WASSERBAU-DEICH

For dyke applications, geosynthetics perform important functions,
such as long-term stability and waterproofing. Geosynthetics from NAUE
have been used in these exacting applications for decades.

Reduction of the decrease in pore pressure

Load filters are placed downstream (air side) to improve stability
and to reduce the seepage line in the case of flooding. By collecting
water downstream, the filter reduces existing pore pressure in the dyke
and prevents excess pore pressure build up, thus providing stability to
the dyke. Terrafix® needle-punched non woven geotextiles fulfill the
challenging filter stability requirements – they can be effectively
employed as a filter layer between the dyke core and the filter as well
as in the foundation of the dyke itself. Upstream (water side),
Terrafix® geotextiles prevent permanent soil washout which could
significantly reduce the dyke stability. The threedimensional,
labyrinth-like pore channels of Terrafix® provide excellent filter stabi
lity due to their similar structure to the soil. In addition, Terrafix®
geotextiles are ex tremely robust due to their high elongation capacity
allowing them to easily accommodate irregular or soft subsoil.

Sealing

For the repair or the new construction of a fresh water dyke, the 7
mm thick Bentofix® geosynthetic clay liner is an economical alternative
when compared to the typical 60 cm thick compacted clay liner. When
installed on the upstream surface, the high-swelling powdered sodium
bentonite offers an excellent low permeability seal. Bentofix® is
manufactured with direction independent needle punching, with more than
two million fibres per square metre. Slope angles of 2.5 h : 1 v or
greater are possible due to the surface structure of the needle-punched
cover and carrier nonwovens as well as the large internal and external
shear strength. In poor soil conditions or on steeper slopes, Secugrid®
geogrids can be used to further ensure slope stability.

Due to their thin profile, Bentofix® clay liners consume less volume
than compacted clay, and can require significantly less soil removal –
especially in the case of dyke repair. The Bentofix® BFG 5000 also
features a cover nonwoven geotextile that has been uniformly impregnated
with a second layer of sodium bentonite powder over its entire surface
area. The additional bentonite in the cover nonwoven geotextile can help
the installation proceed more efficiently versus installations where
the overlaps must be sealed with additional bentonite.

The cover and carrier geotextiles of Bentofix® geosynthetic clay
liners protect the bentonite core while providing sufficient robustness
for on-site handling. When high normal loads are anticipated, Bentofix®
manufactured with nonwoven geotextiles exhibiting a mass per unit area
of 300 g/m² should be used.

Alternatively, 1.5 mm thick Carbofol® HDPE geomembranes can be
installed. Not only is placement simple, Carbofol® HDPE geomembranes are
easy to weld due to the favorable Melt Flow Index of the resin.

Surface texturing is available to effectively transfer shear forces
on slope locations. Regardless, project-specific direct shear tests
should be performed to verify the required shear strength parameters of
the confining soils and to calculate the stability.

Depending on the requirements, needle-punched nonwoven geotextiles
such as Terrafix® or Secutex® may be installed above and below the
Carbofol® geomembranes for added protection. For slightly gravelly-sand
(gravel portion ≤ 30 %) protection nonwovens with a mass per unit area
of 400 g/m² should be used to protect the Carbofol® geomembrane. Coarser
grained soils may require protection nonwovens, exhibiting a mass per
unit area of 1,200 g/m².

Protection against rooting

Roots from shrubs or trees can find their way into the downstream
filter or into the body of the dyke – which may reduce the drainage
performance of the filter or impact the permeability of dyke liner. The
vertical placement of 1 mm thick Carbofol® geomembranes ensures the
effective protection against root penetration and long-term stability in
critical areas. With a thickness of 2 mm Carbofol® also provides
long-term resistance to rodents.

Erosion control

On steep slopes, heavy rainfall may cause rutting or wash away young
grass seed. Secumat® erosion control mats in hibit surface erosion and
rutting by retaining the soil and seed in a convoluted three-dimensional
structure. Secumat® is installed directly on the slope and filled with
soil. Roots gradually intertwine with the threedimensional structure of
Secumat®, efficiently interlocking roots and the Secumat® with the
surrounding soil.

Conclusion

Dykes are built for protection against flooding and must perform
properly during this limited, yet demanding period. Terrafix®
geotextiles are used upstream to prevent soil washout as well as
downstream in the outflow area of the seepage lines to prevent erosion.
With Terrafix geotextiles, the full drainage performance of the filter
is maintained and the stability of the structure is ensured. Bentofix®
geosynthetic clay liners and Carbofol® geomembranes are used extensively
as sealing components while Terrafix® and Secutex® nonwoven geotextiles
can effectively protect the Carbofol® from damage. Secugrid® geogrids
further improve stability in the slope area while Secumat® or Carbofol®
can provide erosion control and protection against root penetration.
When you require complete system solutions for safe and stable dyke
construction, think of the products available from NAUE – the natural
choice.