Construction of a Cut-Off Wall Using Mixed-In-Place Technology for a Flood Retention Basin in Southern Germany

In the area of Feldolling, a village south of Munich, Bavaria, Germany, a flood water retention basin for the river Mangfall is planned and still under construction. In the event of heavy rains or seasonal ice-melting in the Alpes, the flood-prone region can suffer from severe damage to the infrastructure and the residential areas. Those events can therefore even threaten people´s lives. The planned flood retention basin will store more than 6 Mio m3 of water. For the construction of the retention basin, the authorities are building a few dikes of different lengths in addition to a dam to capture the flood water in the retention basin. The inner sealing and the underground cut-off barrier of one of the dikes was constructed using deep soil mixing wall. The implemented deep soil mixing technique is the Mixed-In-Place technology (MIP). The MIP wall had a width of 550 mm and reached a maximum depth of 23 m. The soil conditions were not uniform and varied from gravel and sand to silt and clay. The cut-off wall had to have a strength not exceeding 3 MPa and should be 1.5 MPa on average. To take into account the different soil characteristics and to achieve the required material properties, a lab testing program took place before construction.