The Huangtupo landslide was one of the largest and most harmful geo-hazards in the Three Gorges Area, China. With the periodical water level fluctuation of the Three Gorges Reservoir, partial regions,especially the sliding zones that are the weakest parts in sliding mass, are under circulating drying and wetting conditions. This study employs the transient water release and imbibition method (TRIM) to test the soil water characteristic curve (SWCC) and hydraulic conductivity function (HFC) of sliding zone soils during drying and wetting paths. Combining suction stress theory and saturated-unsaturated direct shear tests, the soil-water interaction and strength variation properties of sliding zone soils with variable saturation are studied quantitatively. The tests and analysis results indicate that the suction,
permeability and suction stress of sliding zone soils are related closely to the water content. The soil water characteristic curve, hydraulic conductivity function and suction stress characteristic curve (SSCC) exhibit significant hysteresis. By calculating the strength of unsaturated sliding zone soils by generalized the Mohr-Coulomb failure criterion based on suction stress theory, researchers can conveniently and accurately assess the unsaturated strength properties of sliding soils in slope stability analysis.
Key Words : Huangtupo landslide, unsaturated soil, soil water characteristic curve, suction stress.