Effects of drying-induced shrinkage on thermal and hydraulic properties of clayey soils

Abstract

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.