Geomembranes are used in waste containment barrier systems to limit to movement of contaminants. The geomembrane is placed over a clay liner, and a drainage blanket consisting of highly permeable coarse aggregate is placed above the geomembrane for removal of leachate to control the hydraulic head. Coarse uniform gravel is typically used as a drainage layer. Where such gravel is scarce or expensive, there has been a trend in recent years to use tire derived aggregate (TDA). Differential loading of the geomembrane by the large TDA or gravel particles over a yielding compacted-clay subgrade leads to indentations. The high localised strain that occurs around indentations may lead to stress cracking. Protection layers are now designed to minimize the development of high localised strain rather than ductile punctures.
A photogrammetry method was developed and performed on over 60 laboratory tests to evaluate variables controlling geomembrane strain. Clay properties play a key role in the magnitude of resulting strains. Fast loading rates (over less than 1 hour) resulted in higher strains when compared to slow incremental loading (over 6 months). The role of the clay in the deformation of geomembranes is a significant factor that must be taken into account when designing composite barrier systems. The final component of this study involved a comparison of tensile strain induced by TDA and gravel. High-localised strain from TDA was less than for angular gravel, and substantially less bending strains occurred, indicating that differences in indentation size and shape from different aggregates should be considered.
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