The hydraulic parameters of gravelly soil are difficult to determine due to its high gravel content and large grain size. The field permeability tests of gravelly soils layer of the slidebody of Xietan landslide have been carried out by double ring; and the test results are analyzed by empirical formulas

considering the soil porosity

grain-size distribution etc. Then

the soil-water characteristic curve (SWCC) is tested by the method of tensiometer-moisture content and fitted by Fredlund model. And finally

the unsaturated permeability coefficient of gravelly soil is calculated by empirical formulas based on its SWCC and saturated permeability coefficient. The test data demonstrate that

the saturated permeability coefficient of gravelly soil layer is quite good with permeability coefficient varied between 1.78×10-2cm/s to 3.2×10-2 cm/s; smaller fine grain content

bigger effective grain size and controlling grain size will lead to larger permeability coefficient. Through these works

the unsaturated hydraulic parameters are determined for the unsaturated seepage analysis of Xietan landslide; and the technique can be used as reference for similar soils.