The Mechanical Behaviour of Tailings

Abstract

Tailings materials have a high risk of failure, due to the small particle sizes and high water contents. There were more than 240 tailings dam incidents between 1917 and 2014, which caused significant loss of life. Among those failures, unusually heavy rain is the most common cause of tailings dam failures, and the second cause is liquefaction under either static or seismic loading. Usually liquefaction may exacerbate an initial failure. It is therefore important to study further the underlying mechanics of tailings materials.
In this study, the mechanical behaviour of tailings from three different origins; iron tailings from Panzhihua, China, gold tailings from Brazil and a copper tailing from Dexing, China, were investigated. For all the tailings, the experimental work focused predominantly on three parts: material characterization, compression behaviour and shearing behaviour. Additionally, the small-strain stiffness and anisotropy of the tailings were investigated by conducting bender element tests.
The results show that none of these tailings show real transitional behaviour, and a unique normal compression line (NCL) and a unique critical state line (CSL) can be identified for each tailing, which is independent of the sample preparation method. In general, the rates of convergence to the NCLs are slow, and so the depositional density would affect the in-situ volume to far higher stresses than the materials would ever experience. For different tailings, even if the D50 values range from 0.011 to 0.220mm, the horizontal asymptotes of the CSLs show significant variation but are reasonably constant in between the maximum and minimum specific volumes, when plotted against either fc or D50, in contrast to the findings of Lade and Yamamuro (1997). The implication of this is that in general neither the pond nor the upper beach is more susceptible to liquefaction, but for individual tailings, for example the iron tailings tested in this study or the fluorite tailings tested by Carrera et al. (2011), the susceptibility may be different. The small strain stiffness data from bender elements analyses show that samples prepared with the compaction or slurry methods had similar moduli, whilst the analyses of the vertical and lateral bender elements showed isotropic behaviour. Interestingly, an expression proposed in the literature developed on the basis of experiments on quartz type sands predicted within satisfactory limits the behaviour of the tailings.

Date of Award	17 Jul 2017
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Matthew Richard COOP (Supervisor), Kostas SENETAKIS (Supervisor), Yu WANG (Supervisor) & Matthew Richard COOP (External Co-Supervisor)