Characterizing the ageing of a geosynthetic clay liner through electrical resistivity

In closed hazardous waste landfills, impermeable layered covers mainly composed of clays, geosynthetic clay liner (GCL) or geomembrane, etc. are used to seal in the waste to minimize water infiltration and accumulation of leachate inside the waste. An experimental site of landfill cap was realized with sodium-activated calcium bentonite GCL at a depth of 0.45 m covered by gravels and top soil. The monitoring of this site was performed during 32 months with measurements of weather conditions, and electrical resistivity tomography (ERT) and geotechnical measurements at the end of the monitoring. The two different methods underlined that the GCL’s electrical resistivity decreased after 22 months subsequent to its installation; moreover, it was possible to detect the defects that had been made in the GCL prior to closure, to simulate factors affecting GCL performance. Thereby the analyses made on the GCL samples taken at two locations in the vicinity of the ERT profile highlighted changes in the intrinsic properties of the material. Changes in the proportion of sodium and calcium cations occurred and its hydraulic conductivity increased from 5 × 10−11 to 3 × 10−6 m/s. Thus, this study shows that electrical resistivity is suitable to characterize the ageing of a GCL.