Application of Synthetic Nets as an Enabler of Optimised Pit Slopes at Skorpion Zinc Mine

  • Amory Mumba
  • Bunda BesaEmail author
Conference paper
Part of the Springer Series in Geomechanics and Geoengineering book series (SSGG)


Pit slope optimization is a fundamental design requirement for open pit mines. Several input parameters are incorporated into the slope design process including the slope angle, commodity price, recoveries and equipment size among others. The quality of the rock mass determines how steep the slopes should be designed for a safe and economic open pit mine. Despite rigorous efforts to optimize pit slopes, rock falls from extremely poor zones still occur. A complex and highly heterogeneous rock mass at Skorpion Zinc mine presents a challenge in steepening the hanging wall slopes for maximum resource recovery; competent limestone rock hosts intrusions and shear zones with extremely weathered sheared sericite schists. These ground conditions have resulted in significant rock falls from shear zones onto existing ramps and often-disrupting production. This paper presents how synthetic high wall safety nets have been applied at Skorpion Zinc mine in optimizing the pit slope angles, reducing clean-up cost and enhancing safety. Slope Stability analysis, using Rocscience software, was conducted on interim pit designs, incorporating angles of slopes with and without safety nets. Results show that the slopes were more stable when covered with synthetic nets than the ones left without support. Hence, the hanging wall inter-ramp slope angles were increased from the actual slope angle of 54° to 61° with an optimal angle being 61°. At this optimal slope angle, Probability of Failure (PoF) of <25% and Factor of Safety (FoS) of 1.2, there is a cost-saving of 8.42% of the total waste stripping i.e., a saving of US$9.6 m. The use of synthetic nets has therefore, enhanced the confidence in optimizing pit slope angles and justified the application in rock fall management at Skorpion Zinc Mine.


Optimisation Skorpion Zinc mine Slope stability analysis Rockfall Synthetic net 


  1. 1.
    Rocscience Inc.: Slide Version 8.0 - 2D Limit Equilibrium Slope Stability Analysis, Toronto, Ontario, Canada (2018).
  2. 2.
    Alford, G.G., Whittle, J.: Application of Lerchs-Grossman pit optimisation to the design of open pit mines. In: Open Pit Mining Conference, Calgary, Canada, pp. 201–207 (1986)Google Scholar
  3. 3.
    Lerchs, H., Grossmann, I.F.: Optimum design of open pit mines. CIM Bull. 58, 47–54 (1965)Google Scholar
  4. 4.
    François-Bongarçon, D., Guibal, D.: Algorithms for parameterizing reserves under different geometrical constraints. In: Proceedings of 17th Symposium on the Application of Computers and Operations Research in the Mineral Industries (APCOM: AIME), New York, pp. 297–230 (1982)Google Scholar
  5. 5.
    Yegulalp, T.M., Arias, J.A.: A fast algorithm to solve the ultimate pit limit problem. In Proceedings of 23rd Symposium on the Application of Computers and Operations Research in the Mineral Industries (APCOM: AIME), Littleton, Colorado, pp. 391–397 (1992)Google Scholar
  6. 6.
    Berlanga, J.M., Cardona, R., Ibarra, M.A.: Recursive formulae for the floating cone algorithm. In: Mine Planning and Equipment Selection, Rotterdam, Netherlands, pp. 15–25 (1988)Google Scholar
  7. 7.
    Lemieux, M.: Moving cone optimizing algorithm. In: Weiss, A. (ed.) Computer Methods for the 80 s in the Mineral Industry, AIME, New York, pp. 329–345 (1979)Google Scholar
  8. 8.
    Korobov, S.: Method for determining optimal open pit limits. Ecole Polytechnique de l’Université de Montréal, Montreal, Technical report EP74-R-4, p. 24 (1974)Google Scholar
  9. 9.
    Dowd, P.A., Onur, A.H.: Open-pit optimization—part 1: optimal open-pit design. Trans. Inst. Min. Metall. (Sect. A: Min. Ind.) 102, 95–104 (1993)Google Scholar
  10. 10.
    Matheron, G.: Paramétrage des contours optimaux (Centre de Géostatistique et de Morphologie mathématique), Internal report N-403; Note géostatistique 128, Fontainebleau, p. 54 (1975)Google Scholar
  11. 11.
    Johnson, T.B., Sharp R.W.: A three-dimensional dynamic programming method for optimal ultimate open pit design. Bur. Min. Invest. 7553 (1971)Google Scholar
  12. 12.
    Koenigsberg, E.: The optimum contours of an open pit mine: an application of dynamic programming. In: APCOM, New York, vol. 17, pp. 274–287 (1982)Google Scholar
  13. 13.
    Wilke, F.L., Wright, E.A.: Determining the optimal ultimate pit design for hard rock open pit mines using dynamic programming. Erzmetall 37, 139–144 (1984)Google Scholar
  14. 14.
    Wright, A.: The use of dynamic programming for open pit mine design, some practical implications. Min. Sci. Technol. 4, 97–104 (1987)CrossRefGoogle Scholar
  15. 15.
    Yamatomi, J., et al.: Selective extraction dynamic cone algorithm for three-dimensional open pit designs. In: Proceedings of 25th Symposium on the Application of Computers and Operations Research in the Mineral Industries (APCOM) (Australasian Institute of Mining and Metallurgy), Brisbane, pp. 267–274 (1995)Google Scholar
  16. 16.
    Galić, I.: Mining design using specialized software, Master’s thesis, Faculty of Mining, Geology and Petroleum Engineering, Zagreb, p. 95 (2002). (in Croatian)Google Scholar
  17. 17.
    Zhenhua, H., Seifollar, N.: Understanding and optimizing the geosynthetic-reinforced steep slopes 19, 5802 (2014). Texas, USA (2015)Google Scholar
  18. 18.
    Terbrugge, P., et al.: A risk evaluation approach for pit slope design, Johannesburg, South Africa (2008)Google Scholar
  19. 19.
    Priest, S.D., Brown, E.T.: Probabilistic stability analysis of variable rock slopes. Trans. Inst. Min. Metall. Sect. A: Min. Ind. 92, A1–12 (1983)Google Scholar
  20. 20.
    SRK Consulting: Acceptable probabilities of failure, mining rock slopes (Fitwaola report) (2011)Google Scholar
  21. 21.
    Read, J., Stacey, P. (eds.): Guidelines for Open Pit Slope Design, CSIRO Publishing (2009)Google Scholar

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© Springer Nature Switzerland AG 2020

Authors and Affiliations

  1. 1.Skorpion Zinc MineRosh PinahNamibia
  2. 2.School of MinesThe University of ZambiaLusakaZambia

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