Small scale hydroelectric power station on the Danube Island
January 27, 2017 | Markus Lackner
With projected power generation of some 400,000 kilowatt hours per year, even among small hydroelectric power plants the power station is not a Goliath. But, as Construction Manager, Volker Brand, from Felbermayr's power plant construction division points out, from a civil engineering perspective it is an outstanding solution. As a result, the power station will be integrated into the already existing weir system, »Wehranlage 1«, on the Danube Island. As the main components of the power plant are built underground, there is no noise nuisance for the visitors to the Danube Island and visually the recreational area for the Viennese population is not affected at all.
Special feat of civil engineering
The civil engineering techniques deployed over an area of 2,500 square metres have been more than challenging. "For example, in sealing the excavation pit for the so-called Archimedean screw shaft, we have used high-pressure soil compaction and driven 900 metres of drilled piles, as a secant pile wall, with a pile diameter of 90 centimetres,” comments Brand. However, the construction of the penstock and draft tube structures also created challenges. For this reason, a sealed formwork box structure first had to be installed in the New Danube. This was then pumped empty. Only then was it possible to use core drilling and a sawing rope to produce the intersection in the river bank walls for the penstock. As Brand explains, the measures for driving a 1.4 metre diameter and 55 metre long concrete pipe included, "pressure grouting using full face tunnel boring, in order to be able to subsequently pass under an operating building between the turbine housing and the draft tube structure".
So that the pipe could be correctly driven forward after passing under the operating building, a thirteen metre deep target cavity was necessary. This was formed with the use of sheet piling. However, jet grouting was also used for sealing and improving the static loading capacity of the subsoil. "This required mixing the soil under high pressure with a cement containing binder suspension", explains Brand. In this excavation pit, the flow of the water was turned through approximately 90 degrees. This gave the shortest route to the river bank wall, and the water could be returned to the New Danube, after a further intersection in the wall.
The power plant is a joint project between the Wien Energie and the Municipal Department 45 responsible for Vienna's waterways.
The project is funded by the European Regional Development Fund. Commissioning of the power station is scheduled for spring 2017.
