The shrinkage and swelling phenomenon of clayey soils induces substantial effects on measurement and modeling of soil thermal and hydraulic properties. This study developed a combined heat-pulse and evaporation method for simultaneous measurement of soil deformation, thermal, and hydraulic properties of clayey soils during drying-shrinkage processes. Four clayey soils with different textures and initial bulk densities (ρb) were subjected to evaporative-drying experiments. The results showed that the shrinkage process significantly altered the soil pore structure, water-holding capacity, and hydraulic conductivity. Neglecting the soil volume change during drying led to an underestimation of soil water retention, with maximum biases of 0.05–0.09 cm3 cm−3 in the water content (θ) at the same metric potential, and resulted in errors spanning several orders of magnitude in hydraulic conductivity at the same θ condition. The soil thermal properties, including volumetric heat capacity (C), thermal conductivity (λ), and thermal diffusivity (α), exhibited distinct trends with changing θ and ρb compared to rigid soils. The C showed strong positive linear correlations with the θ, but the slopes were lower than those for rigid soils due to the offsetting effect of increasing ρb. The λ first increased and then decreased with the increasing θ, in contrast to the monotonic increase observed in rigid soils. The α had a strong negative linear relationship with the θ, contrary to the typical positive correlation in rigid soils. Meanwhile, effects of the changing ρb on the thermal properties were opposite than did the variation in θ. The findings highlight the importance of considering soil volume change when characterizing the coupled water-heat transport processes in expansive clayey soils. The developed method provides a useful tool for investigating the complex interactions between soil deformation, thermal and hydraulic properties during drying-wetting cycles.

中文翻译：

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干燥收缩对粘土热力和水力特性的影响


粘土质土壤的收缩和膨胀现象对土壤热和水力特性的测量和建模产生了重大影响。本研究开发了一种热脉冲和蒸发相结合的方法，用于同时测量干燥收缩过程中粘土的土壤变形、热和水力特性。对 4 种不同质地和初始体积密度 （ρb） 的粘土进行了蒸发干燥实验。结果表明，收缩过程显著改变了土壤孔隙结构、持水能力和导水率。忽视干燥过程中的土壤体积变化会导致土壤保水能力被低估，在相同的公制电位下，含水量 （θ） 的最大偏差为 0.05-0.09 cm3 cm-3，并导致在相同 θ 条件下水力传导率的误差跨越几个数量级。与刚性土壤相比，土壤的热特性，包括体积热容 （C）、热导率 （λ） 和热扩散率 （α），随着 θ 和 ρb 的变化而表现出明显的趋势。C 与 θ 呈较强的正线性相关，但由于增加 ρb 的抵消效应，坡度低于刚性土的坡度。λ 首先增加，然后随着 θ 的增加而减小，这与在刚性土壤中观察到的单调增加相反。α 与 θ 具有很强的负线性关系，这与刚性土壤中典型的正相关相反。同时，变化的 ρb 对热性能的影响与 θ 的变化相反。 这些发现强调了在描述膨胀粘土中的耦合水热传输过程时考虑土壤体积变化的重要性。开发的方法为研究干湿循环过程中土壤变形、热和水力特性之间的复杂相互作用提供了有用的工具。