Comparisons of Evaluation Factors and Application Effects of the New [BQ]GSI System with International Rock Mass Classification Systems

The basic quality (BQ) system is regarded as the national rock mass classification system that can be appropriate for use in most types of rock engineering in China. Two underlying parameters that the uniaxial compressive strength (UCS) and the rock intactness index (KV) are taken into account to access the basic BQ value. However, The KV was usually measured by an indirect acoustic wave approach which often cannot reflected the actual conditions. In this study, a direct measured parameter KGSI is recommended to obtain by means of the GSI system to replace the original KV, and a new method [BQ]GSI expressed by the new parameter KGSI is proposed. In particular, a graphic method is also presented to determine rapidly and rationally the rock mass classification by the X, Y coordinates of the UCS and the KGSI. In order to further compare the evaluation results and application effects between the [BQ]GSI and the international rock mass classification systems, a comprehensive solution is carried out. First, the evaluation factors of rock mass qualities from all these system are classified according to three groups: the rock mass inherent parameters, external parameters, and construction parameters. Second, the correlations among these evaluation factors in the new [BQ]GSI system and the common international systems (i.e. RMR, Q, and RMi) were compared. And the formulas or charts among the three groups are presented. Finally, five hydropower underground excavations are chosen to analysis the comparison results of the [BQ]GSI system and the international common RMR, Q, or RMi systems. The applicability scope of these international RMR, Q, or RMi systems is also discussed in the context of China’s rock characteristics and geological stress conditions.