The long and short of it

THE FREUDENAU power station in Vienna, Austria, is one of the world’s first big run-of-river power stations. Completed in 1998, the output of Freudenau corresponds to the consumption of about half of all private households in Vienna.

During the floods in Austria in the spring of 2002, considerable damage was sustained to the side walls of sluice 1 and sluice 2, making opening impossible. This meant that operation of the power station and controlled overflow in the event of renewed flooding could no longer be assured.

Support was requested from Hilti Austria, together with local engineering consultants, with the aim of developing a special anchor rod for this repair work. After on-the-spot tests, it was decided that Hilti HIT-RE 500, supplied in 500ml cartridges, would be injected into diamond cored holes. Two DD 160 diamond coring machines equipped with special DDBU 40 and DDBU 28 core bits in special lengths of 500mm and 2000mm were used for the coring work. The Hilti DD 160 diamond coring tool is used for precise holes in the 25-202mm diameter range in reinforced concrete but also in natural stone, synthetic stone and asphalt. As the concrete was heavily reinforced, 70% rebar contact was experienced during the coring work. Core bit life was thus relatively short (7m). The total depth cored was 135m. Workers from contractors Voest Alpine Montagen of Wels, Austria, used the adhesive mortar to secure Hilti M 24 and M 36 hot-dip galvanised 8.8 grade steel anchor rods, each with a length of 2.8m, in the heavily reinforced concrete. Making allowance for future high water levels after torrential rain, each anchor was designed to take up a load of 17t. The anchor rods provided secure mounting points for the installation of two new supporting arches for the floodgates designed to allow the floodgates to be opened in the event of renewed flooding.

A number of major technical obstacles had to be overcome in order to ensure the success of the project: It proved very difficult to find a supplier of hot-dip galvanised anchor rods in M36 and M24 sizes with a continuous thread over their entire length of 2.8m. A supplier was eventually found in Austria. The working conditions on site were difficult due to the changing water level.

A total of 240 anchors in the M36 size and 170 in the M24 size were secured with the HIT-RE 500 in the heavily reinforced concrete. The HIT RE 5000 is a high performance injection adhesive system for reinforcement bars and threaded rod applications in concrete, suitable especially for big diameters and deep embedments due to slow curing process.The PR 16 rotating laser measuring tool, Hilti electric drills and other products were also used for the project. The new HIT-RE 500 injectable adhesive mortar is the ideal solution for this type of application. The work was carried out by Voest Alpine Montagen of Wels, Austria.

Both side walls are now in place and the sluice has been in operation since the beginning of 2004. The total cost of the repair work was about US$1.8M. The second sluice will probably not be repaired for the time being as the power station operators assume that a sufficiently large volume of water can be released by opening one floodgate in future high-water situations.