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Sydney Lenssen Foundation costs defy market forces

One good bit of news from Turkey is that the devastating earthquake has done no harm to the two Bosporus suspension bridges. It was my good fortune to visit both several times during construction.

The first bridge's west tower sits on two 15m diameter cofferdams taken some 20m down into the ground. When the formation was inspected, the contractor pressed hard to take one foundation deeper. But Dr Bill Brown, the engineer on site, was dubious about finding sounder material, and argued that the bearing pressure was modest at less than 100kN/m2 anyway.

The contractor no doubt had a good rate in for the work, and as clients find it difficult to argue against foundations being too strong, the extra 4m was excavated causing some delay.

In the current Civil Engineering Proceedings, Martin Goldsworthy, a geotechnical consultant, derives a formula to optimise what clients should spend on ground investigations to minimise project cost overruns. For a typical civil engineering project - not high risk like a tunnel or low risk such as a building with shallow foundations - he shows it is worth spending 4%, not the usual 1%, on site investigation.

That begs the question: how does the client avoid overspending when it is so much more rewarding to be safe than sorry - even when the ground is known?

A radiographer friend of mine recently bemoaned the changes made on the night shift at his hospital. The 15-hour duty is well paid and earns an extra day off. The big bonus used to be that four nights out of five you could catch up with sleep once the evening patients had been X-rayed.

Not the case today, he informed me. A&E consultants now insist that every patient on admittance must have a chest X-ray, even if there's no obvious need. Consultants justify the extra costs as insurance against increasingly litigious customers.

Why has this priority been introduced in cash-strapped hospitals? Simply because it is hard to argue against a 'better safe than sorry' approach, and since costs come out of the X-ray department budget, there's nothing to discourage consultants, especially as the new rule makes their own life easier.

Most structural engineers agree that both foundation design and installation are conservative, firstly in the choice of foundation type and also in the loads to be carried. For designers, it is cheaper to specify piles than to detail a raft or spread footing. The only party who might question the choice is the quantity surveyor, particularly if he or she has been responsible for a similar building with cheaper foundations.

If consulted, all clients want only the best foundations. Even speculative developers will scrimp finishes rather than foundations. Public clients are even more frightened of risk, and don't care about extra costs providing they can sleep at night.

At the same time the piling industry has helped itself by reducing the real cost of piling, simplifying its techniques and improving productivity and reliability. Better piling is allowing society to exploit much of the marginal ground in many parts of the country. It would seem, for once, that only sheer professionalism contains foundation costs.

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