The concept of representative elementary length (REL) as an effective tool to study scale effects in rock engineering problems

Abstract

In this paper, a discrete fracture network approach (DFN) is used to study scale effects on rock quality designation (RQD) measurements. RQD is a parameter that describes rock mass quality and represents a fundamental component of several rock mass classification systems. The results demonstrate that it is possible to define a representative elementary length (REL), above which RQD measurements represent an average indicator of rock mass quality. However, the directional bias of RQD measurements is such that the choice of REL is itself a function of the orientation of the sampling line used to estimate RQD. By considering multiple sampling directions, this paper introduces the concept of a REL Ellipsoid, whereby the normalized value of the REL along three sampling directions indicates the degree of homogeneity and isotropy of the rock mass with increase in problem scale. In the authors’ opinion, the REL Ellipsoid concept allows to better capture the nature of the 3D representative elementary volume (REV) for both isotropic and anisotropic rock masses Mapping data from a room-and-pillar mine are used in the initial validation of the proposed REL Ellipsoid concept.