Approximate analytical solution to the axisymmetric model for PVD-enhanced in-situ flushing of double-layered contaminated soils

Abstract

The in-situ soil flushing technique which utilizes prefabricated vertical drains (PVDs) is an effective remediation method for sandy, silt, and low-permeability clayey soils. It offers several advantages, such as reducing the seepage path, achieving uniform flushing of contaminated areas, and shortening the construction time. This paper proposes an axisymmetric analytical model for PVD-enhanced in-situ flushing remediation of double-layered contaminated soils considering the decay of the initial contaminant concentration along the depth. The derived solutions are then verified against experimental results and existing analytical solutions. The accuracy of the simplified solution is found to improve as the number of stratifications increases by vertically dispersing the initial contaminant concentration, as compared to the numerical results obtained from COMSOL Multiphysics. The study also reveals that a decrease in the spacing between adjacent injection and extraction PVDs or an increase in the injection/extraction rate enhances the flushing efficiency. However, the effects of the two parameters on soil remediation are non-linear and linear, respectively. Furthermore, the difference in the geotechnical properties of the upper soil layers in a bi-layered contaminated soil leads to a variation in the contaminant concentration at any depth and this variation grows larger with time until the soil is completely remediated.