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The dry stacking of filtered tailings has emerged as an alternative way of dealing with the safety-related problems of conventional slurry disposal in reservoirs behind upstream dams. Incorporating a cementing agent into the tailings before compaction can enhance the overall geomechanical behaviour of these structures, giving rise to more stable and safer stackings. However, few dry stacks are in operation worldwide and their field performance needs to be better understood. In addition, the addition of cement provides further challenges to the design of these structures. Obtaining reliable laboratory data for properly designing these tailings storage facilities is thus essential. Accordingly, the mechanical behaviour of artificially cemented iron ore tailings for dry stacking purposes was evaluated, with a focus on comparing the responses between field-compacted samples and laboratory-assembled specimens. To do this, ultrasonic pulse velocity, unconfined compression, split tensile and triaxial compression tests were carried out. Both the stiffness and strength data were well described by the porosity/cement index and, despite minor differences, good agreement was found between the responses of the laboratory-assembled and field-compacted samples. The findings highlight the adequacy of laboratory procedures for reflecting the material's real-field conditions. [ABSTRACT FROM AUTHOR]

Disposal of iron ore tailings (IOT) in dry stacks is increasingly common in Brazil. IOT are compacted in layers using drum rollers that cause compaction and vibration effects on the ground. Particle breakage is usually observed in granular materials when subjected to large static loads, as can occur depending on the stacking height achieved. This study investigates the breakage behaviour of IOT, simulating load conditions that may arise during compaction of the layers for dry stack construction. Two IOT samples with different amounts of clay-sized particles but similar mineralogy (about 77% quartz and 19% iron oxide – typical of IOT in Brazil) were subject to three different laboratory tests simulating cyclic, compaction and vibration loading. Particle size distribution analyses were performed before and after testing all specimens. Both IOT samples suffered only particle breakage (relative breakage between 0.12 and 0.14 for tailings A and between 0.14 and 0.16 for tailings B) under extremely high pressures (σ′v = 85 MPa) applied by oedometer testing, above those usually found in the field. For the usual pressures applied in the field, the frequency of load and number of cycles were not significant in particle breakage. [ABSTRACT FROM AUTHOR]

Mine tailings have been disposed of in a slurry form in tailings dams for many years. However, recent disasters involving conventional disposal in dams reinforced the need for alternative structures to store these materials safely. One alternative is dry stacking of tailings. In these structures, tailings are filtered to low moisture content and then compacted in layers. Due to material compaction, dry stacks tend to be stable and are usually built with elevated heights to use the available area better. So, it becomes essential to understand the mechanical behavior of tailings subjected to high pressures, especially concerning the possibility of grain breakage. In this context, the present research focuses on studying the geotechnical behavior of iron ore tailings from different stages of ore beneficiation plants in Quadrilátero Ferrífero, Brazil, when subjected to high pressures both in compression and in shear paths. The results demonstrate that the inclusion of fines can change the geotechnical performance of the dry stack tailings considering the same compaction energy (greater strength, stiffness, and lower permeability) both in drained and undrained conditions. No breakage could be identified for the stress level studied (6 MPa).

Soil mechanics traditionally have focused on studying pure clays and clean sands. However, natural soils and other geomaterials usually do not fall into these two classes. Most geomaterials are a complex matrix of fines and coarser particles, with distinct shapes and mineralogy interacting. This paper studied iron ore tailings over a broad range of pressures and stress histories to investigate the mechanical behavior of this nontextbook geomaterial. A thorough experimental program was conducted, and aspects of the stress–strain response, yielding, hardening, and critical state were evaluated. The state boundary surface of iron ore tailings also was investigated. The results demonstrated that the stress history of tailings affects the tailings' behavior only at elevated stress levels. The existence of particles with distinct mineralogy in the iron ore tailings (mainly iron oxide and quartz) could have induced different breakage patterns, with an evolving particle morphology being the dominant mechanism up to the pressures achieved. [ABSTRACT FROM AUTHOR]

Tailings dams constructed using the upstream method are generally less stable, because of its operational and constructive approach; this presents increased risks, which is the reason why such structures are being closed in Brazil. A feasible option to ensure the safety of closing operations in such dams consists of extracting tailings from behind the dam (reservoir), reducing moisture content through dewatering and compacting it into stable stacks. This demands knowledge of the compacted material's response. Thus, the present research assesses the mechanical response of compacted copper ore tailings extracted from two different sampling locations within the dam reservoir (i.e. about to be de-characterised) from northern Brazil. For this, drained and undrained triaxial compression tests were carried out on compacted dewatered dense, medium and loose specimens, which were assembled using the tailings retrieved from upper and lower beaches to evaluate the influence of grading, as well as the influence of the fabric arising from the initial compaction on the critical state lines (CSLs) of these saturated non-plastic silty sand tailings. The results indicated that the critical state parameters, in the υ–ln p′ space, are dependent on the fabric arising from the initial compaction. Distinct CSLs, which are all curvilinear and parallel to each other, were found in the research. [ABSTRACT FROM AUTHOR]

The filtered tailings disposal (dry stacking) up to 300 m high is an alternative to overcome the drawbacks related to the slurry tailings storage in large impoundments as it is safer and demands smaller portions of the existing landform. Even so, the understanding of the denser and dewatered material response over a broad range of confining pressures is essential to safely design tall dry stacking tailings facilities. Accordingly, the present research assesses the mechanical behavior of compacted iron ore tailings through triaxial tests. A series of compression and extension drained and undrained triaxial tests were conducted over a wide spectrum of confinements (σ ́ 3 ranging from 75 to 8,000 kPa) to check possible particle breakage occurrence and effects. The influence of the initial density due to compaction was, as well, evaluated since the tests were performed using specimens molded at distinct dry unit weight values. The results were analyzed in the light of the critical state soil mechanics and have indicated the existence of a curvilinear critical state line in the ν: log ṕ plane. Small particle breakage has occurred and can be associated with reduction in surface roughness, breakage of asperities, and reduction in particle angularity. Moreover, a tendency for static liquefaction was observed amongst the loosest specimens sheared under the lowest confining levels. [ABSTRACT FROM AUTHOR]