Porr Spezialtiefbau has installed permanent anchors 650m deep into rock for the crane runway at the Forbach pumped storage power plant.
Since autumn 2023, Porr Tunnelbau has been constructing a cavern and tunnel system for the conversion of the Rudolf Fettweis plant in Forbach into a pumped storage power plant on behalf of EnBW Energie Baden-Württemberg AG.
The crane runway will be used to transport materials during the construction and later during operation and last week Porr reported it had completed the concreting of the crane runway beams.
The crane runway must be anchored into the rock for permanent load transfer. For this, Porr Spezialtiefbau manufactured 50 four-strand permanent anchors with double corrosion protection and a grout body length of 3m, with a total length of 18m. They were drilled uncased into the rock at a 27-degree incline and a starting height of approximately 5.5m.
The Klemm 806 GS drilling rig, specially adapted for uphill drilling, and a Wassarahammer were used. This hydraulic hammer drill uses clean water instead of compressed air as the drive medium. Although this method requires more effort in water logistics, Porr says the advantages over dry drilling far outweigh the disadvantages.
Firstly, emissions are very low because no dust is generated, and secondly, drilling can be carried out more efficiently. Wear on the drilling tool is also reduced because of the constant cooling and continuous flushing with water.
To ensure a constant water supply, there are two fresh water reservoirs in the cavern that are continuously filled with water. The river water is pumped via a settling basin into a storage tank and filtered before being fed into the drilling rig.
Porr Spezialtiefbau site manager Benedikt Lohoff said the team mastered the challenges of working underground.
“The available space was extremely limited, and the noise levels were sometimes high, despite wearing hearing protection,” he said. “Furthermore, the alternating operation of the large equipment and transport vehicles required the full attention of everyone involved. Thanks to close co-ordination between the trades and a sophisticated occupational safety concept, we were able to complete the work safely and on schedule.”
