Project Portugal 2030

Summary

The general objective of this study will be to conduct an exhaustive, but optimized, geotechnical investigation of hypersaline tailings in a storage facility (TSF), which present expected transient hydro-mechanical characteristics as a result of including hypersaline porous fluid that tends to evolve from a fluid to a cementitious ionized structure that will be lost over time. The evolution of susceptibility to contractile behavior – eventually collapsible – that results in the increasing “danger” of state parameters increasing in a positive sign, leads to increasing vulnerability to factors that trigger liquefaction and rupture. This work will be carried out on the resistance side, under laboratory conditions and circumstantially in an international reference laboratory, the FEUP geotechnical laboratory. This will be complemented by some tests on systems not available at Labgeo, in the laboratory at the Polytechnic of Madrid, coordinated by one of the team members, and in Brazil by UFSC laboratory with recognized skills on these specific materials, also coordinated by a team member. In all three countries, large investments are underway in mining the most available of the 17 Rare Earth Elements (REE) or others close to them, such as lithium and even copper, which generate waste with characteristics that are currently little known, in their evolution throughout leaching. In fact, while Portugal has the largest lithium reserve in Europe, Spain is the third country in the EU with the largest mineral resources so that the Iberian Peninsula is the only area in Europe with the capacity to supply a third of the EU's needs. By testing these materials with advance testing procedures deriving the hydro-mechanical parameters along the time of exposing to lixiviation of the salts, identify how available constitutive models can reproduce this change of stress-strain response when subjected to distinct trigger mechanisms, allowing to be improved and implemented in recognized commercial numerical codes where assertive simulations will look for understanding the increasing vulnerability of REE TSF. With this research the expected risk can be envisaged and the earth structures will be sufficiently resilient if measures to mitigate the evolutive collapsible characteristics of these TSF are predicted. Different design and/or risk mitigation solutions depend on a study like this. An efficient calibration of the material constitutive parameters requires the characterisation of physical and geomechanics features to model their response (such as critical state, boundary and dilatancy surfaces, as well as stress-dilatancy relationship), expressed in the parameters required by the constitutive laws based on plastic hardening frames, as well as others conditioning factors like the shearing-induced fabric and inherent fabric anisotropy components. In view of these gaps, this project aims to contribute to potentate the capabilities of new procedures to assess the vulnerability of REE TSF to failure due to flow liquefaction. Numerical models will verify if a set of actions (triggered by overtopping, overloading, dynamic loading, changes in pore pressure and reduction of mean effective stress) that induce undrained shear in the tailings, resulting in a progressive failure and instability. This assessment will be done during construction, after the design phase, by updating in time the hydro-mechanical properties, and therefore de model parameters.