Similar to the fluid permeability problem [1], the deformation problem of fractured rock masses can make use of either implicit (equivalent continuum) approach [2-4] or explicit (discrete) approach [5,6]. The former takes into account the influences of fractures by means of the elastic (compliance) matrix but neglects their exact positions, and is able to simulate fractures of large quantity; the latter considers the geological and mechanical properties of each fracture deterministically, and is often adopted for large-scaled fractures. The need to use, for a particular problem, implicit or explicit approach depends on the size (or scale) of the fractures with respect to the scale of the problem that needs to be solved. There are no universal quantitative guidelines to determine when one approach should be used instead of the other [7].The applicability of implicit approach for the deformation problem of the fractured rock masses is linked to the existence of elastic compliance matrix and representative element volume (REV). The quantitative solution for this issue usually should be obtained through physical tests (laboratory and field). In recent years the numerical techniques are also developed for the evaluation of the permeability tensor [8-11] and elastic compliance matrix [12-14] of the fractured rock masses. The algorithm is a kind of numerical test system (NTS) and is generally formulated as follows: first, a discrete fracture network in a sampling window is generated, which will be used as the parent stochastic discrete fracture network (DFN); next, a series of fractured rock blocks with different sizes and orientations are defined as test samples for each stochastic DFN; then the numerical methods (e.g. FEM or DEM) are applied to the fractured rock samples to evaluate their fluid flow fields or deformation fields; finally the permeability matrices or elastic compliance matrices of the samples are obtained and the existence of REV is identified.
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