Soil-water Characteristic And Hydraulic Conductivity Models From Capillary Theory And Pore-size Distribution Function

Soil-water characteristic curve refers to the realationship between the soil moisture state and the suction. SWCC is the important tool of describing unsaturated soil properties because the unsaturated soil permeability,strength,volume change associated with it.The hydraulic conductivity refers to the ease of fluid through porous skeleton,which is a basic parameter to be used to the soil seepage calculation.The air is a part of the unsaturated soil’s pore,which leads to unsaturated permeability coefficient is always less than the saturated permeability coefficient. The hydraulic conductivity is a variable and a function of soil volumetric moisture content.In geotechnical engineering practice, only using the analytical expression of soil-water characteristics and unsaturated permeability coefficient,which can be used to predict the soil mechanics and hydraulics. Therefore, building the reasonable soil-water characteristic curve equation and hydraulic conductivity model is an important issue in the study of unsaturated soil mechanics.Based on the theory of capilary and pore-size distribution,we can build the soil-water characteristic curve equation and the hydraulic conductivity model.The main conclusions are as follows:(1) If the pore-size distribution function subjects to the exponential distribution, the soil-water characteristic curve equation can be builded,the saturation as the dependent variable and the suction for single variable parameters in which.The parameter λ in the equation has definite physical meaning,1/λ is the expectation for the pore radius. Numerical simulation shows that this model can effectively describe soil water characteristics of sand, silt and clay. The equation is simple and easy to use.(2) As the single parameter model, the fitting effect of this soil-water characteristic curve equation of sand, silt and clay soil water characteristic curve test data are far superior to Brooks-Corey model.(3) Based on statistics theory and the pore-size distribution, substituting soil-water characteristic curve equation into Burdine’s equation,can be obtained the hydraulic conductivity model respectively with the saturation and relative permeability coefficient suction of unsaturated soil. Numerical simulation shows that this model’s unsaturated relative permeability coefficient equation can more accurately predict the unsaturated permeability coefficient of sand, silt and clay.(4) This soil-water characteristic curve equation and hydraulic conductivity model can predict unsaturated permeability coefficient and soil water characteristic curve at the same time.