Performance of Geomembranes Exposed to Extreme Weather Conditions on High-Elevation Dams on the Alps

The aim of this paper is to present the performance of different types of geomembranes used for the rehabilitation of concrete and masonry dams in Europe, particularly in Italy and France. In all these applications, the geomembranes used were made by plasticized polyvinyl chloride (PVC-P) and have been left exposed on the upstream face, without external protection, to very extreme environmental factors and atmospheric agents, especially to Ultraviolet (UV) rays, at high elevations on the Alps. To verify the effective performance of the barrier system over time, several geomembrane samples—taken from a considerable number of dams—have been subjected to destructive chemical, physical, and mechanical tests. The results were interpreted with reference to the measure of some main properties, as plasticizer content, tensile characteristics, flexibility at low temperatures, volumic mass, and water vapor permeability. In particular, the plasticizer content plays a fundamental role in terms of variation of the intrinsic properties of the PVC-P geomembranes. In some cases, when the results of tests on virgin samples were available and several data points of plasticizer content versus time are available, the service life of the PVC-P geomembrane can be predicted. In fact, the prediction of the time in which it could be necessary to replace the geomembrane becomes of a crucial importance also for the owner of the dam.