Experimental investigation of flow rates through composite liners at the metric scale

Abstract

The hydraulic behaviour of 17 composite liners was investigated at the metric scale in the laboratory using 1 m diameter cells. A 0.27 m thick layer of clay was compacted in all celis. In 12 cases a geotextile was inserted at the interface between the clay and the HDPE geomembrane. In 3 cases a GCL was used under the geomembrane and in 2 cases the clay was in direct contact with the geomembrane. The influence of a geotextile in the interface was deeply investigated as it corresponds to a common practice in France and its real impact is unknown. A 4 mm diameter hole was drilled in the flat HDPE geomembrane in all experiments. The hydraulic head on top of the composite liner was equal to 0.3 m in all cases. Normal stresses in the range 6 to 134 kPa were used. The longest tests, that did not include geotextiles, lasted up to 9 months. The liquid used was either real leachate, a low ionic strength solution or distilled water. Flow rates were measured at the upstream side of the composite liners. In the case GCLs were used, the influence of the pre-hydration of the GCL at the beginning of the test was studied when the liquid used was real leachate. When comparing situations where geotextiles and GCLs were used, results tend to show that even if GCLs incorporate a geotextile the flow rates obtained with GCLs are clearly lower that flow rates obtained in the case there is a geotextile in the interface, even when the geotextile is not fully saturated. Flow rates obtained with clay and GCLs, measured with identical devices and under comparable normal stresses are comparable.