Accounting for Rockmass Structure in Underground and Open Pit Mine Design

The overall strength of a rockmass, as determined by traditional rockmass characterization methods, typically involves an assessment of the intact rock strength and rockmass structure. This paper investigates a variety of approaches to account for the effect of intrablock structure (veins) on rockmass strength. Triaxial and direct shear test data were generated numerically for a theoretical andesitic tuff using FEM. The triaxial results were applied to a deep underground mine drift design case. Direct shear results were compared to an open pit slope case. The approach previously developed by the authors to account for intrablock structure using GSI was compared to a new approach that degrades the intact strength parameters of the material based on UCS and triaxial tests. The GSI and intact parameter approaches were found to be comparable, with only slight differences near zero confining stress. The numerical simulation of direct shear tests showed the importance of veins in the way failure initiates and propagates under that particular loading condition.