The soil-water characteristic curve (SWCC) is defined as the relationship between the suction and the water content or degree of saturation. The soil-water characteristics and related mathematical models can be used to model the unsaturated soil properties such as the permeability and the shear strength. Conventionally, only the drying soil-water characteristic curve of soil is determined. In this work, the influences of initial water content, initial dry density, the vertical stress and drying and wetting cycles are examined and discussed in detail. The SWCCs and hysteresis loops of residual soils in Xiamen were obtained by the filter paper method. The results show that the initial water content has negligible effect on SWCCs. The specimen at the wet of optimum moisture content (OMC) has the higher air entry value and the larger hysteresis loop than that of the soil specimen at the dry of OMC. The specimen with OMC lies between them. While, the initial dry density has considerable influence on SWCCs. The specimen at lower initial dry density exhibits smaller air entry value and higher rate of desorption than that of the specimen at higher initial dry density. The size of hysteresis loop decreases as the initial dry density increases. The specimens subjected to different vertical stresses have different SWCCs. The higher the applied load on the specimen, the higher the air entry value, the higher the rate of desorption, the smaller the size of hysteresis loop. In the drying and wetting process, the size of hysteresis loop has been substantially affected by the first drying and wetting cycle. With the increasing of drying and wetting cycle, the air entry value and the size of hysteresis hoop decrease. Since the features of soil-water characteristic of sandy clay are not well defined especially for the residual state of saturation, which desaturates continuously without a distinct break point, the residual suction or residual water content, one of the key parameters in the mathematical models of SWCC, is not well defined. As a result five improved models without the residual water content are proposed to describe the SWCCs of residual soil. The improved Gardner model has been found to be the most suitable model for all SWCCs of the residual sandy clay in Xiamen.
