Factors affecting the hydraulic performance of a geosynthetic clay liner overlap

Geosynthetic clay liners (GCL) are increasingly being used as a major component of barrier systems replacing compacted clay liners due to their very low permeability and speed of installation. Researchers and practitioners have identified the critical role of the GCL overlap that presents constant challenges encountered in maintaining the designed hydraulic conductivity. This study presents a series of flow box tests conducted to evaluate and improve understanding of the combined effect of each of the four contributing factors, namely, overlap width, supplemental bentonite applied at the overlap, the overburden confining stress, and the hydraulic head acting on the GCL overlap. The findings reveal that the overlap width is the most significant parameter affecting the design hydraulic conductivity. The application of a minimum overburden stress to maintain the designed hydraulic performance is also recognised as important. The effect of confinement due to higher hydraulic heads is of interest to practitioners. The supplemental bentonite has the least effect on the GCL overlap hydraulic performance even though it enhances the function of the overlap seam. This knowledge addresses the inadequacy of published GCL overlap experimental data comparing the effect of different factors affecting its hydraulic performance. It also assists industry practitioners to design and specify the overlap criterion for a specific application depending on the product specifications and site conditions. The results of this research will help minimise failures of liner systems in barrier applications such as landfills, mines, tailing dams substantially to reduce the potential risk of groundwater contamination.