Mine excavation design should incorporate rock mechanics input, but the difficulty in transferring mine planning data to geotechnical software means that such input is rarely available. Recently completed links between the SURPAC mine planning package and stress analysis codes BITEMJ and UDEC are described. Case histories of an open-pit and an underground mine demonstrate the benefits of integrating stress analysis with mine planning: availability of integrated software could have facilitated identification of potential rock instabilities, thus avoiding costly failures.
Rock mechanics issues need to be considered in planning a mining extraction strategy to ensure safe and economic recovery of the largest possible proportion of a mineral resource, and also to help miners to engineer around any unanticipated rock failures. For example, in an open pit, a design goal may be to maximise the slope angle, so as to minimise the amount of waste rock which must be excavated, subjecto continuing stability of the slopes to ensure that access to the pit is not affected. In an underground operation, the objective may be to maximise stope dimensions and minimise pillar thicknesses, whilst still ensuring safety of miners from rock falls and avoiding sterihsation of part of the resource, or dilution of recovered ore, by failure of walls or pillars. The design of rock support and reinforcement mechanisms is another area in which rock mechanics should be considered.
Existing commercial mine planning programs, when used to design mine excavations, are largely restricted to considering the geometry of the system, e.g. they can take account of the shape of an orebody inferred from borehole logs, and previous experience of stable slope angles or stope/pillar dimensions, but do not consider the mechanical response of the rock mass. Computational stress analysis is a powerful tool for investig- ating rock mechanics, but is as yet only used by the larger or more forward-looking mine operators. In particular, CSIRO has available a range of computer programs it has developed and/or applied in research projects in mining geomechanics.
Even when rock mechanics is included in the design cycle, existing software usually requires manual transfer of information from mine data bases to stress analysis programs, or re-digitising of key geometrical information. This data transfer is inefficient, limiting the number of analyses which can be performed to assess possible extraction options. A challenge facing the research community is to make computational stress analysis more accessible to practising mining engineers, so that rock mechanics can be fully integrated into the mine planning process. New software is therefore being developed to link mine planning and stress analysis programs, with a view to improving productivity directly, by speeding the design process, and indirectly, by allowing engineers to discover more effective extraction strategies through numerical experimentation.
