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Geofabrics Coastal & River Defence
On one hand, storms and flash flooding cause high-profile failures, but a slow-moving, low-level stream is just as capable of undercutting its banks and causing slope instability.
Protection to combat erosion currently tends towards soft and natural solutions including beach nourishment and rock armour, the size of which is determined by the anticipated wave or erosional scour action. Filter layers are required beneath rock armour to prevent erosion of the underlying soil. Otherwise, the armour would progressively drop into the increasing void and its effectiveness would be diminished.
Historically, graduated granular filter layers, with progressively larger grain size, were used to prevent this type of erosion. Installation was time-consuming and they could be difficult to install, particularly if this involved inter-tidal working. The environmental impact of importing thousands of tonnes of stone of the required gradings, often with restricted access, and their expense, meant that there was scope for alternative solutions.
Revetments constructed from rock armour or pre-cast concrete units require a filter to prevent mobilisation of underlying soil and to allow the free movement of water in both directions. Without the ability to provide these functions over the entire life of the revetment, there is the potential for the armour to be undermined, as beach material is progressively eroded, or for a build-up in hydrostatic pressure. Of equal importance is the ability of the HPS filter/separator to withstand the rigours of installation and the in-service conditions. Materials susceptible to puncture, tearing and abrasion would exclude them from consideration.
There is a diversity of geotextile types available. To make the appropriate selection a design engineer needs to match their functions and properties with the requirements of the project, to ensure the selected geotextile is both fit for purpose and will function as intended for the design lifetime.
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