Upper reservoir renovation - pumped storage power plant

Situation

The Happurg pumped-storage power station in the Nürnberger Land region (Germany), which came into operation in 1958, is one of the oldest facilities of its kind in Germany. After 47 years of operation, the plant had to be taken out of service in 2011 due to damage to the base of the upper reservoir. 

Since then, the operator, Uniper, has been exploring various options for revitalising the site. In addition to the enormous scale of the project and the extremely unfavourable ground conditions, the strict deformation limits and the highest standards for safety, durability and watertightness presented an exceptionally challenging engineering task. The primary focus was on securing the reservoir base against subsidence whilst ensuring the long-term serviceability of the reservoir. 

Following an extensive analysis of alternative options, the operator opted in 2024 for a remediation concept using vibro-compaction columns in combination with high-tensile geosynthetic reinforcement as the central stabilisation element.

Solution

The technical implementation combines several coordinated measures.
First, extensive vibro-compaction was carried out in certain areas to improve the subsoil. To prevent ground subsidence and distribute loads, approximately 232,600 m² of high-tensile Stabilenka Xtreme geotextile was also used. This geotextile is made of polyvinyl alcohol (PVA), which exhibits consistently high chemical resistance even in alkaline environments. The reinforcement was installed in two layers and supplemented by an intermediate layer of crushed stone. The overlying waterproofing was provided by a two-layer, redundant waterproofing system.

An applied asphalt waterproofing layer served as the primary waterproofing throughout the entire basin. In addition, approximately 51,000 m² of NaBento IR-N clay sealing membranes were installed as a secondary seal in the area of the ring embankment. Plastic sealing membranes were used in the area of the basin floor.

Due to the complexity of the construction, the entire renovation project required particularly precise planning of the installation sequence, overlaps and connections. HUESKER Synthetic GmbH supported the planning and construction process with, among other things, detailed installation plans. The renovation planning was carried out by AFRY and the work was executed by the Josef Rädlinger Group, taking into account the high standards of quality and installation precision.

Advantages

The chosen renovation solution meets all safety-related and functional requirements and emerged from a comparison of alternatives as the most technically reliable and cost-effective solution. The combination of vibro-compaction columns, high-performance reinforcement mesh and a redundant sealing system ensures the long-term stability and serviceability of the reservoir whilst adhering to strict deformation limits. The project thus lays the foundation for the sustainable recommissioning of the pumped-storage power station and makes a significant contribution to long-term, secure and flexible energy generation.