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 Palmstrom 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 I-b 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.
Discontinuum approach or equivalent continuum approach is usually adopted in order to model the behavior of rock masses. The latter approach is more frequently used. However, this approach might be unacceptable for slightly-jointed rock masses. The continuity factor (CF), mainly derived from empirical experience, is defined as the ratio of the tunnel span to the block diameter. It is commonly used to determine whether a rock mass should be modeled as a continuum or a discontinuum material. Only a few analyses regarding the CF have been performed previously. In order to study the limits between continuous and discontinuous behavior, nu-merical analyses with UDEC have been performed. In these analyse, a rock mass with two sets of orthogonal joints are initially generated. From this rock mass, square areas corresponding to a certain CF are randomly chosen as models in UDEC. Confined compression test is conducted on the mentioned model and the constrained modulus (Dm) regarding this rock mass is calculated. Due to the variations of the relative loca-tions between the square and the joints cut inside, as well as the joint quantity and the joint lengths, several Dm are yielded for each CF. Several CFs are also analyzed and the results are compared with previous suggested limits between continuous and dis-continuous behaviors.