The permeability coefficient of the unsaturated soil can be got from the seepage test with the triaxial test instrument for unsaturated soils controlled by stress and strain in the laboratory. Based on this

under the environment of rain and flood we analyze the variability of the seepage field of unsaturated levee slopes in the lower reaches of Yellow River with the finite element method. From this we get the extent influenced by rain or flood infiltration in front of the saturation curve. The extent is about 2 meters. We analyze the co-operated influence of rain and flood infiltration and get that whether the flood infiltration can easily change the seepage field or not is determined by the rainfall intensity and rainfall duration.