In crowded cities the ground is often congested with old foundations, leaving no alternative but to reuse them. Nick Clarke reports on a new handbook that offers some help.
Reusing foundations may not, at fi rst sight, have a major contribution to make to the sustainability of new developments, and the purely fi nancial grounds for reuse are not always compelling. But the message from the October two-day international conference - Reuse of Foundations for Urban Sites (RuFUS) - was that, in the right circumstances, reusing foundations can have tremendous benefits programme, cost and sustainability.
The conference was held at BRE, Watford in Hertfordshire, where experts gave presentations on foundation reuse and the RuFUS handbook was offi cially launched.
This handbook has been written by a pan-European team of foundation and structural engineers under the editorship of Tony Butcher, John Powell and Hilary Skinner of BRE's Geotechnical Group, who also coordinated the whole RuFUS project. It is the principal outcome of the EU-funded scheme, which has been running since 2001 and aims to give confi dence to anyone considering foundation reuse, not least because of the wide range of case studies of successful projects that are included.
The redevelopment cycle of city centre sites is becoming shorter, and many central London buildings are being redeveloped in as little as 25 years. As a result, the ground can become completely congested with old foundations. There is simply no room for new piles, so innovative engineering is needed to fi nd foundation solutions. The fact that the existing piles have already performed satisfactorily under load for decades should indicate that they are likely to be able to carry the load from the new structure.
But the practical issues should not be underestimated: Do the existing and new column layouts match?
How deep are the existing piles?
Is the original concrete durable?
Can the original piling contractor's records be traced- What is the view of the funders on the concept of foundation reuse?
Around 30 presentations were made at the conference, and are featured in a 400-page volume of proceedings. This features further case studies of successful reuse and of some projects where the case for reuse was not accepted, for reasons relating to technical, contractual, or construction issues.
The supporting exhibition and practical demonstrations provided an opportunity for the delegates to see technology in action, and the reception hosted by Cementation Foundations Skanska proved fertile ground for discussions.
Presentations at the conference by developer Stanhope project director Andy Butler and Geotechnical Consulting Group director Hugh St John spelt out the essential requirements for foundation reuse.
These are: Good records of the foundations as-built (locations, dimensions, type, materials, pile test data etc); time for investigation, at the desk study stage and on site; a reasonably good match between the existing and new structural layout - in some of the case studies only a modest 15-30% of the piles were reused; a commercial/contractual environment that allows the risks to be fairly assessed and apportioned; a collaborative approach by the design and construction team.
'Sustainability will become a building regulations requirement, ' said City of London district surveyor David Banks. One of the consequences, he suggested, would be that pressures on developers and building owners to retain good records of their structures for future reuse would increase.
This point was echoed by Arup director Tim Chapman, who said a foundation reuse 'time bomb' would hit every major city in the world in 10 years. Sites are simply becoming full of piles and it is becoming impossible or hugely expensive to install new foundation structures.
At the very least, engineers should avoid simply adding to the detritus in the ground that could render sites unusable in the future, he said. He also anticipated that reuse of bridge foundations in connection with motorway widening schemes would grow rapidly. The crucial role that good records for foundations in current use play in the potential for reuse was again emphasised.
The handbook was welcomed at the conference as a valuable tool for convincing doubtful clients, developers, architects and planners that foundation reuse is an option.
It may not yet be common, but rapid growth and development of the RuFUS approach are certain.
Nick Clarke is publisher, IHS BRE Press.