Abstract: Residual soil which widely distributes in south China is one of the major soils encountered in engineering construction and geological disasters evaluation. The engineering properties of residual soil are dependent on the composition, structure, and stress of soil, and also on the matric suction. Soil-water characteristic curve expressing the relationship between soil water content and matric suction is an important part of research on non-saturated soil. In this research we select granite porphyry residual soil, tuff residual soil and conglomerate residual soil, which are typically representative in Fujian province, as test sample soils to determine the soil-water characteristic curve in the process of Dehumidification and moisture absorption. Then we explain lag effects of soil water characteristic curve from the microscopic point of view. Based on Barden’s unsaturated soil classification, we put forward a simple method to predict the matric suction with saturation by analyzing the practical engineering significant moisture (saturation between 50%-90%) in view of the difficulties in measuring matric suction.

Key words: residual soil, soil-water characteristic curve, Barden’s unsaturated soil classification, matric suction, saturation