Investigating the effect of variation of Geology Strength Index (GSI) on the geomechanical parameters of rock mass

Determining the geomechanical parameters of rock mass is of particular importance in the design of industrial projects such as dams and tunnels. One of the most useful methods for determining these parameters is Hoek-Brown failure criterion. Because, rock mass quality is considered in this criterion on the basis of Geological Strength Index (GSI). Various methods were developed for determining GSI, and the results of each method differ from the results of the others. So far, the effect of these differences on the geomechanical parameters was not studied. The purpose of this research is to investigate the effects of GSI on the geomechanical parameters. Hence, different methods are reviewed and investigated at first. Latter, with the collected data (field study), this index is predicted and the effects of index variations on Hook-Brown constant parameters, strength parameters and deformation modulus with the proposed relationships are investigated. Results show that the difference in methods has a significant effect on geomechanical parameters. So that, a difference of 9 units in the geological strength index leads to more than 7GPa difference in the modulus of deformation.