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Ground Engineering

THE MAGAZINE OF THE BRITISH GEOTECHNICAL SOCIETY

Ralph Peck and Alan Powderham assess why the Observational Method is not more widely applied.

We should aim to produce designs that are right the first time, but we should always leave the door open for improvement. Well-documented case histories could significantly enhance continuous improvement. While ground engineering has a better record in

documenting case histories than other areas, more could be done to exploit this rich resource of information and experience. We need to increase efficiency and add value. The observational method offers a way forward.

The observational method has specific objectives: to ensure safety, and to save time or money. Yet it is significantly under-used. Apart from the potential to deliver substantial savings, it can provide a range of additional benefits that would enrich the feedback to industry for future projects, including high quality proven case history data. The method also stimulates innovation and promotes teamwork and motivation.

So why is it not more widely applied? There seem to be two main reasons. First there is a strong desire for certainty of cost and outcome before construction begins. This is understandable, but it is likely to be achieved by high cost and undue conservatism. The observational method requires the ability to make design changes during construction. This touches on the second reason, which relates to perceived low safety levels and is often voiced in terms of high risk. These views lead to inappropriate association of the observational method with low factors of safety coupled with the risk of additional cost and delay of contingency measures. Another constraining factor arises from contractual conditions that traditionally tend to separate design from construction. This prevents design changes from being effectively introduced during construction.

There is no need for the observational method to threaten either certainty or safety. Correctly applied, it should enhance both. Every project entails unknowns or uncertainties. New and potentially important information will be progressively disclosed as the project is implemented. While the focus is often on geotechnical matters, circumstances that influence the function, safety, or progress of a project include such matters as who will carry out the work and their training and experience, not to mention how they react under unusual conditions.

The observational method is one strategy for dealing with this situation. It is designed to forewarn of problems by measuring deviations from expected behaviour and adopting a course of action for which provisions have already been made. This is its role in controlling and reducing unforeseen risks. It leads to material savings and reduced construction times.

But the observational method can also deliver added value as has been demonstrated on a range of major projects. This can be done by progressively introducing beneficial design modifications and increased motivation and efficiency.

Civil engineering design involves a creative process that requires judgement and experience. We never have perfect and complete information. The observational method is a natural approach that recognises the inherent limitations of our knowledge and manages the associated risk. Its overall concept is straightforward, and we must avoid the temptation to over-complicate it. Actions and responsibilities must be clearly defined, and lines of communication kept as simple as possible.

Clear and timely communication based on the identification and collection of the critical observations is essential. In these times of electronic data capture there is a danger of information overload. While much of this extra information may be interesting and useful (for example in research) it may adversely affect communication. This will impair the implementation of the method and unnecessarily increase risks. For example, every instrument should have a clear and defined purpose. It should be selected and located to address a specific question.

Too much instrumentation is often installed. Each instrument needs to be the right type in the right place. So, as in other aspects of engineering design, simplicity is important. Simplicity is at the heart of the observational method - a simplicity made comprehensive by good judgement. The critical observations are the resolution and synthesis of the complexity inherent in sub-surface construction. Correctly identified and obtained they hold the key to opportunity and progress.

Ralph Peck is professor of foundation engineering emeritus at the University of Illinois, and consulting civil engineer. He is co-author with Karl Terzaghi of Soil Mechanics in Engineering Practice which first appeared in 1948.

Alan Powderham is civils and transportation board director and manager of the foundations and geotechnics division of Mott MacDonald Group. He now specialises in foundation engineering and is a visiting lecturer at the University of Illinois.

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