The Influence Of The Multi-Scale Structure Of Soil Pores On Its Permeability

Soil is a three-phase system composed of particles,water and gas,and its pore structure is complex.The complex structure of soil is related to the multi-scale of internal pores,which makes the mechanism of water transport more complicated.Generally,it takes time and effort to study the seepage characteristics of soil macroscopically by obtaining relevant indexes through experiments,or by using empirical formulas to calculate the permeability coefficient,but errors often occur in this way.Therefore,the seepage of soil is studied from the perspective of soil microstructure and the results can better reflect the seepage characteristics of soil.Many studies suggest that the soil pore fractal scaling characteristics in porous media,the carpet in the theory of fractal model can reflect the characteristics of the soil pore multiscale structure,so the introduction of fractal theory to study the internal structure of complex soil,based on the fractal theory to describe the soil pore multi-scale structure,soil pore fractal dimension introduced to characterize the microstructure of porous media,The seepage model of porous media in soil was established.The research contents and conclusions of this paper are as follows:(1)The soil pore structure was studied by introducing soil-water characteristic curve,and the corresponding relationship between matric suction and equivalent pore size was deduced.Combined with fractal theory,the pore fractal model reflecting the carpet model was selected to deduce the calculation model of pore fractal dimension representing the microstructure of soil porous media.Based on Yu Boming’s fractal permeability model,the soil permeability coefficient model is derived by using the piecewise summation method.Permeability coefficient is expressed as a function of porosity,boundary pore diameter and pore fractal dimension.(2)Substitute the literature data into the pore fractal dimension calculation model and the soil permeability coefficient model,respectively,and calculate the permeability coefficient model value.The correctness of the theoretical derivation is verified by comparing the calculated results of the model with the seepage test results.According to the grain size distribution,the soil can be divided into six types: gravelly sand,coarse sand,medium sand,fine sand and silty sand.The applicability of these six types of soil to soil permeability coefficient model is compared respectively.(3)Choose too him formula,China iwhr formula,chong-hui zhu formula,the formula and Zhang Yijian formula that the permeability coefficient of five kinds of traditional empirical formula,calculated by the empirical formula of soil and the permeability coefficient of permeability coefficient model values,and the penetration test results were analyzed,the results show that the permeability coefficient of the model prediction effect is better than the empirical formula,It is verified that the soil permeability coefficient model is more suitable.