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<p>Thermal conductivity (<i>λ</i>) serves as a fundamental physical property governing heat transfer in soil. In practice, the soil can be subjected to wetting and drying that cause variations in <i>λ</i>. The reason behind such phenomenon is still vague, since the effects of suction path and void ratio&#xa0;(<i>e</i>) were not distinguished in previous limited works, especially for clayey soils. In this study, water retention curve and <i>λ</i> are measured over the full moisture range on wetting and drying path, with influence of void ratio being excluded by special experimental design. Results indicate that under the same <i>e</i> condition, the hydraulic hysteresis is obvious for the water retention curves of clayey soils, due to the contact angle and interlayer cation hydration mechanism. For specimens with identical <i>e</i>, <i>λ</i> upon drying is higher than that upon wetting, probably suggesting that <i>s</i> cannot be directly related to changes in <i>λ</i>. In <i>λ</i>-water content (<i>w</i>) plane, there exists a threshold <i>w</i>: Below this value, differences in <i>λ</i> are noticeable for specimens experiencing wetting and drying at identical <i>w</i>; otherwise, <i>λ</i> is independent of suction path. Microstructural observations from mercury intrusion porosimeter and scanning electron microscope confirm that at <i>s</i> = 71.1&#xa0;MPa, the specimens exhibit comparatively more and/or larger inter-aggregate pores in drying path, accompanied with clear agglomeration of clay aggregates. It implies that comparing to wetting, drying leads to increase in aggregate size and decrease in physical contacts among aggregates, in which the former enables to widen the heat flow path in aggregate region and the latter signifies reduced thermal resistance, thereby enhancing thermal conduction at microscale and resulting higher <i>λ</i> under relatively low moisture condition. By contrast, the hysteresis loop in <i>λ</i>-<i>w</i> curve is comparatively narrower than that in <i>λ</i>-<i>s</i> curve for clays, due to the hydraulic hysteresis mechanism over the full suction range. This research contributes to clarify the role of moisture on <i>λ</i> for clayey soils upon wetting and drying, and also provide a more comprehensive understanding of thermal conduction in variably saturated soils for geotechnical and geoenvironmental applications.</p>

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Investigation on thermal conductivity of clayey soils upon wetting and drying

  • 期刊论文

  • 发表日期：

    2025年7月21日

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  • Fan Peng,
  • Yeting Qiu,
  • Bo Chen,
  • De’an Sun,
  • Yunzhi Tan,
  • You Gao

摘要

Thermal conductivity (λ) serves as a fundamental physical property governing heat transfer in soil. In practice, the soil can be subjected to wetting and drying that cause variations in λ. The reason behind such phenomenon is still vague, since the effects of suction path and void ratio (e) were not distinguished in previous limited works, especially for clayey soils. In this study, water retention curve and λ are measured over the full moisture range on wetting and drying path, with influence of void ratio being excluded by special experimental design. Results indicate that under the same e condition, the hydraulic hysteresis is obvious for the water retention curves of clayey soils, due to the contact angle and interlayer cation hydration mechanism. For specimens with identical e, λ upon drying is higher than that upon wetting, probably suggesting that s cannot be directly related to changes in λ. In λ-water content (w) plane, there exists a threshold w: Below this value, differences in λ are noticeable for specimens experiencing wetting and drying at identical w; otherwise, λ is independent of suction path. Microstructural observations from mercury intrusion porosimeter and scanning electron microscope confirm that at s = 71.1 MPa, the specimens exhibit comparatively more and/or larger inter-aggregate pores in drying path, accompanied with clear agglomeration of clay aggregates. It implies that comparing to wetting, drying leads to increase in aggregate size and decrease in physical contacts among aggregates, in which the former enables to widen the heat flow path in aggregate region and the latter signifies reduced thermal resistance, thereby enhancing thermal conduction at microscale and resulting higher λ under relatively low moisture condition. By contrast, the hysteresis loop in λ-w curve is comparatively narrower than that in λ-s curve for clays, due to the hydraulic hysteresis mechanism over the full suction range. This research contributes to clarify the role of moisture on λ for clayey soils upon wetting and drying, and also provide a more comprehensive understanding of thermal conduction in variably saturated soils for geotechnical and geoenvironmental applications.