"We don't have a 90 degree angle here".

Concrete production at the foot of the wall

The concrete used, with a low cement content and fly ash, is produced in the mixing plant directly at the foot of the dam. Since 2022, construction foreman Julia Geist has been supervising concrete production as well as the work in the company's own gravel plant at 1,650 meters above sea level, about three kilometers down the road.

"In contrast to otherwise standard concrete, here the client specifies the composition of the concrete precisely," Julia explains. "That really only exists for dam walls. We use aggregates up to 125 mm in diameter. This is a very exceptional concrete!"

The material for concrete production comes from the immediate surroundings, as Julia points out, "We extract the rock and aggregates ourselves. At first, we recycled the rock excavated from the dam for this purpose. In the meantime, we use old-legal dumps from the 1980s that were made for tunnel excavations for the Grimsel system."

Short distances are good for the environment

Before the rock can be used for concrete production, a number of work steps are necessary that must be coordinated in terms of quality and timing. "We first remove plastic and wood from the landfill, among other things. Then the pre-crushed raw material is further crushed, washed and screened in the gravel plant, preparing it for the various rock components for concrete. Afterwards, we drive it about 3 km by truck up to the concrete plant and fill it into the appropriate silos there."

Short distances save time and are good for the environment. And where there is no other way, the team relies on transport that is as environmentally friendly as possible, as Julia explains: "Cement and fly ash are the only things we have to bring up from the valley. Some of this material is brought up by electric trucks."

The concrete itself is mixed right at the foot of the dam - strictly according to specifications to meet the high quality requirements. "We operate our own construction site laboratory, and that's where the material is continuously tested and the process documented," Julia emphasizes.

40 km of water pipes in the concrete

To ensure that the new dam wall does not develop any cracks, however, it is not only the right concrete mix and proper placement that are relevant; the concrete must also cure evenly. For this purpose, it is already cooled during installation - with water that is fed through a total of around 40 km of water pipes through the new dam.

The cold water comes from the reservoir and is returned to the Grimsel system after use, as Daniel Seliner explains: "The water in the lake contains a lot of sediment. After we use it, we clean it - and then feed it back cleaner than we took it out. We check and document the water quality every day. We feel the need to take good care of the environment."

Against the clock in 3-meter steps

Once the planned block has been formed, the cooling and injection lines laid and joint tapes, recesses and formwork for the inspection walkways etc. installed, the work begins: the concrete is conveyed by a large forklift truck to the concrete bucket on the crane and lifted up onto the new wall being built, where the team is already waiting for it with the spreading excavator and the vibro-excavator. By 3 a.m. every day, around 500 m3 of concrete are placed in a prepared block. In this way, the wall grows a little further in height every day.

Towards the end of the intensive construction season, Daniel Seliner looks at the day's work with satisfaction: "This is the third concreting season here on the site, and it's really going extremely well. The teams got together quickly at the beginning of the season, and people are enjoying working on such a project of the century. We are fully motivated and even ahead of schedule. With that, I'm confident that we'll be able to hand over the dam to the client in the fall of 2025."