Authors: Duran, A


Cite As:
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,

Download citation as:   ris   bibtex   endnote   text   Zotero

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.

Campbell, D.B. (2000) The Mechanism Controlling Angle of Repose Stability in Waste Rock Embankments, Slope Stability in Surface Mining, W.A. Hustrulid, M.K. McCarter and D.J.A. Van Zyl (eds), Society for Mining, Metallurgy, and Exploration, Inc. (SME), Colorado, USA, pp. 285–291.
Duran, A. (2012) Spoil Piles - Comparison of Stability Analysis Methods, Australian Geomechanics, Australian Geomechanics Society, Vol. 47, No. 4, pp. 33–42.
Lamb, T.W. and Whitman, R.V. (1969) Soil Mechanics, John Wiley & Sons, 452 p.
Osterman, J. (1959) Notes on the shearing Resistance of Soft Clays, Acta Polytechnica.
Seed, H.B. and Sultan, H.A. (1967) Stability analyses for a sloping core embankment, Journal of the Soil Mechanics Founds Division, American Society of Civil Engineers, Vol. 93, No. SM4, pp. 69–83.
Seedsman, R.W., Richards, B.G. and Williams, D.J. (1988) The Probability of Undrained Failure in Bowen Basin Spoil Piles, in Proceedings Fifth Australian-New Zealand Conference on Geomechanics, 22–26 August 1988, Sydney, Australia, Institution of Engineers, Barton, pp. 404–409.
Seedsman, R.W., Cameron, M. and Peou, S. (1995) Geotechnical Investigations and Pit Wall Designs in Faulted Ground at Eastern Creek South, Bowen Basin Symposium, pp. 191–195.
Simmons, J.V. and McManus, D.A. (2004) Shear Strength Framework for Design of Dumped Spoil Slopes for Open Pit Coal Mines, Advances in Geotechnical Engineering: The Skempton Conference, 29–31 March 2004, London, UK, Thomas Telford, London, pp. 981–991.
Rocscience Inc. (2013) SLIDE Version 6.0, 2D Limit Equilibrium Slope Stability Analysis Software,

© Copyright 2022, Australian Centre for Geomechanics (ACG), The University of Western Australia. All rights reserved.
Please direct any queries or error reports to