Geomembrane Strain Observed in Large-Scale Testing of Protection Layers

Abstract

A method for estimating the local strain in a geomembrane due to the indentation of gravel particles is presented. The accuracy of various strain calculation methods is evaluated by a series of tests, and it is shown that the traditional arch elongation method provides only an approximate estimate of the magnitude of strain induced in the geomembrane due to indentation and does not adequately define the distribution of strain. Consideration of the combined membrane and bending strains as proposed here is shown to provide a better representation of the distribution of strains and enhances the evaluation of the peak strains in the geomembrane caused by local indentations. Large-scale tests are conducted using different protection layers, and the strains are reported based on both the arch elongation method and the combined bending and membrane theory. The results indicate that the best protection for the underlying geomembrane was provided by a sand-filled geocushion or a special rubber geomat, which limited strains induced by coarse (40–50 mm) angular gravel to 0.9% at 900 kPa and 1.2% at 600 kPa. The poorest performance was achieved using nonwoven geotextiles with a maximum strain of 8% being obtained with a 435 g/m² geotextile at 250 kPa and 13% with two layers of 600 g/m² geotextile at 900 kPa.