Influence of grading and fabric arising from the initial compaction on the geomechanical characterisation of compacted copper tailings

Tailings dams constructed using the upstream method are generally less stable, because of its operational and constructive approach; this presents increased risks, which is the reason why such structures are being closed in Brazil. A feasible option to ensure the safety of closing operations in such dams consists of extracting tailings from behind the dam (reservoir), reducing moisture content through dewatering and compacting it into stable stacks. This demands knowledge of the compacted material's response. Thus, the present research assesses the mechanical response of compacted copper ore tailings extracted from two different sampling locations within the dam reservoir (i.e. about to be de-characterised) from northern Brazil. For this, drained and undrained triaxial compression tests were carried out on compacted dewatered dense, medium and loose specimens, which were assembled using the tailings retrieved from upper and lower beaches to evaluate the influence of grading, as well as the influence of the fabric arising from the initial compaction on the critical state lines (CSLs) of these saturated non-plastic silty sand tailings. The results indicated that the critical state parameters, in the υ–ln p′ space, are dependent on the fabric arising from the initial compaction. Distinct CSLs, which are all curvilinear and parallel to each other, were found in the research.