Fine Fissuring of Clay Fill Materials for Flood Defence Embankments

Abstract

The UK Environment Agency currently maintains over 35,000 km of coastal and flood defence embankments in England and Wales with an annul expenditure of approximately £400m. The majority of the flood defences are earth embankments built from locally available materials using traditional construction methods. Although the performance of the flood defence embankment can be jeopardised by several different failure modes, instability due to the fine;l,,,lay fill has been identified as one of the main causes of failure especially along the eastern coast and Tha dfg mes Estuary. At these locations medium to highly plastic clays are commonly used as fill material. The fine fissuring of these clay fills can reduce the mass permeability of the embankment, leading to a rapid ingress of floodwater with catastrophic collapse of the inward face. As part of a wider research programme into the fine fissuring of clays, preliminary laboratory tests have been carried out into the formation of fissures for a variety of clays with different plasticities. The tests investigated an empirical relationship between the geometry of thin discs of soil with the onset of fissuring for different plastic indices.