Effects of low suction and wetting–drying cycles on filtered tailings shear strength

Abstract

Filtered tailings management has many advantages over traditional slurry tailings management, such as improved water recovery and recirculation, and a reduction of geotechnical risk. However, the long-term evolution of the water content in filtered tailings exposed to climatic conditions could affect its geotechnical properties. Shear strength properties of unsaturated tailings have a critical role when evaluating the geotechnical stability of a dry stack facility, especially in the context of climate change. The objective of this research was, therefore to investigate the influence of drying and wetting cycles on the shear strength of filtered tailings for a low matric suction range (i.e. 0~50 kPa). A series of consolidated-drained (CD) direct shear tests were conducted on re-compacted unsaturated filtered tailings specimens. For each matric suction achieved by following either the wetting or drying curve, three direct shear tests were performed with varying normal stresses. Direct shear test results showed a nonlinear increase in the unsaturated shear strength with the normal stress and matric suction. Empirical hyperbolic functions were used to fit experimental data and evaluate the shear strength of unsaturated filtered tailings for a higher matric suction range. Test results also indicated some hysteresis, and the shear strength during drying was smaller than during wetting for the same matric suction. However, matric suction and water retention curve (WRC) hysteresis had no significant impact on the measured effective friction angle.