Stress effects on thermal conductivity of soils and heat transfer efficiency of energy piles in the saturated and unsaturated soils

She-qiang  Cui; Chao Zhou; Jin-quan  Liu; Damilola Bashir Akinniyi

doi:10.1016/j.compgeo.2023.105549

Stress effects on thermal conductivity of soils and heat transfer efficiency of energy piles in the saturated and unsaturated soils

She-qiang Cui
, Chao Zhou
, Jin-quan Liu
, Damilola Bashir Akinniyi

Hong Kong Polytechnic University

Research output: Contribution to journal › Article › peer-review

39 Citations (Scopus)

102 Downloads (Pure)

Abstract

Soils surrounding energy piles are often subjected to high overburden pressure. So far, the stress effects on the thermal conductivity of soils and hence the thermal performance of energy piles have not been well investigated. This study proposed a new model for the stress-dependent thermal conductivity of saturated and unsaturated soils. It was validated using the data from a series of new tests and the literature and is able to capture stress induced variations of thermal conductivity. Then, it was applied to finite element analysis of energy piles’heat transfer efficiency. The numerical results reveal that ignoring stress effects on thermal conductivity, as in the conventional analysis, underestimates the heat exchange rate between energy piles and ground. The underestimation is more significant for piles with a larger aspect ratio and a faster pipe flow velocity, especially when the ground is drier and more compressible. For example, when the pile is 0.6 m in diameter and 50 in aspect ratio, the underestimation is up to 18%, 15% and 4% for the clay, silt and sand, respectively. These results
suggest that stress effects on thermal conductivity should be considered for better assessing the heat transfer efficiency of energy piles and other thermal geostructures.

Original language	English
Article number	105549
Number of pages	13
Journal	Computers and Geotechnics
Volume	160
Early online date	24 May 2023
DOIs	https://doi.org/10.1016/j.compgeo.2023.105549
Publication status	Published - 1 Aug 2023

Bibliographical note

© 2023, Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0/

Copyright © and Moral Rights are retained by the author(s) and/ or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This item cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder(s). The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the copyright holders.

This document is the author’s post-print version, incorporating any revisions agreed during the peer-review process. Some differences between the published version and this version may remain and you are advised to consult the published version if you wish to cite from it.

Funder

The National Science Foundation of China supports this work through research grant 52022004 . The authors also would like to thank the Research Grants Council (RGC) of the HKSAR for providing financial support through grant 15200120 . This work was also supported by RISUD/ PolyU under Grant 1-BBWS . Publisher Copyright: © 2023 Elsevier Ltd

Keywords

Thermal conductivity
Stress effects
Energy pile
Unsaturated soil
Heat exchange rate

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10.1016/j.compgeo.2023.105549

Akinniyi2023AAMAccepted author manuscript, 1.62 MBLicence: CC BY-NC-ND

Cite this

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title = "Stress effects on thermal conductivity of soils and heat transfer efficiency of energy piles in the saturated and unsaturated soils",

abstract = "Soils surrounding energy piles are often subjected to high overburden pressure. So far, the stress effects on the thermal conductivity of soils and hence the thermal performance of energy piles have not been well investigated. This study proposed a new model for the stress-dependent thermal conductivity of saturated and unsaturated soils. It was validated using the data from a series of new tests and the literature and is able to capture stress induced variations of thermal conductivity. Then, it was applied to finite element analysis of energy piles{\textquoteright}heat transfer efficiency. The numerical results reveal that ignoring stress effects on thermal conductivity, as in the conventional analysis, underestimates the heat exchange rate between energy piles and ground. The underestimation is more significant for piles with a larger aspect ratio and a faster pipe flow velocity, especially when the ground is drier and more compressible. For example, when the pile is 0.6 m in diameter and 50 in aspect ratio, the underestimation is up to 18\%, 15\% and 4\% for the clay, silt and sand, respectively. These results suggest that stress effects on thermal conductivity should be considered for better assessing the heat transfer efficiency of energy piles and other thermal geostructures. ",

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N2 - Soils surrounding energy piles are often subjected to high overburden pressure. So far, the stress effects on the thermal conductivity of soils and hence the thermal performance of energy piles have not been well investigated. This study proposed a new model for the stress-dependent thermal conductivity of saturated and unsaturated soils. It was validated using the data from a series of new tests and the literature and is able to capture stress induced variations of thermal conductivity. Then, it was applied to finite element analysis of energy piles’heat transfer efficiency. The numerical results reveal that ignoring stress effects on thermal conductivity, as in the conventional analysis, underestimates the heat exchange rate between energy piles and ground. The underestimation is more significant for piles with a larger aspect ratio and a faster pipe flow velocity, especially when the ground is drier and more compressible. For example, when the pile is 0.6 m in diameter and 50 in aspect ratio, the underestimation is up to 18%, 15% and 4% for the clay, silt and sand, respectively. These results suggest that stress effects on thermal conductivity should be considered for better assessing the heat transfer efficiency of energy piles and other thermal geostructures.

AB - Soils surrounding energy piles are often subjected to high overburden pressure. So far, the stress effects on the thermal conductivity of soils and hence the thermal performance of energy piles have not been well investigated. This study proposed a new model for the stress-dependent thermal conductivity of saturated and unsaturated soils. It was validated using the data from a series of new tests and the literature and is able to capture stress induced variations of thermal conductivity. Then, it was applied to finite element analysis of energy piles’heat transfer efficiency. The numerical results reveal that ignoring stress effects on thermal conductivity, as in the conventional analysis, underestimates the heat exchange rate between energy piles and ground. The underestimation is more significant for piles with a larger aspect ratio and a faster pipe flow velocity, especially when the ground is drier and more compressible. For example, when the pile is 0.6 m in diameter and 50 in aspect ratio, the underestimation is up to 18%, 15% and 4% for the clay, silt and sand, respectively. These results suggest that stress effects on thermal conductivity should be considered for better assessing the heat transfer efficiency of energy piles and other thermal geostructures.

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Stress effects on thermal conductivity of soils and heat transfer efficiency of energy piles in the saturated and unsaturated soils

Abstract

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Keywords

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