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Filtered tailings and dry stacking are gaining attention due to problems with slurry-deposited tailings facilities and consequent catastrophic failures around the world. Factors such as recent technological advancements in filtration, lack of water, regulatory pressures and societal demands are shifting focus towards dry stacking. With the growing attention to filtered tailings, a major challenge is the knowledge gap on unsaturated soil properties required to understand the performance of unsaturated tailings in the dry stack facility, especially the hydraulic and shear strength behaviours. This paper presents details of investigations to characterise unsaturated properties of filtered tailings material in a large-scale dry stack facility located in a highly net positive evaporation area in Western Australia. Field and laboratory tests were conducted to understand (i) hydraulic and water retention/storage functions, and (ii) shear strength responses to relevant stress state variables. Historical cone penetration tests with pore pressure measurements (CPTus) conducted annually between 2013 and 2017 consistently indicate negative pore pressures within the dry stack up to 25 m depth.

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