Depositing thickened tailings over a conventional tailings deposit leads to a raft of considerations and risks relating to the interaction of the two tailings layers , and these must be identified and evaluated before making the significant financial investment involved in changing a disposal system.
As part of a selection process for a thickened tailings disposal strategy that involved placing thickened tailings over a conventional tailings deposit at an existing mine in Mexico, two alternative thickened tailings streams were characterised. One of these was a total tailings product, and the other was a fine product with coarse particles removed. Two issues were identified as key assessment criteria to enable an informed choice between thickening either the fine or total tailings: the evolution of density and pore pressures through self-weight consolidation and the potential for liquefaction of the composite tailings deposit. This paper discusses the considerations and methodology of assessing these two criteria.
The evaluation process involved a geotechnical laboratory test work program on both tailings materials. The test results provided inputs for a transient large-strain consolidation model and for stress-strain dynamic analyses. The consolidation model results were used to compare storage capacity estimation. These results provided critical inputs for a dynamic evaluation of bot h tailings composites. Liquefaction conditions were assessed through a dynamic analysis that compared the cyclic shear stress associated to dynamic loads with the mobilised cyclic shear strength of the tailings material. Associated plastic deformations were obtained for each scenario studied.
