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Recent disasters involving upstream raised tailings dams in Brazil have caused regulatory agencies to prohibit the construction of new upstream dams and demand the decommissioning of existing ones. As such, new alternatives are being sought to safely dispose of iron ore exploitation byproducts. The dry stacking of filtered tailings is an option to diminish the risks associated with tailings storage facilities and cope with new legislation. Accordingly, this paper studies new solutions for enhancing the performance of tailings for dry stacking purposes. The behavior of reinforced and nonreinforced iron ore tailings-alkaline-activated cement (AAC) blends was studied through unconfined compressive strength tests and conventional triaxial testing. The AAC is produced from the residues of iron ore exploitation (waste and tailings). The addition of fibers has enhanced the performance of cemented iron ore tailings with increased strength regardless of the fiber content and ductility. Also, reinforcement effectiveness values were greater than those reported for other cement agents, due to the lower stiffness of the cemented matrix from AAC compared with others. A comparative analysis between using only AAC and ACC plus 0.5% of fibers within the η/Biv framework was proposed. The dosage curves for the same qu value yielded an AAC=20.80% for AAC only and AAC=3.80% when using 0.5% of fibers. Therefore, using fibers can collaborate with the feasibility of using a new waste-based AAC to construct dry stacking facilities. [ABSTRACT FROM AUTHOR]

Numerous recent failures of tailings storage facilities (TSFs) (e.g., the 2019 Brumadinho failure in Brazil, the 2018 Cadia failure in Australia) have occurred in the last decade, providing important case histories and lessons to improve the design of TSF facilities. This study is focused on the Cadia TSF failure; specifically, we reexamine and expand the triggering analyses conducted in the forensic study after the failure. In addition, this study also presents the first comprehensive posttriggering and runout assessment of the Cadia failure. The triggering mechanisms were evaluated through Lagrangian-based analyses with the finite-difference method (FDM), which is well suited for small to moderate deformations, whereas the posttriggering mechanisms and runout were evaluated using the material point method (MPM), which is well suited for the evaluation of large deformations. The FDM-based analyses show that the interaction between a relatively weak layer in the foundation [Forest Reef Volcanic Unit A (FRV-A)], the deposited tailings, and the construction of a buttress system is critical in explaining the failure triggering. The MPM-based assessments are useful in investigating posttriggering mechanisms, suggesting a retrogressive failure and stress redistribution occurring within the mine tailings. In addition, the MPM-based assessments also explore the influence of key factors on the posttriggering mechanisms and runout. These factors include the tailings liquefaction extent and strength, the failure propagation rate, the strength of the foundation materials, and the buttress construction. The analyses suggest that the foundation strength, mine tailings liquefaction extent, and buttressing affect the runout assessments significantly. In this context, MPM proves to be especially useful in investigating postfailure conditions. [ABSTRACT FROM AUTHOR]

An essential process in earthworks is projecting effective routes for material allocation. In highway construction, haul road planning is a challenge for practitioners once there are few consolidated methodologies to rationally select existing haul routes or construct new ones. Some authors indicated geographic information system (GIS)-based methods for routing through least-cost algorithms. However, most proposed methodologies overlook the logistics related to allocations, not considering supply–demand relations in their criteria. Consequently, through a case study in Brazil, we present an earthwork optimization system that integrated established mathematical programming techniques for allocation and a GIS-based algorithm for haul road construction. In summary, we formulated a model capable of selecting different routes based on their impact on earthworks logistics cost. Thus, we built several paths between source and demand points utilizing two methods. First, based on recent literature, we used a GIS-based least-cost algorithm using the measuring attractiveness by a categorical-based evaluation technique (MACBETH) as a multicriteria support system incorporating multiple economic and environmental parameters. Second, we built routes based on Euclidian distance between the same source and demand points, analyzing if the savings in operational costs would payoff additional expenses of choosing a shorter route. After applying our methodology to the case study, we observed that the proposed procedure presented a lower budget in a reasonable processing time compared with the original project. Therefore, we inferred that the strategy of proposing path alternatives can be significantly efficient when applied to highways. Based on the results, we also found opportunities for improvement of our GIS step once it generated long paths when the distance between source and demand was short. [ABSTRACT FROM AUTHOR]