Estimating the in situ state that will be achieved within a thickened tailings storage facility is often challenging, as laboratory-prepared specimens are known to not necessarily reproduce the fabric and density of the tailings when they settle under full-scale high energy deposition. Samples prepared in the laboratory from non-segregating slurries often result in quite dense states, which may not occur in full-scale deposition. Some of these issues were investigated during a recent geotechnical investigation of a thickened tailings deposit. The investigation consisted of cone penetration test (CPT) probes followed by piston samples at locations directly adjacent to the probes within saturated regions near the base of the tailings. The piston samples were used to estimate in situ density by means of gravimetric water content (GWC) of the entire sample, and to provide material for preparing loose, moist tamped, reconstituted samples for measuring the critical state line (CSL) of the recovered tailings. The resulting state indicated by comparing the in situ GWCs and the CSLs agreed well with that inferred by CPT-based methods, providing additional confidence in both techniques. A reconstituted sample prepared as a slurry in the lab exhibited a denser state than that indicated from in situ GWCs, raising questions about the accuracy of laboratory-prepared slurries for investigating the density likely to be achieved in situ.
Over the last few years, there has been a substantial increase in the degree of complexity of requirements regarding the licensing of tailings dams in Brazil. The stacking of filtered tailings is currently proposed as an alternative solution for tailings storage facilities; however, there are numerous challenges to understand and manage these structures in regions of high rainfall and high disposal rates. In this context, the objective of this article is to evaluate the liquefaction susceptibility of filtered iron ore tailings, based on field (piezocone) and laboratory tests (characterization and triaxial compression), both performed at an experimental landfill, located in the Iron Quadrangle (Quadrilátero Ferrífero), Minas Gerais state, Brazil. Therefore, a few methodologies were used to evaluate liquefaction susceptibility by means of the critical state theory, furthermore the fragility index of the material were also evaluated. Results indicated that the constructive method used in the experimental landfill (i.e., compaction energy, moisture and layer thickness) resulted in variability in the in-situ void ratio, indicating susceptibility to liquefaction for materials on depths greater than 0.75 m from compaction surface. In addition, from laboratory tests it was possible to determine the critical state line of the filtered tailings.