A new arch dam will be built in front of the huge Spitallamm dam on the Grimsel mountain pass that needs renovation. SBM has installed two LINEMIX 3500 CM 800-6 H plants, plus a recycling plant for residual concrete at this challenging large-scale construction site located at 1,900m above sea level.
The Spitallamm dam – one of the first and biggest arch-gravity dams - was built around 1930 in the Swiss region Bernese Oberland. It adds that the need for action now arose because of a crack that has been running through the wall interior for some time.
Instead of demolishing or renovating the massive dam, it was decided to build a new double curvature arch dam immediately in front of the existing dam at a cost of CHF125m (€114.25m).
SBM says that a big advantage of the new dam is that the power plant operator KWO can continue to produce environmentally friendly hydro energy from Lake Grimsel during the 6-year construction period. The concrete required for the replacement dam wall is supplied by SBM high-performance plants. Below the old dam wall, the two LINEMIX 3500 CM 800-6 H plants have been installed to ensure output peaks of more than 900m³ hardened concrete per day and production reliability in the short but very intensive construction seasons.
At almost 2,000m above sea level, logistics is a major challenge. Transportation over mountain roads, through tunnels and via material ropeways, confined space conditions, wind speeds far exceeding 200km/h, snow dust avalanches, heavy snow loads and extreme temperatures make working conditions very difficult. Because of the long and snowy winters, building seasons last only from May to October, when more than 70 experts of the Grimsel joint venture work on the project.
The large high-alpine construction site was developed in 2019 and SBM Mineral Processing won the plant order. Construction work began in the summer of 2020. SBM completed the installation of the big LINEMIX plants in close co-operation with Swiss service partner and spare parts provider Amatech in just three months. After testing, the plants and the special concrete mixtures were certified in September 2020 so that the concrete production for the construction of the new dam wall was able to start in June 2021.
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 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,” said Olivier Balmer, construction manager for the ARGE Grimsel joint venture. For the latter concrete type grain sizes up to 125 mm can be used, which is twice as big as usual. This means that nearby material – 700,000 tons of 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 six different types, and three cement silos. Concrete is mainly discharged to 7-m³ crane buckets.
SBM says that 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. The new dam must withstand the hydrostatic pressure for at least 100 years.
SBM Mineral Processing provided a recycling plant for residual concrete for the project. “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," said Helmuth Neubacher, who is responsible for the sale of concrete mixing plants in Switzerland at SBM.
The new dam is set for completion in 2025, almost a century after construction of the old dam was started. It will be the same height as the previous dam and construction will again have taken six years.
