The Influence of Model Parameters of Soil-Water Characteristic Curve to the Seepage

The model parameters of Soil-Water Characteristic Curve and the hydraulic conductivity may be obtained by the method of the back analysis according to the permeability test data. In order to raise the efficiency of the back analysis calculation, it is necessary to study the influence of the parameters of SWCC model to the seepage. The matrix suctions of Q2 loess were measured by the indoor test of the pressure plate extractor, and SWCC of Q2 loess was fitted with the Van Genuchten's three-parameter model. The influences of SWCC model parameters a, n,theta s,theta r and Ksat on the range of seepage was studied. The results show that the air-entry value of Q2 loess is 18.48kPa, the saturated volumetric water content is 45.82% and the residual volumetric water content is 3.91%. It is found that the permeability sensitivity is different to different parameters. The influence of SWCC model parameters to the seepage depth from the big to the small is Ksat,theta s, n, a and theta r, and that to the thickness of the unsaturated infiltration from the big to the small is Ksat, n,theta s, a and theta r. The seepage range is the most sensitive with the change of Ksat, and there is the least sensitive with the change of theta r. The influence of theta r is evidently lower than that of other parameters. The seepage range increases with the increase of parameters "a" and Ksat; while the seepage range reduces as parameters n and theta s are added. Suggest that step size of the parameter is determined according to its influence degree to the seepage in the process of the back analysis of SWCC model parameters.