Influência do grau de compactação na estabilidade e na deformabilidade de pilhas de rejeito filtrado de minério de ferro

Abstract

The mining industry plays a significant role in the Brazilian economy, especially in the iron ore extraction sector, an activity that generates large volumes of tailings, which demand environmentally sound and geotechnically safe disposal solutions. In this context, dry stacking with filtered tailings has become established as an alternative to conventional tailings dams, as it reduces risks associated with liquefaction and environmental impacts. Despite advances, a gap is observed in the literature regarding the integrated and systematic evaluation of the influence of the degree of compaction (DC) as a design variable on the geotechnical stability and deformational behavior of filtered iron ore tailings piles, especially considering different geometric conditions and water levels. Given this, the present research aims to comparatively and integrally evaluate the influence of the degree of compaction on the geotechnical performance and deformational behavior of stockpiles constructed with filtered iron ore tailings (FIOT), seeking to contribute to the definition of technical criteria that allow for optimization between safety and operational cost. The study's distinguishing feature lies in the combination of laboratory tests of physical characterization, compaction, direct shear, oedometer consolidation, and permeability, performed on specimens with three different degrees of compaction (99%, 93%, and 88%), with computational analyses of stability and deformability for different geometries and saturation conditions of the stockpiles. The experimentally obtained parameters, including shear strength (effective cohesion and friction angle), stiffness (oedometer modulus), and permeability (permeability coefficient), supported stability simulations using the limit equilibrium method (LEM) in Slide2 software and the finite element method (FEM) in Plaxis 2D, considering different slopes (25°, 32°, and 39°) and water table conditions (normal and critical). Additionally, deformational analyses were performed in Plaxis 2D, allowing the evaluation of displacements and zones susceptible to pile plasticization. The results indicated that reducing the degree of compaction causes a decrease in shear strength and stiffness of the FIOT piles, impacting stability and increasing displacements in up to 34%, especially under conditions of greater inclination and saturation. However, it was found that intermediate degrees of compaction (93% and 88%) can present factors of safety (FoS) that exceed the minimum FoS required by NBR 13029 by up to 45%, in certain geometry configurations and water level conditions, highlighting the possibility of optimizing the design without compromising safety. It is concluded that the degree of compaction is a determining parameter for the geotechnical performance of FIOT piles and should be treated as a strategic design variable, recommending integrated laboratory and numerical analyses for each specific case.