Variability of tailings; Characterization of the reservoir; statistical analysis 

Mining activities corresponds to a considerable part of the Brazilian Gross Domestic Product. Ore mining activities generate two types of waste, sterile and tailings. Tailings are usually disposed hydraulically in tailings dams, generating a high degree of saturation, in addition to material heterogeneity spatially in the reservoir. Mining tailings tend to be characterized as granular and/or fine non-plastic materials, which can increase the susceptibility to liquefaction of geotechnical structures. Different methodologies for assessing susceptibility to liquefaction were proposed, mainly considering historical cases of rupture, which obtain different classifications regarding the contractile/dilating behavior of tailings. Thus, the present work proposed the spatial characterization of the iron ore tailings from the reservoir of a dam located in the Iron Quadrangle using statistical tools. Also, using data obtained from characterization and piezocone tests, the assessment of susceptibility to liquefaction was performed using seven methodologies: Tsuchida (1970) apud Terzaghi et al. (1996), Ishihara (1985), Senneset et al. (1989), Plewes et al. (1992), Shuttle & Cunning (2008), Olson (2001), Robertson (2010), Robertson (2016) and Smith et al. (2021). The results showed that the tailings were disposed from upstream to downstream, with the most granular and sandy material located at the back of the reservoir and the finest clayey material close to the dam. The tailings studied are mostly contractile, especially in the vicinity of the dam, where the finer material was deposited. Olson's methodology (2001) was found to be the most conservative, but it does not take into account important aspects, such as pore pressure performance or clayey/sandy behavior of the material. Robertson (2010;2016) does not consider pore pressure correction, however, he evaluated in more detail the behavior of cohesive and granular soils, resulting in a greater amount of contractile material compared to the methodology of Plewes et al. (1992) Shuttle & Cunning (2008) and Smith et al. (2021). These last three methodologies perform the correction of the pore pressure action and the drainage condition of CPTu spiking. It is concluded that it is possible to observe a biased susceptibility behavior to liquefaction in the reservoir, mainly associated with the presence of water table and tailings disposal strategy. The proposed methodologies applied result in different amounts of contractile material, being differentiated by the considerations and limitations of each methodology.