Investigation Of Factors Affecting Rock Joint Roughness Quantification Using 2-D And 3-D Statistical Roughness Parameters

Rock joint roughness influences the mechanical properties of joints.Contradictory results on roughness scale effects due to joint size appear in the literature.To find reasons for these contradictory findings,the surface roughness of a large rock joint was digitized using a triangulation algorithm and then quantified using six statistical parameters.The results obtained for the statistical parameters were then compared with a set of fractal parameter results obtained through the variogram method.This study systematically investigated the factors that have led to contradictory findings on scale effects due to joint size.The effect of non-stationarity of profiles resulting from a global linear trend was found to be negligible on the computed roughness parameters apart from the root means square(RMS)parameter,which was found to be inferior to the rest of the considered roughness parameters.Computed roughness parameter values showed significant roughness heterogeneity of the rock joint surface.Roughness heterogeneity has often been neglected in the literature in making decisions on scale effects due to joint size.Therefore,the influence of roughness heterogeneity on the joint size effect was investigated carefully in this study.Highly consistent results were obtained for both the statistical and fractal parameters for different joint sizes.No joint size effect was found on all the important roughness parameters when those were applied to relatively homogeneous sections of the rock joint.Negligible or slight joint size effect was found on all the important roughness parameters when those were applied to heterogeneous rock joint profiles.The possibility of having a joint size effect with increasing heterogeneity was found.Theoretically,no joint size effect exists on 100% smooth joints.Based on this theory and the results obtained from this study,it can be asserted that the contradictory findings that appear in the literature on joint size effects for more than 40 years have resulted from roughness heterogeneity.The studied rock joint showed significant roughness anisotropy and sampling interval effects.The RMS parameter was found to be an unsuitable parameter to quantify rock joint roughness.Useful comparisons are made between several 2-D and 3-D roughness parameters.