Site investigation contractors have faced resistance for many years from a hard core of developers who viewed their work as a costly and largely unnecessary hindrance to property construction. But imminent changes to legislation and a growing awareness of the problems associated with uncharted brownfield sites have led to a softening of attitudes and an upturn in orders, say contractors.
The Government is set to incorporate a new chapter on site assessment into existing environmental legislation when a section of the Environmental Protection Act 1990 is implemented next year.
The chapter deals with geotechnical and contamination hazards on sites and takes into account developments in contaminated land legislation.
The new legislation should reinforce what site investigation contractors have been saying for some time. Their work is a necessary expense which benefits landowners, builders and occupants in the long run. Geotechnical engineer for Albury Site Investigation Keith Clark says: 'Establishing the ground conditions for each individual site is crucial, even though a nearby site is known to be free of contamination or unstable ground conditions.'
Traditionally, some site investigation contractors are approached by developers for assistance at a late stage after foundations for a new property have already been laid.
'Occasionally we get asked to look at a building site that is half constructed because investigation was not carried out and developers suspect a problem with the site. There can be a panic if we find that ground conditions are not entirely safe and the buildings should really be pulled down,' says Clark.
The cost of investigation and laboratory analysis has to be viewed as relative to the proposed development. An appropriate number of boreholes on a site can cost 3,500, with physical work taking around a week and laboratory testing taking another six weeks. Despite the initial outlay, the trouble a developer could save himself might run into millions of pounds if testing is specified sooner rather than later. Soils Ltd's company manager Darren Seeley says: 'For a housing estate with 20 units to have the correct testing specified could cost the client upwards of 2,000 for a day's work. But when you consider that a housing developer's properties could total 4M, then you can see the cost is totally justified.
'We are always saying to clients that what appears to be a greenfield site may be contaminated. A rural site could contain tin from Roman times, mercury from a textile production unit long gone or herbicides and pesticides used on farmland,' says Seeley.
Some site investigation contractors have become more thorough in recent years. 'We now suggest a historic map search of a site and surrounding area as well as a geotechnical investigation. We also like to be present at any remediation stage to oversee that recommendations based on our site investigations are being carried out properly,' says Seeley.
The range of techniques and equipment at a contractor's disposal is great, from trial pits to percussion drilling and window sampling, most of them well tried and tested. Contracts manager of Sub Soils Surveys John Ingham says: 'There has not been much change of kit over the last 30 years.' Specialist knowledge of the equipment and their best uses, however, comes only from many years of experience in the field.
'Cable percussion methods are not usually suited to drilling through bedrock, but after chiselling for up to 2m in this way you can be sure whether or not a problem of underlying boulders is localised, for instance,' he says. Around 80% of the company's work involves soft ground drilling for foundation design, but the other 20% involves rotary drilling to identify shallow coal workings.
'It is not possible to generalise ground conditions at all, especially in difficult regions such as the redundant Lancashire coal fields around Manchester. There are many glacial deposits from the Ice Age in north west England and situations can vary greatly over short distances,' says Ingham.
Because of this, specific site investigation methods are used according to the particular project and what the land is due to be used for. 'We will use rotary drilling to determine whether coal measures are at problematic depths so they can be stabilised if necessary for the construction of a large structure like a multi-story car park,' he says.
GB Geotechnics director George Ballard says the importance of human interpretation can not be over emphasised and that non - destructive instruments can also play an important part in site investigation.
'A borehole or a trial pit must be analysed correctly by a trained engineer and such methods can be complemented with geophysical non-destructive techniques. Digging individual holes only takes point measurements, whereas non-destructive methods using acoustic wave technology and high frequency radars can analyse much wider areas,' he says.
The climate can affect ground conditions in different ways. Clark says excessive rainwater can have a greater impact on land in some areas than others.
Marine site investigation presents additional problems for the site investigation contractor before investigation can begin. Specialist overwater contractor Seacore bears in mind natural constraints such as high tide downtime and extreme weather conditions which can affect the selection of plant for marine structures such as windfarms.
Estimating manager Matt Sneddon says: 'There is always a way to overcome any forms of sea conditions and seabed by tailoring the jack-up rigs to accommodate anticipated conditions. We carry out a detailed site analysis before proposing any piece of plant as there is nothing more embarrassing than getting on to a site and discovering plant is inadequate in any way or will be put in danger.
'We perform full environmental loading analysis for the rig, a review of weather conditions and an examination of the present seabed conditions before we can begin investigating in earnest.'
Mike Walter is a reporter with Barrett, Byrd Associates.