The influence of thermally and mechanically induced short-term strains on smooth HDPE geomembrane properties

Abstract HDPE geomembranes are usually used in bottom liners in landfills. Their integrity is required during installation and during the lifetime of the landfill. It is commonly accepted by researchers and suggested by different technical specifications that there should be no strain present during the installation of a geomembrane, although some of them propose that the strain during the installation should be no more than 3%. This is not easy to satisfy in some situations. Strains in the geomembranes can be induced by overnight temperature changes, before covering of the geomembrane (cold weather causes stretching of the geomembrane), which in turn may create trampoline effect in the veneer of sloped foundation soil. Covering of the geomembrane can wait higher temperatures to bring geomembrane into good close contact with the substructure profile or can be forced in order to bring the geomembrane into that position, which means accumulation of strains in the geomembranes. The question arises: What are the changes that occur in geomembrane properties for thermally and/or mechanically induced strains in the geomembranes, are they different, and how the level of induced strain and aging of strained geomembrane can change its properties? This paper presents a large project related to laboratory study of this phenomenon, and the first results regarding its short-time behaviour. Mechanical and structural changes of the geomembrane properties are tested and monitored in the first few days after inducing thermal and/or mechanical strains of 0%, 3% and 6%. Specially developed frames were used for the preparation and conditioning of the geomembrane samples. Test results suggest that strains induced by temperature drop and/or mechanical extension do not affect short-term geomembrane properties. Research continues on samples that will be monitored for four years.