Dammed-up waters

For centuries, water has been stored or transported in manmade canals and reservoirs to make it usable for transportation, as a source of energy, or for irrigation. A wide range of geosynthetic products can be used in order to create more efficient shipping routes, including those used for the construction or repair of canals and docks. Geosynthetics facilitate economical and ecological methods for the construction of retention reservoirs or barrages.

Filtration

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.

Sealing

In inland fresh water shipping routes where the water level is at an elevation higher than the natural groundwater level, artificial sealing is required to prevent the water from “draining” to the groundwater level. Bentofix® geosynthetic clay liners or Carbofol® geomembranes are well suited lining products for dry installations. When using geomembranes, Terrafix® or Secutex® needle-punched nonwoven geotextiles are recommended as a protective layer. Structured or textured Carbofol® geomembranes are available to effectively transfer shear forces on challenging slope designs. Regardless, projectspecific direct shear tests should be performed to verify the required shear strength parameters in order to use them for calculating slope stability analysis.

When inland ship traffic cannot be interrupted, the underwater installation of Bentofix® BZ 13-B geosynthetic clay liner is recommended. It features a bentonite clay liner with an additional sand ballast layer and an encapsulating nonwoven geotextile. Due to our unique technology, this geotextile/liner composite is uniformly reinforced with direction-independent needle punching over its entire surface area. With a mass per unit area of 8 kg/m², the heavy, sand fill performs several functions: it facilitates the uniform swelling of the bentonite which ensures consistent hydraulic function throughout the entire GCL; it protects against impact stress during the installation of covering stones; and with the appropriate installation technology, it ensures precise positioning so that the Bentofix® BZ 13-B clay liner and sand ballast remain in a permanent, stable position even during shipping traffic. Bentofix® BZ 13-B is also uniformly impregnated with bentonite powder over its entire edge surface area to ensure the proper sealing performance in the overlaps.

Protection

Depending on the subgrade and the cover material, properly specified needle-punched protective nonwoven geotextiles such as Terrafix® or Secutex® both above and below the Carbofol® geomembrane will minimise the potential for damage from surrounding soils. For slightly gravely-sand (≤ 30 % gravel portion) or corresponding cover material, a needlepunched nonwoven geotextile with a mass per unit area of 400 g/m² should be used. Coarser grained soils may require nonwovens exhibiting a mass per unit area of at least 1,200 g/m².

Erosion control

On slopes with especially fine grained soils, heavy precipitation and wave impact may cause surface erosion. Significant erosion and rutting can occur if the slope is poorly vegeta ted. Geosynthetic erosion control mats are commonly used to address difficult, erosion-prone slope conditions. Secumat® erosion control mat can significantly reduce soil washout during heavy rainfalls – its three-dimensional, irregular labyrinth-like structure is designed to allow both fine grained and gravelly soils to fill the open convoluted structure. The irregular Secumat® structure holds the soil in position on steeper slopes and provides structural support to vegetation during the early stages of plant growth. The use of high quality propylene (PP) resins make Secumat® resistant to naturally occurring soil chemicals, soil microorganisms and UVradiation. The Secumat® product range is also available with a needle-punched nonwoven geotextile attached to the bottom side. Installed with the three-dimensional mesh surface side-up, it will then perform two functions – soil separation as well as erosion control.

Conclusion

Robust Terrafix® geotextiles can be effectively employed under permeable revetments to provide filter stability to the subsoil. Bentofix® geosynthetic clay liners and Carbofol® geomembranes are ideal products for a myriad of sealing applications. Carbofol® must be installed under dry conditions and is protected against mechanical loads by Terrafix® or Secutex® nonwoven geotextiles. Conversely, Bentofix® can be installed under water – the integrated sand mat provides a controlling confining load during the swelling of the bentonite and protects the bentonite mat when it is covered with cover stones. In areas where wave impact occurs, Secumat® protects slopes from erosion during the early stages of plant growth.