A new area of reclaimed land is being created in Hamburg's free port, next to Köhlbrandbrücke: new warehouses will soon be springing up on the spot where ships once passed into the Rodewischhafen / Ellerholzkanal, offering new storage facilities.

The Rodewischhafen, situated between Travehafen and Rosshafen, is a rather restricted harbour basin, which could only take small ships and became commercially unattractive. In 1992 / 93 the harbour was divided by an embankment running between Travehafen and Rosshafen. The basin was then hydraulically filled with dredged material.

To maintain an adequate draught in the navigation channels throughout the year, material has to be dredged from the port and the river Elbe; some 2 million m³ of sediment annuallly. Part of this material was placed in the Rodewischhafen basin and Ellerholzkanal, where only slight sedimentation occured. A thin crust, supporting limited growth of grass and shrubs, gradually formed on the surface of this deposit.

To infill the Rodewischhafen and Ellerholzkanal the client, the Hamburg Authority for Electricity and Harbours and the other companies involved, namely iwb Ingenieurgesellschaft mbH (design and site supervision), the contractor Wellmann, both from Hamburg, and HUESKER were faced with the task of draining the subgrade and preparing the area for sand importation and its ultimate future commercial use.

"Our job is to ensure the fill can be reliably placed and mechanically compacted with the help of our geosynthetics," says HUESKER engineer Hartmut Hangen, explaining the part to be played by the Gescher company.

Two factors in the Hamburg project ensured its success. The first was that after clearing the site of the vegetation, the surface was left with a root crust, which stabilised the working area. The second factor was the use of a high-strength woven geotextile, Stabilenka® 150/45, and a reinforcement geogrid, Fortrac® R 150/30-30. Olaf Stahlhut from consultants iwb: "The subsoils originally had very low shear strength and therefore could not cope with construction traffic. The combination of the root crust and geotextiles allowed light construction plant to be used." The use of Stabilenka® provided two simultaneous advantages; by acting as a separation layer as well as a reinforcement. The woven geotextile, being placed directly onto the crust and immediately below the Fortrac® geogrid, had to be very stable under load as it had to protect and stabilise the subgrade during the placement and compaction of 150,000m³ of sand. A total of around 45,000m² of Fortrac® geogrid and a similar quantity of Stabilenka® woven geotextile were installed.

Thanks to the versatility of the HUESKER products and the use of high-output construction equipment the project moved quickly forward. The horizontal drainage, installed below the and-fill and about 100mm above the geotextile layer, was linked to a pump outlet designed to draw off an estimated 50,000m³ of water. The first layers of sand (total thickness 3.3m) are already in place in the Rodewischhafen and Ellerholzkanal. Eventually the former harbour basin and canal will be in use again, but this time as valuable warehouse space for the Port of Hamburg.

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