基于VG模型确定土水特征曲线基本参数

土水特征曲线基本参数(进气值、残余吸力值和反弯点的斜率等)在非饱和土的强度理论、渗流理论以及体变特性等方面都是非常重要的参数,常常通过传统画图法来确定,其精确度难以保证。以洛川标准剖面4层原状黄土为研究对象,基于VG模型提出单峰和双峰SWCC基本参数的确定方法;采用滤纸法测得SWCC数据点,基于VG模型进行最优化拟合,获取拟合参数,利用单峰和双峰SWCC数据点验证该方法的可行性;进行自然状态下的水分蒸发试验,根据质量含水率与蒸发时间的关系确定蒸发残余饱和度Srzf,依据Sr1、Sr2(Sr1和Sr2分别由确定残余状态的两种方法得到)与Srzf的相对误差值,比较了两种确定残余状态的方法。结果表明:对于单峰和双峰SWCC曲线,该方法都可以得到合理的基本参数并有效地确定其残余状态。

DETERMINATION OF SOIL-WATER CHARACTERISTIC CURVE VARIABLES BASED ON VG MODEL

The variables of the soil-water characteristic curve(air-entry value, residual suction and slope at the inflection point) are very critical parameters in the strength theory, percolation theory and volume change behavior of unsaturated soil. It is often obtained by conventional graphical method, which is subjective and inaccurate. This study presents the methods for determining the variables of unimodal and bimodal SWCC based on VG model using the measured SWCC data of the four layers of undisturbed loess in Luochuan standard section. SWCC data were measured by filter paper method and best fitted using Van Genuchten's equation. Consequently the best fitting parameters were obtained, and the proposed methods were validated using the measured unimodal and bimodal SWCC data. The water evaporation test in the natural state was carried out. Then the evaporation residual saturation S_rzf was determined according to the relationship between the mass moisture content and the evaporation time. According to the relative errors between S_r1, S_r2 and S_rzf(S_r1 and S_r2 were acquired from the two methods for determining the residual state, respectively), the comparison was made between the two methods for determining the residual state. The results suggest that the proposed methods can produce reasonable variables and determine the residual state effectively related to the unimodal and bimodal SWCC.