Harman, J, Hormazabal, E & Martinez, C 2007, 'Fact and Fiction About Pit Slope Depressurization', in Y Potvin (ed.), Proceedings of the 2007 International Symposium on Rock Slope Stability in Open Pit Mining and Civil Engineering
, Australian Centre for Geomechanics, Perth, pp. 362-370.
The adverse effects of groundwater pressures on slope stability have been recognised for many years, and
measures to mitigate such effects in civil engineering projects have been developed to a high degree of
sophistication. Engineers routinely provide for groundwater in their analyses, especially when working with
soils or weak rock, in projects such as road cuttings, soil slopes, etc.
In recent years the effects of water pressures on pit slope stability have increasingly concerned open pit
designers and geotechnical engineers. The concerns have grown as deeper open pits are considered and
optimization (steepening) of the wall angle becomes a critical aspect. A number of pit wall failures have
been attributed, at least in part, to the aggravating effects of water. In the past, engineers have factored (the
effects of) water into their analyses as one of the many variables together with geology, rock quality
characteristics, etc. The use of numerical modelling is now being used increasingly to predict pore pressures.
This paper argues that the recent availability and ease of use of sophisticated numerical techniques, both for
modelling groundwater flow and for geotechnical analysis, may have led to the overdependence on a ‘black
box’ solution with a lesser reliance being placed on solid engineering and geological judgment. Critical field
investigations are often not carried out or are downgraded in importance.
The paper discusses the concerns of the authors that arise from the wide variation in the approaches taken to
address what is seen as a very important topic in current geotechnical design and the lack of importance that
is generally given to adequate data gathering which is critical if advances are to be made.
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Fact and Fiction About Pit Slope Depressurisation J. Harman, et al.
370 Slope Stability 2007, Perth, Australia