Reclamation of a Conventional Tailings Facility for Long Term Dry Stacking Operations in Western Australia

Abstract

Residue storage ponds constructed prior to the 1980s were built to the engineering standards that applied at that time. Clay liners were typically used to provide a barrier to flow of contaminants into the natural groundwater system. More recent storage areas include a composite liner consisting of a clay liner and geomembrane and have a drainage layer placed above the liner to reduce the hydrostatic head. This paper presents the engineering design and planning for the conversion of an older residue storage area which had a natural clay liner only into a dry stacking residue storage area to increase the residue storage capacity within the area and at the same time reduce the potential for long term seepage from the area. Field investigations including Piezo-cone Penetrometer Testing (CPTu) and pumping well tests were undertaken. Monitoring instrumentation including Vibrating Wire Piezometers (VWPs) was installed within the saturated residue materials. Dewatering technologies such as deliquoring bores, wick drains and geosynthetic liners between the older deposit of residue and the dry stack deposit were recommended for the control of pore pressures within the existing pond. Numerical analyses to predict the pore-water pressure build-up at the pond base, the influence zone of deliquoring bores, and predicted differential settlements of the surface were also examined.