ABSTRACT
The construction of pumped storage plants is increasing due to the need of providing grid balance as wind and solar production increases. Pumped storage plants are demanding structures, due to the continuous variations of the water level that result in repeated loading and unloading conditions impacting on all the components of the plant. In particular, since the upper and lower reservoirs are often formed by excavating the natural slopes and by earthen or rock embankments, it is important to ensure that possible settlements and differential displacements will not affect the watertightness and will not cause uncontrolled water seepage. Waterproofing the reservoirs with conventional liners, such as concrete or bituminous concrete, has shown some drawbacks. The rigid liners demonstrated a poor capability to accommodate settlements, to provide efficient joint sealing, and to preserve the dimensional stability under temperature variations. As a consequence, the rigid liners often need maintenance, which in some cases implies outage of the plant and revenue losses. Geomembrane liners are characterised by outstanding endurance properties and are considered an efficient and durable alternative to more rigid liners, especially when important settlements are expected. Geomembrane liners provide a quicker installation, an early exploitation of the plant, and in case of accidental damage the possibility to be easily repaired, even underwater, without impacting on the plant operation. The 18 Water Saving Basins of the Third Set of Locks of the Panama Canal expansion project can be considered the first geomembrane application in new pumped storage plants, since they have an average of 5 to 6 fill/empty cycles/day. In this project, several anchorage systems were used to retain the exposed geomembrane liner stable and taut to the surface of the basins under daily varying water levels and against wind uplift. The paper discusses the design, characteristics and advantages of advanced exposed geomembrane systems in recent new projects. At Kokhav Hayarden pumped storage project in Israel, completed in 2022, the anchorage system consists of heat-seaming the geomembrane liner to geomembrane anchor bands embedded in vertical trenches. The connection to the concrete structures (water intakes) consists of a mechanical anchorage designed to accept large settlements and differential displacements. At Abdelmoumen pumped storage project in Morocco, completed in 2023, the concept of heat-seaming the geomembrane liner to geomembrane anchor bands was maintained, while a specific construction method was defined to conform to different embankment materials and subgrade preparation. The liner is a lacquered geomembrane, intended to enhance durability in an environment with particularly high UV radiation. At Pinnapuram pumped storage project in India, currently on-going, the geomembrane liner will be installed on three large embankment dams in the lower reservoir and a 6.6 km long continuous embankment dam in the upper reservoir. The anchorage on the dam face will be obtained by geomembrane anchor bands embedded in vertical trenches and created into a bedding layer of porous concrete.
