Abstract: Soil-water characteristic curve (SWCC) is a very important curve in the study of unsaturated soil mechanics; and the curve fitting parameters of SWCC are significant for analyzing the properties of unsaturated soils. To obtain the curve fitting parameters of SWCC accurately and efficiently, the experimental design and the curve fitting method of SWCC are studied. Based on the osmotic method and the filter paper method, a SWCC of an unsaturated expansive soil in a construction site in Hefei is measured. The van Genuchten model is used to represent the relationship between gravity water content and matric suction of the tested soil. The Lsqcurvefit function of the scientific language Matlab is adopted for carrying out the curve fitting of SWCC because the Lsqcurvefit function can set the lower limits and upper limits of fitting parameters. The problem of multi solutions of curve fitting parameters of SWCC and its influence factors are studied. It is demonstrated that when only the experimental data of the osmotic method is used, the range of suction is relatively small; and the multi solution phenomenon of SWCC’s fitting parameters is obvious. However, if the experimental data of both the osmotic method and the filter paper method are used, the range of suction is relatively large. Then, the multi solution phenomenon of SWCC’s fitting parameters can be diminished. And if the range of suction is large enough to represent the shape of the whole SWCC, the number of experimental data points need not be too much. Based on these conclusions, the experiment for measuring the soil-water characteristic curve can be designed more efficiently; and then the curve fitting parameters can be obtained more accurately.

Key words: soil-water characteristic curve, curve fitting, unsaturated soil, expansive soil, osmotic method, filter paper method