Field survey of desiccation fissuring of flood embankments

Early studies on the 1953 North Sea floods showed that desiccation fissuring of clay fill can play a major role in the failure of flood embankments under overflow conditions. However, the onset of desiccation fissuring in embankments and its contribution towards breach initiation has not been fully researched. Field and laboratory studies were thus carried out into the desiccation fissuring of clay flood embankments in the UK. The work found that a critical condition is reached when desiccation creates an interconnected network of sub-vertical and sub-horizontal fissures, which significantly increases the mass permeability of the fill material and hence allows rapid seepage of flood water through the surface layer of the embankment. It is suggested high rates of seepage cause localised uplifting of clay blocks, leading to progressive slope failure and successive breaching. Small-scale desiccation tests carried out on discs of soil in pressure plates showed very good agreement between the onset of cracking in the pressure plates and the moisture content recorded in the field. This suggests that it is possible to assess the susceptibility of a fill material to desiccation fissuring from the soil water characteristic curve.