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Effect of soil saturation and grain size on coupled hydrothermal flow in fine sands based on X-ray μCT imaging

Effect of soil saturation and grain size on coupled hydrothermal flow in fine sands based on X-ray μCT imaging
Effect of soil saturation and grain size on coupled hydrothermal flow in fine sands based on X-ray μCT imaging

Coupled hydrothermal flow can occur in soils, for example in applications such as ground heat storage and nuclear waste disposal. Therefore, approaches to quantitative analysis of water transfer in response to imposed thermal gradients are required, especially in unsaturated conditions. Analysis methods also require validation by laboratory and field data, which can be hard to obtain. This paper explores the possibility of using X-ray μCT techniques to observe and quantify water content changes in soils under thermal gradients. Specimens of a fine sand and a silty fine sand were prepared at degrees of saturation between 20% and 50%, before being subjected to heating from their base. Repeated scans, set up to balance image quality and scan duration, were carried out during the heating process, and Gaussian decomposition techniques were used to determine the changing soil phase proportions throughout the experiments. Based on these results and the accompanying numerical simulation of the experiments, it is shown that rapid vapour diffusion plays a more significant role than liquid flow in all cases. The rate of water content and hence degree of saturation change was more rapid in the less saturated specimens, especially for the fine sand. In practical terms, these moisture changes would result in reduction in thermal conductivity, especially in the soils of lower saturation. As well as providing insight into the dominant water transfer processes, the experiments show the feasibility of applying X-ray μCT techniques to thermal problems in soil mechanics.

Grain size, Hydrothermal flow, Soil saturation, Unsaturated soils, X-ray μCT techniques
2352-3808
Liu, Kui
eeadfb38-005d-45a0-bb01-8b8eb734918b
Loveridge, Fleur A.
495228dc-4e97-4393-a1b5-7f1a1a800848
Boardman, Richard
5818d677-5732-4e8a-a342-7164dbb10df1
Powrie, William
600c3f02-00f8-4486-ae4b-b4fc8ec77c3c
Liu, Kui
eeadfb38-005d-45a0-bb01-8b8eb734918b
Loveridge, Fleur A.
495228dc-4e97-4393-a1b5-7f1a1a800848
Boardman, Richard
5818d677-5732-4e8a-a342-7164dbb10df1
Powrie, William
600c3f02-00f8-4486-ae4b-b4fc8ec77c3c

Liu, Kui, Loveridge, Fleur A., Boardman, Richard and Powrie, William (2022) Effect of soil saturation and grain size on coupled hydrothermal flow in fine sands based on X-ray μCT imaging. Geomechanics for Energy and the Environment, 32, [100380]. (doi:10.1016/j.gete.2022.100380).

Record type: Article

Abstract

Coupled hydrothermal flow can occur in soils, for example in applications such as ground heat storage and nuclear waste disposal. Therefore, approaches to quantitative analysis of water transfer in response to imposed thermal gradients are required, especially in unsaturated conditions. Analysis methods also require validation by laboratory and field data, which can be hard to obtain. This paper explores the possibility of using X-ray μCT techniques to observe and quantify water content changes in soils under thermal gradients. Specimens of a fine sand and a silty fine sand were prepared at degrees of saturation between 20% and 50%, before being subjected to heating from their base. Repeated scans, set up to balance image quality and scan duration, were carried out during the heating process, and Gaussian decomposition techniques were used to determine the changing soil phase proportions throughout the experiments. Based on these results and the accompanying numerical simulation of the experiments, it is shown that rapid vapour diffusion plays a more significant role than liquid flow in all cases. The rate of water content and hence degree of saturation change was more rapid in the less saturated specimens, especially for the fine sand. In practical terms, these moisture changes would result in reduction in thermal conductivity, especially in the soils of lower saturation. As well as providing insight into the dominant water transfer processes, the experiments show the feasibility of applying X-ray μCT techniques to thermal problems in soil mechanics.

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Accepted/In Press date: 7 July 2022
e-pub ahead of print date: 12 July 2022
Published date: 23 November 2022
Additional Information: Funding Information: The work reported in this paper forms a part of a project funded by the Royal Academy of Engineering , the Doctoral Training Centre at University of Southampton and EPSRC ( EP/G036896/1 ).
Keywords: Grain size, Hydrothermal flow, Soil saturation, Unsaturated soils, X-ray μCT techniques

Identifiers

Local EPrints ID: 472803
URI: http://eprints.soton.ac.uk/id/eprint/472803
ISSN: 2352-3808
PURE UUID: 692e49f4-c380-4a3a-9c9b-31a1b9d9a815
ORCID for Kui Liu: ORCID iD orcid.org/0000-0002-7533-1272
ORCID for Richard Boardman: ORCID iD orcid.org/0000-0002-4008-0098
ORCID for William Powrie: ORCID iD orcid.org/0000-0002-2271-0826

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Date deposited: 19 Dec 2022 17:44
Last modified: 17 Mar 2024 02:58

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Contributors

Author: Kui Liu ORCID iD
Author: Fleur A. Loveridge
Author: William Powrie ORCID iD

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