Construction of the Lehen run-of-river power station in Salzburg is exceptional in many ways: the project’s offbeat architecture, unusual location and extreme dimensions all present some major challenges – in formwork-engineering terms as well. The ARGE KW Lehen consortium, comprising G. Hinteregger & Söhne, Porr Bau GmbH and Teerag Asdag AG, has risen to these challenges successfully, having fetched a strong partner on board for the forming operations – Doka.
Challenge mastered in two phases
The challenge was to get tonnes of concrete and steel into an exceedingly appealing and functional shape in a confined site in the middle of the River Salzach, while minimising the impact on nearby residents and the environment. To accomplish these goals, the consortium is carrying out the projects in two separate phases. For Phase 1, the Salzach was first diverted to make room for a building pit on the right bank of the river. In this pit, the site crew built the first three bays of the weir, and the bridge that crosses it, between September 2010 and December 2011. The distinctively shaped weir piers are 2.5 m wide and up to 50 m long. They were each poured in four casting sections. The high-performing Wall formwork FF20 system was used for forming these up to 4.70 m high and up to 12 m long sections. With its ready-assembled standard elements, this formwork system combines the advantages of timber-beam formwork (no frame imprints) with the grid-related advantages of a framed formwork system. The special FF20 formwork element connectors ensure crane-handling-safe, tight, slippage-free gangs. The site crew used custom elements as the stop-end formwork for the ‘swan-necks’ and sidewalls; these elements were tailor-made by the Doka Ready-to-Use Service from Large-area formwork Top 50, profiled timber formers and Dokaplex formwork sheets, and delivered to the site ready for use. The use of Dokaplex formwork sheets for the form facing resulted in flawless fair-faced concrete surfaces. The large, stepped custom platforms provided a safe working environment during the pouring operations and were easy to reposition by crane as needed.
Following completion of the structures in the building pit on the right bank, the Salzach has been routed over the newly built bays of the weir since January 2012, to leave space for the second building pit. In Phase 2, from January 2012 until the middle of 2013, work is proceeding on the left bank to build the dividing pier, the powerhouse for the two Kaplan shaft turbines and the abovewater/underwater sidewalls with their integrated fish ladder. The two hydroelectric generating sets are due to go into service in May 2013. Manfred Heimgartner (Site Manager, G. Hinteregger & Söhne) is full of praise for Doka’s collaborative performance: “Doka are taking excellent care of us. Having the Doka Salzburg Branch so near means that we get really quick responses whenever we have any questions or need equipment at short notice.”