Mining Geotechnics: A Glimpse into the Dark Art

Ian de Bruyn
Tuesday, February 11, 2014
First presented: 
Australian Geomechanics Society & Australasian Institute of Mining and Metallurgy Event

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 in to design evaluations. Despite the best intentions, data of all types is s eldom of sufficient density to allow for rigorous s tatistical 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 geotechnic s is based on solid scientific and engineering foun dations, 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 th e 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.

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