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Rock Mass Classification Applied to Volta Grande Underground Mine Site in Brazil



Author(s)

Daniel Jaques, Klinger Rezende and Eduardo Marques

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DOI:10.17265/2328-2193/2015.04.004

Rock mass classification is a key procedure for evaluation of rock mass behavior under underground excavation. This paper presents part of the results of a rock mass classification applied to the Volta Grande mine, located at Nazareno city, Minas Gerais State, Brazil, in order to evaluate its implantation feasibility and to define the most favorable design. Currently, Volta Grande operates an open pit mine in an intrusive pegmatitic body with amphibolite and graphite-rich schist as surrounding rock. All data to be used on RMR and Q classification schemes were collected on twenty-nine boreholes, selected according to their position and to provide an adequate knowledge of both geology and geomechanical characteristics of the project area. However, this paper presents only the results for three boreholes in only one geological cross-section (NS06), considered representative of Volta Grande mine rock mass, as the volume of data from all boreholes is too large. Samples were collected on these boreholes for all rock types and weathering grades, in quantities sufficient to allow physical and mechanical tests and to represent variations in depth and in area. Results show that despite Q system is more sensible to rock type and weathering grade changes when compared to the RMR system, dividing the rock mass in more different compartments, this division did not show good agreement to field and borehole samples observations, as the rock mass do not show such fragmentation and, so, these compartments do not control the overall behavior of the rock mass. As a general result, the rock mass classification results point out that underground mining is feasible for the studied area.

RMR, Q system, underground mining, intact rock, compressive strength, metamorphic rocks