Authors: Davies, P; Zargarbashi, S; McQueen, L


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Davies, P, Zargarbashi, S & McQueen, L 2013, 'Flow failure in coal stockpiles – how to reduce risk', 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. 881-895,

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This paper presents findings from a geotechnical study undertaken to reduce the risk of coal stockpile instability, following a flow failure observed in New South Wales. To characterise the stockpile behaviour, key input parameters such as permeability, shear strength and compressibility have been assessed for different in situ densities. Excess pore water pressure developed within the stockpile has been estimated by finite element analyses, using 2D PLAXIS, for different stockpile filling rates and target heights and taking into account the stockpile loading/unloading operations adopted in the mine. PLAXIS pore pressures were then incorporated into a series of limit equilibrium stability analyses conducted for three stockpile heights at different filling rates to study variation of Factor of Safety (FS) with the rate of stockpile filling rate, stockpile height and groundwater level. Conclusions from this modelling case study show that loading rates as high as 5 m/day may be adopted to raise the stockpile to a maximum height of about 10 m. Placement rates faster than 3 m/day result in an elevated risk of instability for higher stockpiles. Placement rates faster than 1 m/day increase the risk of flowslides for stockpiles of 15 m or higher. The analysis also shows that loader reclamation from the toe shortly after stockpile filling escalates the risk of instability for stockpiles above 10 m placed faster than 1 m/day. The results were used to update a mine stockpile risk management plan to include consideration of stockpile filling rates, coal placement/reclamation method and stockpile height. A monitoring strategy was also developed to assist with risk management.

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