Performances of the Soil–Bentonite Cutoff Wall Composited with Geosynthetic Clay Liners: Large-Scale Model Tests and Numerical Simulations

Abstract

The geosynthetic clay liner (GCL) overlap plays a key role in maintaining hydraulic performance of the barrier systems, e.g., the bottom liner and cover systems. However, its influences on the behavior of the vertical barrier have been rarely investigated. This paper aims to address this issue using the large-scale model test and 3-dimensional finite element (FE) modeling. In the model test, the GCL overlap at the width of 500 mm was tested under a constant hydraulic head of 1 m and confining stress ranging from 10 to 150 kPa using a newly developed large-scale apparatus. Compared with the flexible wall permeameter, this apparatus could guarantee full field-scale GCL overlap to be tested. Results showed that the effective hydraulic conductivity of the GCL overlap decreased from 10−8 to 10−9 cm/s as the confining stress increased from 10 to 150 kPa. The addition of supplemental bentonite paste in between the overlap with a water-to-bentonite ratio of 19:1 contributed to reducing the effective hydraulic conductivity by 60% compared with that for a GCL overlap without bentonite paste. The breakthrough time for the soil-bentonite (SB) cutoff wall composited with GCLs was 64% longer in comparison with that for the single SB wall. Additionally, the breakthrough after 50 years is made for the entire depth of the single SB wall while at the depth no more than 0.9 m for the composite wall with bentonite paste at the GCL overlap. With consideration that the depth of the groundwater table is generally greater than 1 m, the GCL–SB composite cutoff wall will exhibit a good performance in containing groundwater contaminants in the field, especially when applying bentonite paste at the GCL overlap.