the IBSD. Another is the so-called Equation Method, which uses a set of empirical equations, derived from the dissection method, to estimate the IBSD.

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