CIRIA Publication C573 Guide to ground treatment, London 2002;
CIRIA Publication SP123 Soil reinforcement with geosynthetics, London 1996;
DEFRA Making the best of byways: A practical guide for local authorities managing and maintaining byways which carry motor vehicles, London 2005;
TRL Report 657 Improved design of overlay treatments to concrete pavements. Final report on the monitoring of trials and schemes, Crowthorne 2006;
TRL Report RR140 Deformation of road foundations with geogrid reinforcement, Crowthorne 1988;
TRL Report RR382 Installation damage trials on geotextiles, Crowthorne 1994; and
BRE Report 470 Working platforms for tracked plant: good practice guide to the design, installation, maintenance and repair of ground supported working platforms, Watford 2004.

Compliance references

BS EN 1997-1: 2004 Eurocode 7: Geotechnical design;
BS EN 15381:2008 Geotextiles and geotextile-related products - characteristics required for use in pavements and asphalt overlays;
BS EN 13249:2001 Geotextiles and geotextile-related products. Characteristics required for use in the construction of roads and other trafficked areas (excluding railways and asphalt inclusion);
BS EN 13251:2001 Geotextiles and geotextile-related products. Characteristics required for use in earthworks, foundations and retaining structures;
BS 7533-13:2009 Pavements constructed with clay, natural stone or concrete pavers. Guide for the design of permeable pavements constructed with concrete paving blocks and flags, natural stone slabs and setts and clay pavers;
BS EN 15382:2008 Geosynthetic barriers. Characteristics required for use in transportation infrastructure;
Defence Estates Design & Maintenance Guide 33 Reflection cracking on airfield pavements – a design guide for assessment, treatment, selection and future minimisation, Sutton Coldfield, 2005;
Interim Advice Note (IAN) 73/06, Revision 1 (2009) Design guidance for road pavement foundations (Draft HD25); and
Manual of Contract Documents for Highway Works, Volume 1 - Specification for Highway Works, Series 0600 Earthworks, Clause 609.

Technical references

CIRIA Publication C573 Guide to ground treatment, London 2002;
CIRIA Publication SP123 Soil reinforcement with geosynthetics, London 1996;
DEFRA Making the best of byways: A practical guide for local authorities managing and maintaining byways which carry motor vehicles, London 2005;
TRL Report 657 Improved design of overlay treatments to concrete pavements. Final report on the monitoring of trials and schemes, Crowthorne 2006;
TRL Report RR140 Deformation of road foundations with geogrid reinforcement, Crowthorne 1988; and
TRL Report RR382 Installation damage trials on geotextiles, Crowthorne 1994.

Typical criteria

Are there site or material availability constraints limiting the thickness of the pavement or surface course overlay?
Are the pavements experiencing an increased level of traffic?
Are the pavements prone to near surface cracking/reflection cracking?
Are the access roads or haul roads being used by heavy vehicles/ construction plant?
Are the access/haul roads built on cohesive formations?
Are the access/haul roads temporary or likely to be incorporated into the permanent works?

Technical considerations

Paved roads

Construction of paved roads can benefit from the application of geosystems. They are claimed to improve durability and resistance to thermal stress, cycling fatigue and cracking of the bituminous bound layers and to increase load bearing capacity of the sub-base/foundation layer. These in turn result in significant reduction of thickness of the layers and might increase significantly the life of the pavement.

It is argued that geosynthetic reinforcement of the asphalt laid on top of a concrete pavement delays the appearance of reflection cracking. However, trialling and long term monitoring of road and airfield sites where this technique has been applied is still underway in the UK. The interim results of this research are that the beneficial effect of the geogrids/geotextiles varies depending on the specific product and that geosynthetics are potentially more difficult to install and more costly than other techniques. Use of geosynthetics in asphalt overlay still requires special approval by the Highways Agency and the Defence Estates

Unpaved roads

Unpaved roads, used as haulage or temporary roads, can be effectively reinforced by geogrids/steel mesh inserted within the base layers. This enables a reduction in the thickness of the granular material used. Durability and resistance to chemical attacks are important considerations in the choice of geogrids if the unpaved roads are to be incorporated into permanent works. Further information on this application is given in the application specifically on “working platforms”.

Geotextiles and geogrids can be used in the maintenance of byways which might be used by motor vehicles. Geotextiles provide a separation layer between the subgrade and the granular material used to build the byway thus avoiding degradation of the granular layers. Geogrids are used to reinforce the granular layer, thus allowing for the use of lower quality materials or lower thicknesses.

Economic considerations

Geosynthetics can be used to reinforce both paved and unpaved roads and increase their load carrying capacity and durability, thus realising both immediate and long term savings. These are some examples of the benefits that can be realised:

The amount of granular material required for temporary roads and for sub-base/foundation to permanent works can be significantly reduced through the incorporation of suitable reinforcing geogrids or steel mesh. This might be also an important consideration if the site constraints impose thickness restrictions. Specific reinforcements can be incorporated to improve uni-, bi- or tri-axial bearing capacity. Reduced quantities of imported material might reduce expenditure and result in avoidance of transport costs.
The longer term drainage and load bearing capacity of granular material placed over cohesive soils can be improved by incorporating geotextiles that act as filter, stopping the migration of fines and the eventual formation of voids. This results in reduced maintenance requirements and their associated costs.
Improved durability and resistance to cracking of bituminous layers reinforced with geosynthetics would result in longer maintenance intervals and subsequent savings.

Environmental considerations

The savings highlighted above are matched by environmental benefits. Geosystems achieve resource efficiency through reduction of the need for virgin/imported materials.

This results in savings of natural resources. Furthermore, the considerable reduction in transport requirements (less haulage of new materials and disposal of waste) results in significant avoidance of greenhouse gas emissions.

In many cases the requirement for maintenance interventions is reduced with environmental benefits in terms of reduced construction noise and less traffic disruption in the neighbouring area.

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