Authors: Duran, A


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Duran, A 2013, 'Undrained behaviour in spoil piles', in PM Dight (ed.), Slope Stability 2013: Proceedings of the 2013 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering, Australian Centre for Geomechanics, Perth, pp. 853-865,

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Stability of spoil piles has been traditionally undertaken with the use of drained strength parameters and utilising groundwater profiles within the spoil which are appropriate. Moreover, whilst the author’s experience suggests this is by far generally the case, review of recent failures at two strip mining operations suggests scenarios where there is a strong indication that undrained strength parameters could be assigned. The author presents seven case studies. As an alternative to undrained strength parameters, the author has considered; low strength shears in the sub-floor or spoil loading providing short term pore pressure increases in the sub-floor. The former provides unrealistic estimates of shear strengths applicable at both operations whilst the latter requires invoking groundwater assumptions, which although appearing reasonable, are difficult to readily implement in stability analyses. Accepting that undrained behaviour is appropriate, based on the seven case studies this paper highlights three key aspects: scenarios where undrained strengths are developed; materials that are likely to allow development of undrained strengths; and typical values of undrained shear strength indicated by back−analysis.

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