Valais, Switzerland
07/2021
Grande Dixence dam is one of the largest structures built within the last century in Switzerland. Here, the potential of water resources and topography for electricity production was recognised early. From 1945 onwards, the heyday for hydroelectric power began, and many new plants were built. The heart of them: the Grande Dixence dam located in the Valais Alps. A total of 3600 workers were involved in the construction from 1950 to 1961 in the mountains at over 2400 meters above sea level.
The water from the mountains is first collected and then fed through a large intake tunnel into the reservoir. Due to its ideal location, the power plant can access a catchment area of 420 km2 and thus collects water from 35 glaciers. 40% of the dam water enters the reservoir naturally, 60% of the water has to be pumped to the required level.
Water is stored as potential energy in the Lac de Dix. To achieve the impoundment of the required water-volume, the dam is needed. From there, it is supplied to four different power plants. The electricity produced is equivalent to one fifth of the electrical energy that can be stored in Switzerland. After the water has driven the turbines, it flows into the Rhone.
The Grand Dixence dam is the highest gravity dam in the world. In contrary to the more common arch dams, which have a narrow and curved shape that corresponds to occurring forces, a gravity dam withstands the water pressure by its weight alone. This construction method was chosen as it was the safest construction method for this location while the old dam still had to remain in operation during construction. The wall is 200m thick at the base, 15m thick at the top of the crown, is 700m long and has a volume of 6 million m3 of concrete.
The success of Grande Dixence was largely due to the constant supply of material, which enabled a regular rhythm of work around the clock. For the dam alone, more than 1.3 million tons of cement were needed. To cover this production volume 9 Swiss cement factories were in operation. The basic material for the dam (aggregate for concrete) came from the surrounding moraines.
Still on site, the stone chunks were crushed into gravel. The rock was then transported on long conveyor belts to the concrete center. The stretch between the two rock faces of the Val des Dix was bridged with cable cranes to pour up to 15t of concrete into the wall every minute. In addition to the dam, over 100km of tunnels were built, to channel water into the lake and to feed the power plants.
The Lac de dix is the largest artificial lake, a water reservoir that contains up to 400 million m3 water. During the summer, the lake is filled up to store energy for the winter. Therefore, the water level fluctuates constantly throughout the year.
