Geocomposites

31 Drainage geocomposites (a) geonet and (b) cuspated. inset magnified portion of the geocomposite. 

Both woven and non-woven geotextiles can serve as moisture barriers when impregnated with bituminous, rubber-bitumen, or polymeric mixtures. Such impregnation reduces both the cross-plane and in-plane flow capacity of the geotextiles to a minimum. However, for liquid containment applications, what is referred to as a GCL will be more effective. 

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The drainage materials for the liquid management system must allow for unimpeded flow of liquids for the intended lifetime of the facility. In a leachate collection system, the drains may consist of pipes, soil (gravel), geonets, or geocomposites. 

Surface water drainage systems can be composed of granular soils, geonets, or geocomposites, but the majority of drainage systems use granular soil. This is particularly true in frost regions where it is necessary to have 3-6 ft of soil above the FML to satisfy the requirements for frost... 

The design for the surface water-collector system is determined by an allowable flow rate divided by a required flow rate. Allowable rates for geocomposites are determined experimentally by exactly the same method as for geonets. The specific cross section used in the test procedure should replicate the intended design as closely as possible. For the required flow rate, Darcy s law or HELP36 37 can be used. Then the design-by-function concept is used to determine the DR, or FS. 

From the wide range of geosynthetic products, the ones used in asphalt rehabilitation works are the geotextiles, geogrids and geocomposites, all able to sustain the high temperature of the asphalt during application. 

The following are the properties required for a geosynthetic to be used in pavement rehabilitation or new pavement asphalt works tensile strength and elongation (in both directions), bitumen retention, durability, alkaline resistance (in case a geogrid or a geocomposite is used over concrete surface) and melting point, to name a few. Property requirements and other characteristics are specified in CEN EN 15381 (2008), ASTM D 7239 (2013) or other relevant standards. 

The use of geogrids or geocomposites effectively results in the reduction of the thickness of the asphalt overlay. For the determination of the resulting reduction in thickness, special calculations are needed to be carried out. However, the thickness of the asphalt layer above the reinforcement should never be less than 50 mm or the minimum value required by the supplier. This minimises the horizontal tensile forces that may cause slippage of the geocomposite or the overlay. 

With respect to choosing between geotextile and geocomposite material, it is advised to... 

Drainage Sand or gravel Geonet or geocomposite Recycled or reused waste (e.g., tire chips)... 

Key words geosynthetics, geotextiles, geocomposites, structures, properties, functions, multifunctionality, applications. 

Figure 8.1 indicates that geotextile structures include continuous sheets of non-woven, woven, and warp knitted fabrics, and stitch-bonded fibres or yams. The woven and warp knitted materials can be made to have a similar structure to certain of the textile-related products (essentially geogrids) to be used as alternatives. The non-woven geotextiles can be combined with the textile-related structures to make geocomposite products that are multifunctional. 

For example, the ingress of a rising water table can be restricted by a cross-slope drainage geocomposite with a GCL layer or geomembrane placed above to act as a capillary break in the water flow. A second drainage geocomposite above the impermeable layer would then remove surface... 

Backfills for geosynthetic reinforced walls should be free draining,because unexpected failure of these structures can be caused by lack of control of groundwater or seepage. An appropriate geocomposite can therefore be incorporated horizontally and/or vertically to provide adequate drainage. 

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