Abstract: Cement-soil vertical cutoff wall is extensively applied to the remediation of industrial contaminated sites, but its impermeability needs to be improved and also the chemical compatibility under the effect of high concentration and toxic heavy metal contamination needs to be studied. Through laboratory tests, physical, strength and permeability properties of different cement-soil vertical cutoff wall samples based on different mixing ratios of GGBS (ground granulated blast furnace slag), bentonite, and curing agent were studied. Considering the quality of the vertical cutoff wall and economic cost, the curing agent dosage of 20% (the mixing ratios of PC, GGBS and bentonite are 8%, 8% and 4%, respectively) was validated as the optimal ratio for the amended cement-soil vertical cutoff wall. The chemical compatibility of cement-soil vertical cutoff wall materials under the effects of heavy metal zinc and lead pollution, in terms of hydraulic conductivity, is examined by a flexible-wall permeability test. The result shows that the decrease in the impermeability of the cement-soil vertical cutoff wall under the action of heavy metal solutions is jointly dominated by three factors, i.e., heavy metal species, the concentration of heavy metal, and the pH of pore solution. The adverse effect of the type of heavy metals on the impermeability of the samples is in this order: zinc nitrate-lead nitrate solution> zinc nitrate solution> lead nitrate solution. The hydraulic conductivities of the samples permeated with different heavy metal solutions are between 1.49 and 10.10 times that of sample permeated with tap water and increase with the increase of concentration of the heavy metal solution. Under the premise of meeting the requirement of hydraulic conductivity, the amended cement-soil vertical cutoff wall could barrier 50 mmol/L of zinc nitrate solution, 100 mmol/L of lead nitrate solution and 10 mmol/L of zinc nitrate-lead nitrate solution.

Key words: cement-soil, vertical cutoff wall, heavy metal, hydraulic conductivity, chemical compatibility