Influence of the textured structure of geomembranes on the flow rate through geomembrane-GCL composite liners

Abstract

Laboratory tests for measuring the flow rate through composite liners due to geomembrane (GM) defects were carried out. Composite liners consisted of a GM, with a circular hole, a geosynthetic clay liner (GCL) and a compacted clay liner (CCL). Four GMs were used: one smooth and three different textured GMs (sprayed-on structure, embossed honeycomb and dimpled structures). Tests were conducted simultaneously at two laboratories (Portugal and France) to check test reproducibility. They were conducted under a hydraulic head equal to 0.3 m and a confining stress equal to 50 kPa. The main goal of this research was to study the influence of the textured structure of GMs on the flow rate and on the corresponding interface transmissivity. Results showed that the tests are reproducible and that the GMs textured surfaces have a small impact on final flow rates (obtained at steady-state), although, at the beginning of the tests, higher flow rates were obtained with smooth GM than textured GMs. This suggests that, at the early phases of the tests, the water flows easily at the interface when smooth GMs are used. The texture seems to reduce the space available at the interface for the water flow. However, with time, the sodium bentonite in the GCL swells and creates an intimate contact between the GCL and the GM. Based on final flow rates and on observed wetted areas, interface transmissivities were calculated. Values obtained were similar regardless the type of GM used. Also, transmissivities obtained were smaller than the ones estimated by using the empirical equation proposed by Touze-Foltz & Barroso (2006) for "GM-GCL Contact Condition" which was initially defined as a maximum from experimental data presented by Barroso et al. (2006). Thus, data obtained in this study are consistent with previously obtained data. Results obtained also suggest that, after steady state achievement, smooth and textured GMs can perform very similarly while contacting GCLs.