Study On Soil Microstructure Seepage And Solute Transport Based On Fractal Theory

As a porous medium,soil is a bridge connecting the atmosphere and groundwater,and the foundation for human survival.Human industrial activities have caused serious soil pollution.Therefore,soil remediation and remediation have become a hot research topic at present.Before,people mainly study the migration law of pollutants in soil from the perspective of soil macroscopic physical characteristics,and the influence of soil microstructure on the migration of pollutants is less.With the development of fractal theory and the progress of computer image recognition technology,the quantitative description of soil microstructure is possible.The establishment of a functional model of soil micro structure and pollutant migration has become a hot spot.This paper,based on the key topic of Sichuan Provincial Education Hall,"Studies on the hydrodynamic dispersion characteristics based on the fractal of soil pore",based on the application of the fractal theory at home and abroad in the soil study and the current situation of the theory of soil solute transport,formulated the experiment scheme for the solute transport of saturated soil column,and using three different graded quartz with 60 orders,80 orders and 100 orders.The sand has six kinds of soil microstructure,A,B,C,D,E and F.Using the laboratory soil column experiment,the NaCl migration in the saturated soil column is taken as the main line and the saturated permeability coefficient test is used to study the influence of the seepage characteristics of the soil on the solute transport.According to the SEM scanning experiment,the fractal dimension of the pore size and the fractal dimension of the particle volume obtained by the SEM image analysis were used to study the relationship between the soil microstructure and the seepage characteristics of the soil.Based on the function model of soil microstructure and soil seepage characteristics,combining with the data of hydrodynamic dispersion coefficient,the function model of pore fractal dimension,fractal dimension of particle volume and hydrodynamic dispersion coefficient is obtained,and the effect of soil microstructure characteristics to solute transport is discussed.The conclusions are as follows:1.The permeability coefficient K,the seepage velocity V and the hydrodynamic dispersion coefficient D data are analyzed.The statistical model of K and V,V and D is established,and the two models above are derived and analyzed.The permeability coefficient K is linearly and positively correlated with the seepage velocity V and the hydrodynamic dispersion coefficient D;the better the seepage characteristic of the soil is,the solute in the soil is the solute in the soil the faster the movement;According to the laser particle size analyzer to obtain the fractal dimension Dv of the particle volume,the statistical model of the fractal dimension and permeability coefficient of the particle volume is established.This model reveals that the coarse size of the particle size and the law of the seepage characteristics of the soil are that the smaller the particle size is,the smaller the pore space between the soils leads to the water in the soil.The percolation in the body is slowed down.3.According to the fractal dimension Dv and the permeability coefficient K,the permeability coefficient K and the percolation velocity V,the seepage velocity V and the hydrodynamic dispersion coefficient D,the model of Dv and D is derived.The model shows a linear positive correlation between Dv and D.Combined with the previous statistical models of Dv and K,it is found that the smaller the particle size of the soil is,the lower the hydrodynamic dispersion coefficient of solute moving in the soil.4.The fractal dimension D_f data of pore fractal dimension is obtained by PCAS software,and a statistical model of K and D_f is established.The model reflects the influence of pore size distribution on the seepage characteristics of soil in a certain range,and the correlation degree of pore size larger than that in this range is not high with the seepage characteristics of soil.5,combining the statistical models of D_f and K,V and K and D,we deduce the models of D_f and D.Combining the experimental data of pore fractal dimension and hydrodynamic dispersion coefficient,this model reveals that the pore diameter decreases and the pore channel narrowing in the soil makes the permeability coefficient decrease,the velocity of solute transport slows down,and the hydrodynamic dispersion coefficient decreases.6.Through the analysis of the relationship between the fractal dimension Dv of the soil particle volume and the fractal dimension Df of the pore volume in the experiment,it is found that the particle size decreases,which leads to the decrease of the pore pipe in the soil.It is shown that the basic determinant of the seepage characteristics of the same soil and the solute transport is the particle size distribution.