Theoretical And Experimental Study On Electro-osmotic Reinforcement And Electrical Remediation Of Contaminated Foundation Soil

A large number of weak soils with high water content,poor permeability and high compressibility are distributed in the southeast coastal areas of China.With the impact of urbanization and human activities,the contaminated area of the weak foundation soil is also increasing.In 2014,the Ministry of Environmental Protection and the Ministry of Land and Resources conducted a census of soil pollution in China and released a pollution data report.It was found that the pollution situation is not optimistic.The percentage of soil pollutants in various typical plots exceeds 25%.After the soft foundation soil is contaminated,its specific parameters such as permeability and liquid-plastic limit will change greatly.It is difficult to achieve the desired effect by traditional methods of reinforcement and remediation.A large number of studies have shown that electro-osmotic reinforcement and electro-kinetic remediation technology have obvious advantages in the reinforcement and remediation of low-permeability soil.The continuous development of urbanization requires more land resources for construction.In order to obtain more land resources that can be constructed and used,relevant research work on the consolidation and remediation of contaminated foundation soil in coastal areas is urgently needed.Based on previous researches,this paper systematically studies the reinforcement and remediation of contaminated foundation soil(organic contaminated soil and heavy metal inorganic contaminated soil)from four aspects:indoor macro-micro test,coupling theoretical model and its analytical solution,comsol numerical simulation and field test.The main research work and results of this article include:(1)Experiment on life source organic polluted foundation soil:after 27 sets of comparative tests,the sequence of the primary and secondary factors and the optimal level combination that affect the reinforcement effect of the electro-osmotic drainage of the soil are obtained.The ion concentration of Na+、K+、Mg2+、Ca2+in life source organic polluted foundation soil is high,which contains a certain concentration of organic matter and CH3COOH"(organic acid radical)ion.The complex composition of ions and organic matter in the test soil caused severe corrosion of the electrode and resulted in a larger pH range before and after the test than the uncontaminated ordinary clay.Aiming at the complex pore fluid components of life source organic polluted foundation soil,based on the assumption of non-uniform change of water content,a piecewise function is established to obtain the empirical relationship between conductivity and drainage.Finally,the author puts forward the design proposal of electroosmosis after the clay is contaminated.(2)Heavy metal inorganic contaminated soil test:carry out a comparative test and put forward a "calculation method of soil pollutant concentration based on soil temperature,water content,and electrical conductivity".Analyze the changes of pH,zeta potential,energy consumption,conductivity and other parameters,it was found that the change in the conductivity of the cathode cell(exhaust fluid)of different test groups was obviously divided into three stages.Through the data fitting of the conductivity and heavy metal concentration in the cathode cells of multiple experiments,the empirical relationship between the two was obtained.Explained the mechanism of heavy metal desorption and metal electrode reaction and Cu(Ⅱ)-EDTA chelate competition interference remediation,it was found that the Fe3+ ions produced by the metal electrode reaction will affect the removal rate of heavy metals by about 10.6%.In the laboratory test,the author recommends the use of electric geotechnical materials,which can avoid the negative effects of electrode reactions.According to the quantitative calculation of EKG electrode,the variation of the number of "lapped pores"was obtained.The reasons for the low contact resistance of EKG electrode were analyzed in combination with electron microscope pictures and experimental observation.(3)Coupling theory research:previous studies on the application of electric fields in soil often focused solely on electroosmotic consolidation or the migration and remediation of heavy metal pollutants.The related theoretical research on the coupling between pollutant migration and soil deformation is still in its infancy.This article focuses on physical processes such as electromigration,electroosmotic flow,and diffusion.The adsorption equilibrium formulas in the liquid phase and the solid phase are derived.The one-dimensional pollutant transport equation of the adsorption of pollutants in the solid phase under the action of the electric field into the Langmuir adsorption mode and the Freundlich adsorption mode were obtained.Therefore,the concentration term of the pollutants adsorbed on the solid particles is introduced into the pollutant transport model,which considering the influence of soil deformation on pollutant transport.(4)Analytical solution and numerical simulation:Combining Esrig electroosmosis consolidation theory,theory of electro-kinetic remediation of pollutant transport and Biot consolidation theory without considering physical strength.A one-dimensional mathematical model of contaminant transport in deformed porous media under the electric field considering soil deformation and solid-phase adsorption is derived.The equation is simplified based on the actual situation,and the analytical solution of the model is derived.The analytical solution is compared with the laboratory test data,and with the numerical solution obtained by the comsol finite element method,which comprehensively verifies the correctness of the analytical solution.The numerical simulation software comsol was used to calculate the concentration distribution of pollutants with and without considering soil deformation under different potentials and different energization times.It was found that as the potential gradient increased,the average "contaminant removal rate difference" near the anode gradually increased.After applying voltage of 25 V and energizing for 720 hours,the "contaminant removal rate difference" near the anode is 6.42%.But under high voltage as the power-on time continues to increase,the effect of soil deformation on the concentration distribution of pollutants becomes smaller and smaller.5)Field test:The analysis found that the site soil contains multiple heavy metals and there is competitive desorption,the removal efficiency of the chelating agent simultaneously desorbing and removing multiple heavy metals is lower than that of removing a single heavy metal.Excessive fulvic acid affects the soil pH and thus affects the drainage rate and the migration of heavy metals.Combined with "size effect",the difference between indoor and field tests was analyzed.