van Zyl, D 2008, 'Integrated Heap Leach Design — Incorporating Unsaturated Material Considerations', in AB Fourie (ed.), Rock Dumps 2008: Proceedings of the First International Seminar on the Management of Rock Dumps, Stockpiles and Heap Leach Pads, Australian Centre for Geomechanics, Perth, pp. 153-166, https://doi.org/10.36487/ACG_repo/802_14
(https://papers.acg.uwa.edu.au/p/802_14_van Zyl/)
Abstract: Heap leaching of gold/silver and copper ores are carried out under unsaturated flow conditions.  While the 
mechanics of unsaturated flow through porous media is well understood, the large diameter particles 
typically present in heap leach operations present special challenges.  The unsaturated flow characterisation 
of these materials is one such challenge.  This paper will review unsaturated flow observations in heap leach 
materials under laboratory and field conditions.  Specific attention will be paid to characterising the 
parameters for unsaturated flow through coarse heap leach materials and its impact on the subsequent 
modelling of unsaturated flow.  Flow conditions during closure will also be evaluated as the drain down rate 
of heap leach facilities is dependent on the heap material characteristics.  
Recent observations and evaluations of the unsaturated behaviour of materials removed from dynamic (on 
off pad) heap leach operations for placement in spent ore disposal areas will be presented.  These materials 
must be sufficiently dry to provide the shear strength and trafficability required for stacking conveyors 
typically used in the spent ore disposal area.  A range of geotechnical and unsaturated flow evaluations can 
be used to evaluate the material behaviour. 
It is concluded that 21st century designers of heap leach facilities must include full consideration of the 
unsaturated behaviour of the heap leach materials, both as it relates to flow and strength of such materials.  
Recommendations are made for the integrated development of heap leach projects incorporating 
unsaturated material considerations.