Rao Sudhakar M, Rekapalli Monica
Professor, Department of Civil Engineering, Indian Institute of Science, Bengaluru, 560012, India.
Research Associate, Department of Civil Engineering, Indian Institute of Science, Bengaluru, 560012, India.
Sci Rep. 2020 Mar 9;10(1):4322. doi: 10.1038/s41598-020-61302-w.
Diffusion of capillary water and water vapor during moisture loss in an unsaturated soil is impeded by the chemical and geometrical interactions between water molecules/vapor and the soil structure. A reduction in moisture content contracts the diffuse and adsorbed water layers in the partly saturated soil and disturbs the connected capillary network for flow of liquid water. With further drying, the dry soil layer expands and moisture is predominantly lost as vapor through continuous air-flow channels. The water-filled capillary network and air-filled channels are moisture conduits during different stages of soil drying. It is important to identify zones of dominant moisture transport and to select appropriate tortuosity equations for correct prediction of moisture flux. Laboratory experiments were performed to determine moisture flux from compacted soil specimens at environmental relative humidity of 33, 76 and 97% respectively. Analysis of the resultant τ - θ (tortuosity - volumetric water content) relations, illustrated the existence of a critical water content (θ), that delineates the dominant zones of capillary liquid flow and vapor diffusion. At critical water content, the pore-size occupied by the capillary water is governed by the generated soil suction. Generalized equations are proposed to predict tortuosity factor in zones of dominant capillary liquid flow and vapor transport over a wide range of relative humidity (33 to 97%).
在非饱和土壤水分损失过程中，毛细管水和水蒸气的扩散会受到水分子/水蒸气与土壤结构之间化学和几何相互作用的阻碍。含水量的降低会使部分饱和土壤中的扩散水层和吸附水层收缩，并扰乱液态水流动的连通毛细管网络。随着进一步干燥，干燥土层膨胀，水分主要通过连续的气流通道以水蒸气形式损失。充满水的毛细管网络和充满空气的通道在土壤干燥的不同阶段都是水分传输通道。识别主要水分传输区域并选择合适的曲折度方程以正确预测水分通量非常重要。进行了实验室实验，以分别测定在环境相对湿度为33%、76%和97%时压实土壤试样的水分通量。对所得的τ-θ（曲折度-体积含水量）关系进行分析，表明存在一个临界含水量（θ），它划分了毛细管液体流动和水蒸气扩散的主要区域。在临界含水量时，毛细管水占据的孔径由产生的土壤吸力控制。提出了广义方程，以预测在广泛的相对湿度范围（33%至97%）内主要毛细管液体流动和水蒸气传输区域的曲折度因子。
