A coupled nonlinear long-term consolidation and solute transport model for PVD-enhanced flushing remediation analysis of multi-layered contaminated soils

The remediation of contaminated fine-grained soils through flushing, enhanced by prefabricated vertical drains (PVDs), involves a complex coupled process of axisymmetric consolidation and solute transport. However, existing models often oversimplify these interactions and fail to accurately capture real vacuum pressure boundary conditions. This study presents a coupled nonlinear model that integrates PVD-assisted consolidation and solute transport for multilayered contaminated soils. The governing equations are solved using the finite difference method, and the numerical solution is validated against first analytical solutions for simplified axisymmetric models, then soil-flushing experiments and consolidation-induced solute transport tests. Furthermore, the developed model is applied to assess the effects of key engineering design parameters, including vacuum pressure in PVD, PVD spacing, and PVD penetration length, on cleanup efficiency. Parametric analyses indicate that increasing vacuum pressure and reducing the PVD spacing can improve the cleanup efficiency along the radial direction. However, the treatment depth cannot be significantly enhanced by merely increasing vacuum pressure or reducing the PVD spacings. These findings provide insights into optimizing the design of PVD-enhanced soil flushing systems.