Abstract
This paper presents the relationship between Rock Mass Quality (Q-system) and the Geological Strength Index (GSI) parameters. Equations are suggested based on field data and calculations of the empirical results of granitic rock masses (Hungary) and siltstones, sandstones and quartzite formations (Australia). Measured and calculated GSI values vs Q values are given for granitic rocks, showing a higher correlation than that of the sedimentary rocks of Australia. The different behaviors of rock masses explain the higher correlation between GSI vs Q and GSI chart vs GSI calculated for igneous rock bodies. Despite the differences in stress fields and the highly tectonised structural geological setting of the granitic rock mass, the isotropic nature of granitic rocks vs. anisotropy of sedimentary rock bodies is reflected in the correlation coefficients.