Analysis of dewatering and desaturation of generic field deposition scenarios for thickened tailings

Qi, Suitao; Simms, Paul

doi:10.36487/acg_rep/1805_33_simms

Cited by 3 publications

(18 citation statements)

References 13 publications

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“…Because of the creep effect, many natural clays show deformation behaviour even under a constant load or effective stress. When the engineering applications involve determining the long-term settlement of the large structures on natural clays such as the construction of Kansai International Airport in Japan, they require careful consideration of the rate-dependent compression behaviour of natural clays (Qi et al, 2018). The Kansai International Airport was constructed 5 km off the coast of Senshu on two artificial islands built in 18~20-metre-deep seawater in Osaka Bay (Mesri and Funk, 2014).…”

Section: Case Studies Of Creep In Natural Clay Deposits/slurriesmentioning

confidence: 99%

“…A time-dependent thixotropic behaviour in remoulded or reconstituted clays, which results in an increase in undrained shear strength is also typically accompanied by an increase in preconsolidation pressure (due to the structuration effect) (Mesri, 1975). The only difference between them is that the structuration effect leads to a gradual recovery of stiffness in a remoulded or reconstituted clay sample, whereas thixotropy results in recovery of strength with time (Qi et al, 2018).…”

Section: Thixotropic Behaviour Of Claysmentioning

confidence: 99%

“…Recently, three commonly used creep models (Leoni et al 2008;Graham, 1994, Rowe and have been incorporated into the UNSAT-CON deposition simulation platform (Qi et al, 2018). When applied to the tailings deposits, the program was found capable of simulating simultaneous consolidation-creep effects in the flocculated tailings and the creep models generated similar results.…”

Section: Consolidation Theories and Modelsmentioning

confidence: 99%

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Effects of Polymers on short-and long-term dewatering of oil sands tailings

Salam¹

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Each year, while extracting bitumen from the oil sands ores, the oil sands industry generates a large volume of tailings. Although the polymers have been found to improve the release of water from the tailings and accelerate the dewatering and settling processes in the shortterm, longer-term dewatering processes such as consolidation are crucial for making the tailings deposits safe and strong enough for reclamation. Unamended tailings have been found to demonstrate time-dependent creep and thixotropic behaviour. However, whether such behaviour influences the long-term dewatering and consolidation performance of polymer amended/flocculated tailings deposits is unknown. This research investigated the creep, thixotropy, and structuration in polymer amended tailings from an experimental perspective using different polymer dosages, mixing methods, and boundary conditions. Flocculated tailings developed a thixotropic strength and also a higher preconsolidation pressure and reduced compressibility, which was clearly a structuration effect that impeded the self-weight consolidation in longer-term by limiting the creep compression. Similar experiments performed on the Leda clay showed that the structuration effect observed in flocculated tailings is not atypical of the structuration effect observed in natural clays. The potential of the UV-vis spectrophotometry and torque rheometry techniques for determining the optimum polymer dosage was investigated. The results indicated that the techniques could determine the optimum polymer dosage and help to minimize the operational costs and improve the dewaterability in the short-term. Longer-term column dewatering tests showed that the choice of polymer dosage could influence the dewatering and settlement behaviour of tailings in the long-term. Different polymer dosages resulted in different degrees of structuration with the higher dosages showing a relatively prominent iii structuration behaviour but also a suboptimal dewaterability. Hence, if the structuration effect is considered, the optimum polymer dosage for the long-term dewatering mechanisms may not be the same as the polymer dosage that produces optimum dewatering performance in the short-term. Based on the experimental findings, an empirical method was proposed for predicting the degree of structuration in a particular tailings-polymer mixture; such a method would allow the operators to minimize the negative effects of structuration through the selection of an appropriate polymer dosage or deposition management plan.

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Section: Case Studies Of Creep In Natural Clay Deposits/slurriesmentioning

confidence: 99%

Section: Thixotropic Behaviour Of Claysmentioning

confidence: 99%

Section: Consolidation Theories and Modelsmentioning

confidence: 99%

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Effects of Polymers on short-and long-term dewatering of oil sands tailings

Salam¹

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“…The clayey tailings remains close to the PE. Limited data from field experiments (Fujiyasu et al 2000), pilots (Dunmola et al 2013), and back-calculations using models such as UNSATCON (Qi et al 2017b;Qi & Simms 2018b) support the rule of thumb that cumulative AE will vary between cumulative PE and 0.7 × cumulative PE. To simulate multilayer deposition, simple boundary conditions where the evaporation ceases when the surface suction achieves a certain value (usually between 5 and 10 MPa) are sufficient to conservatively characterise the contribution of evaporation to dewatering.…”

Section: Elements Of Unsaturated Soils Applicable To Tailings Drying ...mentioning

confidence: 99%

“…Even in quite northern and wet climates, drying can play an important role in strength development in thickened or filtered tailings impoundments, provided the rate of rise is not too high; e.g. one site in Northern Ontario rates of rise up to 3 m/year still allowed for desiccation to influence strength behaviour (Qi & Simms 2018b).…”

Section: Introductionmentioning

confidence: 99%

Unsaturated soil behaviour in thickened and filtered tailings

Simms¹

2023

Paste 2023: 25th International Conference on Paste, Thickened and Filtered Tailings

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Proper application of unsaturated soils to thickened or filtered tailings has substantial potential to optimise such tailings deposition. Unsaturated behaviour bears on both the geotechnical and geo-environmental performance of these deposits. Geotechnically, there is an increase in strength through both additional densification, and the presence of suction, as well as a stress history effect. The latter is especially important to understand in situ measurements in previously desiccated deposits; geo-environmentally, unsaturated behaviour strongly bears on seepage generation, as well as management or mitigation of acid generation. This paper summarises a body of work on experimentation, numerical simulation, and field data relating to different aspects of unsaturated behaviour and their relevance to practical outcomes for design of thickened or filtered tailing deposits. An important new outcome from this summary is the suggestion to characterise the extent of the stiffness imparted by drying, especially due to the possible risk of strength loss in thick deposits when the tailings eventually yield under self-weight.

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Coupling elasto-plastic behaviour of unsaturated soils with piecewise linear large-strain consolidation

Simms

Daliri³

et al. 2020

Géotechnique

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Slurried soils or tailings are often deposited in layers that undergo complex stress paths in terms of desiccation and loading, as a given layer may undergo variable degrees of desiccation before burial by subsequent layers, which has implications for geotechnical stability and geo-environmental performance. Proper analysis therefore requires not only an effective coupling of unsaturated flow with large-strain consolidation, but also inclusion of hysteresis effects. This paper presents the development and testing of a coupled unsaturated flow–large-strain consolidation model, UNSATCON, initially formulated for only monotonic dewatering, to include such effects. UNSATCON operates by a novel numerical algorithm that ensures mass conservation and handles the saturated/unsaturated transition smoothly. Differently from conventional integration schemes commonly embedded in finite-element formulations, this algorithm, tracking the void ratio change explicitly for large deformation, is shown to be applicable for most constitutive models of unsaturated soils under one-dimensional or isotropic stress conditions. Three constitutive models are implemented: a modified state surface model and the original and a minor variant of the Glasgow coupled model (GCM). The numerical model is evaluated using a recently published experimental study on multilayer deposition of thickened gold tailings. The model adequately reproduces the essential features of the dewatering processes, including the irrecoverable deformation induced by desiccation, the interlayer water exchange governed by deformation and deformation-dependent hysteretic retention behaviour. All three implemented constitutive models can reasonably simulate these experimental observations, despite some trivial discrepancies in magnitude. Point-level inspection, however, reveals some fundamental differences that may have important practical implications. For example, the additional plastic strain that occurs in GCM type models over multiple wetting–drying cycles may explain observed trends in increased strength in the simulated experiment.

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Analysis of dewatering and desaturation of generic field deposition scenarios for thickened tailings

Cited by 3 publications

References 13 publications

Effects of Polymers on short-and long-term dewatering of oil sands tailings

Effects of Polymers on short-and long-term dewatering of oil sands tailings

Unsaturated soil behaviour in thickened and filtered tailings

Coupling elasto-plastic behaviour of unsaturated soils with piecewise linear large-strain consolidation

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