By rosebell
In order to advancing the crane runway at the Forbach pumped storage power plant, Porr Spezialtiefbau has installed permanent anchors 650m deep into rock.
With the aim of conversion of the Rudolf Fettweis plant in Forbach into a pumped storage power plant on behalf of EnBW Energie Baden-Württemberg AG, Porr Tunnelbau has been constructing a cavern and tunnel system since autumn 2023.
`Being used to transport materials during the construction and later during operation, concreting of the crane runway beams was completed last week.
Considering that for permanent load transfer, the crane runway must be anchored into the rock, 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.
Due to the low generation of dust, emissions are very low and drilling can be carried out more efficiently, whereas wear on the drilling tool is also reduced because of the constant cooling and continuous flushing with water.
There are two fresh water reservoirs in the cavern that are continuously filled with water to ensure a constant water supply and the river water is pumped via a settling basin into a storage tank and filtered before being fed into the drilling rig.
According to Porr Spezialtiefbau site manager Benedikt Lohoff: “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.”
