When used for transportation hydraulic engineering, Terrafix® needle-punched nonwoven geotextiles can be used effectively below permeable revetments as a filter layer. They are selected and designed in accordance with the established technical guideline «Instructions for the use of geotextile filters in waterways» (MAG) of the Federal Institute of Hydraulic Engineering (BAW, Karlsruhe, Germany, 1993). Depending on the existing soil type and revetment, Terrafix® nonwoven geotextiles that are at least 4.5 mm to 6.0 mm thick are best suited to prevent erosion and soil displacement (please refer to chapter «Filtration»). Even under high hydrodynamic loads caused by rapid water level fluctuations or by the turbulence from ship propellers, Terrafix® nonwoven geotextiles maintain their mechanical properties and filter efficiency. Composite Terrafix® products which exhibit a coarse fibre layer can be effectively employed to stabilise the soil/filter boundary layer in soils with high single grain mobility, preventing particle displacement under the Terrafix® filter geotextile.
High mechanical stresses can occur during the installation process as well as from ship traffic. For this reason, the geotextile filters must exhibit adequate impact and abrasion resistance. Terrafix® geotextiles offer these properties and more! Their high elongation capacity and robustness allow them to easily accommodate irregular or soft subgrades while preventing damage to the nonwoven structure itself when covered with stone. The three-dimensional needle-punched structure of crimped fibres provides high abrasion characteristics and resistance to any movement of the revetment.
In fast flowing or turbulent waters caused by propeller wash, the general physical characteristics make the installation and positioning of a nonwoven geotextile an inexact science. However, the Terrafix® sand mat enables the filter geotextile to be placed quickly and accurately underwater due to the ballast of an encapsulated sand mass, providing simple permanent stability. Terrafix® offers filter stability against finely grained soils while sufficiently robust to resist damage from stone cover.