ABSTRACT:
The application of Geological Strength Index (GSI) to Japanese rocks is discussed. There have been very few attempts at using the GSI in Japan. First, we tried to compare GSI to the Japanese conventional classification for NATM tunneling. The support requirement of a tunnel in Japan is derived from the distribution of P-wave velocity over objective areas. In our case histories the authors considered that the GSI was close to the Japanese system. Second, we discuss the relationship between GSI and deformability of soft sedimentary rocks through borehole loading tests. Rocks are soft sedimentary, but discontinuities are dominant in some depth. We analyzed the influence of discontinuities by identifying moduli of elasticity, deformability and moduli of permanent deformation in comparison of those obtained through GSI for each result of loading test. The moduli of deformability estimated by GSI are pretty close to those of permanent deformation.
1 INTRODUCTION
Rock mass classification has been used for characterizing rock masses in designing rock structures. It has provided some approximate properties of rock, such as rock mass strength and deformability. Systems commonly used worldwide are the Rock Mass Rating (RMR) by Bieniawski (1976), the Q-system by Barton et al. (1974), and the Geological Strength Index (GSI) by Hoek (1994). In particular, we focus here on the application of the GSI to Japanese rocks. First, we tried to compare the GSI to the Japanese conventional classification for NATM tunneling, which is based on the description of the structure of discontinuities in a rock mass. Second, we discussed the relationship between GSI and the deformability of soft sedimentary rocks through borehole loading tests. We analyzed the influence of discontinuities by identifying the elastic moduli, deformability and moduli of permanent deformation in comparison to those obtained through the GSI for each result of the loading test.
