Large-scale tests for leachate flow through composite liner due to geomembrane defects

Large-scale and relatively long-term model tests of leachate flow through a composite liner due to geomembrane defects were conducted. The model composite liner consisted of a 0.363 m thick soil layer and one layer of geomembrane. The diameter of the model device is about 1.2 m. The equipment used is capable of applying up to 200 kPa effective overburden pressure, p, to the model composite liner. Test and analysis results indicate that increasing the p value on the geomembrane reduces the leachate flow rate significantly. It is considered that this reduction is due mainly to the reduction of geomembrane/soil interface transmissivity, θ. After a leachate flow test, by measuring the concentration of target source ions, it was confirmed that there was flow at the geomembrane/soil interface. Comparing the measured data with predicted values using existing equations shows that assuming a perfect contact condition at the geomembrane/soil interface is not applicable for the conditions tested. Empirical equations by Giroud and Touze-Foltz for the good contact condition can provide a reasonable prediction of the flow rate through a defect in a geomembrane of composite liner under lower p values (close to zero). Based on the test results of this study, equations by Giroud and Touze-Foltz are modified to consider the effect of the p value. Using analytical solutions by Rowe and Touze-Foltz et al., the θ values are back-evaluated from the test results.