Medmerry Realignment Scheme: Design and Construction of an Earth Embankment on Soft Clay Foundation

The Medmerry Realignment Scheme will provide increased protection against flooding for the communities near Selsey on the south coast of England by realigning sea defences up to 2km inland whilst creating a new intertidal area for improving the region’s wildlife habitats. The new flood defences comprise a 7km-long embankment constructed from layers of site-won cohesive fill with a height of up to 5m. Since parts of the earth embankment were founded on alluvial soft clay, an accurate prediction of pore water pressure dissipation in the foundation was the key to adoption of a safer and more economical construction method.

The Environment Agency (EA) is charged with maintaining the flood defence assets on the Medmerry coastline, which is located on the south coast of England approximately 10km to the south of Chichester, West Sussex (Figure 1). The Medmerry coastline extends from Bracklesham in the northwest to Selsey in the southeast, being one of the stretches of coastline most at risk of flooding in southern England, and being also threatened by sea level rise. The existing frontage comprises a shingle flood defence ridge which is at risk of breaching annually.