Abstract: Loess in China is thick, and groundwater levels are always very deep in loess area where is characterized by low precipitation, which makes loess always at unsaturated state. Soil-water characteristic curve is the foundation of researches on stress state, strength and permeability of unsaturated loess. This paper experiments on typical Malan loess in Longdong plateau, the soil-water characteristic curve of undisturbed sample is determined by tensionmeter, and the experimental data are then fitted with three theoretical models, of which Gardner model is the simplest with the least parameters, while Fredlund & Xing model has the best fitting effect. The relationship between permeability coefficient and matric suction or water content of unsaturated loess is built based on the measured soil-water characteristic curve by Childs & Collis-Geroge model which is commonly used to predict unsaturated permeability coefficient. The results show that the permeability coefficient decreases dramatically as saturated loess becoming unsaturated, the relationships between permeability coefficient and matric suction or volume water content of unsaturated loess can all be expressed in exponential form. Study of the soil-water characteristic curve and permeability coefficient prediction of typical loess provides loess engineering problems, such as the slope stability evaluation with the effects of rain infiltration and the computation of collapsible deformation of unsaturated foundation, with theoretical basis.

Key words: unsaturated loess, soil-water characteristic curve, tensionmeter method, matric suction, volume water content, permeability coefficient function