Viscoplastic modelling of HDPE geomembrane local stresses and strains

摘要

The formulation, validation and application of a viscoplastic constitutive model for numerical analysis of HDPE geomembrane stresses and strains induced by overlying coarse gravel is presented. Model parameters were obtained from uniaxial tensile experiments conducted over a range of displacement rates. The model was implemented in geometrically-nonlinear finite-element-analysis and was able to match the force, displacement and strain measured from wide-width strip tensile experiments. The analysis also matched the geomembrane response measured from axisymmetric force-displacement experiments, where a 60-mm-diam. specimen, clamped around its perimeter, was subjected to loading normal to its plane from a steel probe machined to mimic the shape of a coarse gravel particle. The analysis matched: i) probe forces when loaded at a constant rate of displacement, ii) displacements when loaded with step function increments of probe force, iii) creep displacements under a constant probe force for 1000 h, and iv) decreases in probe force from stress relaxation when held at a constant displacement for 1000 h. The analysis was used to further validate the applicability of thin plate theory to calculate geomembrane strains from measured deformations and provide first estimates of stress that develop beneath a gravel particle.