Avaliação do potencial de liquefação e análises 2D e 3D da percolação e estabilidade de uma barragem de rejeitos, alteada por montante, a partir de métodos de elementos finitos e equilíbrio limite

Abstract

Tailings dams constructed using the upstream method may have their main failure mode as instability due to liquefaction of the tailings in the reservoir. Thus, structures built using this method must be subject to careful analysis regarding the susceptibility of the stored tailings to liquefaction and the impact of this phenomenon on dam stability. This study aims to present an evaluation of the liquefaction potential of the tailings contained in an upstream raised dam, referred to as GR Dam in this work. Additionally, the study presents a seepage analysis and stability through three-dimensional (3D) numerical modeling for the dam under study, comparing the results with conventional 2D analyses. The 3D geological-geotechnical model of the structure was developed based on available investigations and project data. The 3D percolation analysis was calibrated based on permeability test data of the materials and instrumentation of the dam, using the software RS3 from Rocscience™'. Stability analyses were performed using the limit equilibrium method (Slide3 software) and the finite element method (RS3 software) employing the Mohr-Coulomb constitutive model. For the stability analyses, the susceptibility to liquefaction was evaluated, and the peak and residual undrained strength ratio of the tailings were estimated based on correlations with CPTu tests. The result of the 3D flow analysis indicated a good fit of the model to the field data. In the stability analyses, considering the peak undrained strength for the tailings, the 3D factor of safety obtained using both the limit equilibrium and finite element methods was approximately 10% higher than that obtained from the 2D analyses. However, even the 3D factor of safety obtained is still below the minimum required by national regulations.