Research On The Prediction Model Of Soil Water Characteristic Curve

The soil water characteristic curve (SWCC) for a soil is defined as the relationship between water content or saturation degree and matric suction for the soil, which is the reflection of energy and water quantity in unsaturated soil. It has become an acceptable way to predict the shear-strength, volume strain, permeability of an unsaturated soil by the SWCC. Since the soil water characteristic curve is used as the basis for the prediction of other unsaturated soil parameters, it is important to have a reasonably accurate characterization of this curve. In this thesis, an estimating model of SWCC is proposed from some fundamental soil physical properties (particle-size distribution, bulk density, porosity). The main contents are described as follows:1. Based on the basic characters of unsaturated water, the relations among the matric suction, surface-tension and pore radius are presented emphatically. In the meanwhile, the physical meaning and factors affecting the SWCC are also discussed.2. The suitability of four common parametric models to describe the particle-size distribution is evaluated based on experimental data from UNSODA. It is indicated that both the modified logistic growth model and Fredlund model can fit the particle-size distribution curve better.3. Linear and nonlinear fittings of the empirical parameter a_i from Arya-Paris model are suggested, and then a modified predicting method of SWCC is built up by the calculation of 12 samples which are sand, loam, clay from UNSODA as before, respectively.4. The SWCCs derived from the modified predicting method and the hydraulic conductivity of unsaturated soils from the SWCCs are applied to an embankment example in the middle and lower reaches of Yangtze River. The variation of saturated-unsaturated seepage field and the slope stability with the groundwater level, flood duration and river water drawdown are researched.