Geomembrane strain observed in large-scale testing of protection layers

A method for estimating the local strain in a geomembrane due to the indent ation of gravel particles is presented. The accuracy of various strain calc ulation methods is evaluated by a Series of tests, and it is shown that the traditional arch elongation method provides only an approximate Estimate o f the magnitude of strain induced in the geomembrane due to indentation and does not adequately define the distribution of strain. Consideration of th e combined membrane and bending strains as proposed here is shown to provid e a better representation of the distribution of strains and enhances the e valuation of the peak strains in the geomembrane caused by local indentatio ns. Large-scale tests are conducted using different protection layers, and the strains are reported based on both the arch elongation method and the c ombined bending and membrane theory. The results indicate that the best pro tection for the underlying geomembrane was provided by a sand-filled geocus hion or a special rubber geomat, which limited strains induced by coarse (4 0-50 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/m(2) geotextile at 250 kPa and 13% with t wo layers of 600 g/m(2) geotextile at 900 kPa.