de Bruyn, I, Prado, D, Mylvaganam, J & Walker, D 2019, 'Geotechnical considerations for the stability of open pit excavations at mine closure: some scenarios', in AB Fourie & M Tibbett (eds), Proceedings of the 13th International Conference on Mine Closure
, Australian Centre for Geomechanics, Perth, pp. 235-248, https://doi.org/10.36487/ACG_rep/1915_19_de_Bruyn
In the current mining industry climate, early and detailed planning for mine closure is becoming increasingly important. Geotechnical inputs relating to stability of open pit excavations were often limited or cursory in past mine closures. Although broad guidelines based on general observations do exist in some countries, detailed deterministic approaches and design criteria specifically applicable to open pit excavations during mine closure have not been well established. Large open pits may be most sensitive to the economic impacts of geotechnical requirements/constraints for closure, particularly if unduly conservative approaches are employed. It is therefore necessary for these requirements and constraints to be carefully assessed for each pit, and for the most cost-effective measures to be identified. It is important that slope instabilities are
well-documented during operations, and that good communication between various technical departments is maintained for closure planning and coordination.
This paper presents examples of several scenarios in which pit slope stability assessment may be required at mine closure. These are focused specifically on the long-term stability of the open pit excavations, not the stability of any adjacent structures. The paper does not attempt to propose a set of guidelines but discusses techniques that may be used for assessment under various scenarios. Topics include estimation of rock mass degradation over time, assessment of long-term instability around pits, evaluation of slope buttressing options, and determination of exclusion zones around pit crests (and in-pit floors that must remain open to access).
Keywords: geotechnical, open pit, closure
Department of Minerals and Energy, Western Australia 1999, Geotechnical Considerations in Open Pit Mines – Guideline, Version 1.0.
Department of Mines and Petroleum, Western Australia 1997, Safety Bund Walls Around Abandoned Open Pit Mines – Guideline, Revision 1.0, Document ZMA048HA.
Earth Resources 2019, Guidelines for the assessment of geotechnical risks in open pit mines and quarries, Victoria State Government, Department of Jobs, Precincts and Regions website, page updated 13 May 2019,
Hoek, E & Brown, E 1988, ‘The Hoek-Brown failure criterion – a 1988 update’, in JH Curran (ed.), Proceedings of 15th Canadian Rock Mechanics Symposium, Toronto, pp. 31–38.
Marinos, P & Hoek, E 2000, ‘GSI: a geological friendly tool for rock mass strength estimation’, Proceedings of the International Conference on Geotechnical and Geological Engineering, GeoEng 2000, International Society for Rock Mechanics, Lancaster, pp. 1422–1446.
Read, J & Stacey, P (eds) 2009, Guidelines for Open Pit Slope Design, CSIRO Publishing, Collingwood.
van Zyl, D 2009, ‘Open pit closure’, in J Read and P Stacey (eds), Guidelines for Open Pit Slope Design, CSIRO Publishing, Collingwood.