土-水特征曲线滞后现象的微观机制与计算分析

对吸湿与脱湿过程中引起非饱和土土-水特征曲线滞后性质进行机制分析，认为在微观角度看，接触角的差异是主要原因。基于热力学原理，假定粒间弯液面为一圆弧，综合考虑不等径颗粒半径比、接触角等因素，应用几何关系导得了两接触土颗粒填充角之间的迭代关系，并进行编程计算。在此基础上，引入热力学弯液面压强计算公式和水量体积计算公式，得到了不等径土颗粒间基质吸力－水量计算方法。应用该方法对不同接触角条件下的单个弯液面和不同堆积形式土粒的土-水特征曲线进行了解算，结果表明，由于接触角不同，土-水特征曲线具有明显的滞后现象；孔隙填充将引起低吸力状态土体含水率增加，其对松散颗粒影响较大，含水率可增大达90%；颗粒堆积形式及级配对接触角不同引起的滞后现象影响不大。此外，仅考虑接触角因素无法解释滞回圈的形成，其计算理论有待进一步深入研究。

Theoretical study of microscopical mechanisms and computational method of hysteresis in SWCCs

The fundamental mechanisms responsible for drying/wetting hysteresis in the relationship between metric suction and water content, and relevant computational method were studied. The difference between drying and wetting contact angles was considered as the principal factor in terms of microscopic view. Then, based on thermodynamic principle and the assumption that the meniscus among soil particles is a crown face, the iteration relation of filling angles was deduced by studying geometrical properties and taking into account the factors such as radius ratio of soil particles and wetting/drying contact angles. And the relationship between suction and volume of filled water among soil particles with different radii was developed by introducing formulas which solve intensity of pressure on meniscus and volume of filled water. The soil-water characteristic curves (SWCCs) of single meniscus and soil particles with different accumulation styles were solved; the results indicate that: the change of contact angles will cause the hysteresis of SWCCs; filling the pore between particles will raise the water content in lower suction status; and it is more remarkable for loose particles, in which the water content can be enlarged by 90%; the influence of accumulation style and graduation of soil particles on hysteresis is paltry comparatively. Besides, the hysteresis loop of SWCCs can not be interpreted only by hysteresis of contact angles, the relevant theory still under developing.