Miscellaneous offshore use

Geotextiles are used for many different types of offshore engineering applications. Four applications are discussed here underwater dykes, scour protection for offshore wind turbines and support and protection for offshore pipelines. 

Underwater dykes are constructed for a variety of reasons ranging from the underwater containment of hll to the reduction of underwater currents. Historically, the conventional form of underwater dyke has been a rubble mound structure, but rubble hll has become expensive and in some cases hard to obtain. Also, rubble hll can provide a danger to shipping during periods of low tide. Consequently, soft solutions that do not rely on rubble hll or endanger shipping have become attractive. 

Geotextile containers are discussed in Section 20.2.4.3. Lawson (2008) and Bezuijen and Vatenbuig (2012) give design guidance on geotextile containers Bezuijen and Vastenburg (2012) also provide information on accuracy of container installation under different water conditions. 

Offshore wind turbines normally have a large monopile foundation (typically 6 m in diameter) that has been driven into the seabed to a stable depth. To prevent scour around these monopUe foundations (which can lead to monopile instability), scour protection measures are employed. Generally, two different procedures are used to prevent foundation scour. First, a scour protection system is placed on the seabed around the base of the monopUes during the installation process (Fig. 20.39). Second, some scour is allowed to occur around the monopile after installation the resulting scour hole is then filled with erosion-resistant materials. 

In applying a scour protection system as part of the monopile installation (Fig. 20.39), a geotextile filter and stone protection layer are first placed on the seabed to the required horizontal extent to prevent future scour. Then the monopile is driven through the stone layer (and geotextile) and into the seabed to the necessary depth. Finally, an armour protection layer is placed on top of the stone layer around the base of the monopUe. 

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