Technical Information

As part of the site specific design approach, it may be necessary to include geotextiles or geomembranes, and for specific loading requirements, geogrids may be required.

Geomembranes are used for System C, Attenuation systems, where the design requires the prevention of water entering the sub-grade. The choice of membrane will be made upon consideration of the importance of preventing leakage, typical materials used being polypropylene, HDPE or EPDM. As the sub-base aggregate is angular in type, membranes must be capable of resisting puncture due to loading on sharp points of the aggregate. A geotextile fleece to protect the membrane, should be specified where puncture must be prevented. For detailed advice on membranes, consult CIRIA C582 section 6.

Geotextiles are used with Systems A & B to line the surface of the sub-grade preventing punching of aggregate into the sub-grade. Typically monofilament products manufactured from polypropylene or polyethylene or similar are used, as the geotextile must remain capable of allowing free movement of water whilst dealing with the loadings both during construction and during the pavement lifetime. Specify products to BS EN 13252 :2001.

In certain circumstances, layers of geogrid may be introduced into the pavement construction to ensure the completed pavement is capable of carrying the design loadings. Site conditions will determine the type and the number of layers required.

Geotextiles geogrids and geomembranes used in the construction of permeable pavements, are subject to high stresses both during construction and during the pavements lifetime. Additionally, they must remain unaffected by water either alkaline or acidic, and indeed any pollutants therein. These materials must be durable and robust and specialist advice should be sought from the supplier to ensure suitability for use.