The Study On Fractal Of Soil Hydraulic Properties

Numerous empirical models exist for soil hydraulic properties including soil water retention curve, unsaturated hydraulic conductivity and difiusivity. It has generally been recognized that the empirical fitting coefficients in these models are somehow related to soil texture. By using the concept of fractal geometry, Tyler and Wheatcraft (1990) proposed a physical conceptual model for soil texture and pore structure, and then a two-dimension fractal model for soil water retention curve was derived. This model is related to the intrinsic nature of the fractal porous structure. In this paper, the soil hydraulic properties parameters were studied by field experimentand theoretical analyses. The structures of ten different soils were tested with the method of particle-mass distribution. Results indicate that the fractal dimension of soil structure fractal changes from 2.489 to 2.896, and the change in fractal dimension implies the change of content of clay, silt and sand for the soil particle. A three-dimensional fractal model for soil water retention curve was derived with Menger Sponge model on the based of Tyler and Wheatcrafts' theory, and the relative permeability functions of Burdine and Mualem are also shown to be fractal and directly related to the fractal of water retention curve. The fractal dimension in these models are calibrated with experimental data for ten soils, and the values of the calibrated fractal dimension are approximately equal to those fractal dimension of soil structure. And therefore, the derived models incorporated with soil structure fractal dimension can be used to describe the real soil hydraulic properties. At the same time, the spatial variation of soil properties was primarily studied by using the fractal model in power form, and results were synthetically analyzed.