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Contrasting approaches to problem soils

MEETING REPORT: Report on the ICE East Midlands Geotechnical Group special meeting 'Problematic soils'held at Nottingham Trent University on 8 November 2001, by Professor Ian Smalley, Geography Department, Leicester University.

Quaternary geology's importance to all involved in the construction industry was emphasised by Professor Martin Culshaw of the British Geological Survey in the opening paper at the problematic soils meeting in November.

He made the point that many of the problems encountered in ground engineering are caused by Quaternary processes - which produced, among other things, peat, very sensitive clays and loess.

Culshaw's view of the 'geological' approach to ground engineering made an interesting contrast to the ideal 'engineering' view advanced by Professor Serge Leroueil in the last paper of the day.

The second presentation at the meeting was by Dr Ian Jefferson, the secretary of the International Association of Engineering Geology's Collapsing Soils commission. Jefferson has a growing reputation as a world leader in the study of loess, widely regarded as the most widespread and damaging of the collapsible soils.

There is more loess in Britain than previously thought and a joint BGS-NTU team is actively investigating the problem.

The BGS started to look at collapsible loess many years ago when there was a proposal to site a major airport in the Thames Estuary.

Dr R Chown of the BRE was next, talking about shrinkage and swelling of clays.

He was followed by Eric Farrell of Trinity College Dublin on the behaviour of highly compressible clays and silts. EJ Wilson spoke on the long-term performance of foundations on peat, with particular reference to the Somerset Levels.

The morning session was closed by Dr MA Czerewko, who considered the development of methods for identifying problem mud rocks using index tests.

After lunch the focus changed from natural ground to anthropogenic ground, specifically manmade collapse problems.

Dr D Bunce of Arup spoke on the reclamation of contaminated land with reference to the Pride Park development in Derby. In an impressive presentation, Bunce demonstrated how a wide range of problems was tackled.

Dr Hilary Skinner of BRE talked about construction on fill and R Coombs of Innogy considered whether engineers are faced with problematic soils or problematic specifications.

This was followed by presentations on ground improvement using dewatering by Dr Martin Preene of Arup and deep compaction of problematic soils by Barry Solcombe of Keller Ground Engineering.

The final paper in this section was by A Maries of Skanska Technology on enhanced cement stabilisation of contaminated clay soils.

A keynote address by Professor Serge Leroueil of Laval University, Quebec City, Canada, wound up the meeting.

The 1999 Rankine lecturer proposed that there are no problem soils, only engineering solutions, a view contrasting markedly with that offered by Martin Culshaw during his address earlier in the day.

Leroueil's approach was a pure engineering one: find out all the facts about the ground and, safe in the possession of all the facts, design a suitable structure.

Culshaw's approach was the much more cautious one of someone dealing with a 2.4M year sequence of events.

Culshaw said the focus should not just be on a few square metres of ground; there also has to be awareness of the local geology.

He warned engineers that it is essential to be aware of geological events that may cause problems to construction.

The problem soil is one which does not obey the usual rules. It obeys some sort of rules - but problems arise because these may not be the ones that you know. Remember that ground engineering is two words: ground (where you keep your wits about you) and engineering (where you display your skills).

The special meeting was chaired by Nottingham Trent University's Professor Mike Rosenbaum.

The book Problematic Soils, edited by I Jefferson, EJ Murray, E Faragher and PR Fleming and published by Thomas Telford, was also distributed on the day.

Ian Smalley, Black Earth Institute, Geography Department, Leicester University email: ijs4@le. ac. uk

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