Unravelling structural fabric — a necessity for realistic rock mass characterisation for deep mine design

Authors: Carter, TG; Rogers, SF; Taylor, JJL; Smith, J Download Paper

DOI https://doi.org/10.36487/ACG_rep/1511_19_Carter

Cite As:
Carter, TG, Rogers, SF, Taylor, JJL & Smith, J 2015, 'Unravelling structural fabric — a necessity for realistic rock mass characterisation for deep mine design', in Y Potvin (ed.), Design Methods 2015: Proceedings of the International Seminar on Design Methods in Underground Mining, Australian Centre for Geomechanics, Perth, pp. 317-338, https://doi.org/10.36487/ACG_rep/1511_19_Carter



Abstract:
In recent years, there has been a spate of quite unexpected major failures within surface and underground mines that have significantly compromised mine stability and resulted in sustained loss of production. In the majority of these cases, evidence suggests that incipient, weak, generally incoherent structural fabric within the rock mass played a significant role in influencing the failure development. With the trend towards underground mines going ever deeper, and many of the large open pits transitioning to block cave operations, more focus is needed on gaining better structural geological understanding of incipient rock mass fabric within and outside the mining block so that such failure risks can be minimised. Current trends towards mine scale quantification of rock mass characteristics and development of local and regional scale discrete fracture network simulations, as basis for generation of synthetic rock mass models based on rigorous quantification of geological fabric assessments, is allowing better appreciation of the variability within a rock mass. However, comprehensive understanding of key elements of the geological fabric is often missing. This can lead, in worst case scenarios, to situations when the resulting models cannot be expected to capture the controlling mechanisms. This paper presents several structural geology techniques that are not widely known, or even commonly applied, either for large deep open pit design studies or for deep high stress underground mining. These techniques have merit for aiding risk minimisation for deep excavation through improved insight. Guidelines are provided for using fault striae data and applying stress inversion, slip tendency and critical stress evaluation approaches for advancing understanding of past and present day stress states — both key factors important to establishing the current stability state of major geologic structures transecting or bounding large surface or underground mining extraction blocks. Some techniques for estimating likely risk for inducing adverse slip on incipient geologic structures, potentially affected by mining, are also explored in the final sections of the paper.

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