Authors: Baczynski, NRP; Sheppard, IK; Smith, KJ; Simbina, P; Sakail, R


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Baczynski, NRP, Sheppard, IK, Smith, KJ, Simbina, P & Sakail, R 2008, 'Toppling Slope Failure — Predicted Versus Actual, Ok Tedi, Papua New Guinea', in Y Potvin, J Carter, A Dyskin & R Jeffrey (eds), SHIRMS 2008: Proceedings of the First Southern Hemisphere International Rock Mechanics Symposium, Australian Centre for Geomechanics, Perth, pp. 419-431,

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This paper describes a classic toppling failure that has moved eight metres whilst retaining overall slope integrity. The failure is in the current Ok Tedi Mine open pit which is 3000 by 2000 m in plan and 700 m deep; final depth will be 1000 m; although the final depth beneath the failure will be increased by only 30 m. Large fault-defined block toppling failure was anticipated for some slope areas on the basis of kinematic stability analyses, and FLAC and UDEC numerical modelling undertaken during the 1997–2000 Risk-Based Slope Design Optimization Study. Signs of toppling instability were first noted in 2005. Ground displacements accelerated rapidly in 2006 during mining at the slope toe. Additional UDEC modelling predicted cyclic, stop-start type, cumulative displacements of 10–11 m as successive benches were mined down; with the slope face ravelling but the overall slope remaining stable. Actual slope behaviour and failure mode have largely mirrored modelling predictions. Spasms of ground displacement have been triggered by mining activity and, in some instances, compounded by intense rainfall and major pit blasting events. Further movement is expected as the slope is mined down to its final design depth.

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