WASSERBAU-KANAL

Geosynthetics are used as filters, sealing elements as well as for
scour protection in flowing waters. Natural construction materials are
often found to be inadequate in performance without significant
over-engineering – the use of geosynthetics is frequently required in
support of natural systems for both performance and savings. Ecological
aspects play an important role in hydraulic engineering as it is im port
ant to protect as well as preserve the natural flora and fauna habitat.
Systems from NAUE offer ecological, technical as well as economic
benefits together in a single solution.

Filtration

Terrafix® needle-punched nonwoven geotextiles significantly enhance
system performance when two soil layers with dissimilar or non
filter-stable grain structures are used as well as when a revetment is
installed. Even where only hydro static loads are anticipated it is
generally recommended to follow the requirements of the MAG
(Instructions for the use of geotextile filters in waterways, Federal
Institute for Hydraulic Engineering (BAW), Karlsruhe, Germany 1993). In
filter applications for soil types 1 to 3, Terrafix® 609 with a minimum
thickness of 4.5 mm is well suited (for further details please refer to
the chapter “Filtration”, pages 6-7), whereas for soil types 1 to 4,
Terrafix® 813 with a minimum thickness of 6.0 mm would be appropriate.
The installation instructions for different current velocities described
in the chapter “Filtration” should be observed during common underwater
installations. In the case of deeper water and higher current
velocities, the use of Terrafix® sand mats or Terrafix Soft Rock® sand
containers is recommended as they provide excellent stability. The
three-dimensional fibre structure of Terrafix® nonwoven geo textiles
exhibit high elongation capacity and robustness. With these
characteristics, they easily accommodate irregular or soft subgrades and
are capable of withstanding installation loads when covered with stone,
without loss of their filtration performance. The large effective pore
space of the Terrafix® nonwoven geotextile structure offers an excellent
environment for the establishment or continued propagation of local
flora and fauna.

Protection from scouring

There is always a risk of scouring where current velocities are high.
With turbulent currents typical of artificial structures such as bridge
piers and ford foundations, the risk of scouring is particularly high.
Terrafix Soft Rock® sand containers are an ideal solution to repair
existing scoured cavities in river beds or other water channels. The
containers can be filled with local sandy material under dry conditions
and placed in the desired position with appropriate equipment. Using
robust, needle-punched nonwoven geotextiles, Terrafix Soft Rock® sand
containers easily accommodate and resist rough site conditions while
preventing further scouring.

Groynes manufactured from Terrafix®
sand containers are used to prevent scouring in river bends when
constructed at rightangles to the river bank. If the subsoil is
particularly soft, the ground can be stabilised with Terrafix® sand
mats. The additional use of Secugrid® geogrids may be required in
certain cases where substantial subgrade reinforcement is required. The
wide range of Terrafix® geosynthetic products offer long lasting and
economical solutions to resist natural destructive forces, regardless of
the soil type or design of the revetment.

Sealing

In some cases it is necessary to construct an artificial seal in
flowing inland waters (fresh water). Bentofix® offers geosynthetic clay
liner product variations that can be installed in both dry and wet
conditions for this purpose (for further details please refer to the
chapter “Sealing”). Dams and dyke seals may also be necessary to prevent
protected areas from flooding. Since this work is usually carried out
under dry conditions, Bentofix® as well as Carbofol® geomembranes –
combined with Terrafix® or Secutex® protective nonwoven geotextiles,
offer one of the industry’s best lining solutions.

For slightly gravely-sands, needle-punched nonwoven geotextiles with a
mass of 400 g/m² can be used as a protective layer for the lining
component, while nonwoven geotextiles with a mass of 1,200 g/m² will
work well for coarsely grained soils.

Conclusion

Terrafix® nonwoven geotextiles are effective filters for subgrade
erosion control on slopes as well as the base of flowing waters. Due to
their robust nonwoven geotextile structure as well as the high
elongation capacity and flexibility, they can resist difficult
installation conditions while creating a favorable habitat for local
flora and fauna. Bentofix® GCLs and Carbofol® geomembranes are used for
sealing while Terrafix® or Secutex® nonwoven geotextiles protect the
Carbofol® from undue damage from surrounding soils. Terrafix Soft Rock®
sand containers protect against scouring in hydraulic structures, such
as bridge foundations and piers. They are particularly well suited for
the construction of groynes and thus, capable of preventing further
scouring.