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In the project DredgDikes the different research dike embankments were tested with respect to overflowing water induced erosion. Therefore, flumes were installed on the land side embankments in which the effect of overflowing water on the vegetated surface was investigated. On the Polish DredgDikes research dike near Gdansk, Poland, two parallel flumes were installed and the surface of the dike made of different mixtures of ash, silt and sand as well as clay was tested both in vegetated and unvegetated state. The results showed that the grass sods placed on the dike embankment had a comparably low erosion stability, particularly if placed directly on the hardened ash/silt dike cover with better results if placed on a clay cover, while the ash/silt mixture showed a high erosion resistance without vegetation. This results in the recommendation to use a thicker vegetation layer on top of the ash composite dike if the vegetation shall account for the erosion resistance or else, that even if the grass cover is washed away, a very solid cover made of the ash composite can withstand an overflowing event for considerable time. [ABSTRACT FROM PUBLISHER]

Abstract: In the project DredgDikes with partners from Poland and Germany different dredged materials from the South Baltic Sea region are investigated for their application in dike construction. Two large-scale experimental dikes have been built, one in Germany and one in Poland. Additionally, a large variety of laboratory tests and experiments have been performed and a considerable monitoring test programme will be followed. This paper contains a general description of the project as well as first results from a laboratory flume test, field investigations on seepage and the information about a planned climatic chamber experiment, all performed at the University of Rostock, where the focus is laid on fine-grained dredged materials in combination with geosynthetics solutions. The flume experiments showed a very high strength of the dredged materials samples with grass cover. The first seepage test at the large-scale test dike in Rostock showed good performance of the geosynthetic drainage solution applied as well as the stability of the dredged material with respect to rapid drawdown of the water level. The comparison of measurements inside the dike and a seepage model showed considerably higher hydraulic conductivity in the field compared to that determined in the laboratory, however still in the range suited for coastal dike cover materials. To investigate the cracking behaviour of the ripened fine-grained dredged material a climatic chamber experiment has been set up which is also discussed briefly. [Copyright &y& Elsevier]