Effect of core composition on seismic stability of earth dams

It is current practice to employ composite clay –a mixture of clay and aggregates that floats within the clayey matrix – as the core of embankment dams, which were previously constructed from pure clays. Experience has shown that significant pore pressure can build up during cyclic loading in composite clays. In this paper, the results of dynamic analyses performed on the Karkheh dam in Iran, incorporating different core materials, are presented. Pure clay and composite clay are used as the core materials and the results of the analyses are compared. It is shown that significant seismic pore pressure build-up in composite clays can significantly reduce the factor of safety against sliding for the fragment of the slip surface passing through the core, even though the overall factor of safety falls within a reasonable level.