Geotechnical characterisation of coal tailings down the beach and constant rate of loading consolidation in a slurry consolidometer

Abstract

The conventional disposal of slurried tailings in a tailings storage facility (TSF) leads to the formation of a beach, on which the tailings sort hydraulically, settle, consolidate, and desiccate upon exposure. Basic geotechnical testing, such as specific gravity, Atterberg limits, and particle size distribution, found that there was no particular trend of changes in the tailings properties down the beach. The settled sediment found in a settling test was slurry-like and unsuitable for conventional oedometer testing. Constant rate of loading (CRL) consolidation testing is more representative of the continuous disposal of tailings slurry than conventional step loading. Consolidation testing in a slurry consolidometer was conducted and captured from a slurry-like to soil-like state. A slow rate of loading increased the test time, while a too quick rate of loading built up very high excess PWP. The test results showed different stages of consolidation, depending on excess PWP development and dissipation, and applied stress.

Effect of initial specimen height and solids concentration on the consolidation parameters of fine-grained coal tailings

“…The base PWP of the specimen with 100 mm ISH and 38.2% ISC started to dissipate before reaching its peak in the CRL stage of loading, while the base PWP of other specimens with higher ISH or ISC began to dissipate with some delay after entering the maintained stress stage. Specimens with higher ISH took more time to initiate PWP dissipation than for specimens with lower ISH, as they have a greater dissipation length to overcome before reaching the intrinsic point, where the excess PWP started to dissipate significantly and the state of the specimen changed from slurry-like to soil-like (Islam et al 2020(Islam et al , 2021. Similarly, the duration between the onset of base PWP dissipation and test completion increased with an increase in ISH, which was consistent with the findings by Watabe et al (2008), where an increase in specimen height increased test duration by square of the ratio of specimen height increment, provided all other variables are unchanged.…”

“…The friction loss between the specimen and confining cell wall should, therefore, be taken into account. Assuming a parabolic distribution of stress over the height of the specimen, the average effective stress can be determined using the equation below (Shokouhi 2017;Shokouhi and Williams 2017;Islam et al 2021):…”

“…The settling efficiency of fine-grained tailings, such as coal tailings, mature oil sands tailings, is low, due to its low specific gravity and presence of clay minerals, and the tailings remain slurrylike (Alam et al 2014;Islam and Shang 2019;Islam et al 2020Islam et al , 2021. Conventional consolidation testing in an oedometer is not suitable for slurrylike material (Bo et al 2010), because the application of top load displaces tailings through the gap between the top cap and the ring.…”

“…The Rowe cell applies the load via a rubber diaphragm, which would be required to stretch excessively to accommodate the large deformation induced in a slurry and would cause excessive dishing on the specimen's top surface and the porous disc. A large, stress-controlled, purpose-built slurry consolidometer available in the Geotechnical Engineering Centre at The University of Queensland can overcome the issues encountered during testing in an oedometer or Rowe cell and can consolidate tailings slurry from slurry-like to soil-like states (Shokouhi 2017;Shokouhi and Williams 2017;Shokouhi et al 2018;Islam et al 2020Islam et al , 2021.…”

Coal Sludge Permeability Assessment Based on Rowe Cell Consolidation, and Filtration Investigations

“…Because the use of fine-grained tailings in geoengineering is much more prevalent in the case of flotation tailings from ore processing [23,24], and not for coal, it is all the more worth exploring. The research on the properties of coal sludge waste is currently mainly focused on analyzing its filtration and physicomechanical parameters [19,[25][26][27] but geotechnical properties of flotation wastes from hard coal processing (e.g., consistency limits, strength and deformation parameters) become at present more often the subject of scientific research [1,2,4,[27][28][29][30].…”