For a soil that is contractive and strain softening at fully saturated conditions the question remains on which degree of saturation can trigger a strain softening response. A common engineering practice is to adopt a saturation threshold (e.g., 85%) and then assume a fully saturated response when saturation is above that value. This study aims to understand how the strain softening response change when tailings are not fully saturated and to propose a systematic method for determining the saturation threshold. A restraint when preparing unsaturated loose samples is that it is likely to have collapse during flashing, thus changing void ratio and making comparisons between different degrees of saturation problematic. A simple procedure to obtain loose samples at different degrees of saturation but at similar post-flushing void ratios is explained and preliminary results of undrained shear strength obtained for gold tailings in triaxial device are presented and discussed.

Significant reduction in the brittleness of sandy silt/silty sand tailings at high stresses has frequently been observed in laboratory element testing owing to curvature of the critical state line (CSL) and the limiting compression curve (LCC). This has led to discussions regarding the range of effective stresses across which such materials can exhibit brittle undrained shearing such that flow liquefaction could occur. However, much testing of such tailings appears to involve saturation of the tailings under relatively low confining stresses. This differs from the potential in situ loading within a filtered tailings stack, where material placed in a loose, unsaturated state may be subjected to significant overburden pressures prior to potential subsequent saturation. A series of isotropically consolidated triaxial tests were carried out on a sandy silt gold tailings to investigate the effects of the saturation process of loose moist tamped specimens occurring at different confining stresses. The tests indicated much looser states were achievable when saturation occurred at higher confining pressures, with resulting undrained shearing for such specimens being of similar magnitudes of brittleness as observed in flow liquefaction case histories. Consideration of saturation overburden pressure of filtered tailings stacks therefore appears warranted.