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Don't let systems dull your senses, says geotechnical guru

GEOTECHNICAL legend Ralph Peck regrets trying to formalise the observational method in his Rankine lecture of 1969 - a landmark event in UK geotechnics that led to the introduction of the observational method in this country.

Speaking at a half-day seminar at the ICE last week, Professor Peck said: 'As soon as I tried to formalise the process, I wished I hadn't.'

Commenting in the discussion shortly after Arup director Duncan Nicholson had outlined the contents of CIRIA's new report R185 The Observational Method in ground engineering, Peck said 'there has been a proliferation in attempts to structure the method, but there is a danger that such systems dull our senses over what is going on.

Engineers become intrigued and hypnotised by their systems and fail to see when something is going wrong, how it is going wrong and what needs to be done about it'.

Nicholson replied: 'Our aim in the CIRIA report was to come up with a definition of the observational method and a loose framework to provide a robust system for its use. Only time will tell if it is too constrained.'

Earlier, Peck described his experiences as Karl Terzaghi's site agent during construction of the Chicago subway in the 1940s.

He recalled how measurements taken during the tunnelling were correlated to settlement at surface and showed for the first time that there was some kind of relationship between the two.

He explained that in the light of this observation, contractors modified their construction procedures to minimise settlement.

'Contractors were able to find the optimum way of doing the job and reduced settlement by two thirds based on observations only. There was no supporting theory other than the general concept that the clay moved towards the centre of the tunnel and this was linked to surface settlement. That was the beginning of the observational method, ' he said.

Peck added that there were many special circumstances at Chicago which fortuitously combined to provide an opportunity to see how the system worked without constraint. Chicago was in the depths of recession, he explained, and unemployment was high. When the city secured a windfall to pay for the subway, the message was 'go out and build - nobody paid attention to the niceties of the legal system.

Contractors were given just three weeks to start work on site'.

Professor John Burland chaired the meeting, which included four case studies on recent applications of the observational method from Mott MacDonald director Alan Powderham.

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