The geomechanics of thickened and paste tailings

Abstract

The overall objective of thickened and paste tailings disposal has been stated many times: it is to thicken a tailings slurry to the point where it is non-segregating, and will beach to form a sloping, sub-aerial deposit. The advantages of this type of scheme have been stated to include higher density, higher strength (including avoidance of a slimes pond), improved seismic resistance, and better closure and rehabilitation prospects (including lower compressibility). The aim of this paper is to show how these outcomes are a product of the interaction of fundamental tailings properties, site management practices, and climatic conditions of the site. A typical set of test results is presented and discussed in the context of unsaturated soil mechanics. The absence of segregation in thickened and paste tailings is an important factor, but it is often overlooked. The paper addresses the influence of evaporative drying on the sub-aerial beach. The induced suction stresses, combined with compressibility (consolidation) largely influence the rate and extent of density and strength gain that is attributable to the thickened discharge method. Finally, the influence of overall site management practices (e.g. filling rate), together with climatic conditions, are discussed to illustrate how these may act as constraints on the potential to achieve optimum results.