Scour Countermeasures Using Geosynthetics and Partially Grouted Riprap

The main requirement of any scour countermeasure or scour protection measure is to prevent erosion, so a top layer has to be built that is sufficiently resistant against the hydrodynamic loads and that protects the subsoil. Single elements have to be large enough to withstand the scouring forces and require an appropriate layer thickness. Smaller, mutually connected elements allow for a moderate layer thickness but provide the same resistance. To avoid excess water pressures below the top layer, permeable systems are recommended. A very reliable system is partially grouted riprap, which meets all the requirements of strength, flexibility, and permeability. Permeable systems need a well-designed filter. Placement of a grain filter or a geotextile filter is complicated by the current, so special equipment is needed. In mild currents a “sandmat” (a sand-filled nonwoven geotextile) can be used. In stronger currents use of geosynthetic geocontainers is proposed to achieve both a high resistance against the current and a well-performing filter.