The paper deals with 2 applications of geotextiles in coastal and hydraulic engineering: Geotextiles in filters and revetments, and in sand filled structures. Geotextiles are often replacing granular filters. However, they have different properties than a granular filter. For a the application of geotextiles in revetments, the consequences of the different properties will be shown: How permeability is influenced by a geotextile and what can be the consequences of the weight differences between granular and geotextile filters. In another application, the filter properties of geotextiles are only secondary. In geotextile tubes and containers the geotextile is used as ‘wrapping material’ to create large units that will not erode during wave attack. The structures with geotextile tubes and containers serve as an alternative for rock based structures. The first of these structures were more or less constructed by trial and error, but research on the shape of the structures, the stability under wave attack and the durability of the used material has given the possibility to use design tools for these structures. Recently also the morphological aspects of these structures have been investi-gated. This is of importance because regularly structures with geotextile tubes fail due to insufficient toe protection against the scour hole that develops in front of the structure, leading to undermining of the structure. Recent research in the Delta Flume of Deltares and the Large Wave Flume in Hannover has led to better understanding what mechanisms determine the stability under wave attack. It is shown that therefore also the degree of filling is of importance and the position of the water level with respect to the tube has a large influence.
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