Two-dimensional migration of contaminants in non-homogeneous cutoff wall considering consolidation

Soil-bentonite cutoff walls are widely used in the remediation and control of contaminated sites. Under the action of wall self-weight and lateral earth pressure, the wall shows non-homogeneous along with depth. Based on the bidirectional consolidation theory, a two-dimensional contaminant transport model for a non-homogeneous cutoff wall-aquifer system is developed. The model uses the Gaussian functions to characterize the local non-uniform distribution of the contaminant source and considers the convection-dispersion-adsorption-degradation coupled transport processes of pollutants in a barrier system. With the aid of the boundary conditions and the continuity conditions at the layer interfaces, the transient advection-diffusion equation module of COMSOL multiphysics, a finite element calculation software, is selected for the solution. The influences of concentration distribution of contaminant source and mechanical parameters of wall on contaminant migration are analyzed. The results show that: (1) The homogeneous cutoff wall models will overestimate the wall breakthrough time and underestimate the mass flux through the wall exit. (2) The service performance of a cutoff wall decreases with the increase of the shear strength of the wall material, but it is slightly affected by its compressive strength. (3) Finally, the design idea of the enhanced cutoff wall in the shallow region is given based on the proposed non-homogeneous model.