Pollutant transport and performance evaluation in defective composite cutoff walls: centrifuge test and numerical simulation

The composite geomembrane-soil-bentonite (CGSB) cutoff wall is one of the most effective barriers to prevent pollutant transport in groundwater. However, geomembranes may have defects during construction, significantly increasing the risk of pollutant leakage. Currently, little is known about pollutant transport at the interface between defective geomembranes and soil-bentonite (SB) cutoff walls. This paper presents the results from centrifuge experiments modelling pollutants transport within a defective CGSB wall to investigate interface transport behavior and its performance. Additionally, a parallel test on the SB wall is performed simultaneously to evaluate the enhancement effect of a defective geomembrane on the performance of SB walls. The results show that although the proportion of defect areas on the geomembrane is minimal, the lateral fluid flow at the interface significantly increases both the leakage and pollution area of the CGSB wall. The breakthrough points of pollutants in the SB and CGSB walls differ, with one occurring in the shallow part of the wall and the other at the center of the geomembrane defect. Numerical simulations are conducted at the centrifuge model scale, and the calculated results are consistent with the experiments. Simulation results suggest that although the CGSB wall with geomembrane defects does not significantly prolong breakthrough time compared to the SB wall, it markedly reduces pollutant flux.