Two weighty dams

Published on 31 January 2008 (updated on 1 February 2008)
Map showing the geographical location of the two dams
Map showing the geographical location of the two dams
(EDF)

In order to withstand the pressure of water, the hardcore of the two dams consists of a dyke. In the Grand’Maison dam this is made from earth and rockfill and in the Verney dam alluvial soil is used.

The Grand’Maison and Verney dams are "gravity dams", which means that the water pressure acts on the dam rather than being pushed sideways as is the case with an arch dam. This explains the importance of the dyke.

The Grand’Maison dam was built usinge earth and rockfill. At its centre, on rock foundations, is a 160 metre high dyke with a watertight core made from moraine soil which is more than 100 metres thick at its base. Rockfill and earthfill upstream and downstream ensures its stability. Transition materials, filters and vetical drains protect the core andgive the structure additional strength.

To strengthen the dam’s foundations concrete has been injected into the rock underneath from a gallery that runs the entire width of the structure. The same galery is used for structural monitoring measurements which are transmited to a surveillance room on the dam’s crest

The crest of the Verney dam is 430m in length and crosses the Eau D’Olle valley just upstream of the village of La Fonderie d’Allemont. The dyke is more than 40 metres high and made from alluvial soil. This dam has been made watertight by a bituminous concrete facing.