Comparison between GSI-based implicit and explicit structure models

Abstract

The Geological Strength Index, GSI, is a rockmass classification system based on two fundamental parameters: the blockiness of the rockmass, and discontinuity condition. The Hoek-Brown failure criterion is used with GSI to estimate the strength and stiffness of jointed rockmasses. This strength estimation method considers the effect of isotropic structure implicitly in continuum rockmass analyses. Modern numerical tools allow the creation of models where dense networks of structure are represented explicitly, with assigned properties based on site investigation data. In this paper, equivalent explicit and implicit models of the rockmass around a tunnel are produced and compared to theoretical depth of yield and closure estimates, for multiple cells in the GSI chart. This verification provides greater confidence in traditional continuum modelling methods, which continue to have practical value for analyzing engineered excavations.