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talking point

The wide range of geosynthetics products gives the ground engineer a variety of flexible design solutions, says Derek Smith.

Geosynthetics is very large family. Geotextiles and geogrids are probably the two that first spring to ground engineering professionals' minds, closely followed by geomembranes. The family also includes geofoams, geowebs, geonets, geodrains and geobags.

Geocomposites combining the properties of two or more types of geosynthetic to provide versatile multifunctional products are increasingly available.

The International Geosynthetics Society (IGS) is dedicated to the scientific and engineering development of geotextiles, geomembranes, related products, and associated technologies. Its UK Chapter publicises the benefits of geosynthetics by arranging evening meetings around the UK with other learned bodies such as the ICE local associations.

As activities co-ordinator for the UK Chapter, I have the challenging task of finding subjects and speakers for the meetings. Some of them provide overviews of geosynthetic usage and some explore more detailed case histories or research. The international body (based in the US) arranges conferences and publishes books and technical journals, all aimed at assisting the professional to design confidently with geosynthetics.

Their value in ground engineering is well established, with their use in place of and combined with traditional construction materials often proving to be more costeffective than traditional materials alone.

Developments in the field are likely to strengthen the value of geosynthetics. A paper in this issue looking at steepwall liner systems for landfills illustrates one example. Landfill air space is a valuable commercial and environmental resource and systems are continually being developed to maximise available space using a combination of geosynthetic products with more traditional materials. A further example is provided by research at Bolton Institute into the use of degradable geotextiles for reinforcement. We may well be on the way to a more sustainable construction option where the strength offered by geosynthetic reinforcement is only required in the short term. Problems of cohesive fill within reinforced soil are being addressed at UMIST, using geotextiles for both reinforcement and drainage. Another interesting use of geosynthetics can be found in Warrington, where soil-filled geobags are on trial for use in providing the basis for a river closure project.

The range of excellent products provides the ground engineer with a variety of flexible design solutions. What more can be done to raise the awareness of the benefits of the use of geosynthetics? A year ago Talking Point spoke of the need for better education of undergraduates in designing with geosynthetics. The need is still there. The IGS continues its quest to develop a suitable short lecture to introduce undergraduates to geosynthetics. This is under preparation by the international body. However, by its very nature it will be generalised and will only be a stepping stone. Nottingham Trent University offers a short course introduction to geosynthetics, based on its MSc module, usually run over three days, which could be used as a template for a more detailed lecture series. The IGS can also provide a series of videos that show the use of geosynthetics in landfill, highways and reinforced soil applications and their potential to add value to these projects.

It is essential that all ground engineers, not just undergraduates, are aware of the benefits and options available through the use of geosynthetics and that they know how to design with these products. There are plenty of literature examples. There are also British Standards for geotextile testing (BS6906), although none for geomembranes, and a British Standard for the design of reinforced soil structures (BS8006). The Highways Agency provides further guidance with HA68/94 for reinforced soil slopes and BD70/97 for vertical walls. Further work is being undertaken by BSI and CEN, which will provide the designer with even more assistance.

Most ground engineering projects use geosynthetics in some way. A designer must fully understand the properties of the soil and of the particular geosynthetic and the interaction between the two.

Whether it is simple geotextile wrapped gravel drainage trenches, more complex uses of reinforcing geotextile (or geogrid) or incorporating geocomposites, a comprehensive knowledge of the properties of all the materials is essential. The designer must also recognise that different polymers function and perform in different ways. Manufacturers can help by providing data sheets with all relevant details. Particular attention could be paid to the provision of the partial factors that are applied to material strengths in the BS design code for reinforced soil.

These are product specific factors and should be determined by the polymer scientists who are most qualified to do so.

The UK Chapter of the IGS would be very interested to hear from any users of geosynthetics willing to share their experiences (good and bad) ofmanufacture, design, specification and construction using geosynthetics.

Derek Smith is principal engineer with EDGE Consultants UK Ltd and a committee member of the UK chapter of the International Geosynthetics Society.

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