The city of Duisburg in Germany has commissioned German engineering specialists Bauer Spezialtiefbau with the construction of a mixed-inplace (MIP) cut-off wall, in order to bolster flood defences along the River Rhine.
The Rhine is one of the busiest rivers in the world. With a total length of over 1,200km, it is also the second-longest river in the German-speaking region.
A number of dykes along the Rhine river offer permanent flood protection, including one located in immediate proximity to the Muendelheim district in Duisburg.
To give the river more room to expand at high water and thus avoid peak levels, the existing dyke at Muendelheim will be relocated, creating approximately 60 hectares of retention space.
In preparation for the relocation, a cut-off wall is being constructed along the line of the future dyke to protect the adjacent city district from groundwater pressure.
In this method of constructing a mixed-inplace (MIP) cut-off wall, the soil is broken up with a triple auger, shifted, and then mixed with a binder slurry in the resulting bore hole.
Mike Schwermer, project manager at Bauer Spezialtiefbau, said, “The big advantage of the MIP method is that there is no excavation. The soil doesn’t have to be removed from the site; it can be used directly as aggregate. That is a definite plus, especially for the local residents.”
The finished MIP cut-off wall will measure 1.6km in length. With a width of 550mm and a depth of up to 20m, the total volume of the wall will be around 28,000m².
Schwermer said, “The strict quality requirements for the MIP wall pose a particular challenge. It must have exceptional leak tightness and a final rigidity within a specific bandwidth.”
The cut-off wall will be constructed parallel to the Rhine river on the future route of the dyke. Work on the project began in July 2019 using an RTG RG 25 S pile driver with MIP equipment.
Bauer expects to complete the cut-off wall in March 2020.