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Avoiding archaeological calamities

How do you ensure the foundations for a development do not damage precious archaeological remains? English Heritage offers some advice

There is a curiously symbiotic relationship between developers and archaeologists. If it wasn't for developers, much of what lies beneath the ground would never be discovered. And yet, if it wasn't for archaeologists, developers wouldn’t be quite so limited in what and where they can build.

Since 1990, planning rules in England have required developers to submit their plans to the relevant local authority's archaeological department and to foot the bill for any subsequent investigation. As a result, says Dr Jim Williams, regional archaeological science advisor for English Heritage, "most archaeology takes place within the context of development".

The planning rules also work on the principle that remains should be preserved in situ rather than excavated, which puts pressure on the developer and foundation designers to minimise damage.

Williams is one of three authors of a new guidance document that has just been produced by English Heritage, looking at the impact of piling on archaeological remains. The guide is intended to help engineers, piling contractors and archaeologists come to some agreement as to the best piling solution for each development.

"In an urban centre, one outcome of wanting to develop a site where you have archaeological remains is either that the remains are so significant that the development is refused or the developer must find a way of avoiding the ground altogether," says William. "Otherwise, if piled foundations are the only way of building, then the guidance note is there to try and work out ways in which the two can fit together."

Williams and his colleagues have studied different types of piles in different ground conditions so the guidance can help engineers come up with the right solution. "One of our major conclusions is that there isn't one pile type that we would recommend for all archaeological deposits," he says. "There are sound engineering and archaeological reasons why different piles are more suitable in different situations."

In the past 10 years, engineers have realised how damaging piling can be, with a lot of the emphasis on displacement (driven) piles. "They cause damage not just in the area they displace but in the deposits around them," explains Williams, who says that a backlash against driven piles has led to more bored and CFA piles, where the only material being lost is within the borehole itself. But if the pile has to go through an underground obstruction, such as a buried wall, CFA might not be the best option.

"We can accept there is a trade-off, and what's best to use will depend partly on the nature of the archaeological deposits and partly on the engineering issues," says Williams. "What we've done in the guidance is set out the implications of the different types of piles in different ground conditions."

The aim, he says, is to encourage dialogue between the developer and the archaeologists at the earliest stage, rather than incurring conflict if the developer presents a piling design that is unacceptable.

"If the developer goes along to the local authority with a foundation design, they're on the back foot because they've already paid someone to do it," he explains. "If the archaeologist says it's inappropriate, they have to go back and start again. "By having the discussions earlier, you are likely to avoid this conflict, and cut down on wasted time."

Williams will be giving away copies of the new guidance document, "Piling and Archaeology" and answering questions on this subject on the English Heritage stand, G77, at Civils 2007.

Geotechnical Trial

If you have a particular interest in foundation design and ground engineering, follow the Geotechnical Trail at Civils 2007.

The trail, which is sponsored by Hanson Formpave, identifies all the exhibitors at the event that work on this area by highlighting them in the show guide and with special carpet tiles in front of their stands.

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