| Construction


can then reliably produce concrete, and they need not be tempered in the long winter break when they sometimes stand in metres of snow. Technical support will be supplied by Amatech GmbH with its spare parts store and decades of branch experience.


Up-to-date technology While the existing arch-gravity dam with a concrete


thickness of up to 70m at the base withstands the water pressure also due to its own mass, the new dam wall is designed as a slim, double curvature arch dam. This poses very special demands on the concrete mix and requires an extremely high dosing accuracy which is assured by the latest technology of the SBM plants. The height of 113m and the crest length of 212m result in a concrete volume of 210,000m3


– all mixed


in the container-mobile high-performance plants made by SBM Mineral Processing. The plant LINEMIX 3500 CM 800-6 H convinced the Joint Venture ARGE Grimsel thanks to its excellent concrete quality, simple and easy maintenance, optimum spaciousness, and profitability. “The SBM plants meet the very specific demands of dam concrete according to EN 206: face concrete, contact concrete, and mass concrete for the core zone,” explains construction manager Olivier Balmer. For the latter concrete type grain sizes up to 125 mm can be used, which is twice as big as usual. Therefore, nearby material – 700,000 tons Grimsel granite originating from a power plant construction in the 1970s – can be processed to produce the concrete required for the replacement dam. Both mixing plants are equipped with twin shaft batch


mixers for dams, aggregate feed by conveyors, aggregate storage for 6 different types, and 3 cement silos. Concrete is mainly discharged to 7m3


crane buckets. No comparable dam wall has been built in


Switzerland in the last 40 years. The challenge was all the greater to develop concrete mixtures that optimally fulfil the extreme demands of the different parts of the wall. After all, the new dam must withstand the hydrostatic pressure for at least 100 years. Good processability, resistance to weather conditions and temperature fluctuations, and the reuse the existing material were also essential issues in the test phase lasting several months. The various concrete mixtures were poured in cubes and tested both on the site and in external laboratories concerning compressive strength and heat development, as quality and safety have the highest priority.


Sophisticated economic and ecologic


project As an environmentally and economically very useful supplement SBM Mineral Processing provided a recycling plant for residual concrete to the Swiss “multi-tasking construction site“. “The washing water used to clean mixer trucks, crane buckets and mixers is processed, and residues are re-fed to concrete production creating a closed material cycle,“ explains Helmuth Neubacher who is responsible for the sale of concrete mixing plants in Switzerland at SBM. In 2025, almost a century after the construction of the old dam was started, the new dam will be finished. It will have the same height, and construction time will again be six years, but this time only a small number of people will be required. Whereas back then 600 workers were employed at the large-scale construction site, now fewer than 100 will be needed – thanks to modern technology and powerful plants like those made by SBM, but also because there is no special time pressure as the operation of the power plant continues as before. Due to their modular design the LINEMIX plants can be easily dismantled and then moved on to their new place of action. As soon as the new dam can come on stream, lower discharge tunnel and operational discharge tunnel of the existing dam will be opened in the winter season, and additional flooding holes will be bored above the old dam to evenly distribute the stress on the new dam wall. This decision was made for reasons of the preservation of historic monuments and to save the immense effort and costs otherwise required for the demolition and disposal of the concrete. ●


Above left: The two highly compact LINEMIX 3500 CM 800- 6 H units only take up around 650m² of floor space. Together, both systems guarantee daily peaks of around 900 m³ of hardened concrete


Above right: Thanks to the fully thermally insulated cladding, the mobile SBM concrete mixing technology is proof even without additional heating during the winter break


Below left: The modular design of the LINEMIX technology enables quick assembly and dismantling and ensures the long-term use in follow-up projects


Below right: The transport- optimized dimensions of the LINEMIX container modules also enabled fast and uncomplicated delivery of the individual components in high alpine terrain (all photos: SBM Mineral Processing)


www.waterpowermagazine.com | August 2021 | 31


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