Assessment of Local Strains in Geomembranes at Gravel Indentations

Abstract

Tensile strains that occur in geomembrane liners that are induced by local gravel indentations are investigated, with an emphasis on how the strains are calculated and what testing methods are used to obtain the deformed shape of the geomembrane. This involved the use of established test methods and apparatuses but using a 3D laser scanner to obtain the deformed shape and a recently developed theoretical technique to calculate strain in a geomembrane. Full-scale geosynthetic protection efficiency tests were conducted to test the influence of subgrade on the geomembrane strains. The subgrades examined included no subgrade, a firm rubber pad and a compacted clay liner. The results showed that the tests with no subgrade and rubber subgrades significantly overestimated and underestimated, respectively, the strain in the geomembrane when compared to results from the compacted clay liner tests. Smaller-scale index tests were also conducted to determine the ability of previously developed single-point test apparatuses to simulate the maximum, rather than mean, strain found in a corresponding full-scale test. Two apparatuses machined to simulate the average response of nominal 25 and 50 mm gravels with a single gravel particle were tested. Results showed that the strains induced in the 25 mm cell tests should be multiplied by a factor of at least 2 to reach the maximum strain in the corresponding full-scale test. The effect of strain calculation method was also investigated, where it was shown that a strain of 6% calculated using an established method considering small-displacement-membrane plus bending effects but ignores large displacement effects from lateral displacements is closer to a “true” strain of 8% when radial displacements are included providing the first quantification of simplifying calculation assumptions for actual 25 mm gravel.