Calculating local geomembrane indentation strains from measured radial and vertical displacements

An experimental technique to measure the radial and vertical components of displacement from local gravel indentations in a geomembrane is presented. Results from short-term physical experiments are reported where vertical displacement was imposed by one of three machined steel probes (round, cone, and flat) to a 1.5-mm-thick high-density polyethylene geomembrane. The experiments were intended to simulate the idealised response with nominal 50 mm coarse gravel above the geomembrane under controlled experimental conditions. Measurements of vertical and radial displacements were used to quantify the influence of probe shape on maximum strain in a geomembrane when calculated with large strain–displacement theory. For both the round and cone probes, the maximum strain in the geomembrane was located directly beneath the centre of the probe, while the maximum strain with the flat probe was near the edge of the probe. Strains calculated using large strain–displacement theory are then compared with thin shell theory and the arc elongation method. Thin shell theory and the arc elongation method were both found to calculate incorrect strain distributions and also provide magnitudes that can significantly underestimate the maximum strain in a geomembrane.