Breakthrough time of amended cement-soil cutoff wall permeated by heavy metal solutions

In order to investigate the performance of the amended cement-soil cutoff wall (PC: GGBS: bentonite=8%: 8%: 4%) permeated by lead (Pb) and zinc (Zn) and its influencing factors, the transport parameters of Pb and Zn through the amended cement-soil cutoff wall are characterized through the soil column tests. The van Genuchten analytic solution is used to analyze the influences of seepage velocity, hydrodynamic dispersion coefficient and retardation factor for breakthrough time on breakthrough time of the cutoff wall. The service lives of the cutoff wall with different thicknesses and water heads are also given, as well as the thicknesses meeting the temporary and long-term service conditions. The simplified formulae for the thickness and service time of the amended cement-soil cutoff wall are obtained numerically based on the Van Genuchten analytical solution. The results show that the transport of Zn through the amended cement-soil cutoff wall is faster than that of Pb, and the hydrodynamic dispersion coefficient increases with the increasing heavy metal concentration, while the retardation factor decreases. When the seepage velocity is higher than 10^-11 m/s, the breakthrough time is controlled by the seepage velocity, and conversely, by the hydrodynamic dispersion coefficient and retardation factor. When the thickness of the amended cement-soil cutoff wall is 0.6 m, it can meet the barrier requirements of Pb and Zn within 5 years. When the wall thickness is greater than 1.2 m, it can meet the service requirements of 50 years. The service time is proportional to the squared wall thickness and retardation factor, and inversely related to the hydrodynamic dispersion coefficient.