RQD calculation method based on 3D rock discontinuity network simulation in the dam foundation of Baihetan hydropower station

Abstract

The original rock quality designation (RQD) index has several limitations, such as one-dimensional (1D) direction and a single threshold. For these reasons, a novel RQD calculation method is proposed by using 3D discontinuity network simulation. In this method, a 3D discontinuity network model (3D-DNM) of the rock mass is generated by Monte–Carlo analogy procedure, in accordance with the optimal probability models of the rock discontinuity’s geometrical elements. Then, the RQD values at different azimuth on the three orthogonal planes of the 3D-DNM can be analyzed statistically. Based on the analysis result, the novel index RQD t is put forward. In this index, the threshold corresponding to the maximum standard deviation of the RQD t is defined as the optimal threshold. The RQD t with an optimal threshold has the greatest capacity to reflect the heterogeneity and anisotropy of rock mass. To illustrate the effectiveness of the proposed method, we apply it on the foundation rock mass of Baihetan hydropower station on Jinsha River. Finally, the optimal threshold is determined as 0.6 m, and the quality and anisotropy of the dam foundation rock mass are fully demonstrated by the generalized RQD 0.6.