Cyclic behaviour of reconstituted and desiccated–rewet thickened gold tailings in simple shear

Abstract

A simple-shear apparatus (Norwegian Geotechnical Institute (NGI) type) has been used to investigate the mechanical behaviour of gold tailings under monotonic, cyclic, and post-cyclic loading. Specimens were prepared either by reconstituting the tailings at different water contents or by employing a “dry–wet” preparation technique. The latter technique attempted to simulate a realistic stress history for thickened tailings deposition by preparing the specimen at the pumping water content, and subsequently allowing it to settle and then desiccate to a target water content. Subsequently, these specimens are rewetted and then consolidated. Cyclic resistance ratios for specimens prepared by the dry–wet preparation technique were considerably higher than those of specimens prepared by the standard technique, though there appears to be no advantage in drying the tailings past the shrinkage limit. In general, the tailings could experience significant deformation during cyclic and post-cyclic loading irrespective of whether the monotonic response at a given stress state was contractive or dilative. Shear strength normalized with consolidation pressure, and cyclic resistance ratios, can be plotted as unique functions of void ratio. Post-cyclic strengths require considerable strain to be mobilized. It is recommended that site-specific tolerable strain criteria be adopted to design thickened gold tailings stacks to resist earthquake loading.