Modification of the BQ system based on the Lugeon value and RQD: a case study from the Maerdang hydropower station, China

Current rock mass quality classification methods include the rock mass rating (RMR), the Q system, the geological strength index (GSI) and the basic quality (BQ) system. Among these methods, the BQ system has been adopted as the standard for engineering classification of rock mass in China. The base value of the BQ system is determined by the intactness index of the rock mass (K_v) and the uniaxial compressive strength of intact rocks (UCS). However, it is not always possible to calculate K_v in engineering processes, thus making it difficult to classify a rock mass. In this study, the relationship among the K_v, the rock quality designation (RQD), and the Lugeon value (ω) is established using Maerdang hydropower station, China, as a case study. Results from this study enable the proposal of a modified BQ system based on UCS, RQD, and the Lugeon value. By comparing evaluation results obtained using the original BQ system with this proposed system, very similar results were obtained for rock mass at the Maerdang hydropower station. The addition of more engineering examples over time will enable further verification of the proposed modified BQ system.