Study On Interception Of Groundwater Chlorinated Hydrocarbons By Modified Vertical Barrier

With the dramatic progress of China’s industrialization and modernization,various industrial pollution sites are rapidly increasing,and the threat to the groundwater environment is rising exp onentially.In order to prevent and control the migration of pollutants in the soil-water environme nt,efficient and low-cost vertical barrier technology is an important guarantee before the current site pollution remediation.With dihexadecyl dimethyl ammonium chloride-modified sodium bent onite-cement-soil barrier wall as the main body of research,through indoor tests and theoretical a nalysis,revealed the impermeability improvement mechanism and pollution control performance,to promote the bentonite-based vertical barrier wall technology in the application of remediation of contaminated sites in China with a scientific basis,the main research results are as follows:（1）in order to change the ordinary bentonite system barrier wall only for heavy metals applicable de fects,the hydrophobicity,specific surface area and surface pore of sodium-based bentonite are gr eatly increased after modified by dihexadecyl dimethyl ammonium chloride.The expansion capa city decreased by 5.6 times,thus engineering safety factor will be increased.When the field sam ple is not distinguished,the permeability of the barrier wall requires bentonite admixture greater t han 10%to meet the hydraulic conductivity k≤10^-7cm/s,then the moisture content of the materia l for the slump（100-150mm）suitable for engineering backfill grouting should be 22.17%-25.09%.The unconfined compressive strength of the wall is positively correlated with age.The strength a t 180d is nearly 4 times higher than that at 14d.The strength and permeability are degraded to a g reat extent under strong acid-base conditions.（2）The adsorption capacity of the organic modified wall material is 2-15 times stronger than that of the raw material for CHCs.The p H of groundwa ter does not affect the wall performance,and the rise of water temperature facilitates the adsorpti on.The whole process of adsorption conforms to the quasi-secondary kinetic equation,and both physical and chemical adsorption exist.Adsorption force is reflected by the partitioning effect of the hydrophobic medium with long carbon chains on the organic bentonite.It is found that methy lene chloride is more difficult to be adsorbed by the wall material due to its low octanol-water pa rtition coefficient log value and high saturation vapor pressure.The correctness of the nonlinear model was verified mathematically and the thermodynamic parameters were calculated in an erro r-corrected way,demonstrating that CHCs are entropy-driven processes with stable enthalpy of s pontaneous adsorption on wall materials.（3）The indoor self-made box test simulates point sourc e pollution,and it is clear that the growth of pollutant concentration is inversely proportional to th e percolation distance,the pollutant is subject to molecular diffusion and hydrodynamic transport into the percolation.A 30-d penetration test was conducted to obtain the early penetration curve of CHCs,and a continuous infiltration hydraulic model was established from the calculated trans port parameters based on the one-dimensional unsaturated solute vertical transport control equati on considering adsorption hindrance.Analytical calculation found that the penetration rate of CH Cs was mainly affected by the hindrance factor R_d and hydraulic gradient I,and the solute concen tration in each profile of the wall showed a nonlinear performance.An insurance prediction is tha t the durability of 1m thick barrier wall under I=25 is 13.5～34.5 years,which can meet the deman d of actual project service life.