This following blog on geomembranes in pumped storage schemes was submitted by CarpiTech

A geomembrane is a synthetic, impermeable sheet that controls the movement of liquids and gases in a structure, system, or project.

Geomembrane lining systems can be used to waterproof any of the structures that make up pumped storage schemes (PSS).

This includes the entire upper and lower reservoirs or parts of them – the waterways (canals, shafts, tunnels) with water velocity up to 5-6 m/s – and in some cases the underground powerhouse.

The design of geomembrane systems is based on experience in hundreds of hydropower schemes, with the additional issues that must be considered when dealing with a pumped storage structure.

These issues include repeated loading/unloading by the water pressure – with the associated higher impact on slopes stability – higher exposure of the liner to UV and to wind uplift, higher potential for fatigue phenomena, and the reversibility of the water current, which can amplify formation of wrinkles and folds.

Things to consider on Pumped Storage Schemes

· Watertightness is needed to preserve water volume and is also critical to avoid potential dam or embankment stability issues.

· Maintenance should be minimised, to not affect the production of electricity. Therefore, durable liners are required.

· In new construction, geomembranes must line the upper and lower reservoir and other structures in the scheme. Such as hydro tunnels, shafts, canals.

· In rehabilitation, geomembranes must restore watertightness of structures in the scheme and line leaking areas, leaking joints and cracks.

The benefits of geomembranes

· They allow steeper embankment faces to maximise the volume of water.

· They provide a good performance with settlements and deformation in earthquakes.

· They don’t require routine maintenance. Repairs are quick and simple, avoiding and minimising downtime.

Choosing the right materials

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Statistically, flexible thermoplastic geomembranes made of plasticised polyvinylchloride (PVC) are the most used for hydraulic applications.

When a geomembrane liner is used to waterproof pumped storage schemes, the following performance criteria are crucial for a durable and effective installation:

· Watertightness, to provide an effective sealing and prevent water leakage.

· Durability, to provide a long-lasting waterproofing and ensure a continuous and safe operation.

· Resistance to puncture and burst, to accommodate the surface irregularities and settlements.

· Extensibility, to follow large deformations, differential displacements and withstand earthquakes.