任意干湿路径下非饱和岩土介质的土水特征关系模型

A MODEL OF SOIL-WATER CHARACTERISTICS FOR UNSATURATED GEOTECHNICAL MATERIALS UNDER ARBITRARY DRYING- WETTING PATHS

土水特征曲线(SWCC)代表着基质吸力与含水量关系不是一一对应的,在反复干湿循环路径下该曲线呈现出循环滞回特性。岩土介质在经历反复干湿循环之后,部分气体会以气泡的形式残留于孔隙中;这种残留的气体会对土水特征关系和流体的渗透系数产生重要影响。基于毛细循环滞回的内变量理论和传统的土水特征关系经验模型,提出了一个能模拟在任意干湿循环路径下土水特征关系的数学模型。特别地,该模型考虑了介质中的残余含气量对循环土水特征关系的影响。在循环滞回边界给定的情况下,该模型只包含一个材料参数;该材料参数可以由任意一条一阶扫描线(或其上的一个数据点)来确定。利用所提出的数学模型结合欧拉迭代计算方法,对已有文献中的粉土、烧结玻璃珠、石灰岩及白云岩等不同岩土介质在任意干湿循环路径下的SWCC试验曲线进行了模拟。通过将预测结果与现有试验数据进行对比,验证了该模型对描述复杂干湿循环路径下的土水特征关系的有效性。

Soil-water characteristic is one of important hydraulic parameters for geotechnical media. A soil-water characteristic curve（SWCC） represents a relationship between moisture content and matrix suction, and this relationship is generally nonmonotonic, showing hysteretic behaviors under drying-wetting cyclic paths. When a geological material experiences drying-wetting cycles, part of air phase will be trapped as air bubbles in the pore space. Such air entrapment has significant influences on the soil-water characteristics and the permeability of the porous media. Based on the internal-variable theory of capillary hysteresis and an empirical model of soil-water characteristics, a mathematical model is developed that can be used to describe the soil-water characteristics of geotechnical media experiencing arbitrary drying-wetting paths. In particular, the effect of air entrapment is fully taken into account in this model. Provided that the hysteresis loop is given, the proposed model includes only one material parameter, which can be determined by using any first-order scanning curve（or one datum point on the curve）. The model is numerically solved using the forward Euler iterative scheme. Numerical simulations are compared with the experimental data of the soil-water characteristic curves for four different types of geotechnical media, i.e. a silt loam, sintered glass beads, a limestone and a dolomite. It is found that the computational results agree very well with the measured data; and it is shown that the proposed model is capable of describing the soil-water characteristic curves of geotechnical media experiencing complicated drying-wetting paths.