Investigation of RQD variation with scanline length and optimal threshold based on three-dimensional fracture network modeling

Rock-quality designation （RQD） plays a significant role in rock mass analysis and is an important parameter in geotechnical and geological engineering. However, the RQD variation with scanline length has not yet been comprehensively considered in RQD. In this study, three-dimensional fracture network modeling was used to simulate actual rock mass, and numerous scan- lines were set in the fracture network for investigation on RQD variation. Models and equations （i.e., models A-A, N-N, and A-A-S, as well as the Priest-Hudson and Sen-Kazi equations） were summarized for the study. A corrected equation was pro- posed to eliminate the errors from using the Priest-Hudson and Sen-Kazi equations. In addition, inhomogeneous and aniso- tropic features were investigated, and the optimal thresholds for RQD calculation were determined, which varied with the study orientation and rock mass feature. When the inhomogeneity was studied in the x direction, the optimal threshold was found to be 4 m. When anisotropy was studied, the optimal threshold was found to be 3 m.