Feedback from an important site of a vibrating thin diaphragm cut-off wall on the EDF diversion canal at Strasbourg

Abstract

Certain sections of the structures which divert the Rhine river in Alsace area have a double function: ensuring, of course, the lateral retention of water for navigation in the canal, but also contributing to the closing of several retention basins dedicated to the peak attenuation (mitigation) of large floods on the Rhine river. The retention basin at Strasbourg, which straddles the short-circuited section of the Rhine river, experienced partial first-filling in 1999. The untimely up-welling of alluvial groundwater on the French side halted the filling process. At the conclusion of a long process of studies, piloted by the German organisations in charge of the management of floods and lead by German specialists, the German party proposed at its expense the construction of an impervious barrier anchored into the ancient alluvium, 2.8 km in length, matching up the recent alluvial deposits and the more ancient river course, under the right-hand bank of the EDF diversion canal. The project was remarkable both by the height of the curtain in the ground (around 22 m) and by the area continuously treated (58,000 m2). The very short timeframe for completion of the project required by the Germans (20 months) nevertheless included time for a European competitive bidding process technically opened. The solution accepted after this bidding process (vibrating thin diaphragm cut-off wall combined with high pressure jetting injection) was achieved in Spring 2002 and required the use of huge site equipments.