New GSI correlations with different RMR adjustments for an eastern mine of the Quadrilátero Ferrífero

Abstract

Two of the major classification systems currently used to predict the behavior of rock masses are the RMR (Rock Mass Rating) and the GSI (Geological Strength Index).The RMR was developed with the aim of recommending conceptual engineering solutions, while the purpose of the GSI is to estimate the strength and deformability parameters of rock masses. In an attempt to quantify the GSI from, it was introduced a formula, based on RMR values. Additionally, it was defined the GSI as being 5 points lower than the RMR's 1989 proposal (RMR89). However, since this correlation was defined only for RMR89 values, it should not be employed with any RMR later versions. In this context, this paper presents the results obtained from quantitative and qualitative methods proposed for GSI determination applied to itabirite rock masses in different weathering grades. In addition, another paper's goal comprises the proposal of correlations for defining GSI values from different adjustments suggested for the RMR classification. These proposals were applied to the rock masses of Tamanduá and Sapecado mines, both located in the eastern part of the Quadrilátero Ferrífero, in the state of Minas Gerais, Brazil. Even though the qualitative and quantitative methods of defining GSI values resulted in similar zones in the GSI chart, they have also presented difficulties for defining good correlations specifically for soft rock masses. The new correlations found on this paper resulted in satisfactory results and showed the potential of aiding in the decision-making process in projects involving soft (poor) rock masses, composed by low-strength lithotypes and similar weathering grades.