The REV (Representative Elementary Volume) is widely employed to define the scale limit when the continuum or discontinuum method is suitable for rock mass analyses. A simplified tool is needed as an aid to approximate this limit. The Continuity Factor (CF) was proposed by Palmström for this purpose. The definition of the CF implies that the joint spacing is the most significant parameter for the REV. However, other parameters might also influence the REV. In this paper, a literature review of derived REVs is performed. For each REV, the average block size is calculated. The correlation between the REV and the average block size index Ib is thereafter analyzed. The results show that a CF limit of approximately four may exist for the geometrical and the mechanical REV. If other parameters exists that significantly influence the REV are discussed.
The continuum method and the discontinuum method are widely used for jointed rock mass analysis. Often, the continuum method is preferred due to its simplicity and convenience. If continuum or discontinuum methods should be used mainly depends on the scale of the problem in relation to the geological features of the rock mass (Hoek and Brown 1980).
The scale effect on the parameters of rock masses has been studied by many authors. In order to illustrate this scale effect, considerable work has been conducted by seeking the representative elementary volume (REV) for different rock masses. The REV was introduced by Bear (1972), and it was defined as the minimum volume or range beyond which the characteristics or properties of the domain remain basically constant (Figure 1).
The REV of the rock mass has been employed as the scale limit when the continuum method is suitable. Based on the REV, the REV side length has to be compared with the size of the rock mechanical structure in order to decide if a continuum or discontinuum approach should be applied. However, the evaluation of REV takes time since it is mainly obtained based on numerical tests on synthetic rock mass (SRM) samples of different sizes. A need therefore exists for a simplified tool as an aid in the engineering process to decide when the continuum or discontinuum method is appropriate.