Authors: Rimmelin, R; Vallejos, J

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Rimmelin, R & Vallejos, J 2020, 'Rock mass behaviour of deep mining slopes: a conceptual model and implications', in PM Dight (ed.), Slope Stability 2020: Proceedings of the 2020 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering, Australian Centre for Geomechanics, Perth, pp. 591-608,

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The present study proposes a conceptual model to estimate the rock mass behaviour of deep mining slopes in porphyry copper deposits, which in some mines may reach more than 1 km, such as Chuquicamata (Chile) or Bingham Canyon (USA). It was proposed that deep mining slopes (more than 500 m depth), should be differentiated from shallow or less deep slopes, in the geomechanical behaviour of the rock mass. Close to surface, an elastic-perfectly plastic behaviour was generally assumed to represent the rock mass behaviour. For deep mining slopes, the behaviour of the rock mass may change to a strain-weakening or brittle response. The limit between the two geomechanical behaviours depends on the geological features of the recognised sulphide limit. The geomechanical response of a conceptual model of a deep mining slope is analysed using two dimensional numerical models, based on a parametrisation of the wall geometry (depth and overall angle), sulphide limit depth and stress ratio (ratio between the horizontal and the vertical in situ stresses). The results of the parametric analysis were presented in terms of the factor of safety. It was found that the stress ratio does not significantly affects the factor of safety of a deep slope for the range of overall angles considered in the analysis (25–45°). From the results, a limit equilibrium relationship between the wall geometry/sulphide limit and depth was proposed. The implications of the results of the study were related to the expected overall failure mechanism of the wall and the type of monitoring systems that should be considered.

Keywords: deep slopes, open pit, porphyry copper deposits, sulphide limit, constitutive model, numerical modelling

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