On Site Behavior of PVC Exposed Geomembranes Used for the Upstream Face Rehabilitation of Dams in the Italian Alps

The use of exposed geomembranes for the rehabilitation of concrete and masonry dams was introduced in Italy in 1976, when the entire upstream face of an 11 m high masonry dam was lined with a 2 mm thick PVC (polyvinyl chloride) geomembrane as the waterproofing element (Lago Miller). In subsequent applications, the system progressively evolved. From 1988 to present, this technique underwent several other changes, mainly thanks to the use of additional geosynthetics, such as geonets and as thick nonwoven needle-punched geotextiles which allow to avoid the surface irregularities before the geomembrane installation. In all of these applications, the geomembranes were left exposed on the upstream face, without any external protection, to environmental factors and weather conditions, especially to UV rays, which are very intense because many of these dams are at high elevation (typically around 2.000 m above the sea level). On the other hand, the fact that geomembranes are exposed makes it easier to control and monitor their behavior over time. Therefore, in order to verify the performance of the waterproofing system, several geomembrane samples have been taken in different years from a considerable number of dams. These samples have then been subjected to physical and mechanical tests, in order to observe the change of the properties of the geomembranes over the years. In several cases, particularly when the results of tests on virgin samples were available, it was possible to evaluate the residual life of exposed geomembranes on the different types of dams. The main updated results of this large research program will be reported in the paper.