Abstract
Failures of tailings dams, primarily due to liquefaction, have occurred in Brazil in recent years. These events have prompted the Brazilian government to place restrictions on the construction of new dams, as iron ore tailings deposited behind upstream dams by spigotting have been shown to have low in situ densities and strengths and are prone to failure. This work proposes a new trend for tailings disposal: stacking compacted filtered ore tailings–Portland cement blends. As part of the proposal, it analyses the behaviour of compacted iron ore tailings–Portland cement blends, considering the use of small amounts of Portland cement under distinct compaction degrees. With the intention of evaluating the stress–strain–strength–durability behaviour of the blends, the following tests were carried out: unconfined compression tests; pulse velocity tests; wetting–drying tests; and standard drained triaxial compression tests with internal measurement of strains. This is the first study performed to determine the strength and initial shear stiffness evolution of iron ore tailings–Portland cement blends during their curing time, as well friction angle and cohesion intercept. This manuscript postulates an analysis of original experimental results centred on the porosity/cement index (η/Civ). This index can help select the cement quantity and density for important design parameters of compacted iron ore tailings–cement blends required in geotechnical engineering projects such as the proposed compacted filtered iron ore tailings–cement blends stacking.
Highlights
Tailings are the residues derived from ore extraction and processing and are mainly constituted by crushed rock fines, chemicals and water [1,2]
The peak failure envelope leads to a peak angle of shearing resistance (φ peak) of about 34.1◦ for both dry unit weights and a peak cohesion intercept of (c peak) of 80.9 kPa for of 17 kN/m3 and 157.2 kPa for of 19 kN/m3
The increase of the degree of compaction at standard Proctor energy from 89% to 99% did not cause any change in φ peak but almost double c peak
Summary
Tailings are the residues derived from ore extraction and processing and are mainly constituted by crushed rock fines, chemicals and water [1,2] This combination results in a material having an aqueous slurry consistency which facilitates the disposal in large impoundments designated as tailings dams. Jefferies and Been [14] define soil liquefaction as a phenomenon in which soil loses much of its strength or stiffness for a generally short time but long enough to cause failures which result in large financial losses, environmental damage and, in the worst cases, loss of life This is important, since there are many incidents on tailings impoundments that are claimed to be related to liquefaction
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