SIZE EFFECTS FOR MULTIAXIAL TENSION TESTING OF HDPE AND PVC GEOMEMBRANES

Geosynthetics may be subjected to multi-axial stress states from plane strain loading, such as dragdown along lined slopes and from out-of-p lane loading conditions imposed by localized subsidence beneath waste containment cover and liner systems. The multiaxial tension test is us eful in evaluating the performance of geosynthetics subjected to multi -axial stress states. However, widespread acceptance and use of this t est has been slow due to the perceived requirement of a large-diameter test apparatus with its corresponding high cost. The development of a fully automated axisymmetric tension test apparatus and the results f rom laboratory testing of two geomembranes (HDPE and PVC) are presente d in this paper. With this test apparatus, any one of four clamping ri ngs of different diameters may be used to restrain the geomembrane dur ing a particular test. Critical aspects of the test equipment and test procedures are described. The laboratory results indicate that use of a clamping ring with a significantly smaller diameter than currently required will provide comparable results provided that guidelines conc erning the ratio of the clamping ring diameter to the material thickne ss are adopted and that stress-strain-time compatibility is maintained . This finding is supported by relevant membrane theory.