Difficult soil conditions caused problems

The previous container terminal construction projects on the mouth of the Weser had repeatedly encountered problems with difficult soil conditions. Down to a depth of 16 metres below mean sea level, the port planning engineers had to cope with unstable alluvial deposits, generally known as marsh soil. These deposits consist of alternate layers of sand and mud. The depth of the sand layers varies between a few millimetres and one metre. Although the foundation had better bearing capacity, it is by no means homogeneous. It consists of coarse sand, gravel, rubble, glacial loam, clay, silt and silty fine sand.

Special action had to be taken to solve the problem of these unstable layers to enable construction of the quay and the subsequent working areas. In previous quay construction projects at Bremerhaven, replacing the unstable layers with sand had proved successful.

On the Container Terminal 4 site, soil had to be replaced over a length of approx. 1100 metres, in other words along roughly two thirds of the total quay length. In the northern part of the planned terminal facility, the upper edge of the stable layers is higher, so that only the thin layers of marsh soil had to be removed there. At the part of the site off the coast of Weddewarden, a total of 400,000 cubic metres of unstable marsh soil had to be excavated and replaced with sand.

It also had to be remembered that the brackish water at the mouth of the Weser contains large quantities of fine sediment. In parts of the port where the current has been stilled, this can lead to deposits of up to three metres every year. Especially during the soil replacement phase and subsequent backfilling with sand, considerable effort is required to prevent mud from settling or remove any deposits which occur. This was done by a special water injection dredger which whirls up the sediment and keeps it suspended.

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