# The Experimental Characterization of Iron Ore Tailings from a Geotechnical Perspective
###### Abstract
In fact, the UN urges for further research on innovations in tailings' reuse, namely with respect to the potential to reuse at least part of the mining waste as an alternative to natural aggregates in construction [9]. Some attempts have been made to reuse tailings in construction, namely those resulting from iron ore mining, with the experimental results suggesting promising applications for the waste analyzed, which was processed by pliquetting [10]. Using iron ore tailings in geotechnical  
Figure 1: The number of serious and very serious tailings dam failures observed in the past in the world and predictions of similar failures in the future, based on data from WMTF [7]. works can be even more attractive, due to the large volume of materials that are often required to build embankments, land reclamation works, etc. Yet, sustainable geotechnical applications require control of the environmental safety of the applications, namely through suitable physicochemical and ecotoxicological analysis that must be carried out, similarly to other unconventional geomaterials used in construction [11; 12]. On the other hand, the safety of tailings dams and other tailings storage facilities must be enhanced in order to protect human life, the environment and the economy. In fact, as mining is currently trying to cope with falling ore grades, increasingly larger projects are required to manage growing amounts of tailings. This creates continuous pressure in tailings management, namely with respect to stability to avoid catastrophic failures and other short- and long-term problems [2]. Also, there is increasingly growing pressure from society to avoid the consequences of dramatic failures such as the 2019 Brumadinho tailings dam collapse, which is believed to be the most serious social and environmental disaster that affected Brazil [13]. In addition, at least three different outstanding international teams reached inconsistent conclusions with respect to the causes of failure [14; 15; 16], which suggests that the mechanical behavior of tailings is still poorly understood. But even if the Brumadinho tailings dam collapse did not seem to be caused by earthquake loading, many of these structures are built in seismically active areas and are prone to earthquake-induced liquefaction [17]. This complex phenomenon can cause dramatic failures in granular saturated geomaterials due to the reduction in effective stress induced by large excess pore pressure generation, with its analysis and mitigation requiring proper mechanical characterization [18] and advanced modeling tools incorporating the intricate nature of local earthquakes [19]. But even if excess pore pressure generation induced by static or cyclic loading plays a role in major failures of tailings dams [20], the behavior of tailings still requires further clarification due to their rather peculiar man-made origin [21]. Considering the relevant problem faced by the mining industry regarding the reduction in the volume and the enhancement of the safety of tailings storage facilities in a challenging environment, this paper focus on the experimental characterization of iron ore tailings, which are the most abundant type of mining waste produced in the world. Iron ore samples representing real tailings and compacted tailings were tested to assess the most relevant physical, identification and mechanical properties governing their performance under different conditions that may exist in the field, namely when used as a building material. The tailings tested can be described as low-plasticity silty sand materials with average solids density of 4.7, a maximum dry unit weight close to 3 g/cm\({}^{3}\) and an angle of friction and liquefaction resistance exceeding the values usually found in common granular materials. The experimental results highlight the particular features of the behavior of iron ore tailings and emphasize the potentially promising combination of high shear resistance and high density that favors particular geotechnical applications.