NaCl溶液对土体持水特性影响的试验研究

分别采用不同浓度的NaCl溶液对低塑性黏土进行饱和，然后进行压力板和蒸汽平衡法试验，获得整个吸力范围内的土-水特征曲线（SWCC）。分析不同浓度的孔隙溶液对SWCC的影响规律，结果表明：盐分对基质吸力的影响较小，对总吸力影响较大，这主要是因为盐溶液引起的渗透吸力所致。在蒸汽平衡法试验中，随着含水率的降低，孔隙浓度增大，渗透吸力增大。然而，基质吸力随着含水率的减小迅速增大，使得渗透吸力所占的比例逐渐减小。在非饱和土中，总吸力包括基质吸力和渗透吸力；基质吸力包括毛细部分和吸附部分，当土体中含水率较低时，主要是吸附效应在起作用；渗透吸力与溶液浓度有关。根据试验结果深入分析了吸附水膜和土颗粒之间的相互作用，得出由于溶质的存在对分子间吸附力的影响规律。根据表面化学原理，建立了分子间作用力和吸附水膜厚度之间的关系，以描述处于吸附状态的土-水特征曲线。

An experimental study of effect of NaCl solution on soil water characteristics

The soil-water characteristic curve (SWCC) of a low-plasticity clay over a wide range of suction was determined based on the pressure plate and vapor equilibrium techniques. The soil samples were prepared by saturating the low-plasticity clay with NaCl solutions with different concentrations. The effect of pore solution concentration on the SWCC was analyzed. The experimental results show that the effect of salt content has little influence on the matric suction, and has great influence on the total suction, the reason for this is that the saline solution induces the osmosis suction. In the vapor equilibrium experiments, it is found that the solution concentration increases with the decrease of water content, and correspondingly the osmosis suction increases. With the decrease of water content, however, the matric suction increases rapidly, while the contribution of osmosis suction decreases gradually. In unsaturated soils, the total suction (the negative value of pore water potential) includes the matric suction and the osmosis suction, where the matric suction has two contributions, i.e. capillary and adsorption, and the osmosis suction depends on the concentrations of pore solution. When the water content of the sample is low, the adsorption effect is dominant. Based on the experimental results, the interaction between adsorption water film and the soil particles is analyzed, and the influence of the solute on the intermolecular forces is also investigated. According to the surface chemistry theory, a relationship between intermolecular forces and adsorbed water film is proposed to describe the soil-water characteristics at low water potential.