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Groundwater protection in transport infrastructure 2017-05-10T10:43:37+00:00

Groundwater protection in transport infrastructure

Various national guidelines for road construction in environmentally sensitive areas require the subsoil be sealed and effective construction measures be taken to protect the groundwater in transport infastructure near to water catchment areas. In numerous projects, Bentofix® geosynthetic clay liners and Carbofol® geomembranes have proven to be effective, economical sealing systems. They are used under roads, railways and for retention basins.

Sealing

As an alternative to a 60 cm thick compacted cohesive soil, the approximately 10 mm thick Bentofix® geosynthetic clay liner, manufactured with high swelling natural sodium bentonite, is used. The robust cover and carrier geotextiles used in the construction of Bentofix® are designed to withstand rough installation loads. Bentofix® is uniformly manufactured with direction-independent needlepunching (fibre reinforcement) over its entire surface area, with more than 2 million fibres per square metre. Depending on the existing soil conditions and slope lengths, slope inclinations of 2.5h:1v or greater are possible, due to the surface structure of the needlepunched cover and carrier geotextiles and the large internal friction angle. In poor soil conditions or on steeper slopes, Secugrid® geogrid can be used to further ensure slope stability.

Due to their thin profile, Bentofix® geosynthetic clay liners consume less airspace than compacted clay, and can require less soil excavation and removal. The Bentofix® BFG 5000 features a cover geotextile that has been uniformly impregnated with bentonite powder over it entire surface area. This bentonite treatment in the cover geotextile can make the installation more efficient as the field application of bentonite paste to the overlaps is not required.

The Bentofix® encapsulating geotextiles are typically made from polypropylene (PP) resin and therefore sufficiently resistant to a wide range of conventional chemicals, such as diesel fuel, oil and benzene. In cases where aggressive chemicals may be encountered, the Bentofix® geotextiles can be manufactured with high density polyethylene (HDPE). Alternatively, 2.0 mm thick Carbofol® HDPE geomembranes can be installed. Carbofol® HDPE geomembranes are best suited to aggressive conditions due to their wide range of chemical and natural element resistance (e. g. to UV-radiation, rodents, chemicals). Not only is placement easy, it is also easy to weld Carbofol® HDPE geomembranes due to the favorable Melt Flow Index of the base resin.

Structured and Friction Carbofol® geomembranes are available to effectively transfer shear forces on the most challenging slope locations. Regardless, project specific direct shear tests should be performed to verify the required shear strength parameters are being met by the components selected for use.

Protection

The encapsulating geotextiles of Bentofix® geosynthetic clay liners protect the bentonite, as well as providing sufficient robustness for on site handling. When high normal installation loads are anticipated, Bentofix® manufactured with nonwoven geotextiles with a minimum mass per unit area of 270 g/m² should be used. Performance of the Carbofol® HDPE geomembrane is assured when the installation is performed by industry experts. Depending on the regulatory requirements as well as site conditions, needlepunched protection nonwoven geotextiles, such as Secutex® (from PP) or Depotex® (from HDPE) may be installed both above and below the Carbofol® geomembrane.

For slightly gravelly sand (gravel portion < 30 %), the Secutex® or Depotex® 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 heavier styles of Secutex® protection nonwovens, exhibiting a mass per unit area of 1,200 g/m². In cases where high chemical concentrations are expected, Depotex® protection nonwovens are recommended.

Erosion Control

In steep slope areas, heavy rainfall may cause erosion ruts or wash away the young grass seed. Secumat® erosion control mats prevent surface erosion and rutting by retaining the soil and seed in a convoluting threedimensional structure. Secumat® is installed directly on the slope and filled with soil. Roots of the vegetation gradually enclose the convoluting layer of Secumat®, efficiently interlocking it with the surrounding soil.

Conclusion

When constructing roads, railways or retention basins in groundwater protection areas, Bentofix® geosynthetic clay liners and Carbofol® geomembranes can be effectively used. Needlepunched Secutex® protection nonwoven geotextiles ensure a long-term protection of the Carbofol® geomembranes. Secugrid® geogrids can ensure the stability of steep slopes while Secumat® helps to prevent surface erosion. Complete geosynthetic system solutions from Naue are economical as well as ecologically superior alternatives for groundwater protection applications.