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Installing confidence In a special spotlight on trenchless technology Ground Engineering looks at the factors inhibiting acceptance of trenchless methods.

Trenchless technology, meaning techniques for installing, and maintaining and renovating utility infrastructure with reduced surface excavation, has for more than a decade been proclaimed as 'next year's technology'.

In some respects it has fulfilled this challenge. In particular maintenance and renovation techniques such as relining pipelines and sewers with soft form epoxy coated linings or plastic, or respraying using miniature robots, have become widely accepted as cost effective alternatives to open cut repair or replacement.

In contrast contractors and manufacturers of systems for the installation of new cables and pipelines by trenchless methods still face an uphill struggle for acceptance. Moling, pipebursting, directional drilling and microtunnelling are by now all proven techniques, but clients - mostly privatised utilities and local authorities - are more often than not reluctant to specify them.

It is probably significant that the trenchless industry has developed in the main with little input so far from the geotechnical community. While Oxford and Loughborough Universities have undertaken excellent and practical research on soil mechanics aspects of trenchless installations, this information appears to be largely ignored during day to day contracting.

Equally, few undergraduate civil engineering courses offer more than a cursory look at the available methods and not many of the accepted geotechnical consultants offer expertise in trenchless installation methods.

This is a great loss since input from geotechnical engineers would significantly help to overcome the main inhibiting factors to acceptance. There is, among the trenchless community, a general lack of awareness of the importance of ground variation, the need to match techniques to ground conditions, and the benefits in terms of risk control and cost savings that understanding the ground before a project is undertaken can bring.

This is certainly borne out by a study in Italy in which Italian Telecom looked at the causes of problems during 538 directional drilling runs covering 41km of installation. Some 54% of problems were put down to the nature of the soil, and 39% were put down to pre-existing utilities and buried objects. Since these are precisely what geotechnical engineers address, it is clear that modest investment in good geotechnical engineering could do much for the success rate of directional drilling and improve acceptance of the method.

Some contractors are wising up to this. Kent-based Powermole recently purchased Italian ground proving radar manufacturer IDS, so that it now offers pre-drilling radar surveys to determine obstructions, utilities and soil profiling.

IDS' radar system uses a multi-channel array in which a frequency sweep is undertaken and the results superimposed. This gives fine detail near surface where existing utilities and obstructions are likely to be found, and the potential to look in general to greater depths, typically to 3m, but dependent upon the soil conditions.

In addition Powermole, winner of a DTi SMART award for its moling equipment, has developed an innovative directional drilling system which incorporates a pneumatic down the hole hammer, supplied by Compair Holman. This automatically activates if rock is encountered, and at a recent demonstration in West Sussex the rig successfully bored through Cretaceous sandstone. According to Powermole the system has been used to penetrate marble in Italy without problem.

The Powermole system is driven by high powered compressed air, which means the system is dry and much cleaner to use than bentonite-lubricated systems. This is a particular advantage in urban areas where directional drilling in principle offers the greatest benefits. It also avoids the costs of recycling, and finally disposing of the ben- tonite slurry which may be classed as contaminated waste.

Sven Erik Petersen, chairman of Powermole, believes there is great potential for trenchless technology. He believes the methods offer social and environmental advantages over traditional trenching.

He puts the lack of acceptance of trenchless methods down to the lack of understanding surrounding the techniques, coupled with the give it a go approach of many contractors. 'Clients want to be sure the job will get done without opening themselves up to excessive risk - they need peace of mind.'

Petersen is confident Powermole's new total package approach and upgraded equipment can overcome the technology issues. Powermole is nevertheless supporting an attempt to address these factors further through a study by University of Sussex on the use and perceptions of trenchless technology in the UK. (e-mail T.Heighes@sussex.ac.uk).

Another interesting develop- ment is the move to trenchless methods by some established open cut utility contractors.

Peter Duffy of Wakefield-based Peter Duffy Ltd says it is 'horses for courses', in that you cannot expect the trenchless method to be the most appropriate every time. 'If you have close spaced service connections on a sewer, you would in any case dig up almost the whole route, but it would be more expensive than straight trenching,' he explains. 'However if there are few connections, there is a real opportunity.'

Duffy feels there is a strong future for trenchless technology, but not for any particular technique.

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