For mine wastes such as coal tailings, management of these materials requires complex geotechnical engineering that uses many soil properties, such as water retention. However, coal itself is chemically heterogeneous and often appears to be partially hydrophobic, which affects its water retention properties. This study aims to outline how hydrophobic soil particles and coal alter water retention curves compared to hydrophilic materials. The study involves four materials: sand, hydrophobized sand, crushed rock and crushed coal. Mixtures of sand with different proportions of hydrophobic particles had their water retention curves measured and compared, with the only variable being the particle surface characteristics. The rock and coal were separated into different particle size fractions and had their water retention curves measured and compared, with the only variable being particle hydrophobicity. A clear trend was observed for the sand mixtures: the degree of saturation at any suction was reduced when increasing the hydrophobicity of the material. This trend indicates the fundamental water retention behavior expected for soils more hydrophobic than is typical, which was not clearly demonstrated in previous studies. However, a similar trend was not seen when comparing the rock and otherwise identical hydrophobic coal samples, which actually appeared hydrophilic in terms of water retention. ESEM imaging shows a dual hydrophilic and hydrophobic behavior for coal which may explain the result. However, further research is required to understand the discrepancy, which appears to be caused by an unknown coal–water phenomena.
For safe and efficient mining operations to occur the management of waste materials is required, which often takes the form of geotechnical structures constructed from this waste. The safe use of these structures requires a number of resources, one of these being sufficient information about the waste material properties. For example, the drying process of a tailings dam is predicted with the water retention and permeability of the tailings. When considering coal tailings, which are comprised of coal and mineral soil particles (typically), the presence of coal may be problematic. The localised hydrophobicity of coal molecules may have a unique effect on water permeability and retention; this is relevant to geotechnical analysis where hydrophilic behaviour is assumed. To explore the possible effect of localised hydrophobicity, mine tailings were obtained from a coal mine of the Hunter Valley, NSW, Australia, and the coal fraction was separated via density separation. After this, three materials were available: unchanged mine tailings and a coal and mineral fraction of tailings. The goal was to characterise the three materials and allow deeper insight on what effect the addition of coal has on retention and hydraulic properties. Characterization involved measuring particle size distribution, pore size distribution, soil water retention curve, and saturated water permeability. The results show that there are distinct differences in the water retention and permeability properties of each material, and a number of these differences could be explained by the differing particle/pore sizes observed in each material. However, the coal containing materials desaturated at low suctions (< 10 kPa) compared to the mineral fraction, which could not be explained by particle/pore size differences and points towards localised hydrophobicity as a possible cause.
Analysing unsaturated soil response often requires the soil-water-retention-curve (SWRC). The SWRC depends upon the soil microstructure, which evolves with hydromechanical loading such as in-situ exposure to wetting-drying cycles. If in-situ response is of interest and studied in the laboratory, it is essential specimens have a structure representative of in-situ conditions. Simulating wetting-drying cycles in the laboratory is possible albeit time-consuming and a faster alternative procedure would be preferred, which is the focus of this paper. Mixtures of two soils were prepared in the laboratory by either: exposure to three simulated wetting-drying cycles, or one of two compaction approaches. The microstructure and drying-path SWRC of the specimens prepared with each method were measured. Most of the compacted specimens achieved similar pore size distributions to the cycled samples though the outcomes in terms of achieving a target SWRC, which was the objective of the study, are mixed. The SWRCs of most compacted samples had similar gravimetric water contents yet significantly higher saturation degree at every suction measured. This is explained by the compacted samples containing less macro pores than cycled samples. The compaction procedure, designed to produce specimens having a SWRC similar to that of cycled materials, seems promising but needs modification.
The Hunter valley region in NSW Australia is an area with a heavy coal mining presence. As some mines come to their end of life, options are being investigated to improve the topsoil on post mining land for greater plant growth, which may allow economically beneficial farmland to be created. This research is part of an investigation into mixing a mine waste material, coal tailings, with topsoil in order to produce an improved soil for plant growth. Implementing such a solution requires estimation of the drying path of the water retention curves for the tailings and topsoil used. Instead of a lengthy laboratory measurement, a prediction of the drying curve is convenient in this context. No existing prediction models were found that were suitable for these mine materials, hence this paper proposes a simple and efficient model that can more accurately predict drying curves for these mine materials. The drying curves of two topsoils and two tailings from Australian coal mines were measured and compared with predictions using the proposed model, which performs favorably compared to several existing models in the literature. Additionally, the proposed model is assessed using data from a variety of fine- and coarse-grained materials in the literature. It is shown that the proposed model is overall more accurate than every other model assessed, indicating the model may be useful for various materials other than those considered in this study.
Woody plants on earthen slopes are a bioengineering solution for the prevention of shallow landslides that occur mostly during a wet season. From a soil-hydrological point of view, slope stability is influenced by plant roots reducing soil water content through transpiration. Despite this, conventional engineering practice tends to ignore the effects of Root Water Uptake (RWU), in part due to the complexity of soil-vegetation-atmosphere interactions. This paper investigates the hydrological effects of plants, which involved seepage simulations performed on two different soil types. Each soil was exposed to different rainfall intensities, and the influence of plants over time was seen from the RWU over time for different configurations of plant spacing and canopy densities. This information with in-situ rainfall data, is useful to assess the effectiveness of plants for slope stability. Further, the relative importance of different mechanisms acting in soil-plant-atmosphere interactions was seen in the RWU data. Although the conducted simulations refer to a horizontal soil profile, the results are useful in more complex geometries such as earthen slopes and may help the design of bioengineering solutions (woody plants) and slope stability assessment. Future research is aimed to investigate additional soil-vegetation-atmosphere mechanisms and additional model geometries and plant species.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.