A danger foreseen is half avoided

Torrent control in Austria keeps nature in check and protects residents

Data & Facts

  • Project
    • Blausee Dam on the Obersulzbach
  • Principal
    • Wildbachwassergenossenschaft Obersulzbach, Neukirchen, Austria
  • Contractor
    • Forsttechnischer Dienst für Wildbach und Lawinenverbauung, Pinzgau office
  • MEVA systems
    • StarTec wall formwork
    • Triplex bracing
    • Support frame STB 300
    • BKB folding access platform
    • KAB foldable working platform
  • Support
    • Alzner Baumaschinen Ges.m.b.H.

 

StarTec suitable for high loads

Particularly the mountain streams in the Alpine region pose a severe risk for the people who live in the valleys. When the streams swell significantly and, besides large masses of water, carry debris such as stones, boulders and logs, they pose a serious hazard to man and beast. For this reason, people have been building dams to provide protection from these natural hazards since the end of the nineteenth century.

Between 1893 and 1952 the inhabitants of the Obersulzbach valley in Austria built a 20-metre-high protective barrier in four stages. The so-called Blausee Dam was constantly renewed and improved over the years. The construction on the Großvenediger, one of the highest mountains in Austria, was found to be in a poor state of repair during regular inspections. Due to the effects of frost, large blocks had already broken out of the old dam wall.

New location for the key structure 
Since it is classified as a key structure for protection against natural hazards in accordance with the Austrian standard ONR 24800, the construction of a replacement dam had to commence without delay. The supporting surface of the existing dam proved to be unsuitable due to the risk of ground failure. Hence, it was decided to relocate the dam approximately 100 metres downstream. Using MEVA formwork systems provided by our sales partner Alzner Baumaschinen Ges.m.b.H., a new and robust reinforced-concrete slab dam was erected. The supporting surface at the site of the new dam was made of rock, and a local depression in the bedrock was filled with loose rock material and had to be grouted using the high-pressure jet grouting method. A total of 12,700 m³ of rock were removed. It was thus possible to erect the piers together with the left-hand side of the structure (as seen from the direction of flow) on bedrock.

StarTec suitable for high loads
The experts at the Forsttechnischen Dienst für Wildbach und Lawinenverbauung (Austrian Forestry Service for Torrent and Avalanche Control) in 
Pinzgau relied on high-quality and robust formwork systems from MEVA for the entire construction. The approximately 25-metre-high dam has a span of about 75 metres and is supported downstream on two end piers and one central pier with trapezoidal cross-sections. Inclined surfaces were formed using the StarTec wall formwork and a special wooden construction. In addition, wall thicknesses up to 5 metres were required to build the transverse dam wall due to the high water pressure in the vicinity of the foundations.

Project mastered throughstrong partnership
The dam’s end piers were poured up against the lateral rock faces. To do so, the forces created by the single-sided formwork had to be transferred to the ground via robust support frames. Hence, Gerhard Alzner, our business partner of many years, provided 20 STB 300 support frames to allow the work to progress quickly. “We have been working regularly with the Pinzgau Forestry Service since 1997. Our working relationship based on strong partnership makes many processes easier and also helped make this construction project a huge success,” observed Gerhard Alzner.
The STB 300 support frames convinced the Forestry Service staff across the board. Upon completion of the new Blausee Dam, they thus decided to add this type of support frame to their own stock of MEVA formwork.

Heat of hydration in focus
Besides the load transfer from single-sided formwork, particular attention had to be paid to the temperature increase in the impermeable concrete. The heat created when concrete sets (heat of hydration) is dissipated relatively quickly via the surface of thin structures. However, massive structures in particular, such as the transverse wall of a dam, display only a low level of heat exchange. An excessively high temperature difference between the surface and the core of the structure can thus result in stresses and cracks. To guarantee the stability of the dam, the engineers precisely monitored the temperature increase inside the structure. During the setting process an average increase of 20 Kelvin in the structures – as specified in the regulations – was not exceeded.

Constructionin harmony with nature
By its very nature, the torrent pays scant regard to the needs of the construction work. Hence, the work always had to be carried out while taking the flow conditions into consideration. In winter the water level in the torrent is lower, which allowed the foundations to be poured at the start of the construction project. During the rest of the project the course of the stream had to be altered to suit the construction progress to ensure that the project proceeded quickly and safety.
Higher up, the MEVA BKB and KAB safety scaffolds guaranteed that the work could be performed safely. The BKB folding access platform can be hooked onto the StarTec wall formwork with ease and the KAB foldable working platform can also be used on the construction site without prior assembly work.

To build the Blausee Dam, a total of about 580 tons of rebar material and around 8,000 m3 of concrete were used, and the dam was formed using 800 m2 of StarTec formwork panels – a large project with a huge task: to protect the surrounding villages against the forces of nature.