Fractal Study On Seepage Characteristics Of Soil-rock Mixtures

Soil-rock mixtures is a compound that soil and stone mixed in a certain proportion.Its material composition is complex and the physical and mechanical properties of each other are greatly different.Many scholars have shown great interest in their mechanical properties,and carried out corresponding research,which greatly enriched the mechanics theoretical system of soil-rock mixtures.However,few scholars have been involved in the research on the theory of seepage flow in soil-rock mixtures.In this paper,a large-scale seepage test device which can change water head was made,and the seepage characteristics of the soil-rock mixture were studied in the laboratory.Considering the advantages of fractal theory in describing complex structures compared with traditional Euclidean geometry theory,the seepage characteristics of soil-rock mixtures are theoretically analyzed by using fractal theory.The main contents and achievements of this paper are as follows:?1?Because of the relatively large particle size of soil-rock mixtures,the size of conventional indoor seepage test device can not meet the corresponding requirements,a large indoor variable head seepage test device was made.The experimental study on the seepage characteristics of soil-rock mixture with different rock content,different porosity and different grades was carried out.The variation of the permeability coefficient of soil-rock mixture with three factors and the J-v curve with different stone content were obtained.?2?Using the fractal theory to describe the particle size characteristics of the soil-rock mixture,the fractal dimension of the particle size of the soil-rock mixture is obtained,The expression for predicting the rock content by fractal dimension of particle size is proposed,as well as the relationship between particle size distribution and fractal dimension of particle size.?3?The fractal theory is used to describe the pore characteristics of soil-rock mixtures,and a fractal expression for calculating the porosity by particle size is proposed.By comparing the expression with that proposed by other scholars,the applicability of the proposed expression is verified.Based on the comparison results,the application conditions of the expression are pointed out.?4?Based on the curved capillary equation and fractal theory,the fractal expression of permeability of soil-rock mixture is derived.The expression reflects the permeability as a function of the porosity?and the mean particle diameter d₅₀.The correctness of the expression and its applicable conditions are verified.The influence of?and d50 on the permeability is analyzed.?5?Fractal analysis of specific surface area and KC constant in the Kozeny-Carman equation for calculating permeability is carried out..The analysis shows that the specific surface area is a function of particle size fractal dimension D,maximum particle size d_max,porosity?,and the sensitivity of the specific surface area affected by three factors is analyzed.The KC constant is not constant,its size is related to fractal dimension D_f,porosity?and tortuosity?.?6?Based on the curved capillary and the unequal diameter sphere model,the viscous resistance and inertial resistance of the soil-rock mixture were analyzed by fractal analysis.The basic equation of seepage flow of the soil-rock mixture was derived.The equation is a Forcheimer-type quadratic equation.Then the correctness of the equation is verified by dimensional analysis and the results of this paper and others.Finally,in the equation,parameters a and b are introduced and the influencing factors of the two parameters are analyzed.?7?The non-Darcy equivalent permeability Ke is obtained by comparing the basic seepage equation with Darcy's law.The ratio?of non-Darcy equivalent permeability to Darcy's permeability is introduced.A critical Reynolds number calculation method based on different values?is proposed to determine the seepage state of water in porous medium.