by G. More O’Ferrall

Introduction

Numerous studies have been undertaken to develop a pillar design methodology for the UG2 seam in the Bushveld Complex of South Africa. Collaborative (PlatMine) and independent (Anglo Platinum, Lonmin Platinum, Impala Platinum and academic) research has been undertaken over a few decades in order to determine the load on a UG2 pillar, with the purpose being to develop a pillar design methodology (or empirical design formula) that would enable the Rock Engineering practitioner to optimise the mining layouts with appropriately-dimensioned pillars on the UG2 seam.

Formation of the UG2 pillar design interest group

During the second half of 2016, Michael du Plessis, approached various rock engineering and structural geology persons to form a collaborative practitioner-focused pillar design and performance interest group. The interest group comprises senior (in both age, in most cases, and experience) Rock Engineering personnel from Lonmin, Anglo, Impala, Northam and Sibanye Platinum, as well as a couple of external ‘interested parties’ comprising a ‘renowned’ structural geologist and a ‘global traveller’.

Initial gathering of the druids

The group held it first (of hopefully many) information-sharing sessions kindly hosted by Northam Platinum Limited at their Booysendal South and Everest Mines, at the end of November 2016. Presentations were made by a couple of the senior Rock Engineering practitioners on the evening that the group got together. The presentations covered in-house research initiatives as well as highlighting potential issues which the group should consider in the pursuit of understanding the performance of pillars on the UG2 seam.

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Figure 1: Some of the interest group viewing core from Booysendal South Mine.

Underground visits were conducted to both Booysendal South and Everest Mines in order to get an appreciation of the pillar-forming material, difficulties that are associated with pillar cutting, and conduct a visual assessment of the pillars in the underground workings.

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Figure 2: Pillar-forming material at Booysendal South Mine.

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Figure 3: Pillar-forming material at Everest Mine which includes an altered layer along the top of the pillar contributing to the pillar instabilities experienced at the mine.

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Figure 4: The interest group at the top of the Everest portal. The group consisted of (left to right); Gregory More O’Ferrall, Michael du Plessis, Alida Hartzenberg, Andy Friese, Omberai Mandingaisa, Noel Fernandez, Riaan Carstens and Francois Malan.

Planting the seed

Following the site visits the various members of the interest group shared information that they gleaned from the site visits, and formulated a process in which to follow to obtain a better understanding of pillar performance. A large scale instrumentation trial is underway. This process is being led by Northam Platinum, with input from various parties in the interest group. Progress of the research project will be shared amongst participating members of the interest group.

Acknowledgements

SANIRE would like to thank Northam Platinum Limited’s Paul Dunne, Noël Fernandes, Willie Theron and the management teams at Booysendal South and Everest Mines for accommodating the interest group, providing access to their core shed and underground workings, and sharing their experience with the group.

The group members, and their respective employers, are thanked for making their time available to participate in the site visit and for contributing to the information-sharing sessions held over the three days in Mpumalanga.