Advantages of geotechnical data collection during pit wall construction for open pit slope design optimisation

Authors: Darakjian, T; McIlquham, J; Weller, M; Morrell, C; Tennant, D Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2535_18

Cite As:
Darakjian, T, McIlquham, J, Weller, M, Morrell, C & Tennant, D 2025, 'Advantages of geotechnical data collection during pit wall construction for open pit slope design optimisation', in JJ Potter & J Wesseloo (eds), SSIM 2025: Fourth International Slope Stability in Mining Conference, Australian Centre for Geomechanics, Perth, https://doi.org/10.36487/ACG_repo/2535_18



Abstract:
Pit slope design is often considered final at the detailed design for life of mine pit walls. During construction of these walls, critical information from newly exposed benches can be overlooked, particularly if a slope reconciliation plan has not been produced. The absence of slope reconciliation may lead to unexpected slope instability, which could result in not achieving design acceptance criteria values, increased effort being required to maintain bench width for management of rockfall risk, mitigation measures to manage loss of benches, step-outs to manage multi-bench and inter-ramp instabilities, or complete loss of a pit wall. The purpose of geotechnical rock mass and structural models generated for slope stability analysis is to predict the conditions at the time of construction. As these models are only as good as the data provided, they often include gaps in knowledge where little or no data is available. This is particularly challenging in areas of variable rock mass and structural conditions. This paper documents the approach used to consider the high degree of spatial variability in geotechnical properties during construction of the Lihir Mine, located in Papua New Guinea. Lihir Mine is geotechnically characterised through geostatistical block modelling approaches to better identify the spatial variability of geotechnical properties within geotechnical domains. The use of block modelling tools has allowed for greater resolution of predicted input parameters for slope stability analyses. During construction, variation of predicted versus as-built geotechnical conditions are observed and documented as part of the slope reconciliation study. Onsite geologists and engineers collect key information from exposed faces through geological mapping, rock core logging, observations during construction and monitoring data review, where these data are compared to predicted conditions. The magnitude of variation is then assessed to determine its potential impact on slope stability and areas where additional slope stability analyses may be required.

Keywords: stability analysis, geotechnical characterisation, slope optimisation, slope stability, geotechnical model

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