PDF - 9Mo - Grande Dixence SA

GD. P.29The highest wallin the world!A record-breaking damHalf a century has passed since human endeavour builtthe Grande Dixence dam. And fifty years later, the wallnestling between the flanks of the Dix Valley remainsunique. At 285 metres, it is still the highest wall in theworld!In order to be able to contain the more than 400 million m 3of water stored each year (a volume equal to 8000years of the Valais grape harvest for example), theGrande Dixence gravity dam has beaten many records.No fewer than 6 million m 3 of concrete were pouredbetween the mountains: a wall 1.5 metre high and 10cm wide could be built around the equator with thatvolume of concrete. At its base, the dam is two hundredmetres thick (equal to the length of two footballpitches). At the top - in technical terms the crest of thedam - it narrows to a ribbon of only… 15 metres.To make the soil foundation watertight, the grout curtainsurrounding the dam goes down 200 metres intothe gneiss and granite of the surrounding mountainmass. It extends 100 m into each valley bank. The wallitself is made up of 16 m x 16 m concrete blocks jointedtogether in a way that ensures maximum cohesion,strength and impermeability.Visitors entering the Grande Dixence cavern on footare always surprised by the bottomless shafts thatallow the structure to be monitored. Stretched by 150kilo counterweights, seven pendulums plunge silentlyacross the full depth of the wall. They measure deformationin the retaining wall continuously. This systemallows the movements of the dam to be checked toan accuracy of 5 hundredths of a millimeter.Because the concrete monster breathes! This 15-million-tonnegravity dam, this colossus that is heavier thanthe Great Pyramid of Cheops is sensitive to change.Depending on whether its stomach - its lake - is fullor empty, the crest moves 11 centimetres downstreamor back to its initial position.Apparently peaceful, Lake Dix is surging energy domesticatedby man. 3.65 km 2 in area (for comparison,the area of Lake Joux, in Vaud canton, is 9.5 km 2 ), itis 5.3 km long and has a maximum depth of 227 metres.This energy reserve enables enough electricity tobe supplied throughout the year to meet the needs ofa region of around 400,000 households.