Tailings and Mine Waste Conference

A comparison of different laboratory techniques to simulate stress and moisture history of hard rock mine tailings Daliri, Farzad; Simms, Paul; Sivathayalan, Siva


In thickened tailings technology, tailings are deposited at solids concentrations sufficient to prevent segregation and allow for formation of gently sloped stacks. Post-deposition, thickened tailings are known to gain strength through a combination of hindered settling, desiccation, and consolidation. Recently, it is understood that the shear strength and geotechnical stability of the stack is dependent on the degree of desiccation or drying time for a given layer, as well as consolidation history during subsequent deposition. This paper presents some preliminary investigations into how best to reproduce this stress history for element testing. Three laboratory methods for simulating stress history of thickened tailings layers are introduced for preparing samples for testing in an NGI type simple shear apparatus. In the first method, tailings are reconstituted in the simple shear mold, desiccated to different degrees, and re-wetted before shearing. The second method consists of simulating the thickened tailings deposition in a column, followed by sample extraction using a shearing thin-wall sampler. In the third method, a flume is employed to simulate the movement of thickened tailings layers from the deposition point down the beach. The third method is intended to assess whether the movement of tailings down the beach constitutes an important part of stress history, and influences the evolution of the fabric. This paper recommends the most appropriate method for preparing samples to assess the geotechnical behaviour of thickened tailings. It is concluded that desiccation to the shrinkage limit could significantly increase the monotonic shear strength of hard rock mine tailings; however, with continuing desiccation beyond the shrinkage limit, additional monotonic strength gain is minimal. [All papers were considered for technical and language appropriateness by the organizing committee.]

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