Mechanical Response of Mine Tailings under Constant Shear Drained Loading

Several tailings dam failures have highlighted the potential for instability under prevailing drained conditions, which can be represented in the laboratory using constant shear drained (CSD) loading. In this study, the mechanical response of three mine tailings gradations (coarse, intermediate, and fine) from a tin ore tailings storage facility subjected to CSD loading were evaluated. The experimental results were interpreted using the critical state soil mechanics framework and different instability criteria. Salient findings include the following: (1) the onset of instability in initially loose specimens was dictated by a tradeoff of volumetric strain components (i.e., elastic and plastic), which in turn governed the evolution of the dilatancy and plastic modulus, key properties for modern constitutive models that were also investigated in this study; (2) dense-type instabilities may occur for initial states above the critical state line; this response was observed in the fine tailings due to their compressibility and initial state before CSD stress relief; (3) variable rate tests suggested that drained creep in the intermediate tailings made the second-order work instability criterion unattainable; variable rate effects were manifested in the postinstability responses of the intermediate and fine tailings but not in those of the coarse tailings; and (4) existing instability criteria perform similarly when applicable, but they also have limitations. In this context, a new criterion is proposed by modifying an existing criterion. This study advances the understanding of the mechanical response of mine tailings, under nonstandard stress paths.