A1. ASSESSING GEOMEMBRANE RESISTANCE for ARCTIC WASTE COVERS

The cold-temperature resistance of geomembranes in covers is being investigated in terms of both the short-term cold-temperature resistance and how these properties may change with chemical aging. Consideration is being given to aging of both the geomembrane sheet and the dual wedge welds to explore the effect of polymer degradation on cold temperature resistance. While the welds represent only a small part of the lined area there are more than 1500 m of welds per hectare and failure due to rapid crack growth is often initiated at the weld and then propagates through the sheet. The weld and sheet performance is different due to the: (a) material changes adjacent to the weld after heating and subsequent rapid cooling from welding, and (b) the magnification of the stresses/strains relative to the adjacent sheet. Even with no weld failure, the sheet can experience tensile stress due to stones in the cover soil or foundation below will be investigated. PhD students are examining polyethylene (William Francey) and bituminous (Mathew Clinton) geomembranes.

A2. CALCULATING GEOMEMBRANE STRESSES and STRAINS for ARCTIC WASTE COVERS

Postdoctoral Fellow Hesham Eldesouky is developing two modelling techniques needed to calculate cover geomembrane stresses and strains from differential settlement of waste material for field geometries. The two techniques are being adopted to provide a cross-check on the theoretical results. The first approach involves making significant modifications to a large-displacement finite-element model (ABAQUS) so that geomembrane strains induced by differential settlement of the waste (e.g., from variable density as placed or thawing of near surface waste placed when frozen) can be calculated. The second, and very new, technique to be developed by Eldesouky, involves adapting and applying engineering mechanics plate theory. This novel approach was just recently developed to model the local geomembrane response beneath drainage gravel particles for bottom liners in landfills and looks well suited for application to waste covers.

A3. COLD-TEMPERATURE THERMAL STRESSES FROM SEASONAL and RAPID COOLING

Experiments are being conducted to investigate the impact of thermal stresses that develop from seasonal and rapid cooling of cover geomembranes resulting from arctic weather. In addition to measuring stress, these experiments will also provide assessment of material resistance under thermally induced stresses and examine the effect a notch or weld may have on the geomembrane when subjected to thermal stresses.