Rimmelin, R & Vallejos, J 2020, 'Rock mass behaviour of deep mining slopes: a conceptual model and implications', in PM Dight (ed.), Slope Stability 2020: Proceedings of the 2020 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering
, Australian Centre for Geomechanics, Perth, pp. 591-608, https://doi.org/10.36487/ACG_repo/2025_36
The present study proposes a conceptual model to estimate the rock mass behaviour of deep mining slopes in porphyry copper deposits, which in some mines may reach more than 1 km, such as Chuquicamata (Chile) or Bingham Canyon (USA). It was proposed that deep mining slopes (more than 500 m depth), should be differentiated from shallow or less deep slopes, in the geomechanical behaviour of the rock mass. Close to surface, an elastic-perfectly plastic behaviour was generally assumed to represent the rock mass behaviour. For deep mining slopes, the behaviour of the rock mass may change to a strain-weakening or brittle response. The limit between the two geomechanical behaviours depends on the geological features of the recognised sulphide limit.
The geomechanical response of a conceptual model of a deep mining slope is analysed using two dimensional numerical models, based on a parametrisation of the wall geometry (depth and overall angle), sulphide limit depth and stress ratio (ratio between the horizontal and the vertical in situ stresses). The results of the parametric analysis were presented in terms of the factor of safety. It was found that the stress ratio does not significantly affects the factor of safety of a deep slope for the range of overall angles considered in the analysis (25–45°). From the results, a limit equilibrium relationship between the wall geometry/sulphide limit and depth was proposed.
The implications of the results of the study were related to the expected overall failure mechanism of the wall and the type of monitoring systems that should be considered.
Keywords: deep slopes, open pit, porphyry copper deposits, sulphide limit, constitutive model, numerical modelling
Carter, TG & Diederichs, MS 2008, ‘Application of modified Hoek-Brown transition relationships for assessing strength and post yield behaviour at both ends of the rock competence scale’, Proceedings of the 6th International Symposium on Ground Support in Mining and Civil Engineering Construction, Southern African Institute of Mining and Metallurgy, Johannesburg.
Diederichs, MS 2003, ‘Proceedings of the the 2003 Canadian Geotechnical Colloquium: mechanistic interpretation and practical application of damage and spalling prediction criteria for deep tunnelling’, Canadian Geotechnical Journal, vol. 44, no. 9, pp. 1082–1116.
Hoek, E, Carrranza-Torres, C & Corkum, B 2002, ‘Hoek–Brown failure criterion – 2002 edition’, Proceedings of the NARMS-TAC Conference, University of Toronto Press, Toronto.
Hoek, E & Karzulovic, A 2000, ‘Rock mass properties for surface mines’, in WA Hustralid, MK McCarter & DJA van Zyl (eds), Slope Stability in Surface Mining, Society for Mining, Metallurgy and Exploration, Inc., Littleton.
Hoek, E, Read, J, Karzulovic, A & Chen, ZY 2000, ‘Rock slopes in civil and mining engineering’, International Conference on Geotechnical and Geological Engineering (GeoEng 2000), International Society for Rock Mechanics, Melbourne.
Marinos, V, Marinos, P & Hoek, E 2005, ‘The geological strength index: applications and limitations’, Bulletin of Engineering Geology and the Environment, vol. 64, iss. 1, pp. 55–65.
Ossandón, G, Fréraut, R & Gustafson, L 2001, ‘Geology of the Chuquicamata mine: a progress report’, Economic Geology, vol. 96, pp. 240–270.
Read, J & Stacey, PF 2009, Guidelines for Open Pit Design, CSIRO Publishing, Clayton.
Robotham, M 2011, ‘Slope design in large open pit mines’, International Symposium on Rock Slope Stability in Open Pit Mining and Civil Engineering, Canadian Rock Mechanics Association, .
Septian, A 2016, Influence of Geotechnical Properties on the Run-Out Process at Bingham Canyon Slope Failure, thesis, Mining Research Project II, The University of Queensland, Brisbane.
Sillitoe, R 2010, ‘Porphyry copper systems’, Economic Geology, vol. 105, pp. 3–41.
Sillitoe, R & Perelló, J 2005, ‘Andean Copper Province: tectonomagmatic settings, deposit types, metallogeny, exploration, and discovery’, Society of Economic Geology 100th Anniversary Volume, pp. 845–890.
Tooker, EW 1990, ‘Gold in Bingham District, Utah’, USGS Bulletin 1857: Gold in Copper Porphyry Copper Systems, United States Government Printing Office, Washington DC.
Ward, JT 2015, Bingham Canyon Landslide: Analysis and Mitigation, Bachelor of Science in Geological Engineering, University of Reno.
Weis, P, Driesner, T & Heinrich, CA 2018, ‘Porphyry-copper ore schells form at stable pressure-temperature fronts within dynamic fluid plumes’, Science, vol. 338, iss. 6114, pp. 1613–1616.
Wyllie, DC & Mah, CW 2004, Rock Slope Engineering, Civil and Mining, 4th edn, Spon Press, New York.