Authors: Darakjian, T; Luck, S; Luck, D; Xu, C; Moffitt, K; Nicoll, S; Tennant, D; Pothitos, F

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Darakjian, T, Luck, S, Luck, D, Xu, C, Moffitt, K, Nicoll, S, Tennant, D & Pothitos, F 2023, 'Challenges of characterising a highly altered and variable rock mass for open pit slope design optimisation', in PM Dight (ed.), SSIM 2023: Third International Slope Stability in Mining Conference, Australian Centre for Geomechanics, Perth, pp. 359-372,

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Geotechnical characterisation is generally carried out by subdividing a rock mass into a number of unique geotechnical domains, each exhibiting similar geotechnical properties. Geotechnical data for each domain are then analysed to develop representative parameters for each domain. This approach is not optimal for rock masses that have significant local-scale variability in geotechnical character. This paper documents the approach used to consider the high degree of spatial variability in geotechnical properties for the Lihir Mine, located in Papua New Guinea. The Lihir Mine is situated within the Luise volcanic crater, part of a volcanic island arc chain within the New Ireland arc-trench complex, southwest of an inactive subduction zone. The Luise volcano has previously been interpreted as a mafic to intermediate volcano, with an underlying porphyry system. Following volcanic sector collapse, the lithostatic load was rapidly decreased. This led to boiling of mineralised fluids and resulted in the formation of an epithermal gold deposit (Blackwell et al. 2010). Maar-diatreme activity then continued within the caldera, leading to the formation of diatreme eruptive centres and crater lake sediments. The geological history has resulted in a complex geological and structural environment with a high degree of geotechnical variability. Geotechnical characterisation has involved the use of geostatistical block modelling approaches to better identify the spatial variability of geotechnical properties within each geotechnical domain. The use of block modelling tools has allowed for greater resolution of input parameters for both 2D and 3D stability analyses.

Keywords: caldera, diatreme, ordinary kriging, 3D modelling, continuity, data spatial distribution, block model, stability analysis, geotechnical characterisation, slope optimisation, slope stability, weak rocks

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