A probabilistic structural design process for bord and pillar workings in chrome and platinum mines in South Africa
Kersten, Rudiger Welf Olgert
The aim of this research was to investigate the bord and pillar design procedure in use at the time on chrome and platinum mines and subject it to a critical appraisal and, if necessary, propose an improved methodology. An analysis of the current method and some of the alternatives proposed in the literature has shown that the methodologies suffer from drawbacks that can be detrimental to the mining industry due to overdesign or rendering an excavation unsafe. The conclusion was that improvement is essential. The influence of the variability of the rock mass properties input parameters on the factor of safety in the current equation was calculated and the findings were that the value of the factor of safety can vary by up to 30 percent due to these variation. The proposed process adopted FLAC2D Hoek-Brown simulations to develop full stress deformation curves for typical pillars. The mine stiffness concept was introduced to determine the pillar load which automatically included the influence of the pillar and strata stiffness, excavation spans, pillar yield and failure. The factor of safety was obtained by dividing the pillar strength by the stress value of the intersection point of the two linear equations for the stiffness of the system and the pillar respectively. The proposed methodology was calibrated by applying it to two mines in the Bushveld. The conclusion was that the methodology is a significant improvement over the one in use. It was shown that a combination of the FLAC2D Hoek Brown and the System Pillar Equilibrium Concept can predict the extent of the fracture zones and, to certain extent, the pillar stresses. The stage has been reached where the methodology can be used to predict the most likely commencement of failure of pillars at greater depth and alternative pillar mining methods can be modelled.
A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, September 2016
Kersten, Rudiger Welf Olgert (2016) A probabilistic structural design process for bord and pillar workings in chrome and platinum mines in South Africa, University of Witwatersrand, Johannesburg, <http://wiredspace.wits.ac.za/handle/10539/22290>