Authors: Wines, DR; Zhang, W; van Rensburg, J; Lucarelli, A

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Wines, DR, Zhang, W, van Rensburg, J & Lucarelli, A 2023, 'Selection of appropriate strength envelopes for open pit slope stability analyses in soils and weak rocks', in PM Dight (ed.), SSIM 2023: Third International Slope Stability in Mining Conference, Australian Centre for Geomechanics, Perth, pp. 277-290,

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Soils and weak rocks are often encountered in the upper benches of open pit mines. The exposure depth of these materials is often insignificant and therefore limited effort may be committed to their characterisation and analysis. For example, these materials may be represented using a simple linear Mohr–Coulomb model with the properties based on limited testing data. However, observations of soil and weak rock behaviour (including laboratory testing) indicate that the strength envelopes are often non-linear. When deeper exposures of these relatively weak materials are encountered, providing a more rigorous numerical representation of their expected behaviour may be important to the safety and economic viability of an operation. Compared to linear strength envelopes, non-linear strength envelopes can provide an improved understanding of the expected behaviour of soils and weak rocks. In this paper, numerical analyses were used to illustrate the difference in slope stability analysis results obtained using linear and non-linear strength envelopes. The paper also discussed case studies from three different open pit mines where non-linear strength envelopes provided more plausible and realistic representations of observed slope behaviour.

Keywords: soil, weak rock, non-linear strength, Mohr–Coulomb, confining stress

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