Effect of saturation confining pressure on accessible density and shear behaviour of sandy silt tailings

Significant reduction in the brittleness of sandy silt/silty sand tailings at high stresses has frequently been observed in laboratory element testing due to curvature of the critical state line and the limiting compression curve. 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 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.

Automated summary

The laboratory element testing shows that sandy silt/silty sand tailings exhibit significant reduction in brittleness at high stresses due to the curvature of critical state line and limiting compression curve. However, most of the testing involves low-confining stresses during saturation, which differs from the potential in situ loading within a filtered tailings stack. A series of isotropically consolidated triaxial tests were conducted to investigate the effects of saturation process at different confining stresses, indicating similar magnitudes of brittleness as observed in flow liquefaction case histories.