TRANSACTION PAPERS

 

Design of Merensky Reef crush pillars

 

 

B.P. Watson^I; J.S. Kuijpers^II; T.R. Stacey^III

^IGoldfields Ltd and University of the Witwatersrand, Johannesburg, South Africa
^IICSIR, Johannesburg, South Africa
^IIIUniversity of the Witwatersrand, Johannesburg, South Africa

 

 

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SYNOPSIS

The Bushveld platinum group metal deposits are two distinct, shallow-dipping stratiform tabular orebodies which strike for many hundreds of kilometres. Mining is extensive, with depths ranging from close-to-surface to 2 300 m. The mining method is a variation of planar open stoping. Pillars are widely employed to support the open stopes. In the deeper levels, in-stope pillars are required to fail in a stable manner soon after being cut, and the residual pillar strength is used to stabilize the hangingwall. These pillars are commonly known as crush pillars. Little work has been done in the past to determine pillar peak and residual strengths, and pillars have been designed using experience and formulae developed for other hard-rock mines. This has led to over and undersize pillars with consequential loss of ore, pillar bursts and potential collapses. This paper describes a crush pillar design methodology, and provides design charts. Three mining environments were incorporated in the investigations, which included underground and laboratory measurements, analytical solutions, numerical models and back analyses. The results of the study are suitable for the areas where the research was carried out, and may also be applied with caution in other similar environments.

Keywords: Crush pillar design, peak pillar strength, residual pillar strength, in situ measurements, design charts

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References

1. ROBERTS, M.K.C., GRAVE, D.M.H., JAGER, A.J., and KLOKOW, J. Rock Mass Behaviour of the Merensky Reef at Northam Platinum Mine. Proc. SARES, Johannesburg, S. Afr. National Inst. For Rock Engng. 1997.         [ Links ]

2. ROBERTS, D.P., ROBERTS, M.K.C., JAGER, A.J., and COETZER, S. The determination of the residual strength of hard rock crush pillars with a width to height ratio of 2:1, Jl S.Afr. Inst. Min. Metall., vol. 105, 2005. pp. 401-408.         [ Links ]

3. WATSON, B.P., RYDER, J.A., KATAKA, M.O., KUIJPERS, J.S., and LETEANE, F.P. Merensky pillar strength formulae based on back-analysis of pillar failures at Impala Platinum, Jl S.Afr. Inst. Min. Metall., vol. 108, 2008. pp. 449-461.         [ Links ]

4. WATSON, B.P. Rock behaviour of the Bushveld Merensky Reef and the design of crush pillars, PhD thesis, School. of Mining Engineering, University of Witwatersrand, Johannesburg, RSA. 2010.         [ Links ]

5. SPENCER, D and YORK, G. Back-analysis of yielding pillar system behaviour at Impala Platinum Mine, Proc. SARES99, Johannesburg, S. Afr. National Inst. For Rock Engng, 1999. pp 44-52.         [ Links ]

6. YORK, G. and CANBULAT, I. The scale effect, critical rock mass strength and pillar system design, Jl S.Afr. Inst. Min. Metall., vol. 98, no. 1 Jan/Feb, 1998. pp. 27-37.         [ Links ]

7. ITASCA CONSULTING GROUP, INC. Fast Lagrangian Analysis of Continua (FLAC), Vers. 3.2. Minneapolis Minnesota USA. 1993.         [ Links ]

8. BARRON, K. An analytical approach to the design of pillars in coal, Contract Report No. 1SQ80-00161, Canada Centre for Mineral and Energy Technology, Energy, Mines and Resources, Canada, 1983. pp. 36-42.         [ Links ]

9. SALAMON, M.D.G. Strength and stability of coal pillars, Workshop on coal pillar mechanics and design, US Bureau of the Interior, US Bureau of Mines, Santa Fe, USA. 1992.         [ Links ]

10. MEYERHOF, G.G. The ultimate bearing capacity of foundations, Geotechnique, vol. 5, 1951. pp. 301-332.         [ Links ]

11. FANG, Z. and HARRISON, J.P. Application of a local degradation model to the analysis of brittle fracture of laboratory scale rock specimens under triaxial conditions, Int. J. of Rock Mech. and Min. Sci., vol. 39, 2002. pp. 459-476.         [ Links ]