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Mining Geotechnics: A glimpse into the “Dark Art”

Ian de Bruyn

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It has been called a “Dark Art”. Perhaps more than any other field of engineering, mining geotechnics embraces uncertainty. Comparatively, information is sparse, scope can be fickle, and compromise is your constant companion. There is art in the science and alchemy in the engineering. Rock is the game and geology is king.

Soil mechanics, often such an important aspect of civil engineering, plays a significant role only in the design of very shallow excavations. Even rock mechanics in its pure form may be of limited application for design of large open pit excavations, where the behaviour of the pit slopes is governed by fracture networks and rock bridges that are difficult to accurately define and model. Laboratory testing in reality provides only basic and idealised input into design evaluations. Despite the best intentions, data of all types is seldom of sufficient density to allow for rigorous statistical approaches to be confidently applied. A good understanding of the impacts of groundwater is very important, however hydrogeology is often considered the Dark Art’s shadier cousin.

The difficulties notwithstanding, mining geotechnics is based on solid scientific and engineering foundations, tempered with experience and a sound understanding of risk. One of the great challenges of this field is that every project is different and requires a careful identification of the most appropriate approach. “Cookbook” methodology is applied at your peril. A comprehensive toolbox of methods for investigation and evaluation is required and there is no small degree of skill in selecting the right ones for each situation. Experience is crucial in refining the scope of works to meet the required levels of confidence, and proceeding in the most practical manner. The investigation methods that can best be accommodated are selected, and the design evaluations carried out in such a manner that the sensitivities and risks are understood.

With all this in mind, it would be mischievous to try and provide a comprehensive overview of mining geotechnics. Instead, this presentation provides just a glimpse into the “Dark Art”, using a few case studies for illumination.

Speaker biography

Ian de Bruyn originally hails from Durban in South Africa. Having little talent as a surfer, he studied geology and engineering geology at the University of Natal. After dabbling in all manner of geological, civils and mining work, he moved to Australia 10 years ago and sought fame and fortune in mining geotechnics. Ian now has 17 years’ experience over a wide range of geotechnical engineering projects in many countries, including both actual and “imaginary” mining projects.

Ian’s main expertise is in geotechnical investigation, assessment and design of slopes for open pit mining operations. He has worked on projects involving very large pits in challenging rock mass conditions, including Ok Tedi (PNG), Esperanza (Chile) and Oyu Tolgoi (Mongolia) to name a few, as well as many Iron Ore pits in WA. He is also well versed in rock mass characterisation and domain modelling for input into fragmentation analysis, selection of mining method and support design for underground mines.

Ian is currently a Principal and team leader of the SRK geotechnical group in the Perth office.

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