If the infiltration intensity is less then the saturated permeability coefficient, the surface soil finally reaches to an unsaturated infiltration stage instead of saturated infiltration stage.
For complexity and diversity of unsaturated soil behaviors, there lies a great difference in permeability characteristics between unsaturated soil and saturated soil.
由于非饱和土的复杂性和多变性，其渗透特性明显不同于饱和土，并且试验难度较大。
3
Based on the equation of soil water feature curve and the relationship between soil water feature curve and permeability function, the permeability function equation of unsaturated soil is derived.