Abstract: The Soil Water Characteristic Curve (SWCC) is an important hydraulic parameter of soils, which can reflect the properties of soil samples such as the permeability and the shear strength. To facilitate the determination of the SWCC curve of a granite residual soil sample and to explore a more convenient as well as faster model and the method to fit the SWCC curve of granite residual soil, firstly, the data points corresponding to the suction and moisture content in the process of dehumidification and hygroscopicity of granite residual soil are measured by using an indoor plate pressure instrument. The Gardner model was used for the dehumidification process and the hygroscopic process. The results of lsqcurvefit and nlinfit functions in the MATLAB software are similar, and the sum of the squared residuals is less than 0.0001. The results show that both lsqcurvefit and nlinfit functions are good for the fitting SWCC curves of granite residual soils, and either one can be used in future studies.

Key words: Granite Residual Soil, Soil Water Characteristic Curve, Plate Pressure Instrument, MATLAB Fitting