There are different methods for determining the elastic strength of fractured rock masses. The hybrid numerical Discrete Fracture Network–Distinct Element Method (DFN-DEM) approach which is used for more realistic geometrical represen-tation of fractured rocks (DFN) and facilitated a strong numerical tool (DEM) shows effective methods for calculating mechanical properties of fractured rocks. The effect of geometrical properties of fracture network such as fracture intensity on mechanical elastic strength and Representative Elementary Volume (REV) has not been investi-gated and reported in the literature. A numerous numbers of DFN models with varia-ble fracture densities and sizes are generated using Monte Carlo simulation method. A numerical uniaxial compressive stress test is conducted on all models and the elastic strength and REV for different fracture patterns are calculated. In this paper, according to the maximum allowance of 10% set for the Coefficient of Variance (CV) for determination of the REV size, the values of this size concerning the elastic strength are 9m, 8m, 10m for fracture intensities of 2.3m-2, 4.6m-2 and 6.9m-2 respec-tively. With increasing the fracture density, the elastic strength is decreased.


The elastic strength of rock masses in-situ is considerably different with the laboratory testing results using small samples without large-sized fractures. Larger volumes of rocks in-situ contain much more fractures of varying sizes which contribute to the changes, often as reduction, in strength and Young's modulus (Heuze 1980, Hoek & Brown 1980, Kemeny & Cook 1986, Tsoutrelis & Exadaktylos 1993, Beiniawski 1968) of the fractured rock masses. Even if there is no change in fracture density, which by definition is the number of the fractures per square meter, with size increase still the scale effect on mechanical properties will exist (Glucklich & Cohen 1967, Glucklich & Cohen 1968).

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