Study On Mixing Ratio And Antifouling Performance Of Vertical Isolation Barrier In Barrier In Biological Grouting Site

With the implementation of the policies of "returning to the city and entering the garden"and "industrial transfer",enterprises in the heavily polluting industries have closed down and moved away from the urban areas,resulting in serious land pollution.The heavy metal pollution is especially prominent.With the development of modern biotechnology,microbial treatment of heavy metal pollution has been paid more and more attention.MICP technology,based on the induction principle of urease-producing bacteria,is a recently developed method of soil microbial reinforcement and remediation.Considering the adverse environmental effects of ammonia release during MICP grouting,the vertical isolation barrier can be used to set up grouting repair system and regional overall treatment to promote the application of this technology in the field of rock and soil reinforcement and restoration.In view of silty soil geology in YangZhou area,based on the service cycle and functional requirements of vertical isolation barrier,silty soil-cement-bentonite as barrier material is selected in the paper to study the proportion of vertical isolation barrier,which is divided into four processes:(1)the slump test,permeability test and mechanical test of silt-cement-bentonite composite materials were carried out in order to find a reasonable mixing ratio interval which met the requirements of construction and service of impervious wall;(2)study the chemical compatibility of barrier materials with three heavy metals ion,Cu2+,Cr6+and Mn2+,including the immersion test of polluted solution based on the change of permeability coefficient at all stages of the material as well as the content of exchangeable heavy metal ions in the inner layer of the materials was determined in order to explore the erosion trajectory and degree of heavy metal ions in the materials;(3)the influence of MICP grouting on barrier material was studied;(4)the effect of anti-fouling and seepage isolation of vertical barrier was investigated by field grouting test.The conclusions are as follows:(1)Bentonite has a leading role in the increase of the permeability of mixed materials;when a small amount of cement is added,increasing the content of bentonite can obviously improve the impermeability of bentonite to increase the permeability of mixed materials.With the increase of cement content,a large amount of Ca2+in cement replace the low sodium ions in the bentonite layer,resulting in loss of swelling properties,and also resulting in the increase of permeability coefficient of the material.Through the unconfined compressive test,it can be concluded that the lower the cement content is,the greater the ultimate strain will be and the smaller the strength and deformation modulus of the material will be.Combined with the permeability test and pressure resistance test,the optimum content of bentonite and cement in silty-cement-bentonite isolation material is 6%and 8%respectively,and the optimum content of bentonite is 6%and 8%respectively in the isolation materials of silty soil-cement-bentonite;(2)After immersion in the solution of CuSO4,K2Cr2O7 and MnCl2 with different concentrations,the permeability coefficient of the barrier material increased to some extent,and increased most rapidly at the first 7 d,and the speed of 7d-60d gradually slowed down,The main reason is the reduction of the swelling properties of bentonite by metal cations.After comparison,the results show that the influence of copper sulfate solution on the permeability coefficient of the material is greater than that of manganese chloride,and potassium dichromate has the least effect on the permeability coefficient of the material at the later stage of immersion.The higher the content of bentonite is,the more the permeability coefficient increases after immersion is;(3)After immersed in heavy metal solution,the infiltration depth of exchangeable Cu2+,Cr6+ and Mn2+content was determined.The results showed that The blocking effect of the materials on Cr6+ was better,The blocking effect of the materials on Cu2+and Mn2+ was relatively weak,and the difficulty of metal ions migration in the materials increased with the increase of bentonite content,and the blocking effect of the materials containing 8%and 10%bentonite on heavy metal ions was better;(4)The permeability coefficient of the material can be increased by one or two orders of magnitude after fracturing.After immersion in the bio-slurry,due to microbial mineralization and deposition,the film-covering effect occurs,and the surface and cracks of the material are covered and filled with fine aragonite and calcite.The permeability coefficient of samples can be reduced by 37.9%on average,and some of them can reach more than 50%.However,with the increase of immersion time,the permeability coefficient of samples increased slightly due to the adverse effects of calcium ion on bentonite;(5)After on-site biological grouting,the total nitrogen content of groundwater decreased by about 50%under the barrier of vertical isolation barrier with target ratio,the reasonable installation of silt-cement-bentonite impervious wall can prevent the migration of microbial repairers and polluted water.