Flowing waters

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.